DOE-HDBK-1169-2022 Chg Notice 1, Handbook for use with DOE-STD-1269-2022, "Air Cleaning Systems in DOE Nuclear Facilities"

i DOE-HDBK-1169-2022 Change Notice No. 1 DOE HANDBOOK HANDBOOK FOR USE WITH DOE-STD-1269-2022, “AIR CLEANING SYSTEMS IN DOE NUCLEAR FACILITIES” U.S. Department of Energy Washington, D.C. 20585 NOT MEASUREMENT SENSITIVE DOE-HDBK-1169-2022 ii Change Notice No. 1 February 2023 Table of Changes Page/Section Change Page 11/ Section 3.5 Edited third column within Table 3.3 with original DAC, Air (µCi/ml) values from 2003 version. The only exception is the value used for Hazard Class 4 which is revised from “10^-6” to “>10^-6” DOE-HDBK-1169-2022 iii FOREWORD This handbook is approved for use by all Department of Energy (DOE) components and their contractors. It provides advice and recommended good practices for implementing DOE-Standard (STD)-1269-2022, Air Cleaning Systems in DOE Nuclear Facilities. It does not add any new requirements to those stated in DOE-STD-1269-2022, nor does it alter in any respect that standard’s requirements or recommended practices. Taken together, DOE-STD-1269-2022 and this handbook replace DOE-HDBK-1169-2003, Nuclear Air Cleaning Handbook, which is now archived and may be viewed at https://www.standards.doe.gov/. Comments (recommendations, additions, and deletions), as well as any pertinent data that may be of use in improving this document, should be emailed to: nuclearsafety@hq.doe.gov or sent to: Office of Nuclear Safety (AU-30) Office of Environment, Health, Safety and Security U.S. Department of Energy 19901 Germantown Road Germantown, MD 20874 Phone (301-903-2996) https://www.standards.doe.gov/ mailto:nuclearsafety@hq.doe.gov DOE-HDBK-1169-2022 iv Table of Contents 1.0 Introduction ...................................................................................................................... 1 1.1 Purpose ............................................................................................................................. 1 1.2 Applicability ....................................................................................................................... 1 1.3 Organization ...................................................................................................................... 1 2.0 Terminology ...................................................................................................................... 2 2.1 Acronyms & Abbreviations ................................................................................................ 2 3.0 System Design ................................................................................................................... 3 3.1 Introduction ....................................................................................................................... 3 3.2 Contaminants .................................................................................................................... 3 3.3 Environmental Conditions ................................................................................................. 6 3.4 Backup Power .................................................................................................................. 10 3.5 Work Area Ventilation ..................................................................................................... 10 3.6 References ....................................................................................................................... 14

4.0 Component Level Guidance and Best Practices ............................................................... 16 4.1 Filtration Components and Filter Testing ........................................................................ 16 4.1.1 Introduction: Filtration Components ....................................................................... 16 4.1.1.1 Air Filter Types ................................................................................................. 16 4.1.1.2 Filtration ........................................................................................................... 17 4.1.1.3 Particle Collection by Filters ............................................................................. 17 4.1.1.4 Particle Retention in Filters .............................................................................. 19 4.1.1.5 Airflow Resistance of Filters ............................................................................. 20 4.1.1.6 HEPA Filters: Historical Background ................................................................. 20 4.1.1.7 Filter Medium ................................................................................................... 21 4.1.1.8 HEPA Filter Construction .................................................................................. 21 4.1.1.9 Separators ........................................................................................................ 22 4.1.1.10 Filter Case ....................................................................................................... 22 4.1.1.11 Sealants .......................................................................................................... 23 4.1.1.12 Gaskets ........................................................................................................... 23 4.1.1.13 Faceguards ..................................................................................................... 24 4.1.1.14 Separatorless HEPA Filters ............................................................................. 24 4.1.1.15 Mini-Pleat HEPA Filters................................................................................... 25 4.1.2 HEPA Filter Classes and Sizes ................................................................................... 27 4.1.2.1 Filter Construction Grades ............................................................................... 27 4.1.2.2 Filter Performance Levels ................................................................................. 27 4.1.2.3 Enclosed Filters ................................................................................................ 28 4.1.2.4 Cylindrical Filters .............................................................................................. 29 4.1.2.5 Filter Sizes ........................................................................................................ 30 4.1.2.6 Filter Weight .................................................................................................... 30 DOE-HDBK-1169-2022 v

4.1.3 HEPA Filter Performance Characteristics ................................................................. 31 4.1.3.1 Airflow Resistance ............................................................................................ 31 4.1.3.2 Dust-Holding Capacity ...................................................................................... 31 4.1.3.3 Shock and Blast Resistance .............................................................................. 32 4.1.3.4 Heat from Fire and Explosion ........................................................................... 33 4.1.3.5 Moisture and Corrosion Effects ........................................................................ 34 4.1.3.6 Radiation Resistance ........................................................................................ 35 4.1.4 HEPA Filter Performance Testing for Nuclear Service .............................................. 36 4.1.4.1 Airflow Resistance ............................................................................................ 37 4.1.4.2 Quality Control/Assurance Considerations ...................................................... 38 4.1.5 Effects of Aging, Wetting, and Environmental Upsets on HEPA Filter Performance 39 4.1.5.1 Aging ................................................................................................................ 39 4.1.5.2 Upset Environmental Conditions ...................................................................... 40 4.1.5.3 In-Place Testing of Filter Installations ............................................................... 41 4.1.5.4 Packaging, Storage, and Handling of HEPA Filters ............................................ 41 4.1.6 Medium Efficiency Filters (Prefilters) for HEPA Filters ............................................. 42 4.1.6.1 Filter Descriptions ............................................................................................ 42 4.1.6.2 Classes, Sizes, and Performance Characteristics of Medium Efficiency Filters . 43 4.1.6.3 Commercial and Industrial Grade Filters Performing as Medium Efficiency Filters ................................................................................................................ 44 4.1.6.4 Electrostatic and Electrified Filters ................................................................... 45 4.1.6.5 Operation and Maintenance of Medium Efficiency Filters (Prefilters) ............. 46 4.1.7 Deep-Bed Filters ...................................................................................................... 46 4.1.7.1 Deep-Bed Sand Filters ...................................................................................... 47 4.1.7.2 Deep-Bed Glass Fiber Filters ............................................................................. 48 4.1.7.3 Deep-Bed Metal Filters ..................................................................................... 49 4.1.7.4 Moisture Separators (Demisters) ..................................................................... 50 4.1.8 Testing ..................................................................................................................... 51 4.1.8.1 Introduction ..................................................................................................... 51 4.1.8.2 Proof of Design – HEPA Filter Design Qualification Testing for Nuclear Service

.......................................................................................................................... 52 4.1.8.2.1 Penetration (Efficiency) ................................................................................. 52 4.1.8.2.2 Airflow Resistance ......................................................................................... 53 4.1.8.2.3 Aerosol Test .................................................................................................. 53 4.1.8.2.4 Resistance to Rough Handling Qualification Test .......................................... 53 4.1.8.2.5 Moisture and Overpressure Resistance Qualification Test ............................ 54 4.1.8.2.6 Fire and Hot Air Resistance Qualification Test............................................... 54 4.1.8.2.7 Spot Flame Resistance ................................................................................... 54 4.1.8.2.8 Quality Control, Inspection and Testing of HEPA Filters ................................ 54 DOE-HDBK-1169-2022 vi 4.1.9 Filter Qualification, Quality Assurance Inspection, and Testing of HEPA Filters ....... 55 4.1.9.1 Introduction ..................................................................................................... 55 4.1.9.3 In-Place Component Tests and Criteria ............................................................ 55 4.1.9.4 Component Acceptance Testing ....................................................................... 55 4.1.9.5 Duct and Housing Leak Test ............................................................................. 57 4.1.9.6 Mounting Frame Pressure Leak Test ................................................................ 57 4.1.9.7 Airflow Capacity and Distribution Test ............................................................. 58 4.1.9.8 Air-Aerosol Mixing Uniformity Test .................................................................. 58 4.1.9.9 Duct Damper Bypass Test ................................................................................. 59 4.1.9.10 System Bypass Test ........................................................................................ 60 4.1.9.11 Duct Heater Performance Test ....................................................................... 60 4.1.10 Surveillance Testing ............................................................................................... 60 4.1.10.1 Introduction ................................................................................................... 60 4.1.10.2 In-Place System Leak Test, HEPA Filter Banks ................................................ 61 4.1.10.3 In-Place Testing for Adsorbers ........................................................................ 62 4.1.10.4 Nonradioactive Tracer Gas Test ..................................................................... 63 4.1.10.5 Radioactive Iodine Tests ................................................................................. 63 4.1.10.6 Test Sequence and Frequency ........................................................................ 64 4.1.10.7 In-Place Testing for Multistage Systems ......................................................... 64 4.1.10.8 First-stage Downstream Sample ..................................................................... 65 4.1.10.9 In-Place Testing for Multistage Adsorber Systems ......................................... 66 4.1.10.10 Test Aerosol/Gas Injection, throughout Second-Stage Upstream Sample ... 66

4.1.11 Adsorbent Sampling and Laboratory Testing ......................................................... 68 4.1.11.1 Sampling ......................................................................................................... 68 4.1.11.2 Laboratory Testing ......................................................................................... 69 4.1.11.3 Frequency of Testing ...................................................................................... 70 4.1.12 Testing of Deep Bed Sand Filters ............................................................................ 71 4.1.13 Testing Portable HEPA Filtration Systems .............................................................. 71 4.1.13.1 General Testing and Periodic Maintenance Considerations ........................... 71 4.1.13.2 Portable Filtration Systems Testing Applications ........................................... 72 4.1.13.3 Testing Problems and Special Considerations ................................................ 73 4.1.14 Testing HEPA Filter Vacuum Cleaners .................................................................... 73 4.1.14.1 Description of Radiological Vacuum Cleaners ................................................ 74 4.1.14.2 Operation ....................................................................................................... 75 4.1.14.3 HEPA Filter Vacuum Cleaner Tests ................................................................. 75 4.1.15 References ............................................................................................................. 76 4.2 Glovebox Filtration .......................................................................................................... 81 4.2.1 Introduction: Filtration Components ....................................................................... 81 4.2.2 Glovebox Types and Characteristics ......................................................................... 81 DOE-HDBK-1169-2022 vii 4.2.3 Importance of Glovebox Ventilation and Filtration .................................................. 83 4.2.4 Design of Glovebox Ventilation Systems .................................................................. 83 4.2.4.1 Introduction ..................................................................................................... 83 4.2.4.2 Blowers ............................................................................................................ 84 4.2.4.3 Filter Housings .................................................................................................. 85 4.2.5 Dilution of Evolved Gases......................................................................................... 90 4.2.6 Heat Dissipation ....................................................................................................... 90 4.2.7 Empirical Flow Rates ................................................................................................ 90 4.2.8 Exhaust Requirements ............................................................................................. 91 4.2.9 Vacuum-and Pressure-Surge Relief .......................................................................... 92 4.2.10 Glovebox Exhaust Manifold ................................................................................... 93 4.2.11 Exhaust Cleanup Criteria ........................................................................................ 93 4.2.12 HEPA Filters ............................................................................................................ 93

4.2.12.1 HEPA Filter Selection Criteria ......................................................................... 95 4.2.13 Medium Efficiency Filter (Prefilter) Selection ........................................................ 96 4.2.14 Inlet HEPA Filters ................................................................................................... 96 4.2.15 Roughing Filters ..................................................................................................... 97 4.2.16 Filter Replacement ................................................................................................. 98 4.2.17 Protection Against Fire and Explosion .................................................................. 100 4.2.17.1 General Guidance ......................................................................................... 100 4.2.17.2 Detection ...................................................................................................... 101 4.2.17.3 Suppression .................................................................................................. 101 4.2.17.4 Inert Environments ...................................................................................... 102 4.2.18 Control and Instrumentation ............................................................................... 102 4.2.19 Challenge Aerosol Testing of Glovebox Filters ..................................................... 106 4.2.20 Glovebox Shielding............................................................................................... 109 4.2.21 Criticality Considerations ..................................................................................... 109 4.2.22 References ........................................................................................................... 110 4.3 Small Air Cleaning Units ................................................................................................. 111 4.3.1 Introduction ........................................................................................................... 111 4.3.2 Housings ................................................................................................................ 113 4.3.3 Component Installation ......................................................................................... 113 4.3.4 Housing Construction ............................................................................................. 117 4.3.5 Bagging .................................................................................................................. 118 4.3.6 Housing Installation ............................................................................................... 120 4.3.7 Cylindrical Filter Elements ...................................................................................... 121 4.3.8 Installation and Human Factors ............................................................................. 126 4.3.9 Fume Hoods ........................................................................................................... 127 4.3.10 Portable Air Cleaning Units .................................................................................. 127 DOE-HDBK-1169-2022 viii

4.3.10.1 Operational Considerations .......................................................................... 128 4.3.10.2 Component Considerations .......................................................................... 129 4.3.10.3 Construction ................................................................................................. 131 4.3.10.4 Testing and Inspection ................................................................................. 132 4.3.10.5 Vacuum Cleaning Systems ............................................................................ 133 4.3.11 References ........................................................................................................... 133 4.4 Housing Design and System Layout ............................................................................... 135 4.4.1 Introduction ........................................................................................................... 135 4.4.2 Housing System Design .......................................................................................... 135 4.4.2.1 Man-entry Housing System Design ................................................................ 136 4.4.2.2 Arrangement and Location ............................................................................. 137 4.4.3 Component Installation ......................................................................................... 139 4.4.3.1 General ........................................................................................................... 139 4.4.3.2 Housing Construction ..................................................................................... 139 4.4.3.3 Potential Housing Leakage ............................................................................. 140 4.4.3.4 Paints and Protective Coatings ....................................................................... 140 4.4.4 Man Entry Housing ................................................................................................ 141 4.4.4.1 General ........................................................................................................... 141 4.4.4.2 Structural ....................................................................................................... 141 4.4.4.3 Structural Design ............................................................................................ 142 4.4.4.4 Mounting Frame Configuration ...................................................................... 143 4.4.4.5 Frame Fabrication .......................................................................................... 145 4.4.4.6 Clamping and Sealing ..................................................................................... 145 4.4.4.7 Filter Support ................................................................................................. 149 4.4.4.8 Size and Arrangement of Filter and Adsorber Banks ...................................... 150 4.4.4.9 Vertical Filter Banks ........................................................................................ 150 4.4.4.10 Location of Filters on Mounting Frame ........................................................ 151 4.4.4.11 Size of Banks ................................................................................................. 152 4.4.4.12 Arrangement of Banks .................................................................................. 152 4.4.4.13 Floor Plan of Filter Banks .............................................................................. 153 4.4.4.14 Steel Housings .............................................................................................. 153 4.4.4.15 Masonry and Concrete Housings .................................................................. 158 4.4.4.16 Housing Floor ............................................................................................... 158 4.4.4.17 Housing Doors .............................................................................................. 159 4.4.4.18 Housing Drains ............................................................................................. 160 4.4.4.19 Other Housing Requirements ....................................................................... 163

4.4.5 Design of Side-Access Housings ............................................................................. 167 4.4.6 Recommended Design Features ............................................................................ 167 DOE-HDBK-1169-2022 ix 4.4.7 Differences Between Nuclear Filtration Systems and Commercial/Industrial Filtration Systems ................................................................................................... 169 4.4.8 Advantages of Stainless Steel Over Heavy Carbon Steel Construction ................... 170 4.4.9 Side-Access Housings For Radial Flow Cylindrical HEPA Filters .............................. 170 4.4.10 References ........................................................................................................... 173 4.5 External Components .................................................................................................... 174 4.5.1 Introduction ........................................................................................................... 174 4.5.2 Ductwork ............................................................................................................... 174 4.5.2.1 Functional Design ........................................................................................... 174 4.5.2.2 Mechanical Design ......................................................................................... 175 4.5.2.3 Engineering Analysis ....................................................................................... 181 4.5.2.4 Engineered Ductwork ..................................................................................... 182 4.5.2.5 Materials of Construction ............................................................................... 183 4.5.2.6 Paints and Protective Coatings ....................................................................... 183 4.5.2.7 Supports ......................................................................................................... 184 4.5.2.8 Thermal Insulation and Acoustic Considerations ........................................... 184 4.5.2.9 Ductwork Leakage .......................................................................................... 184 4.5.3 Dampers and Louvers ............................................................................................ 186 4.5.3.1 Damper Descriptions ...................................................................................... 186 4.5.3.2 Design and Fabrication ................................................................................... 190 4.5.3.3 Structural Design ............................................................................................ 191 4.5.3.4 Design and Construction Considerations ........................................................ 191 4.5.3.5 Damper Operators ......................................................................................... 191 4.5.3.6 Limit Switches ................................................................................................ 192 4.5.3.7 Performance Requirements ................................................................................ 192 4.5.3.8 Qualification Testing ........................................................................................... 193 4.5.3.9 Louvers ............................................................................................................... 194 4.5.4 Fans and Motors .................................................................................................... 195

4.5.4.1 Fan Types and Applications ............................................................................ 195 4.5.4.2 Fan Performance ............................................................................................ 196 4.5.4.3 Fan Leakage Flexible Connection Leakage ...................................................... 200 4.5.4.4 Fan Construction ............................................................................................ 204 4.5.4.5 Qualification and Testing................................................................................ 204 4.5.4.6 Fan Reliability and Maintenance .................................................................... 205 4.5.4.7 Special Duty Considerations Temperature, Pressure, and Humidity .............. 205 4.5.5 Air Intakes and Stacks ............................................................................................ 206 4.5.5.1 Locating Intakes and Stacks ............................................................................ 206 4.5.5.2 Sizing Intakes and Stacks ................................................................................ 207 4.5.5.3 Structural Design Aspects ............................................................................... 208 DOE-HDBK-1169-2022 x 4.5.6 Instrumentation and Control ................................................................................. 209 4.5.6.1 Codes and Standards Requirements .............................................................. 209 4.5.6.2 Functional Requirements ............................................................................... 209 4.5.6.3 Airflow Control ............................................................................................... 209 4.5.6.4 Pressure Control ............................................................................................. 211 4.5.6.5 Qualification and Testing................................................................................ 211 4.5.7 References ............................................................................................................. 211 5.0 SPECIAL TOPICS ............................................................................................................. 214 5.1 Fire Protection of Air Cleaning Systems ......................................................................... 214 5.1.1 DOE Fires Affecting Air Cleaning Systems .............................................................. 214 5.1.2 Fire Phenomena ..................................................................................................... 215 5.1.2.1 Smoke Generation .......................................................................................... 215 5.1.2.2 Water Generation .......................................................................................... 216 5.1.2.3 Heat Loss in Ducts .......................................................................................... 216 5.1.2.4 Smoke and Water Loss in Ducts ..................................................................... 216 5.1.2.5 Effects on Filters of Heat, Smoke, and Related Products ................................ 217 5.1.2.6 HEPA Filter Response to Temperature ........................................................... 217 5.1.2.7 HEPA Filter Response to Smoke and Water Loading ...................................... 218 5.1.2.8 Filter Exposure to Water ................................................................................ 218 5.1.2.9 Effects on Physical Integrity of the Confinement Ventilation System

