United States Office of Solid Waste EPA 550­B­99­009

Environmental Protection and March 2009

Agency Emergency Response www.epa.gov/emergencies

RISK MANAGEMENT

PROGRAM

GUIDANCE

FOR OFFSITE

CONSEQUENCE

ANALYSIS

Office of Emergency Management
This document provides guidance to the owner or operator of processes covered by the Chemical Accident 

Prevention Program rule in the analysis of offsite consequences of accidental releases of substances regulated 

under section 112(r) of the Clean Air Act. This document does not substitute for EPA's regulations, nor is it 

a regulation itself. Thus, it cannot impose legally binding requirements on EPA, States, or the regulated 

community, and may not apply to a particular situation based upon the circumstances. This guidance does 

not constitute final agency action, and EPA may change it in the future, as appropriate. 
TABLE OF CONTENTS
 

Chapter Page 

Table of Potentially Regulated Entities ............................................ viii
 

Roadmap to Offsite Consequence Analysis Guidance by Type of Chemical .................. x 
 

1 Introduction ................................................................... 1- 1 
 

1.1 Purpose of this Guidance .................................................. 1-1 
 

1.2 This Guidance Compared to Other Models .................................... 1-4 
 

1.3 Number of Scenarios to Analyze ............................................ 1-4 
 

1.4 Modeling Issues ......................................................... 1-5 
 

1.5 Steps for Performing the Analysis ........................................... 1-6 
 

1.5.1 Worst-Case Analysis for Toxic Gases ................................. 1-7 
 

1.5.2 Worst-Case Analysis for Toxic Liquids ................................ 1-7 
 

1.5.3 Worst-Case Analysis for Flammable Substances ........................ 1-8 
 

1.5.4 Alternative Scenario Analysis for Toxic Gases .......................... 1-8 
 

1.5.5 Alternative Scenario Analysis for Toxic Liquids ......................... 1-9 
 

1.5.6 Alternative Scenario Analysis for Flammable Substances .................. 1-9 
 

1.6 Additional Sources of Information .......................................... 1-10 
 

2 Determining Worst-Case Scenario ................................................. 2-1 
 

2.1 Definition of Worst-Case Scenario .......................................... 2-1 
 

2.2 Determination of Quantity for the Worst-Case Scenario .......................... 2-3 
 

2.3 Selecting Worst-Case Scenarios ............................................. 2-3 
 

3 Release Rates for Toxic Substances ................................................ 3-1 
 

3.1 Release Rates for Toxic Gases .............................................. 3-1 
 

3.1.1 Unmitigated Releases of Toxic Gas ................................... 3-2 
 

3.1.2 Releases of Toxic Gas in Enclosed Space .............................. 3-2 
 

3.1.3 Releases of Liquefied Refrigerated Toxic Gas in Diked Area ............... 3-3 
 

3.2 Release Rates for Toxic Liquids ............................................ 3-4 
 

3.2.1 Releases of Toxic Liquids from Pipes ................................. 3-5 
 

3.2.2 Unmitigated Releases of Toxic Liquids ................................ 3-5 
 

3.2.3 Releases of Toxic Liquids with Passive Mitigation ....................... 3-7 
 

3.2.4 Mixtures Containing Toxic Liquids .................................. 3-11 
 

3.2.5 Release Rate Correction for Toxic Liquids Released at Temperatures 

Be e o n o tw en 25 C a d 50 C .......................................... 3-12

3.3 Release Rates for Common Water Solutions of Toxic Substances and for Oleum ..... 3-14 
 

4 Estimation of Worst-Case Distance to Toxic Endpoint ................................. 4-1 
 

April 15, 1999 i 
TABLE OF CONTENTS 

(Continued) 

Chapter Page 

5 Estimation of Distance to Overpressure Endpoint for Flammable Substances ............... 5-1 
 

5.1 Flammable Substances Not in Mixtures ...................................... 5-1 
 

5.2 Flammable Mixtures ..................................................... 5-2 
 

Reference Tables of Distances for Worst-Case Scenarios ............................... 5-4

 Table
 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by
 

Endpoint, F Stability, Wind Speed 1.5 Meters per Second:
 

1 10-Minute Release, Rural Conditions ........................................ 5-4 
 

2 60-Minute Release, Rural Conditions ........................................ 5-5 
 

3 10-Minute Release, Urban Conditions ........................................ 5-6 
 

4 60-Minute Release, Urban Conditions ........................................ 5-7 
 

Dense Gas Distances to Toxic Endpoint, F Stability, Wind Speed 1.5 Meters per Second:
 

5 10-Minute Release, Rural Conditions ........................................ 5-8 
 

6 60-Minute Release, Rural Conditions ........................................ 5-9 
 

7 10-Minute Release, Urban Conditions ....................................... 5-10 
 

8 60-Minute Release, Urban Conditions ....................................... 5-11 
 

Chemical-Specific Distances to Toxic Endpoint, Rural and Urban Conditions, F Stability,
 

Wind Speed 1.5 Meters per Second:
 

9 Anhydrous Ammonia Liquefied Under Pressure ............................... 5-12 
 

10 Non-liquefied Ammonia, Ammonia Liquefied by Refrigeration, or Aqueous
 

Ammonia ............................................................. 5-13 
 

11 Chlorine .............................................................. 5-14 
 

12 Sulfur Dioxide (Anhydrous) ............................................... 5-15 
 

Vapor Cloud Explosion Distances for Flammable Substances:
 

13 Distance to Overpressure of 1.0 psi for Vapor Cloud Explosions
 

of 500 - 2,000,000 Pounds of Regulated Flammable Substances .................. 5-16 
 

6 Determining Alternative Release Scenarios ........................................... 6-1 
 

7 Estimation of Release Rates for Alternative Scenarios for Toxic Substances ................ 7-1 
 

7.1 Release Rates for Toxic Gases .............................................. 7-1 
 

7.1.1 Unmitigated Releases of Toxic Gases ................................. 7-1 
 

7.1.2 Mitigated Releases of Toxic Gases ................................... 7-4 
 

April 15, 1999 ii 
TABLE OF CONTENTS 

(Continued) 

Chapter	 Page 

7.2	 Release Rates for Toxic Liquids ............................................ 7-6 
 

7.2.1	 Liquid Release Rate and Quantity Released for Unmitigated Releases ........ 7-7 
 

7.2.2	 Liquid Release Rate and Quantity Released for Mitigated Releases ......... 7-10 
 

7.2.3	 Evaporation Rate from Liquid Pool .................................. 7-10 
 

7.2.4	 Common Water Solutions and Oleum ................................ 7-14 
 

8	 Estimation of Distance to the Endpoint for Alternative Scenarios for Toxic Substances ....... 8-1 
 

9	 Estimation of Release Rates for Alternative Scenarios for Flammable Substances ............ 9-1 
 

9.1 	 Flammable Gases ........................................................ 9-1 
 

9.2	 Flammable Liquids ....................................................... 9-2 
 

10	 Estimation of Distance to the Endpoint for Alternative Scenarios for Flammable
 

Substances ................................................................... 10-1 
 

10.1	 Vapor Cloud Fires ...................................................... 10-1 
 

10.2	 Pool Fires ............................................................. 10-5 
 

10.3	 BLEVEs .............................................................. 10-6 
 

10.4	 Vapor Cloud Explosion .................................................. 10-6 
 

Reference Tables of Distances for Alternative Scenarios ............................... 10-9

 Table
 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by
 

Endpoint, D Stability, Wind Speed 3.0 Meters per Second:
 

14 10-Minute Release, Rural Conditions ....................................... 10-9 
 

15 60-Minute Release, Rural Conditions ...................................... 10-10 
 

16 10-Minute Release, Urban Conditions ...................................... 10-11 
 

17 60-Minute Release, Urban Conditions ...................................... 10-12 
 

Dense Gas Distances to Toxic Endpoint, D Stability, Wind Speed 3.0 Meters per Second:
 

18 10-Minute Release, Rural Conditions ...................................... 10-13 
 

19 60-Minute Release, Rural Conditions ...................................... 10-14 
 

20 10-Minute Release, Urban Conditions ...................................... 10-15 
 

21 60-Minute Release, Urban Conditions ...................................... 10-16 
 

April 15, 1999	 iii 
TABLE OF CONTENTS 

(Continued) 

Chapter Page 

 Table
 

Chemical-Specific Distances to Toxic Endpoint, D Stability, Wind Speed 3.0 Meters per
 

Second:
 

22 Anhydrous Ammonia Liquefied Under Pressure .............................. 10-17 
 

23 Non-liquefied Ammonia, Ammonia Liquefied by Refrigeration, or Aqueous
 

Ammonia ............................................................ 10-18 
 

24 Chlorine ............................................................. 10-19 
 

25 Sulfur Dioxide (Anhydrous) .............................................. 10-20 
 

Neutrally Buoyant Plume Distances to Lower Flammability Limit (LFL) for Release Rate
 

Divided by LFL:
 

26 Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second ............... 10-21 
 

27 Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second ............... 10-21 
 

Dense Gas Distances to Lower Flammability Limit:
 

28 Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second ............... 10-22 
 

29 Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second ............... 10-23 
 

BLEVE Distances for Flammable Substances:
 

30 Distance to Radiant Heat Dose at Potential Second Degree Burn Threshold Assuming
 

Exposure for Duration of Fireball from BLEVE .............................. 10-24 
 

11 Estimating Offsite Receptors ..................................................... 11-1 
 

12 Submitting Offsite Consequence Analysis Information for Risk Management Plan .......... 12-1 
 

12.1 RMP Data Required for Worst-Case Scenarios for Toxic Substances .............. 12-1 
 

12.2 RMP Data Required for Alternative Scenarios for Toxic Substances .............. 12-2 
 

12.3 RMP Data Required for Worst-Case Scenarios for Flammable Substances .......... 12-3 
 

12.4 RMP Data Required for Alternative Scenarios for Flammable Substances .......... 12-3 
 

12.5 Submitting RMPs ....................................................... 12-4 
 

12.6 Other Required Documentation ............................................ 12-4 
 

APPENDICES 

Appendix A: References for Consequence Analysis Methods .................................. A-1 
 

Appendix B: Toxic Substances .......................................................... B-1 
 

B.1 Data for Toxic Substances ................................................. B-1 
 

B.2 Mixtures Containing Toxic Liquids ......................................... B-10 
 

April 15, 1999 iv 
TABLE OF CONTENTS 

(Continued) 

APPENDICES Page 

Appendix C: Flammable Substances ...................................................... C-1 
 

C.1 Equation for Estimation of Distance to 1 psi Overpressure for Vapor Cloud 
 

Explosions ............................................................. C-1 
 

C.2 Mixtures of Flammable Substances .......................................... C-1 
 

C.3 Data for Flammable Substances ............................................. C-2 
 

Appendix D: Technical Background ....................................................... D-1 
 

D.1 Worst-Case Release Rate for Gases ......................................... D-1 
 

D.1.1 Unmitigated Release .............................................. D-1 
 

D.1.2 Gaseous Release Inside Building ..................................... D-1 
 

D.2 Worst-Case Release Rate for Liquids ........................................ D-1 
 

D.2.1 Evaporation Rate Equation .......................................... D-1 
 

D.2.2 Factors for Evaporation Rate Estimates ................................ D-2 
 

D.2.3 Common Water Solutions and Oleum ................................. D-4 
 

D.2.4 Releases Inside Buildings ........................................... D-5 
 

D.3 Toxic Endpoints ......................................................... D-7 
 

D.4 Reference Tables for Distances to Toxic and Flammable Endpoints ................ D-8 
 

D.4.1 Neutrally Buoyant Gases ........................................... D-8 
 

D.4.2 Dense Gases ..................................................... D-9 
 

D.4.3 Chemical-Specific Reference Tables ................................. D-10 
 

D.4.4 Choice of Reference Table for Dispersion Distances ..................... D-10 
 

D.4.5 Additional Modeling for Comparison ................................ D-12 
 

D.5 Worst-Case Consequence Analysis for Flammable Substances ................... D-12 
 

D.6 Alternative Scenario Analysis for Gases ..................................... D-13 
 

D.7 Alternative Scenario Analysis for Liquids .................................... D-15 
 

D.7.1 Releases from Holes in Tanks ...................................... D-15 
 

D.7.2 Releases from Pipes .............................................. D-17 
 

D.8 Vapor Cloud Fires ...................................................... D-18 
 

D.9 Pool Fires ............................................................. D-18 
 

D.10 BLEVEs .............................................................. D-21 
 

April 15, 1999 v 
TABLE OF CONTENTS 

(Continued) 

APPENDICES Page 

D.11 Alternative Scenario Analysis for Vapor Cloud Explosions ...................... D-23 
 

Appendix E: Worksheets for Offsite Consequence Analysis .................................... E-1 
 

Worksheet 1. Worst-case Analysis for Toxic Gas ..................................... E-1 
 

Worksheet 2. Worst-case Analysis for Toxic Liquid ................................... E-2 
 

Worksheet 3. Worst-case Analysis for Flammable Substance ............................ E-5 
 

Worksheet 4. Alternative Scenario Analysis for Toxic Gas .............................. E-6 
 

Worksheet 5. Alternative Scenario Analysis for Toxic Liquid ........................... E-9 
 

Worksheet 6. Alternative Scenario Analysis for Flammable Substance ................... E-13 
 

Appendix F: Chemical Accident Prevention Provisions ........................................ F-1 
 

April 15, 1999 vi 
LIST OF EXHIBITS
 

Exhibit Page
 

1 Required Parameters for Modeling ................................................. 1-3 
 

2 Generic Reference Tables of Distances for Worst-case Scenarios ......................... 4-3 
 

3 Chemical-Specific Reference Tables of Distances for Worst-case Scenarios ................ 4-3 
 

4 Generic Reference Tables of Distances for Alternative Scenarios ......................... 8-2 
 

5 Chemical-Specific Reference Tables of Distances for Alternative Scenarios ................. 8-2 
 

6 Reference Tables of Distances for Vapor Cloud Fires as Alternative Scenario for Flammable
 

Substances ................................................................... 10-2 
 

A-1 Selected References for Information on Consequence Analysis Methods ................... A-2 
 

B-1 Data for Toxic Gases ............................................................ B-2 
 

B-2 Data for Toxic Liquids ........................................................... B-4 
 

B-3 Data for Water Solutions of Toxic Substances and for Oleum ............................ B-7 
 

B-4 Temperature Correction Factors for Liquids Evaporating from Pools at Temperatures
 o o o o Between 25 C and 50 C (77 F and 122 F) ......................................... B-8 
 

C-1 Heats of Combustion for Flammable Substances ...................................... C-3 
 

C-2 Data for Flammable Gases ........................................................ C-6 
 

C-3 Data for Flammable Liquids ...................................................... C-9 
 

April 15, 1999 vii 
TABLE OF POTENTIALLY REGULATED ENTITIES
 

This table is not intended to be exhaustive, but rather provides a guide for 

readers regarding entities likely to be regulated under 40 CFR part 68. This 

table lists the types of entities that EPA is now aware could potentially be 

regulated by this rule (see Appendix B of the “General Guidance for Risk 

Management Programs” for a more detailed list of potentially affected NAICS 

codes). Other types of entities not listed in this table could also be affected. To 

determine whether your facility is covered by the risk management program rules 

in part 68, you should carefully examine the applicability criteria discussed in 

Chapter 1 of the General Guidance and in 40 CFR 68.10. If you have questions 

regarding the applicability of this rule to a particular entity, call the 

EPCRA/CAA Hotline at (800) 424-9346 (TDD: (800) 553-7672). 

Category NAICS 

Codes 

SIC 

Codes 

Examples of Potentially Regulated 

Entities 

Chemical 

manufacturers 

325 28 Petrochemicals 

Industrial gas 

Alkalies and chlorine 

Industrial inorganics 

Industrial organics 

Plastics and resins 

Agricultural chemicals 

Soap, cleaning compounds 

Explosives 

Miscellaneous chemical manufacturing 

Petroleum refineries 32411 2911 Petroleum refineries 

Pulp and paper 322 26 Paper mills 

Pulp mills 

Paper products 

Food processors 311 20 Dairy products 

Fruits and vegetables 

Meat products 

Seafood products 

Polyurethane foam 32615 3086 Plastic foam products 

Non-metallic mineral 

products 

327 32 Glass and glass products 

Other non-metallic mineral products 

Metal products 331 

332 

33 

34 

Primary metal manufacturing 

Fabricated metal products 

April 15, 1999 viii 
Category NAICS 

Codes 

SIC 

Codes 

Examples of Potentially Regulated 

Entities 

Machinery 

manufacturing 

333 35 Industrial machinery 

Farm machinery 

Other machinery 

Computer and 

electronic equipment 

334 36 Electronic equipment 

Semiconductors 

Electric equipment 335 36 Lighting 

Appliance manufacturing 

Battery manufacturing 

Transportation 

equipment 

336 37 Motor vehicles and parts 

Aircraft 

Food distributors 4224 

4228 

514 

518 

Frozen and refrigerated foods 

Beer and wines 

Chemical distributors 42269 5169 Chemical wholesalers 

Farm supplies 42291 5191 Agricultural retailers and wholesalers 

Propane dealers 454312 5171 

5984 

Propane retailers and wholesalers 

Warehouses 4931 422 Refrigerated warehouses 

Warehouse storing chemicals 

Water treatment 22131 4941 Drinking water treatment systems 

Wastewater treatment 22132 

56221 

4952 

4933 

Sewerage systems 

Wastewater treatment 

Waste treatment 

Electric utilities 22111 4911 Electric power generation 

Propane users Manufacturing facilities 

Large institutions 

Commercial facilities 

Federal facilities Military installations 

Department of Energy installations 

April 15, 1999 ix 
Roadmap to Offsite Consequence Analysis Guidance by Type of Chemical 

Type of Chemical and Release Scenario Applicable Sections and Ap

Toxic Gas 

Worst-Case Scenario 

1) Define Worst Case Section 2.1 

2) Select Scenario 3) Calculate Release Rates 

Sections 2.2 and 2.3 

Unmitigated Section 3.1.1 Passive Mitigation Section 3.1.2 Refrigerated Section 3.1.3 

4) Find Toxic Endpoint Appendix B (Exhibit B-1) 5) Determine Reference Table and Distance Section 3.1.3, 3.2.3 

Dense or Neutrally Buoyant Plume Chapter 4 and Appendix B (Exhibit B-1Chemical-Specific Tables (ammonia, chlorine, sulfur dioxide) Chapter 4 Urban or Rural Section 2.1 and Chapter 4 Release Duration Section 2.1 

Alternative Scenario 

1) Define Alternative Scenario Chapter 6 2) Select Scenario 3) Calculate Release Rates 

Chapter 6 

Unmitigated (from tanks and pipes) Section 7.1.1 Active or Passive Mitigation Section 7.1.2 

4) Find Toxic Endpoint 5) Determine Reference Table and Distance 

Appendix B (Exhibit B-1) 

Dense or Neutrally Buoyant Plume Chapter 8 and Appendix B (Exhibit B-1Chemical-Specific Tables (ammonia, chlorine, sulfur dioxide) Chapter 8 Urban or Rural Section 2.1 and Chapter 8 Release Duration Section 7.1 

April 15, 1999 x 
Roadmap to Offsite Consequence Analysis Guidance by Type of Chemical (continued

Type of Chemical and Release Scenario Applicable Sections and Ap

Toxic Liquid 

Worst-Case Scenario 

1) Define Worst Case Section 2.1 

2) Select Scenario 3) Calculate Release Rates 

Sections 2.2 and 2.3 

Releases from Pipes Section 3.2.1 Unmitigated Pool Evaporation Section 3.2.2 Passive Mitigation (dikes, buildings) Section 3.2.3 Release at Ambient Temperature Section 3.2.2, 3.2.3 Release at Elevated Temperature Section 3.2.2, 3.2.3 Releases of Mixtures Section 3.2.4 and Appendix B (Section Temperature Corrections for Liquids at 25-50 C o Section 3.2.5 and Appendix B (Exhibit 

Releases of Solutions 

4) Find Toxic Endpoint 

Section 3.3 and Appendix B (Exhibit B-

For Liquids/Mixtures Appendix B (Exhibit B-2) For Solutions 

5) Determine Reference Table and Distance 

Appendix B (Exhibit B-3) 

Dense or Neutrally Buoyant Plume (liquids) Chapter 4 and Appendix B (Exhibit B-2Dense or Neutrally Buoyant Plume (solutions) Chapter 4 and Appendix B (Exhibit B-3Chemical Specific Table (aqueous ammonia) Chapter 4 Urban or Rural Section 2.1 and Chapter 4 Release Duration (liquids) Section 3.2.2 Release Duration (solutions) Chapter 4 

April 15, 1999 xi 
Roadmap to Offsite Consequence Analysis Guidance by Type of Chemical (continued

Type of Chemical and Release Scenario Applicable Sections and Ap

Toxic Liquid 

Alternative Scenario 

1) Define Alternative Scenario Chapter 6 

2) Select Scenario Chapter 6 3) Calculate Release Rates Section 7.2 

Unmitigated (from tanks and pipes) Section 7.2.1 Active or Passive Mitigation Section 7.2.2 Release at Ambient Temperature Section 7.2.3 Release at Elevated Temperature Section 7.2.3 Release of Solution 

4) Find Toxic Endpoint 

Sections 7.2.4 and 3.3 and Appendix B 

For Liquids/Mixtures Appendix B (Exhibit B-2) For Solutions 

5) Determine Reference Table and Distance 

Appendix B (Exhibit B-3) 

Dense or Neutrally Buoyant Plume (liquids/mixtures) Chapter 8 and Appendix B (Exhibit B-2Dense or Neutrally Buoyant Plume (solutions) Chapter 8 and Appendix B (Exhibit B-3Chemical-Specific Table (aqueous ammonia) Chapter 8 Urban or Rural Section 2.1 and Chapter 8 Release Duration (liquids/mixtures) Section 7.2 Release Duration (solutions) Chapter 8 

April 15, 1999 xii 
Roadmap to Offsite Consequence Analysis Guidance by Type of Chemical (continued

Type of Chemical and Release Scenario Applicable Sections and Ap

Flammable Substance 

Worst-Case Scenario 

1) Define Worst Case Sections 5.1 and 2.1 

2) Select Scenario 3) Determine Distance to Overpressure Endpoint 

Sections 5.1, 2.2, and 2.3 

For Pure Flammable Substances Section 5.1 For Flammable Mixtures Section 5.2 

Alternative Scenario 

1) Define Alternative Scenario Chapter 6 

2) Select Scenario 3) For Vapor Cloud Fires 

Chapter 6 

Calculate Release Rates (gases) Section 9.1 and Appendix C (Exhibit C-Calculate Release Rates (liquids) Section 9.2 and Appendix C (Exhibit C-Find Lower Flammability Limit (gases) Appendix C (Exhibit C-2) Find Lower Flammability Limit (liquids) Appendix C (Exhibit C-3) Dense or Neutrally Buoyant (gases) Appendix C (Exhibit C-2) Dense or Neutrally Buoyant (liquids) Appendix C (Exhibit C-3) Urban or Rural Section 10.1 Release Duration Section 10.1 Determine Distance Section 10.1 

4) For Pool Fires Section 10.2 and Appendix C (Exhibit C5) For BLEVEs Section 10.3 6) For Vapor Cloud Explosions Section 10.4 

April 15, 1999 xiii 
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1 INTRODUCTION

1.1 Purpose of this Guidance

This document provides guidance on how to conduct the offsite consequence analyses for

Risk Management Programs required under the Clean Air Act (CAA). Section 112(r)(7) of the CAA

directed the U.S. Environmental Protection Agency (EPA) to issue regulations requiring facilities

with large quantities of very hazardous chemicals to prepare and implement programs to prevent the

accidental release of those chemicals and to mitigate the consequences of any releases that do occur.

EPA issued that rule, “Chemical Accident Prevention Provisions” on June 20, 1996. The rule is

codified at part 68 of Title 40 of the Code of Federal Regulations (CFR). If you handle, manufacture,

use, or store any of the toxic or flammable substances listed in 40 CFR 68.130 above the specified

threshold quantities in a process, you are required to develop and implement a risk management

program under part 68 of 40 CFR. The rule applies to a wide variety of facilities that handle,

manufacture, store, or use toxic substances, including chlorine and ammonia, and highly flammable

substances, such as propane. If you are not sure whether you are subject to the rule, you should

review the rule and Chapters 1 and 2 of EPA’s General Guidance for Risk Management Programs

(40 CFR part 68), available from EPA at www.epa.gov/emergencies/rmp.

If you are subject to the rule, you are required to conduct an offsite consequence analysis to

provide information to the state, local, and federal governments and the public about the potential

consequences of an accidental chemical release. The offsite consequence analysis consists of two

elements:

� A worst­case release scenario, and

� Alternative release scenarios.

To simplify the analysis and ensure comparability, EPA has defined the worst­case scenario

as the release of the largest quantity of a regulated substance from a single vessel or process line

failure that results in the greatest distance to an endpoint. In broad terms, the distance to the endpoint

is the distance a toxic vapor cloud, heat from a fire, or blast waves from an explosion will travel

before dissipating to the point that serious injuries from short­term exposures will no longer occur.

Endpoints for regulated substances are specified in 40 CFR 68.22(a) and Appendix A of part 68 and

are presented in Appendices B and C of this guidance.

Alternative release scenarios are scenarios that are more likely to occur than the worst­case

scenario and that will reach an endpoint offsite, unless no such scenario exists. Within these two

parameters, you have flexibility to choose alternative release scenarios that are appropriate for your

site. The rule, in 40 CFR 68.28 (b)(2), and the General Guidance for Risk Management Programs (40

CFR part 68), Chapter 4, provide examples of alternative release scenarios that you should consider

when conducting the offsite consequence analysis.

March 2009
 

 

 

 

Chapter 1 

Introduction 

RMP*CompTM 

To assist those using this guidance, the National Oceanic and Atmospheric Administration 

(NOAA) and EPA have developed a software program, RMP*CompTM, that performs the 

calculations described in this document. This software can be downloaded from the 

EPA/OEM website at www.epa.gov/emergencies/rmp. 

This guidance document provides a simple methodology for conducting offsite consequence 

analyses. You may use simple equations to estimate release rates and reference tables to determine 

distances to the endpoint of concern. This guidance provides generic reference tables of distances, 

applicable to most of the regulated toxic substances, and chemical-specific tables for ammonia, 

chlorine, and sulfur dioxide. This guidance also provides reference tables of distances for 

consequences of fires and explosions of flammable substances. In some cases, the rule allows users of 

this document to adopt generic assumptions rather than the site-specific data required if another model 

is employed (see Exhibit 1). 

The methodology and reference tables of distances presented here are optional. You are not 

required to use this guidance. You may use publicly available or proprietary air dispersion models to 

do your offsite consequence analysis, subject to certain conditions. If you choose to use models 

instead of this guidance, you should review the rule and Chapter 4 of the General Guidance for Risk 

Management Programs, which outline required conditions for use of models. In selected example 

analyses, this document presents the results of some models to provide a basis for comparison. It also 

indicates certain conditions of a release that may warrant more sophisticated modeling than is 

represented here. However, this guidance does not discuss the procedures to follow when using 

models; if you choose to use models, you should consult the appropriate references or instructions for 

those models. 

This guidance provides distances to endpoints for toxic substances that range from 0.1 miles 

to 25 miles. Other models may not project distances this far (and some may project even longer 

distances). One commonly used model, ALOHA, has an artificial distance cutoff of 6 miles (i.e., any 

scenario which would result in an endpoint distance beyond 6 miles is reported as “greater than 6 

miles”). Although you may use ALOHA if it is appropriate for the substance and scenario, you should 

consider choosing a different model if the scenario would normally result in an endpoint distance 

significantly greater than 6 miles. Otherwise, you should be prepared to explain the difference 

between your results and those in this guidance or other commonly used models. Also, you should be 

aware that the RMP*eSubmit system accepts only numerical entries (i.e., it will not accept a “greater 

than” distance). If you do enter a distance in RMP*eSubmit that is the result of a particular model’s 

maximum distance cutoff (including the maximum distance cutoff in this guidance), you can explain 

this in the executive summary of your RMP. 

March 2009 1 - 2 
Exhibit 1
 

Required Parameters for Modeling (40 CFR 68.22)
 

WORST CASE ALTERNATIVE SCENARIO 

Endpoints (§68.22(a)) 

Endpoints for toxic substances are specified in part 68 Appendix A. Endpoints for toxic substances are specified in part 68 Appendix A. 

For flammable substances, endpoint is overpressure of 1 pound per square 

inch (psi) for vapor cloud explosions. 

For flammable substances, endpoint is: 

�Overpressure of 1 psi for vapor cloud explosions, or 

�Radiant heat level of 5 kilowatts per square meter (kW/m ) for 40 2 

seconds for heat from fires (or equivalent dose), or 

�Lower flammability limit (LFL) as specified in NFPA documents or 

other generally recognized sources. 

Wind speed/stability (§68.22(b)) 

This guidance assumes 1.5 meters per second and F stability. For other 

models, use wind speed of 1.5 meters per second and F stability class 

unless you can demonstrate that local meteorological data applicable to 

the site show a higher minimum wind speed or less stable atmosphere at 

all times during the previous three years. If you can so demonstrate, these 

minimums may be used for site-specific modeling. 

This guidance assumes wind speed of 3 meters per second and D 

stability. For other models, you must use typical meteorological 

conditions for your site. 

Ambient temperature/humidity (§68.22(c)) 

This guidance assumes 25�C (77�F) and 50 percent humidity. For other 

models for toxic substances, you must use the highest daily maximum 

temperature and average humidity for the site during the past three years. 

This guidance assumes 25�C and 50 percent humidity. For other 

models, you may use average temperature/humidity data gathered at the 

site or at a local meteorological station. 

Height of release (§68.22(d)) 

For toxic substances, you must assume a ground level release. This guidance assumes a ground-level release. For other models, release 

height may be determined by the release scenario. 

Surface roughness (§68.22(e)) 

Use urban (obstructed terrain) or rural (flat terrain) topography, as 

appropriate. 

Use urban (obstructed terrain) or rural (flat terrain) topography, as 

appropriate. 

Dense or neutrally buoyant gases (§68.22(f)) 

Tables or models used for dispersion of regulated toxic substances must 

appropriately account for gas density. If you use this guidance, see Tables 

1-4 for neutrally buoyant gases and Tables 5-8 for dense gases, or Tables 

9-12 for specific chemicals. 

Tables or models used for dispersion must appropriately account for gas 

density. If you use this guidance, see Tables 14-1 7 for neutrally 

buoyant gases and Tables 18-21 for dense gases, or Tables 22-25 for 

specific chemicals. 

Temperature of released substance (§68.22(g)) 

You must consider liquids (other than gases liquefied by refrigeration) to 

be released at the highest daily maximum temperature, from data for the 

previous three years, or at process temperature, whichever is higher. 

Assume gases liquefied by refrigeration at atmospheric pressure to be 

released at their boiling points. This guidance provides factors for 

estimation of release rates at 25�C or the boiling point of the released 

substance, and also provides temperature correction factors. 

Substances may be considered to be released at a process or ambient 

temperature that is appropriate for the scenario. This guidance 

provides factors for estimation of release rates at 25 �C or the boiling 

point of the released substance, and also provides temperature 

correction factors. 

April 15, 1999 1 - 3 
Chapter 1 

Introduction 

1.2 This Guidance Compared to Other Models 

Results obtained using the methods in this document are expected to be conservative (i.e., they will 

generally, but not always, overestimate the distance to endpoints). The chemical-specific reference tables in 

this guidance provide less conservative results than the generic reference tables, because the chemical-specific 

tables were derived using more realistic assumptions and considering more factors. 

Complex models that can account for many site-specific factors may give less conservative estimates 

of offsite consequences than the simple methods in this guidance. This is particularly true for alternative 

scenarios, for which EPA has not specified many assumptions. However, complex models may be expensive 

and require considerable expertise to use; this guidance is designed to be simple and straightforward. You 

will need to consider these tradeoffs in deciding how to carry out your required consequence analyses. 

Appendix A provides information on references for some other methods of analysis; these references do not 

include all models that you may use for these analyses. You will find that modeling results will sometimes 

vary considerably from model to model. 

1.3 Number of Scenarios to Analyze 

The number and type of analyses you must perform depend on the “Program” level of each of your 

processes. The rule defines three Program levels. Processes are eligible for Program 1 if, among other 

criteria, there are no public receptors within the distance to the endpoint for the worst-case scenario. Because 

no public receptors would be affected by the worst-case release, no further modeling is required for these 

processes. For processes subject to Program 2 or Program 3, both worst-case release scenarios and 

alternative release scenarios are required. To determine the Program level of your processes, consult 40 CFR 

68.10(b), (c), and (d), or Chapter 2 of EPA’s General Guidance for Risk Management Programs (40 CFR 

part 68). 

Once you have determined the Program level of your processes, you are required to conduct the 

following offsite consequence analyses: 

� One worst-case release scenario for each Program 1 process; 

� One worst-case release scenario to represent all regulated toxic substances in Program 2 and 

Program 3 processes; 

� One worst-case release scenario to represent all regulated flammable substances in Program 

2 and Program 3 processes; 

� One alternative release scenario for each regulated toxic substance in Program 2 and 

Program 3 processes; and 

� One alternative release scenario to represent all regulated flammable substances in Program 

2 and Program 3 processes. 

NOTE: You may need to analyze additional worst-case scenarios if release scenarios for regulated 

flammable or toxic substances from other covered processes at your facility would affect different public 

April 15, 1999 1 - 4 
 

 

 

Chapter 1 

Introduction 

receptors. For example, worst-case release scenarios for storage tanks at opposite ends of your facility 

may potentially reach different areas where people could be affected. In that case, you will have to 

conduct analyses of and report on both releases. 

GUIDANCE FOR INDUSTRY-SPECIFIC RISK MANAGEMENT PROGRAMS 

EPA developed guidance for industry-specific risk management programs for the following industries: 

Ø Propane storage Ø Warehouses 

facilities Ø Ammonia refrigeration 

Ø Chemical distributors Ø Small propane retailers & 

Ø Waste water treatment users 

plants 

Industry-specific guidance is either appended to this guidance or is contained in stand-alone documents 

that you can obtain from EPA's website at www.epa.gov/emergencies/rmp. If an industry-specific 

appendix or guidance document exists for your process(es), you should consider using it because it will 

provide more information that is specific to your process(es), including dispersion modeling and 

prevention program elements. 

1.4 Modeling Issues 

The consequences of an accidental chemical release depend on the conditions of the release 

and the conditions at the site at the time of the release. This guidance provides reference tables of 

distances, based on results of modeling, for estimation of worst-case and alternative scenario 

consequence distances. Worst-case consequence distances obtained using these tables are not intended 

to be precise predictions of the exact distances that might be reached in the event of an actual 

accidental release. For this guidance, worst-case distances are based on modeling results assuming the 

combination of worst-case conditions required by the rule. This combination of conditions occurs 

rarely and is unlikely to persist for very long. To derive the alternative scenario distances, less 

conservative assumptions were used for modeling; these assumptions were chosen to represent more 

likely conditions than the worst-case assumptions. Nevertheless, in an actual accidental release, the 

conditions may be very different. Users of this guidance should remember that the results derived 

from the methods presented here are rough estimates of potential consequence distances. Other 

models may give different results; the same model also may give different results if different 

assumptions about release conditions and/or site conditions are used. 

The reference tables of distances in this guidance provide results to a maximum distance of 

25 miles. EPA recognizes that modeling results at such large distances are highly uncertain. Almost no 

experimental data or data from accidents are available at such large distances to compare to modeling 

results. Most data are reported for distances well under 10 miles. Modeling uncertainties are likely to 

increase as distances increase because conditions (e.g., atmospheric stability, wind speed, surface 

roughness) are not likely to remain constant over large distances. Thus, at large distances (e.g., greater 

than about 6 to 10 miles), the modeling results should be viewed as very coarse estimates of 

consequence distances. EPA believes, 

March 2009 1 - 5 
Chapter 1 

Introduction 

however, that the results, even at large distances, can provide useful information for comparison purposes. 

For example, Local Emergency Planning Committees (LEPCs) and other local agencies can use relative 

differences in distance to aid in establishing chemical accident prevention and preparedness priorities among 

facilities in a community. Since worst-case scenario distances are based on modeling conditions that are 

unlikely to occur, and since modeling of any scenario that results in large distances is very uncertain, EPA 

strongly urges communities and industry not to rely on the results of worst-case modeling or any modeling 

that results in very large toxic endpoint distances in emergency planning and response activities. Results of 

alternative scenario models are apt to provide a more reasonable basis for planning and response. 