Components .................................................................................................... 219 5.1.2.10 Effects of Wildland Fires ............................................................................... 219 5.1.2.11 Fires Occurring within Confinement Ventilation Systems ............................ 219 5.1.2.12 Generation of Heat, Smoke, and Related Products ...................................... 219 5.1.2.13 Transport of Heat, Smoke, and Related Products ........................................ 220 5.1.2.14 Effects on Filters of Heat, Smoke, and Related Products .............................. 220 5.1.3.1 Objectives and Requirements ........................................................................ 221 5.1.3.2 Fuel Control .................................................................................................... 221 5.1.3.3 Control of Energy Sources .............................................................................. 222 5.1.3.4 Passive Design Features ................................................................................. 222 5.1.3.5 Duct Response to Fire .................................................................................... 222 5.1.3.6 Air Supply and Extraction ............................................................................... 223 5.1.3.7 Entrance Filters .............................................................................................. 223 5.1.3.8 Medium Efficiency Filters ............................................................................... 223 5.1.3.9 Filter Housings ................................................................................................ 224 5.1.3.10 Fire Screens .................................................................................................. 224 5.1.3.11 Materials ...................................................................................................... 224 5.1.3.12 Wood Filter Frames ...................................................................................... 224 5.1.3.13 Fire Barriers .................................................................................................. 225 DOE-HDBK-1169-2022 xi 5.1.3.14 Active Design Features and Fire Hazard Controls ......................................... 226 5.1.3.15 Fire Dampers ................................................................................................ 226 5.1.3.16 Fire Detection and Suppression Systems ...................................................... 226 5.1.3.17 Wet Pipe Sprinkler Systems .......................................................................... 227 5.1.3.18 Deluge and Water Spray Systems ................................................................. 227 5.1.3.19 Water Mist Systems ..................................................................................... 229 5.1.3.20 Sprinklers within Ductwork .......................................................................... 229 5.1.3.21 Demisters and HEPA Filters .......................................................................... 229 5.1.3.22 Fire Department Standpipe Systems ............................................................ 230 5.1.3.23 Water Runoff Collection ............................................................................... 230 5.1.3.24 Gaseous Agent Systems ............................................................................... 230 5.1.3.25 Flammable Gas Detection ............................................................................ 230 5.1.3.26 Protection of Carbon-Filled Adsorption Systems .......................................... 231 5.1.3.27 Filter Assemblies in Plywood Enclosures ...................................................... 232 5.1.3.28 High-Efficiency Metal Fiber Filter Systems ................................................... 232 5.1.3.29 Radioiodine Absorber Air Cleaning Systems ................................................. 232 5.1.3.30 Deep-Bed Fiberglass Filter Systems .............................................................. 233 5.1.3.31 Deep-Bed Sand Filter Systems ...................................................................... 233 5.1.3.32 Self-Cleaning Viscous Liquid Filters .............................................................. 234 5.1.3.33 Electrostatic Precipitator Prefilter ................................................................ 234 5.1.3.34 Ceramic HEPA Filters .................................................................................... 234

5.1.4 Fire Protection Concepts for Gloveboxes ............................................................... 234 5.1.4.1 Protective Atmospheres ................................................................................. 235 5.1.5 Operations and Maintenance Practices for Fire Protection of Confinement Ventilation Systems ................................................................................................ 236 5.1.5.1 Essential Elements .......................................................................................... 236 5.1.5.2 Fire Prevention ............................................................................................... 237 5.1.5.3 Procedures ..................................................................................................... 237 5.1.5.4 Inspection, Testing, and Maintenance ........................................................... 237 5.1.5.5 Impairment Planning ...................................................................................... 238 5.1.5.6 Modifications ................................................................................................. 238 5.1.5.7 Emergency Planning ....................................................................................... 238 5.1.5.8 Technical Safety Requirements Tie-in ............................................................ 238 5.1.5.9 Quality Assurance........................................................................................... 238 5.1.5.10 Assessments ................................................................................................. 238 5.1.6 Generic Firefighting Procedures ............................................................................. 238 5.1.6.1 Control Ventilation Configurations, Volumes, and Flow Rates in the Field .... 239 5.1.6.2 Activation of the Manual Deluge System ....................................................... 240 5.1.6.3 Deluge System Flow Times ............................................................................. 241 DOE-HDBK-1169-2022 xii 5.1.6.4 Manual Activation of the Automatic Deluge System ...................................... 241 5.1.7 References ............................................................................................................. 241 5.2.1 Introduction ........................................................................................................... 244 5.2.2 DOE Order 420.1C and DOE Guide 420.1-1A ......................................................... 244 5.2.3 DOE-STD-1020-2016 and DOE-HDBK-1220-2017 ................................................... 244 5.2.4 Additional References ............................................................................................ 244 5.3 Occupational Safety and Health .................................................................................... 245 5.3.1 Introduction ........................................................................................................... 245 5.3.2 Confined Space Entry ............................................................................................. 245 5.3.3 Excessive Noise ...................................................................................................... 246 5.3.4 Excessive Heat ....................................................................................................... 246 5.3.5 Hazardous Biological and Chemical Substances ..................................................... 247 5.3.6 Respiratory Protection ........................................................................................... 248 5.3.7 Radiation Exposure and the ALARA Principle ......................................................... 249

5.4 Deep-Bed Sand Filters ................................................................................................... 250 5.4.1 Introduction ........................................................................................................... 250 5.4.2 Overview of Deep-Bed Sand Filters ........................................................................ 250 5.4.3 Deep-Bed Sand Filter Design .................................................................................. 253 5.4.4 Deep-Bed Sand Filter Plugging ............................................................................... 255 5.4.5 Spent Media Disposal ............................................................................................ 255 5.4.6 Burial in Place ........................................................................................................ 256 5.4.7 Decontamination ................................................................................................... 256 5.4.8 References ............................................................................................................. 256 DOE-HDBK-1169-2022 1 1.0 Introduction 1.1 Purpose This handbook is a companion document to DOE-STD-1269-2022, Air Cleaning Systems in DOE Nuclear Facilities (referred to hereafter as “the Standard”). It identifies good practices drawn from operational experience at DOE components and commercial nuclear facilities, industry input, and the advice of technical experts that can be used to meet the Standard’s requirements and guidance. It also offers general technical advice on topics related to air cleaning systems needed for nuclear and worker safety. The handbook provides clarification of the rationale for some provisions in the Standard and cites references to assist all DOE components and their contractors in applying the Standard. With respect to the Standard’s requirement statements, the handbook should be viewed as an implementation aid, not as an interpretation of the requirements. 1.2 Applicability The handbook applies to new and existing Category 1, 2, and 3 nuclear facilities. 1.3 Organization The handbook follows the format and organization of the Standard. DOE-HDBK-1169-2022 2 2.0 Terminology 2.1 Acronyms & Abbreviations This document uses a large number of acronyms and abbreviations. Some are well-known in the nuclear industry at large (such as DOE, NRC, and ASTM) while others such as HEPA and ASHRAE are familiar to any engineer working on air cleaning systems. In each case where a less familiar acronym or abbreviation is used (e.g., DAC for derived air concentration), an explanation is provided on first use. DOE-HDBK-1169-2022 3 3.0 System Design 3.1 Introduction Design of an air cleaning system in a nuclear facility is a complex task that requires the careful integration of numerous primary and support systems. The system should be capable of providing a clean, healthy working environment for personnel in the facility, contain radioactive and chemical hazards in both normal and accident conditions, and remain operational when challenged by events such as earthquakes or fires. This section of the handbook provides a wide range of guidance on system design, based upon many decades of DOE experience dating back to the Manhattan project. 3.2 Contaminants

Intake air cleaning systems or supply systems filter the atmospheric dust and other contaminants brought into the facility. Recirculating systems, if used, clean the air in a building or location and return the air to that location. Other sources of particulate and gaseous contamination are infiltration and “people-generated” particulates (e.g., lint, skin, hair) and off- gassing of materials such as paint, solvents, carpets, and furniture. All of these factors should be considered in determining the parameters for proper system design. These contaminants may become radioactive when exposed to certain environments (e.g., by adsorption of radioactive vapors or gases or by agglomeration with already radioactive particles). Because particles in the size range of 0.05 to 5 micrometers (µm) tend to be retained by the lungs when inhaled, they are of primary concern in operations that involve radioactive material. They are also recognized as among the health hazards of nonradioactive air pollution. As shown in Table 3.1, over 99 percent, by count, of typical urban air samples have a mean particle size of 0.05 µm. Reports of dust concentrations in air are generally based on the masses of the particulate matter present. As shown in Table 3.1, mass accounts for only a negligible portion of the total number of particles in the air. This is important in filter selection because it indicates that some filters with a high efficiency based on weight may be inefficient on a true count basis. That is, the filters are efficient for large particles, but inefficient for small (less than 0.75 µm) particles. This is true of most common air filters used as medium efficiency filters. On the other hand, the High-Efficiency Particulate Air (HEPA) filter is highly efficient for all particle sizes down to and including the smallest shown in Table 3.1. The 99.97 percent minimum efficiency for these filters is actually for the most penetrating size particles, i.e., those ranging in size from 0.07 to 0.3 µm. Dust concentrations vary widely from place to place and, for the same location, from season to season and from time to time during the same day. Concentrations in the atmosphere may vary from as low as 20 micrograms per cubic meters (µg/m3) in rural areas to more than 20 mg/m3 in heavily industrialized areas. DOE-HDBK-1169-2022 4 Table 3.1: Distribution of Particles in Typical Urban Air Sample Mean Particle Size (µm) Particle Size Range (µm) Approximate Particles Count per Cubic Foot of Air Percent by Weight Percent by Count 20.0 50-10 12.5 x 103 28 1 x 10-10 7.5 10-5 10 x 104 63 8 x 10-10 2.5 5-1 12.5 x 106 6 1 x 10-7 0.75 1-0.5 10 x 107 2 8 x 10-7 0.25 0.5-0.1 12.5 x 109 1 1 x 10-4 0.05 0.1-0.001 12.5 x 1015 <1 99.9999 Dust-producing operations may generate concentrations as great as several thousand g/m3 at the workplace. Because the weight percent determinations on which these concentrations are based account for only a small fraction of the number of particles present, the true count of particles smaller than 5 µm may number in the billions per 1000/ft3. Atmospheric dust concentrations can vary significantly through the year. Filter selection, particularly medium efficiency filter and building supply filter selection, should be based on the atmospheric dust concentrations that can be encountered at a particular site at any time of the year.

Figure 3.1 below, “Distribution of Particles,” shows the distribution of particles (by weight percent) in atmospheric air as a function of particle shape. Variations in particle shape, mean particle size, particle size range, and concentration affect filter life, maintenance costs, and operational effectiveness. The size range of various types of particles, the technical nomenclature of various types of aerosols, and the applicability of various types of air cleaning devices as a function of particle size are shown in Figure 3.2. A major source of the lint often found on filters is derived from the operations, which generate droplets and solid abrasion of clothing as people move about. In addition, a person at rest gives off more than 2.5 million particles (e.g., skin, hair) and moisture droplets/minute in the size range of 0.3 to 1 mm3. Figure 3.1: Distribution of Particles DOE-HDBK-1169-2022 5 Figure 3.2: Characteristics of Atmospheric and Process-Generated Particulates, Fumes, and Mists and Effective Range of Air DOE-HDBK-1169-2022 6 Process-generated airborne contaminants fall into two general size ranges. Those produced by machining, grinding, polishing, and other mechanical operations are generally large, (from one to several hundred µm), based on the process. Particles less than 100 microns can be picked up by the respiratory tract through the nose and mouth. Particles greater than one micron can be removed effectively by commercial air filters or other conventional air cleaning techniques. The other size particle range includes those produced by evaporation/condensation and other processes that are less than one micron in size. Nuclear-grade HEPA and Ultra Low Penetration Air (ULPA) filters provide a higher cleaning efficiency to remove those submicron particles; ULPA filters can remove 99.999 percent of sub-micrometer particles. The need for ULPA filters at DOE sites is only occasionally seen and is site-specific to the DOE application. HEPA filters are less expensive than ULPA filters and are acceptable for removing submicron particles in most applications. For reactor operations, process-generated contaminants include radioactive noble gases and halogens. Because of their chemical inertness, limited reactivity with available sorbents, and the great difficulty of separating them, the noble gases (xenon and krypton) have been treated in the past by simple holdup to allow time for radioactive decay of the shorter half-life elements, as well as dilution with clean air before discharge to the atmosphere. They can also be separated by cryogenic fractionation, charcoal adsorption, or fluorocarbon adsorption and stored until a significant degree of radioactive decay takes place. Halogen gases, essentially elemental iodine and certain volatile organic iodides are captured by adsorption either on activated carbon or certain synthetic zeolites. 3.3 Environmental Conditions Although some air cleaning system components are prequalified to operate in a given temperature range, the air cleaning system designer should verify all components of the system will function between the maximum and minimum temperature conditions for the specified application. If the temperature range of the specific application exceeds the components’ design qualification temperature, requalification is necessary to meet the operational and design life requirements of the system.

In general, continuous operation at high temperature (greater than 250 degrees Fahrenheit) is detrimental to both HEPA filters and activated carbon adsorbers. At high temperatures, the shear strength of adhesives and binders used in the manufacture of HEPA filters and filter media may diminish, thereby limiting the safe pressure drop to which they can be subjected. The limiting temperature varies with the specific adhesive and binders used. Filter manufacturers have designed HEPA filters for temperatures above 250 degrees Fahrenheit (a 500-degree Fahrenheit filter is also available). The filter manufacturer should provide objective data that the filters are qualified for the higher-temperature environments of the specific application. Alternatively, for high-temperature applications, particulate filtration can be DOE-HDBK-1169-2022 7 accomplished with the use of metal filters constructed of sintered metal or metal mesh.1 Ceramic filters are an emerging alternative (see Section 5.1.3.34). Metal filters are manufactured for medium efficiency and HEPA efficiency ranges. Due to their relatively high cost, metal filters should be considered only for those applications where standard glass fiber filters would not meet the environmental or design conditions. The limiting temperature of adsorbents for capturing radioactive iodine and iodine compounds is related to the desorption temperature of the adsorbed compound and the chemicals with which it has been impregnated to enhance its adsorption of organic radioiodides. For example, the limiting temperature of adsorbents impregnated with chemicals (e.g., triethylene-diamine- and potassium iodine-impregnated activated carbon) is 280 degrees Fahrenheit. When temperatures higher than the operating limits of air cleaning system components need to be accommodated, chilled water coils, heat sinks, dilution with cooler air, or some other means of cooling should be provided to reduce temperatures to levels that the components can tolerate. Environmental qualification of an air cleaning system should address thermal expansion and the heat resistance of ducts, dampers, filter housings, component mounting frames and clamping devices, and fans. Operational consideration also should be given to the flammability of dust collected in the ducts and on the filters. The complexity of the air cleaning system needed to provide satisfactory working conditions for personnel and to prevent the release of radioactive or toxic substances to the atmosphere depends on the following factors: • Nature of the contaminants to be removed (e.g., radioactivity, toxicity, corrosivity, particle size and size distribution, particle shape, and viscidity); • Temperature (e.g., process heat, fire); • Moisture (e.g., sensible humidity process vapors, water introduced from testing); • Radiation (e.g., personnel exposure and material suitability considerations); • Other environmental conditions to be controlled; and • Upset or accident hazard considerations. In designing an air cleaning system, development of the environmental operating conditions is the first step. Before appropriate individual system components can be environmentally qualified, the designer should consider all environmental parameters on an integrated basis. This may require additional qualifications.

The facility owner normally identifies the design and environmental parameters that are compatible with the overall facility design. These parameters should be identified prior to system design because they are the basis for the equipment design. If the environmental parameters are carefully considered, a detailed analysis of cost versus long-term operation will 1 The construction and performance requirements for metal filters will be found in Section FI, Metal Media Filters, of ASME AG-1 (Code on Nuclear Air and Gas Treatment). DOE-HDBK-1169-2022 8 provide an environmental maintenance schedule for replacing components and parts throughout the intended operational life of the system. This will ensure that the system will perform its intended function properly, efficiently, and cost-effectively. Table 3.2 lists some common system environmental parameters that should be considered for system design. Table 3.2: Environmental Parameters for System Design Parameters Examples Types of gases treated Air, hydrogen, oxygen, nitrogen, and argon. Flow rate(s) The maximum and minimum operating flow rates for normal and accident conditions. Pressure and pressure drop The external pressure and/or vacuum pressure at the inlet and/or outlet of the system; the maximum system pressure, usually accident or upset mode; the maximum allowable pressure drop across the air cleaning system components. Temperatures The maximum and minimum operating temperatures of the airstream and equipment. Radiation The maximum expected alpha, beta, and gamma radiation dose rates (rads/hour) and cumulative levels (rads). Relative humidity, condensation, and direct introduction of liquids The maximum and minimum relative humidity of the gas entering the air cleaning system, condensation with potential for wicking. Contaminants that may be removed (or not) from the gas stream Removal efficiencies for particulate, gaseous, entrained water, chemical, radiological, volatile organic chemicals, and other materials, as well as considerations of other materials’ capabilities for air contaminants. Seismic requirements Seismic response curves for the expected equipment location. Pressure-time transients Deflagration, detonation (internal), and tornado (external). Design life and operating life Projected facility and equipment operating life [e.g., filter service life]. Concentration of contaminants within the facility or area to be ventilated Specified amounts of identified contaminants, in curies per volumetric unit, grams per volumetric unit, or particles per volumetric unit. Allowable concentrations of contaminant in the occupied areas of the facility Specified amounts of identified contaminants, in curies per volumetric unit, grams per volumetric unit, or particles per volumetric unit. Regulatory limits for stack release of contaminants Specified amounts of identified contaminants, in curies per volumetric unit, grams per volumetric unit, or particles per volumetric unit. This may also be expressed in dose units of exposure to radiation. DOE-HDBK-1169-2022 9 Many radiochemical operations generate acid or caustic fumes that can damage or destroy filters, system components, and construction materials. Some products of radiochemical operations can produce shock-sensitive salts (e.g., perchlorate acid salts and ammonium nitrate) that should be considered in the design and operation. The air cleaning system designer should select components and materials of construction suitable for the corrosive environment to ensure high levels of system performance and reliability. Acid-resistant medium efficiency filters and HEPA filters are available. These filters utilize media constructed with Nomex® or Kevlar® fibers mixed with glass fibers during manufacturing, epoxy-coated separators to extend the life of the aluminum separators, and stainless-steel frames.

Metal filters with a demonstrated suitability for a moist corrosive atmosphere, in accordance with ASME AG-12 code requirements, are recommended for hydrogen fluoride or other highly acidic applications. Hydrogen fluoride is a concern because it will attack the glass media. Wood- case filters are vulnerable to attack by nitric acid that will form nitrocellulose and negatively affect filter performance. Stainless steel is recommended for ductwork and housings when corrosion can be expected. Since this material may be insufficient in some cases, coated (e.g., vinyl, epoxy) stainless steel or fiber-reinforced plastics may be necessary.3 The system designer can either: (1) use existing databases containing information about the performance of materials (including the filter media) exposed to various concentrations of corrosive contaminants, or (2) perform actual testing to validate the air cleaning system design. Scrubbers or air washers may be employed to pretreat the air or gas before it enters the air cleaning system or to scrub the airstream of perchlorate and ammonium nitrate salts and other corrosive materials, but consideration should also be given to moisture carryover if the scrubbers or air washers are not designed and operated properly. ASME AG-1 moisture separators are recommended ahead of the filters. Corrosion is not always an obvious threat. In activated carbon-filled adsorbers, for example, even trace amounts of nitrous oxide or sulfur dioxide will concentrate in the adsorbent over time, and negatively affect the ability of the carbon to remove radioactive contaminants. In the presence of moisture, these compounds can form nitric or sulfuric acids that are capable of corroding the stainless-steel parts of the adsorber, i.e., the perforated metal screens. Aluminum and carbon steel are subject to corrosion when in contact with moisture-laden carbon. For this reason, stainless steel is always specified for adsorber cells and for adsorber-cell mounting frames. Electrical and electronic components are particularly susceptible to corrosive atmospheres. Plastics become brittle over time, and contacts can corrode. For this reason, all electronic components are environmentally qualified for the intended application. 2 ASME AG-1, Code on Nuclear Air and Gas Treatment, 2019 ed. 3 Corrosion-resistant coatings are covered by ASTM D5144, Standard Guide for Use of Protective Coating Standards in Nuclear Power Plants. DOE-HDBK-1169-2022 10 Care should be exercised in selecting and using gaskets, as some gasket material reacts with the moisture in the airstream and releases chlorides that can corrode steels (including stainless steel). Gasket material selection should also include consideration of the effects of the material’s use in acidic, radioactive, or other harsh environments. Note that radiation may cause undesirable reactions such as decomposition of TeflonTM into hydrofluoric acid. The ASME AG-1 Code (Articles FC-3120 and FK-3120) contains specifications for acceptable gasket material. 3.4 Backup Power Backup electrical power is required when specified by facility design and safety documentation. The amount of backup power needed for fans, dampers, valves, controls, and electrical heaters to control the relative humidity of the effluent airstream (as dictated by the facility design requirements) should be estimated for both off-normal and accident conditions. Close coordination between the system designers of both the air cleaning and electrical systems is needed to ensure that there is adequate backup power available.4

3.5 Work Area Ventilation Work area ventilation systems should be designed to ensure that concentrations of radioactive gases and aerosols in the air of occupied and occasionally occupied areas do not exceed the derived air concentrations (DAC) established for occupationally exposed persons under normal or abnormal operating conditions. Workroom ventilation rates are based primarily on heating and cooling requirements, the potential combustion hazard, and the potential inhalation hazard of substances that are present in or could be released to the workroom. Releases to the atmosphere should not exceed permissible limits for nonoccupationally exposed persons (see 40 Code of Federal Regulations (CFR) Part 61 Subpart H). Because radioactive gases and aerosols might be released accidentally in the event of an equipment failure, a spill, or a system upset, the ventilation and air cleaning facilities should be designed to maintain airborne radioactive material within prescribed limits during normal operations. In addition, the ventilation and air cleaning facilities should perform in accordance with expectations established during the evaluation of potential accident conditions. The current DACs for radioactive substances in air are specified in 10 CFR Part 835, Appendix A. These DACs should be applied to the design of a ventilation system using a hazard categorization process where the level of ventilation control is commensurate with the radiological risk present in the proposed operation. (In a similar manner, the same conceptual process can also be applied to non-radiological airborne hazards.) NRC’s rule 10 CFR Part 20 provides regulatory guidance on the use of DACs. Based on the guidance cited above, one approach would be to group the material in use into the hazard classes shown in Table 3.3, and then to zone the facility ventilation systems based 4 See NFPA 110, “Standard for Emergency and Standby Power Systems” and IEEE 446-1995, “IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications.” DOE-HDBK-1169-2022 11 on the criteria shown in Table 3.4.5 An alternative approach would be to classify the risk based on the anticipated airborne and surface contamination levels, as shown in Table 3.5. The user should note that these criteria are based on the potential for the activity to generate airborne radioactive materials; they do not consider the direct radiation from the material, which would require separate shielding considerations. By introducing such indexes of potential hazards and limitations on the quantities of materials that can be handled, it is possible to establish a basis for ventilation and air cleaning requirements in various parts of a building or plant. Figure 3.3 illustrates a typical zoning plan for a nuclear facility. Not all of the confinement zones listed in Table 3.4 would be required in all buildings, and an entire building could possibly be designated a single zone. Confinement zones are defined with respect to function and permitted occupancy in the following paragraphs. Confinement Zones

As shown in Figure 3.3, the general approach is to establish ventilation zones in a three-tiered manner. Multizone buildings are usually ventilated so that air flows from the less contaminated zone to the more contaminated zone. The interiors of exhaust and recirculating ductwork are considered to be of the same hazard classification as the zone they serve. Airflow should be sufficient to provide the necessary degree of contaminant dilution and cooling and to maintain sufficient pressure differentials between zones where there can be no backflow of air spaces of lower contamination, even under upset conditions. The pressure differentials should be determined during the facility’s design and should be in accordance with the applicable standards. Substantially higher differentials are often specified between Primary and Secondary Confinement Zones (see below) than for other boundaries. Table 3.3: Hazard Classification of Radioisotopes Hazard Class Relative Hazard DAC, Air (µCi/ml) 1 Very High <10-10 2 High 10-10 to 10-8 3 Moderate 10-8 to 10-6 4 Negligible >10-6 Table 3.4: Zoning of Facilities Based on Radiotoxicity of Materials Handled Quantity of Material Permitted in Zone at any One-Time a, b Radiotoxicity of Isotopes Primary Confinement Secondary Confinement Tertiary Confinement Very High > 10 mCi 0.1 µCi-10mCi 0-0.1 µCi High > 100 mCi 1.0 µCi-100mCi 0-1.0 µCi Moderate >1 Ci 10 µCi-1 Ci 0-10 µCi Negligible >10 Ci 100 µCi-10 Ci 0-100 µCi 5 The limits given in the tables are guides and should not be considered absolute. DOE-HDBK-1169-2022 12 a There are practical upper limits to the quantities of materials in any particular zone, based on the type of material and design of the confinement systems. For example, criticality safety concerns may restrict the amount of fissile material that can be handled at one time, fire protection concerns may limit the amount of pyrophoric materials, and shielding considerations may limit the amount of materials when penetrating radiation is emitted. An activity- specific hazards analysis should always be conducted to determine the actual limits to be applied in practice. b These criteria are based on the potential for the activity to generate airborne radioactive materials. Table 3.5: Zoning of Facilities Based on Contamination Levels Anticipated Contamination Levels Type of Contamination Primary Confinement Secondary Tertiary Airborne a >100 x DAC 1 x DAC to 100 x DAC < 1 x DAC Removable Surface b >>RSCV c >RSCV c <RSCV a For airborne contamination, the DAC value is listed in 10 CFR Part 835, Appendix A, for the type and chemical form of the material being handled. b For removable contamination, the RSCV is the removable surface contamination value listed in 10 CFR 835, Appendix D, for the type of the material being handled. c Removable surface contamination levels do not always directly lead to an increasing level of airborne contamination. The level of airborne contamination strongly depends on the potential for the particular activity to resuspend the deposited particles into the atmosphere. For this reason, it is difficult to establish a generic correlation. If the RSCV is the main consideration for differentiating between a secondary and primary confinement specification, then the approach established in Tables 2.3 and 2.4 should be applied.

Areas from which air is not recirculated include areas that produce or emit dust particles, heat, odors, fumes, spray, soot, smoke, or other contaminants that cannot be sufficiently treated and could be potentially injurious to health and safety of personnel or are potentially damaging to equipment. These areas are 100 percent exhausted. Recirculation within a zone (circulating the air through a high-efficiency air cleaning system before discharge back to the zone) is permitted, but recirculation from a zone of higher contamination back to a zone of lesser contamination is typically prohibited. The methodology used above is based on the DACs for radioactive substances in air, as specified in 10 CFR Part 835. For toxics and noxious substances, the DACs should be replaced with Permissible Exposure Limits (PEL), including irritant and nuisance substances, as specified in 29 CFR 1910. The federal PELs are obsolete in some cases. A more convenient (and generally more current) tabulation of occupational exposure limits is published by the American Council of Governmental Industrial Hygienists (ACGIH) in the annual issue of Threshold Limit Values (TLV). The latter reference includes a procedure for determining TLVs for mixed toxicants, as well as limit values for heat stress, nonionizing radiation, and noise. DOE Order (O) 440.1B, Worker Protection Management for DOE Federal and Contractor Employees, specifies how to select PELs and TLVs.6 Primary Confinement Zone The primary confinement zone comprises those areas where high levels of airborne contamination are anticipated during normal operations. Facility personnel do not normally 6 See Section 4m.(9) of the Order. DOE-HDBK-1169-2022 13 enter primary confinement zones. When entry is necessary, it is done under tightly controlled conditions. This zone includes the interior of a hot cell, glovebox, piping, vessels, tanks, exhaust ductwork, primary confinement HEPA filter plenums, hood, canyon, or other confinement for handling highly radioactive material. Confinement features should prevent the spread of radioactive material within the building under both normal operating and upset conditions up to and including the Design Basis Accident (DBA) for the facility. Complete isolation (physical separation) from neighboring facilities, laboratories, shop areas, and operating areas is necessary. Unavoidable breaches in the primary confinement barrier should be compensated for by an adequate inflow of air or safe collection of the spilled material. The exhaust system should be sized to ensure an adequate inflow of air in the event of a confinement breach. An air exhaust system that is independent of those serving surrounding areas is desirable. HEPA filters are typically required in air inlets, and independent testable HEPA filters should be installed in the exhaust, depending on the application. The exact number of testable stages is determined by safety analysis. Secondary Confinement Zone

The secondary confinement zone comprises those areas where airborne contamination could be generated during normal operations or as a result of a breach of a primary confinement barrier. This zone consists of the walls, floors, ceilings, and associated ventilation systems that confine any potential release of hazardous materials from primary confinement. Related areas include glovebox operating areas, hot cell service or maintenance areas, and the ventilation system servicing the operating areas. Pressure differentials should be available to produce inward airflow into the primary confinement should a breach occur. These pressure differentials should be established in conjunction with particle recommended capture velocities across boundaries between primary and secondary confinement zones. A rule of thumb for capture velocities is 100 fpm. Penetrations of the secondary confinement barrier typically require positive seals to prevent migration of contamination out of the secondary confinement zone. Air locks or a personnel clothing-change facility are installed at the entrance to the zone. Restricted access areas are generally included in the secondary confinement zone. Tertiary Confinement Zone The tertiary confinement zone comprises those areas where airborne contamination is not expected during normal facility operations. This zone consists of the walls, floors, ceilings, and associated exhaust system of the process facility. It is the final barrier against release of radioactive and toxic material to the environment. The secondary and tertiary boundaries may exist in common, as in a single-structure envelope. DOE-HDBK-1169-2022 14 Figure 3.3: Typical Process Facility Confinement Zones 3.6 References 1. 10 CFR Part 20 (Code of Federal Regulations), 2019, Energy: Standards for Protection Against Radiation, Appendix B, Washington, DC. 2. 10 CFR Part 835 (Code of Federal Regulations), 2019, Occupational Radiation Protection Program, U.S. Department of Energy, Washington, DC. 3. 29 CFR §1910 (Code of Federal Regulations), 2019, Occupational Safety and Health Standards, Occupational Safety and Health Administration, Washington, DC. 4. 40 CFR 61 (Code of Federal Regulations), 2019, National Emission Standards for Hazardous Air Pollutants, Subpart H, Washington, DC. 5. ACGIH (American Conference of Governmental Industrial Hygienists), Annual Issue, TLVs— Threshold Limit Values for Chemical Substances and Physical Agents in the Workroom Environment, Cincinnati, OH. 6. ACGIH (American Conference of Governmental Industrial Hygienists), 2001, Industrial Ventilation – A Manual of Recommended Practices, 28th Edition, Cincinnati, OH. 7. AIHA (American Industrial Hygiene Association), Laboratory Ventilation, ASSP/AIHA Z9.5- 2012. 8. ASHRAE (American Society of Heating Refrigerating and Air Conditioning Engineers), 2017, Fundamentals Handbook of HVAC Systems, [I-P Edition] Atlanta, GA. 9. ASHRAE (American Society of Heating, Refrigerating and Air Conditioning Engineers), 1993, Heating, Ventilating and Air Conditioning Design Guide for Department of Energy Nuclear Facilities, Atlanta, GA. DOE-HDBK-1169-2022 15 10. ASHRAE, 2017, Method of Testing General Ventilation Air Cleaning Devices for Removal Efficiency by Particle Size, Standard 52.2-17, Atlanta, GA. 11. ASME (American Society of Mechanical Engineer), 2019, Code on Nuclear Air and Gas Treatment, ASME AG-1, New York, NY.

12. ASTM (American Society for Testing and Materials), 2016, Standard Guide for Use of Protective Coating Standards in Nuclear Power Plants, Standard D5144-(08), West Conshohocken, PA. 13. Burchsted, C. A., 1968, “Environmental Properties and Installation Requirements for HEPA Filters,” Symposium on Treatment of Airborne Radioactive Wastes,” IAEA, Vienna, Austria. 14. DOE, 2012, Nonreactor Nuclear Safety Design Criteria and Explosive Safety Criteria Guide for use with DOE O 420.1A, DOE G 420.1-1A, Washington, DC. 15. DOE, 2013, Worker Protection for DOE Contractor Employees, DOE O 440.1B, Washington, DC. 16. DOE, 2018, Facility Safety, DOE O 420.1C, Washington, DC. 17. First, M. W., and L. Silverman, 1962, “Cost and Effectiveness of Air Cleaning Systems,” Nuclear Safety, 4(1), pp. 61-66. 18. Harrington, R. E., 1974, “Fine Particulates—The Misunderstood Air Pollutant,” Journal of Air Pollution Control Association 24(10), pp. 927-929, Pittsburgh, PA. 19. IEEE (Institute of Electrical and Electronic Engineers), 2003 (R2008) Standard for Qualifying Class 1E Electrical Equipment for Nuclear Power Generating Stations, IEEE Standard 323, New York, NY. 20. IEEE (Institute of Electrical and Electronic Engineers), 2013, Recommended Practice for Seismic Qualification of Class 1E Equipment in Nuclear Generating Stations, IEEE Standard 344, New York, NY. 21. ASME N511-2017, “In-Service Testing of Nuclear Air-Treatment, Heating, Ventilating, and Air-Conditioning Systems.” 22. ANSI/ISA 84.00.01-2004, Functional Safety: Safety Instrumented Systems for the Process Industry Sector. 23. ERDA 76-21, Nuclear Air Cleaning Handbook: Design Construction, and Testing of High- Efficiency Air Cleaning Systems for Nuclear Applications, 1979. DOE-HDBK-1169-2022 16 4.0 Component Level Guidance and Best Practices 4.1 Filtration Components and Filter Testing 4.1.1 Introduction: Filtration Components Filters are widely used in nuclear ventilation, air cleanup, and confinement systems to remove particulate matter from air and gas streams. Air filters are defined as porous structures through which air is passed to separate out entrained particulate matter. The word “filter” is derived from a word for the fabric called felt, pieces of which have been used for air and liquid filtration for hundreds of years. The porous structures of a filter may also be composed of granular material such as sand or fibers derived from cotton, minerals (glass, asbestos), ceramics, metals, or a wide selection of plastic materials. For filtration purposes, although all filters do not contain fibers, fibers in filters may be woven or felted into a cloth or formed into a paper-like structure. Filters may also be constructed in the form of highly porous fibrous beds of considerable depth. Additional information on ceramic filters is contained in Section. 5.1.3.34. The porous structure can be produced as high strength media with a fiberglass woven fabric laminated to one or both sides of the media for added strength and durability. Other kinds of air cleaning devices (e.g., adsorbers, liquid scrubbers, electrostatic precipitators (ESP)) are sometimes referred to as “filters” because they are capable of removing particles from an airstream. For clarity, the strict definition of a filter (given above) will be used in this chapter. 4.1.1.1 Air Filter Types

Air filters of many types and materials of construction have been designed, manufactured, and applied to meet a wide variety of industrial and commercial requirements for clean air. The nuclear industry makes full use of all filter types. Commercially available filters are divided into three distinct categories based on how they operate to remove suspended particulate matter from the air passing through them. The largest category, often referred to as ventilation or heating, ventilation, and air conditioning (HVAC) filters, is composed of highly porous beds of resin-bonded glass or plastic fibers with diameters ranging from 1 to 40 micrometers (µm). The fibers act as targets for collecting airborne dust. As their name indicates, HVAC filters are widely used for air cleaning in mechanical ventilation systems. They are almost all single-use, disposable items, and are used in all sectors of the nuclear industry, including as medium efficiency filters that reduce the amount of coarse dust reaching more efficient filters located downstream. A second category also is comprised of single-use, disposable filters called HEPA filters. By definition, a HEPA filter is a throwaway, extended-medium, dry-type filter with a rigid casing enclosing the full depth of the pleats, with a minimum efficiency of 99.97 percent when tested with an aerosol of 0.3-µm diameter test aerosol particles. (Filters of different flows and resistances are allowable by the ASME AG-1, Code on Nuclear Air and Gas Treatment.) A filter of identical construction and appearance but having a filtering medium with a retention of DOE-HDBK-1169-2022 17 99.999 percent for 0.1 µm particles, is referred to as an ULPA. The filtering medium of HEPA filters is thinner and more compressed and contains smaller diameter fibers than HVAC filters. HEPA filters are widely used throughout all phases of the nuclear industry. A third category of commercial air filters is known as industrial cleanable cloth filters. As the designation indicates, these filters have built-in mechanisms for periodically cleaning the filtering surfaces of accumulated dust. Unlike the first two types, industrial cleanable cloth filters rely on building a thick layer of dust on the surface of the cloth to provide a high- efficiency filtering medium. This type of filter is used in the nuclear industry for ore processing and refining and for similar tasks involving high concentrations of coarse mineral dusts. There are also special types of particulate filters for chemical and combustion operations. These include deep beds of sand in graded granular sizes, deep beds of glass fibers, and stainless-steel membranes formed from compressed and sintered granules or fibers. Stainless steel membrane filters operate like industrial cleanable cloth filters in that they depend on a dust layer for high- efficiency particle removal and should be cleaned periodically, usually by reverse compressed air jets. 4.1.1.2 Filtration The high porosity of air filters is associated with low resistance to airflow (e.g., low-resistance HVAC filters contain approximately 97 percent voids). In a uniformly dispersed filter medium, the individual fibers are relatively far apart—so far apart that the gaps between them are larger than the particles removed from the air. This means that sieving (particle removal via openings that are smaller than the particle dimensions) is not an important filtration mechanism. In fact, a sieve would make a poor air filter, even one containing sub-micrometer openings, because each collected particle closes a sieve opening so that very soon no air can pass through.