1.5 Steps for Performing the Analysis 

This Chapter presents the steps you should follow in using this guidance to carry out an offsite 

consequence analysis. Before carrying out one or more worst-case and/or alternative release analyses, you 

will need to obtain several pieces of information about the regulated substances you have, the area 

surrounding your site, and typical meteorological conditions: 

� Determine whether each regulated substance is toxic or flammable, as indicated in the rule or 

Appendices B and C of this guidance. 

� For the worst-case analysis, determine the quantity of each substance held in the largest 

single vessel or pipe. 

� Collect information about any passive or active (alternative scenarios only) release 

mitigation measures that are in place for each substance. 

� For toxic substances, determine whether the substance is stored as a gas, as a liquid, as a gas 

liquefied by refrigeration, or as a gas liquefied under pressure. For alternative scenarios 

involving a vapor cloud fire, you may also need this information for flammable substances. 

� For toxic liquids, determine the highest daily maximum temperature of the liquid, based on 

data for the previous three years, or process temperature, whichever is higher. 

� For toxic substances, determine whether the substance behaves as a dense or neutrally 

buoyant gas or vapor (see Appendix B, Exhibits B-1 and B-2). For alternative scenarios 

involving a vapor cloud fire, you will also need this information for flammable substances 

(see Appendix C, Exhibits C-2 and C-3). 

� For toxic substances, determine whether the topography (surface roughness) of your site is 

either urban or rural as thse terms are defined by the rule (see 40 CFR 68.22(e)). For 

alternative scenarios involving a vapor cloud fire, you will also need this information for 

flammable substances. 

After you have gathered the above information, you will need to take three steps (except for 

flammable worst-case releases): 

(1) Select a scenario; 

April 15, 1999 1 - 6 
Chapter 1 

Introduction 

(2) Determine the release or volatilization rate; and 

(3) Determine the distance to the endpoint. 

For flammable worst-case scenarios, only steps one and three are needed. Sections 1.5.1 through 1.5.6 

outline the procedures to perform the analyses. In addition to basic procedures, these sections provide 

references to sections of this guidance where you will find detailed instructions on carrying out the applicable 

portion of the analysis. Sections 1.5.1 through 1.5.3 below provide basic steps to analyze worst-case 

scenarios for toxic gases, toxic liquids, and flammable substances. Sections 1.5.4 through 1.5.6 provide 

basic steps for alternative scenario analysis. Appendix E of this document provides worksheets that may help 

you to perform the analyses. 

1.5.1 Worst-Case Analysis for Toxic Gases 

To conduct worst-case analyses for toxic gases, including toxic gases liquefied by pressurization (see 

Appendix E, Worksheet 1, for a worksheet that can be used in carrying out this analysis): 

Step 1: Determine worst-case scenario. Identify the toxic gas, quantity, and worst-case release scenario, as 

defined by the rule (Chapter 2). 

Step 2: Determine release rate. Estimate the release rate for the toxic gas, using the parameters required by 

the rule. This guidance provides methods for estimating the release rate for: 

� Unmitigated releases (Section 3.1.1). 

� Releases with passive mitigation (Section 3.1.2). 

Step 3: Determine distance to endpoint. Estimate the worst-case consequence distance based on the release 

rate and toxic endpoint (defined by the rule) (Chapter 4). This guidance provides reference tables of 

distances (Reference Tables 1-12). Select the appropriate reference table based on the density of the 

released substance, the topography of your site, and the duration of the release (always 10 minutes 

for gas releases). Estimate distance to the endpoint from the appropriate table. 

1.5.2 Worst-Case Analysis for Toxic Liquids 

To conduct worst-case analyses for toxic substances that are liquids at ambient conditions or for 

toxic gases that are liquefied by refrigeration alone (see Appendix E, Worksheet 2, for a worksheet for this 

analysis): 

Step 1: Determine worst-case scenario. Identify the toxic liquid, quantity, and worst-case release scenario, as 

defined by the rule (Chapter 2). To estimate the quantity of liquid released from piping, see Section 

3.2.1. 

Step 2: Determine release rate. Estimate the volatilization rate for the toxic liquid and the duration of the 

release, using the parameters required by the rule. This guidance provides methods for estimating the 

pool evaporation rate for: 

April 15, 1999 1 - 7 
Chapter 1 

Introduction 

� Gases liquefied by refrigeration alone (Sections 3.1.3 and 3.2.3). 

� Unmitigated releases (Section 3.2.2). 

� Releases with passive mitigation (Section 3.2.3). 

� Releases at ambient or elevated temperature (Sections 3.2.2, 3.2.3, and 3.2.5). 

� Releases of mixtures of toxic liquids (Section 3.2.4). 

� Releases of common water solutions of regulated substances and of oleum (Section 3.3). 

Step 3: Determine distance to endpoint. Estimate the worst-case consequence distance based on the release 

rate and toxic endpoint (defined by the rule) (Chapter 4). This guidance provides reference tables of 

distances (Reference Tables 1-12). Select the appropriate reference table based on the density of the 

released substance, the topography of your site, and the duration of the release. Estimate distance to 

the endpoint from the appropriate table. 

1.5.3 Worst-Case Analysis for Flammable Substances 

To conduct worst-case analyses for all regulated flammable substances (i.e., gases and liquids) (see 

Appendix E, Worksheet 3, for a worksheet for this analysis): 

Step 1: Determine worst-case scenario. Identify the appropriate flammable substance, quantity, and worstcase scenario, as defined by the rule (Chapter 2). 

Step 2: Determine distance to endpoint. Estimate the distance to the required overpressure endpoint of 1 psi 

for a vapor cloud explosion of the flammable substance, using the assumptions required by the rule 

(Chapter 5). This guidance provides a reference table of distances (Reference Table 13) for worstcase vapor cloud explosions. Estimate the distance to the endpoint from the quantity released and the 

table. 

1.5.4 Alternative Scenario Analysis for Toxic Gases 

To conduct alternative release scenario analyses for toxic gases, including toxic gases liquefied by 

pressurization (see Appendix E, Worksheet 4, for a worksheet for this analysis): 

Step 1: Select alternative scenario. Choose an appropriate alternative release scenario for the toxic gas. This 

scenario should have the potential for offsite impacts unless no such scenario exists. (Chapter 6). 

Step 2: Determine release rate. Estimate the release rate and duration of the release of the toxic gas, based 

on your scenario and site-specific conditions. This guidance provides methods for: 

� Unmitigated releases (Section 7.1.1). 

� Releases with active or passive mitigation (Section 7.1.2). 

April 15, 1999 1 - 8 
Chapter 1 

Introduction 

Step 3: Determine distance to endpoint. Estimate the alternative scenario distance based on the release rate 

and toxic endpoint (Chapter 8). This guidance provides reference tables of distances (Reference 

Tables 14-25) for alternative scenarios for toxic substances. Select the appropriate reference table 

based on the density of the released substance, the topography of your site, and the duration of the 

release. Estimate distance to the endpoint from the appropriate table. 

1.5.5 Alternative Scenario Analysis for Toxic Liquids 

To conduct alternative release scenario analyses for toxic substances that are liquids at ambient 

conditions or for toxic gases that are liquefied by refrigeration alone (see Appendix E, Worksheet 5, for a 

worksheet for this analysis): 

Step 1: Select alternative scenario. Choose an appropriate alternative release scenario and release quantity 

for the toxic liquid. This scenario should have the potential for offsite impacts (Chapter 6), unless no 

such scenario exists. 

Step 2: Determine release rate. Estimate the release rate and duration of the release of the toxic liquid, based 

on your scenario and site-specific conditions. This guidance provides methods to estimate the liquid 

release rate and quantity of liquid released for: 

� Unmitigated liquid releases (Section 7.2.1). 

� Mitigated liquid releases (Section 7.2.2). 

The released liquid is assumed to form a pool. This guidance provides methods to estimate the pool 

evaporation rate and release duration for: 

� Unmitigated releases (Section 7.2.3). 

� Releases with passive or active mitigation (Section 7.2.3). 

� Releases at ambient or elevated temperature (Sections 7.2.3). 

� Releases of common water solutions of regulated substances and of oleum (Section 7.2.4). 

Step 3: Determine distance to endpoint. Estimate the alternative scenario distance based on the release rate 

and toxic endpoint (Chapter 8). This guidance provides reference tables of distances (Reference 

Tables 14-25) for alternative scenarios for toxic substances. Select the appropriate reference table 

based on the density of the released substance, the topography of your site, and the duration of the 

release. Estimate distance to the endpoint from the appropriate table. 

1.5.6 Alternative Scenario Analysis for Flammable Substances 

To conduct alternative release scenario analyses for all regulated flammable substances (i.e., gases 

and liquids) (see Appendix E, Worksheet 6, for a worksheet for this analysis): 

April 15, 1999 1 - 9 
 

 

 

 

Chapter 1 

Introduction 

Step 1: Select alternative scenario. Identify the flammable substance, and choose the quantity 

and type of event for the alternative scenario consequence analysis (Chapter 6). 

Step 2: Determine release rate. Estimate the release rate to air of the flammable gas or liquid, if 

the scenario involves a vapor cloud fire (Section 9.1 for flammable gases, Section 9.2 for 

flammable liquids). 

Step 3: Determine distance to endpoint. Estimate the distance to the appropriate endpoint 

(defined by the rule). This guidance provides methods for: 

•	 Vapor cloud fires (Section 10.1 and Reference Tables 26-29); select the appropriate 

reference table based on the density of the released substance and the topography of your 

site, and estimate distance to the endpoint from the appropriate table. 

•	 Pool fires (Section 10.2); estimate distance from the equation and chemical-specific 

factors provided. 

•	 BLEVEs (Section 10.3 and Reference Table 30); estimate distance from the quantity of 

flammable substance and the table. 

•	 Vapor cloud explosions (Section 10.4 and Reference Table 13); estimate quantity in the 

cloud from the equation and chemical-specific factors provided, and estimate distance 

from the quantity, the table, and a factor provided for alternative scenarios. 

1.6 Additional Sources of Information 

EPA’s risk management program requirements may be found at 40 CFR part 68. The 

relevant sections were published in the Federal Register on January 31, 1994 (59 FR 4478) and 

June 20, 1996 (61 FR 31667). Final rules amending the list of substances and thresholds were 

published on August 25, 1997 (62 FR 45130) and January 6, 1998 (63 FR 640). A consolidated 

copy of these regulations is available in Appendix F. 

EPA is working with industry and local, state, and federal government agencies to assist 

sources in complying with these requirements. For more information, refer to the General 

Guidance for Risk Management Programs Appendix E (Technical Assistance). Appendices C and 

D of the General Guidance also provide points of contact for EPA and Occupational Safety and 

Health Administration (OSHA) at the state and federal levels for your questions. Your LEPC also 

can be a valuable resource. 

Finally, if you have access to the Internet, EPA has made copies of the rules, fact sheets, 

and other related materials available from EPA’s website at www.epa.gov/emergencies/rmp. Please 

check the site regularly, as additional materials are posted when they become available. If you do 

not have access to the Internet, you can call EPA’s hotline at (800) 424-9346. 

March 2009	 1 - 10 
2 DETERMINING WORST-CASE SCENARIOS 

In Chapter 2 

� 2.1 EPA’s definition of a worst-case scenario. 

� 2.2 How to determine the quantity released. 

� 2.3 How to identify the appropriate worst-case scenario. 

2.1 Definition of Worst-Case Scenario 

A worst-case release is defined as: 

The release of the largest quantity of a regulated substance from a vessel or process line 

failure, and 

�

The release that results in the greatest distance to the endpoint for the regulated toxic or 

flammable substance. 

�

You may take administrative controls into account when determining the largest quantity. 

Administrative controls are written procedures that limit the quantity of a substance that can be stored or 

processed in a vessel or pipe at any one time or, alternatively, procedures that allow the vessel or pipe to 

occasionally store larger than usual quantities (e.g., during shutdown or turnaround). Endpoints for regulated 

substances are specified in the rule (40 CFR 68.22(a), and Appendix A to part 68 for toxic substances). For 

the worst-case analysis, you do not need to consider the possible causes of the worst-case release or the 

probability that such a release might occur; the release is simply assumed to take place. You must assume all 

releases take place at ground level for the worst-case analysis. 

This guidance assumes meteorological conditions for the worst-case scenario of atmospheric stability 

class F (stable atmosphere) and wind speed 1.5 meters per second (3.4 miles per hour). Ambient air o o temperature for this guidance is 25 C (77 F). If you use this guidance, you may assume this ambient 

temperature for the worst case, even if the maximum temperature at your site in the last three years is higher. 

The rule provides two choices for topography, urban and rural. EPA (40 CFR 68.22(e)) has defined 

urban as many obstacles in the immediate area, where obstacles include buildings or trees. Rural, by EPA’s 

definition, means there are no buildings in the immediate area, and the terrain is generally flat and 

unobstructed. Thus, if your site is located in an area with few buildings or other obstructions (e.g., hills, 

trees), you should assume open (rural) conditions. If your site is in an area with many obstructions, even if it 

is in a remote location that would not usually be considered urban, you should assume urban conditions. 

Toxic Gases 

o Toxic gases include all regulated toxic substances that are gases at ambient temperature (25 C, 77 o

F), with the exception of gases liquefied by refrigeration under atmospheric pressure and released into diked 

areas. For the worst-case consequence analysis, you must assume that a gaseous release of the total quantity 

occurs in 10 minutes. You may take passive mitigation measures (e.g., enclosure) into account in the analysis 

of the worst-case scenario. 

April 15, 1999 
Chapter 2 

Determining Worst-Case Scenarios 

Gases liquefied by refrigeration alone and released into diked areas may be modeled as liquids at 

their boiling points and assumed to be released from a pool by evaporation (40 CFR 68.25(c)(2)). Gases 

liquefied by refrigeration alone that would form a pool one centimeter or less in depth upon release must be 

modeled as gases. (Modeling indicates that pools one centimeter or less deep formed by gases liquefied by 

refrigeration would completely evaporate in 10 minutes or less, giving a release rate that is equal to or greater 

than the worst-case release rate for a gaseous release. In this case, therefore, it is appropriate to treat these 

substances as gases for the worst-case analysis.) 

Endpoints for consequence analysis for regulated toxic substances are specified in the rule (40 CFR 

part 68, Appendix A). Exhibit B-1 of Appendix B lists the endpoint for each toxic gas. These endpoints are 

used for air dispersion modeling to estimate the consequence distance. 

Toxic Liquids 

For toxic liquids, you must assume that the total quantity in a vessel is spilled. This guidance 

assumes the spill takes place onto a flat, non-absorbing surface. For toxic liquids carried in pipelines, the 

quantity that might be released from the pipeline is assumed to form a pool. You may take passive mitigation 

systems (e.g., dikes) into account in consequence analysis. The total quantity spilled is assumed to spread 

instantaneously to a depth of one centimeter (0.033 foot or 0.39 inch) in an undiked area or to cover a diked 

area instantaneously. The temperature of the released liquid must be the highest daily maximum temperature 

occurring in the past three years or the temperature of the substance in the vessel, whichever is higher (40 

CFR 68.25(d)(2)). The release rate to air is estimated as the rate of evaporation from the pool. If liquids at 

your site might be spilled onto a surface that could rapidly absorb the spilled liquid (e.g., porous soil), the 

methods presented in this guidance may greatly overestimate the consequences of a release. Consider using 

another method in such a case. 

Exhibit B-2 of Appendix B presents the endpoint for air dispersion modeling for each regulated toxic 

liquid (the endpoints are specified in 40 CFR part 68, Appendix A). 

Flammable Substances 

For all regulated flammable substances, you must assume that the worst-case release results in a 

vapor cloud containing the total quantity of the substance that could be released from a vessel or pipeline. 

For the worst-case consequence analysis, you must assume the vapor cloud detonates. If you use a TNTequivalent method for your analysis, you must assume a 10 percent yield factor. 

The rule specifies the endpoint for the consequence analysis of a vapor cloud explosion of a regulated 

flammable substance as an overpressure of 1 pound per square inch (psi). This endpoint was chosen as the 

threshold for potential serious injuries to people as a result of property damage caused by an explosion (e.g., 

injuries from flying glass from shattered windows or falling debris from damaged houses). (See Appendix D, 

Section D.5 for additional information on this endpoint.) 

April 15, 1999 2 - 2 
Chapter 2 

Determining Worst-Case Scenarios 

Effect of Required Assumptions 

The assumptions required for the worst-case analysis are intended to provide conservative worst-case 

consequence distances, rather than accurate predictions of the potential consequences of a release; that is, in 

most cases your results will overestimate the effects of a release. In certain cases, actual conditions could be 

even more severe than these worst-case assumptions (e.g., very high process temperature, high process 

pressure, or unusual weather conditions, such as temperature inversions); in such cases, your results might 

underestimate the effects. However, the required assumptions generally are expected to give conservative 

results. 

2.2 Determination of Quantity for the Worst-Case Scenario 

EPA has defined a worst-case release as the release of the largest quantity of a regulated substance 

from a vessel or process line failure that results in the greatest distance to a specified endpoint. For 

substances in vessels, you must assume release of the largest amount in a single vessel. For substances in 

pipes, you must assume release of the largest amount in a pipe. The largest quantity should be determined 

taking into account administrative controls rather than absolute capacity of the vessel or pipe. Administrative 

controls are written procedures that limit the quantity of a substance that can be stored or processed in a 

vessel or pipe at any one time, or, alternatively, occasionally allow a vessel or pipe to store larger than usual 

quantities (e.g., during turnaround). 

2.3 Selecting Worst-Case Scenarios 

Under part 68, a worst-case release scenario analysis must be completed for all covered processes, 

regardless of program level. The number of worst-case scenarios you must analyze depends on several 

factors. You need to consider only the hazard (toxicity or flammability) for which a substance is regulated 

(i.e., even if a regulated toxic substance is also flammable, you only need to consider toxicity in your analysis; 

even if a regulated flammable substance is also toxic, you only need to consider flammability). 

For every Program 1 process, you must report the worst-case scenario with the greatest distance to an 

endpoint. If a Program 1 process has more than one regulated substance held above its threshold, you must 

determine which substance produces the greatest distance to its endpoint and report on that substance. If a 

Program 1 process has both regulated toxics and flammables above their thresholds, you still report only the 

one scenario that produces the greatest distance to the endpoint. The process is eligible for Program 1 if there 

are no public receptors within the distance to an endpoint of the worst-case scenario for the process and the 

other Program 1 criteria are met. For Program 2 or Program 3 processes, you must analyze and report on one 

worst-case analysis representing all toxic regulated substances present above the threshold quantity and one 

worst-case analysis representing all flammable regulated substances present above the threshold quantity. 

You may need to submit an additional worst-case analysis if a worst-case release from elsewhere at the source 

would potentially affect public receptors different from those affected by the initial worst-case scenario(s). 

If you have more than one regulated substance in a class, the substance chosen for the consequence 

analysis for each hazard for Program 2 and 3 processes should be the substance that has the potential to cause 

the greatest offsite consequences. Choosing the toxic regulated substance that might lead to the greatest 

offsite consequences may require a screening analysis of the toxic regulated substances on site, because the 

potential consequences are dependent on a number of factors, including quantity, toxicity, and volatility. 

April 15, 1999 2 - 3 
Chapter 2 

Determining Worst-Case Scenarios 

Location (distance to the fenceline) and conditions of processing or storage (e.g., a high temperature process) 

also should be considered. In selecting the worst-case scenario, you may want to consider the following 

points: 

Toxic gases with low toxic endpoints are likely to give the greatest distances to the endpoint 

for a given release quantity; a toxic gas would be a likely choice for the worst-case analysis 

required for Program 2 and 3 processes (processes containing toxic gases are unlikely to be 

eligible for Program 1). 

�

Volatile, highly toxic liquids (i.e., liquids with high ambient vapor pressure and low toxic 

endpoints) also are likely to give large distances to the endpoint (processes containing this 

type of substance are unlikely to be eligible for Program 1). 

�

Toxic liquids with relatively low volatility (low vapor pressure) and low toxicity (large toxic 

endpoint) in ambient temperature processes may give fairly small distances to the endpoint; 

you probably would not choose such substances for the worst-case analysis for Program 2 or 

3 if you have other regulated toxics, but you may want to consider carrying out a worst-case 

analysis to demonstrate potential Program 1 eligibility. 

�

For flammable substances, you must consider the consequences of a vapor cloud explosion in the 

analysis. The severity of the consequences of a vapor cloud explosion depends on the quantity of the released 

substance in the vapor cloud, its heat of combustion, and other factors that are assumed to be the same for all 

flammable substances. In most cases, the analysis probably should be based on the regulated flammable 

substance present in the greatest quantity; however, a substance with a high heat of combustion may have a 

greater potential offsite impact than a larger quantity of a substance with a lower heat of combustion. In 

some cases, a regulated flammable substance that is close to the fenceline might have a greater potential 

offsite impact than a larger quantity farther from the fenceline. 

You are likely to estimate smaller worst-case distances for flammable substances than for similar 

quantities of most toxic substances. Because the distance to the endpoint may be relatively small, you may 

find it worthwhile to carry out a worst-case analysis for each process containing flammable substances to 

demonstrate potential eligibility for Program 1, unless there are public receptors close to the process. 

April 15, 1999 2 - 4 
3 RELEASE RATES FOR TOXIC SUBSTANCES 

In Chapter 3 

�	 3.1 Estimation of worst-case release rates for toxic gases. 

�	 3.2 Estimation of release rates for toxic liquids evaporating from pools. 

�	 3.3 Estimation of release rates for common water solutions of toxic substances 

and for oleum. 

This chapter describes simple methods for estimating release rates for regulated toxic substances for 

the worst-case scenario. Simple release rate equations are provided, and factors to be used in these equations 

are provided (in Appendix B) for each regulated substance. The estimated release rates may be used to 

estimate dispersion distances to the toxic endpoint for regulated toxic gases and liquids, as discussed in 

Chapter 4. 

3.1	 Release Rates for Toxic Gases 

In Section 3.1 

�	 3.1.1 Method to estimate worst-case release rates for unmitigated releases 

(releases directly to the air) of toxic gas. 

�	 3.1.2 Method to estimate worst-case release rates for toxic gas in enclosures 

(passive mitigation). 

�	 3.1.3 Method to estimate worst-case release rates for liquefied refrigerated 

toxic gases in diked areas (as toxic liquid - see Section 3.2.3), including 

consideration of the duration of the release. 

o o Regulated substances that are gases at ambient temperature (25 C, 77 F) should be considered 

gases for consequence analysis, with the exception of gases liquefied by refrigeration at atmospheric pressure. 

Gases liquefied under pressure should be treated as gases. Gases liquefied by refrigeration alone and released 

into diked areas may be treated as liquids at their boiling points if they would form a pool upon release that is 

more than one centimeter (0.033 foot) in depth. Gases liquefied by refrigeration alone that would form a pool 

one centimeter (0.033 foot) or less in depth should be treated as gases. Modeling shows that the evaporation 

rate from such a pool would be equal to or greater than the rate for a toxic gas, which is assumed to be 

released over 10 minutes; therefore, treating liquefied refrigerated gases as gases rather than liquids in such 

cases is reasonable. You may consider passive mitigation for gaseous releases and releases of gases liquefied 

by refrigeration. 

April 15, 1999 
Chapter 3 

Release Rates for Toxic Substances 

3.1.1 Unmitigated Releases of Toxic Gas 

If no passive mitigation system is in place, estimate the release rate for the release over a 10-minute 

period of the largest quantity resulting from a pipe or vessel failure, as required by the rule (40 CFR 

68.25(c)). For a release from a vessel, calculate the release rate as follows: 

QS QR	 � (3-1) 10 

where:	 QR = Release rate (pounds per minute) 

QS = Quantity released (pounds) 

Example 1. Gas Release (Diborane) 

You have a tank containing 2,500 pounds of diborane gas. Assuming the total quantity in the tank is released 

over a 10-minute period, the release rate (QR), from Equation 3-1, is: 

QR = 2,500 pounds/10 minutes = 250 pounds per minute 

3.1.2 Releases of Toxic Gas in Enclosed Space 

If a gas is released in an enclosure such as a building or shed, the release rate to the outside air may 

be lessened considerably. The dynamics of this type of release are complex; however, you may use the 

simplified method presented here to estimate an approximate release rate to the outside air from a release in 

an enclosed space. The mitigation factor (i.e., 55 percent) presented in this method assumes that the release 

occurs in a fully enclosed, non-airtight space that is directly adjacent to the outside air. If you are modeling a 

release in an interior room that is enclosed within a building, a smaller factor (i.e., more mitigation) may be 

appropriate. On the other hand, a larger factor (i.e., less mitigation) should be used for a space that has doors 

or windows that could be open during a release. If any of these special circumstances apply to your site, you 

may want to consider performing site-specific modeling to determine the appropriate amount of passive 

mitigation. In addition, you should not incorporate the passive mitigation effect of building enclosures into 

your modeling if you have reason to believe the enclosure would not withstand the force of the release or if 

the chemical is handled outside the building (e.g., moved from one building to another building). 

For the worst case, assume as before that the largest quantity resulting from a pipe or vessel failure is 

released over a 10-minute period. Determine the unmitigated worst-case scenario release rate of the gas as 

the quantity released divided by 10 (Equation 3-1). The release rate from the building will be approximately 

55 percent of the worst-case scenario release rate (see Appendix D, Section D.1.2 for the derivation of this 

factor). Estimate the mitigated release rate as follows: 

April 15, 1999	 3 - 2 
Chapter 3 

Release Rates for Toxic Substances 

QS QR × 0.55 � (3-2) 10 

where: QR = Release rate (pounds per minute) 

QS = Quantity released (pounds) 

0.55 = Mitigation factor (discussed in Appendix D, Section D.1.2) 

Example 2. Gas Release in Enclosure (Diborane) 

Suppose the diborane gas from Example 1 is released inside a building at the rate of 250 pounds per minute. 

The mitigated release to the outside air from the building would be: 

QR = 250 pounds/minute × 0.55 = 138 pounds per minute 

3.1.3 Releases of Liquefied Refrigerated Toxic Gas in Diked Area 

If you have a toxic gas that is liquefied by refrigeration alone, and it will be released into an area 

where it will be contained by dikes to form a pool more than one centimeter (0.033 foot) in depth, you may 

carry out the worst-case analysis assuming evaporation from a liquid pool at the boiling point of the liquid. If 

your gas liquefied by refrigeration would form a pool one centimeter (0.033 foot) or less in depth, use the 

methods described in Section 3.1.1 or 3.1.2 above for the analysis. For a release in a diked area, first 

compare the diked area to the maximum area of the pool that could be formed. You can use Equation 3-6 in 

Section 3.2.3 to estimate the maximum size of the pool. Density factors (DF), needed for Equation 3-6, for 

toxic gases at their boiling points are listed in Exhibit B-1 of Appendix B. If the pool formed by the released 

liquid would be smaller than the diked area, assume a 10-minute gaseous release, and estimate the release rate 

as described in Section 3.1.1. If the dikes prevent the liquid from spreading out to form a pool of maximum 

size (one centimeter in depth), you may use the method described in Section 3.2.3 for mitigated liquid 

releases to estimate a release rate from a pool at the boiling point of the released substance. Use Equation 3-

8 in Section 3.2.3 for the release rate. The Liquid Factor Boiling (LFB) for each toxic gas, needed to use 

Equation 3-8, is listed in Exhibit B-1 of Appendix B. See the example release rate estimation on the next 

page. 

After you have estimated the release rate, estimate the duration of the vapor release from the pool 

(the time it will take for the pool to evaporate completely) by dividing the total quantity spilled by the release 

rate. You need to know the duration of release to choose the appropriate reference table of distances to 

estimate the consequence distance, as discussed in Section 4. (You do not need to consider the duration of the 

release for chlorine or sulfur dioxide, liquefied by refrigeration alone. Only one reference table of distances is 

provided for worst-case releases of each of these substances, and these tables may be used regardless of the 

release duration. The principal reason for making no distinction between 10-minute and longer releases for 

the chemical-specific tables is that the differences between the two are small relative to the uncertainties that 

have been identified.) 

April 15, 1999 3 - 3 
Chapter 3 

Release Rates for Toxic Substances 

Example 3. Mitigated Release of Gases Liquefied by Refrigeration (Chlorine) 

You have a refrigerated tank containing 50,000 pounds of liquid chlorine at ambient pressure. A diked area 

around the chlorine tank of 275 square feet is sufficient to hold all of the spilled liquid chlorine. Once the o liquid spills into the dike, it is then assumed to evaporate at its boiling point (-29 F). The evaporation rate at 

the boiling point is determined from Equation 3-8. For the calculation, wind speed is assumed to be 1.5 meters 

per second and the wind speed factor is 1.4, LFB for chlorine (from Exhibit B-1) is 0.19, and A is 275 square 

feet. The release rate is: 

QR = 1.4 × 0.19 × 275 = 73 pounds per minute 

The duration of the release does not need to be considered for chlorine. 

3.2 Release Rates for Toxic Liquids 

In Section 3.2 

�	 3.2.1 Method to estimate the quantity of toxic liquid that could be released from 

a broken pipe. 

�	 3.2.2 Method to estimate the release rate of a toxic liquid evaporating from a 

pool with no mitigation (no dikes or enclosures), including: 

o -- Releases at ambient temperature (25 C),
 

-- Releases at elevated temperature, and
 

-- Estimation of the duration of the release.
 

�	 3.2.3 Method to estimate the release rate of a toxic liquid evaporating from a 

pool with passive mitigation, including: 

-- Releases in diked areas, 
 

-- Releases into other types of containment, and 
 

-- Releases into buildings.
 

�	 3.2.4 Estimation of release rates for mixtures containing toxic liquids. 

�	 3.2.5 Method to correct the estimated release rate for liquids released at o o temperatures between 25 C and 50 C.

 For the worst-case analysis, the release rate to air for toxic liquids is assumed to be the rate of 

evaporation from the pool formed by the released liquid. This section provides methods to estimate the 

evaporation rate. Assume the total quantity in a vessel or the maximum quantity from pipes is released into 

the pool. Passive mitigation measures (e.g., dikes) may be considered in determining the area of the pool and 

April 15, 1999	 3 - 4 
Chapter 3 

Release Rates for Toxic Substances 

the release rate. To estimate the consequence distance using this guidance, you must estimate how long it will 

take for the pool to evaporate (the duration of the release), as well as the release rate, as discussed below. 

The rule (40 CFR 68.22(g)) requires you to assume that liquids (other than gases liquefied by 

refrigeration) are released at the highest maximum daily temperature for the previous three years or at process o o temperature, whichever is higher. This chapter provides methods to estimate the release rate at 25 C (77 F) o or at the boiling point, and also provides a method to correct the release rate at 25 C for releases at o o temperatures between 25 C and 50 C. 

The calculation methods provided in this section apply to substances that are liquids under ambient 

conditions or gases liquefied by refrigeration alone that are released to form pools deeper than one centimeter 

(see Section 3.1.3 above). You must treat gases liquefied under other conditions (under pressure or a 

combination of pressure and refrigeration) or gases liquefied by refrigeration alone that would form pools one 

centimeter or less in depth upon release as gas rather than liquid releases (see Sections 3.1.1 and 3.1.2 

above). 

3.2.1 Releases of Toxic Liquids from Pipes 

To consider a liquid release from a broken pipe, estimate the maximum quantity that could be 

released assuming that the pipe is full of liquid. To estimate the quantity in the pipe, you need to know the 

length of the pipe (in feet) and cross-sectional area of the pipe (in square feet). Note also that liquid may be 

released from both directions at a pipe shear (both in the direction of operational flow and the reverse 

direction, depending on the location of the shear). Therefore, the length would be the full length of pipe 

carrying the liquid on the facility grounds. Then, the volume of the liquid in the pipe (in cubic feet) is the 

length of the pipe times the cross-sectional area. The quantity in the pipe (in pounds) is the volume divided 

by the Density Factor (DF) times 0.033. (DF values are listed in Appendix B, Exhibit B-2. Density in 

pounds per cubic foot is equal to 1/(DF times 0.033).) Assume the estimated quantity (in pounds) is released 

into a pool and use the method and equations described below in Section 3.2.2 (unmitigated releases) or 3.2.3 

(releases with passive mitigation) to determine the evaporation rate of the liquid from the pool. 

3.2.2 Unmitigated Releases of Toxic Liquids 

If no passive mitigation measures are in place, the liquid is assumed to form a pool one centimeter 

(0.39 inch or 0.033 foot) deep instantaneously. You may calculate the release rate to air from the pool (the 

evaporation rate) as discussed below for releases at ambient or elevated temperature. 

Ambient Temperature 

If the liquid is always at ambient temperature, find the Liquid Factor Ambient (LFA) and the Density o Factor (DF) in Exhibit B-2 of Appendix B. The LFA and DF apply to liquids at 25 C; if your ambient o o temperature is between 25 C and 50 C, you may use the method described here and then apply a 

Temperature Correction Factor (TCF), as discussed in Section 3.2.5 below, to correct the calculated release o rate. Calculate the release rate of the liquid at 25 C from the following equation: 

QR QS � × 1.4 × LFA × DF (3-3) 

April 15, 1999 3 - 5 
Chapter 3 

Release Rates for Toxic Substances 

where: QR = Release rate (pounds per minute) 

QS = Quantity released (pounds) 

1.4 = Wind speed factor = 1.50.78, where 1.5 meters per second (3.4 miles per 

hour) is the wind speed for the worst case 

LFA = Liquid Factor Ambient 

DF = Density Factor 

Example 4. Unmitigated Liquid Release at Ambient Temperature (Acrylonitrile) 

You have a tank containing 20,000 pounds of acrylonitrile at ambient temperature. The total quantity in the 

tank is spilled onto the ground in an undiked area, forming a pool. Assume the pool spreads out to a depth of 

one centimeter. The release rate from the pool (QR) is calculated from Equation 3-3. For the calculation, the 

wind speed is assumed to be 1.5 meters per second and the wind speed factor is 1.4. From Exhibit B-2, 

Appendix B, LFA for acrylonitrile is 0.018 and DF is 0.61. Then: 

QR = 20,000 × 1.4 × 0.018 × 0.61 = 307 pounds per minute 

The duration of the release (from Equation 3-5) would be: 

t = 20,000 pounds/307 pounds per minute = 65 minutes 

Elevated Temperature 

o If the liquid is at an elevated temperature (above 50 C or at or close to the boiling point), find the 

Liquid Factor Boiling (LFB) and the Density Factor (DF) in Exhibit B-2 of Appendix B (see Appendix D, o Section D.2.2, for the derivation of these factors). For temperatures up to 50 C, you may use the method 

above for ambient temperature and apply the Temperature Correction Factors, as discussed in Section 3.2.5. o If the temperature is above 50 C, or the liquid is at or close to its boiling point, or no Temperature Correction 

Factors are available for your liquid, calculate the release rate of the liquid from the following equation: 

QR QS � × 1.4 × LFB × DF	 (3-4) 

where:	 QR = Release rate (pounds per minute) 

QS = Quantity released (pounds) 

1.4 =	 Wind speed factor = 1.50.78, where 1.5 meters per second (3.4 miles per 

hour) is the wind speed for the worst case
 

LFB = Liquid Factor Boiling
 

DF = Density Factor
 

April 15, 1999	 3 - 6 
Chapter 3 

Release Rates for Toxic Substances 

Example 5. Unmitigated Release at Elevated Temperature (Acrylonitrile) 

You have a tank containing 20,000 pounds of acrylonitrile at an elevated temperature. The total quantity in the 

tank is spilled onto the ground in an undiked area, forming a pool. Assume the pool spreads out to a depth of 

one centimeter. The release rate from the pool is calculated from Equation 3-4. For the calculation, the wind 

speed factor for 1.5 meters per second is 1.4. From Exhibit B-2, Appendix B, LFB for acrylonitrile is 0.11 and 

DF is 0.61. Then: 

QR = 20,000 × 1.4 × 0.11 × 0.61 = 1,880 pounds per minute 

The duration of the release (from Equation 3-5) would be: 

t = 20,000 pounds/1880 pounds per minute = 11 minutes 

Duration of Release 

After you have estimated a release rate as described above, determine the duration of the vapor 

release from the pool (the time it will take for the liquid pool to evaporate completely). If you calculate a o corrected release rate for liquids above 25 C, use the corrected release rate, estimated as discussed in Section 

3.2.5 below, to estimate the release duration. To estimate the time in minutes, divide the total quantity 

released (in pounds) by the release rate (in pounds per minute) as follows: 

QS t � (3-5) QR 

where: t = Duration of the release (minutes) 

QR = Release rate (pounds per minute) (use release rate corrected for 

temperature, QR , if appropriate) C 

QS = Quantity released (pounds) 

You will use the duration of the vapor release from the pool to decide which table is appropriate for 

estimating distance, as discussed in Chapter 4 below. 