In contrast, filters collect particles from air and gas streams in well-defined ways that are associated with the dynamic properties of airborne particles. The filters respond to the physical forces present as an aerosol passes through a porous medium composed of small granules, fibers, or other shapes. 4.1.1.3 Particle Collection by Filters Figure 4.1 shows the streamlines around a spherical granule or a single filter fiber lying normal to the flow direction. A particle entering the flow field surrounding the fibers should follow the curved path of the streamlines so it can pass around the obstacle. When particles possess sufficient inertia, they resist following the curvature of the airstream and come in contact with the fiber because of their higher momentum relative to that of the conveying gas molecules. The capturing effect of inertial impaction (I in Figure 4.1) becomes greater as both aerodynamic equivalent diameter7 and the velocity of the air approaching the fiber increase. When suspended particles are very small, however, they tend to follow the curved streamlines closely; that is, they have little inertia, but are in vigorous, random (Brownian) motion (II in 7 The aerodynamic equivalent diameter can be defined as that of a sphere with a certain density and settles in still air at the same velocity as the particle of interest. This does not necessarily correlate to specific particle sizes listed throughout this handbook. DOE-HDBK-1169-2022 18 Figure 4.1). Therefore, when a streamline passes close to the fiber surface, the random movements around the streamline may result in some of the particles contacting the fiber and adhering to it. This sets up a concentration gradient between the zone close to the fiber and the bulk of the aerosol which, in turn, results in particle diffusion in the direction of the fiber surface. The smaller the particles, the more vigorous their Brownian motion and the more effective their filtration by diffusion. Because the rate at which small particles cross streamlines under the influence of diffusional forces is slow compared to rate of the effects of inertial force on large particles, separation of small particles by diffusion is enhanced by slower velocities through a filter. Figure 4.1: Streamlines Around a Filter Fiber DOE-HDBK-1169-2022 19 Particle collection by interception (III in Figure 4.1) occurs when a particle traveling in a streamline that approaches a fiber within one particle radius contacts the fiber and adheres to it. Interception is independent of flow velocity and is enhanced when the diameter of the collecting fiber or granule approaches the geometric diameter of the particle. The several filtration mechanisms of importance are shown together in Figure 4.2, where penetration (equal to 100 minus collection efficiency) is plotted against particle size. The penetration lines are not cumulative, as particles can be collected but once; however, the net effect can be approximated by the redlined summation curve. Figure 4.2 makes it clear there is a particle size where both inertial and diffusional forces are minimal and only interception is unaffected. This explains the concept of a minimum filterable particle size. The exact minimum size depends on fiber diameter, filter construction, and flow velocity. The effect of flow velocity on particle penetration for HEPA filter medium also shows a minimum efficiency point. Figure 4.2: The Effects of Inertia, Diffusion, and Interception on the Penetration-Velocity Curve

4.1.1.4 Particle Retention in Filters After an airborne particle contacts a filter element, retention forces prevent re-entrainment under the influence of the drag of the air. For small particles, the principal retentive force is a surface phenomenon called the Van der Waals force, which is proportional to the total area of DOE-HDBK-1169-2022 20 contact. For small spherical particles, the fraction of the total surface area in contact with a filter fiber will be relatively large, resulting in a retention force that exceeds the re-entrainment force of the air drag. 4.1.1.5 Airflow Resistance of Filters Filter resistance is directly related to airflow rate and filter construction details. Decreasing the diameter of filter fibers or granules produces higher resistance for the same overall unit volume of the solid fraction of the filter medium. Greater filter depth at the same porosity increases resistance in proportion to the increase in depth. As particles collect on the surfaces of fibers or granules or become entrapped in the interstices between upstream elements of the filter, the collected particles tend to form a coherent dust layer known as a filter cake. When this occurs, particle collection gradually shifts from media filtration (i.e., particle removal by individual filter fibers or granules) to cake filtration, and the filter shares the characteristics of the industrial cloth filter because the original structure now has the sole function of providing support for the filter cake and the filter cake completely takes over the particle separation function. This transformation produces two important changes: (1) efficiency increases in proportion to the increase in thickness of the cake; and (2) after formation of a coherent filter cake, resistance of the filter to airflow, which initially increased at a slow, steady rate as particles accumulated, now increases at an accelerating rate in response to additional particle deposition and narrowing of the pathways. 4.1.1.6 HEPA Filters: Historical Background The original specifications for HEPA filter media and cased filters were concealed under a veil of military secrecy because of their use for chemical, biological, and radiological defense purposes. Following World War II, the Atomic Energy Commission (AEC) chose the military's HEPA filters as their principal device for particle removal in all exhaust air systems of nuclear facilities. Eventual expansion of the use of HEPA filters for nonmilitary applications required declassification and release of information about HEPA filter components and manufacturing methods. For this reason, military standards MIL-F-51068, MIL-F-51079 (filter construction and filter medium preparation), and MIL-STD-282 (filter testing) were issued in an unclassified format. MIL-F-51068 and MIL-F-51079 were withdrawn by the U.S. Department of Defense (DoD) and replaced by ASME AG-1 and DOE-STD-3020-2015. While MIL-F-51068 and MIL-F-51079 were active, the Edgewood Chemical and Biological Center in Maryland prepared a procurement guide for military and nuclear agencies, the Qualified Products List (QPL), which is based on exhaustive tests of manufacturers’ filter media and filters. The QPL referenced available American Society for Testing and Materials (ASTM), Technical Association of the Pulp and Paper Industry (TAPPI), and other standard test procedures and equipment in its documentation of products. Though the process remains basically the same, Edgewood now issues letters to manufacturers after qualification testing in accordance with DOE STD-3020-2015.

DOE-HDBK-1169-2022 21 4.1.1.7 Filter Medium HEPA filter media used for nuclear service consistently provide collection efficiencies greater than 99.99 percent when qualified in accordance with ASME AG-1 and DOE STD 3020-2015. By increasing the fraction of fine glass fibers in the paper that are less than 0.25 µm in diameter, it is possible to obtain efficiencies in excess of 99.999 percent for 0.1- to 0.3-µm particles with a modest increase in filter resistance—typically about 25 percent. 4.1.1.8 HEPA Filter Construction HEPA filter units have historically been constructed via a continuous length of filter medium folded back and forth into pleats and corrugated separators are inserted between each fold. The assembly is then sealed into a rigid, open-faced rectangle. Additionally, separatorless designs, radial designs, metal media filters, and ceramic filters have different methods of construction. The components of a fabricated HEPA filter include: (1) extensively pleated filter medium, (2) separators that provide air passages and keep adjacent pleats apart, (3) a rigid filter case that encloses and protects the fragile filter medium, (4) sealants used to bond the filter pack (consisting of the assembled pleated medium and separators) to the filter case and to eliminate leak paths between filter pack components, and (5) gaskets attached to the filter case on one or both open faces to provide an airtight seal between the filter and the mounting frame. Some filter construction methods form the filter medium on the papermaking machine using an interval means to keep the adjacent folds apart, thereby eliminating a need for corrugated separators. These filters are called separatorless HEPA filters, discussed in Section 4.1.1.14., Figure 4.3 shows the assembled components of an open-face, deep-pleat HEPA filter with corrugated separators. DOE-HDBK-1169-2022 22 Figure 4.3: Open-Face Deep-Pleat HEPA Filter – Type A Filter Pack 4.1.1.9 Separators The most widely used material for the interleaved corrugated separators is tempered aluminum foil. The aluminum foils currently used for separators are identified as ASTM B209, Standard Specification for Aluminum and Aluminum Alloy Sheet and Plate. ASME AG-1 provides specific guidance on allowable alloys, depending on whether the separators are aluminum or acid resistant aluminum. When corrugating the aluminum sheet into separators, edges are often hemmed (turned back on themselves) to prevent the sharp edges from puncturing or tearing the part of the filter medium folded around the separator. When greater chemical resistance is required, a plastic coating of an epoxy, thermo-set vinyl (or a similar compound) is applied to the aluminum sheet.8 A dye should be added to clear coating materials so that defects in the plastic coating can be easily detected. ASME AG-1 FC-4150 should be consulted for additional information on separator coatings. According to ASME AG-1, any coatings are required (a) to meet a 3A rating of ASTM D3359, (b) not provide excessive off-gas volatiles, and (c) pass a flexibility test in accordance with FED-STD-141C. 4.1.1.10 Filter Case The filter case is constructed of materials that correspond to the specific application, decontamination requirements, and considerations of disposal ease and cost. Commonly used 8 If significant radiation is a concern, the use of organic materials may not be appropriate. DOE-HDBK-1169-2022 23

case materials include fire-retardant plywood9 and stainless steel in accordance with ASME AG- 1 Article FC-3000. The minimum thicknesses required to maintain rigidity under compressive loads ranging up to 1,400 pounds when the filter is clamped to a mounting frame, are 3/4 inch for wood and 14-gauge sheet metal. Grade A-C, American Plywood Association (APA) PS-1 fire- retardant-treated plywood is acceptable, but the “A” face should be on the inside, facing the pack, and should be assembled with this face completely coated with a sealant to close off any leak paths. For wooden case filters, case panels are joined with rabbeted joints, which are assembled by gluing with an adhesive and double nailing or doubling screwing with coated box nails, corrosion-resistant plated screw nails, or flat-head wood screws. Metal cases should be used in instances of potential wetting or high humidity at elevated temperatures and when the filter will be exposed to corrosive chemicals. 4.1.1.11 Sealants Sealants used to provide a leak-free bond between the filter pack and case should be resistant to heat and moisture, noncombustible, fire-resistant, or self-extinguishing, as well as capable of maintaining a reliable seal under continuous exposure to design operating conditions. Rubber- based adhesives compounded with chlorine or bromine to ensure self-extinguishing when exposed to ignition are acceptable, but catalytically cured solid and foamed polyurethanes containing additives for combustion suppression are the sealants of choice for most filter manufacturers. Sealants should maintain their integrity over a wide temperature range. Filters designed to operate at temperatures above 392 degrees Fahrenheit (200 degrees Celsius) have been sealed with compression-packed glass fibers and with ceramic cements reinforced with glass fibers and have been hardened thermally. Room temperature vulcanizing silicone rubber sealants have been used successfully at operating temperatures up to 392 degrees Fahrenheit (200 degrees Celsius). Additional materials may be used as research and operations experience indicate is appropriate. The continuous updating and re-issuance of ASME AG-1 will reflect these latest advances. ASME AG-1 Sections FC and FK contain additional information on sealants. 4.1.1.12 Gaskets Filters should be installed so that even the smallest volume of air or gas does not escape filtration; therefore, gaskets sealing filter units to the mounting frames play a critical role in the satisfactory operation of HEPA filters. The most widely used sealing method is a flexible gasket attached to the open face of the filter case and pressed against the flat face of the mounting framework. The second most popular method is referred to as a “fluid seal.” This method uses a channel formed or routed in the peripheral face of the filter case that is filled with a highly viscous, very low volatility, nonflammable (or self-extinguishing), odor-free, non-Newtonian fluid such as a silicone. The fluid flows around and over imperfections yet does not relax or separate from the surfaces it contacts. For installation, the matching framework face is equipped with a continuously protruding knife-edge that mates with the fluid-filled channel in the filter case. 9 The use of plywood casing is discouraged in DOE nuclear facilities. DOE-HDBK-1169-2022 24

Gaskets should be oil- and ozone-resistant. Closed-cell sponge gaskets composed of synthetic rubber (neoprene) that conforms to grade 2C3 or 2C4 of ASTM D1056, Sponge and Cellular Rubber Products, are required by Article FC-3000 of ASME AG-1. Gaskets should have a minimum thickness of 1/4 inch and width of 3/4 inch. The gasket face attached to the filter case should be free of any adhesion-resistant mold-release contaminant that may have been acquired when the gasket material was molded. To ensure an absence of residual mold release chemical, only cut surfaces are permitted on both gasket faces. Gaskets may be cut out of a sheet of stock as a single piece or may be made of strips joined at the corners by dovetail or other interlocking arrangement. Joints are sealed against air leakage with a rubber-base adhesive, usually the same adhesive used to attach the gasket to the filter case. Manufacturers of neoprene gaskets recommend a shelf life not to exceed 3 years. 4.1.1.13 Faceguards To guard against damage from careless handling and faulty installation, a recessed faceguard across both faces of the filter is required according to ASME AG-1 Article FC-4160 and Article FK-4160. Woven or expanded 4X4 mesh metal have proven satisfactory in largely preventing the inadvertent intrusion of hands or other objects into the filter pack. In addition, a metal mesh faceguard provides added strength to the filter unit, increasing resistance to transportation damage and shock overpressure. ASME AG-1 requires faceguards conforming to either galvanized steel ASTM A740, or 304 stainless steel ASTM A580. 4.1.1.14 Separatorless HEPA Filters A separatorless HEPA filter design, shown in Figure 4.4, is constructed without corrugated spacers inserted between the folds of the filter medium. Instead, a continuous sheet of filter medium is molded on the papermaking machine with corrugations at intervals. When it is folded back and forth upon itself, it becomes a self-supporting pack where the peaks of the interval corrugations of successive layers contact each other to form a honeycomb-like filter pack. For the same filter frame size, a separatorless filter contains more useful filter medium surface than the corrugated separator type, and thus provides greater airflow capacity at equal resistance. Tests of Type C filters conducted at Mississippi State University10 have suggested that failures may occur under certain accident conditions. These filters are no longer being manufactured. 10 19-REP-DOE-SEP/SEPLESS-FINAL, December 17, 2019, Mississippi State University Institute for Clean Energy Technology, work performed under DOE Contract DE-EM0003163. DOE-HDBK-1169-2022 25 Figure 4.4: Separatorless Style Filter – Type C Filter Pack A similar filter with more useful filter medium is the ASME Type D filter. This filter does not have a metal separator but contains glass ribbons for support. It is regularly used in nuclear installations and has shown excellent operating performance. The Type D filter is commonly referred to as a “separatorless filter” since there is no metal filter, but it does have a glass ribbon that functions as a separator. Separatorless HEPA filter designs can be more susceptible to pleat collapse than separator filters as documented in DOE Operating Experience-3: 2013-02 “Laboratory Tests Indicate Conditions that Could Potentially Impact Certain Type of HEPA Filter Performance”. 4.1.1.15 Mini-Pleat HEPA Filters

Mini-pleat filter construction methods utilize 7/8 to 1 1/4-inch-deep pleats with very narrow air spaces (1/8-inch) between, making it possible to pack more filter medium into the standard frame sizes than can be done with deep-pleat, corrugated separators, or even by using separatorless construction methods. Abutting folds are separated by threads, ribbons, tapes, strips of medium, or continuous beads of glass, foam, or plastic spaced across the width of the medium. Mini-pleat filters contain almost twice as much filter medium as deep-pleat, corrugated separator filters of equal frame size (Figure 4.5). They are rated to have an airflow DOE-HDBK-1169-2022 26 resistance of 0.25 Kilopascals (kPa) when operated at 3,060 cubic meters per hour (m3 /hr), compared to the same resistance for a flow rate of 1,700 to 2,040 m3/hr for deep-pleat corrugated separator filters. This gives the user of mini-pleat filters the option of utilizing space- saving higher airflow or extending filter life by operating at lower than rated airflow capacity. This is called downrating a filter. When a mini-pleat filter rated for 3,060 m3/hr is downrated to service at 1,700 m3/hr, it theoretically should extend service life more than threefold before it reaches its final permissible resistance increase. In practice, filter life extension is 1.6-fold due to the higher media velocity affecting efficiency, and dust bridging across the very narrow air passages between the paper pleats to form a filter cake covering the face area. An efficient medium efficiency filter might be used to prevent the formation of a surface filter cake and extend the service life of the mini-pleat filter. Cased mini-pleat HEPA filters are formed from subcomponents assembled in a continuous “V” array. Figure 4.5: Mini-Pleat (Thread Separator) Filter – Type B Filter Pack DOE-HDBK-1169-2022 27 The subcomponents are panels that hold the pleated filter medium in metal frames approximately 23.62 inches wide, 11.81 inches high, and the depth of the paper pleats. A seal is made between framed filter packs and the standard frame using rubber-based adhesives, polyurethane, or some other plastic-based material, all of which are chemically compounded to inhibit their support of combustion. 4.1.2 HEPA Filter Classes and Sizes In addition to being the workhorse filter for the nuclear industry, HEPA filters have found many important applications in the industrial, medical, pharmaceutical, and microelectronic sectors. These diverse applications have resulted in a number of industrial and governmental specifications. In general, these specifications can be grouped into five construction grades and three performance types that provide a range of materials, manufacturing techniques, performance characteristics, and costs for different applications and user preferences. A standard covering the grades and types of HEPA filters has been issued by the Institute of Environmental Sciences and Technology (IEST) as IEST-RP-CC001.3. This standard lists the classifications described below. 4.1.2.1 Filter Construction Grades Grade 1 – Fire-Resistant Filters. Filters of this grade contain fire-resistant materials that may ignite when the filter is exposed to hot air or fire but will not continue to burn once the ignition source is removed. The filter should exhibit a specified retention efficiency after exposure to no more than 700 ± 50 degrees Fahrenheit (371 ± 10 degrees Celsius). These filters comply with ASME AG-1, Section FC or FK.