3.2.3 Releases of Toxic Liquids with Passive Mitigation 

Diked Areas 

If the toxic liquid will be released into an area where it will be contained by dikes, compare the diked 

area to the maximum area of the pool that could be formed; the smaller of the two areas should be used in 

determination of the evaporation rate. The maximum area of the pool (assuming a depth of one centimeter) 

is: 

April 15, 1999 3 - 7 
Chapter 3 

Release Rates for Toxic Substances 

A � QS × DF	 (3-6) 

where:	 A = Maximum area of pool (square feet) for depth of one centimeter 

QS = Quantity released (pounds) 

DF = Density Factor (listed in Exhibit B-2, Appendix B) 

Maximum Area Smaller than Diked Area. If the maximum area of the pool is smaller than the diked 

area, calculate the release rate as described for "no mitigation" above. 

Diked Area Smaller than Maximum Area. If the diked area is smaller than the maximum pool area, 

go to Exhibit B-2 in Appendix B to find the Liquid Factor Ambient (LFA), if the liquid is at ambient 

temperature, or the Liquid Factor Boiling (LFB), if the liquid is at an elevated temperature. For liquids at o o temperatures between 25 C and 50 C, you may use the method described here and then apply a 

Temperature Correction Factor (TCF), as discussed in Section 3.2.5 below, to correct the calculated release 

rate. For gases liquefied by refrigeration alone, use LFB from Exhibit B-1. Calculate the release rate from 

the diked area as follows for liquids at ambient temperature: 

QR � 1.4 × LFA × A	 (3-7) 

or, for liquids at elevated temperature or for gases liquefied by refrigeration alone: 

QR � 1.4 × LFB × A (3-8) 

where:	 QR = Release rate (pounds per minute) 

1.4 =	 Wind speed factor = 1.50.78, where 1.5 meters per second (3.4 miles per 

hour) is the wind speed for the worst case 

LFA = Liquid Factor Ambient (listed in Exhibit B-2, Appendix B) 

LFB = Liquid Factor Boiling (listed in Exhibit B-1 (for liquefied gases) or B-2 (for 

liquids), Appendix B)
 

A = Diked area (square feet)
 

Potential Overflow of Diked Area. In case of a large liquid spill, you also need to consider whether 

the liquid could overflow the diked area. Follow these steps: 

Determine the volume of the diked area in cubic feet from surface area times depth or length 

times width times depth (in feet). 

�

Determine the volume of liquid spilled in cubic feet from QS × DF × 0.033 (DF × 0.033 is 

equal to 1/density in pounds per cubic foot). 

�

Compare the volume of the diked area to the volume of liquid spilled. If the volume of 

liquid is greater than the volume of the diked area: 

�

-- Subtract the volume of the diked area from the total volume spilled to determine the 

volume that might overflow the diked area. 

April 15, 1999	 3 - 8 
Chapter 3 

Release Rates for Toxic Substances 

-- Estimate the maximum size of the pool formed by the overflowing liquid (in square 

feet) by dividing the overflow volume (in cubic feet) by 0.033 (the depth of the pool 

in feet). 

-- Add the surface area of the diked area and the area of the pool formed by the 

overflow to estimate the total pool area (A). 

-- Estimate the evaporation rate from Equation 3-7 or 3-8 above. 

After you have estimated the release rate, estimate the duration of the vapor release from the pool by 

dividing the total quantity spilled by the release rate (Equation 3-5 above). 

Example 6. Mitigated Liquid Release at Ambient Temperature (Bromine) 

o You have a tank containing 20,000 pounds of bromine at an ambient temperature of 25 C. Assume that the 

total quantity in the tank is spilled into a square diked area 10 feet by 10 feet (area 100 square feet). The dike 

walls are four feet high. The area (A) that would be covered to a depth of 0.033 feet (one centimeter) by the 

spilled liquid is given by Equation 3-6 as the quantity released (QS) times the Density Factor (DF). From 

Exhibit B-2, Appendix B, DF for bromine is 0.16. Then: 

A = 20,000 × 0.16, or 3,200 square feet 

The diked area is smaller than the maximum pool area. The volume of bromine spilled is 20,000 × 0.16 × 

0.033, or 106 cubic feet. The spilled liquid would fill the diked area to a depth of a little more than one foot, 

well below the top of the wall. You use the diked area to determine the evaporation rate from Equation 3-7. 

For the calculation, wind speed is 1.5 meters per second, the wind speed factor is 1.4, LFA for bromine (from 

Exhibit B-2) is 0.073, and A is 100 square feet. The release rate is: 

QR = 1.4 × 0.073 × 100 = 10 pounds per minute 

The maximum duration of the release would be: 

t = 20,000 pounds/10 pounds per minute = 2,000 minutes 

Other Containment 

If the toxic liquid will be contained by other means (e.g., enclosed catch basins or trenches), consider 

the total quantity that could be spilled and estimate the surface area of the released liquid that potentially 

would be exposed to the air. Look at the dimensions of trenches or other areas where spilled liquids would be 

exposed to the air to determine the surface area of pools that could be formed. Use the instructions above to 

estimate a release rate from the total surface area. 

April 15, 1999 3 - 9 
Chapter 3 

Release Rates for Toxic Substances 

Releases into Buildings 

If the toxic liquid is released inside a building, compare the area of the pool that would be formed 

(depending upon floor space or passive mitigation) to the maximum area of the pool that could be formed (if 

the liquid is not contained); the smaller of the two areas should be used in determining the evaporation rate. 

The maximum area of the pool is determined as described above for releases into diked areas, using Equation 

3-6. If the toxic liquid would spread to cover the building floor, you determine the area of the building floor 

as: 

A L � × W	 (3-9) 

where:	 A = Area (square feet) 

L =	 Length (feet) 

W =	 Width (feet) 

If there are obstacles such as dikes inside the building, determine the size of the pool that would be formed 

based on the area defined by the dikes or other obstacles. 

The evaporation rate is then determined for a worst-case scenario (i.e., wind speed is 1.5 meters per 

second (3.4 miles per hour)), using Equation 3-3 or 3-4, if the liquid spreads to its maximum area, or 

Equation 3-7 or 3-8, if the pool area is smaller than the maximum. The maximum rate of evaporated liquid 

exiting the building is taken to be 10 percent of the calculated worst-case scenario evaporation rate (see 

Appendix D, Section D.2.4 for the derivation of this factor), as follows: 

QR � B 0.1 ×	 QR (3-10) 

where:	 QRB = Release rate from building 

QR = Release rate from pool, estimated as discussed above 

0.1 = Mitigation factor, discussed in Appendix D, Section D.2.4 

Note that the mitigation factor (i.e., 0.1) presented in this method assumes that the release occurs in a 

fully enclosed, non-airtight space that is directly adjacent to the outside air. It may not apply to a release in 

an interior room that is enclosed within a building, or to a space that has doors or windows that could be open 

during a release. In such cases, you may want to consider performing site-specific modeling to determine the 

appropriate amount of passive mitigation. 

April 15, 1999	 3 - 10 
Chapter 3 

Release Rates for Toxic Substances 

Example 7. Liquid Release Inside Building (Bromine) 

Suppose that your tank of bromine from Example 6 is contained inside a storage shed 10 feet by 10 feet (area 

100 square feet). There are no dikes inside the shed. From Example 6, you see that the area covered by the 

bromine in an unenclosed space would be 3,200 square feet. The building area is smaller than the maximum 

pool area; therefore, the building floor area should be used to determine the evaporation rate from Equation 3-

7. For the calculation, first determine the worst-case scenario evaporation rate: 

QR = 1.4 × 0.073 × 100 = 10 pounds per minute 

The release rate to the outside air of the evaporated liquid leaving the building would then be: 

QRB = 0.1 × 10 pounds per minute = 1 pound per minute 

3.2.4 Mixtures Containing Toxic Liquids 

Mixtures containing regulated toxic substances do not have to be considered if the concentration of 

the regulated substance in the mixture is below one percent by weight or if you can demonstrate that the 

partial vapor pressure of the regulated substances in the mixture is below 10 millimeters of mercury (mm 

Hg). Regulated substances present as by-products or impurities would need to be considered if they are 

present in concentrations of one percent or greater in quantities above their thresholds, and their partial vapor 

pressures are 10 mm Hg or higher. In case of a spill of a liquid mixture containing a regulated toxic 

substance with partial vapor pressure of 10 mm Hg or higher (with the exception of common water solutions, 

discussed in the next section), you have several options for estimating a release rate: 

Carry out the analysis as described above in Sections 3.2.2 or 3.2.3 using the quantity of the 

regulated substance in the mixture and the liquid factor (LFA or LFB) and density factor for 

the regulated substance in pure form. This is a simple approach that likely will give 

conservative results. 

�

If you know the partial pressure of the regulated substance in the mixture, you may estimate 

a more realistic evaporation rate. An equation for the evaporation rate is given at the end of 

Section B.2 in Appendix B. 

�

-- In this case, estimate a pool size for the entire quantity of the mixture, for an 

unmitigated release. If you know the density of the mixture, you may use it in 

estimating the pool size; otherwise, you may assume the density is the same as the 

pure regulated substance (in most cases, this assumption is unlikely to have a large 

effect on the results). 

You may estimate the partial pressure of the regulated substance in the mixture by the 

method described in Section B.2 in Appendix B and use the equation presented there to 

estimate an evaporation rate. This equation is appropriate to mixtures and solutions in 

�

April 15, 1999	 3 - 11 
Chapter 3 

Release Rates for Toxic Substances 

which the components do not interact with each other. It is probably inappropriate for most 

water solutions. It is likely to overestimate the partial vapor pressure of regulated 

substances in water solutions in which hydrogen bonding may occur (e.g., solutions of acids 

or alcohols). As discussed above, use the pool size for the entire quantity of the mixture for 

an unmitigated release. 

Example 8. Mixture Containing Toxic Liquid (Acrylonitrile) 

You have a tank containing 50,000 pounds of a mixture of acrylonitrile (a regulated substance) and N,Ndimethylformamide (not regulated). The weight of each of the components of the mixture is known 

(acrylonitrile = 20,000 pounds; N,N-dimethylformamide = 30,000 pounds.) The molecular weight of 

acrylonitrile, from Exhibit B-2, is 53.06, and the molecular weight of N,N-dimethylformamide is 73.09. Using 

Equation B-3, Appendix B, calculate the mole fraction of acrylonitrile in the solution as follows: 

Xr

 = (20,000/53.06) 

 (20,000/53.06) + (30,000/73.09)
 

Xr

 = 377
 

 377 + 410 

Xr = 0.48 

Estimate the partial vapor pressure of acrylonitrile using Equation B-4 as follows (using the vapor pressure of 

acrylonitrile in pure form at 25�C, 108 mm Hg, from Exhibit B-2, Appendix B): 

VPm = 0.48 × 108 = 51.8 mm Hg 

Before calculating evaporation rate for acrylonitrile in the mixture, you must determine the surface area of the 

pool formed by the entire quantity of the mixture, using Equation 3-6. The quantity released is 50,000 pounds 

and the Density Factor for acrylonitrile is 0.61 in Exhibit B-2; therefore: 

A = 50,000 × 0.61 = 30,500 square feet 

Now calculate the evaporation rate for acrylonitrile in the mixture from Equation B-5 using the VPm and A 

calculated above: 

QR = 0.0035 × 1.0 × (53.06)� × 30,500 × 51.8 

 298
 

QR = 262 pounds per minute 

3.2.5 Release Rate Correction for Toxic Liquids Released at Temperatures o o Between 25 C and 50 C 

o o o o If your liquid is at a temperature between 25 C (77 F) and 50 C (122 F), you must use the higher 

temperature for the offsite consequence analysis. You may correct the release rate calculated for a pool at 25 

April 15, 1999 3 - 12 
Chapter 3 

Release Rates for Toxic Substances 

o

C to estimate from a pool at the higher temperature using Temperature Correction Factors (TCF) provided in 

Appendix B, Exhibit B-4. Calculate a corrected release rate as follows: 

o o Calculate the release rate (QR) of the liquid at 25 C (77 F) as described in Section 3.2.2 

(for unmitigated releases) or 3.2.3 (for releases with passive mitigation). 

�

� From Exhibit B-4 in Appendix B: 

-- Find your liquid in the left-hand column of the table. 

-- Find the temperature closest to your temperature at the top of the table. If your 

temperature is at the midpoint between two temperatures, go to the higher 

temperature; otherwise go to the closest temperature (higher or lower than your 

temperature). 

-- Find the TCF for your liquid in the column for the appropriate temperature. 

� Estimate a corrected release rate (QR ) by multiplying the estimated release rate by the TCF; C 

i.e., 

QR � C QR × TCF (3-11) 

where: QRC = Corrected release rate o QR = Release rate calculated for 25 C
 

TCF = Temperature Correction Factor (from Exhibit B-4, Appendix B)
 

The derivation of the Temperature Correction Factors is discussed in Appendix D, Section D.2.2. If 

you have vapor pressure-temperature data for a liquid not covered in Exhibit B-4, you may correct the 

evaporation rate using the method presented in Section D.2.2. 

April 15, 1999 3 - 13 
Chapter 3 

Release Rates for Toxic Substances 

o o Example 9. Liquid Release at Ambient Temperature Between 25 C and 50 C (Bromine) 

o Assume the tank containing 20,000 pounds of bromine, from Example 6, is at an ambient temperature of 35 C o (95 F). As in Example 6, the total quantity in the tank is spilled into a diked enclosure that completely contains o the spill. The surface area is 100 square feet. In Example 6, the release rate (QR) at 25 C was calculated from o Equation 3-7 to be 10 pounds per minute. To adjust the release rate for the temperature of 35 C, you find the o Temperature Correction Factor (TCF) for bromine at 35 C from Exhibit B-4 in Appendix B. The TCF at this o temperature is 1.5; the corrected release rate (QR ) at 35 C, from Equation 3-11, is C 

QRC = 10 × 1.5 = 15 pounds per minute 

The duration of the release (from Equation 3-5) would be: 

t = 20,000 pounds/15 pounds per minute = 1,300 minutes 

3.3 Release Rates for Common Water Solutions of Toxic Substances and for 

Oleum 

In Section 3.3 

�	 Methods to estimate the release rates for several common water solutions and 

for oleum, including: 

-- Evaporation from pools with no mitigation (see 3.2.2), 

-- Evaporation from pools with dikes (see 3.2.3), 

-- Releases at elevated temperatures of solutions of gases, and 

-- Releases at elevated temperatures of solutions of liquids. 

This section presents a simple method of estimating the release rate from spills of water solutions of 

several substances. Oleum (a solution of sulfur trioxide in sulfuric acid) also is discussed in this section. 

The vapor pressure and evaporation rate of a substance in solution depends on its concentration in 

the solution. If a concentrated water solution containing a volatile toxic substance is spilled, the toxic 

substance initially will evaporate more quickly than water from the spilled solution, and the vapor pressure 

and evaporation rate will decrease as the concentration of the toxic substance in the solution decreases. At 

much lower concentrations, water may evaporate more quickly than the toxic substance. There is one 

concentration at which the composition of the solution does not change as evaporation occurs. For most 

situations of interest, the concentration exceeds this concentration, and the toxic substance evaporates more 

quickly than water. 

For estimating release rates from solutions, this guidance lists liquid factors (ambient) for several 

common water solutions at several concentrations that take into account the decrease in evaporation rate with 

decreasing concentration. Exhibit B-3 in Appendix B provides LFA and DF values for several concentrations 

April 15, 1999	 3 - 14 
Chapter 3 

Release Rates for Toxic Substances 

of ammonia, formaldehyde, hydrochloric acid, hydrofluoric acid, and nitric acid in water solution. Factors for 

oleum are also included in the exhibit. Chlorine dioxide also may be found in water solutions; however, 

solutions of chlorine dioxide commonly are below one percent concentration. Solutions below one percent 

concentration do not have to be considered. Chlorine dioxide, therefore, is not included in Exhibit B-3. These 

factors may be used to estimate an average release rate for the listed substances from a pool formed by a spill 

of solution. Liquid factors are provided for two different wind speeds, because the wind speed affects the rate 

of evaporation. 

For the worst case, use the factor for a wind speed of 1.5 meters per second (3.4 miles per hour). 

You need to consider only the first 10 minutes of the release for solutions under ambient conditions in 

estimating the consequence distance, because the toxic component in a solution evaporates fastest during the 

first few minutes of a spill, when its concentration is highest. Modeling indicates that analysis considering 

the first 10 minutes of the release gives a good approximation of the overall consequences of the release. 

Although the toxic substance will continue to evaporate from the pool after 10 minutes, the rate of 

evaporation is so much lower that it can safely be ignored in estimating the consequence distance. (See 

Appendix D, Section D.2.3, for more information.) Estimate release rates as follows: 

Ambient Temperature 

Unmitigated. If no passive mitigation measures are in place, and the solution is at ambient 

temperature, find the LFA at 1.5 meters per second (3.4 miles per hour) and DF for the 

solution in Appendix B, Exhibit B-3. Follow the instructions for liquids presented in 

Section 3.2.2 above to estimate the release rate of the listed substance in solution. Use the 

total quantity of the solution as the quantity released (QS) in carrying out the calculation of 

release rate. 

�

Mitigated. If passive mitigation is in place, and the solution is at ambient temperature, find 

the LFA at 1.5 meters per second (3.4 miles per hour) in Appendix B, Exhibit B-3, and 

follow the instructions for liquids in Section 3.2.3 above. Use the total quantity of the 

solution to estimate the maximum pool area for comparison with the diked area. 

�

April 15, 1999 3 - 15 
Chapter 3 

Release Rates for Toxic Substances 

Example 10. Evaporation Rate for Water Solution at Ambient Temperature (Hydrochloric Acid) 

You have a tank containing 50,000 pounds of 37 percent hydrochloric acid solution, at ambient temperature. 

For the worst-case analysis, you assume the entire contents of the tank is released, forming a pool. The release 

occurs in a diked area of 9,000 square feet. 

From Exhibit B-3, Appendix B, the Density Factor (DF) for 37 percent hydrochloric acid is 0.42. From 

Equation 3-6, the maximum area of the pool would be 50,000 times 0.42, or 21,000 square feet. The diked 

area is smaller; therefore, the diked area should be used in the evaporation rate (release rate) calculation, using 

Equation 3-7. 

For the calculation using Equation 3-7, you need the pool area (9,000 square feet) and the Liquid Factor 

Ambient (LFA) for 37 percent hydrochloric acid; you assume a wind speed of 1.5 meters per second, so the 

wind speed factor is 1.4. From Exhibit B-3, Appendix B, the LFA is 0.0085. From Equation 3-7, the release 

rate (QR) of hydrogen chloride from the pool is: 

QR = 1.4 × 9,000 × 0.0085 = 107 pounds per minute 

You do not need to consider the duration of the release, because only the first ten minutes are considered. 

Elevated Temperature 

Known Vapor Pressure. If the solution is at an elevated temperature, the vapor pressure of 

the regulated substance and its release rate from the solution will be much higher. This 

guidance does not include temperature correction factors for evaporation rates of regulated 

substances from solutions. If you know the partial vapor pressure of the toxic substance in 

solution at the relevant temperature, you can carry out the calculation of the release rate 

using the equations in Appendix D, Sections D.2.1 and D.2.2. As for releases of solutions at 

ambient temperature, you only need to consider the first 10 minutes of the release, because 

the evaporation rate of the toxic substance from the solution will decrease rapidly as its 

concentration decreases. 

�

Unknown Vapor Pressure. If you do not know the vapor pressure of the substance in 

solution, as a conservative approach for the worst-case analysis, use the appropriate 

instructions, as follows: 

�

-- Solutions containing substances that are gases under ambient conditions. The 

list of regulated substances includes several substances that, in their pure form, are 

gases under ambient conditions, but that may commonly be found in water 

solutions. These substances include ammonia, formaldehyde, hydrogen chloride, 

and hydrogen fluoride. For a release of a solution of ammonia, formaldehyde, 

hydrochloric acid, or hydrofluoric acid above ambient temperature, if you do not 

have vapor pressure data for the temperature of interest or prefer a simpler method, 

assume the quantity of the pure substance in the solution is released as a gas over 10 

April 15, 1999 3 - 16 
Chapter 3 

Release Rates for Toxic Substances 

minutes, as discussed in Section 3.1 above. You may determine the amount of pure 

substance in the solution from the concentration (e.g., a solution of 37 percent 

hydrochloric acid by weight would contain a quantity of hydrogen chloride equal to 

0.37 times the total weight of the solution). 

Example 11. Evaporation Rate for Gas in Water Solution at Elevated Temperature (Hydrochloric 

Acid) 

You have 50,000 pounds of 37 percent hydrochloric acid solution in a high-temperature process. For the 

worst-case analysis, you assume the entire contents of the process vessel is released. In this case, because the 

solution is at an elevated temperature, you consider the release of gaseous hydrogen chloride from the hot 

solution. 

The solution would contain 50,000 × 0.37 pounds of hydrogen chloride, or 18,500 pounds. You assume the 

entire 18,500 pounds is released over 10 minutes. From Equation 3-1, the release rate is 18,500 divided by 10, 

or 1,850 pounds per minute. 

-- Liquids in solution. If you have vapor pressure data for the liquid in solution 

(including nitric acid in water solution and sulfur trioxide in oleum) at the 

temperature of interest, you may use that data to estimate the release rate, as 

discussed above. You only need to consider the first 10 minutes of the evaporation. 

For a release of nitric acid solution at a temperature above ambient, if you do not 

have vapor pressure data or prefer to use this simpler method, determine the 

quantity of pure nitric acid in the solution from the concentration. Assume the 

quantity of pure nitric acid is released at an elevated temperature and estimate a 

release rate as discussed in Section 3.2 above, using the LFB. For temperatures o o between 25 C and 50 C, you may use the LFA and the temperature correction 

factors for the pure substance, as described in Section 3.2.5. You do not need to 

estimate the duration of the release, because you only consider the first 10 minutes. 

Similarly, for a release of oleum at an elevated temperature, determine the quantity 

of free sulfur trioxide in the oleum from the concentration and assume the sulfur 

trioxide is released at an elevated temperature. Use the LFB or the LFA and 

temperature correction factors for sulfur trioxide to estimate a release rate as 

discussed in Section 3.2. You only need to consider the first 10 minutes of the 

release in your analysis. 

For a spill of liquid in solution into a diked area, you would need to consider the 

total quantity of solution in determining whether the liquid could overflow the diked 

area (see the steps in Section 3.2.3). If you find that the liquid could overflow the 

dikes, you would need to consider both the quantity of pure substance remaining 

inside the diked area and the quantity of pure substance spilled outside the diked 

area in carrying out the release rate analysis as discussed in Section 3.2.3. 

April 15, 1999 3 - 17 
Chapter 3 

Release Rates for Toxic Substances 

Example 12. Evaporation Rate for Liquid in Water Solution at Elevated Temperature (Nitric Acid) 

You have 18,000 pounds of 90 percent nitric acid solution in a high temperature process. The solution would 

contain 18,000 x 0.90 pounds of nitric acid, or 16,200 pounds. You assume 16,200 pounds of pure nitric acid 

is released at an elevated temperature. 

For the calculation using Equation 3-4, you need the quantity released (16,200); the Liquid Factor Boiling 

(LFB) for nitric acid (0.12 from Exhibit B-2); the Density Factor (DF) for nitric acid (0.32 from Exhibit B-2); 

and you assume a wind speed of 1.5 meter per second, so the wind speed factor is 1.4. From Equation 3-4, the 

release rate (QR) of hot nitric acid is: 

QR = 16,200 × 1.4 × 0.12 × 0.32 = 870 pounds per minute 

You do not need to estimate the duration of release, because you only consider the first 10 minutes. 

April 15, 1999 3 - 18 
4 ESTIMATION OF WORST-CASE DISTANCE TO TOXIC 

ENDPOINT 

In Chapter 4 

� Reference tables of distances for worst-case releases, including: 

-- Generic reference tables (Exhibit 2), and 

-- Chemical-specific reference tables (Exhibit 3). 

� Considerations include: 

-- Gas density (neutrally buoyant or dense), 

-- Duration of release (10 minutes or 60 minutes), 

-- Topography (rural or urban). 

This guidance provides reference tables giving worst-case distances for neutrally buoyant gases and 

vapors and for dense gases and vapors for both rural (open) and urban (obstructed) areas. This chapter 

describes these reference tables and gives instructions to help you choose the appropriate table to estimate 

consequence distances for the worst-case analysis. 

Neutrally buoyant gases and vapors have approximately the same density as air, and dense gases and 

vapors are heavier than air. Neutrally buoyant and dense gases are dispersed in different ways when they are 

released; therefore, modeling was carried out to develop separate reference tables. These generic reference 

tables can be used to estimate distances using the specified toxic endpoint for each substance and the 

estimated release rate to air. In addition to the generic tables, chemical-specific reference tables are provided 

for ammonia, chlorine, and sulfur dioxide. These chemical-specific tables were developed based on modeling 

carried out for industry-specific guidance documents. All the tables were developed assuming a wind speed 

of 1.5 meters per second (3.4 miles per hour) and F stability. To use the reference tables, you need the worstcase release rates estimated as described in the previous sections. For liquid pool evaporation, you also need 

the duration of the release. In addition, to use the generic tables, you will need to determine the appropriate 

toxic endpoint and whether the gas or vapor is neutrally buoyant or dense, using the exhibits in Appendix B. 

You may interpolate between entries in the reference tables. 

Generic reference tables are provided for both 10-minute releases and 60-minute releases. You 

should use the tables for 10-minute releases if the duration of your release is 10 minutes or less; use the tables 

for 60-minute releases if the duration of your release is more than 10 minutes. For the worst-case analysis, all 

releases of toxic gases are assumed to last for 10 minutes. You need to consider the estimated duration of the 

release (from Equation 3-5) for evaporation of pools of toxic liquids. For evaporation of water solutions of 

toxic liquids or of oleum, you should always use the tables for 10-minute releases. 

The generic reference tables of distances (Reference Tables 1-8), which should be used for 

substances other than ammonia, chlorine, and sulfur dioxide, are found at the end of Chapter 5. The generic 

tables and the conditions for which each table are applicable are described in Exhibit 2. Chemical-specific 

reference tables of distances (Reference Tables 9-12) follow the generic reference tables at the end of Chapter 

5. Each of these chemical-specific tables includes distances for both rural and urban topography. These 

tables are described in Exhibit 3. 

April 15, 1999 
Chapter 4 

Estimation of Worst-Case Distance to Toxic Endpoint 

Remember that these reference tables provide only rough estimates, not accurate predictions, of the 

distances that might be reached under worst-case conditions. In particular, although the distances in the 

tables are as great as 25 miles, you should bear in mind that the larger distances (more than six to ten miles) 

are very uncertain. 

To use the reference tables of distances, follow these steps: 

For Regulated Toxic Substances Other than Ammonia, Chlorine, and Sulfur Dioxide 

Find the toxic endpoint for the substance in Appendix B (Exhibit B-1 for toxic gases or 

Exhibit B-2 for toxic liquids). 

�

Determine whether the table for neutrally buoyant or dense gases and vapors is appropriate 

from Appendix B (Exhibit B-1 for toxic gases or Exhibit B-2 for toxic liquids). A toxic gas 

that is lighter than air may behave as a dense gas upon release if it is liquefied under 

pressure, because the released gas may be mixed with liquid droplets, or if it is cold. 

Consider the state of the released gas when you decide which table is appropriate. 

�

� Determine whether the table for rural or urban conditions is appropriate. 

-- Use the rural table if your site is in an open area with few obstructions. 

-- Use the urban table if your site is in an urban or obstructed area. The urban tables 

are appropriate if there are many obstructions in the area, even if it is in a remote 

location, not in a city. 

� Determine whether the 10-minute table or the 60-minute table is appropriate. 

-- Always use the 10-minute table for worst-case releases of toxic gases. 

-- Always use the 10-minute table for worst-case releases of common water solutions 

and oleum from evaporating pools, for both ambient and elevated temperatures. 

-- If you estimated the release duration for an evaporating toxic liquid pool to be 10 

minutes or less, use the 10-minute table. 

-- If you estimated the release duration for an evaporating toxic liquid pool to be more 

than 10 minutes, use the 60-minute table. 

April 15, 1999 4 - 2 
Chapter 4 

Estimation of Worst-Case Distance to Toxic Endpoint 

Exhibit 2
 

Generic Reference Tables of Distances for Worst-case Scenarios
 

Applicable Conditions Reference Table 

Number 

Gas or Vapor Density Topography Release Duration 

(minutes) 

Neutrally buoyant Rural 10 1 

60 2 

Urban 10 3 

60 4 

Dense Rural 10 5 

60 6 

Urban 10 7 

60 8 

Exhibit 3
 

Chemical-Specific Reference Tables of Distances for Worst-case Scenarios
 

Substance 

Applicable Conditions 

Table 

Reference 

Gas or Vapor Number 

Density 

Topography Release Duration 

(minutes) 

Anhydrous ammonia 

liquefied under pressure 

Dense Rural, Urban 10 9 

Non-liquefied ammonia, 

ammonia liquefied by 

refrigeration, or aqueous 

ammonia 

Neutrally buoyant Rural, Urban 10 10 

Chlorine Dense Rural, Urban 10 11 

Sulfur dioxide (anhydrous) Dense Rural, Urban 10 12 

April 15, 1999 4 - 3 
Chapter 4 

Estimation of Worst-Case Distance to Toxic Endpoint 

Neutrally Buoyant Gases or Vapors 

If Exhibit B-1 or B-2 indicates the gas or vapor should be considered neutrally buoyant, and 

other factors would not cause the gas or vapor to behave as a dense gas, divide the estimated 

release rate (pounds per minute) by the toxic endpoint (milligrams per liter). 

�

Find the range of release rate/toxic endpoint values that includes your calculated release 

rate/toxic endpoint in the first column of the appropriate table (Reference Table 1, 2, 3, or 

4), then find the corresponding distance to the right (see Example 13 below). 

�

Dense Gases or Vapors 

If Exhibit B-1 or B-2 or consideration of other relevant factors indicates the substance 

should be considered a dense gas or vapor (heavier than air), find the distance in the 

appropriate table (Reference Table 5, 6, 7, or 8) as follows; 

�

-- Find the toxic endpoint closest to that of the substance by reading across the top of 

the table. If the endpoint of the substance is halfway between two values on the 

table, choose the value on the table that is smaller (to the left). Otherwise, choose 

the closest value to the right or the left. 

-- Find the release rate closest to the release rate estimated for the substance at the left 

of the table. If the calculated release rate is halfway between two values on the 

table, choose the release rate that is larger (farther down on the table). Otherwise, 

choose the closest value (up or down on the table). 

-- Read across from the release rate and down from the endpoint to find the distance 

corresponding to the toxic endpoint and release rate for your substance. 

For Ammonia, Chlorine, or Sulfur Dioxide 

Find the appropriate chemical-specific table for your substance (see the descriptions of 

Reference Tables 9-12 in Exhibit 3). 

�

-- If you have ammonia liquefied by refrigeration alone, you may use Reference Table 

10, even if the duration of the release is greater than 10 minutes. 

-- If you have chlorine or sulfur dioxide liquefied by refrigeration alone, you may use 

the chemical-specific reference tables, even if the duration of the release is greater 

than 10 minutes. 

� Determine whether rural or urban topography is applicable to your site. 

-- Use the rural column in the reference table if your site is in an open area with few 

obstructions. 

April 15, 1999 4 - 4 
Chapter 4 

Estimation of Worst-Case Distance to Toxic Endpoint 

-- Use the urban column if your site is in an urban or obstructed area. The urban 

column is appropriate if there are many obstructions in the area, even if it is in a 

remote location, not in a city. 

� Estimate the consequence distance as follows: 

-- In the left-hand column of the table, find the release rate closest to your calculated 

release rate. 

-- Read the corresponding distance from the appropriate column (urban or rural) to the 

right. 

The development of Reference Tables 1-8 is discussed in Appendix D, Sections D.4.1 and D.4.2. 

The development of Reference Tables 9-12 is discussed in industry-specific risk management program 

guidance documents and a backup information document that are cited in Section D.4.3. If you think the 

results of the method presented here overstate the potential consequences of a worst-case release at your site, 

you may choose to use other methods or models that take additional site-specific factors into account. 

Examples 14 and 15 below include the results of modeling using two other models, the Areal 

Locations of Hazardous Atmospheres (ALOHA) and the World Bank Hazards Analysis (WHAZAN) 

systems. These additional results are provided for comparison with the results of the methods presented in 

this guidance. The same modeling parameters were used as in the modeling carried out for development of 

the reference tables of distances. Appendix D, Section D.4.5, provides information on the modeling carried 

out with ALOHA and WHAZAN. 

Example 13. Gas Release (Diborane) 

In Example 1, you estimated a release rate for diborane gas of 250 pounds per minute. From Exhibit B-1, the 

toxic endpoint for diborane is 0.0011 mg/L, and the appropriate reference table for diborane is a neutrally 

buoyant gas table. Your facility and the surrounding area have many buildings, pieces of equipment, and other 

obstructions; therefore, you assume urban conditions. The appropriate reference table is Reference Table 3, for 

a 10-minute release of a neutrally buoyant gas in an urban area. 

The release rate divided by toxic endpoint for this example is 250/0.0011 = 230,000. 

From Reference Table 3, release rate divided by toxic endpoint falls between 221,000 and 264,000, 

corresponding to about 8.1 miles. 

April 15, 1999 4 - 5 
Chapter 4 

Estimation of Worst-Case Distance to Toxic Endpoint 

Example 14. Gas Release (Ethylene Oxide) 

You have a tank containing 10,000 pounds of ethylene oxide, which is a gas under ambient conditions. 

Assuming the total quantity in the tank is released over a 10-minute period, the release rate (QR) from Equation 

3-1 is: 

QR = 10,000 pounds/10 minutes = 1,000 pounds per minute 

From Exhibit B-1, the toxic endpoint for ethylene oxide is 0.09 mg/L, and the appropriate reference table is the 

dense gas table. Your facility is in an open, rural area with few obstructions; therefore, you use the table for 

rural areas. 

Using Reference Table 5 for 10-minute releases of dense gases in rural areas, the toxic endpoint of 0.09 mg/L 

is closer to 0.1 than 0.075 mg/L. For a release rate of 1,000 pounds per minute, the distance to 0.1 mg/L is 3.6 

miles. 

Additional Modeling for Comparison 

The ALOHA model gave a distance of 2.2 miles to the endpoint, using the same assumptions. 

The WHAZAN model gave a distance of 2.7 miles to the endpoint, using the same assumptions and the dense 

cloud dispersion model. 

Example 15. Liquid Evaporation from Pool (Acrylonitrile) 

You estimated an evaporation rate of 307 pounds per minute for acrylonitrile from a pool formed by the release 

of 20,000 pounds into an undiked area (Example 4). You estimated the time for evaporation of the pool as 65 

minutes. From Exhibit B-2, the toxic endpoint for acrylonitrile is 0.076 mg/L, and the appropriate reference 

table for a worst-case release of acrylonitrile is the dense gas table. Your facility is in an urban area. You use 

Reference Table 8 for 60-minute releases of dense gases in urban areas. 

From Reference Table 8, the toxic endpoint closest to 0.076 mg/L is 0.075 mg/L, and the closest release rate to 

307 pounds per minute is 250 pounds per minute. Using these values, the table gives a worst-case 

consequence distance of 2.9 miles. 

Additional Modeling for Comparison 

The ALOHA model gave a distance of 1.3 miles to the endpoint for a release rate of 307 pounds per minute, 

using the same assumptions.

 The WHAZAN model gave a distance of 1.0 mile to the endpoint for a release rate of 307 pounds per minute, 

using the same assumptions and the dense cloud dispersion model. 

April 15, 1999 4 - 6 
5 ESTIMATION OF DISTANCE TO OVERPRESSURE ENDPOINT 

FOR FLAMMABLE SUBSTANCES 

In Chapter 5 

� Methods to estimate the worst-case consequence distances for releases of 

flammable substances. 

-- 5.1 Vapor cloud explosions of flammable substances that are not 

mixed with other substances, and 

-- 5.2 Vapor cloud explosions of flammable substances in mixtures. 

For the worst-case scenario involving a release of flammable gases and volatile flammable liquids, 

you must assume that the total quantity of the flammable substance forms a vapor cloud within the upper and 

lower flammability limits and the cloud detonates. As a conservative worst-case assumption, if you use the 

method presented here, you must assume that 10 percent of the flammable vapor in the cloud participates in 

the explosion. You need to estimate the consequence distance to an overpressure level of 1 pound per square 

inch (psi) from the explosion of the vapor cloud. An overpressure of 1 psi may cause partial demolition of 

houses, which can result in serious injuries to people, and shattering of glass windows, which may cause skin 

laceration from flying glass. 

This chapter presents a simple method for estimating the distance to the endpoint for a vapor cloud 

explosion of a regulated substance. The method presented here for analysis of vapor cloud explosions is 

based on a TNT-equivalent model. Other methods are available for analysis of vapor cloud explosions, 

including methods that consider site-specific conditions. You may use other methods for your worst-case 

analysis if you so choose, provided you assume the total quantity of flammable substance is in the cloud and 

use an endpoint of 1 psi. If you use a TNT-equivalent model, you must assume a yield factor of 10 percent. 

Appendix A includes references to documents and journal articles on vapor cloud explosions that may 

provide useful information on methods of analysis. 

5.1 Flammable Substances Not in Mixtures 

For the worst-case analysis of a regulated flammable substance that is not in a mixture with other 

substances, you may estimate the consequence distance for a given quantity of a regulated flammable 

substance using Reference Table 13. This table provides distances to 1 psi overpressure for vapor cloud 

explosions of quantities from 500 to 2,000,000 pounds. These distances were estimated by a TNTequivalent model, Equation C-1 in Appendix C, Section C.1, using the worst-case assumptions described 

above and data provided in Exhibit C-1, Appendix C. If you prefer, you may calculate your worst-case 

consequence distance for flammable substances from the heat of combustion of the flammable substance and 

Equation C-1 or C-2. 

April 15, 1999 
Chapter 5 

Estimation of Distance to Overpressure Endpoint for Flammable Substances 

Example 16. Vapor Cloud Explosion (Propane) 

You have a tank containing 50,000 pounds of propane. From Reference Table 13, the distance to 1 psi
 

overpressure is 0.3 miles for 50,000 pounds of propane.
 

Alternatively, you can calculate the distance to 1 psi using Equation C-2 from Appendix C:
 

D = 0.0081 × [ 0.1 × 50,000 × (46,333/4,680) ]1/3 

D = 0.3 miles 

5.2 Flammable Mixtures 

If you have more than 10,000 pounds of a mixture of flammable substances that meets the criteria o o o for listing under CAA section 112(r) (flash point below 22.8 C (73 F), boiling point below 37.8 C (100 o

F), National Fire Protection Association (NFPA) flammability hazard rating of 4), you may need to carry out 

a worst-case consequence analysis for the mixture. (If the mixture itself does not meet these criteria, it is not 

covered, and no analysis is required, even if the mixture contains one or more regulated substances.) You 

should carry out the analysis using the total quantity of all regulated flammable substance or substances in the 

mixture. Non-flammable components should not be included. However, if additional (non-regulated) 

flammable substances are present in the mixture, you should include them in the quantity used in the analysis. 

For simplicity, you may carry out the worst-case analysis based on the predominant regulated 

flammable component of the mixture or a major component of the mixture with the highest heat of 

combustion if the whole vapor cloud consists of flammable substances (see Exhibit C-1, Appendix C for data 

on heat of combustion). Estimate the consequence distance from Reference Table 13 for the major 

component with the highest heat of combustion, assuming that the quantity in the cloud is the total quantity 

of the mixture. If you have a mixture in which the heats of combustion of the components do not differ 

significantly (e.g., a mixture of hydrocarbons), this method is likely to give reasonable results. 

Alternatively, you may estimate the heat of combustion of the mixture from the heats of combustion 

of the components of the mixture using the method described in Appendix C, Section C.2, and then use 

Equation C-1 or C-2 in Appendix C to determine the vapor cloud explosion distance. This method may be 

appropriate if you have a mixture that includes components with significantly different heats of combustion 

(e.g., a mixture of hydrogen and hydrocarbons) that make up a significant portion of the mixture. 

Examples 17 and 18 illustrate the two methods of analysis. In Example 17, the heat of combustion 

of the mixture is estimated, and the distance to the endpoint is calculated from Equation C-2. In Example 18, 

the component of the mixture with the highest heat of combustion is assumed to represent the entire mixture, 

and the distance to the endpoint is read from Reference Table 13. For the mixture of two hydrocarbons used 

in the example, the methods give very similar results. 

April 15, 1999 5 - 2 
Chapter 5 

Estimation of Distance to Overpressure Endpoint for Flammable Substances 

Example 17. Estimating Heat of Combustion of Mixture for Vapor Cloud Explosion Analysis 

You have a mixture of 8,000 pounds of ethylene (the reactant) and 2,000 pounds of isobutane (a catalyst 

carrier). To carry out the worst-case analysis, estimate the heat of combustion of the mixture from the heats of 

combustion of the components of the mixture. (Ethylene heat of combustion = 47,145 kilojoules per kilogram; 

isobutane heat of combustion = 45,576). Using Equation C-3, Appendix C: 

HCm = [ (8,000/2.2) × 47,145 ] + [ (2,000/2.2) × 45,576 ] 

 (10,000/2.2) (10,000/2.2) 

HCm = (37,716) + (9,115) 

HCm = 46,831 kilojoules per kilogram 

Now use the calculated heat of combustion for the mixture in Equation C-2 to calculate the distance to 1 psi 

overpressure for vapor cloud explosion. 

D = 0.0081 × [ 0.1 × 10,000 × (46,831/4,680) ]�

D = 0.2 miles 

Example 18. Vapor Cloud Explosion of Flammable Mixture (Ethylene and Isobutane) 

You have 10,000 pounds of a mixture of ethylene (the reactant) and isobutane (a catalyst carrier). To carry out 

the worst-case analysis, assume the quantity in the cloud is the total quantity of the mixture. Use data for 

ethylene because it is the component with the highest heat of combustion. (Ethylene heat of combustion = 

47,145 kilojoules per kilogram; isobutane heat of combustion = 45,576, from Exhibit C-1, Appendix C). From 

Reference Table 13, the distance to 1 psi overpressure is 0.2 miles for 10,000 pounds of ethylene; this distance 

would also apply to the 10,000-pound mixture of ethylene and isobutane. 

April 15, 1999 5 - 3 
Reference Table 1 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint 

10-Minute Release, Rural Conditions, F Stability, Wind Speed 1.5 Meters per Second 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

0 - 4.4 0.1 

4.4 - 37 0.2 

37 - 97 0.3 

97 - 180 0.4 

180 - 340 0.6 

340 - 530 0.8 

530 - 760 1.0 

760 - 1,000 1.2 

1,000 - 1,500 1.4 

1,500 - 1,900 1.6 

1,900 - 2,400 1.8 

2,400 - 2,900 2.0 

2,900 - 3,500 2.2 

3,500 - 4,400 2.4 

4,400 - 5,100 2.6 

5,100 - 5,900 2.8 

5,900 - 6,800 3.0 

6,800 - 7,700 3.2 

7,700 - 9,000 3.4 

9,000 - 10,000 3.6 

10,000 - 11,000 3.8 

11,000 - 12,000 4.0 

12,000 - 14,000 4.2 

14,000 - 15,000 4.4 

15,000 - 16,000 4.6 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

16,000 - 18,000 4.8 

18,000 - 19,000 5.0 

19,000 - 21,000 5.2 

21,000 - 23,000 5.4 

23,000 - 24,000 5.6 

24,000 - 26,000 5.8 

26,000 - 28,000 6.0 

28,000 - 29,600 6.2 

29,600 - 35,600 6.8 

35,600 - 42,000 7.5 

42,000 - 48,800 8.1 

48,800 - 56,000 8.7 

56,000 - 63,600 9.3 

63,600 - 71,500 9.9 

71,500 - 88,500 11 

88,500 - 107,000 12 

107,000 - 126,000 14 

126,000 - 147,000 15 

147,000 - 169,000 16 

169,000 - 191,000 17 

191,000 - 215,000 19 

215,000 - 279,000 22 

279,000 - 347,000 25 

>347,000 >25* 

 *Report distance as 25 miles 

April 15, 1999 5 - 4 
Reference Table 2 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint 

60-Minute Release, Rural Conditions, F Stability, Wind Speed 1.5 Meters per Second 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

0 - 5.5 0.1 

5.5 - 46 0.2 

46 - 120 0.3 

120 - 220 0.4 

220 - 420 0.6 

420 - 650 0.8 

650 - 910 1.0 

910 - 1,200 1.2 

1,200 - 1,600 1.4 

1,600 - 1,900 1.6 

1,900 - 2,300 1.8 

2,300 - 2,600 2.0 

2,600 - 2,900 2.2 

2,900 - 3,400 2.4 

3,400 - 3,700 2.6 

3,700 - 4,100 2.8 

4,100 - 4,400 3.0 

4,400 - 4,800 3.2 

4,800 - 5,200 3.4 

5,200 - 5,600 3.6 

5,600 - 5,900 3.8 

5,900 - 6,200 4.0 

6,200 - 6,700 4.2 

6,700 - 7,000 4.4 

7,000 - 7,400 4.6 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

7,400 - 7,700 4.8 

7,700 - 8,100 5.0 

8,100 - 8,500 5.2 

8,500 - 8,900 5.4 

8,900 - 9,200 5.6 

9,200 - 9,600 5.8 

9,600 - 10,000 6.0 

10,000 - 10,400 6.2 

10,400 - 11,700 6.8 

11,700 - 13,100 7.5 

13,100 - 14,500 8.1 

14,500 - 15,900 8.7 

15,900 - 17,500 9.3 

17,500 - 19,100 9.9 

19,100 - 22,600 11 

22,600 - 26,300 12 

26,300 - 30,300 14 

30,300 - 34,500 15 

34,500 - 38,900 16 

38,900 - 43,600 17 

43,600 - 48,400 19 

48,400 - 61,500 22 

61,500 - 75,600 25 

>75,600 >25* 

 *Report distance as 25 miles 

April 15, 1999 5 - 5 
Reference Table 3 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint 

10-minute Release, Urban Conditions, F Stability, Wind Speed 1.5 Meters per Second 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

0 - 21 0.1 

21 - 170 0.2 

170 - 420 0.3 

420 - 760 0.4 

760 - 1,400 0.6 

1,400 - 2,100 0.8 

2,100 - 3,100 1.0 

3,100 - 4,200 1.2 

4,200 - 6,100 1.4 

6,100 - 7,800 1.6 

7,800 - 9,700 1.8 

9,700 - 12,000 2.0 

12,000 - 14,000 2.2 

14,000 - 18,000 2.4 

18,000 - 22,000 2.6 

22,000 - 25,000 2.8 

25,000 - 29,000 3.0 

29,000 - 33,000 3.2 

33,000 - 39,000 3.4 

39,000 - 44,000 3.6 

44,000 - 49,000 3.8 

49,000 - 55,000 4.0 

55,000 - 63,000 4.2 

63,000 - 69,000 4.4 

69,000 - 76,000 4.6 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

76,000 - 83,000 4.8 

83,000 - 90,000 5.0 

90,000 - 100,000 5.2 

100,000 - 110,000 5.4 

110,000 - 120,000 5.6 

120,000 - 130,000 5.8 

130,000 - 140,000 6.0 

140,000 - 148,000 6.2 

148,000 - 183,000 6.8 

183,000 - 221,000 7.5 

221,000 - 264,000 8.1 

264,000 - 310,000 8.7 

310,000 - 361,000 9.3 

361,000 - 415,000 9.9 

415,000 - 535,000 11 

535,000 - 671,000 12 

671,000 - 822,000 14 

822,000 - 990,000 15 

990,000 - 1,170,000 16 

1,170,000 - 1,370,000 17 

1,370,000 - 1,590,000 19 

1,590,000 - 2,190,000 22 

2,190,000 - 2,890,000 25 

>2,890,000 >25* 

 *Report distance as 25 miles 

April 15, 1999 5 - 6 
Reference Table 4 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint 

60-Minute Release, Urban Conditions, F Stability, Wind Speed 1.5 Meters per Second 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

0 - 26 0.1 

26 - 210 0.2 

210 - 530 0.3 

530 - 940 0.4 

940 - 1,700 0.6 

1,700 - 2,600 0.8 

2,600 - 3,700 1.0 

3,700 - 4,800 1.2 

4,800 - 6,400 1.4 

6,400 - 7,700 1.6 

7,700 - 9,100 1.8 

9,100 - 11,000 2.0 

11,000 - 12,000 2.2 

12,000 - 14,000 2.4 

14,000 - 16,000 2.6 

16,000 - 17,000 2.8 

17,000 - 19,000 3.0 

19,000 - 21,000 3.2 

21,000 - 23,000 3.4 

23,000 - 24,000 3.6 

24,000 - 26,000 3.8 

26,000 - 28,000 4.0 

28,000 - 30,000 4.2 

30,000 - 32,000 4.4 

32,000 - 34,000 4.6 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

34,000 - 36,000 4.8 

36,000 - 38,000 5.0 

38,000 - 41,000 5.2 

41,000 - 43,000 5.4 

43,000 - 45,000 5.6 

45,000 - 47,000 5.8 

47,000 - 50,000 6.0 

50,000 - 52,200 6.2 

52,200 - 60,200 6.8 

60,200 - 68,900 7.5 

68,900 - 78,300 8.1 

78,300 - 88,400 8.7 

88,400 - 99,300 9.3 

99,300 - 111,000 9.9 

111,000 - 137,000 11 

137,000 - 165,000 12 

165,000 - 197,000 14 

197,000 - 232,000 15 

232,000 - 271,000 16 

271,000 - 312,000 17 

312,000 - 357,000 19 

357,000 - 483,000 22 

483,000 - 629,000 25 

>629,000 >25* 

 *Report distance as 25 miles 

April 15, 1999 5 - 7 
Reference Table 5

Dense Gas Distances to Toxic Endpoint

10-minute Release, Rural Conditions, F Stability, Wind Speed 1.5 Meters per Second

Release 

Rate 

Toxic Endpoint (mg/L) 

0.0004 0.0007 0.001 0.002 0.0035 0.005 0.0075 0.01 0.02 0.035 0.05 0.075 0.1 

(lbs/min) Distance (Miles) 

1 2.2 1.7 1.5 1.1 0.8 0.7 0.5 0.5 0.3 0.2 0.2 0.2 0.1 

2 3.0 2.4 2.1 1.5 1.1 0.9 0.7 0.7 0.4 0.3 0.3 0.2 0.2 

5 4.8 3.7 3.0 2.2 1.7 1.5 1.2 1.0 0.7 0.5 0.4 0.3 0.3 

10 6.8 5.0 4.2 3.0 2.4 2.1 1.7 1.4 1.0 0.7 0.6 0.5 0.4 

30 11 8.7 6.8 5.2 3.9 3.4 2.8 2.4 1.7 1.3 1.1 0.9 0.7 50 14 11 9.3 6.8 5.0 4.2 3.5 3.0 2.2 1.7 1.4 1.1 0.9 

100 19 15 12 8.7 6.8 5.8 4.8 4.2 2.9 2.2 1.9 1.6 1.3 

150 24 18 15 11 8.1 6.8 5.7 5.0 3.6 2.7 2.3 1.9 1.6 250 >25 22 19 14 11 8.7 7.4 6.2 4.5 3.4 2.8 2.3 2.0 500 * >25 >25 19 14 12 9.9 8.7 6.2 4.7 3.8 3.1 2.7 

750 * * * 23 17 15 12 11 7.4 5.5 4.5 3.7 3.2 

1,000 * * * >25 20 17 14 12 8.1 6.2 5.2 4.2 3.6 

1,500 * * * * 24 20 16 14 9.9 7.4 6.2 5.0 4.3 

2,000 * * * * >25 23 19 16 11 8.7 6.8 5.6 4.8 

2,500 * * * * * >25 20 18 12 9.3 8.1 6.2 5.3 

3,000 * * * * * * 23 20 14 9.9 8.7 6.8 5.6 

4,000 * * * * * * >25 22 16 11 9.3 7.4 6.2 

5,000 * * * * * * * 25 17 13 11 8.7 6.8 

7,500 * * * * * * * >25 20 15 12 9.9 8.7 

10,000 * * * * * * * * 24 17 14 11 9.3 15,000 * * * * * * * * >25 20 17 13 11 20,000 * * * * * * * * * 23 19 15 12 

50,000 * * * * * * * * * >25 >25 21 18 

75,000 * * * * * * * * * * * >25 21 

100,000 * * * * * * * * * * * * 24 

150,000 * * * * * * * * * * * * >25 

200,000 * * * * * * * * * * * * * 

* > 25 miles (report distance as 25 miles) # <0.1 mile (

5 - 8 
Reference Table 6

Dense Gas Distances to Toxic Endpoint

60-minute Release, Rural Conditions, F Stability, Wind Speed 1.5 Meters per Second

Release 

Rate 

Toxic Endpoint (mg/L) 

0.0004 0.0007 0.001 0.002 0.0035 0.005 0.0075 0.01 0.02 0.035 0.05 0.075 0.1 

(lbs/min) Distance (Miles) 

1 3.7 2.7 2.2 1.4 1.0 0.8 0.6 0.5 0.3 0.2 0.2 0.1 0.1 

2 5.3 4.0 3.2 2.2 1.6 1.2 1.0 0.8 0.5 0.4 0.3 0.2 0.2 

5 8.7 6.8 5.3 3.7 2.7 2.2 1.7 1.4 0.9 0.6 0.5 0.4 0.3 

10 12 9.3 8.1 5.3 4.0 3.3 2.7 2.2 1.4 1.0 0.8 0.6 0.5 30 22 16 14 9.9 7.4 6.1 4.9 4.1 2.9 2.1 1.6 1.2 1.0 50 >25 21 18 12 9.3 8.1 6.2 5.4 3.8 2.7 2.2 1.7 1.4 

100 * >25 >25 18 13 11 9.3 7.4 5.5 4.0 3.2 2.5 2.1 

150 * * * 22 17 14 11 9.9 6.8 4.9 4.0 3.1 2.7 250 * * * >25 22 18 14 12 8.7 6.2 5.2 4.1 3.5 500 * * * * >25 25 20 17 12 9.3 7.4 5.8 5.0 750 * * * * * >25 25 22 15 11 9.3 7.4 6.1 

1,000 * * * * * * >25 25 17 12 11 8.1 6.8 

1,500 * * * * * * * >25 20 16 12 9.9 8.7 

2,000 * * * * * * * * 24 17 14 11 9.9 

2,500 * * * * * * * * >25 20 16 13 11 

3,000 * * * * * * * * * 21 17 14 12 

4,000 * * * * * * * * * 24 20 16 14 

5,000 * * * * * * * * * >25 22 17 15 

7,500 * * * * * * * * * * >25 21 18 

10,000 * * * * * * * * * * * 24 20 15,000 * * * * * * * * * * * >25 24 20,000 * * * * * * * * * * * * >25 50,000 * * * * * * * * * * * * * 

75,000 * * * * * * * * * * * * * 

100,000 * * * * * * * * * * * * * 150,000 * * * * * * * * * * * * * 200,000 * * * * * * * * * * * * * 

* > 25 miles (report distance as 25 miles) # <0.1 mile (

5 - 9 
Reference Table 7

Dense Gas Distances to Toxic Endpoint

10-minute Release, Urban Conditions, F Stability, Wind Speed 1.5 Meters per Second

Release 

Rate 

Toxic Endpoint (mg/L) 

0.0004 0.0007 0.001 0.002 0.0035 0.005 0.0075 0.01 0.02 0.035 0.05 0.075 0.1 

(lbs/min) Distance (Miles) 

1 1.6 1.2 1.1 0.7 0.6 0.4 0.4 0.3 0.2 0.2 0.1 0.1 0.1 

2 2.2 1.7 1.4 1.1 0.8 0.6 0.5 0.4 0.3 0.2 0.2 0.1 0.1 

5 3.5 2.7 2.2 1.6 1.2 1.0 0.8 0.7 0.5 0.4 0.3 0.2 0.2 

10 4.9 3.8 3.1 2.2 1.7 1.4 1.2 1.0 0.7 0.5 0.4 0.3 0.2 

30 8.1 6.2 5.3 3.7 2.9 2.4 2.0 1.7 1.2 0.9 0.7 0.6 0.4 

50 11 8.1 6.8 4.8 3.7 3.1 2.5 2.1 1.5 1.1 0.9 0.7 0.6 

100 15 11 9.3 6.8 5.2 4.2 3.5 3.0 2.1 1.6 1.3 1.0 0.9 

150 19 14 12 8.1 6.1 5.2 4.3 3.6 2.5 1.9 1.6 1.2 1.1 250 24 18 15 11 8.1 6.8 5.4 4.6 3.3 2.4 2.0 1.6 1.4 500 >25 >25 21 15 11 9.3 7.4 6.2 4.5 3.4 2.8 2.2 1.9 750 * * >25 18 14 11 9.3 8.1 5.5 4.1 3.3 2.6 2.2 

1,000 * * * 21 16 13 11 9.3 6.2 4.6 3.8 3.0 2.5 1,500 * * * >25 19 16 12 11 7.4 5.6 4.6 3.7 3.0 

2,000 * * * * 22 18 15 12 8.7 6.2 5.2 4.1 3.5 

2,500 * * * * 24 20 16 14 9.9 6.8 5.8 4.7 3.8 

3,000 * * * * >25 22 18 16 11 7.4 6.2 5.0 4.2 

4,000 * * * * * 25 20 17 12 8.7 6.8 5.6 4.8 

5,000 * * * * * >25 23 20 14 9.9 8.1 6.2 5.3 

7,500 * * * * * * >25 24 16 12 9.9 7.4 6.2 

10,000 * * * * * * * >25 19 14 11 8.7 7.4 15,000 * * * * * * * * 22 16 13 11 8.7 20,000 * * * * * * * * >25 19 15 12 9.9 50,000 * * * * * * * * * >25 23 17 15 

75,000 * * * * * * * * * * >25 21 17 

100,000 * * * * * * * * * * * 24 20 

150,000 * * * * * * * * * * * >25 23 

200,000 * * * * * * * * * * * * >25 

* > 25 miles (report distance as 25 miles) # <0.1 mile (

5 - 10 
Reference Table 8

Dense Gas Distances to Toxic Endpoint

60-minute Release, Urban Conditions, F Stability, Wind Speed 1.5 Meters per Second

Release 

Rate 

Toxic Endpoint (mg/L) 

0.0004 0.0007 0.001 0.002 0.0035 0.005 0.0075 0.01 0.02 0.035 0.05 0.075 0.1 

(lbs/min) Distance (Miles) 

1 2.6 1.9 1.5 1.1 0.7 0.6 0.4 0.4 0.2 0.2 0.1 0.1 0.1 

2 3.8 2.9 2.3 1.5 1.1 0.9 0.7 0.6 0.4 0.2 0.2 0.1 0.1 

5 6.2 4.7 3.9 2.6 1.9 1.5 1.2 0.9 0.6 0.4 0.3 0.2 0.2 

10 9.3 6.8 5.6 3.9 2.9 2.3 1.8 1.5 0.9 0.7 0.5 0.4 0.3 

30 16 12 9.9 7.4 5.3 4.3 3.4 2.9 1.9 1.3 1.0 0.7 0.6 50 22 16 14 9.3 6.8 5.7 4.5 3.8 2.6 1.8 1.4 1.1 0.9 

100 >25 24 20 14 9.9 8.1 6.8 5.7 3.8 2.7 2.2 1.7 1.4 

150 * >25 24 17 12 11 8.1 6.8 4.8 3.5 2.8 2.2 1.8 250 * * >25 22 16 14 11 9.3 6.2 4.5 3.7 2.9 2.4 500 * * * >25 24 19 16 13 9.3 6.8 5.4 4.2 3.5 750 * * * * >25 24 19 16 11 8.1 6.8 5.2 4.3 

1,000 * * * * * >25 22 19 13 9.3 7.4 6.0 5.0 

1,500 * * * * * * >25 24 16 12 9.3 7.4 6.2 

2,000 * * * * * * * >25 19 13 11 8.7 7.4 

2,500 * * * * * * * * 20 15 12 9.3 8.1 

3,000 * * * * * * * * 22 16 13 11 8.7 

4,000 * * * * * * * * >25 19 16 12 9.9 

5,000 * * * * * * * * * 21 17 14 11 

7,500 * * * * * * * * * >25 20 16 14 

10,000 * * * * * * * * * * 24 19 16 15,000 * * * * * * * * * * >25 22 19 20,000 * * * * * * * * * * * >25 21 50,000 * * * * * * * * * * * * >25 

75,000 * * * * * * * * * * * * * 

100,000 * * * * * * * * * * * * * 150,000 * * * * * * * * * * * * * 200,000 * * * * * * * * * * * * * 

* > 25 miles (report distance as 25 miles) # <0.1 mile (

5 - 11 
Reference Table 9
 

Distances to Toxic Endpoint for Anhydrous Ammonia Liquefied Under Pressure
 

F Stability, Wind Speed 1.5 Meters per Second
 

Release Rate Distance to Endpoint (miles) 

(lbs/min) 

Rural Urban 

1 0.1 <0.1* 

2 0.1 0.1 

5 0.1 0.1 

10 0.2 0.1 

15 0.2 0.2 

20 0.3 0.2 

30 0.3 0.2 

40 0.4 0.3 

50 0.4 0.3 

60 0.5 0.3 

70 0.5 0.3 

80 0.5 0.4 

90 0.6 0.4 

100 0.6 0.4 

150 0.7 0.5 

200 0.8 0.6 

250 0.9 0.6 

300 1.0 0.7 

400 1.2 0.8 

500 1.3 0.9 

600 1.4 0.9 

700 1.5 1.0 

750 1.6 1.0 

800 1.6 1.1 

900 1.7 1.2 

Release Rate Distance to Endpoint (miles) 

(lbs/min) 

Rural Urban 

1,000 1.8 1.2 

1,500 2.2 1.5 

2,000 2.6 1.7 

2,500 2.9 1.9 

3,000 3.1 2.0 

4,000 3.6 2.3 

5,000 4.0 2.6 

6,000 4.4 2.8 

7,000 4.7 3.1 

7,500 4.9 3.2 

8,000 5.1 3.3 

9,000 5.4 3.4 

10,000 5.6 3.6 

15,000 6.9 4.4 

20,000 8.0 5.0 

25,000 8.9 5.6 

30,000 9.7 6.1 

40,000 11 7.0 

50,000 12 7.8 

75,000 15 9.5 

100,000 18 10 

150,000 22 13 

200,000 ** 15 

250,000 ** 17 

750,000 ** ** 

*Report distance as 0.1 mile ** More than 25 miles (report distance as 25 miles) 

April 15, 1999 5 - 12 
Reference Table 10

 Distances to Toxic Endpoint for Non-liquefied Ammonia, Ammonia Liquefied by Refrigeration, or 

Aqueous Ammonia
 

F Stability, Wind Speed 1.5 Meters per Second
 

Release Rate Distance to Endpoint (miles) 

(lbs/min) 

Rural Urban 

1 0.1 

<0.1* 

2 0.1 

5 0.1 

10 0.2 0.1 

15 0.2 0.1 

20 0.3 0.1 

30 0.3 0.1 

40 0.4 0.1 

50 0.4 0.1 

60 0.4 0.2 

70 0.5 0.2 

80 0.5 0.2 

90 0.5 0.2 

100 0.6 0.2 

150 0.7 0.2 

200 0.8 0.3 

250 0.8 0.3 

300 0.9 0.3 

400 1.1 0.4 

500 1.2 0.4 

600 1.3 0.4 

700 1.4 0.5 

750 1.4 0.5 

800 1.5 0.5 

900 1.5 0.6 

Release Rate Distance to Endpoint (miles) 

(lbs/min) 

Rural Urban 

1,000 1.6 0.6 

1,500 2.0 0.7 

2,000 2.2 0.8 

2,500 2.5 0.9 

3,000 2.7 1.0 

4,000 3.1 1.1 

5,000 3.4 1.2 

6,000 3.7 1.3 

7,000 4.0 1.4 

7,500 4.1 1.5 

8,000 4.2 1.5 

9,000 4.5 1.6 

10,000 4.7 1.7 

15,000 5.6 2.0 

20,000 6.5 2.4 

25,000 7.2 2.6 

30,000 7.8 2.8 

40,000 8.9 3.3 

50,000 9.8 3.6 

 75,000 12 4.4 

100,000 14 5.0 

150,000 16 6.1 

200,000 19 7.0 

250,000 21 7.8 

750,000 ** 13 

*Report distance as 0.1 mile ** More than 25 miles (report distance as 25 miles) 

April 15, 1999 5 - 13 
Reference Table 11
 

Distances to Toxic Endpoint for Chlorine
 

F Stability, Wind Speed 1.5 Meters per Second
 

Release Rate Distance to Endpoint (miles) 

(lbs/min) 

Rural Urban 

1 0.2 0.1 

2 0.3 0.1 

5 0.5 0.2 

10 0.7 0.3 

15 0.8 0.4 

20 1.0 0.4 

30 1.2 0.5 

40 1.4 0.6 

50 1.5 0.6 

60 1.7 0.7 

70 1.8 0.8 

80 1.9 0.8 

90 2.0 0.9 

100 2.2 0.9 

150 2.6 1.2 

200 3.0 1.3 

250 3.4 1.5 

300 3.7 1.6 

400 4.2 1.9 

500 4.7 2.1 

600 5.2 2.3 

700 5.6 2.5 

Release Rate Distance to Endpoint (miles) 

(lbs/min) 

Rural Urban 

750 5.8 2.6 

800 5.9 2.7 

900 6.3 2.9 

1,000 6.6 3.0 

1,500 8.1 3.8 

2,000 9.3 4.4 

2,500 10 4.9 

3,000 11 5.4 

4,000 13 6.2 

5,000 14 7.0 

6,000 16 7.6 

7,000 17 8.3 

7,500 18 8.6 

8,000 18 8.9 

9,000 19 9.4 

10,000 20 9.9 

15,000 25 12 

20,000 * 14 

25,000 * 16 

30,000 * 18 

40,000 * 20 

50,000 * * 

* More than 25 miles (report distance as 25 miles) 

April 15, 1999 5 - 14 
Reference Table 12

 Distances to Toxic Endpoint for Anhydrous Sulfur Dioxide
 

F Stability, Wind Speed 1.5 Meters per Second
 

Release Rate Distance to Endpoint (miles) 

(lbs/min) 

Rural Urban 

1 0.2 0.1 

2 0.2 0.1 

5 0.4 0.2 

10 0.6 0.2 

15 0.7 0.3 

20 0.9 0.4 

30 1.1 0.5 

40 1.3 0.5 

50 1.4 0.6 

60 1.6 0.7 

70 1.8 0.7 

80 1.9 0.8 

90 2.0 0.8 

100 2.1 0.9 

150 2.7 1.1 

200 3.1 1.3 

250 3.6 1.4 

300 3.9 1.6 

400 4.6 1.9 

500 5.2 2.1 

600 5.8 2.3 

700 6.3 2.5 

Release Rate Distance to Endpoint (miles) 

(lbs/min) 

Rural Urban 

750 6.6 2.6 

800 6.8 2.7 

900 7.2 2.9 

1,000 7.7 3.1 

1,500 9.6 3.8 

2,000 11 4.5 

2,500 13 5.0 

3,000 14 5.6 

 4,000 17 6.5 

5,000 19 7.3 

6,000 21 8.1 

7,000 23 8.8 

7,500 24 9.1 

8,000 25 9.5 

9,000 * 10 

10,000 * 11 

15,000 * 13 

20,000 * 16 

25,000 * 18 

30,000 * 19 

40,000 * 23 

50,000 * * 

* More than 25 miles (report distance as 25 miles) 

April 15, 1999 5 - 15 
Reference Table 13

Distance to Overpressure of 1.0 psi for Vapor Cloud Explosions of 500 - 2,000,000 Pounds of Regulated Flamm

Based on TNT Equivalent Method, 10 Percent Yield Factor

Quantity in Cloud (pounds) 500 2,000 5,000 10,000 20,000 50,000 100,000 200,000 500,000 

CAS No. Chemical Name Distance (Miles) to 1 psi Overpressure 

75-07-0 Acetaldehyde 0.05 0.08 0.1 0.1 0.2 0.2 0.3 0.4 0.5 74-86-2 Acetylene 0.07 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.7 

598-73-2 Bromotrifluoroethylene 0.02 0.04 0.05 0.06 0.08 0.1 0.1 0.2 0.2 

106-99-0 1,3-Butadiene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

106-97-8 Butane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

25167-67-3 Butene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

590-18-1 2-Butene-cis 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 624-64-6 2-Butene-trans 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

106-98-9 1-Butene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 107-01-7 2-Butene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 463-58-1 Carbon oxysulfide 0.04 0.06 0.08 0.1 0.1 0.2 0.2 0.3 0.4 

7791-21-1 Chlorine monoxide 0.02 0.03 0.04 0.05 0.06 0.08 0.1 0.1 0.2 

590-21-6 1-Chloropropylene 0.05 0.08 0.1 0.1 0.2 0.2 0.3 0.4 0.5 557-98-2 2-Chloropropylene 0.05 0.08 0.1 0.1 0.2 0.2 0.3 0.4 0.5 460-19-5 Cyanogen 0.05 0.08 0.1 0.1 0.2 0.2 0.3 0.4 0.5 

75-19-4 Cyclopropane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

4109-96-0 Dichlorosilane 0.04 0.06 0.08 0.1 0.1 0.2 0.2 0.3 0.4 

75-37-6 Difluoroethane 0.04 0.06 0.09 0.1 0.1 0.2 0.2 0.3 0.4 

124-40-3 Dimethylamine 0.06 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.6 

463-82-1 2,2-Dimethylpropane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

74-84-0 Ethane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

107-00-6 Ethyl acetylene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

75-04-7 Ethylamine 0.06 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.6 

April 15, 1999 5 - 16 
Reference Table 13 (continued) 

Quantity in Cloud (pounds) 500 2,000 5,000 10,000 20,000 50,000 100,000 200,000 500,000 

CAS No. Chemical Name Distance (Miles) to 1 psi Overpressure 

75-00-3 Ethyl chloride 0.05 0.08 0.1 0.1 0.2 0.2 0.3 0.4 0.5 74-85-1 Ethylene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.7 60-29-7 Ethyl ether 0.06 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.6 75-08-1 Ethyl mercaptan 0.05 0.09 0.1 0.2 0.2 0.2 0.3 0.4 0.5 

109-95-5 Ethyl nitrite 0.05 0.07 0.1 0.1 0.2 0.2 0.3 0.3 0.5 

1333-74-0 Hydrogen 0.09 0.1 0.2 0.2 0.3 0.4 0.5 0.6 0.9 

75-28-5 Isobutane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 78-78-4 Isopentane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 78-79-5 Isoprene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 75-31-0 Isopropylamine 0.06 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.6 75-29-6 Isopropyl chloride 0.05 0.08 0.1 0.1 0.2 0.2 0.3 0.4 0.5 

74-82-8 Methane 0.07 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.7 

74-89-5 Methylamine 0.06 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.6 

563-45-1 3-Methyl-1-butene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 563-46-2 2-Methyl-1-butene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 115-10-6 Methyl ether 0.05 0.09 0.1 0.1 0.2 0.3 0.3 0.4 0.5 107-31-3 Methyl formate 0.04 0.07 0.1 0.1 0.2 0.2 0.3 0.3 0.4 

115-11-7 2-Methylpropene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 504-60-9 1,3-Pentadiene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

109-66-0 Pentane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

109-67-1 1-Pentene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

646-04-8 2-Pentene, (E)- 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

627-20-3 2-Pentene, (Z)- 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

463-49-0 Propadiene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

April 15, 1999 5 - 17 
Reference Table 13 (continued) 

Quantity in Cloud (pounds) 500 2,000 5,000 10,000 20,000 50,000 100,000 200,000 500,000 

CAS No. Chemical Name Distance (Miles) to 1 psi Overpressure 

74-98-6 Propane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

115-07-1 Propylene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

74-99-7 Propyne 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

7803-62-5 Silane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

116-14-3 Tetrafluoroethylene 0.02 0.03 0.04 0.05 0.07 0.09 0.1 0.1 0.2 

75-76-3 Tetramethylsilane 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

10025-78-2 Trichlorosilane 0.03 0.04 0.06 0.08 0.1 0.1 0.2 0.2 0.3 

79-38-9 Trifluorochloroethylene 0.02 0.03 0.05 0.06 0.07 0.1 0.1 0.2 0.2 75-50-3 Trimethylamine 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.6 

689-97-4 Vinyl acetylene 0.06 0.1 0.1 0.2 0.2 0.3 0.4 0.5 0.6 

75-01-4 Vinyl chloride 0.05 0.08 0.1 0.1 0.2 0.2 0.3 0.4 0.5 

109-92-2 Vinyl ethyl ether 0.06 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.6 

75-02-5 Vinyl fluoride 0.02 0.04 0.05 0.06 0.08 0.1 0.1 0.2 0.2 

75-35-4 Vinylidene chloride 0.04 0.06 0.08 0.1 0.1 0.2 0.2 0.3 0.4 

75-38-7 Vinylidene fluoride 0.04 0.06 0.09 0.1 0.1 0.2 0.2 0.3 0.4 

107-25-5 Vinyl methyl ether 0.06 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.6 

April 15, 1999 5 - 18 
6 DETERMINING ALTERNATIVE RELEASE SCENARIOS 

In Chapter 6 

� Considerations for alternative release scenarios for regulated substances in 

Program 2 or Program 3 processes. 