Grade 2 – Semicombustible Filters. This grade costs less but provides a lower level of protection against elevated temperature than Grade 1. For this reason, the user should evaluate application of this filter grade with the individual fire propagation hazards in the area of use. This filter type will fail at temperatures much lower than Grade 1. These filters comply with Underwriters Laboratories (UL) UL 586. Grade 3 – Combustible Filters. This grade covers filters required for certain service requirements that permit acceptance of the combustibility hazard. Grade 3 filters are readily combustible and are used only where high-value product recovery by incineration is desirable, disposal of volumes are critical, or exposure to chemical atmospheres might be incompatible with the use of a HEPA filter incorporating a medium of glass fibers. These filters comply with UL 900. 4.1.2.2 Filter Performance Levels IEST-RP-CC001 classifies filter performance levels as: Type A Filter Performance. Sometimes referred to as industrial types, these filters are tested for overall penetration at rated flow only. The filter retention (inverse of penetration) should exceed 99.97 percent for 0.3-µm particles. Type B Filter Performance. In addition to the basic requirements for Type A filters, Type B units are certified free of significant pinhole leaks that would cause penetration at low flow rates. DOE-HDBK-1169-2022 28 This type is tested at 20 percent of rated airflow as well as at rated flow with the filter encapsulated to disclose casing or gasket leaks. This type is sometimes referred to as “nuclear- type.” Type C Filter Performance. In addition to the performance required of Type A filters, Type C filters, are tested with the use of air-generated test aerosols at 80 to 100 feet per minute (fpm) face velocity. The units are fully face-scanned to detect and eliminate all significant leakage streams greater than 0.01 percent of the upstream test aerosol concentration to which the filter is subjected. Type D Filter Performance. In addition to the testing required for Type C filters, Type D filters should be retested at their rated airflow and penetration, which should be no more than 0.001 percent of the upstream concentration. The filter unit should be encapsulated so that all components, including the filter pack, frame, and gasket, are subjected to testing. In the U.S., laser spectrometers are used to measure efficiencies of ULPA filters (>99.999 percent). Type E Filter Performance. Type E filters are designed, constructed, and tested in strict accordance with military specifications for HEPA filters intended for biological use. This type is for application in air cleaning or filtering systems involving toxic chemical, carcinogenic, radiogenic, or hazardous biological particulates. This type is referred to as a “biological unit.” Type B filters are recommended for most nuclear applications, particularly in single-pass systems, and should be qualified in accordance with UL-900. These units comprise a large part of those manufactured by industry and are used extensively in nonnuclear industries as well. Type C filters are common in clean room applications where laminar flow requirements are coupled with low particle penetration and should be qualified in accordance with UL-900. Type D filters presently are used in printed-circuit or microprocessor clean rooms and should be qualified in accordance with UL-900. 4.1.2.3 Enclosed Filters

Most HEPA units are used in the open-face configuration (Figure 4.3). When used in this manner, the filter is secured firmly to a rigid framework by a pressure device such that a leak- free seal exists between the unit and the framework. The HEPA filter may also be placed completely within an enclosing casing that is equipped with nipples at both ends for attachment to existing ventilation ducts (Figure 4.6). Enclosing casings may be metal or plywood, but care should be taken to ensure the casing material is compatible with UL requirements for resistance of the filter to heated air and flame. The enclosing casing forms the leak-free pressure boundary in addition to the filter case, and care should be taken to ensure that it is treated as an encapsulated design for both performance and leak-acceptance testing. Enclosed HEPA units have significantly higher resistance to airflow than the open-faced design because of the added restrictions of the duct transitions. DOE-HDBK-1169-2022 29 Figure 4.6: Enclosed HEPA Filter Enclosed filters are sometimes referred to as encapsulated (nipple-connected, closed-face, or self-contained) HEPA filters. ASME AG-1, Section FK contains information on Special HEPA Filters, including radial flow filters that may be considered a subset of encapsulated HEPA filters. Specific guidance applicable to nipple-connected filters is currently not available but is under development by ASME for inclusion in ASME AG-1. 4.1.2.4 Cylindrical Filters Cylindrical filters may be either open-faced cylindrical axial (Figure 4.7) or radial flow (Figure 4.8). Filters fabricated with cylindrical cases are easily mounted in circular ducts and offer significant advantages regarding simplified gasketing and automated filter-changing techniques. A “push-through filter system” permits changing of cylindrical filters by loading a clean filter that has gaskets on the top and bottom filter flanges into the filter housing tube from the “clean side,” then pushing it through until it ejects the old, contaminated filter into the “dirty side” of a cell or glovebox. Figure 4.7: Open-Faced, Cylindrical Axial Flow HEPA Filter DOE-HDBK-1169-2022 30 Figure 4.8: Radial Flow HEPA Filter 4.1.2.5 Filter Sizes The physical dimensions shown in Table 4.1 have been standardized for the HEPA filters currently used in nuclear service and by U.S. Government agencies. Other sizes can be manufactured and purchased but are considered “special orders.” Special applications such as clean rooms, biological safety cabinets, and medical facilities, generally use the same filter height and depth dimensions shown in Table 4.1 but may have lengths up to 72 inches. Filter configurations for computer applications use many different sizes and shapes depending on the volume available within the computer cabinet. Table 4.1 (from ASME AG-1, Section FC-4100, “HEPA Filters,” by permission) Table FC-4110-1 Nominal Sizes and Ratings Number Designation Size Minimum Rated Airflow Maximum Resistance in. mm scfm m3/h in. wg Pa 1 8 × 8 × 31∕16 203 × 203 × 78 25 40 1.3 320 2 8 × 8 × 57∕8 203 × 203 × 150 50 80 1.3 320 3 12 × 12 × 57∕8 305 × 305 × 150 125 210 1.3 320 4 24 × 24 × 57∕8 610 × 610 × 150 500 850 1.0 250 5 24 × 24 × 111∕2 610 × 610 × 292 1000 1700 1.0 250 6 24 × 24 × 111∕2 610 × 610 × 292 1250 2100 1.3 320 7 24 × 24 × 111∕2 610 × 610 × 292 1500 2500 1.3 320 8 24 × 24 × 111∕2 610 × 610 × 292 2000 3400 1.3 320 9 12 × 12 × 111∕2 305 × 305 × 292 250 420 1.3 320

4.1.2.6 Filter Weight The weight of a filter unit is an important factor in design and maintenance. Table 4.2 lists the weight of clean, open-faced filters and enclosed filters of rectangular design (ASME AG-1 Section FC). The weights for radial, metal, and ceramic filters differ. For design purposes, the weight of a dirty filter that is ready for change-out is approximately 4 pounds heavier per 1,000 cubic feet per minute (cfm) of rate capacity. Because many applications employ multiple filter units in banks that are as many as 6 to 10 units in height, minimal filter weight without loss of performance is critical to the ease of original installation and replacement. New and modified DOE-HDBK-1169-2022 31 ventilation system designs should consider the recommendation in USNRC11 Regulatory Guide 1.52 that filter housings are no more than 3 HEPA units high for ease of maintenance and changeout. Table 4.2: Weight of Unused HEPA Filters Filter Size (inches) Nominal Airflow Capacity (cfm) Approximate Weight (pounds) of Filters Wood Case Steel Case Open-face 8 x 8 x 5-7/8 50 3.6 5.8 12 x 12 x 5-7/8 125 4.8 7.3 24 x 24 x 5-7/8 500 17 22 24 x 24 x 11-1/2 1000, 1250, 1500 32 40 24 X 24 X 11-1/2 2000 NA 85 Enclosed 8 x 8 cross-section 25 5 9 8 x 8 cross-section 50 7 10.5 12 x 12 cross-section 125 17 20 24 x 24 cross-section 500 64 72 24 X 24 cross-section 1000 78 95 4.1.3 HEPA Filter Performance Characteristics 4.1.3.1 Airflow Resistance Resistance to airflow (pressure drop) of a clean nuclear-grade, 1,000 cfm capacity filter should not exceed 1 inch water gauge (in. wg) when tested at rated airflow for ASME AG-1 Section FC, HEPA Filters. See Table 4.1 for additional filter capacities and pressure drops. Pressure drop may vary for other filter types, e.g., metal, radial flow, and ceramic filters. For these filters, higher initial pressure drop may result in higher rated flow. The pressure drop for ULPA filters is frequently greater than for standard HEPA filters, and this feature is subject to negotiation between customer and vendor. Resistance increases with particulate loading. A new nuclear- grade filter is qualified by a wet overpressure test up to 10 in. wg for 1 hour; however, this should not be confused with normal in-service operating pressures. Normal in-service pressures should be limited to 3 to 5 in. wg above startup pressure to maintain reliable operation. 4.1.3.2 Dust-Holding Capacity The dust-holding capacity of a filter is a function of the type, shape, size, and porosity of the filter as well as the aerosol size, shape, and concentration characteristics to which the filter is exposed. As HEPA filters are designed to filter out the smallest particles, they can accommodate only extremely light particulate loadings without experiencing a rapid pressure drop increase. HEPA filters are affected particularly adversely by fibers, lint, and other materials that exhibit a 11 U.S. Nuclear Regulatory Commission DOE-HDBK-1169-2022 32 large length-to-diameter ratio because they tend to bridge the air entrance gaps between the adjacent pleats of medium, thereby preventing particles from accessing the full depth of the filter. A HEPA filter can be protected by a medium efficiency filter capable of removing the bulk of large particles and fibers, thereby extending its useful lifetime.

As noted earlier, a dust-holding capacity of 4 pounds per 1000 cfm of rated airflow capacity may be assumed for design purposes for ASME AG-1 Section FC, HEPA Filters. Different dust- holding capacities should be considered when using emerging technology filters, such as metal, high-strength, or ceramic filters. An increase in dust accumulation on the filter medium improves filtration efficiency and increases resistance to airflow. One of the limitations of HEPA filters is their low-dust-holding capacity and their need for frequent replacement when exposed to high aerosol concentrations. The pressure rise curve experienced by HEPA filters also depends on the particulate composition and concentration of the atmosphere to which it is exposed. A filter installed in a moderately contaminated urban area will show as much as a six- fold increase in resistance in a year's time, whereas a unit in a clean room application may last ten years or longer before reaching a sixfold pressure increase. The use of a medium efficiency filter (described in Section 4.1.5) increases the service life of HEPA filters and helps make the combined filtration system cost effective. For high dust-loading applications, bag house filters are useful due to the ability to self-clean by intermittent back-pulsing of the filters. 4.1.3.3 Shock and Blast Resistance The resistance of HEPA filters to shock and blast is important because these filters are often the final barrier between a highly contaminated enclosure and the environment. Shock stress may occur from disruptive natural phenomena (e.g., earthquakes) or from internal and external explosions. The values listed in Table 4.3 are the maximum shocks that can be tolerated without visible damage or loss of filtration efficiency. These data show that: (1) filters with faceguards on both faces had about a 40 percent greater resistance to shock than those without faceguards; (2) dirt-loaded filters had 15 percent less shock resistance than clean filters; (3) the smaller the filter face area, the greater the resistance to shock; (4) the greater the filter depth, the greater the resistance to shock. At overpressures exceeding those listed in Table 4.3 by 0.5 to 1.0 psi, the filter medium ruptured or experienced cuts on the downstream face. At pressures 2 pounds per square inch (psi) greater than those listed in Table 4.3, extensive damage occurred. At pressures above 5 psi, the entire filter pack within the frame was dispersed. No significant differences were found between successive tests of increasing shock force on the same filter and a one-shot test of the same force—both procedures produced the same failure modes. DOE-HDBK-1169-2022 33 Table 4.3: Shock Overpressure Resistance of Open-face HEPA Filters Filter Dimensions (inches) Overpressure (psig) Recommended Design Limit for Used Filters Face Depth Overpressure at Failure a With Faceguards Without Faceguards 8 x 8 3 1/16 3.7 b 2.0 8 x 8 5 7/8 4.5 b 2.5 12 x 12 5 7/8 3.6 b 2.0 24 x 24 5 7/8 2.2 1.7 1.2 24 x 24 11 1/2 3.2 1.7 1.8 a Clean filter with 4 by 4 mesh faceguards on both faces. b These filters when tested did not have faceguards. 4.1.3.4 Heat from Fire and Explosion

Grade 1 fire-resistant filters as defined by IEST are fabricated from a glass medium with flame- inhibited or self-extinguishing adhesive or sealant, aluminum alloy separators, and fire- retardant wood or metal frames. Nevertheless, the material that collects on the filters poses special fire and explosion hazards when it contains substantial amounts of organic or pyrophoric substances. Fires from this source can produce undiluted hot gases that attain temperatures as high as 1,830 degrees Fahrenheit. The softening point of glass fibers used in currently manufactured HEPA filter media is about 1,250 degrees Fahrenheit, and direct impingement of a 1,700 degrees Fahrenheit flame will cause immediate melting. A glowing solid particle that lands on HEPA filter media will perforate it if it continues to burn. Explosions that could destroy or seriously damage the filter from high pressure, shock waves (overpressures), or an excessive temperature excursion can also occur from ignition of organic or pyrophoric dusts, vaporized organics, or combustible gas products of combustion. The spark and flame arresters installed upstream of the filters are designed to alleviate this problem. Spark arresters constructed of coarse glass fibers provide reasonable protection at low cost. Spark and flame arresters constructed of grids or heavy wire mesh that provide graduated openings are required to provide a 2-minute delay before flame penetration. Filters using emerging technologies, such as ceramic pre-filters, may also be used to prevent direct flame, or burning ember, impingement on HEPA filters. See DOE STD-1066 and Section 5.1.3.34 for additional information. The recommended limitation for filter operating temperature is 250 degrees Fahrenheit. The filter media binder is assumed to be the HEPA filter component that is most susceptible to failure resulting from elevated temperature. The binder begins burning off at 350 degrees Fahrenheit. Commonly used sealants are also highly susceptible to elevated temperatures. Tables 4.4 and 4.5 list continuous-service temperatures for wood- and steel-cased filters. At temperatures well below the char point of an elastomeric sealant, the sealant loses its shear strength, resulting in a reduction from approximately 6,000 kPa at room temperature to a low of 100 kPa at 300 degrees Fahrenheit. HEPA filters exposed to thermal stress will begin to release contaminates at temperatures above 300 degrees Fahrenheit. DOE-HDBK-1169-2022 34 Table 4.4: Recommended Limited-Service Temperatures for Steel-Framed Fire-Resistant HEPA Filter Units Sealed with Elastomeric Adhesives Temperature to Which Filter was Exposed (degrees Fahrenheit) Sealant Used Up to 10 Min a Up to 2 Hours Up to 48 Hour Up to 10 Days > 10 Years HT-30-FR b 750 350 325 300 260 Z-743 c 750 325 300 275 200 EC-2155 d 750 250 220 200 200 Polyurethane foam 750 325 300 275 230 a Some reduction in efficiency may occur after 5 minutes of exposure. b Goodyear. c Pittsburgh Plate Glass. d Minnesota Mining and Manufacturing (3M). Table 4.5: Recommended Limited-Service Temperatures for Wood-Framed Fire-Resistant HEPA Filter Units a Frame Material Temperature to Which Filter was Exposed (degrees Fahrenheit) Up to 10 Min Up to 2 Hours Up to 48 Hours Up to 10 Days b > 10 Years a ¾ inch thick plywood a, c 750 300 275 200 180 a Subject to sealant limitations given in Table 4.4 b Maximum temperature of 120 degrees Fahrenheit where relative humidity is 75 percent or higher. c Exterior grade, fire-retardant-treated.

4.1.3.5 Moisture and Corrosion Effects Water exposure is unquestionably an important factor leading to the deterioration of HEPA filters. Detrimental effects occur as a result of repeatedly wetting the filter and drying it. Repeat wetting and drying of a HEPA filter causes a loss of strength. There also are very strong effects of operational time on the behavior of HEPA filters under wet conditions. In such conditions, the binder starts to get soft and dissolves at high differential pressures. One of the most serious issues dealing with HEPA filters in DOE facilities is their potential for rupture during accidental fires and the resulting release of radioactive smoke and soot particulates. Moisture and corrosion effects may be minimized by the use of emerging technology filters, such as metal media and ceramic filters. The most likely scenario for filter damage in these systems involves filter plugging by the water spray, followed by fan pressure blowing out of the medium. Water repellency is important for units that are used in laboratory and industrial applications. Repellency is measured by the height of a water column that does not leak through the paper. A water repellency of 20 in. wg is required for filters that are operated in high-humidity conditions and stream-containing DOE-HDBK-1169-2022 35 atmospheres. In the absence of adequate water repellency characteristics, liquid contaminants that collect on the filter medium can be carried through it by air pressure or capillary action and become re-entrained into the downstream air. Humidity High relative humidity can result in high pressure drop and a corresponding decrease in media strength, the combination of which can lead to structural damage and a loss of filter efficiency. The most frequent failure mode is rupture of the downstream pleat. With particle deposits, the filter would absorb water at a lower relative humidity and would rupture even with a demister installed to protect the filter. Corrosion For many industrial applications, a moisture- and chemical-resistant filter should be capable of withstanding attack by acids, most gas-phase alkalis, and solvent droplets and vapors. However, fine glass fibers have poor resistance to hydrogen fluoride (HF), only moderate resistance to other concentrated acids, and fair resistance to water and milder chemical corrosive agents. On occasion, corrosive chemicals in the airstream will condense on the filter medium, accelerating the attack on the finest fibers. Airstreams containing some residual HF and droplets of liquid carryover after treatment by an alkali scrubber produce a severe attack on the glass fiber filter medium. A wooden case is more resistant to chemical attack than is a steel case. Exterior-grade material should be specified, however, because interior-grade plywood is unsuitable for outdoor filter operation or for continuous interior operation in very humid (90 to 100 percent relative humidity) environments at temperatures above 131 degrees Fahrenheit (55 degrees Celsius), particularly when operation and shutdown periods alternate and the environment returns to room temperature. During cooling, moisture may condense on the surfaces of the wooden case and infiltrate the structure, causing swelling of the elements and a separation between the seal and frame. Most exterior-grade wood products employ a moisture-impermeable phenolic resin bonding agent, while water-soluble urea-formaldehyde resins are used as bonding chemicals for interior-grade products. Stainless steel is recommended when a metal frame is required. Mildew growth may occur on the sealant and frame interface in high humidity while the filter is in storage, causing filter degradation.

4.1.3.6 Radiation Resistance Most applications for HEPA and ULPA filters in the electronics and other industries do not involve exposure to high levels of ionizing radiation. However, post-accident cleanup by nuclear reactor containment systems and some fuel reprocessing applications of facilities can involve exposure of filters to high levels of radiation. Reactor accidents can result in an integrated beta- gamma dose to the Engineered Safety Feature (ESF) filters of 3.5 x 107 rads. This radiation level can result in a significant reduction in tensile strength, an increase in penetration, and an impairment of water repellency. For these reasons, emerging technology filters, including metal media and ceramic filters, are better suited to high radiation environments. DOE-HDBK-1169-2022 36 When samples were tested for degradation of water repellency as a function of gamma dose, half of the samples showed hydrophilic action in less than 10 seconds and the remainder in 60 to 100 seconds. The ASME AG-1, Section FN Filter Media: High Efficiency, requires filter media to support a 6-inch column of water after exposure to an integrated gamma dose of 6.0 to 6.5 x 106 rads. Other tests exposed small HEPA filters to a range of radiation doses, and then exposed them to a flowing steam-air mixture to determine the residual resistance to plugging and rupture. Plugging was found to be inversely proportional to radiation dose (e.g., filters exposed to 6 x 10 6 rads ruptured in 100 seconds) but a sample irradiated to only 1 x 106 rads withstood the steam-air mixture for 250 seconds before failure. Despite some blinding (water vapor interference with particulate capture), unirradiated samples did not rupture under the same flow regimen. These tests verified the need to provide filter systems with reliable protection from wetting wherever exposure to spray or condensing steam is possible, particularly when water exposure may be coupled with high levels of radiation. 4.1.4 HEPA Filter Performance Testing for Nuclear Service HEPA filters for nuclear service undergo a qualification procedure and two testing regimens. The first regimen consists of a stringent visual examination and penetration tests at the place of manufacture. The second regimen is an in-place leak test performed at the place of utilization. DOE requires an additional independent inspection and penetration tests at the designated DOE Filter Test Facility (FTF) prior to installation at its destination, in accordance with DOE-STD- 3025. The manufacturer’s testing regimen involves two distinct phases: (1) a quality control (QC) routine to ensure careful manufacture of the product, and (2) a series of tests to verify filter compliance with standards and performance criteria related to collection efficiency and resistance to airflow. When all factors are within the tolerance limits set by applicable specifications, the manufacturer certifies that each filter unit meets the specification acceptance criteria.

In addition, DOE-STD-3020 and DOE-STD-3025 provide additional information on DOE mandated independent inspection and penetration testing for specific types of filter purchases. Testing is currently required for filters installed in Hazard Category 1 and 2 facilities that perform a safety function, and a statistical approach for the balance. The filters are tested for compliance with the requirements for physical characteristics, efficiency, and airflow resistance. This testing is conducted at the DOE-supported independent FTF before the filters are released to the customer’s facility. The purchaser/customer should request that the manufacturer’s test report and a Certificate of Compliance be forwarded for documentation. Filters failing to meet the FTF specification acceptance criteria are rejected and turned over to the purchaser for disposition; typically, they are returned to the manufacturer for credit. Both DOE and the NRC do not permit repairs of HEPA filters intended for nuclear service. In addition to the two regimens, qualification of HEPA filters is performed by the Edgewood Chemical and Biological Center at Aberdeen Proving Grounds, MD. The required qualification tests are specified in DOE-STD-3020-2015. DOE-HDBK-1169-2022 37 4.1.4.1 Airflow Resistance The resistance of a filter to airflow, often expressed as “pressure drop” and “back pressure,” is almost always measured as the height of a water column that exerts an equal pressure. The characteristic flow regime through HEPA filter media is aerodynamically described as laminar. For this reason, the airflow resistance of these filters changes in direct proportion to changes in air volume throughput (expressed as feet per unit area), even though the air approaching the filter may be turbulent. The direct proportionality of resistance to flow rate is not a characteristic of medium efficiency filters. For medium efficiency filters, resistance is a power function of airflow with an exponent larger than 1, but not exceeding 2. The test protocols used to qualify HEPA filters for nuclear service are described below. Testing of all new filters intended for nuclear service in the United States (U.S.) is conducted with a 0.3- µm test aerosol in a rig called a Q107 penetrometer that was designed by the U.S. Army Chemical Corps during the 1950s. Construction and operation are described in MIL-STD-282, Method 102.9. The complete penetrometer consists of test aerosol generator, an instrument that measures the size and uniformity of the particles formed, a clamping device to seal the filter under test into the test rig, a total scattering photometer to measure test aerosol penetration, and a manometer to measure filter resistance at rated airflow. The Q107 penetrometer is used for filters of 1,700 m3/hr rated capacity, and the Q76 penetrometer tests smaller filters. When testing a 1,700 m3/hr filter, about 2,400 m3/hr of outside air is drawn into the system and divided into 3 parallel ducts that carry approximately 170, 500, and 1,350 m3/hr, respectively. The remainder, approximately 350 m3 /hr, is exhausted through another path. The 170 m3/hr duct contains electric heaters that raise the temperature of the air to 374 degrees Fahrenheit (190 degrees Celsius). Other electric heaters keep the liquid test aerosol reservoir heated to approximately 392 degrees Fahrenheit (200 degrees Celsius). The test aerosol is vaporized from the reservoir into the heated airstream as it sweeps across the liquid surface and is mixed with the air in the 500 m3 /hr duct that contains both cooling units and reheaters to provide partial dilution and temperature control of the test aerosol vapor stream.

The temperature of the test aerosol liquid reservoir establishes the mass concentration of the aerosol; a liquid temperature of 392 degrees Fahrenheit (200 degrees Celsius) produces 80 to 100 µg/L of test aerosol when diluted with 2,400 m3 /hr of air. The particle size of the aerosol is determined by the temperature differential between the evaporated test aerosol vapor stream and the much cooler diluting stream—the greater the temperature differential, the smaller the resulting particle size. Temperature fluctuations in both airstreams influence particle size distribution; the greater the fluctuation, the wider the size distribution. The combined flows from the 170- and 500-m3 /hr ducts are diluted further with the air in the 1,350-m3 /hr duct to produce the final aerosol concentration used for filter testing. Baffles are placed upstream and downstream to help mix the aerosol entering and leaving the filter being tested. The test aerosol particle size is determined by passing a sample through an optical particle- sizing instrument called an OWL and noting the degree of polarization of a light beam. A polarization angle of 29 degrees indicates a particle diameter of 0.3 µm when the aerosol is monodispersed. DOE-HDBK-1169-2022 38 The optical device used to measure particle concentration is a forward-angle, light-scattering photometer capable of measuring scattering intensity over a range of at least five orders of magnitude. Current commercial instruments can give a useful signal with a concentration as low as 10 particles/cm when finely tuned and used by a skilled operator. For routine testing, a downstream concentration of 10-4 mg/m can be measured with reliability when the upstream concentration is 10 mg/m, indicating a filter efficiency of 99.99 percent for the test aerosol. This level of measurement is considered adequate for nuclear applications (in view of the lesser efficiency credit regularly assigned to filters by regulatory authorities), however, manufacturers of microelectronic chips have sought filters with much higher retention efficiency. ULPA filters have an efficiency of 99.999 percent for particles in the 0.1-µm range, which is the minimum filterable particle size for currently manufactured HEPA filters operating at their design airflow. This degree of efficiency is beyond the range of the Q107, but a laser spectrometer has been developed that can measure filter performance at much higher efficiencies and for smaller particle diameters. This device measures the sizes of individual particles in an aerosol and displays the particle-size distribution on a screen and a printout. When used with a polydisperse aerosol challenge, it can measure penetration values as low as 1x10- 9 in a range of particle diameters from 0.07 to 3.0 µm. Use of duplicate instruments upstream and downstream permits the determination of a “particle size-collection efficiency” table or chart for individual filters at a modest cost and within a reasonable period of time. Laser spectrometers can also be used to determine such important filter performance parameters as maximum penetrating size, efficiency of filters in series, and the optimum formulation of filter fibers. Operator training is still an important issue, as is recognition that most lasers are calibrated using polystyrene latex (PSL) rather than the test aerosol. The properties of PSL (e.g., refractive index) are not identical to the test aerosol. This can produce inaccurate results unless operators understand the differences and set up the equipment properly. Upstream concentration is also critical because lasers can be blinded by the passage of too many particles to the counter. Most successful applications use calibrated particle diluters to ensure the laser is not overwhelmed.

4.1.4.2 Quality Control/Assurance Considerations Systematic QC and quality assurance (QA) testing are conducted at all stages of the product cycle from development to use. The filter medium receives the most rigorous and extensive control and evaluation, perhaps because its development and manufacture necessarily demand a degree of art as well as science. Performance of the filtration medium is determined by a thermally generated monodispersed aerosol generated by a Q127 penetrometer, a smaller version of the Q107 used to test cased filters. The physical characteristics of the medium are controlled by a battery of standard test protocols developed by the TAPPI, ASTM, and ASME AG-1. After fabrication, in addition to measuring the efficiency and airflow resistance of the filter assembly with a Q107 or a Q76 penetrometer (depending on the rated airflow capacity and physical size of the filter), a series of physical tests described in ASME AG-1, Section FC and FK, are applied to filter prototypes for qualification. These include tests of dimension tolerances DOE-HDBK-1169-2022 39 and resistance to rough handling, pressure, heated air, flame, and unfavorable environments (temperature and moisture extremes). Nebulized Sodium Chloride The standard test method used in Great Britain for new HEPA filters utilizes a dried sodium chloride aerosol generated from solution with a compressed air nebulizer. An emission-flame photometer is used to measure the quantity of sodium chloride entering and leaving the filter being tested. The dried aerosol particles have a concentration of about 3 mg/m3, a mass median diameter of 0.65 µm and a geometric standard deviation of 2.1. The test rig and test procedures employed do not differ significantly from those used in the U.S., Germany, and a number of other countries. Nebulized Uranine The French standard test method, AFNOR NFX 44.011, uses dried particles of uranine, a fluorescent material generated from a solution with a compressed air nebulizer. The aerosol concentration for the test is about 8 × 10-3 mg/m. The mass median diameter of the particles is 0.15 µm, with a geometric standard deviation of 1.55. Aerosol samples are extracted from the test apparatus upstream and downstream of the filter being tested and are collected on filter media. After the sampling period has expired, the filter media are extracted in water and analyzed by fluorimetry. Filter efficiency is expressed as the percent by weight of fluorescent particles collected by the filter. Because of the need to collect samples over some averaging period (e.g., 10 minutes) and then to extract the uranine quantitatively from the filters and read the fluorescence intensity in a fluorimeter, about 30 minutes is required for an analysis. Direct readout of filter efficiency is characteristic of most other standard test procedures. 4.1.5 Effects of Aging, Wetting, and Environmental Upsets on HEPA Filter Performance Intuitively, the aging of filters in storage or in use in-place should lead to a higher probability of media or structural failure. With aging, HEPA filters lose strength and water repellency but do not necessarily become less efficient. Logically, it follows that filter efficiency depends on the physical geometry of the filter media and is not significantly affected when the organic binders and sealants become brittle or degrade with age. Filter strength prevents structural failure during events that produce high stress across filter media, e.g., when particle deposits and water accumulation cause filter plugging.

Historical measures of filter strength are: (1) the tensile strength of the paper in combination with a 10-inch overpressure test on the filter, and (2) burst strength. Burst strength (the pressure required to tear open the media) quantitatively measures two-dimensional stretches as compared to the one dimension used to measure the tensile strength. The brittleness of the media, which is measured by flexing it, is a third major strength measurement, although it is not generally measured in aging studies. 4.1.5.1 Aging The deterioration mechanisms involved in HEPA filter aging are: • Aging and weakening of glass fibers. DOE-HDBK-1169-2022 40 • Deterioration of the resin binder and the organic sealant. • Corrosion of the aluminum separators. • Moisture damage. • Mechanical stresses caused by handling the filter and airflow pulses. Aging of filters leads to degradation in performance. It has generally been accepted that a conservative approach indicates that the maximum total life (storage and in-service) of HEPA filters for consistently removing greater than 99.97 percent of 0.3-micron particles from highly hazardous aerosols is 10 years from the date of manufacture for applications in dry systems, and 5 years in applications where the filter can become wet more than once for short periods of time. If a filter gets wet it should be replaced expeditiously. Guidance and recommendations can be found in ASME AG-1 Non-Mandatory Appendix FK-A, Determination of HEPA Service Life. Ongoing research12 on HEPA filter shelf and service life has begun publication (Refs 20, 21, 22, 59, 60, and 61) and can be referred to as guidance in developing a HEPA filter Service Life program. See also the graded-approach PNNL document TPD-012 for HEPA filters.13 Note that service life as used herein refers to storage and service of the HEPA filter, and thus the manufactured date of the HEPA filter is critical. The date of manufacture may not be retrievable for currently installed filters. If this information is available (without having to remove the filter to retrieve the data on its frame), the filter service life can be determined based on the date of manufacture. If the date of manufacture is not available, the date of installation will be used. If neither is available, the filter will be assumed to be over 10 years old and should be considered for replacement. 4.1.5.2 Upset Environmental Conditions Document 12.5 of the Lawrence Livermore National Laboratory (LLNL) Environment, Safety, and Health Manual, HEPA, HEGA, and ULPA Filter System Design for LLNL Applications, states that continuous exposure to the following operational environments will permanently damage or compromise HEPA filters: • Moisture: 95 to 100 percent relative humidity. • Hot Air: Temperatures higher than 275 degrees Fahrenheit. • Fire: Direct fire or high concentrations of particulate matter produced by fire. • High Pressure: 8.0 in. wg or more, internal or differential across the filter media. • Corrosive Mist: Dilute moist or moderately dry concentrations of acids and caustics. • Any acid and some caustics will attack uncoated aluminum separators. • Hydrofluoric acid will attack the media. 12 For further information, see “Effects of Aging on Nuclear Grade HEPA Media and Filters Summary Report, 21-REP-DOE- AGING-FINAL, July 2021 prepared by Mississippi State University Institute for Clean Energy Technology” 13 https://www.researchgate.net/publication/326882075_PNNL_Technical_Position_Document_TPD- 012_Regulated_HEPA_Filters

https://www.researchgate.net/publication/326882075_PNNL_Technical_Position_Document_TPD-012_Regulated_HEPA_Filters https://www.researchgate.net/publication/326882075_PNNL_Technical_Position_Document_TPD-012_Regulated_HEPA_Filters DOE-HDBK-1169-2022 41 • Nitric acid will attack wooden boxes making highly flammable nitrocellulose. • Shock Pressures: More than 1.7 psig. In addition, the filter exterior should not be exposed directly to outdoor environments. The following criteria are recommended: • Wetting: A single occurrence of filter exposure to water including entrained droplets from actuation of sprinklers in the area upstream of the filters, rain or groundwater, or condensation from a leak of steam or hot water. • Moisture and Hot Air: HEPA filters may be operated continuously at 180 degrees Fahrenheit and between 5 and 75 percent relative humidity, or at 120 degrees Fahrenheit and between 75 and 95 percent relative humidity. HEPA filters are not to be used for installations where there is a possibility of condensation forming on them. They will provide maximum service life when operated below 100 degrees Fahrenheit and 75 percent relative humidity. • Fire: A single occurrence of direct flame impingement.14 • High Differential Pressure: A single occurrence of a differential pressure across a single filter of 8.0 in. wg or more. • Shock Pressure: A single exposure to more than 1.7 psig. • Corrosive Mist: Prolonged exposure (more than 4 weeks) to dilute moist or moderately dry concentrations of acids and caustics. 4.1.5.3 In-Place Testing of Filter Installations An in-place leak test is done after filters are installed at a nuclear facility to ensure the performance of the confinement ventilation system. The in-place leak test is used both for an acceptance and for surveillance leak testing of the installed HEPA filter bank. An in-place leak test and visual inspection of HEPA filters are performed initially upon installation to detect bypasses and damage to filters and periodically to establish current condition of a nuclear air cleaning system and its components. Specific objectives of in-place filter testing are (1) to test the aggregate performance to filters in a filter bank, (2) to evaluate the effectiveness of seals between the filter gasket and the filter housing, (3) to assess the leak-tightness of the filter housing, and (4) to determine whether bypasses exist around the filter housing. Each time repairs are made, the system should be retested until it meets the established criteria for leak- tightness. 4.1.5.4 Packaging, Storage, and Handling of HEPA Filters The manufacturer should have a quality program such as ASME NQA-1 for the packaging, shipping, handling, and storage of HEPA filters. HEPA filters are normally packaged in 14 Filters subjected to smoke from fires should have an in-place leak test performed on them immediately by the responsible in-place testing group (i.e., within 24 hours) and should be replaced if the filter fails the in-place leak test. DOE-HDBK-1169-2022 42

corrugated cardboard cartons that conform to shipping regulations. Additional internal pieces are inserted to protect the filter faces from damage during handling and transit. Palletizing crating should be constructed for ease of disassembly. For multiunit shipments, individual cartons should be crated and palletized to minimize handling, particularly at trans-shipment points when using public carriers. For very large shipments, sealed and dedicated trailers are recommended. Note that filters shipped in less-than-truckload amounts using common carriers are often rearranged incorrectly by the carriers, resulting in damaged filters. Upon delivery at the destination, mechanical warehousing equipment should be used for unloading and transferring the shipment. Cartons should be placed in clean, dry, interior storage until used. They should be positioned as directed on the carton exterior, and no more than three filter cartons should be stacked atop each other. When a filter is inserted in the cardboard shipping container, the pleated folds should be oriented in the vertical direction, except for Type B filters as defined in ASME AG-1, Article FC- 4100). For filters including Type B, both the filter frame and the enclosing carton should be labeled with a vertical arrow or the notation, “This Side Up.” When handling a filter inside a carton, the box should be tilted on one corner, picked up, and carried by supporting it at diagonally opposing corners. Removing the filter from its shipping carton without damaging the medium is best accomplished by opening and folding back the top flaps of the carton, inverting the carton onto a clean surface, and lifting the carton off the filter. Then the filter unit can be grasped by the outer frame surfaces without the danger of personnel coming into contact with the filter pack enclosed within the frame. Additional details can be found in ASME AG-1 Article FC-7000, Packaging, Shipping and Storage. For special HEPA filters, similar information can be found in ASME AG-1 Article FK-7000, Packaging, Shipping and Storage. 4.1.6 Medium Efficiency Filters (Prefilters) for HEPA Filters 4.1.6.1 Filter Descriptions The service life of HEPA filters can often be extended by using less efficient filters that selectively remove the largest particles and fibers from the incoming airstream. In some cases, HEPA filter lifetimes can be increased by as much as four times with multiple medium efficiency filter changes during the interval between HEPA filter changes. It is recommended that HEPA filters be protected from: (1) particles larger than 2 µm in diameter, (2) lint, and (3) particle concentrations greater than 2.3 mg/m. Selection of an appropriate medium efficiency filter includes consideration of: (1) the rapidity of filter resistance buildup and associated energy costs, (2) the size and complexity of the resulting filtration system, (3) the fact that replacement filters and associated costs generally increase with increasing medium efficiency filter efficiency, and (4) the disposal costs for contaminated HEPA filters and potentially uncontaminated medium efficiency filters. It has been estimated that, with frequent medium efficiency filter replacements, savings in filter system operation could be as much as one-third the cost of operating without medium efficiency filters. Assessment of an acceptable combination of medium efficiency filters and HEPA filters depends on the dust-loading and efficiency characteristics of the different filter