� Potential alternative scenarios for releases of flammable substances. 

You are required to analyze at least one alternative release scenario for each listed toxic substance 

you have in a Program 2 or Program 3 process above its threshold quantity. You also are required to analyze 

one alternative release scenario for flammable substances in Program 2 or 3 processes as a class (i.e., you 

analyze one scenario involving a flammable substance as a representative scenario for all the regulated 

flammable substances you have on site in Program 2 or Program 3 processes). You do not need to analyze an 

alternative scenario for each flammable substance. For example, if you have five listed substances – chlorine, 

ammonia, hydrogen chloride, propane, and acetylene – above the threshold in Program 2 or 3 processes, you 

will need to analyze one alternative scenario each for chlorine, ammonia, and hydrogen chloride and a single 

alternative scenario to cover propane and acetylene (listed flammable substances). Even if you have a 

substance above the threshold in several processes or locations, you need only analyze one alternative 

scenario for it. 

According to the rule (40 CFR 68.28), alternative scenarios should be more likely to occur than the 

worst-case scenario and should reach an endpoint offsite, unless no such scenario exists. Release scenarios 

considered should include, but are not limited to, the following: 

� Transfer hose releases due to splits or sudden hose uncoupling; 

Process piping releases from failures at flanges, joints, welds, valves and valve seals, and 

drains or bleeds; 

�

� Process vessel or pump releases due to cracks, seal failure, or drain, bleed, or plug failure; 

Vessel overfilling and spill, or overpressurization and venting through relief valves or 

rupture disks; and 

�

� Shipping container mishandling or puncturing leading to a spill. 

Alternative release scenarios for toxic substances should be those that lead to concentrations above 

the toxic endpoint beyond your fenceline. Scenarios for flammable substances should have the potential to 

cause substantial damage, including on-site damage. Those releases that have the potential to reach the 

public are of the greatest concern. You should consider unusual situations, such as start-up and shut-down, in 

selecting an appropriate alternative scenario. 

For alternative release scenarios, you are allowed to consider active mitigation systems, such as 

interlocks, shutdown systems, pressure relieving devices, flares, emergency isolation systems, and fire water 

and deluge systems, as well as passive mitigation systems, as described in Sections 3.1.2 and 3.2.3. 

For alternative release scenarios for regulated substances used in ammonia refrigeration, chemical 

distribution, propane distribution, warehouses, or POTWs, consult EPA's risk management program guidance 

April 15, 1999 
Chapter 6 

Determining Alternative Release Scenarios 

documents for these industry sectors. 

You have a number of options for selecting release scenarios for toxic or flammable substances. 

You may use your worst-case release scenario and apply your active mitigation system to 

limit the quantity released and the duration of the release. 

�

You may use information from your process hazards analysis, if you have conducted one, to 

select a scenario. 

�

You may review your accident history and choose an actual event as the basis of your 

scenario. 

�

If you have not conducted a process hazards analysis, you may review your operations and 

identify possible events and failures. 

�

Whichever approach you select, the key information you need to define is the quantity to be released 

and the time over which it will be released; together, these allow you to estimate the release rate and use 

essentially the same methods you used for the worst-case analysis. 

For flammable substances , the choice of alternative release scenarios is somewhat more complicated 

than for toxic substances, because the consequences of a release and the endpoint of concern may vary. For 

the flammable worst case, the consequence of concern is a vapor cloud explosion, with an overpressure 

endpoint. For alternative scenarios (e.g., fires), other endpoints (e.g., heat radiation) may need to be 

considered. 

Possible scenarios involving flammable substances include: 

Vapor cloud fires (flash fires) may result from dispersion of a cloud of flammable vapor and 

ignition of the cloud following dispersion. Such a fire could flash back and could represent a 

severe heat radiation hazard to anyone in the area of the cloud. This guidance provides 

methods to estimate distances to a concentration equal to the lower flammability limit (LFL) 

for this type of fire. (See Sections 9.1, 9.2, and 10.1.) 

�

A pool fire, with potential radiant heat effects, may result from a spill of a flammable liquid. 

This guidance provides a simple method for estimating the distance from a pool fire to a 

radiant heat level that could cause second degree burns from a 40-second exposure. (See 

Section 10.2). 

�

A boiling liquid, expanding vapor explosion (BLEVE), leading to a fireball that may 

produce intense heat, may occur if a vessel containing flammable material ruptures 

explosively as a result of exposure to fire. Heat radiation from the fireball is the primary 

hazard; vessel fragments and overpressure from the explosion also can result. BLEVEs are 

generally considered unlikely events; however, if you think a BLEVE is possible at your site, 

this guidance provides a method to estimate the distance at which radiant heat effects might 

lead to second degree burns. (See Section 10.3.) You also may want to consider models or 

�

April 15, 1999 6 - 2 
Chapter 6 

Determining Alternative Release Scenarios 

calculation methods to estimate effects of vessel fragmentation. (See Appendix A for 

references that may provide useful information for estimating such effects.) 

For a vapor cloud explosion to occur, rapid release of a large quantity, turbulent conditions 

(caused by a turbulent release or congested conditions in the area of the release, or both), and 

other factors are generally necessary. Vapor cloud explosions generally are considered 

unlikely events; however, if conditions at your site are conducive to vapor cloud explosions, 

you may want to consider a vapor cloud explosion as an alternative scenario. This guidance 

provides methods you may use to estimate the distance to 1 psi overpressure for a vapor 

cloud detonation, based on less conservative assumptions than the worst-case analysis. (See 

Section 10.4.) A vapor cloud deflagration, involving lower flame speeds than a detonation 

and resulting in less damaging blast effects, is more likely than a detonation. This guidance 

does not provide methods for estimating the effects of a deflagration, but you may use other 

methods of analysis if you want to consider such events. (See Appendix A for references 

that may provide useful information.) 

�

A jet fire may result from the puncture or rupture of a tank or pipeline containing a 

compressed or liquefied gas under pressure. The gas discharging from the hole can form a 

jet that "blows" into the air in the direction of the hole; the jet then may ignite. Jet fires 

could contribute to BLEVEs and fireballs if they impinge on tanks of flammable substances. 

A large horizontal jet fire may have the potential to pose an offsite hazard. This guidance 

does not include a method for estimating consequence distances for jet fires. If you want to 

consider a jet fire as an alternative scenario, you should consider other models or methods 

for the consequence analysis. (See Appendix A for references that may provide useful 

information.) 

�

If you carry out an alternative scenario analysis for a flammable mixture (i.e., a mixture that meets 

the criteria for NFPA 4), you need to consider all flammable components of the mixture, not just the regulated 

flammable substance or substances in the mixture (see Section 5.2 on flammable mixtures). If the mixture 

contains both flammable and non-flammable components, the analysis should be carried out considering only 

the flammable components. 

Chapter 7 provides detailed information on calculating release rates for alternative release scenarios 

for toxic substances. If you can estimate release rates for the toxic gases and liquids you have on site based 

on readily available information, you may skip Chapter 7 and go to Chapter 8. Chapter 8 describes how to 

estimate distances to the toxic endpoint for alternative scenarios for toxic substances. Chapters 9 provides 

information on calculation release rates for flammable substances. Chapter 10 describes how to estimate 

distances to flammable endpoints. 

April 15, 1999 6 - 3 
Chapter 6 

Determining Alternative Release Scenarios 

This page intentionally left blank. 

April 15, 1999 6 - 4 
7 ESTIMATION OF RELEASE RATES FOR ALTERNATIVE 

SCENARIOS FOR TOXIC SUBSTANCES 

For the alternative scenario analysis, you may use typical meteorological conditions and typical 

ambient temperature and humidity for your site. This guidance assumes D atmospheric stability and wind 

speed of 3.0 meters per second (6.7 miles per hour) as conditions likely to be applicable to many sites. 

7.1	 Release Rates for Toxic Gases 

In Section 7.1 

�	 7.1.1 Methods for unmitigated releases of toxic gases, including: 

-- Release of toxic gas from a hole in a tank or pipe (for choked flow 

conditions, or maximum flow rate), 

-- Release of toxic gas from a pipe, based on the flow rate through the 

pipe, or based on a hole in the pipe (using the same method as for a 

hole in a tank), 

-- Puff releases (no method is provided; users are directed to use other 

methods), 

-- Gases liquefied under pressure, including gaseous releases from holes 

above the liquid level in the tank and releases from holes in the liquid 

space, and 

--	 Consideration of duration of releases of toxic gas. 

�	 7.1.2 Methods for adjusting the estimated release rate to account for active or 

passive mitigation, including: 

-- Active mitigation to reduce the release duration (e.g., automatic 

shutoff valves), 

--	 Active mitigation to reduce the release rate to air, and 

--	 Passive mitigation (using the same method as for worst-case 

scenarios). 

7.1.1	 Unmitigated Releases of Toxic Gases 

Gaseous Releases 

Gaseous Release from Tank. Instead of assuming release of the entire contents of a vessel containing 

a toxic gas, you may decide to consider a more likely scenario as developed by the process hazards analysis, 

such as release from a hole in a vessel or pipe. To estimate a hole size you might assume, for example, the 

hole size that would result from shearing off a valve or pipe from a vessel containing a regulated substance. 

If you have a gas leak from a tank, you may use the following simplified equation to estimate a release rate 

based on hole size, tank pressure, and the properties of the gas. This equation applies to choked flow, or 

maximum gas flow rate. Choked flow generally would be expected for gases under pressure. (See Appendix 

D, Section D.6 for the derivation of this equation.) 

April 15, 1999 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

QR � HA × Pt × 

1 

Tt 

× GF (7-1) 

where: QR = Release rate (pounds per minute) 

HA = Hole or puncture area (square inches) (from hazard evaluation or best 

estimate) 

Pt = Tank pressure (pounds per square inch absolute (psia)) (from process 

information; for liquefied gases, equilibrium vapor pressure at 25 C is o 

included in Exhibit B-1, Appendix B) 

Tt = Tank temperature (K), where K is absolute temperature in kelvins; 25 C o 

(77 F) is 298 K o 

GF = Gas Factor, incorporating discharge coefficient, ratio of specific heats, 

molecular weight, and conversion factors (listed for each regulated toxic gas 

in Exhibit B-1, Appendix B) 

You can estimate the hole area from the size and shape of the hole. For a circular hole, you would 2 use the formula for the area of a circle (area = �r , where � is 3.14 and r is the radius of the circle; the radius 

is half the diameter). 

This equation will give an estimate of the initial release rate. It will overestimate the overall release 

rate, because it does not take into account the decrease in the release rate as the pressure in the tank decreases. 

You may use a computer model or another calculation method if you want a more realistic estimate of the 

release rate. As discussed below, you may use this equation for releases of gases liquefied under pressure if 

the release would be primarily gas (e.g., if the hole is in the head space of the tank, well above the liquid 

level). 

Example 19. Release of Toxic Gas from Tank (Diborane) 

You have a tank that contains diborane gas at a pressure of 30 psia. The temperature of the tank and its 

contents is 298 K (25�C). A valve on the side of the tank shears off, leaving a circular hole 2 1⁄2 inches in 2 diameter in the tank wall. You estimate the area from the formula for area of a circle (�r , where r is the 2 radius). The radius of the hole is 1 1/4 inches, so the area is � × (1 1/4) , or 5 square inches. From Exhibit 

B-1, the Gas Factor for diborane is 17. Therefore, the release rate, from Equation 7-1, is: 

QR = 5 × 30 × 1/(298)1⁄2 × 17 = 148 pounds per minute 

Gaseous Release from Pipe. If shearing of a pipe may be an alternative scenario for a toxic gas at 

your site, you could use the usual flow rate through the pipe as the release rate and carry out the estimation of 

distance as discussed in Chapter 8. 

April 15, 1999 7 - 2 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

If you want to consider a release of toxic gas through a hole in a pipe as an alternative scenario, you 

may use the method described above for a gas release from a hole in a tank. This method neglects the effects 

of friction along the pipe and, therefore, provides a conservative estimate of the release rate. 

Puff Releases. If a gaseous release from a hole in a tank or pipe is likely to be stopped very quickly 

(e.g., by a block valve), resulting in a puff of toxic gas that forms a vapor cloud rather than a plume, you may 

want to consider other methods for determining a consequence distance. A cloud of toxic gas resulting from a 

puff release will not exhibit the same behavior as a plume resulting from a longer release (e.g., a release over 

10 minutes). 

Liquefied Gases 

Gases Liquefied Under Pressure. Gases liquefied under pressure may be released as gases, liquids, 

or a combination (two-phase), depending on a number of factors, including liquid level and the location of the 

hole relative to the liquid level. The resulting impact distances can vary greatly. 

For releases from holes above the liquid level in a tank of gas liquefied under pressure, the release 

could be primarily gas, or the release may involve rapid vaporization of a fraction of the liquefied gas and 

possibly aerosolization (two-phase release). It is complex to determine which type of release (i.e., gas, twophase) will occur and the likely mix of gases and liquids in a two-phase release. The methods presented in 

this guidance do not definitively address this situation. As a rule of thumb, if the head space is large and the 

distance between the hole and the liquid level is relatively large given the height of the tank or vessel, you 

could assume the release is gaseous and, therefore, use Equation 7-1 above. (Exhibit B-1, Appendix B, o includes the equilibrium vapor pressure in psia for listed toxic gases liquefied under pressure at 25 C; this 

pressure can be used in Equation 7-1.) However, use of this equation will not be conservative if the head 

space is small and the release from the hole is two-phased. In situations where you are unsure of whether the 

release would be gaseous or two-phase, you may want to consider other models or methods to carry out a 

consequence analysis. 

For a hole in the liquid space of a tank, you may use Equation 7-2 below to estimate the release rate. o Exhibit B-1 in Appendix B gives the equilibrium vapor pressure in psia for listed toxic gases at 25 C; this 

is the pressure required to liquefy the gas at this temperature. You can estimate the gauge pressure in the 

tank from the equilibrium vapor pressure by subtracting the pressure of the ambient atmosphere (14.7 psi). 

Exhibit B-1 also gives the Density Factor (DF) for each toxic gas at its boiling point. This factor can be used o to estimate the density of the liquefied gas (the density at 25 C would not be significantly different from the 

density at the boiling point for most of the listed gases). The equation to estimate the release rate is (see 

Appendix D, Section D.7.1, for more information): 

11.7 669 QR � HA × 6.82 × LH � × P

g (7-2) 

DF 2 DF 

April 15, 1999 7 - 3 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

where: QR = Release rate (pounds per minute) 

HA = Hole or puncture area (square inches) (from hazard evaluation or best 

estimate) 

DF = Density Factor (listed for each regulated toxic gas in Exhibit B-1, Appendix 

B; 1/(DF x 0.033) is density in pounds per cubic foot) 

LH = Height of liquid column above hole (inches) (from hazard evaluation or best 

estimate) 

Pg = Gauge pressure of the tank pressure (pounds per square inch gauge (psig), 

from vapor pressure of gas (listed in Exhibit B-1, Appendix B) minus 

atmospheric pressure (14.7 psi) 

This equation gives the rate of release of liquid through the hole. For a gas liquefied under pressure, assume 

that the released liquid will immediately flash into vapor (or a vapor/aerosol mixture) and the release rate to 

air is the same as the liquid release rate. This equation gives an estimate of the initial release rate. It will 

overestimate the overall release rate, because it does not take into account the decrease in the release rate as 

the pressure in the tank and the height of the liquid in the tank decrease. You may use a computer model or 

another calculation method if you want a more realistic estimate of the release rate. 

For a release from a broken pipe of a gas liquefied under pressure, see equations 7-4 to 7-6 below for 

liquid releases from pipes. Assume the released liquid flashes into vapor upon release and use the calculated 

release rate as the release rate to air. 

Gases Liquefied by Refrigeration. Gases liquefied by refrigeration alone may be treated as liquids. 

You may use the methods described in Section 7.2 for estimation of release rates. 

Duration of Release 

The duration of the release is used in choosing the appropriate generic reference table of distances, as 

discussed in Chapter 8. (You do not need to consider the duration of the release to use the chemical-specific 

reference tables.) You may calculate the maximum duration by dividing the quantity in the tank or the 

quantity that may be released from pipes by your calculated release rate. You may use 60 minutes as a 

default value for maximum release duration. If you know, and can substantiate, how long it is likely to take 

to stop the release, you may use that time as the release duration. 

7.1.2 Mitigated Releases of Toxic Gases 

For gases, passive mitigation may include enclosed spaces, as discussed in Section 3.1.2. Active 

mitigation for gases, which may be considered in analyzing alternative release scenarios, may include an 

assortment of techniques including automatic shutoff valves, rapid transfer systems (emergency deinventory), 

and water/chemical sprays. These mitigation techniques have the effect of reducing either the release rate or 

the duration of the release, or both. 

April 15, 1999 7 - 4 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

Active Mitigation 

Active Mitigation to Reduce Release Duration. An example of a mitigation technique to reduce the 

release duration is automatic shutoff valves. If you have an estimate of the rate at which the gas will be 

released and the time it will take to shut off the release, you may estimate the quantity potentially released 

(release rate times time). You must be able to substantiate the time it will take to shut off the release. If the 

release will take place over a period of 10 minutes or more, you may use the release rate to estimate the 

distance to the toxic endpoint, as discussed in Chapter 8. For releases stopped in less than 10 minutes, 

multiply the initial release rate by the duration of release to estimate the quantity released, then divide the new 

quantity by 10 minutes to estimate a mitigated release rate that you may apply to the reference tables 

described in Chapter 8 to estimate the consequence distance. If the release would be stopped very quickly, 

you might want to consider other methods that will estimate consequence distances for a puff release. 

Active Mitigation to Directly Reduce Release Rate to Air. Examples of mitigation techniques to 

directly reduce the release rate include scrubbers and flares. Use test data, manufacturer design 

specifications, or past experience to determine the fractional reduction of the release rate by the mitigation 

technique. Apply this fraction to the release rate that would have occurred without the mitigation technique. 

The initial release rate, without mitigation, may be the release rate for the alternative scenario (e.g., a release 

rate estimated from the equations presented earlier in this section) or the worst-case release rate. The 

mitigated release rate is: 

QR � � R (1 FR)× QR	 (7-3) 

where: QRR = Reduced release rate (pounds per minute) 

FR	 = Fractional reduction resulting from mitigation 

QR	 = Release rate without mitigation (pounds per minute) 

Example 20. Water Spray Mitigation (Hydrogen Fluoride) 

A bleeder valve on a hydrogen fluoride (HF) tank opens, releasing 660 pounds per minute of HF. Water sprays 

are applied almost immediately. Experimental field and laboratory test data indicate that HF vapors could be 

reduced by 90 percent. The reduced release rate is: 

QRR	 = (1 - 0.9) × (660 pounds per minute)
 

= 66 pounds per minute
 

In estimating the consequence distance for this release scenario, you would need to consider the release both 

before and after application of the water spray and determine which gives the greatest distance to the endpoint. 

You need to be able to substantiate the time needed to begin the water spray mitigation. 

April 15, 1999	 7 - 5 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

Passive Mitigation 

The same simplified method used for worst-case releases may be used for alternative release 

scenarios to estimate the release rate to the outside air from a release in an enclosed space. For alternative 

scenarios, you may use a modified release quantity, if appropriate. You may also adjust the mitigation factor 

to account for the effects of ventilation, if appropriate for the alternative scenario you have chosen. Use the 

equations presented in Section 3.1.2 to estimate the release rate to the outside air. 

Duration of Release 

You should estimate the duration of the release either from your knowledge of the length of time it 

may take to stop the release (be prepared to substantiate your time estimate) or by dividing the quantity that 

may be released by your estimated release rate. (You do not need to consider the release duration to use the 

chemical-specific reference tables of distances.) 

7.2	 Release Rates for Toxic Liquids 

In Section 7.2 

�	 7.2.1 Methods for estimating the liquid release rate and quantity released for 

toxic liquids released without mitigation, including: 

-- Release of toxic liquid from a hole in a tank under atmospheric 

pressure (including toxic gases liquefied by refrigeration alone), 

-- Release of toxic liquid from a hole in the liquid space of a pressurized 

tank (the user is referred to equations provided in the section on toxic 

gases or in the technical appendix), and 

--	 Release of toxic liquid from a broken pipe. 

�	 7.2.2 Methods for estimating the liquid release rate and quantity released for 

toxic liquids released with mitigation measures that reduce the duration of the 

liquid release or the quantity of liquid released (e.g., automatic shutoff valves), 

�	 7.2.3 Methods for estimating the evaporation rate of toxic liquids from pools, 

accounting for: 

-- Ambient temperature,
 

-- Elevated temperature, 
 

-- Diked areas,
 

-- Releases into buildings,
 

-- Active mitigation to reduce the evaporation rate of the liquid, 
 o o -- Temperatures between 25 C and 50 C, and
 

-- Duration of the release.
 

�	 7.2.4 Methods for estimating the evaporation rate for common water solutions 

of regulated toxic substances and for oleum. 

April 15, 1999	 7 - 6 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

This section describes methods for estimating liquid release rates from tanks and pipes. The released 

liquid is assumed to form a pool, and the evaporation rate from the pool is estimated as for the worst-case 

scenario. For the alternative scenario, you may assume the average wind speed in your area in the calculation 

of evaporation rate, instead of the worst-case wind speed of 1.5 meters per second (3.4 miles per hour). For 

the reference tables in this guidance, the wind speed for alternative scenarios is assumed to be 3.0 meters per 

second (6.7 miles per hour). 

If you have sufficient information to estimate the quantity of liquid that might be released to an 

undiked area under an alternative scenario, you may go directly to Section 7.2.3 to estimate the evaporation 

rate from the pool and the release duration. After you have estimated the evaporation rate and release 

duration, go to Chapter 8 for instructions on estimating distance to the toxic endpoint. 

7.2.1 Liquid Release Rate and Quantity Released for Unmitigated Releases 

Release from Tank 

Tank under Atmospheric Pressure. If you have a liquid stored in a tank at atmospheric pressure 

(including gases liquefied by refrigeration alone), you may use the following simple equation to estimate the 

liquid release rate from a hole in the tank below the liquid level. (See Appendix D, Section D.7.1, for the 

derivation of this equation.) 

QRL � HA × LH × LLF (7-4) 

where: QRL = Liquid release rate (pounds per minute) 

HA = Hole or puncture area (square inches) (from hazard evaluation or best 

estimate) 

LH = Height of liquid column above hole (inches) (from hazard evaluation or best 

estimate) 

LLF = Liquid Leak Factor incorporating discharge coefficient and liquid density 

(listed for each toxic liquid in Exhibit B-2, Appendix B). 

Remember that this equation only applies to liquids in tanks under atmospheric pressure. This 

equation will give an overestimate of the release rate, because it does not take into account the decrease in the 

release rate as the height of the liquid above the hole decreases. You may use a computer model or another 

calculation method if you want a more realistic estimate of the liquid release rate. 

You may estimate the quantity that might be released by multiplying the liquid release rate from the 

above equation by the time (in minutes) that likely would be needed to stop the release. You should be able 

to substantiate the time needed to stop the release. Alternatively, you may assume the release would stop 

when the level of liquid in the tank drops to the level of the hole. You may estimate the quantity of liquid 

above that level in the tank from the dimensions of the tank, the liquid level at the start of the leak, and the 

level of the hole. Assume the estimated quantity is released into a pool and use the method and equations in 

Section 7.2.3 below to determine the evaporation rate of the liquid from the pool and the duration of the 

release. As discussed in Section 7.2.3, if you find that your estimated evaporation rate is greater than 

estimated liquid release rate, you should use the liquid release rate as the release rate to air. 

April 15, 1999 7 - 7 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

Example 21. Liquid Release from Atmospheric Tank (Allyl Alcohol) 

You have a tank that contains 20,000 pounds of allyl alcohol at ambient temperature and pressure. A valve on 

the side of the tank shears, leaving a hole in the tank wall 5 square inches in area. The liquid column is 23 

inches above the hole in the tank. From Exhibit B-2, the Liquid Leak Factor for allyl alcohol is 41. Therefore, 

from Equation 7-4, the liquid release rate is: 

QRL = 5 × (23)1⁄2 × 41 = 983 pounds per minute 

It takes 10 minutes to stop the release, so 10 minutes × 983 pounds per minute = 9,830 pounds of allyl alcohol 

released. 

Pressurized Tank. If you have a liquid stored in a tank under pressure, you may estimate a release 

rate for liquid from a hole in the liquid space of the tank using the equation presented above for gases 

liquefied under pressure (Equation 7-2 in Section 7.1.1) or the equations in Appendix D, Section D.7.1. 

Release from Pipe 

If you have a liquid flowing through a pipe at approximately atmospheric pressure, and the pipeline 

remains at about the same height between the pipe inlet and the pipe break, you can estimate the quantity of 

liquid released from the flow rate in the pipe and the time it would take to stop the release by multiplying the 

flow rate by the time. For liquids at atmospheric pressure, assume the liquid is spilled into a pool and use the 

methods in Section 7.2.3 below to estimate the release rate to air. 

For the release of a liquid under pressure from a long pipeline, you may use the equations below (see 

Appendix D, Section D.7.2 for more information on these equations). These equations apply both to 

substances that are liquid at ambient conditions and to gases liquefied under pressure. This method does not 

consider the effects of friction in the pipe. First estimate the initial operational flow velocity of the substance 

through the pipe using the initial operational flow rate as follows: 

FR × DF × 0.033 V � a	 (7-5) A 

p 

where:	 Va = Initial operational flow velocity (feet per minute) 

FR = Initial operational flow rate (pounds per minute) 

DF = Density Factor (from Exhibit B-2, Appendix B) 

Ap = Cross-sectional area of pipe (square feet) 

You can estimate the cross-sectional area of the pipe from the diameter or radius (half the diameter 2 of the pipe) using the formula for the area of a circle (area = �r , where r is the radius). 

The release velocity is then calculated based on the initial operational flow, any gravitational 

April 15, 1999	 7 - 8 
 

Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

acceleration or deceleration effects resulting from changes in the height of the pipeline, and the pressure 

difference between the pressure in the pipe and atmospheric pressure, using a form of the Bernoulli equation: 

�197 × [28.4 × (PT 14.7) × DF] � [5.97 × (Z )] � [2.58×10�5 V � � × V b a Zb a 

2

] (7-6) 

where: Vb = Release velocity (feet per minute) 

PT = Total pressure on liquid in pipe (psia) 

DF = Density factor, see Exhibit B-1 or Exhibit B-2 

Za = Height of pipeline at inlet (feet) 

Zb = Height of pipeline at break (feet) 

Va = Operational velocity (feet per minute), calculated from Equation 7-5 

Please note that if the height of the pipe at the release point is higher than the initial pipe height, then Z -Z is a b 

negative, and the height term will cause the estimated release velocity to decrease. 

The release velocity can then be used to calculate a release rate as follows: 

Vb × A 

p QR � L (7-7) DF × 0.033 

where: QRL = Release rate (pounds per minute) 

Vb = Release velocity (feet per minute) 

DF = Density Factor 

Ap = Cross-sectional area of pipe (square feet) 

You may estimate the quantity released into a pool from the broken pipe by multiplying the liquid 

release rate (QR ) from the equation above by the time (in minutes) that likely would be needed to stop the L 

release (or to empty the pipeline). Assume the estimated quantity is released into a pool and use the method 

and equations described in Section 7.2.3 below to determine the evaporation rate of the liquid from the pool. 

You must be able to substantiate the time needed to stop the release. 

As noted above in Section 7.1.1, for a release from a pipe of gas liquefied under pressure, assume 

that the released liquid is immediately vaporized, and use the calculated liquid release rate as the release rate 

to air. If the release duration would be very short (e.g., because of active mitigation measures), determine the 

total quantity of the release as the release rate times the duration, then estimate a new release rate as the 

quantity divided by 10. This will give you a release rate that you can use with the 10-minute reference tables 

of distances in this guidance to estimate a distance to the endpoint. 

In the case of very long pipes, release rates from a shear or hole will be lower than the estimates from 

this method because of pipe roughness and frictional head loss. If friction effects are deemed considerable, an 

established method for calculating frictional head loss such as the Darcy formula may be used. 

April 15, 1999 7 - 9 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

7.2.2 Liquid Release Rate and Quantity Released for Mitigated Releases 

For alternative release scenarios, you are permitted to take credit for both passive and active 

mitigation systems, or a combination if both are in place. Active mitigation techniques that reduce the rate of 

liquid release or the quantity released into the pool are discussed in this section. Active and passive 

mitigation to reduce the evaporation rate of liquid from a pool are discussed in the next section. 

Active Mitigation to Reduce Quantity Released 

Examples of mitigation techniques to reduce the quantity released into the pool include automatic 

shutoff valves and emergency deinventory. You may use the equations in Section 7.2.1 above for calculating 

liquid release rate, if applicable. Estimate the approximate time needed to stop the release by the mitigation 

technique (you must be able to justify your estimate). Multiply the release rate times the duration of release 

to estimate quantity released. Assume the estimated quantity is released into a pool and use the method and 

equations described in Section 7.2.3 below to determine the evaporation rate of the liquid from the pool. You 

should also consider mitigation (active or passive) of evaporation from the pool, if applicable, as discussed in 

Section 7.2.3 below. 

Example 22. Mitigated Liquid Release 

A bromine injection system suffers a hose failure; the greatly lowered system pressure triggers an automatic 

shutoff valve within 30 seconds of the release. The flow rate out of the ruptured hose is approximately 330 

pounds per minute. Because the release occurred for only 30 seconds (0.5 minutes), the total quantity spilled 

was 330 x 0.5, or 165 pounds. 

7.2.3 Evaporation Rate from Liquid Pool 

After you have estimated the quantity of liquid released, assume that the liquid forms a pool and 

calculate the evaporation rate from the pool as described below. You may account for both passive and active 

mitigation in estimating the release rate. Passive mitigation may include techniques already discussed in 

Section 3.2.3 such as dikes and trenches. Active mitigation to reduce the release rate of liquid in pools to the 

air may include an assortment of techniques including foam or tarp coverings and water or chemical sprays. 

Some methods of accounting for passive and active mitigation are discussed below. 

If the calculated evaporation rate from the pool is greater than the liquid release rate you have 

estimated from the container, no pool would be formed, and calculating the release rate as the evaporation 

rate from a pool would not be appropriate. If the pool evaporation rate is greater than the liquid release rate, 

use the liquid release rate as the release rate to air. Consider this possibility particularly for relatively volatile 

liquids, gases liquefied by refrigeration, or liquids at elevated temperature that form pools with no mitigation. 

April 15, 1999 7 - 10 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

Unmitigated 

Ambient temperature. For pools with no mitigation, if the liquid is always at ambient temperature, 

find the Liquid Factor Ambient (LFA) and the Density Factor (DF) in Exhibit B-2 of Appendix B (see o Appendix D, Section D.2.2 for the derivation of these factors). If your ambient temperature is between 25 C o and 50 C, you may use this method to calculate the release rate, and then use the appropriate Temperature 

Correction Factor from Exhibit B-4, Appendix B, to adjust the release rate, as described below. For gases 

liquefied by refrigeration, use the Liquid Factor Boiling (LFB) and DF from Exhibit B-1. Calculate the 

release rate from the following equation for liquids at ambient temperature with no mitigation: 

QR QS � × 2.4 × LFA × DF	 (7-8) 

where:	 QR = Release rate (pounds per minute) 

QS = Quantity released (pounds) 

2.4	 = Wind speed factor = 3.00.78, where 3.0 meters per second (6.7 miles per 

hour) is the wind speed for the alternative scenario for purposes of this 

guidance 

LFA = Liquid Factor Ambient
 

DF = Density Factor
 

This method assumes that the total quantity of liquid released spreads out to form a pool one 

centimeter in depth; it does not take into account evaporation as the liquid is released. 

Example 23.	 Evaporation from Pool Formed by Liquid Released from Hole in Tank (Allyl Alcohol) 

In Example 21, 9,830 pounds of allyl alcohol were estimated to be released from a hole in a tank. From Exhibit 

B-2, the Density Factor for allyl alcohol is 0.58, and the Liquid Factor Ambient is 0.0046. Assuming that the 

liquid is not released into a diked area or inside a building, the evaporation rate from the pool of allyl alcohol, 

from Equation 7-8, is: 

QR = 9,830 × 2.4 × 0.0046 × 0.58 = 63 pounds per minute 

Elevated temperature. For pools with no mitigation, if the liquid is at an elevated temperature (above o 50 C or at or close to its boiling point), find the Liquid Factor Boiling (LFB) and the Density Factor (DF) in 

Exhibit B-2 of Appendix B (see Appendix D, Section D.2.2, for the derivation of these factors). For liquids o o at temperatures between 25 C and 50 C, you may use the method above for ambient temperature and apply 

the appropriate Temperature Correction Factor from Appendix B, Exhibit B-4, to the result, as discussed o below. For liquids above 50 C, or close to their boiling points, or with no Temperature Correction Factors 

available, calculate the release rate of the liquid from the following equation: 

QR QS � × 2.4 × LFB × DF	 (7-9) 

April 15, 1999	 7 - 11 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

where:	 QR = Release rate (pounds per minute) 

QS = Quantity released (pounds) 

2.4	 = Wind speed factor = 3.00.78, where 3.0 meters per second (6.7 miles per 

hour) is the wind speed for the alternative scenario for purposes of this 

guidance 

LFB = Liquid Factor Boiling
 

DF = Density Factor
 

Mitigated 

Diked Areas. If the toxic liquid will be released into an area where it will be contained by dikes, 

compare the diked area to the maximum area of the pool that could be formed, as described in Section 3.2.3 

(see Equation 3-6). Also verify that the quantity spilled will be totally contained by the dikes. The smaller of 

the two areas should be used in determination of the evaporation rate. If the maximum area of the pool is 

smaller than the diked area, calculate the release rate as described for pools with no mitigation (above). If the 

diked area is smaller, and the spill will be totally contained, go to Exhibit B-2 in Appendix B to find the 

Liquid Factor Ambient (LFA), if the liquid is at ambient temperature, or the Liquid Factor Boiling (LFB), if o o the liquid is at an elevated temperature. For temperatures between 25 C and 50 C, you may use the 

appropriate Temperature Correction Factor from Exhibit B-4, Appendix B, to adjust the release rate, as 

described below. For gases liquefied by refrigeration, use the LFB. Calculate the release rate from the diked 

area as follows for liquids at ambient temperature: 

QR � 2.4 × LFA × A	 (7-10) 

or, for liquids at elevated temperatures or gases liquefied by refrigeration alone: 

QR � 2.4 × LFB × A (7-11) 

where:	 QR = Release rate (pounds per minute) 

2.4	 = Wind speed factor = 3.00.78, where 3.0 meters per second (6.7 miles per 

hour) is the wind speed for the alternative scenario for purposes of this 

guidance 

LFA = Liquid Factor Ambient (listed in Exhibit B-2, Appendix B)
 

LFB = Liquid Factor Boiling (listed in Exhibit B-1 or B-2, Appendix B)
 

A = Diked area (square feet)
 

Releases Into Buildings. If a toxic liquid is released inside a building, compare the area of the 

building floor or any diked area that would contain the spill to the maximum area of the pool that could be 

formed; the smaller of the two areas should be used in determining the evaporation rate, as for the worst-case 

scenario. The maximum area of the pool is determined from Equation 3-6 in Section 3.2.3 for releases into 

diked areas. The area of the building floor is the length times width of the floor (in feet) (Equation 3-9). 

If the floor area or diked area is smaller than the maximum pool size, estimate the outdoor 

evaporation rate from a pool the size of the floor area or diked area from Equation 7-10. If the maximum 

pool area is smaller, estimate the outdoor evaporation rate from a pool of maximum size from Equation 7-8. 

April 15, 1999	 7 - 12 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

Estimate the rate of release of the toxic vapor from the building as five percent of the calculated outdoor 

evaporation rate (multiply your evaporation rate by 0.05). See Appendix D, Section D.2.4 for more 

information on releases into buildings. 

Active Mitigation to Reduce Evaporation Rate. Examples of active mitigation techniques to reduce 

the evaporation rate from the pool include water sprays and foam or tarp covering. Use test data, 

manufacturer design specifications, or past experience to determine the fractional reduction of the release rate 

by the mitigation technique. Apply this fraction to the release rate (evaporation rate from the pool) that 

would have occurred without the mitigation technique, as follows: 

QR � RV (1�FR)× QR (7-12) 

where: QRRV = Reduced evaporation rate (release rate to air) from pool (pounds per 

minute) 

FR = Fractional reduction resulting from mitigation 

QR = Evaporation rate from pool without mitigation (pounds per minute) 

o Temperature Corrections for Liquids at Temperatures between 25 and 50 C 

o o o o If your liquid is at a temperature between 25 C (77 F) and 50 C (122 F), you may use the 

appropriate Temperature Correction Factor (TCF) from Exhibit B-4, Appendix B, to calculate a corrected o o release rate. Calculate the release rate (QR) of the liquid at 25 C (77 F) as described above for unmitigated 

releases or releases in diked areas and multiply the release rate by the appropriate TCF as described in 

Section 3.2.5. 

Evaporation Rate Compared to Liquid Release Rate 

If you estimated the quantity of liquid in the pool based on an estimated liquid release rate from a 

hole in a container or pipe, as discussed in Sections 7.2.1 and 7.2.2, compare the evaporation rate with the 

liquid release rate. If the evaporation rate from the pool is greater than the liquid release rate, use the liquid 

release rate as the release rate to air. 

Duration of Release 

After you have estimated a release rate as described above, determine the duration of the vapor 

release from the pool (the time it will take for the liquid pool to evaporate completely). To estimate the time 

in minutes, divide the total quantity released (in pounds) by the release rate (in pounds per minute) (see 

Equation 3-5 in Section 3.2.2). If you are using the liquid release rate as the release rate to air, as discussed 

in the preceding paragraph, estimate a liquid release duration as discussed in Section 7.2.1 or 7.2.2. The 

duration could be the time it would take to stop the release or the time it would take to empty the tank or to 

release all the liquid above the level of the leak. If you have corrected the release rate for a temperatures o above 25 C, use the corrected release rate to estimate the duration. 

April 15, 1999 7 - 13 
Chapter 7 

Estimation of Release Rates for Alternative Scenarios for Toxic Substances 

7.2.4 Common Water Solutions and Oleum 

You may use the methods described above in Sections 7.2.1, 7.2.2, and 7.2.3 for pure liquids to 

estimate the quantity of a solution of a toxic substance or oleum that may be spilled into a pool. LFA, DF, 

and LLF values for several concentrations of ammonia, formaldehyde, hydrochloric acid, hydrofluoric acid, 

and nitric acid in water solution and for oleum are listed in Appendix B, Exhibit B-3. The LFA for a wind 

speed of 3.0 meters per second (6.7 miles per hour) should be used in the release rate calculations for 

alternative scenarios for pools of solutions at ambient temperature. 

For unmitigated releases or releases with passive mitigation, follow the instructions in Section 7.2.3. 

If active mitigation measures are in place, you may estimate a reduced release rate from the instructions on 

active mitigation in Section 7.2.2. Use the total quantity of the solution as the quantity released from the 

vessel or pipeline (QS) in carrying out the calculation of the release rate to the atmosphere. 

If the solution is at an elevated temperature, see Section 3.3. As discussed in Section 3.3, you may 

treat the release of the substance in solution as a release of the pure substance. Alternatively, if you have 

vapor pressure data for the solution at the release temperature, you may estimate the release rate from the 

equations in Appendix D, Sections D.2.1 and D.2.2. 

If you estimated the quantity of solution in the pool based on an estimated liquid release rate from a 

hole in a container or pipe, as discussed in Sections 7.2.1 and 7.2.2, compare the evaporation rate with the 

liquid release rate. If the evaporation rate from the pool is greater than the liquid release rate, use the liquid 

release rate as the release rate to air. 

April 15, 1999 7 - 14 
8 ESTIMATION OF DISTANCE TO THE ENDPOINT FOR
 

ALTERNATIVE SCENARIOS FOR TOXIC SUBSTANCES
 

In Chapter 8 

� Reference tables of distances for alternative releases, including: 

-- Generic reference tables (Exhibit 4), and 

-- Chemical-specific reference tables (Exhibit 5). 

� Considerations include: 

-- Gas density (neutrally buoyant or dense), 

-- Duration of release (10 minutes or 60 minutes), 

-- Topography (rural or urban). 

For estimating consequence distances for alternative scenarios for toxic substances, this guidance 

provides four generic reference tables for neutrally buoyant gases and vapors and four for dense gases. The 

generic reference tables of distances (Reference Tables 14-21) are found at the end of Chapter 10. The 

generic tables and the conditions for which each table is applicable are described in Exhibit 4. Four chemicalspecific tables also are provided for ammonia, chlorine, and sulfur dioxide. The chemical-specific reference 

tables follow the generic reference tables at the end of Chapter 10. These tables, and the applicable 

conditions, are described in Exhibit 5. 

All the reference tables of distances for alternative scenarios were developed assuming D stability 

and a wind speed of 3.0 meters per second (6.7 miles per hour) as representative of likely conditions for many 

sites. Many wind speed and atmospheric stability combinations may be possible at different times in 

different parts of the country. If D stability and 3.0 meters per second are not reasonable conditions for your 

site, you may want to use other methods to estimate distances. 

For simplicity, this guidance assumes ground level releases. This guidance, therefore, may 

overestimate the consequence distance if your alternative scenario involves a release above ground level, 

particularly for neutrally buoyant gases and vapors. If you want to assume an elevated release, you may want 

to consider other methods to determine the consequence distance. 

The generic reference tables should be used for all toxic substances other than ammonia, chlorine, 

and sulfur dioxide. To use the generic reference tables, you need to consider the release rates estimated for 

gases and evaporation from liquid pools and the duration of the release. For the alternative scenarios, the 

duration of toxic gas releases may be longer than the 10 minutes assumed for the worst-case analysis for 

gases. You need to determine the appropriate toxic endpoint and whether the gas or vapor is neutrally 

buoyant or dense, using the tables in Appendix B and considering the conditions of the release. You may 

interpolate between entries in the reference tables. 

April 15, 1999 
Chapter 8 

Estimation of Distance to the Endpoint for Alternative Scenarios for Toxic Substances 

Exhibit 4
 

Generic Reference Tables of Distances for Alternative Scenarios
 

Applicable Conditions Reference Table 

Number 

Gas or Vapor Density Topography Release Duration 

(minutes) 

Neutrally buoyant Rural 10 14 

60 15 

Urban 10 16 

60 17 

Dense Rural 10 18 

60 19 

Urban 10 20 

60 21 

Exhibit 5
 

Chemical-Specific Reference Tables of Distances for Alternative Scenarios
 

Substance 

Conditions of Release 

Table 

Reference 

Gas or Vapor Number 

Density 

Release Duration 

(minutes) 

Topography 

Anhydrous ammonia 

liquefied under pressure 

Dense 10-60 Rural, urban 22 

Non-liquefied ammonia, 

ammonia liquefied by 

refrigeration, or aqueous 

ammonia 

Neutrally buoyant 10-60 Rural, urban 23 

Chlorine Dense 10-60 Rural, urban 24 

Sulfur dioxide (anhydrous) Dense 10-60 Rural, urban 25 

April 15, 1999 8 - 2 
Chapter 8 

Estimation of Distance to the Endpoint for Alternative Scenarios for Toxic Substances 

Note the following concerning the use of the chemical-specific reference tables for ammonia, 

chlorine, and sulfur dioxide: 

The table for anhydrous ammonia (Reference Table 22) applies only to flashing releases of 

ammonia liquefied under pressure. Use Table 23 for release of ammonia as a gas (e.g., 

evaporation from a pool or release from the vapor space of a tank). 

�

� You may use these tables for releases of any duration. 

To use the reference tables of distances, follow these steps: 

For Regulated Toxic Substances Other than Ammonia, Chlorine, and Sulfur Dioxide 

Find the toxic endpoint for the substance in Appendix B (Exhibit B-1 for toxic gases or 

Exhibit B-2 for toxic liquids). 

�

Determine whether the table for neutrally buoyant or dense gases and vapors is appropriate 

from Appendix B (Exhibit B-1 for toxic gases or Exhibit B-2, column for alternative case, 

for toxic liquids). A toxic gas that is lighter than air may behave as a dense gas upon release 

if it is liquefied under pressure, because the released gas may be mixed with liquid droplets, 

or if it is cold. Consider the state of the released gas when you decide which table is 

appropriate. 

�

� Determine whether the table for rural or urban conditions is appropriate. 

-- Use the rural table if your site is in an open area with few obstructions. 

-- Use the urban table if your site is in an urban or obstructed area. 

� Determine whether the 10-minute table or the 60-minute table is appropriate. 

-- Use the 10-minute table for releases from evaporating pools of common water 

solutions and of oleum. 

-- If you estimated the release duration for gas release or pool evaporation to be 10 

minutes or less, use the 10-minute table. 

-- If you estimated the release duration for gas release or pool evaporation to be more 

than 10 minutes, use the 60-minute table. 

Neutrally Buoyant Gases or Vapors 

If Exhibit B-1 or B-2 indicates the gas or vapor should be considered neutrally buoyant, and 

other factors would not cause the gas or vapor to behave as a dense gas, divide the estimated 

release rate (pounds per minute) by the toxic endpoint (milligrams per liter). 

�

April 15, 1999 8 - 3 
Chapter 8 

Estimation of Distance to the Endpoint for Alternative Scenarios for Toxic Substances 

Find the range of release rate/toxic endpoint values that includes your calculated release 

rate/toxic endpoint in the first column of the appropriate table (Reference Table 14, 15, 16, 

or 17), then find the corresponding distance to the right. 

�

Dense Gases or Vapors 

If Exhibit B-1 or B-2 or consideration of other relevant factors indicates the substance 

should be considered a dense gas or vapor (heavier than air), find the distance in the 

appropriate table (Reference Table 18, 19, 20, or 21) as follows; 

�

-- Find the toxic endpoint closest to that of the substance by reading across the top of 

the table. If the endpoint of the substance is halfway between two values on the 

table, choose the value on the table that is smaller (to the left). Otherwise, choose 

the closest value to the right or the left. 

-- Find the release rate closest to the release rate estimated for the substance at the left 

of the table. If the calculated release rate is halfway between two values on the 

table, choose the release rate that is larger (farther down on the table). Otherwise, 

choose the closest value (up or down on the table). 

-- Read across from the release rate and down from the endpoint to find the distance 

corresponding to the toxic endpoint and release rate for your substance. 

For Ammonia, Chlorine, or Sulfur Dioxide 

Find the appropriate chemical-specific table for your substance (see the descriptions of 

Reference Tables 22-25 in Exhibit 5). 

�

-- If you have ammonia liquefied by refrigeration alone, you may use Reference Table 

23, even if the duration of the release is greater than 10 minutes. 

-- If you have chlorine or sulfur dioxide liquefied by refrigeration alone, you may use 

the chemical-specific reference tables, even if the duration of the release is greater 

than 10 minutes. 

� Determine whether rural or urban topography is applicable to your site. 

-- Use the rural column in the reference table if your site is in an open area with few 

obstructions. 

-- Use the urban column if your site is in an urban or obstructed area. 

� Estimate the consequence distance as follows: 

-- In the left-hand column of the table, find the release rate closest to your calculated 

release rate. 

April 15, 1999 8 - 4 
Chapter 8 

Estimation of Distance to the Endpoint for Alternative Scenarios for Toxic Substances 

-- Read the corresponding distance from the appropriate column (urban or rural) to the 

right. 

The development of the generic reference tables is discussed in Appendix D, Sections D.4.1 and 

D.4.2. The development of the chemical-specific reference tables is discussed in industry-specific risk 

management program guidance documents and a backup information document that are cited in Section 

D.4.3. If you think the results of the method presented here overstate the potential consequences of a your 

alternative release scenario, you may choose to use other methods or models that take additional site-specific 

factors into account. 

Examples 24 and 25 below include the results of modeling using two other models, ALOHA and 

WHAZAN, for comparison with the results of the methods presented in this guidance. Appendix D, Section 

D.4.5 provides additional information on this modeling. 

Example 24. Gas Release of Chlorine 

Assume that you calculated a release rate of 500 pounds per minute of chlorine from a tank. A chemicalspecific table is provided for chlorine, so you do not need to consult Appendix B for information on chlorine. 

The topography of your site is urban. For a release of chlorine under average meteorology (D stability and 3 

meters per second wind speed), go to Reference Table 24. The estimated release rate of 500 pounds per 

minute, with urban topography, corresponds to a consequence distance of 0.4 miles. 

Additional Modeling for Comparison 

The ALOHA model gave a distance of 3.0 miles to the endpoint, using the same assumptions. 

The WHAZAN model gave a distance of 3.2 miles to the endpoint, using the same assumptions and the dense 

cloud dispersion model. 

April 15, 1999 8 - 5 
Chapter 8 

Estimation of Distance to the Endpoint for Alternative Scenarios for Toxic Substances 

Example 25. Allyl Alcohol Evaporating from Pool 

In Example 23, the evaporation rate of allyl alcohol from a pool was calculated as 63 pounds per minute. The total 

quantity in the pool was estimated as 9,830 pounds; therefore, the pool would evaporate in 9,830/63 or 156 

minutes. You would use a 60-minute reference table to estimate the distance to the endpoint. From Exhibit B-2 in 

Appendix B, the toxic endpoint for allyl alcohol is 0.036 mg/L, and the appropriate reference table for the 

alternative scenario analysis is a neutrally buoyant plume table. To find the distance from the neutrally buoyant 

plume tables, you need the release rate divided by the endpoint. In this case, it is 63/0.036, or 1,750. Assuming 

the release takes place in a rural location, you use Reference Table 15, applicable to neutrally buoyant plumes, 60-

minute releases, and rural conditions. From this table, you estimate the distance as 0.4 mile. 

Additional Modeling for Comparison 

The ALOHA model gave a distance of 0.7 mile to the endpoint for a release rate of 63 pounds per minute, using 

the same assumptions and the dense gas model. 

The WHAZAN model gave a distance of 0.5 mile to the endpoint for a release rate of 63 pounds per minute, using 

the same assumptions and the buoyant plume dispersion model. 

April 15, 1999 8 - 6 
9 ESTIMATION OF RELEASE RATES FOR ALTERNATIVE 

SCENARIOS FOR FLAMMABLE SUBSTANCES 

In Chapter 9 

�	 Methods to estimate a release rate to air for a flammable gas (9.1) or liquid 

(9.2). 

9.1	 Flammable Gases 

Gaseous Release from Tank or Pipe 

An alternative scenario for a release of a flammable gas may involve a leak from a vessel or piping. 

To estimate a release rate for flammable gases from hole size and storage conditions, you may use the method 

described above in Section 7.1.1 for toxic gases. This release rate may be used to determine the dispersion 

distance to the lower flammability limit (LFL), as described in Section 10.1. Exhibit C-2 in Appendix C 

includes Gas Factors (GF) that may be used in carrying out the calculations for each of the regulated 

flammable gases. 

Example 26. Release Rate of Flammable Gas from Hole in Tank (Ethylene) 

A pipe tears off a tank containing ethylene. The pipe is in the vapor space of the tank. The release rate from 

the hole can be estimated from Equation 7-1 in Section 7.1. You estimate that the pipe would leave a hole with 

an area (HA) of 5 square inches. The temperature inside the tank (T , absolute temperature, Kelvin) is 282 K, t 

9�C, and the square root of the temperature is 16.8. The pressure in the tank (P ) is approximately 728 pounds t 

per square inch absolute (psia). From Exhibit C-2, Appendix C, the gas factor (GF) for ethylene is 18. From 

Equation 7-1, the release rate (QR) is: 

QR = 5 × 728 × (1/16.8) × 18 = 3,900 pounds per minute 

Gases Liquefied Under Pressure 

A vapor cloud fire is a possible result of a release of a gas liquefied under pressure. You may use the 

methods described in Section 7.1.1 for toxic gases liquefied under pressure to estimate the release rate from a 

hole in a tank for a flammable gas liquefied under pressure. The estimated release rate may be used to 

estimate the dispersion distance to the LFL for a vapor cloud fire. 

Flammable gases that are liquefied under pressure may be released very rapidly, with partial 

vaporization of the liquefied gas and possible aerosol formation. Section 10.4 presents a method for 

estimating the consequences of a vapor cloud explosion from such a release of a gas liquefied under pressure. 

April 15, 1999 
Chapter 9 

Estimation of Release Rates for Alternative Scenarios for Flammable Substances 

Gases Liquefied by Refrigeration 

Flammable gases liquefied by refrigeration alone can be treated as liquids for the alternative scenario 

analysis, as discussed in Section 9.2 and Section 10.2, below. 

9.2 Flammable Liquids 

You may estimate a release rate for flammable liquids by estimating the evaporation rate from a 

pool. Release rates also can be estimated for flammable gases liquefied by refrigeration alone by this method, 

if the liquefied gas is likely to form a pool upon release. You first need to estimate the quantity in the pool. 

You may use the method discussed in Section 7.2.1 to estimate a rate of liquid release for flammable 

liquids into a pool from a hole in a tank or from a pipe shear. Exhibit C-3 in Appendix C includes liquid leak 

factors (LLF) for calculating release rate from a hole. Note that the LLF is appropriate only for atmospheric 

tanks. LLF values are not provided for liquefied flammable gases; you will need to estimate the quantity in 

the pool from other information for liquefied flammable gases. 

Once you have an estimate of the quantity of flammable liquid in a pool, you may use the methods 

presented in Section 7.2.3 to estimate the evaporation rate from the pool. Liquid factors at ambient and 

boiling temperature (LFA and LFB) for liquids for the calculation are listed in Exhibit C-3 in Appendix C, 

and LFBs for liquefied gases are listed in Exhibit C-2. Both passive and active mitigation measures 

(discussed in Sections 7.2.2 and 7.2.3) may be taken into account. You do not need to estimate the duration 

of the release, because this information is not used to estimate distance to the LFL, as discussed in the next 

chapter. 

As for toxic liquids, if the rate of evaporation of the liquid from the pool is greater than the rate of 

release of the liquid from the container, you should use the liquid release rate, not the pool evaporation rate, 

as the rate of release to the air. You should expect rapid evaporation rates for liquefied flammable gases 

from a pool. All of the regulated flammable liquids are volatile, so the evaporation rate from a pool may be 

expected to be relatively high, particularly without mitigation. 

April 15, 1999 9 - 2 
10 ESTIMATION OF DISTANCE TO THE ENDPOINT FOR 

ALTERNATIVE SCENARIOS FOR FLAMMABLE SUBSTANCES 

In Chapter 10 

� 10.1 Method to estimate the dispersion distance to the LFL for vapor cloud 

fires. 

� 10.2 Method to estimate the distance to the heat radiation endpoint for a pool 

fire involving a flammable liquid, based on the pool area and factors provided 

in the appendix. 

� 10.3 Method to estimate the distance to the heat radiation endpoint for a 

fireball from a BLEVE, using a reference table of distances. 

� 10.4 Alternative scenario analysis for vapor cloud explosions, using less 

conservative assumptions than for worst-case vapor cloud explosions. 

10.1 Vapor Cloud Fires 

The distance to the LFL represents the maximum distance at which the radiant heat effects of a vapor 

cloud fire might have serious consequences. Exhibit C-2, Appendix C, provides LCL data (in volume percent 

and milligrams per liter) for listed flammable gases; Exhibit C-3 provides these data for flammable liquids. 

This guidance provides reference tables for the alternative scenario conditions assumed in this guidance (D 

stability and wind speed 3.0 meters per second, ground level releases) for estimating the distance to the LCL. 

Release rate is the primary factor for determining distance to the flammable endpoint. Because the methods 

used in this guidance assumes that the vapor cloud release is in a steady state and that vapor cloud fires are 

nearly instantaneous events, release duration is not a critical factor for estimating vapor cloud fire distances. 

Thus, the reference tables for flammable substances are not broken out separately by release duration (e.g., 

10 minutes, 60 minutes). The development of these tables is discussed further in Appendix D, Section D.4. 

The reference tables for flammable substances (Reference Tables 26-29 at the end of Chapter 10) are listed in 

Exhibit 6. 

To use the reference tables of distances to find the distance to the LFL from the release rate, follow 

these steps: 

Find the LFL endpoint for the substance in Appendix C (Exhibit C-2 for flammable gases or 

Exhibit C-3 for flammable liquids). 

�

Determine from Appendix C whether the table for neutrally buoyant or dense gases and 

vapors is appropriate (Exhibit C-2 for flammable gases or Exhibit C-3 for flammable 

liquids). A gas that is lighter than air may behave as a dense gas upon release if it is 

liquefied under pressure, because the released gas may be mixed with liquid droplets, or if it 

is cold. Consider the state of the released gas when you decide which table is appropriate. 

�

April 15, 1999 
Chapter 10 

Estimation of Distance to the Endpoint for Alternative Scenarios for Flammable Substances 

Determine whether the table for rural or urban conditions is appropriate. 

-- Use the rural table if your site is in an open area with few obstructions. 

-- Use the urban table if your site is in an urban or obstructed area. 

�

Exhibit 6 

Reference Tables of Distances for Vapor Cloud Fires of Flammable Substances 

Applicable Conditions Reference Table 

Number 

Gas or Vapor Density Topography Release Duration 

(minutes) 

Neutrally buoyant Rural 10 - 60 26 

Urban 10 - 60 27 

Dense Rural 10 - 60 28 

Urban 10 - 60 29 

Neutrally Buoyant Gases or Vapors 

If Exhibit C-2 or C-3 indicates the gas or vapor should be considered neutrally buoyant, and 

other factors would not cause the gas or vapor to behave as a dense gas, divide the estimated 

release rate (pounds per minute) by the LFL endpoint (milligrams per liter). 

�

Find the range of release rate/LFL values that includes your calculated release rate/LFL in 

the first column of the appropriate table (Reference Table 26 or 27), then find the 

corresponding distance to the right. 

�

Dense Gases or Vapors 

If Exhibit C-2 or C-3 or consideration of other relevant factors indicates the substance 

should be considered a dense gas or vapor (heavier than air), find the distance in the 

appropriate table (Reference Table 28 or 29) as follows: 

�

-- Find the LFL closest to that of the substance by reading across the top of the table. 

If the LFL of the substance is halfway between two values on the table, choose the 

value on the table that is smaller (to the left). Otherwise, choose the closest value to 

the right or the left. 

-- Find the release rate closest to the release rate estimated for the substance at the left 

of the table. If the calculated release rate is halfway between two values on the 

April 15, 1999 10 - 2 
Chapter 10 

Estimation of Distance to the Endpoint for Alternative Scenarios for Flammable Substances 

table, choose the release rate that is larger (farther down on the table). Otherwise, 

choose the closest value (up or down on the table). 

-- Read across from the release rate and down from the LFL to find the distance 

corresponding to the LFL and release rate for your substance. 

Example 27. Flammable Gas Release (Ethylene) 

In Example 26, you estimated a release rate for ethylene from a hole in a tank of 3,900 pounds per minute. You 

want to estimate the distance to the LFL for a vapor cloud fire resulting from this release. 

From Exhibit C-2, Appendix C, the LFL for ethylene is 31 mg/L, and the appropriate table for distance 

estimation is a neutrally buoyant gas table for flammable substances. Your site is in a rural area, so you would 

use Reference Table 26. 

To use the neutrally buoyant gas tables, you need to calculate release rate/endpoint. In this case, release 

rate/LFL = 3,900/31 or 126. On Reference Table 26, 126 falls in the range of release rate/LFL values 

corresponding to 0.2 miles. 

April 15, 1999 10 - 3 
Chapter 10 

Estimation of Distance to the Endpoint for Alternative Scenarios for Flammable Substances 

Example 28. Vapor Cloud Fire from Evaporating Pool of Flammable Liquid 

You have a tank containing 20,000 pounds of ethyl ether. A likely scenario for a release might be shearing of a 

pipe from the tank, with the released liquid forming a pool. You want to estimate the consequences of a vapor 

cloud fire that might result from evaporation of the pool and ignition of the vapor. 

You first need to estimate the rate of release of the liquid from the tank. You can do this using Equation 7-4, 

Section 7.2.1. For this calculation, you need the area of the hole that would result from shearing the pipe (HA), 

the height of the liquid in the tank above the hole (LH), and the liquid leak factor (LLF) for ethyl ether, from 

Exhibit C-3 in Appendix C. The pipe diameter is 2 inches, so the cross sectional area of the hole would be 3.1 

square inches. You estimate that the pipe is 2 feet, or 24 inches, below the level of the liquid when the tank is 

full. The square root of LH (24 inches) is 4.9. LLF for ethyl ether is 34. From Equation 7-4, the rate of release 

of the liquid from the hole is calculated as: 

QRL	 = 3.1 × 4.9 × 34 

= 520 pounds per minute 

You estimate that the release of the liquid could be stopped in about 10 minutes. In 10 minutes, 10 × 520, or 

5,200 pounds, would be released. 

The liquid would be released into an area without dikes. To estimate the evaporation rate from the pool formed 

by the released liquid, you use Equation 7-8 from Section 7.2.3. To carry out the calculation, you need the 

Liquid Factor Ambient (LFA) and the Density Factor (DF) for ethyl ether. From Exhibit C-3, Appendix C, 

LFA for ethyl ether is 0.11 and DF is 0.69. The release rate to air is: 

QR	 = 5,200 × 2.4 × 0.11 × 0.69 

= 950 pounds per minute 

The evaporation rate from the pool is greater than the estimated liquid release rate; therefore, you use the liquid 

release rate of 520 pounds per minute as the release rate to air. To estimate the maximum distance at which 

people in the area of the vapor cloud could suffer serious injury, estimate the distance to the lower flammability 

limit (LFL) (in milligrams per liter) for ethyl ether, from the appropriate reference table. From Exhibit C-3, 

Appendix C, LFL for ethyl ether is 57 mg/L, and the appropriate reference table is a dense gas table. Your site 

is in a rural area with few obstructions, so you use Reference Table 28. 

From Reference Table 28, the closest LFL is 60 mg/L. The lowest release rate on the table is 1,500 pounds per 

minute, which is higher than the evaporation rate estimated for the pool of ethyl ether. For a release rate less 

than 1,500 pounds per minute, the distance to the LFL is less than 0.1 miles. 

April 15, 1999	 10 - 4 
Chapter 10 

Estimation of Distance to the Endpoint for Alternative Scenarios for Flammable Substances 

10.2 Pool Fires 

Pool fires may be considered as potential alternative scenarios for flammable liquids, including gases 

liquefied by refrigeration alone. You may find, however, that other scenarios will give a greater distance to 

the endpoint and, therefore, may be more appropriate as alternative scenarios. A "Pool Fire Factor" (PFF) 

has been derived for each of the regulated flammable liquids and most of the flammable gases to aid in the 

consequence analysis. The derivation of these factors is discussed in Appendix D, Section D.9. The PFF, 

listed in Appendix C, Exhibit C-2 for flammable gases and C-3 for flammable liquids, may be used to 

estimate a distance from the center of a pool fire where people could potentially receive second degree burns 

from a 40-second exposure. The heat radiation endpoint for this analysis is 5 kilowatts per square meter 2 o o (kW/m ). Ambient temperature is assumed to be 25 C (77 F) for calculation of the PFF for flammable 

liquids. 

To estimate a distance using the PFF, you first need to estimate the size of the pool, in square feet, 

that might be formed by the release of a flammable substance. You may use the methods described above for 

toxic liquids to estimate pool size. Density factors (DF) for the estimation of pool size in undiked areas may 

be found for flammable gases and flammable liquids in Exhibits C-2 and C-3 of Appendix C. For flammable 

gases, the DF is based on the density at the boiling point. You may want to consider whether the released 

substance may evaporate too quickly to form a pool of the maximum size, particularly for liquefied gases. 

Distances may be estimated from the PFF and the pool area as follows: 

d � PFF × A (10-1) 

where: d = Distance (feet) 

PFF = Pool Fire Factor (listed for each flammable substance in Appendix C, 

Exhibits C-2 and C-3) 

A = Pool area (square feet) 

April 15, 1999 10 - 5 
Chapter 10 

Estimation of Distance to the Endpoint for Alternative Scenarios for Flammable Substances 

Example 29. Pool Fire of Flammable Liquid 

For a tank containing 20,000 pounds of ethyl ether, you want to estimate the consequences of a pool fire. You 

estimate that 15,000 pounds would be released into an area without dikes, forming a pool. Assuming the liquid 

spreads to a depth of 1 centimeter (0.39 inches), you estimate the area of the pool formed from Equation 3-6, 

Section 3.2.3. For this calculation, you need the density factor (DF) for ethyl ether; from Exhibit C-3, 

Appendix C, DF for ethyl ether is 0.69. From Equation 3-6, the area of the pool is: 

A = 15,000 × 0.69 = 10,400 square feet 

You can use Equation 10-1 to estimate the distance from the center of the burning pool where the heat radiation 

level would reach 5 kW/m . 2 For the calculation, you need the square root of the pool area (A) and the pool fire 

factor (PFF) for ethyl ether. The square root of A, 10,400 square feet, is 102 feet. From Exhibit C-3, 2 Appendix C, PFF for ethyl ether is 4.3. From Equation 10-1, the distance (d) to 5 kW/m is: 

d = 4.3 × 102 = 440 feet (about 0.08 miles) 

If you have a gas that is liquefied under pressure or under a combination of pressure and 

refrigeration, a pool fire is probably not an appropriate alternative scenario. A fire or explosion involving the 

flammable gas that is released to the air by a sudden release of pressure is likely to have the potential for 

serious effects at a greater distance than a pool fire (e.g., see the methods for analysis of BLEVEs and vapor 

cloud explosions in Sections 10.3 and 10.4 below, or see Appendix A for references that provide more 

information on consequence analysis for fires and explosions). 

10.3 BLEVEs 

If a fireball from a BLEVE is a potential release scenario at your site, you may use Reference Table 

30 to estimate the distance to a potentially harmful radiant heat level. The table shows distances for a range 

of quantities to the radiant heat level that potentially could cause second degree burns to a person exposed for 

the duration of the fire. The quantity you use should be the total quantity in a tank that might be involved in a 

BLEVE. The equations used to derive this table of distances are presented in Appendix D, Section D.10. If 

you prefer, you may use the equations to estimate a distance for BLEVEs, or you may use a different 

calculation method or model. 

10.4 Vapor Cloud Explosion 

If you have the potential at your site for the rapid release of a large quantity of a flammable vapor, 

particularly into a congested area, a vapor cloud explosion may be an appropriate alternative release scenario. 

For the consequence analysis, you may use the same methods as for the worst case to estimate consequence 

distances to an overpressure endpoint of 1 psi (see Section 5.1 and the equation in Appendix C). Instead of 

assuming the total quantity of flammable substance released is in the vapor cloud, you may estimate a smaller 

April 15, 1999 10 - 6 
Chapter 10 

Estimation of Distance to the Endpoint for Alternative Scenarios for Flammable Substances 

quantity in the cloud. You could base your estimate of the quantity in the cloud on the release rate estimated 

as described above for gases and liquids multiplied by the time required to stop the release. 

To estimate the quantity in the cloud for a gas liquefied under pressure (not refrigerated), you may 

use the equation below. This equation incorporates a "flash fraction factor" (FFF), listed in Appendix C, 

Exhibit C-2 for regulated flammable gases, to estimate the quantity that could be immediately flashed into 

vapor upon release. A factor of two is included to estimate the quantity that might be carried along as spray 

or aerosol. See Appendix D, Section D.11 for the derivation of this equation. The equation is: 

QF � FFF × QS ×2 (10-2) 

where: QF = Quantity flashed into vapor plus aerosol (pounds) (cannot be larger than 

QS) 

FFF = Flash fraction factor (unitless) (listed in Appendix C, Exhibit C-2) (must be 

less than 1) 

QS = Quantity spilled (pounds) 

2 = Factor to account for spray and aerosol 

o o For derivation of the FFF, the temperature of the stored gas was assumed to be 25 C (77 F) (except 

as noted in Exhibit C-2). You may estimate the flash fraction under other conditions using the equation 

presented in Appendix D, Section D.11. 

You may estimate the distance to 1 psi for a vapor cloud explosion from the quantity in the cloud 

using Reference Table 13 (at the end of the worst-case analysis discussion) or from Equation C-1 in 

Appendix C. For the alternative scenario analysis, you may use a yield factor of 3 percent, instead of the 

yield factor of 10 percent used in the worst-case analysis. As discussed in Appendix D, Section D.11, the 

yield factor of 3 percent is representative of more likely events, based on data from past vapor cloud 

explosions. If you use the equation in Appendix C, use 0.03 instead of 0.1 in the calculation. If you use 

Reference Table 13, you can incorporate the lower yield factor by multiplying the distance you read from 

Reference Table 13 by 0.67. 

April 15, 1999 10 - 7 
Chapter 10 

Estimation of Distance to the Endpoint for Alternative Scenarios for Flammable Substances 

Example 30. Vapor Cloud Explosion (Propane) 

You have a tank containing 50,000 pounds of propane liquefied under pressure at ambient temperature. You 

want to estimate the consequence distance for a vapor cloud explosion resulting from rupture of the tank. 

You use Equation 10-2 to estimate the quantity that might be released to form a cloud. You base the 

calculation on the entire contents of the tank (QS = 50,000 pounds). From Exhibit C-2 of Appendix C, the 

Flash Fraction Factor (FFF) for propane is 0.38. From Equation 10-2, the quantity flashed into vapor, plus the 

quantity that might be carried along as aerosol, (QF) is: 

QF = 0.38 × 50,000 × 2 = 38,000 pounds 

You assume 38,000 pounds of propane is in the flammable part of the vapor cloud. This quantity falls between 

20,000 pounds and 50,000 pounds in Reference Table 13; 50,000 pounds is the quantity closest to your 

quantity. From the table, the distance to 1 psi overpressure is 0.3 mile for 50,000 pounds of propane for a 10 

percent yield factor. To change the yield factor to 3 percent, you multiply this distance by 0.67; then the 

distance becomes 0.2 mile. 