DOE-HDBK-1169-2022 43 types available for the particular aerosol to be filtered. The clogging susceptibility of HEPA filters will vary with the dust and filtration characteristics of the medium efficiency filters. The types of filters used as medium efficiency filters are also widely used for cleaning ventilation supply air in conventional HVAC systems. The important advantage of filtering ventilation supply air for many operations that generate radioactive particles is a reduction in the dust load that reaches the final contaminated filters. This helps extend the service life of the exhaust filters, thereby reducing overall system costs because the supply air filters can be changed without resorting to radiation protection measures—often the costliest aspect of a contaminated exhaust filter change. These filters have a wide range of efficiencies, including 5 to 10 percent for warm air residential heating systems; 35 to 45 percent for ventilation of schools, stores, and restaurants; and 85 to 95 percent for fully air-conditioned modern hotels, hospitals, and office towers. ASME AG-1 provides information on emerging technology media that can be used for medium efficiency filters, such as metal media and ceramic filters. Section 5.1.3.34 of this Handbook also provides further information. The user/owner of the facility should incorporate written specifications on the service life of the HEPA filters for change-out criteria based on the use and availability of medium efficiency filters. 4.1.6.2 Classes, Sizes, and Performance Characteristics of Medium Efficiency Filters Table 4.6 shows cross-reference and application guidelines for air cleaners with particulate contaminants. For comparison purposes, the HEPA filter is rated at 100 percent for both the stain-efficiency and artificial dust arrestance tests. Because the atmospheric dust test is based on the staining capacity of the dust that penetrates the filter, compared to the staining capacity of the entering dust, it is not a true measure of particle-removal efficiency for any one particle- size range. Values stated in Table 4.6 for dust-holding capacity were determined with resuspended synthetic dust mixtures. Dust-holding capacity varies with the nature and composition of the particles (e.g., carbon black, cotton linters). Dust-holding capacity under service conditions cannot be predicted accurately on the basis of manufacturers’ data. Air resistance is the primary factor in medium efficiency filter replacement. Although manufacturers recommend specific values of resistance for medium efficiency filter replacement, loss of adequate airflow is often a more reliable indicator of system performance and is also more cost effective. Panel filters will plug rapidly under heavy loads of lint and dust. An accumulation of surface lint may increase the efficiency of an extended-medium efficiency filter by adding “cake” filtration principles to the existing physical mechanisms. The extended-medium efficiency filter will plug readily in an airstream carrying profuse smoke and soot from a fire. Operation at airflows below rated capacity will extend the service lives of filters and be more cost effective by reducing the frequency of filter replacement. On the other hand, when airflow exceeds rated values, dust-loading rate and system costs begin to increase exponentially along with proportional increases in airflow. ASHRAE’s Standard 52.2-2017 gives methods for testing filter efficiency by particle size using optical particle counters, including

DOE-HDBK-1169-2022 44 lasers, and defines MERV as the minimum efficiency reporting value corresponding to a specific intended dust spot efficiency. Table 4.6: Dust-Holding Capacity 4.1.6.3 Commercial and Industrial Grade Filters Performing as Medium Efficiency Filters As previously discussed, medium efficiency filters (prefilters) provide protection for HEPA filters and extend their service life by removing large particles and other particulate matter in the flowing air stream. In addition to medium efficiency filters that satisfy the requirements of ASME AG-1 Section FB, ANSI/AHRI Standard 850 (I-P)-2013, provides information and classifies commercial and industrial grade filters that perform the same function. These filters are classified into groups: Group I - Unit or panel Group II - Extended surface Group III - Electronic Air Cleaner Group IV - Air Filter Media Group V - Self-cleaning, Self-renewable Air Cleaner, or any combination thereof Group I panel filters (viscous impingement filters) are shallow, tray-like assemblies of coarse fibers (glass, wool, vegetable, or plastic) or metal mesh enclosed in a steel or cardboard casing. The medium is usually coated with an inhibited viscous oil or adhesive to improve trapping and retention of particles. Single-use disposable and cleanable-reusable types are available. The DOE-HDBK-1169-2022 45 latter have metal mesh and generally are not used in nuclear applications for effluent or process air cleaning because of the high labor costs associated with cleaning and disposal of entrapped radioactive materials. A disposable panel filter has a fairly high dust-holding capacity, low airflow resistance, low initial and operating costs, and high removal efficiency for large particles. It is particularly effective against fibrous dust and heavy concentrations of visible particles but is ineffective for smaller particles. For nuclear service, it is less cost-effective than the more costly Group II or V filters that provide better protection for the HEPA filter. Group V (moderate-efficiency) and Group II (high-efficiency) filters are usually comprised of extended-medium, dry-type, single-use disposable units. The filter medium is pleated or formed into bags or socks to provide a large filter surface area with minimal face area. They are not coated with adhesive. The particle size efficiency of Group V filters is moderate to poor for sub-micrometer-sized particles, but often approaches 100 percent for particles greater than 5 µm. In most cases, the pressure drop of extended-media Group V filters varies directly with efficiency. Group II filters are recommended for high lint- and fiber-loading applications. The large filter area relative to face area permits duct velocities equal to or higher than those of panel filters. For high dust-loading applications, bag house filters are useful due to the ability to self-clean by intermittent back-pulsing of the filters. Group II filters are preferred when higher efficiency for smaller particles is desired. The dust- holding capacity of Group II filters usually is lower than that of Group II filters. Group II filters are recommended for nuclear applications, and ASME AG-1 Section FB, Medium Efficiency Filters, should be consulted for additional guidance on the design, manufacture, operation, and maintenance of medium efficiency filters. 4.1.6.4 Electrostatic and Electrified Filters

An electrostatic charge may be induced on filter fibers by triboelectrification and by sandwiching the fiber bed between a high voltage and a grounded electrode. Tribo- electrification can be used to induce a high electrostatic charge on suitable high dielectric materials, but under practical-use conditions, the charge is subject to rapid dissipation due to air humidity, oily particles, fiber-binding particles, and other interference. Continuously activated electrodes can induce a more permanent charge. Electrofibrous filters provide greater efficiency and longer service life for the medium efficiency filters used to protect HEPA filters. They have been used in gloveboxes and for other applications. Laboratory tests conducted at LLNL using test and sodium chloride aerosols have shown that an electrofibrous medium efficiency filter increases in efficiency from 40 to 90 percent as 10 kV is applied to the electrode. A comparison of uncharged, triboelectrically charged, and permanently charged fibrous filters demonstrated the higher collection efficiency of the permanently charged filter design for sub-micrometer particles. When continuously charged electrofibrous filters were applied as medium efficiency filters for HEPA filters in exhaust air systems or gloveboxes used to burn uranium turnings, they significantly prolonged the life of the final filters. DOE-HDBK-1169-2022 46 4.1.6.5 Operation and Maintenance of Medium Efficiency Filters (Prefilters) All medium efficiency filter construction materials should be compatible with those of the downstream HEPA filters they are designed to protect. Therefore, they should conform to the rigorous physical properties prescribed for HEPA filters (e.g., resistance to shock, vibration, tornado, earthquake, moisture, corrosion, and fire). Survivability under the specific operational conditions and requirements should be addressed when medium efficiency filters are selected because moisture or corrosive products in the airstream may limit the choice of filter. Although many filter media will not withstand acid or caustic attack, glass fibers are corrosion-resistant except for fluorides. However, the casing and face screen materials may be less so. Aluminum may deteriorate in marine air, from caustics, or from carbon dioxide. Plastics have poor heat and hot air resistance and generally will not satisfy UL requirements. Condensation from high humidity and sensible water may plug a medium efficiency filter and result in more frequent replacement. In general, a medium efficiency filter made of construction materials identical to those in the HEPA filter will have equivalent corrosion and moisture resistance. Any increase in resistance from moisture accumulation will be greater for MERV 17-20 filters than for MERV 9- 16 filters (ASHRAE 52.2, Table E-1). Most types of medium efficiency filters are suitable for continuous operation at temperatures not exceeding 149 to 248 degrees Fahrenheit (65 to 120 degrees Celsius). Other types with glass-fiber media in steel or mineral board frames may be used at temperatures as high as 392 degrees Fahrenheit (200 degrees Celsius). Users of high-temperature medium efficiency filters should take a conservative view of performance claims, particularly claims related to efficiency at high operating temperatures.

Because of waste disposal requirements, the preferred choice of a medium efficiency filter for nuclear applications is the single throwaway cartridge. A replaceable-medium efficiency filter offers an advantage over the throwaway because the bulk of material that needs to be discarded is smaller and handling and disposal costs are minimized. However, re-entrainment of contaminants and contamination of the peripheral area are possible because the medium is removed from the system and prepared for disposal. The replaceable-medium type is not recommended for toxic exhaust systems. The cleanable-medium efficiency filter is undesirable for nuclear systems because of the extensive downtime of the system that is required for changing and decontaminating areas in proximity to the filter installation. For this type of application, ASME AG-1 Section FB contains guidance that should be considered for DOE facilities. 4.1.7 Deep-Bed Filters Deep-bed filters were designed, built, and placed in service early in the development of nuclear technology for treating off-gassing from chemical processing operations. The first, a sand filter, was constructed at the Hanford, Washington, nuclear facility in 1948, and deep-bed glass fiber filters were constructed soon after. These were not considered competitive with then-current versions of the HEPA filter but were thought to have a different function. With the thin-bed filters, the intent is usually to replace or clean the filter medium periodically. The deep-bed filter, on the other hand, usually has as its objective the installation of a unit which will have a DOE-HDBK-1169-2022 47 long life, in the dust capacity sense, of say 5 to 20 years, corresponding to either the life of the process or the mechanical life of the system. Thus, when resistance starts increasing rapidly, instead of replacing or cleaning the filter medium, the entire filter installation would be abandoned and replaced with a new unit. A partial explanation for this longevity is the original design concept that deep-bed filters would be used where the total aerosol concentration was usually on the order of or less than normal atmospheric dust concentrations. An important reason for selecting sand for the initial bed material was a need to filter large volumes of wet corrosive aerosols for which more usual filter materials would prove unsatisfactory. Deep beds of crushed coke had been used by the chemical manufacturing industry for many years to remove sulfuric acid mist from the effluent gas of sulfuric acid manufacturing plants prior to 1948. 4.1.7.1 Deep-Bed Sand Filters Initially, sand filters were installed at the Hanford Reservation and at the Savannah River Site (SRS). Following their success, more were added at Hanford and SRS and others were constructed at nuclear facilities in Morris, Illinois, and Idaho Falls, Idaho. The Argonne National Laboratory compiled a bibliography (ANL-7683, Sand-Bed Filtration of Aerosols: A Review of Published Information on Their Use in Industrial and Atomic Energy Facilities) of Deep-Bed Sand (DBS) filters. These DBS filters had collection efficiencies for particles greater than or equal to 0.5 µm that compared favorably with the HEPA filters of that era. Their advantages for the nuclear programs at these sites included large dust-holding capacity, low maintenance, chemical resistance, high heat tolerance, fire resistance, and a capability to withstand large shock and gross pressure changes without operational failures. They also had disadvantages such as high capital costs, need for large areas and volumes, inability to maintain the granular fill, and lack of a reasonable means of disposing of the contaminated fill.

DBS filters contain up to 10 feet of rock, gravel, and sand constructed in graded layers that diminish granule size by a factor of 2 as the layers go from bottom to top. Airflow direction is upward so that granules decrease in size in the direction of flow. A top layer of moderately coarse sand is generally added to prevent fluidization of the finest sand layer underneath. The rock, gravel, and sand layers are positioned and sized to provide the desired structural strength, particle collection ability, dirt-holding capacity, and long service life. Ideally, the layers of the largest granules, through which the gas stream passes first, remove all the large airborne particles, whereas the fine sand layers on top retain the finest smallest particles at high efficiency. Below the granular bed there is a layer of hollow tile that forms passages for air distribution. The use of an elevated steel grating platform can also be used for this purpose, as identified in ASME AG-1, Section FL. The total bed is enclosed in a concrete-lined pit. The superficial velocity is generally 5 to 7 feet per minute, and pressure drop across the seven layers, sized 3 1/2-inch average diameter down to 50 mesh, is from 7 to 11 in. wg. Collection efficiencies as high as 99.98 percent for test aerosols have been reported. More details on DBS Filters are provided in Section 5.4 of this handbook. Detailed guidance on DBS filters is contained in ASME AG-1, Section FL, Deep Bed Sand Filters. This guidance is based on operational experience from the use of DBS filters at SRS. DOE-HDBK-1169-2022 48 4.1.7.2 Deep-Bed Glass Fiber Filters The rapidly emerging glass fiber technology of the late 1940s shifted attention to the use of very deep beds (1 or more meters thick) of graded glass fibers as a satisfactory substitute for sand filters when treating gaseous effluents from chemical operations. They proved to be more efficient, less costly, and to have a lower airflow resistance than the DBS filters they replaced. In addition, these Deep-Bed Glass Fiber (DBGF) filters employ a medium that has more controllable physical features and more assured availability than the DBS to permit a larger airflow per unit volume at lower pressure drop, lower operating costs, and potentially lower spent-filter disposal costs. DBGF filters have been used at Hanford for several decades on their PUREX process effluent streams. However, the DBGF filters do not have the corrosion resistance of the DBS, particularly from HF, and are less fire-resistant. The DBGF is also less of a heat sink and has less capability to resist shock and high-pressure transients. The intake segment of the DBGF filter system was designed with layered beds of uniform- diameter glass fibers to a total depth of 8 to 84 inches. Each layer in the direction of airflow was compressed to a higher density and enclosed in a stainless-steel tray with impermeable walls and a perforated screen above and below. Capacity varied from 200 to 200,000 cfm (350 to 350,000 m3/hr). Although the first unit constructed at Hanford was small (400 m3/hr (240 cfm), many of the 25 subsequent units were much larger and experienced extensive usage from nuclear fuel processing to hot cell ventilation. The glass fiber of preference for this application was Owens-Corning's 115-K, a 29-µm-diameter, curled glass fiber that resisted clumping, settling, and matting. A system that was designed for downward airflow became inoperative from precipitation of ammonium nitrate at the filter face. Subsequent units were designed with air flowing upward and were equipped with water sprays directed from below to dissolve salt precipitation on the intake face to reduce pressure drop buildup.

The design airflow velocity of a typical DBGF was 50 feet per minute, and clean pressure drop was close to 1.5-in.wg. The final pressure drop, after a total particle loading estimated at 10,500 pounds, was 8-in.wg. The final stage of a second-generation DBGF filter system employed two 12-mm blankets of 3.2-µm- and 1.2-µm-diameter glass fibers fabricated as a twin-layer bag stretched over a stainless-steel framework. Airflow from the first stage passed through the filtration blankets from the outside to the inside, then was exhausted from inside the metal framework. The number of bag filters was proportional to the capacity of the intake segment of the DBGF filter. Later designs of the DBGF filter's cleanup stage substituted HEPA filters in a group of manifolded caissons (encapsulating filter holders), and a comparable increase in collection efficiency was realized. Provision for periodic backflushing will often extend the life of the total filter. Most DBGF filter systems, contained in vaults below ground, are resistant to shock and overpressure from natural phenomena. The dust-holding capacities of DBGF filters are very large, and many units have operated for years without attendance or maintenance. Pressure drop sensors can often predict evolving difficulties and indicate when it is time for backflushing, precipitate dissolution, or other preplanned remedial actions. Just as for DBS filters, decontamination and disposal is difficult for small systems and nearly impossible for the larger systems. DOE-HDBK-1169-2022 49 4.1.7.3 Deep-Bed Metal Filters Deep beds of metal fibers have a number of applications in the nuclear industry, particularly where maximum resistance to fires, explosions, and overpressure shocks are essential. In off- gas systems containing substantial concentrations of HF, use of stainless-steel metal fibers has been studied as a substitute for glass. In most cases, the objective when using metal fiber filters is to obtain particle collection efficiencies that duplicate those obtainable with HEPA filters. However, the unavailability of metal fibers with diameters close to or below 1 µm makes it necessary to provide great filter depth as a substitute for small fiber collection efficiencies. For sodium fire aerosols, high collection efficiency can be obtained with relatively large diameter metal fibers because the combustion products in air, sodium oxide, and carbonate rapidly form large flocs that are easily filtered. The ease of filtration results in the extremely rapid formation of a high-resistance filter cake that severely limits the amount of sodium aerosol particles that can accumulate in the filter before the limit of the fan's suction pressure is reached. Here, the requirement is for a graded-efficiency, deep-bed, metal filter with a large storage capacity in the initial layers of the filter for the fluffy sodium aerosol particles, a high efficiency for small particles in most downstream layers of the filter, and the elimination of abrupt interfaces between graded fiber layers where a filter cake might form. This is a different filtration requirement than obtaining high efficiency for low concentrations of small, non-agglomerating particles—instead, the requirement is for uniform particle storage throughout the depth of the filter. Here also, uniform diameter fibers can be used in great depths, as in the DBGF filters, to substitute for the presence of very small-diameter filter fibers.

Other types of metal filters have been constructed by sintering stainless steel powders or fine fibers into a sieve-like structure that function very much like a conventional pulse-jet-cleaned industrial cloth filter. The metal membrane has an inherent high efficiency for particles greater than a few micrometers but depends on the formation of a filter cake to obtain high efficiency with sub-micrometer particles. Clean airflow resistance is high and increases rapidly as cake thickness builds up. It is cleaned periodically by backflow jets of compressed air. Efficiencies are comparable with those of HEPA filters when the sintered metal filters are precoated with filter aids. Because of their high-temperature resistance and ability to handle high concentrations of mineral dusts, these types of filters have been used in nuclear incinerator off-gas cleaning systems, particularly when heat recovery from the hot filtered gases is desired. However, care should be exercised to avoid releasing tar-like combustion products to sintered filters that are operated at high temperatures because the tarry material tends to lodge in the pores and turn to cake that cannot be removed by chemical means or by elevating the temperature to the limit of the metal structure. Another type of sintered filter construction for high-temperature applications has been prepared from a mixture of stainless steel and quartz fibers. The composite material has the same efficiency and pressure drop as HEPA filter glass paper but has 4 times the tensile strength and can operate continuously at temperatures up to 932 degrees Fahrenheit (500 degrees Celsius). DOE-HDBK-1169-2022 50 Ongoing research at several laboratories worldwide is ongoing for metal media filters. A future edition of ASME AG-1 Code will contain applicable sections on this topic. 4.1.7.4 Moisture Separators (Demisters) Liquid droplet entrainment separators, known as moisture separators or demisters, are required in the standby air treatment systems of many water-cooled and -moderated power reactors to protect the HEPA filters and activated-charcoal adsorbers from excessive water deposition should a major high-temperature water or stream release occur as a result of an incident involving the core cooling system. Droplet entrainment separators are also used in fuel processing operations to control acid mists generated during dissolving operations and subsequent separation steps. Entrainment separators consisting of a series of bent plates are widely used in HVAC applications for controlling water carryover from cooling coils and humidifiers; but for nuclear applications, their droplet removal efficiency is inadequate. Therefore, fiber-constraining demisters with a much greater efficiency for small droplets are standard for nuclear service. Entrainment separators utilizing fiber media remove droplets by the same mechanisms that are effective for dry fibrous filters, but they should have the additional important property of permitting the collected water to drain out of the cell before it becomes clogged. Should clogging occur and the pore spaces fill with water, the pressure drop across the separator will rise and some of the water retained in the pore spaces will be ejected from the air discharge side to create sufficient passages for air to pass through. The ejected water can become airborne again by this mechanism.