April 15, 1999 10 - 8 
Reference Table 14 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint 

10-Minute Release, Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

0 - 64 0.1 

64 - 510 0.2 

510 - 1,300 0.3 

1,300 - 2,300 0.4 

2,300 - 4,100 0.6 

4,100 - 6,300 0.8 

6,300 - 8,800 1.0 

8,800 - 12,000 1.2 

12,000 - 16,000 1.4 

16,000 - 19,000 1.6 

19,000 - 22,000 1.8 

22,000 - 26,000 2.0 

26,000 - 30,000 2.2 

30,000 - 36,000 2.4 

36,000 - 42,000 2.6 

42,000 - 47,000 2.8 

47,000 - 54,000 3.0 

54,000 - 60,000 3.2 

60,000 - 70,000 3.4 

70,000 - 78,000 3.6 

78,000 - 87,000 3.8 

87,000 - 97,000 4.0 

97,000 - 110,000 4.2 

110,000 - 120,000 4.4 

120,000 - 130,000 4.6 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

130,000 - 140,000 4.8 

140,000 - 160,000 5.0 

160,000 - 180,000 5.2 

180,000 - 190,000 5.4 

190,000 - 210,000 5.6 

210,000 - 220,000 5.8 

220,000 - 240,000 6.0 

240,000 - 261,000 6.2 

261,000 - 325,000 6.8 

325,000 - 397,000 7.5 

397,000 - 477,000 8.1 

477,000 - 566,000 8.7 

566,000 - 663,000 9.3 

663,000 - 769,000 9.9 

769,000 - 1,010,000 11 

1,010,000 - 1,280,000 12 

1,280,000 - 1,600,000 14 

1,600,000 - 1,950,000 15 

1,950,000 - 2,340,000 16 

2,340,000 - 2,770,000 17 

2,770,000 - 3,240,000 19 

3,240,000 - 4,590,000 22 

4,590,000 - 6,190,000 25 

>6,190,000 >25* 

 *Report distance as 25 miles 

April 15, 1999 10 - 9 
Reference Table 15 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint 

60-Minute Release, Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

0 - 79 0.1 

79 - 630 0.2 

630 - 1,600 0.3 

1,600 - 2,800 0.4 

2,800 - 5,200 0.6 

5,200 - 7,900 0.8 

7,900 - 11,000 1.0 

11,000 - 14,000 1.2 

14,000 - 19,000 1.4 

19,000 - 23,000 1.6 

23,000 - 27,000 1.8 

27,000 - 32,000 2.0 

32,000 - 36,000 2.2 

36,000 - 42,000 2.4 

42,000 - 47,000 2.6 

47,000 - 52,000 2.8 

52,000 - 57,000 3.0 

57,000 - 61,000 3.2 

61,000 - 68,000 3.4 

68,000 - 73,000 3.6 

73,000 - 79,000 3.8 

79,000 - 84,000 4.0 

84,000 - 91,000 4.2 

91,000 - 97,000 4.4 

97,000 - 100,000 4.6 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

100,000 - 108,000 4.8 

108,000 - 113,000 5.0 

113,000 - 120,000 5.2 

120,000 - 126,000 5.4 

126,000 - 132,000 5.6 

132,000 - 140,000 5.8 

140,000 - 150,000 6.0 

150,000 - 151,000 6.2 

151,000 - 171,000 6.8 

171,000 - 191,000 7.5 

191,000 - 212,000 8.1 

212,000 - 233,000 8.7 

233,000 - 256,000 9.3 

256,000 - 280,000 9.9 

280,000 - 332,000 11 

332,000 - 390,000 12 

390,000 - 456,000 14 

456,000 - 529,000 15 

529,000 - 610,000 16 

610,000 - 699,000 17 

699,000 - 796,000 19 

796,000 - 1,080,000 22 

1,080,000 - 1,410,000 25 

>1,410,000 >25* 

 *Report distance as 25 miles 

April 15, 1999 10 - 10 
Reference Table 16 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint 

10-Minute Release, Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to Endpoint 

(miles) 

0 - 160 0.1 

160 - 1,400 0.2 

1,400 - 3,600 0.3 

3,600 - 6,900 0.4 

6,900 - 13,000 0.6 

13,000 - 22,000 0.8 

22,000 - 31,000 1.0 

31,000 - 42,000 1.2 

42,000 - 59,000 1.4 

59,000 - 73,000 1.6 

73,000 - 88,000 1.8 

88,000 - 100,000 2.0 

100,000 - 120,000 2.2 

120,000 - 150,000 2.4 

150,000 - 170,000 2.6 

170,000 - 200,000 2.8 

200,000 - 230,000 3.0 

230,000 - 260,000 3.2 

260,000 - 310,000 3.4 

310,000 - 340,000 3.6 

340,000 - 390,000 3.8 

390,000 - 430,000 4.0 

430,000 - 490,000 4.2 

490,000 - 540,000 4.4 

540,000 - 600,000 4.6 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

600,000 - 660,000 4.8 

660,000 - 720,000 5.0 

720,000 - 810,000 5.2 

810,000 - 880,000 5.4 

880,000 - 950,000 5.6 

950,000 - 1,000,000 5.8 

1,000,000 - 1,100,000 6.0 

1,100,000 - 1,220,000 6.2 

1,220,000 - 1,530,000 6.8 

1,530,000 - 1,880,000 7.5 

1,880,000 - 2,280,000 8.1 

2,280,000 - 2,710,000 8.7 

2,710,000 - 3,200,000 9.3 

3,200,000 - 3,730,000 9.9 

3,730,000 - 4,920,000 11 

4,920,000 - 6,310,000 12 

6,310,000 - 7,890,000 14 

7,890,000 - 9,660,000 15 

9,660,000 - 11,600,000 16 

11,600,000 - 13,800,000 17 

13,800,000 - 16,200,000 19 

16,200,000 - 23,100,000 22 

23,100,000 - 31,300,000 25 

>31,300,000 >25* 

 *Report distance as 25 miles 

April 15, 1999 10 - 11 
Reference Table 17 

Neutrally Buoyant Plume Distances to Toxic Endpoint for Release Rate Divided by Endpoint 

60-Minute Release, Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

0 - 200 0.1 

200 - 1,700 0.2 

1,700 - 4,500 0.3 

4,500 - 8,600 0.4 

8,600 - 17,000 0.6 

17,000 - 27,000 0.8 

27,000 - 39,000 1.0 

39,000 - 53,000 1.2 

53,000 - 73,000 1.4 

73,000 - 90,000 1.6 

90,000 - 110,000 1.8 

110,000 - 130,000 2.0 

130,000 - 150,000 2.2 

150,000 - 170,000 2.4 

170,000 - 200,000 2.6 

200,000 - 220,000 2.8 

220,000 - 240,000 3.0 

240,000 - 270,000 3.2 

270,000 - 300,000 3.4 

300,000 - 320,000 3.6 

320,000 - 350,000 3.8 

350,000 - 370,000 4.0 

370,000 - 410,000 4.2 

410,000 - 430,000 4.4 

430,000 - 460,000 4.6 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

460,000 - 490,000 4.8 

490,000 - 520,000 5.0 

520,000 - 550,000 5.2 

550,000 - 580,000 5.4 

580,000 - 610,000 5.6 

610,000 - 640,000 5.8 

640,000 - 680,000 6.0 

680,000 - 705,000 6.2 

705,000 - 804,000 6.8 

804,000 - 905,000 7.5 

905,000 - 1,010,000 8.1 

1,010,000 - 1,120,000 8.7 

1,120,000 - 1,230,000 9.3 

1,230,000 - 1,350,000 9.9 

1,350,000 - 1,620,000 11 

1,620,000 - 1,920,000 12 

1,920,000 - 2,250,000 14 

2,250,000 - 2,620,000 15 

2,620,000 - 3,030,000 16 

3,030,000 - 3,490,000 17 

3,490,000 - 3,980,000 19 

3,980,000 - 5,410,000 22 

5,410,000 - 7,120,000 25 

>7,120,000 >25* 

 *Report distance as 25 miles 

April 15, 1999 10 - 12 
Reference Table 18

Dense Gas Distances to Toxic Endpoint

10-minute Release, Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second

Release 

Rate 

Toxic Endpoint (mg/L) 

0.0004 0.0007 0.001 0.002 0.0035 0.005 0.0075 0.01 0.02 0.035 0.05 0.075 0.1 

(lbs/min) Distance (Miles) 

1 0.6 0.4 0.4 0.2 0.2 0.1 0.1 0.1 <0.1 <0.1 # # # 

2 0.9 0.6 0.5 0.4 0.3 0.2 0.2 0.1 0.1 0.1 <0.1 <0.1 # 

5 1.4 1.1 0.9 0.6 0.4 0.4 0.3 0.2 0.2 0.1 0.1 0.1 <0.1 

10 2.0 1.5 1.2 0.9 0.6 0.5 0.4 0.4 0.2 0.2 0.1 0.1 0.1 

30 3.7 2.7 2.2 1.5 1.1 0.9 0.7 0.7 0.5 0.3 0.3 0.2 0.2 

50 5.0 3.7 3.0 2.1 1.9 1.2 1.0 0.9 0.6 0.4 0.4 0.3 0.2 

100 7.4 5.3 4.3 3.0 2.3 1.7 1.4 1.2 0.9 0.6 0.6 0.4 0.4 

150 8.7 6.8 5.5 3.8 2.8 2.3 1.9 1.6 1.1 0.8 0.7 0.6 0.5 250 12 8.7 7.4 5.0 3.7 3.0 2.4 2.1 1.4 1.1 0.9 0.7 0.5 500 17 13 11 7.4 5.3 4.5 3.6 3.0 2.1 1.6 1.3 1.1 0.9 750 22 16 13 9.3 6.8 5.6 4.5 3.8 2.7 1.9 1.6 1.3 1.1 

1,000 >25 19 16 11 8.1 6.8 5.2 4.5 3.1 2.3 2.2 1.5 1.3 

1,500 * 23 19 13 9.9 8.1 6.8 5.6 3.9 2.9 2.4 1.9 1.6 

2,000 * >25 22 15 12 9.3 7.4 6.8 4.5 3.4 2.7 2.2 1.9 

2,500 * * 25 17 13 11 8.7 7.4 5.2 3.8 3.2 2.5 2.1 

3,000 * * >25 19 14 12 9.3 8.1 5.7 4.2 3.5 2.8 2.4 

4,000 * * * 22 17 14 11 9.3 6.8 4.9 4.1 3.3 2.8 

5,000 * * * >25 19 16 12 11 7.4 5.6 4.7 3.7 3.1 

7,500 * * * * 24 19 16 13 9.3 6.8 5.8 4.7 4.0 

10,000 * * * * >25 22 18 16 11 8.1 6.8 5.3 4.6 15,000 * * * * * >25 22 19 13 9.9 8.1 6.8 5.7 

20,000 * * * * * * >25 22 16 11 9.3 7.4 6.8 50,000 * * * * * * * >25 24 18 15 12 10 

75,000 * * * * * * * * >25 22 18 15 13 

100,000 * * * * * * * * * >25 21 17 14 

150,000 * * * * * * * * * * >25 20 17 

200,000 * * * * * * * * * * * 23 19 

* > 25 miles (report distance as 25 miles) # <0.1 mile (re

10 - 13 
Reference Table 19

Dense Gas Distances to Toxic Endpoint

60-minute Release, Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second

Release 

Rate 

Toxic Endpoint (mg/L) 

0.0004 0.0007 0.001 0.002 0.0035 0.005 0.0075 0.01 0.02 0.035 0.05 0.075 0.1 

(lbs/min) Distance (Miles) 

1 0.5 0.4 0.3 0.2 0.2 0.1 0.1 0.1 <0.1 # # # # 

2 0.8 0.6 0.5 0.3 0.2 0.2 0.2 0.1 0.1 <0.1 <0.1 <0.1 # 

5 1.6 1.0 0.8 0.5 0.4 0.3 0.2 0.2 0.2 0.1 0.1 0.1 <0.1 

10 2.0 1.4 1.2 0.8 0.6 0.5 0.4 0.3 0.2 0.2 0.1 0.1 0.1 

30 4.0 2.8 2.2 1.5 1.1 0.9 0.7 0.6 0.4 0.3 0.2 0.2 0.2 

50 5.5 3.9 3.1 2.1 1.5 1.2 1.0 0.8 0.6 0.4 0.3 0.3 0.2 

100 8.7 6.1 4.8 3.2 2.2 1.8 1.4 1.2 0.8 0.6 0.5 0.4 0.3 

150 12 8.1 6.2 4.1 2.9 2.3 1.8 1.6 1.1 0.7 0.6 0.5 0.4 250 17 11 8.7 5.6 4.0 3.2 2.5 2.1 1.4 1.1 0.9 0.7 0.6 

500 >25 19 14 9.3 6.2 5.0 3.9 3.3 2.2 1.6 1.3 1.0 0.9 750 * 25 19 12 8.7 6.8 5.1 4.2 2.8 2.0 1.6 1.3 1.1 

1,000 * >25 24 15 11 8.1 6.1 5.2 3.4 2.4 1.9 1.5 1.3 

1,500 * * >25 20 14 11 8.1 6.8 4.3 3.0 2.5 1.9 1.7 

2,000 * * * 24 17 13 9.9 8.1 5.2 3.7 2.9 2.3 1.9 2,500 * * * >25 19 15 12 9.3 6.0 4.3 3.4 2.7 2.2 

3,000 * * * * 22 17 13 11 6.8 4.8 3.8 3.0 2.5 

4,000 * * * * >25 21 16 14 8.7 5.8 4.7 3.6 3.0 

5,000 * * * * * 25 19 16 9.9 6.8 5.3 4.1 3.5 

7,500 * * * * * >25 25 20 13 9.3 6.8 5.4 4.5 

10,000 * * * * * * >25 25 16 11 8.7 6.8 5.4 15,000 * * * * * * * >25 21 14 11 8.7 7.4 20,000 * * * * * * * * 25 17 14 11 8.7 50,000 * * * * * * * * >25 >25 25 19 16 

75,000 * * * * * * * * * * >25 25 20 

100,000 * * * * * * * * * * * >25 24 

150,000 * * * * * * * * * * * * >25 

200,000 * * * * * * * * * * * * * 

* > 25 miles (report distance as 25 miles) # <0.1 mile (re

10 - 14 
Reference Table 20

Dense Gas Distances to Toxic Endpoint

10-minute Release, Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second

Release 

Rate 

Toxic Endpoint (mg/L) 

0.0004 0.0007 0.001 0.002 0.0035 0.005 0.0075 0.01 0.02 0.035 0.05 0.075 0.1 

(lbs/min) Distance (Miles) 

1 0.5 0.3 0.2 0.2 0.1 0.1 0.1 0.1 <0.1 # # # # 

2 0.7 0.5 0.4 0.3 0.2 0.2 0.1 0.1 0.1 <0.1 <0.1 # # 

5 1.1 0.8 0.6 0.5 0.3 0.3 0.2 0.2 0.1 0.1 0.1 <0.1 <0.1 

10 2.1 1.2 1.0 0.7 0.5 0.4 0.3 0.3 0.2 0.1 0.1 0.1 0.1 

30 3.0 2.2 1.9 1.2 0.9 0.8 0.6 0.6 0.4 0.3 0.2 0.2 0.1 

50 4.1 3.0 2.5 1.6 1.2 1.0 0.8 0.7 0.5 0.3 0.3 0.2 0.2 

100 5.8 4.3 3.5 2.7 1.8 1.4 1.2 1.0 0.7 0.6 0.4 0.4 0.3 

150 7.4 5.5 4.5 3.1 2.2 1.9 1.4 1.2 0.9 0.7 0.6 0.4 0.4 250 9.9 7.4 5.8 4.1 3.0 2.5 2.0 1.7 1.1 0.9 0.7 0.6 0.5 500 14 11 8.7 5.9 4.3 3.6 2.9 2.5 1.7 1.2 1.0 0.8 0.7 

750 17 13 11 7.4 5.5 4.5 3.6 3.1 2.1 1.6 1.2 1.0 0.9 

1,000 20 15 12 8.7 6.2 5.3 4.3 3.5 2.5 1.8 1.5 1.2 1.0 

1,500 >25 19 16 11 8.1 6.2 5.2 4.5 3.0 2.2 1.8 1.5 1.2 

2,000 * 22 18 12 9.3 7.4 6.2 5.2 3.7 2.7 2.2 1.7 1.4 

2,500 * 24 20 14 11 8.7 6.8 6.0 3.8 3.0 2.2 1.9 1.7 

3,000 * >25 22 16 11 9.3 7.4 6.8 4.5 3.3 2.7 2.1 1.9 

4,000 * * >25 18 14 11 8.7 7.4 5.3 4.0 3.2 2.6 2.1 

5,000 * * * 20 15 12 9.9 8.7 5.8 4.4 3.6 2.9 2.4 

7,500 * * * >25 19 16 12 11 7.4 5.5 4.5 3.6 3.0 

10,000 * * * * 22 18 14 12 8.7 6.2 5.2 4.2 3.6 

15,000 * * * * >25 22 18 16 11 8.1 6.8 5.2 4.4 20,000 * * * * * >25 20 18 12 9.3 7.4 6.0 5.2 

50,000 * * * * * * >25 >25 20 15 12 9.7 8.3 

75,000 * * * * * * * * 25 18 15 12 10 

100,000 * * * * * * * * >25 21 17 14 12 

150,000 * * * * * * * * * >25 21 17 14 

200,000 * * * * * * * * * * 24 19 16 

* > 25 miles (report distance as 25 miles) # <0.1 mile (re

10 - 15 
Reference Table 21

Dense Gas Distances to Toxic Endpoint

60-minute Release, Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second

Release 

Rate 

Toxic Endpoint (mg/L) 

0.0004 0.0007 0.001 0.002 0.0035 0.005 0.0075 0.01 0.02 0.035 0.05 0.075 0.1 

(lbs/min) Distance (Miles) 

1 0.4 0.3 0.2 0.2 0.1 0.1 0.1 <0.1 # # # # # 

2 0.7 0.5 0.4 0.2 0.2 0.2 0.1 0.1 <0.1 <0.1 # # # 

5 1.1 0.8 0.7 0.4 0.3 0.2 0.2 0.2 0.1 0.1 <0.1 <0.1 <0.1 

10 1.7 1.2 1.0 0.7 0.5 0.4 0.3 0.3 0.2 0.1 0.1 0.1 0.1 

30 3.3 2.4 1.9 1.3 0.9 0.7 0.6 0.5 0.3 0.2 0.2 0.2 0.1 

50 4.7 3.3 2.6 1.7 1.2 1.0 0.8 0.7 0.4 0.3 0.3 0.2 0.2 

100 7.4 5.2 4.1 2.7 1.9 1.5 1.2 1.0 0.7 0.5 0.4 0.3 0.3 

150 9.9 6.8 5.3 3.4 2.4 1.9 1.5 1.3 0.9 0.6 0.5 0.4 0.3 250 14 9.3 7.4 4.7 3.4 2.7 2.1 1.7 1.1 0.8 0.7 0.5 0.4 500 22 16 12 7.4 5.2 4.2 3.2 2.7 1.7 1.2 1.0 0.8 0.7 750 >25 20 16 9.9 6.8 5.4 4.2 3.5 2.2 1.6 1.3 1.0 0.9 

1,000 * 24 19 12 8.1 6.8 5.0 4.2 2.7 1.8 1.6 1.2 1.0 

1,500 * >25 >25 16 11 8.7 6.8 5.5 3.5 1.9 2.0 1.6 1.3 

2,000 * * * 19 14 11 8.1 6.8 4.2 3.0 2.2 1.9 1.6 2,500 * * * 23 16 12 9.3 7.4 4.9 3.4 2.7 2.1 1.7 

3,000 * * * >25 18 14 11 8.7 5.5 3.8 3.0 2.4 2.0 

4,000 * * * * 22 17 13 11 6.8 4.7 3.1 2.8 2.4 

5,000 * * * * >25 20 16 12 8.1 5.3 4.3 3.3 2.7 

7,500 * * * * * 25 20 17 11 6.8 5.6 4.3 3.5 

10,000 * * * * * >25 24 20 13 8.7 6.8 5.2 4.3 

15,000 * * * * * * >25 >25 17 11 8.7 6.8 5.6 20,000 * * * * * * * * 20 14 11 8.1 6.8 50,000 * * * * * * * * >25 >25 20 15 13 

75,000 * * * * * * * * * * >25 20 16 

100,000 * * * * * * * * * * * 24 20 

150,000 * * * * * * * * * * * >25 >25 

200,000 * * * * * * * * * * * * * 

* > 25 miles (report distance as 25 miles) # <0.1 mile (re

10 - 16 
Reference Table 22 

Distances to Toxic Endpoint for Anhydrous Ammonia Liquefied Under Pressure
 

D Stability, Wind Speed 3.0 Meters per Second
 

Release Rate 

(lbs/min) 

Distance to Endpoint (miles) 

Rural Urban 

<10 <0.1* 

<0.1* 

10 0.1 

15 0.1 

20 0.1 

30 0.1 

40 0.1 

50 0.1 

60 0.2 0.1 

70 0.2 0.1 

80 0.2 0.1 

90 0.2 0.1 

100 0.2 0.1 

150 0.2 0.1 

200 0.3 0.1 

250 0.3 0.1 

300 0.3 0.1 

400 0.4 0.2 

500 0.4 0.2 

600 0.5 0.2 

700 0.5 0.2 

750 0.5 0.2 

800 0.5 0.2 

Release Rate 

(lbs/min) 

Distance to Endpoint (miles) 

Rural Urban 

900 0.6 0.2 

1,000 0.6 0.2 

1,500 0.7 0.3 

2,000 0.8 0.3 

2,500 0.9 0.3 

3,000 1.0 0.4 

4,000 1.2 0.4 

5,000 1.3 0.5 

7,500 1.6 0.5 

10,000 1.8 0.6 

15,000 2.2 0.7 

20,000 2.5 0.8 

25,000 2.8 0.9 

30,000 3.1 1.0 

40,000 3.5 1.1 

50,000 3.9 1.2 

75,000 4.8 1.4 

100,000 5.4 1.6 

150,000 6.6 1.9 

200,000 7.6 2.1 

250,000 8.4 2.3 

* Report distance as 0.1 mile 

April 15, 1999 10 - 17 
Reference Table 23 

Distances to Toxic Endpoint for Non-liquefied Ammonia, Ammonia Liquefied by Refrigeration, or 

Aqueous Ammonia
 

D Stability, Wind Speed 3.0 Meters per Second
 

Release Rate 

(lbs/min) 

Distance to Endpoint (miles) 

Rural Urban 

<8 <0.1* 

<0.1* 

8 0.1 

10 0.1 

15 0.1 

20 0.1 

30 0.1 

40 0.1 

50 0.2 0.1 

60 0.2 0.1 

70 0.2 0.1 

80 0.2 0.1 

90 0.2 0.1 

100 0.2 0.1 

150 0.3 0.1 

200 0.3 0.1 

250 0.4 0.2 

300 0.4 0.2 

400 0.4 0.2 

500 0.5 0.2 

600 0.6 0.2 

700 0.6 0.2 

750 0.6 0.2 

Release Rate 

(lbs/min) 

Distance to Endpoint (miles) 

Rural Urban 

800 0.7 0.2 

900 0.7 0.3 

1,000 0.8 0.3 

1,500 1.0 0.4 

2,000 1.2 0.4 

2,500 1.2 0.4 

3,000 1.5 0.5 

4,000 1.8 0.6 

5,000 2.0 0.7 

7,500 2.2 0.7 

10,000 2.5 0.8 

15,000 3.1 1.0 

20,000 3.6 1.2 

25,000 4.1 1.3 

30,000 4.4 1.4 

40,000 5.1 1.6 

50,000 5.8 1.8 

75,000 7.1 2.2 

100,000 8.2 2.5 

150,000 10 3.1 

200,000 12 3.5 

* Report distance as 0.1 mile 

April 15, 1999 10 - 18 
Reference Table 24
 

Distances to Toxic Endpoint for Chlorine
 

D Stability, Wind Speed 3.0 Meters per Second
 

Release Rate 

(lbs/min) 

Distance to Endpoint (miles) 

Rural Urban 

1 <0.1* 

<0.1* 

2 0.1 

5 0.1 

10 0.2 0.1 

15 0.2 0.1 

20 0.2 0.1 

30 0.3 0.1 

40 0.3 0.1 

50 0.3 0.1 

60 0.4 0.2 

70 0.4 0.2 

80 0.4 0.2 

90 0.4 0.2 

100 0.5 0.2 

150 0.6 0.2 

200 0.6 0.3 

250 0.7 0.3 

300 0.8 0.3 

400 0.8 0.4 

500 1.0 0.4 

600 1.0 0.4 

700 1.1 0.4 

Release Rate 

(lbs/min) 

Distance to Endpoint (miles) 

Rural Urban 

750 1.2 0.4 

800 1.2 0.5 

900 1.2 0.5 

1,000 1.3 0.5 

1,500 1.6 0.6 

2,000 1.8 0.6 

2,500 2.0 0.7 

3,000 2.2 0.8 

4,000 2.5 0.8 

5,000 2.8 0.9 

7,500 3.4 1.2 

10,000 3.9 1.3 

15,000 4.6 1.6 

20,000 5.3 1.8 

25,000 5.9 2.0 

30,000 6.4 2.1 

40,000 7.3 2.4 

50,000 8.1 2.7 

75,000 9.8 3.2 

100,000 11 3.6 

150,000 13 4.2 

200,000 15 4.8 

* Report distance as 0.1 mile 

April 15, 1999 10 - 19 
Reference Table 25 

Distances to Toxic Endpoint for Sulfur Dioxide
 

D Stability, Wind Speed 3.0 Meters per Second
 

Release Rate 

(lbs/min) 

Distance to Endpoint (miles) 

Rural Urban 

1 <0.1* 

<0.1* 

2 0.1 

5 0.1 

10 0.2 0.1 

15 0.2 0.1 

20 0.2 0.1 

30 0.2 0.1 

40 0.3 0.1 

50 0.3 0.1 

60 0.4 0.2 

70 0.4 0.2 

80 0.4 0.2 

90 0.4 0.2 

100 0.5 0.2 

150 0.6 0.2 

200 0.6 0.2 

250 0.7 0.3 

300 0.8 0.3 

400 0.9 0.4 

500 1.0 0.4 

600 1.1 0.4 

700 1.2 0.4 

Release Rate 

(lbs/min) 

Distance to Endpoint (miles) 

Rural Urban 

750 1.3 0.5 

800 1.3 0.5 

900 1.4 0.5 

1,000 1.5 0.5 

1,500 1.9 0.6 

2,000 2.2 0.7 

2,500 2.3 0.8 

3,000 2.7 0.8 

4,000 3.1 1.0 

5,000 3.3 1.1 

7,500 4.0 1.3 

10,000 4.6 1.4 

15,000 5.6 1.7 

20,000 6.5 1.9 

25,000 7.3 2.1 

30,000 8.0 2.3 

40,000 9.2 2.6 

50,000 10 2.9 

75,000 13 3.5 

100,000 14 4.0 

150,000 18 4.7 

200,000 20 5.4 

* Report distance as 0.1 mile 

April 15, 1999 10 - 20 
Reference Table 26 

Neutrally Buoyant Plume Distances to Lower Flammability Limit (LFL)
 

For Release Rate Divided by LFL
 

Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second
 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

0 - 28 0.1 

28 - 40 0.1 

40 - 60 0.1 

60 - 220 0.2 

220 - 530 0.3 

530 - 860 0.4 

860 - 1,300 0.5 

1,300 - 1,700 0.6 

1,700 - 2,200 0.7 

2,200 - 2,700 0.8 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

2,700 - 3,300 0.9 

3,300 - 3,900 1.0 

3,900 - 4,500 1.1 

4,500 - 5,200 1.2 

5,200 - 5,800 1.3 

5,800 - 6,800 1.4 

6,800 - 8,200 1.6 

8,200 - 9,700 1.8 

9,700 - 11,000 2.0 

11,000 - 13,000 2.2 

Reference Table 27
 

Neutrally Buoyant Plume Distances to Lower Flammability Limit (LFL)
 

For Release Rate Divided by LFL
 

Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second
 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

0 - 68 0.1 

68 - 100 0.1 

100 - 150 0.1 

150 - 710 0.2 

710 - 1,500 0.3 

1,500 - 2,600 0.4 

2,600 - 4,000 0.5 

4,000 - 5,500 0.6 

Release Rate/Endpoint 

[(lbs/min)/(mg/L)] 

Distance to 

Endpoint 

(miles) 

5,500 - 7,300 0.7 

7,300 - 9,200 0.8 

9,200 - 11,000 0.9 

11,000 - 14,000 1.0 

14,000 - 18,000 1.2 

18,000 - 26,000 1.4 

26,000 - 31,000 1.6 

31,000 - 38,000 1.8 

April 15, 1999 10 - 21 
Reference Table 28

Dense Gas Distances to Lower Flammability Limit

Rural Conditions, D Stability, Wind Speed 3.0 Meters per Second

Release 

Rate 

(lbs/min) 

Lower Flammability Limit (mg/L) 

27 30 35 40 45 50 60 70 100 

Distance (Miles) 

<1,500 # # # # # # # # # 

1,500 <0.1 <0.1 # # # # # # # 

2,000 0.1 0.1 <0.1 # # # # # # 

2,500 0.1 0.1 0.1 <0.1 # # # # # 

3,000 0.1 0.1 0.1 0.1 <0.1 <0.1 # # # 4,000 0.1 0.1 0.1 0.1 0.1 0.1 <0.1 # # 5,000 0.1 0.1 0.1 0.1 0.1 0.1 0.1 <0.1 # 7,500 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 <0.

10,000 0.2 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 

# < 0.1 mile (report distance as 0.1 mile) 

April 15, 1999 10 - 22 
Reference Table 29
 

Dense Gas Distances to Lower Flammability Limit
 

Urban Conditions, D Stability, Wind Speed 3.0 Meters per Second
 

Release 

Rate 

(lbs/min) 

Lower Flammability Limit (mg/L) 

27 30 35 40 >40 

Distance (Miles) 

<5,000 # # # # # 

5,000 <0.1 <0.1 # # # 

7,500 0.1 0.1 <0.1 # # 

10,000 0.1 0.1 0.1 <0.1 # 

# < 0.1 mile (report distance as 0.1 mile) 

April 15, 1999 10 - 23 
Reference Table 30 

Distance to Radiant Heat Dose at Potential Second Degree Burn Threshold Assuming Exposure for Duration of Fir

(Dose = [5 kW/m ]2 4/3 x Exposure Time) 

Quantity in Fireball (pounds) 1,000 5,000 10,000 20,000 30,000 50,000 75,000 100,000 200,000 

Duration of Fireball (seconds) 3.5 5.9 7.5 9.4 10.8 12.7 14.8 15.5 17.4 

CAS No. Chemical Name Distance (miles) at which Exposure for Duration of Fireball May Cause Second Degree Bur

75-07-0 Acetaldehyde 0.04 0.08 0.1 0.1 0.2 0.2 0.3 0.3 0.4 74-86-2 Acetylene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

598-73-2 Bromotrifluoroethylene 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.1 

106-99-0 1,3-Butadiene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

106-97-8 Butane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

106-98-9 1-Butene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

107-01-7 2-Butene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

25167-67-3 Butene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

590-18-1 2-Butene-cis 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

624-64-6 2-Butene-trans 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

463-58-1 Carbon oxysulfide 0.02 0.05 0.06 0.09 0.1 0.1 0.2 0.2 0.2 

7791-21-1 Chlorine monoxide 0.01 0.02 0.02 0.03 0.03 0.04 0.05 0.06 0.08 

557-98-2 2-Chloropropylene 0.03 0.07 0.1 0.1 0.2 0.2 0.2 0.3 0.4 

590-21-6 1-Chloropropylene 0.03 0.07 0.1 0.1 0.2 0.2 0.2 0.3 0.4 460-19-5 Cyanogen 0.03 0.07 0.1 0.1 0.2 0.2 0.2 0.3 0.4 

75-19-4 Cyclopropane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

4109-96-0 Dichlorosilane 0.02 0.04 0.06 0.08 0.1 0.1 0.2 0.2 0.2 

75-37-6 Difluoroethane 0.02 0.05 0.07 0.1 0.1 0.1 0.2 0.2 0.3 

124-40-3 Dimethylamine 0.04 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.5 

463-82-1 2,2-Dimethylpropane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

74-84-0 Ethane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

107-00-6 Ethyl acetylene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

April 15, 1999 10 - 24 
Reference Table 30 (continued) 

Quantity in Fireball (pounds) 1,000 5,000 10,000 20,000 30,000 50,000 75,000 100,000 200,000 

Duration of Fireball (seconds) 3.5 5.9 7.5 9.4 10.8 12.7 14.8 15.5 17.4 

CAS No. Chemical Name Distance (miles) at which Exposure for Duration of Fireball May Cause Second Degree Bur

75-04-7 Ethylamine 0.04 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.5 

75-00-3 Ethyl chloride 0.03 0.07 0.09 0.1 0.2 0.2 0.2 0.3 0.3 74-85-1 Ethylene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

60-29-7 Ethyl ether 0.04 0.09 0.1 0.2 0.2 0.2 0.3 0.3 0.5 

75-08-1 Ethyl mercaptan 0.04 0.08 0.1 0.2 0.2 0.2 0.3 0.3 0.4 

109-95-5 Ethyl nitrite 0.03 0.06 0.09 0.1 0.1 0.2 0.2 0.3 0.3 

1333-74-0 Hydrogen 0.08 0.2 0.2 0.3 0.4 0.5 0.6 0.6 0.9 

75-28-5 Isobutane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 78-78-4 Isopentane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

78-79-5 Isoprene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

75-31-0 Isopropylamine 0.04 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.5 

75-29-6 Isopropyl chloride 0.04 0.07 0.1 0.1 0.2 0.2 0.3 0.3 0.4 

74-82-8 Methane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.6 

74-89-5 Methylamine 0.04 0.08 0.1 0.2 0.2 0.2 0.3 0.3 0.4 

563-45-1 3-Methyl-1-butene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 563-46-2 2-Methyl-1-butene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 115-10-6 Methyl ether 0.04 0.08 0.1 0.2 0.2 0.2 0.3 0.3 0.4 107-31-3 Methyl formate 0.03 0.06 0.08 0.1 0.1 0.2 0.2 0.2 0.3 115-11-7 2-Methylpropene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 504-60-9 1,3-Pentadiene 0.05 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.5 109-66-0 Pentane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

109-67-1 1-Pentene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 646-04-8 2-Pentene, (E)- 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

April 15, 1999 10 - 25 
Reference Table 30 (continued) 

Quantity in Fireball (pounds) 1,000 5,000 10,000 20,000 30,000 50,000 75,000 100,000 200,000 

Duration of Fireball (seconds) 3.5 5.9 7.5 9.4 10.8 12.7 14.8 15.5 17.4 

CAS No. Chemical Name Distance (miles) at which Exposure for Duration of Fireball May Cause Second Degree Bur

627-20-3 2-Pentene, (Z)- 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

463-49-0 Propadiene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

74-98-6 Propane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

115-07-1 Propylene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

74-99-7 Propyne 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

7803-62-5 Silane 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

116-14-3 Tetrafluoroethylene 0.01 0.02 0.02 0.03 0.04 0.05 0.06 0.07 0.09 

75-76-3 Tetramethylsilane 0.05 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.5 

10025-78-2 Trichlorosilane 0.01 0.03 0.04 0.06 0.07 0.08 0.1 0.1 0.2 

79-38-9 Trifluorochloroethylene 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.1 75-50-3 Trimethylamine 0.04 0.09 0.1 0.2 0.2 0.3 0.3 0.4 0.5 

689-97-4 Vinyl acetylene 0.05 0.1 0.1 0.2 0.2 0.3 0.4 0.4 0.5 

75-01-4 Vinyl chloride 0.03 0.07 0.09 0.1 0.2 0.2 0.2 0.3 0.3 

109-92-2 Vinyl ethyl ether 0.04 0.09 0.1 0.2 0.2 0.2 0.3 0.3 0.4 

75-02-5 Vinyl fluoride 0.01 0.02 0.03 0.04 0.05 0.06 0.08 0.09 0.1 

75-35-4 Vinylidene chloride 0.02 0.05 0.07 0.09 0.1 0.1 0.2 0.2 0.3 75-38-7 Vinylidene fluoride 0.02 0.05 0.07 0.09 0.1 0.1 0.2 0.2 0.3 

107-25-5 Vinyl methyl ether 0.04 0.08 0.1 0.2 0.2 0.2 0.3 0.3 0.4 

April 15, 1999 10 - 26 
11 ESTIMATING OFFSITE RECEPTORS
 

In Chapter 11 

� How to estimate the number of offsite receptors potentially affected by your 

worst-case and alternative scenarios. 

� Where to find the data you need. 

The rule requires that you estimate residential populations within the circle defined by the endpoint 

for your worst-case and alternative release scenarios. In addition, you must report in the RMP whether 

certain types of public receptors and environmental receptors are within the circles. 

To estimate residential populations, you may use the most recent Census data or any other source of 

data that you believe is more accurate. Local authorities may be able to provide information on offsite 

receptors. You are not required to update Census data or conduct any surveys to develop your estimates. 

Census data are available in public libraries and in the LandView system, which is available on CD-ROM 

(see box below). The rule requires that you estimate populations to two significant digits. For example, if 

there are 1,260 people within the circle, you may report 1,300 people. If the number of people is between 10 

and 100, estimate to the nearest 10. If the number of people is less than 10, provide the actual number. 

How to obtain Census data and LandView 

Census data can be found in publications of the Bureau of the Census, available in public libraries, including 

County and City Data Book. 