Droplets from condensing vapors originate as sub-micrometer-sized aerosols, but the droplets may grow rapidly to multi-micrometer size by acting as condensation centers for additional cooling vapors and by coagulation when the concentration of droplets exceeds 10 droplets/ml. Firefighting spray nozzles, confinement sprays, and other devices that mechanically atomize liquid jets yield droplets that predominantly range from 50 to more than 1,000 µm in diameter. In USNRC Regulatory Guide 1.52, NRC recommends the use of entrainment separators for engineered safety systems when the air may be carrying entrained liquid droplets or a cooling and condensing vapor. As previously discussed, HEPA filter medium is treated for water repellency, however high-water loadings rapidly saturate the paper leading to degradation of filter performance and potential catastrophic failure of the filter. Therefore, the criteria for entrainment separators used for nuclear service call for: (1) at least 99.9 percent retention by weight of entrained water and condensed steam in the size range 1 to 2,000 µm diameter, at a duct velocity from 250 to 2,500 linear feet per minute, and water delivery rate of 8 gallons per minute (gpm) per 1000 cfm of installed HEPA filter capacity; (2) at least 99 percent retention by count of droplets in the 1- to 10-µm-diameter range, at a duct velocity from 250 to 2,500 linear feet per minute; (3) no flooding or water re-entrainment at a water-steam delivery rate of 8 gpm at a duct velocity of 2,500 linear feet per minute; and (4) a temperature tolerance at least to 320 degrees Fahrenheit (160 degrees Celsius) and gamma radiation exposure up to 8x107 rads integrated dose without visible deterioration or embrittlement of the materials of construction. ASME AG-1 Section FA, Moisture Separators, should be consulted for the specific design criteria for moisture separators. DOE-HDBK-1169-2022 51 An entrainment separator with these characteristics will provide long-term protection for a downstream HEPA filter. Entrainment separators are usually constructed of deep layers of high- porosity metal and glass fibers, either packed or woven into stable batts, and arranged in graded sizes and packing density to give the desired small droplet collection capability with excellent resistance to flooding and re-entrainment. Details of construction can be found in ASME AG-1, Section FA. 4.1.8 Testing 4.1.8.1 Introduction Testing of high-efficiency nuclear air cleaning systems is required to achieve and maintain high performance and continued safe operation of nuclear facilities. In nonreactor nuclear facilities throughout the DOE complex, HEPA filters in confinement ventilation systems can be constantly challenged with radioactive aerosols. Nonreactor nuclear facilities comprise the bulk of DOE nuclear facilities, and failure of their air cleaning system components can lead to uncontrolled atmospheric release of radioactive aerosols. Thus, maintaining nuclear facility operability depends on the performance of these air cleaning components. At the same time that HEPA filters and adsorbers were being developed for nuclear applications, methodologies were being developed to assure their performance. These methodologies eventually evolved into a performance assurance program with three major components: (1) design qualification of individual components through destructive testing, (2) QA of individual components through nondestructive testing, and (3) performance assurance of nuclear confinement ventilation systems through in-place testing. This overall performance assurance program was designed to be hierarchical because components were built on a foundation laid down by preceding components. Design qualification assured that filters produced according to a manufacturer’s design met specific performance criteria for normal and off-normal operation.

HEPA filters for DOE nuclear service now undergo four tests: (1) design qualification test performed by a qualified laboratory, (2) production inspection and testing at the manufacturer, (3) DOE-required QA inspection and testing at a DOE-designated FTF, and (4) receipt inspection and system leak test at the facility where the filter will be used. Manufacturers submit prototype filters for design qualification testing. This testing examines areas such as media penetration and resistance to airflow, rough handling, pressure, heated air, and spot flame. The filter medium receives the most rigorous and extensive control and evaluation. The U.S. Army’s Edgewood Chemical and Biological Center performs the tests required for qualification, with the heated air and spot flame test being performed at UL in accordance with UL-586. This testing is required to be repeated every 5 years. Manufacturers receive a letter stating whether their filter designs passed the qualification tests. Further information can be found in DOE-STD- 3020 and 3025. After being installed at a DOE nuclear facility, an in-place leak test is done to ensure the performance of the confinement ventilation system. Unlike bench tests for new filters that are designed to determine filter quality via a penetration test utilizing an aerosol containing a substantial fraction of particles in the range of the minimum filterable size, in-place tests are designed to reveal the presence of defects in the filter unit that result from such things as DOE-HDBK-1169-2022 52 rough handling during transportation, paper and gasket damage during installation, inadequate pressure against intact gaskets, and penetrations through the housing to which the filter units are attached. Procedures are conducted to locate and correct the defects. Such procedures include increasing gasket compression; examining gaskets for breaks and tears; replacing broken filters (repairs are not permitted for nuclear service in the U.S.); and welding closed any unauthorized penetrations, cracks, and open seams in the filter house and mounting frames (patching with caulking compounds is not permitted for nuclear service in the U.S.). Following each repair, the system should be retested until it meets the established criteria for leak tightness. ASME AG-1, Section TA, Field Testing of Air Treatment Systems, contains information on repairs and required in-place tests after repairs, and ANSI N-511 contains information on in- service testing. When repairs require re-qualification of equipment, the applicable sections of AG-1 apply. The performance of the periodic/surveillance in-place test cannot be overemphasized. The in- place leak test described by ASME/ANSI N-510 has been used to conduct a periodic surveillance to reconfirm the performance of the filter system. This standard is no longer published through ASME and has been superseded by ASME AG-1, Section TA, Field Testing of Air Treatment Systems. This Code section should be referenced for any in-place leak testing done at any DOE facility. The in-place leaks test confirms the safety basis assumptions “system efficiency.” The final result is a measure of efficiency that forms the basis for removal efficiency assumed in the safety bases. The in-place test results may also be credited by the radcon and air emission permits for removal of respirable particles. Unlike the filter penetration test which validates the filter design assumption using a mono-disperse aerosol test, the in-place leak tests use a poly- dispersed (0.7 mean diameter) and determines the system efficiency where the system components (i.e., gaskets, frame, housing) are challenged. The test is performed under actual conditions and at operational airflow. The criteria for the in-place leaks tests are typically provided by the safety basis or other operating licenses/permits. The test results may also be used as a service life indicator.

4.1.8.2 Proof of Design – HEPA Filter Design Qualification Testing for Nuclear Service As discussed previously, the U.S. Army’s Edgewood Chemical and Biological Center tests prototype HEPA filters to qualify the designs for use in DOE nuclear facilities (this testing is required to be repeated every 5 years). ASME AG-1, Section FC and Section FK, requires quality product qualification testing for efficiency, airflow resistance, rough handling, overpressure, heated air, and spot flame. The following subsections discuss each design qualification test and associated acceptance criteria. 4.1.8.2.1 Penetration (Efficiency) The performance of a HEPA filter may be expressed either as a particulate collection efficiency (percent of particulate concentration stopped by the filter) or as a penetration. Penetration where the total aerosol penetration through the filter medium, frame, and gasket of a filter that has been encapsulated should be no greater than 0.03 percent of the upstream concentration at rated airflow and at 20 percent of rated airflow (except for filters rated at 125 cfm or less). The reason for the 20 percent flow test is to increase sensitivity for pinhole determination. Concentration may be given by particle count per unit air volume (emphasizing DOE-HDBK-1169-2022 53 the smallest particles present), particle weight per unit air volume (emphasizing the largest particles present), ionizing radiation intensity per unit volume of air (particle size effect is indeterminate), or light-scattering intensity per unit air volume (emphasizing small particle sizes). 4.1.8.2.2 Airflow Resistance The resistance of a filter to airflow, often called “pressure drop” and “back pressure,” is usually given as the height of a water column (measured in in. wg) that exerts an equal pressure. The characteristic flow regime through HEPA filter media is aerodynamically described as laminar. For this reason, the airflow resistance of these filters changes in direct proportion to changes in air volume even though the air approaching the filter may be turbulent. Resistance to airflow at the rated airflow of the filter should be no greater than 1.0 in. wg for filter sizes 4 and 5, and 1.3 in. wg for filter sizes 1, 2, 3, 6, 7, 8, and 9. (See ASME AG-1, Section FC for filter definitions.) ASME AG-1 also includes information on resistance to airflow for other HEPA filter configurations. 4.1.8.2.3 Aerosol Test Equipment and procedures to aerosol test HEPA filters can be found in ASME AG-1, DOE-STD- 3025, IEST-RP-CC034, and previous versions of this Handbook (with reference to Military Standard MIL-STD-286). Room air is drawn through filters and split into three streams. One stream of 85 cfm is heated to 365 degrees Fahrenheit and is passed over liquid test aerosol heated to 390 ± 20 degrees Fahrenheit. As the heated air passes over the surface of the hot test aerosol, it becomes saturated with aerosol vapor. Traditionally the test aerosol of choice was dioctyl phthalate (DOP). Other non-carcinogenic test aerosols, such as poly-alpha olefin (PAO) are allowable as indicated in ASME AG-1 and DOE-STD-3025. When the test-aerosol-saturated air contacts the second airstream (265 cfm held at approximately 71 degrees Fahrenheit), the condensation aerosol is formed. The third stream of diluent air (850 cfm) is introduced in a mixing chamber to dilute and disperse the aerosol-laden air. A forward light-scattering photometer is used to measure test aerosol penetration, and a manometer is used to measure filter resistance at rated airflow. Modern penetrometers that use jet impactors to obtain the same aerosol without heating the test aerosol liquid are commercially available.

4.1.8.2.4 Resistance to Rough Handling Qualification Test In accordance with ASME AG-1 Section FC and FK, new, unused test filters (at least 2 of the size and design to be qualified) should undergo rough handling for 15 minutes at a total amplitude of 0.75 inches (using sharp cut-off cams that result in both a slow and an instantaneous 0.75- inch drop) and a frequency of 200 Hertz (Hz), with pleats and filter faces in vertical orientation. The filters should withstand this treatment without visible damage (cracked or warped frames, loose corners or joints, cracked adhesive, loose or deformed medium) or a decrease in filtration efficiency from 99.97 percent, as determined with nominal 0.3 rim test aerosol at full and 20 percent flows. DOE-HDBK-1169-2022 54 4.1.8.2.5 Moisture and Overpressure Resistance Qualification Test At least four new, unused filters of the type to be qualified should be aged a minimum of 24 hours under static conditions at 95 ± 5 degrees Fahrenheit and 95 ± 5 percent relative humidity after which they should be installed in a wind tunnel that has been modified to permit the introduction of water spray. After conditioning, the filters should withstand a spray of 1.25 pounds per 1,000 cfm, adjusted to produce a 10-in.wg pressure drop across the filter, and a flow environment of 95 degrees Fahrenheit. The minimum test duration under these specified conditions is 1 hour. After the test and the filters are dried out, there should be no visible evidence of failure. Within 15 minutes after completion of the pressure test and while still wet, the 0.3-rim test aerosol efficiency at full and 20 percent rated flow should be a minimum of 99.97 percent. This is the most stringent test an assembled HEPA filter will undergo and is limited to a 10-in.wg pressure drop. Additional details can be found in ASME AG-1, Section FC and FK. 4.1.8.2.6 Fire and Hot Air Resistance Qualification Test New, unused filters should be exposed to heated air in a wind tunnel at 700 ± 50 degrees Fahrenheit for 5 minutes. After exposure to heat, the filters should be cooled down and tested in-place, with the filter remaining in the heated air tester. An aerosol generator and photometer may be used for the aerosol test. The penetration at equal to or greater than 40 percent of rated flow should be less than 3 percent. Additional details can be found in ASME AG-1 Section FC and FK. 4.1.8.2.7 Spot Flame Resistance In this test, the HEPA filter is inverted in a test duct and operated at its rated airflow. A gas flame from a Bunsen burner is directed against the upstream face of the HEPA filter. The Bunsen burner is adjusted to produce a flame with a blue cone 2.5 inches long with a tip temperature of 1750 ± 50 degrees Fahrenheit. The tip of this flame is applied so that it is not less than 2 inches from the filter face. The flame is applied for 5 minutes at each of 3 separate locations on the filter face. The Bunsen burner flame then is directed into the top corner of the filter unit so that the tip of the blue flame cone contacts the frame, filter pack, and pack sealant. The flame is applied for a period of 5 minutes. After the removal of the test flame at each point of application, there should be no sustained flaming (burning) on the downstream face of the unit. Additional details can be found in ASME AG-1 Section FC and FK. 4.1.8.2.8 Quality Control, Inspection and Testing of HEPA Filters

The manufacturer’s qualification procedure involves two distinct phases: (1) a QA/QC routine intended to ensure careful manufacture of a quality product, and (2) a series of tests to verify filter compliance with preset standards concerning the properties of components and the physical characteristics of the assembled filter, as well as a set of performance criteria related to collection efficiency and resistance to airflow. When all of these factors are within the tolerance limits set by ASME AG-1 Section FC and Section FK (and other applicable sections), the manufacturer certifies that each delivered filter unit meets all acceptance criteria. The manufacturers required tests for HEPA filters are prescribed in ASME AG-1, Section FC, and in ASME AG-1, Section FK for special HEPA filters. DOE-HDBK-1169-2022 55 4.1.9 Filter Qualification, Quality Assurance Inspection, and Testing of HEPA Filters 4.1.9.1 Introduction The operating policy of DOE's filter testing program, contained in DOE-STD-3025, Quality Assurance Inspection and Testing of HEPA Filters, calls for testing all HEPA filters intended for environmental protection at DOE contracted FTF. Specifications for HEPA filters to be used by DOE contractors are contained in DOE-STD-3020-2015, Specifications for HEPA Filters Used by DOE Contractors. The QA activities and testing performed at the DOE contracted FTF are considered defense-in- depth and should not be relied upon to substitute for onsite receipt inspection, or other QA activities, that would normally be conducted for NQA-1 procured equipment or components. 4.1.9.2 Visual Inspection Visual inspection is an integral and vital part of every acceptance or surveillance test. A careful visual examination should be made of each internal and external component prior to installation to verify that the items have been received in satisfactory and serviceable condition. After installation, the system should be checked as part of the acceptance test procedure to make sure that all required items have been properly installed. A required visual inspection checklist is contained in ASME AG-1, Mandatory Appendix TA-I. A suggested checklist is provided in Section 5 of ASME N510, which may be used to verify that system design and construction are in accordance with ASME N509. ASME AG-1 also provides guidance for visual inspection in Section 5.0 and Appendix 1 of Section AA. 4.1.9.3 In-Place Component Tests and Criteria System tests fall in two broad categories: (1) prestart up acceptance tests to verify that components have been installed properly and without damage and that the system can operate as intended, and (2) surveillance tests made periodically after the system has been placed in operation to demonstrate its ability to continue performing its intended air cleaning function. Surveillance tests are leak tests of the HEPA filter and adsorber installations. ASME AG-1 Section TA, Field Testing of Air Treatment Systems, contains requirements for general inspection, field acceptance tests, corrective actions, and necessary instrumentation to perform acceptance tests. DOE facilities conduct surveillance tests with procedures that are adapted to their facility. For nuclear power stations, USNRC Regulatory Guides 1.52 and 1.140 provide guidance that can be used by DOE facilities to prepare their procedures. 4.1.9.4 Component Acceptance Testing

Acceptance tests also fall into two broad categories: (1) those that relate to the permanent elements of the system, ducts, housing, mounting frames, and location of test ports, and (2) those that verify the installation and condition of the primary air cleaning components (HEPA filters and adsorbers). Tests in the first category include leak tests of ducts, housings, and primary-component mounting frames; airflow capacity and distribution tests; gas residence time tests for systems containing adsorbers; duct-heater tests for systems containing heaters; and air-test aerosol mixing-uniformity tests. The acceptance test program for a particular DOE-HDBK-1169-2022 56 system may contain any or all of these tests, depending on the nature of the system and its importance (i.e., the potential consequence of a failure. The basic precepts of acceptance testing as specified ASME AG-1, Section TA are: • All components such as medium efficiency filters, mist eliminators, HEPA filters, and adsorbers are qualified and tested as individual components. Their original efficiency is established, and “as-installed” tests do not require further “efficiency testing.” The in- place test is conducted to ensure the integrity of components is maintained and that no bypass exists. • The housing is of the desired strength and integrity, which can be measured by isolating the unit envelope housing and leak testing under the specified pressure differential conditions. • The framework integrity (framework holding critical components such as HEPA filters and adsorbers) can be measured by using blank off plates and pressure differential leak tests. For clarity, it should be reiterated that the definition of the “Air Cleaning Unit” is an assembly of components that together comprise a single subdivision of a complete air cleaning system, including all the components necessary to achieve the air cleaning function of that subdivision. A unit includes a single housing, with the internal components (e.g., filters, adsorbers, heaters, instruments) installed in or on that housing. Acceptance tests are outlined in ASME AG-1, Section TA. Before assembly, personnel should assure that all components meet the specified criteria. Typical QA acceptance only assures that paperwork is available. This paperwork should be checked both for original supply and for replacement parts. Before installing components, personnel should perform the following tests: • Visual Inspection, • Duct Leak Test, • Housing Leak Test, • Mounting Frame Leak Test. During and immediately after installation of components, personnel should perform the following tests: • Visual Inspection, • Airflow Capacity and Distribution Test, • Air/Aerosol Mixing Uniformity Test, • In-Place Leak Test HEPA Stage, • Remove Adsorbent and Perform Laboratory Testing (to establish baseline carbon efficiency), • In-Place Leak Test Adsorber Stage, and • Duct Damper Bypass Leak Test (if required). DOE-HDBK-1169-2022 57 4.1.9.5 Duct and Housing Leak Test

The level of duct and housing leak tightness (and therefore the acceptance criterion for the test) is based on the type of construction and the potential hazard (consequence) of a leak. Recommended maximum permissible leak rates for various duct and housing constructions are given in AG-1, Mandatory Appendix TA-III, Duct and Housing Leak Test Procedures. The designer may specify tighter requirements based on the confinement requirements of the system. Duct leak tests may be conducted by testing the entire ductwork system at one time or by testing one section at a time and blanking off the ends of the section under test. The second method is more practical for larger systems. When segmented, the permissible leak rate for the individual sections is based on the proportionate volume of that section. The apparatus and procedure for leak testing levels 1 and 2 ducts are described in the Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA) HVAC – Duct Design. ASME AG-1 offers two test methods for housing leak test: (1) the Pressure Decay Method (the most convenient for larger duct and housing systems) and (2) the Constant Pressure Method (the most effective for smaller volumes). Test methods for level 3, 4, and 5 ducts and for housings are described in ASME AG-1. If the specified leak tightness cannot be met, leaks are located, repaired, and retested by one of the methods described in ASME AG-1. When performing the unit housing leak test, it is important to follow the normal procedures (e.g., closing doors) and thereby avoid creating a once-in-a- lifetime condition that does not resemble normal operating procedures and conditions. The test is supposed to demonstrate that the unit housing will maintain the specified leak-tightness during its operating life. To ensure the leak integrity of the housing is maintained due to deterioration of door gaskets, or occurrence of sprung doors, damaged threads on closures, and leaks due to maintenance work on the unit, personnel should perform periodic retesting (every 10 years). Other methods such as acoustical monitoring or tracer gas monitoring may be appropriate when entry into the housing is precluded. 4.1.9.6 Mounting Frame Pressure Leak Test This test is performed to ensure the installed HEPA filter/adsorber mounting frame is installed with no leak paths through the structure. This is considered an optional test because the same evaluation is done after the filters are installed, and an in-place leak test is performed on the bank. However, this test may be useful for determining gross leakage prior to filter installation, and thus maximize the ease of any needed repair