LandView ®III is a desktop mapping system that includes database extracts from EPA, the Bureau of the Census, 

the U.S. Geological Survey, the Nuclear Regulatory Commission, the Department of Transportation, and the 

Federal Emergency Management Agency. These databases are presented in a geographic context on maps that 

show jurisdictional boundaries, detailed networks of roads, rivers, and railroads, census block group and tract 

polygons, schools, hospitals, churches, cemeteries, airports, dams, and other landmark features. 

CD-ROM for IBM-compatible PCS 

CD-TGR95-LV3-KIT $99 per disc (by region) or $549 for 11 disc set 

U.S. Department of Commerce
 

Bureau of the Census
 

P.O. Box 277943
 

Atlanta, GA 30384-7943 
 

Phone: 301-457-4100 (Customer Services -- orders)
 

Fax: (888) 249-7295 (toll-free)
 

Fax: (301) 457-3842 (local)
 

Phone: (301) 457-1128 (Geography Staff -- content)
 

http://www.census.gov/ftp/pub/geo/www/tiger/
 

Further information on LandView and other sources of Census data is available at the Bureau of the Census web 

site at www.census.gov. 

April 15, 1999 
Chapter 11 

Estimating Offsite Receptors 

Census data are presented by Census tract. If your circle covers only a portion of the tract, you 

should develop an estimate for that portion. The easiest way to do this is to determine the population density 

per square mile (total population of the Census tract divided by the number of square miles in the tract) and 

apply that density figure to the number of square miles within your circle. Because there is likely to be 

considerable variation in actual densities within a Census tract, this number will be approximate. The rule, 

however, does not require you to correct the number. 

Other public receptors must be noted in the RMP. If there are any schools, residences, hospitals, 

prisons, public recreational areas, or commercial, office, or industrial areas within the circle, you must report 

that. Any of these locations inhabited or occupied by the public at any time without restriction by the source 

is a public receptor. You are not required to develop a list of all institutions and areas; you must simply 

check off which types of receptors are within the circle. Most of these institutions or areas can be identified 

from local street maps. Recreational areas include public swimming pools, public parks, and other areas that 

are used for recreational activities (e.g., baseball fields). Commercial and industrial areas include shopping 

malls, strip malls, downtown business areas, industrial parks, etc. See EPA’s General Guidance for Risk 

Management Programs (40 CFR part 68) for further information on identifying public receptors. 

Environmental receptors are defined as national or state parks, forests, or monuments; officially 

designated wildlife sanctuaries, preserves, or refuges; and Federal wilderness areas. All of these can be 

identified on local U.S. Geological Survey (USGS) maps (see box below). You are not required to locate 

each of these specifically. You are only required to check off in the RMP that these specific types of areas are 

within the circle. If any part of one of these receptors is within your circles, you must note that in the RMP. 

Important: The rule does not require you to assess the likelihood, type, or severity of potential 

impacts on either public or environmental receptors. Identifying them as within the circle simply indicates 

that they could be adversely affected by the release. 

April 15, 1999 11 - 2 
Chapter 11 

Estimating Offsite Receptors 

How to obtain USGS maps 

The production of digital cartographic data and graphic maps comprises the largest component of the USGS 

National Mapping Program. The USGS's most familiar product is the 1:24,000-scale Topographic Quadrangle 

Map. This is the primary scale of data produced, and depicts greater detail for a smaller area than 

intermediate-scale (1:50,000 and 1:100,000) and small-scale (1:250,000, 1:2,000,000 or smaller) products, which 

show selectively less detail for larger areas. 

U.S. Geological Survey 

508 National Center 

12201 Sunrise Valley Drive 

Reston, VA 20192 

Phone: (703) 648-4000 

http://mapping.usgs.gov 

To order USGS maps by fax, select, print, and complete one of the online forms and fax to 303-202-4693. 

A list of the nearest commercial dealers is available at: http://mapping.usgs.gov/esic/usimage/dealers.html 

For more information or ordering assistance, call 1-800-HELP-MAP, or write: 

USGS Information Services 

Box 25286 

Denver, CO 80225 

For additional information, contact any USGS Earth Science Information Center or call 1-800-USA-MAPS. 

April 15, 1999 11 - 3 
Chapter 11 

Estimating Offsite Receptors 

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April 15, 1999 11 - 4 
 

 

 

 

 

 

12 SUBMITTING OFFSITE CONSEQUENCE ANALYSIS 

INFORMATION FOR RISK MANAGEMENT PLAN 

In Chapter 12 

	 12.1 Information you are required to submit for worst-case scenarios for 

toxic substances. 

	 12.2 Information you are required to submit for alternative scenarios for 

toxic substances. 

	 12.3 Information you are required to submit for worst-case scenarios for 

flammable substances. 

	 12.4 Information you are required to submit for alternative scenarios for 

flammable substances. 

For the offsite consequence analysis (OCA) component of the RMP you must provide 

information on your worst-case and alternative release scenario(s) for toxic and flammable regulated 

chemicals held above the threshold quantity. The requirements for what information you must submit 

differ if your source has Program 1, Program 2, or Program 3 processes. 

If your source has Program 1 processes, you must submit information on a worst-case 

release scenario for each Program 1 process. If your source has Program 2 or Program 3 processes, 

you must provide information on one worst-case release for all toxic regulated substances present 

above the threshold quantity and one worst-case release scenario for all flammable regulated 

substances present above the threshold quantity. You may need to submit an additional worst-case 

scenario if a worst-case release from another part of the source would potentially affect public 

receptors different from those potentially affected by the initial worst-case scenario(s) for 

flammable and toxic regulated substances. 

In addition to a worst-case release scenario, sources with Program 2 and Program 3 

processes must also provide information on alternative release scenarios. Alternative releases are 

releases that could occur, other than the worst-case, that may result in concentrations, overpressures, 

or radiant heat that reach endpoints offsite. You must present information on one alternative release 

scenario for each regulated toxic substance, including the substance used for the worst-case release, 

held above the threshold quantity and one alternative release scenario to represent all flammable 

substances held above the threshold quantity. The types of documentation to submit are presented 

below for worst-case scenarios involving toxic substances, alternative scenarios involving toxic 

substances, worst-case scenarios involving flammable substances, and alternative scenarios involving 

flammable substances. 

12.1 RMP Data Required for Worst-Case Scenarios for Toxic Substances 

For worst-case scenarios involving toxic substances, you will have to submit the 

following information. See the RMP*eSubmit User Manual for complete instructions. 

•	 Chemical name; 

•	 Percentage weight of the regulated liquid toxic substance (if present in a mixture); 

March 2009 
Chapter 12 

Submitting Offsite Consequence Analysis Information for Risk Management Plan 

Physical state of the chemical released (gas, liquid, refrigerated gas, gas liquefied by 

pressure); 

�

Model used (OCA or industry-specific guidance reference tables or modeling; name of other 

model used); 

�

� Scenario (gas release or liquid spill and vaporization); 

� Quantity released (pounds); 

� Release rate (pounds per minute); 

Duration of release (minutes) (10 minutes for gases; if you used OCA guidance for liquids, 

indicate either 10 or 60 minutes); 

�

Wind speed (meters per second) and stability class (1.5 meters per second and F stability 

unless you can show higher minimum wind speed or less stable atmosphere at all times 

during the last three years); 

�

� Topography (rural or urban); 

� Distance to endpoint (miles, rounded to two significant digits); 

Population within distance to endpoint (residential population rounded to two significant 

digits); 

�

Public receptors within the distance to endpoint (schools, residences, hospitals, prisons, 

recreation areas, commercial, office or industrial areas); 

�

Environmental receptors within the distance to endpoint (national or state parks, forests, or 

monuments; officially designated wildlife sanctuaries, preserves, or refuges; Federal 

wilderness areas); and 

�

� Passive mitigation measures considered (dikes, enclosures, berms, drains, sumps, other). 

12.2 RMP Data Required for Alternative Scenarios for Toxic Substances 

For alternative scenarios involving toxic substances held above the threshold quantity in a Program 2 

or Program 3 process, you will have to submit the following information. See the Risk Management Plan 

Data Elements Guide for complete instructions. 

� Chemical name; 

� Percentage weight of the regulated liquid toxic substance (if present in a mixture); 

Physical state of the chemical released (gas, liquid, refrigerated gas, gas liquefied by 

pressure); 

�

Model used (OCA or industry-specific guidance reference tables or modeling; name of other 

model used); 

�

Scenario (transfer hose failure, pipe leak, vessel leak, overfilling, rupture disk/relief valve, 

excess flow valve, other); 

�

� Quantity released (pounds); 

� Release rate (pounds per minute); 

� Duration of release (minutes) (if you used OCA guidance, indicate either 10 or 60 minutes); 

Wind speed (meters per second) and stability class (3.0 meters per second and D stability if 

you use OCA guidance, otherwise use typical meteorological conditions at your site); 

�

� Topography (rural or urban); 

� Distance to endpoint (miles, rounded to two significant digits); 

Population within distance to endpoint (residential population rounded to two significant 

digits); 

�

April 12, 1999 12 - 2 
Chapter 12 

Submitting Offsite Consequence Analysis Information for Risk Management Plan 

Public receptors within the distance to endpoint (schools, residences, hospitals, prisons, 

recreation areas, commercial, office, or industrial areas); 

�

Environmental receptors within the distance to endpoint (national or state parks, forests, or 

monuments; officially designated wildlife sanctuaries, preserves, or refuges; Federal 

wilderness areas); 

�

� Passive mitigation measures considered (dikes, enclosures, berms, drains, sumps, other); and 

Active mitigation measures considered (sprinkler system, deluge system, water curtain, 

neutralization, excess flow valve, flares, scrubbers, emergency shutdown system, other). 

�

12.3 RMP Data Required for Worst-Case Scenarios for Flammable Substances 

For worst-case scenarios involving flammable substances, you will have to submit the following 

information. See the Risk Management Plan Data Elements Guide for complete instructions. 

� Chemical name; 

Model used (OCA or industry-specific guidance reference tables or modeling; name of other 

model used); 

�

� Scenario (vapor cloud explosion); 

� Quantity released (pounds); 

� Endpoint used (for vapor cloud explosions use 1 psi); 

� Distance to endpoint (miles, rounded to two significant digits); 

Population within distance to endpoint (residential population rounded to two significant 

digits); 

�

Public receptors within the distance to endpoint (schools, residences, hospitals, prisons, 

recreation areas, commercial, office, or industrial areas); 

�

Environmental receptors within the distance to endpoint (national or state parks, forests, or 

monuments, officially designated wildlife sanctuaries, preserves, or refuges, Federal 

wilderness areas); and 

�

� Passive mitigation measures considered (blast walls, other). 

12.4 RMP Data Required for Alternative Scenarios for Flammable Substances 

For alternative scenarios involving flammable substances held above the threshold quantity in a 

Program 2 or Program 3 process, you will have to submit the following information. See the Risk 

Management Plan Data Elements Guide for complete instructions. 

� Chemical name; 

Model used (OCA or industry-specific guidance reference tables or modeling; name of other 

model used); 

�

� Scenario (vapor cloud explosion, fireball, BLEVE, pool fire, jet fire, vapor cloud fire, other); 

� Quantity released (pounds); 

Endpoint used (for vapor cloud explosions, the endpoint is 1 psi overpressure; for a fireball 

the endpoint is 5 kw/m2 for 40 seconds. A lower flammability limit (expressed as a 

percentage) may be listed as specified in NFPA documents or other generally recognized 

sources; these are listed in the OCA Guidance); 

�

� Distance to endpoint (miles, rounded to two significant digits); 

April 12, 1999 12 - 3 
 

 

 

 

 

 

Chapter 12 

Submitting Offsite Consequence Analysis Information for Risk Management Plan 

•	 Population within distance to endpoint (residential population rounded to two significant 

digits); 

•	 Public receptors within the distance to endpoint (schools, residences, hospitals, prisons, 

recreation areas, commercial, office, or industrial areas); 

•	 Environmental receptors within the distance to endpoint (national or state parks, forests, or 

monuments, officially designated wildlife sanctuaries, preserves, or refuges, Federal 

wilderness areas); 

•	 Passive mitigation measures considered (e.g., dikes, fire walls, blast walls, enclosures, other); 

and 

•	 Active mitigation measures considered (e.g., sprinkler system, deluge system, water curtain, 

excess flow valve, other). 

12.5 Submitting RMPs 

EPA has made RMP*eSubmit available to complete and file your RMP. RMP*eSubmit does 

the following: 

•	 Provides a user-friendly, web-based RMP Submission System via EPA’s secure Central 

Data Exchange (CDX). 

•	 Performs data quality checks, accepts limited graphics, and provides on-line help 

including defining data elements and providing instructions. 

•	 Online reporting simplifies the process. It saves you time, and improves data quality and 

security. 

•	 EPA uses industry-standard technology, including encryption used by most commercial 

banks, as well as stringent user ID and password protocols to protect your information. 

•	 You will be able to access your RMP online at any time. 

•	 For a facility to submit their RMP, the certifier will first be required to set up a CDX 

account (or use their current one if the facility already submits data via CDX). 

Instructions for obtaining a CDX account and using RMP*eSubmit can be found at: 

www.epa.gov/emergencies/rmp. 

•	 Upon approval of the document in submission, a confirmation e-mail will be sent to the 

certifier. 

12.6 Other Required Documentation 

Besides the information you are required to submit in your RMP, you must maintain other 

records of your offsite consequence analysis on site. Under 40 CFR 68.39, you must maintain the 

following records: 

•	 For worst-case scenarios, a description of the vessel or pipeline and substance selected as the 

worst case, the assumptions and parameters used, and the rationale for selection. Assumptions 

include any administrative controls and any passive mitigation systems that were used to limit 

the quantity that could be released. You must document that anticipated effects of these 

controls and systems on the release quantity and rate. 

March 2009	 12 - 4 
•	 For alternative release scenarios, a description of the scenarios identified the assumptions and 

parameters used, and the rationale for selection of the specific scenarios. Assumptions include 

any administrative controls and any passive mitigation systems that were used to limit the 

quantity that could be released. You must document that anticipated effects of these controls 

and systems on the release quantity and rate. 

•	 Documentation of estimated quantity released, release rate, and duration of the release. 

•	 Methodology used to determine distance to an endpoint. 

•	 Data used to estimate populations and environmental receptors potentially affected. 

You are required to maintain these records for five years. 

March 2009 12 - 5 
Chapter 12 

Submitting Offsite Consequence Analysis Information for Risk Management Plan 

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April 12, 1999 12 - 6 
APPENDIX A

REFERENCES FOR CONSEQUENCE ANALYSIS METHODS

April 15, 1999 
APPENDIX A REFERENCES FOR CONSEQUENCE ANALYSIS

METHODS 

Exhibit A-1 lists references that may provide useful information for modeling or calculation methods 

that could be used in the offsite consequence analyses. This exhibit is not intended to be a complete listing of 

references that may be used in the consequence analysis; any appropriate model or method may be used. 

April 15, 1999 
Appendix A 

References for Consequence Analysis Methods 

Exhibit A-1

Selected References for Information on Consequence Analysis Methods

Center for Process Safety of the American Institute of Chemical Engineers (AIChE). Guidelines for 

Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVEs. New York: 

AIChE, 1994. 

Center for Process Safety of the American Institute of Chemical Engineers (AIChE). Guidelines for Use of 

Vapor Cloud Dispersion Models, Second Ed. New York: AIChE, 1996. 

Center for Process Safety of the American Institute of Chemical Engineers (AIChE). International 

Conference and Workshop on Modeling and Mitigating the Consequences of Accidental Releases 

of Hazardous Materials, September 26-29, 1995. New York: AIChE, 1995. 

Federal Emergency Management Agency, U.S. Department of Transportation, U.S. Environmental Protection 

Agency. Handbook of Chemical Hazard Analysis Procedures. 1989. 

Madsen, Warren W. and Robert C. Wagner. "An Accurate Methodology for Modeling the Characteristics of 

Explosion Effects." Process Safety Progress, 13 (July 1994), 171-175. 

Mercx, W.P.M., D.M. Johnson, and J. Puttock. "Validation of Scaling Techniques for Experimental Vapor 

Cloud Explosion Investigations." Process Safety Progress, 14 (April 1995), 120. 

Mercx, W.P.M., R.M.M. van Wees, and G. Opschoor. "Current Research at TNO on Vapor Cloud Explosion 

Modelling." Process Safety Progress, 12 (October 1993), 222. 

Prugh, Richard W. "Quantitative Evaluation of Fireball Hazards." Process Safety Progress, 13 (April 

1994), 83-91. 

Scheuermann, Klaus P. "Studies About the Influence of Turbulence on the Course of Explosions." Process 

Safety Progress, 13 (October 1994), 219. 

TNO Bureau for Industrial Safety, Netherlands Organization for Applied Scientific Research. Methods for 

the Calculation of the Physical Effects. The Hague, the Netherlands: Committee for the Prevention 

of Disasters, 1997. 

TNO Bureau for Industrial Safety, Netherlands Organization for Applied Scientific Research. Methods for 

the Calculation of the Physical Effects of the Escape of Dangerous Material (Liquids and Gases). 

Voorburg, the Netherlands: TNO (Commissioned by Directorate-General of Labour), 1980. 

TNO Bureau for Industrial Safety, Netherlands Organization for Applied Scientific Research. Methods for 

the Calculation of the Physical Effects Resulting from Releases of Hazardous Materials. Rijswijk, 

the Netherlands: TNO (Commissioned by Directorate-General of Labour), 1992. 

TNO Bureau for Industrial Safety, Netherlands Organization for Applied Scientific Research. Methods for 

the Determination of Possible Damage to People and Objects Resulting from Releases of 

April 15, 1999 A - 2 
Appendix A 

References for Consequence Analysis Methods 

Hazardous Materials. Rijswijk, the Netherlands: TNO (Commissioned by Directorate-General of 

Labour), 1992. 

Touma, Jawad S., et al. "Performance Evaluation of Dense Gas Dispersion Models." Journal of Applied 

Meteorology, 34 (March 1995), 603-615. 

U.S. Environmental Protection Agency, Federal Emergency Management Agency, U.S. Department of 

Transportation. Technical Guidance for Hazards Analysis, Emergency Planning for Extremely 

Hazardous Substances. December 1987. 

U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards. Workbook of 

Screening Techniques for Assessing Impacts of Toxic Air Pollutants. EPA-450/4-88-009. 

September 1988. 

U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards. Guidance on the 

Application of Refined Dispersion Models for Hazardous/Toxic Air Release. EPA-454/R-93-002. 

May 1993. 

U.S. Environmental Protection Agency, Office of Pollution Prevention and Toxic Substances. Flammable 

Gases and Liquids and Their Hazards. EPA 744-R-94-002. February 1994. 

April 15, 1999 A - 3 
APPENDIX B

TOXIC SUBSTANCES

April 15, 1999 
APPENDIX B TOXIC SUBSTANCES 

B.1 Data for Toxic Substances 

The exhibits in this section of Appendix B provide the data needed to carry out the calculations for 

regulated toxic substances using the methods presented in the text of this guidance. Exhibit B-1 presents 

data for toxic gases, Exhibit B-2 presents data for toxic liquids, and Exhibit B-3 presents data for several 

toxic substances commonly found in water solution and for oleum. Exhibit B-4 provides temperature 

correction factors that can be used to correct the release rates estimated for pool evaporation of toxic liquids o o that are released at temperatures between 25 C to 50 C.

The derivation of the factors presented in Exhibits B-1 - B-4 is discussed in Appendix D. The data 

used to develop the factors in Exhibits B-1 and B-2 are primarily from Design Institute for Physical Property 

Data (DIPPR), American Institute of Chemical Engineers, Physical and Thermodynamic Properties of Pure 

Chemicals, Data Compilation. Other sources, including the National Library of Medicine’s Hazardous 

Substances Databank (HSDB) and the Kirk-Othmer Encyclopedia of Chemical Technology, were used for 

Exhibits B-1 and B-2 if data were not available from the DIPPR compilation. The factors in Exhibit B-3 

were developed using data primarily from Perry's Chemical Engineers' Handbook and the Kirk-Othmer 

Encyclopedia of Chemical Technology. The temperature correction factors in Exhibit B-4 were developed 

using vapor pressure data derived from the vapor pressure coefficients in the DIPPR compilation. 

April 15, 1999 
Exhibit B-1

Data for Toxic Gases

CAS Molecular Ratio of Toxic Endpoint a Liquid Factor 

Boiling 

(LFB) 

Density 

Factor (DF) 

(Boiling) 

Gas 

Factor 

(GF) k 

@2

Number Chemical Name Weight Specific 

Heats mg/L ppm Basis 

7664-41-7 Ammonia (anhydrous) c 17.03 1.31 0.14 200 ERPG-2 0.073 0.71 14 

7784-42-1 Arsine 77.95 1.28 0.0019 0.6 EHS-LOC (IDLH) 0.23 0.30 30 

10294-34-5 Boron trichloride 117.17 1.15 0.010 2 EHS-LOC (Tox ) e 0.22 0.36 36 

7637-07-2 Boron trifluoride 67.81 1.20 0.028 10 EHS-LOC (IDLH) 0.25 0.31 28 7782-50-5 Chlorine 70.91 1.32 0.0087 3 ERPG-2 0.19 0.31 29 

10049-04-4 Chlorine dioxide 67.45 1.25 0.0028 1 EHS-LOC 

equivalent (IDLH)g 

0.15 0.30 28 

506-77-4 Cyanogen chloride 61.47 1.22 0.030 12 EHS-LOC 

equivalent (Tox)h 

0.14 0.41 26 

19287-45-7 Diborane 27.67 1.17 0.0011 1 ERPG-2 0.13 1.13 17 

75-21-8 Ethylene oxide 44.05 1.21 0.090 50 ERPG-2 0.12 0.55 22 

7782-41-4 Fluorine 38.00 1.36 0.0039 2.5 EHS-LOC (IDLH) 0.35 0.32 22 

50-00-0 Formaldehyde (anhydrous) c 30.03 1.31 0.012 10 ERPG-2 0.10 0.59 19 74-90-8 Hydrocyanic acid 27.03 1.30 0.011 10 ERPG-2 0.079 0.72 18 

7647-01-0 Hydrogen chloride 

(anhydrous)c 

36.46 1.40 0.030 20 ERPG-2 0.15 0.41 21 

7664-39-3 Hydrogen fluoride 

(anhydrous)c 

20.01 1.40 0.016 20 ERPG-2 0.066 0.51 16 

7783-07-5 Hydrogen selenide 80.98 1.32 0.00066 0.2 EHS-LOC (IDLH) 0.21 0.25 31 

7783-06-4 Hydrogen sulfide 34.08 1.32 0.042 30 ERPG-2 0.13 0.51 20 

74-87-3 Methyl chloride 50.49 1.26 0.82 400 ERPG-2 0.14 0.48 24 

74-93-1 Methyl mercaptan 48.11 1.20 0.049 25 ERPG-2 0.12 0.55 23 

10102-43-9 Nitric oxide 30.01 1.38 0.031 25 EHS-LOC (TLV ) j 0.21 0.38 19 

75-44-5 Phosgene 98.92 1.17 0.00081 0.2 ERPG-2 0.20 0.35 33 

April 15, 1999 B - 2 
Exhibit B-1 (continued) 

CAS Molecular Ratio of Toxic Endpoint a Liquid Factor 

Boiling 

(LFB) 

Density 

Factor (DF) 

(Boiling) 

Gas 

Factor 

(GF) k 

@2

Number Chemical Name Weight Specific 

Heats mg/L ppm Basis 

7803-51-2 Phosphine 34.00 1.29 0.0035 2.5 ERPG-2 0.15 0.66 20 

7446-09-5 Sulfur dioxide (anhydrous) 64.07 1.26 0.0078 3 ERPG-2 0.16 0.33 27 

7783-60-0 Sulfur tetrafluoride 108.06 1.30 0.0092 2 EHS-LOC (Tox ) e 0.25 0.25 

(at -73 C) o 

36 

Notes:a 3 Toxic endpoints are specified in Appendix A to 40 CFR part 68 in units of mg/L. To convert from units of mg/L to mg/m , multiply by 1,0ppm, use the following equation:

Endpointmg/L × 1,000 × 24.5 Endpointppm � Molecular Weight 

b "Buoyant" in the Reference Table column refers to the tables for neutrally buoyant gases and vapors; "Dense" refers to the tables for dense Appendix D, Section D.4.4, for more information on the choice of reference tables. c See Exhibit B-3 of this appendix for data on water solutions. d Gases that are lighter than air may behave as dense gases upon release if liquefied under pressure or cold; consider the conditions of releasappropriate table. e LOC is based on the IDLH-equivalent level estimated from toxicity data. f o Cannot be liquefied at 25 C.g Not an EHS; LOC-equivalent value was estimated from one-tenth of the IDLH.h Not an EHS; LOC-equivalent value was estimated from one-tenth of the IDLH-equivalent level estimated from toxicity data.i Hydrogen fluoride is lighter than air, but may behave as a dense gas upon release under some circumstances (e.g., release under pressure, hreleased cloud) because of hydrogen bonding; consider the conditions of release when choosing the appropriate table.j LOC based on Threshold Limit Value (TLV) - Time-weighted average (TWA) developed by the American Conference of Governmental In(ACGIH).k Use GF for gas leaks under choked (maximum) flow conditions. April 15, 1999 B - 3 
Exhibit B-2

Data for Toxic Liquids

CAS 

Number 

Chemical Name Weight 

Molecular 

at 25 C 

(mm Hg) 

Pressure 

Vapor 

o 

Toxic Endpoint a Liquid Factors 

Factor 

(DF) 

Density 

Factor 

(LLF) 

Leak 

Liquid 

I 

mg/L ppm Basis Ambient 

(LFA) 

Boiling 

(LFB)

107-02-8 Acrolein 56.06 274 0.0011 0.5 ERPG-2 0.047 0.12 0.58 40 107-13-1 Acrylonitrile 53.06 108 0.076 35 ERPG-2 0.018 0.11 0.61 39 

814-68-6 Acrylyl chloride 90.51 110 0.00090 0.2 EHS-LOC (Tox ) c 0.026 0.15 0.44 54 

107-18-6 Allyl alcohol 58.08 26.1 0.036 15 EHS-LOC (IDLH) 0.0046 0.11 0.58 41 107-11-9 Allylamine 57.10 242 0.0032 1 EHS-LOC (Tox ) c 0.042 0.12 0.64 36 

7784-34-1 Arsenous trichloride 181.28 10 0.01 1 EHS-LOC (Tox ) c 0.0037 0.21 0.23 100 

353-42-4 Boron trifluoride compound 

with methyl ether (1:1) 

113.89 11 0.023 5 EHS-LOC (Tox ) c 0.0030 0.16 0.49 48 

7726-95-6 Bromine 159.81 212 0.0065 1 ERPG-2 0.073 0.23 0.16 150 

75-15-0 Carbon disulfide 76.14 359 0.16 50 ERPG-2 0.075 0.15 0.39 60 67-66-3 Chloroform 119.38 196 0.49 100 EHS-LOC (IDLH) 0.055 0.19 0.33 71 

542-88-1 Chloromethyl ether 114.96 29.4 0.00025 0.05 EHS-LOC (Tox ) c 0.0080 0.17 0.37 63 

107-30-2 Chloromethyl methyl ether 80.51 199 0.0018 0.6 EHS-LOC (Tox ) c 0.043 0.15 0.46 51 

4170-30-3 Crotonaldehyde 70.09 33.1 0.029 10 ERPG-2 0.0066 0.12 0.58 41 

123-73-9 Crotonaldehyde, (E)- 70.09 33.1 0.029 10 ERPG-2 0.0066 0.12 0.58 41 108-91-8 Cyclohexylamine 99.18 10.1 0.16 39 EHS-LOC (Tox ) c 0.0025 0.14 0.56 41 

75-78-5 Dimethyldichlorosilane 129.06 141 0.026 5 ERPG-2 0.042 0.20 0.46 51 

57-14-7 1,1-Dimethylhydrazine 60.10 157 0.012 5 EHS-LOC (IDLH) 0.028 0.12 0.62 38 

106-89-8 Epichlorohydrin 92.53 17.0 0.076 20 ERPG-2 0.0040 0.14 0.42 57 

107-15-3 Ethylenediamine 60.10 12.2 0.49 200 EHS-LOC (IDLH) 0.0022 0.13 0.54 43 151-56-4 Ethyleneimine 43.07 211 0.018 10 EHS-LOC (IDLH) 0.030 0.10 0.58 40 

110-00-9 Furan 68.08 600 0.0012 0.4 EHS-LOC (Tox ) c 0.12 0.14 0.52 45 

302-01-2 Hydrazine 32.05 14.4 0.011 8 EHS-LOC (IDLH) 0.0017 0.069 0.48 48 

April 15, 1999 B - 4 
Exhibit B-2 (continued) 

CAS 

Number 

Chemical Name Weight 

Molecular 

at 25 C 

(mm Hg) 

Pressure 

Vapor 

o 

Toxic Endpoint a Liquid Factors 

Factor 

(DF) 

Density 

Factor 

(LLF) 

Leak 

Liquid 

I 

mg/L ppm Basis Ambient 

(LFA) 

Boiling 

(LFB)

13463-40-6 Iron, pentacarbonyl- 195.90 40 0.00044 0.05 EHS-LOC (Tox ) c 0.016 0.24 0.33 70 

78-82-0 Isobutyronitrile 69.11 32.7 0.14 50 ERPG-2 0.0064 0.12 0.63 37 

108-23-6 Isopropyl chloroformate 122.55 28 0.10 20 EHS-LOC (Tox ) c 0.0080 0.17 0.45 52 126-98-7 Methacrylonitrile 67.09 71.2 0.0027 1 EHS-LOC (TLV ) e 0.014 0.12 0.61 38 

79-22-1 Methyl chloroformate 94.50 108 0.0019 0.5 EHS-LOC (Tox ) c 0.026 0.16 0.40 58 60-34-4 Methyl hydrazine 46.07 49.6 0.0094 5 EHS-LOC (IDLH) 0.0074 0.094 0.56 42 

624-83-9 Methyl isocyanate 57.05 457 0.0012 0.5 ERPG-2 0.079 0.13 0.52 45 

556-64-9 Methyl thiocyanate 73.12 10 0.085 29 EHS-LOC (Tox ) c 0.0020 0.11 0.45 51 

75-79-6 Methyltrichlorosilane 149.48 173 0.018 3 ERPG-2 0.057 0.22 0.38 61 

13463-39-3 Nickel carbonyl 170.73 400 0.00067 0.1 EHS-LOC (Tox ) c 0.14 0.26 0.37 63 

7697-37-2 Nitric acid (100%) f 63.01 63.0 0.026 10 EHS-LOC (Tox ) c 0.012 0.12 0.32 73 

79-21-0 Peracetic acid 76.05 13.9 0.0045 1.5 EHS-LOC (Tox ) c 0.0029 0.12 0.40 58 

594-42-3 Perchloromethylmercaptan 185.87 6 0.0076 1 EHS-LOC (IDLH) 0.0023 0.20 0.29 81 

10025-87-3 Phosphorus oxychloride 153.33 35.8 0.0030 0.5 EHS-LOC (Tox ) c 0.012 0.20 0.29 80 

7719-12-2 Phosphorus trichloride 137.33 120 0.028 5 EHS-LOC (IDLH) 0.037 0.20 0.31 75 

110-89-4 Piperidine 85.15 32.1 0.022 6 EHS-LOC (Tox ) c 0.0072 0.13 0.57 41 

107-12-0 Propionitrile 55.08 47.3 0.0037 1.6 EHS-LOC (Tox ) c 0.0080 0.10 0.63 37 109-61-5 Propyl chloroformate 122.56 20.0 0.010 2 EHS-LOC (Tox ) c 0.0058 0.17 0.45 52 

75-55-8 Propyleneimine 57.10 187 0.12 50 EHS-LOC (IDLH) 0.032 0.12 0.61 39 

75-56-9 Propylene oxide 58.08 533 0.59 250 ERPG-2 0.093 0.13 0.59 40 

7446-11-9 Sulfur trioxide 80.06 263 0.010 3 ERPG-2 0.057 0.15 0.26 91 

75-74-1 Tetramethyllead 267.33 22.5 0.0040 0.4 EHS-LOC (IDLH) 0.011 0.29 0.24 96 

509-14-8 Tetranitromethane 196.04 11.4 0.0040 0.5 EHS-LOC (IDLH) 0.0045 0.22 0.30 78 

April 15, 1999 B - 5 
Exhibit B-2 (continued) 

CAS 

Number 

Chemical Name Weight 

Molecular 

at 25 C 

(mm Hg) 

Pressure 

Vapor 

o 

Toxic Endpoint a Liquid Factors 

Factor 

(DF) 

Density 

Factor 

(LLF) 

Leak 

Liquid 

I 

mg/L ppm Basis Ambient 

(LFA) 

Boiling 

(LFB)

7550-45-0 Titanium tetrachloride 189.69 12.4 0.020 2.6 ERPG-2 0.0048 0.21 0.28 82 

584-84-9 Toluene 2,4-diisocyanate 174.16 0.017 0.0070 1 EHS-LOC (IDLH) 0.000006 0.16 0.40 59 

91-08-7 Toluene 2,6-diisocyanate 174.16 0.05 0.0070 1 EHS-LOC (IDLH ) g 0.000018 0.16 0.40 59 

26471-62-5 Toluene diisocyanate 

(unspecified isomer) 

174.16 0.017 0.0070 1 EHS-LOC equivalent 

(IDLH )h 

0.000006 0.16 0.40 59 

75-77-4 Trimethylchlorosilane 108.64 231 0.050 11 EHS-LOC (Tox ) c 0.061 0.18 0.57 41 

108-05-4 Vinyl acetate monomer 86.09 113 0.26 75 ERPG-2 0.026 0.15 0.53 45 

Notes:a 3 Toxic endpoints are specified in the Appendix A to 40 CFR part 68 in units of mg/L. To convert from units of mg/L to mg/m , multiply by to ppm, use the following equation:

Endpointppm 

Endpointmg/L × 1,000 × 24.5 �

Molecular Weight 

b "Buoyant" in the Reference Table column refers to the tables for neutrally buoyant gases and vapors; "Dense" refers to the tables for dense Appendix D, Section D.4.4, for more information on the choice of reference tables. c LOC is based on IDLH-equivalent level estimated from toxicity data. d Use dense gas table if substance is at an elevated temperature. e LOC based on Threshold Limit Value (TLV) - Time-weighted average (TWA) developed by the American Conference of Governmental I(ACGIH). f See Exhibit B-3 of this appendix for data on water solutions. g LOC for this isomer is based on IDLH for toluene 2,4-diisocyanate. h Not an EHS; LOC-equivalent value is based on IDLH for toluene 2,4-diisocyanate. i Use the LLF only for leaks from tanks at atmospheric pressure. April 15, 1999 B - 6 
Exhibit B-3

Data for Water Solutions of Toxic Substances and for Oleum

For Wind Speeds of 1.5 and 3.0 Meters per Second (m/s)

Regulated Toxic Endpoint a Initial 10-min. Average Vapor Liquid Factor at 25 C o Density Liquid 

CAS Substance Molecular Concen- Pressure (mm Hg) (LFA) Factor Leak 

Number in Solution Weight 

mg/L ppm Basis 

tration 

(Wt %) 1.5 m/s 3.0 m/s 1.5 m/s 3.0 m/s 

(DF) Factor 

(LLF) 

7664-41-7 Ammonia 17.03 0.14 200 ERPG-2 30 332 248 0.026 0.019 0.55 43 

24 241 184 0.019 0.014 0.54 44 20 190 148 0.015 0.011 0.53 44 

50-00-0 Formaldehyde 30.027 0.012 10 ERPG-2 37 1.5 1.4 0.0002 0.0002 0.44 53 

7647-01-0 Hydrochloric 36.46 0.030 20 ERPG-2 38 78 55 0.010 0.0070 0.41 57 

acid 

37 67 48 0.0085 0.0062 0.42 57 

36c 56 42 0.0072 0.0053 0.42 57 34c 38 29 0.0048 0.0037 0.42 56 30c 13 12 0.0016 0.0015 0.42 55 

7664-39-3 Hydrofluoric 20.01 0.016 20 ERPG-2 70 124 107 0.011 0.010 0.39 61 

acid 

50 16 15 0.0014 0.0013 0.41 58 

7697-37-2 Nitric acid 63.01 0.026 10 EHS- 90 25 22 0.0046 0.0040 0.33 71 

LOC 

(IDLH) 85 17 16 0.0032 0.0029 0.33 70 

80 10.2 10 0.0019 0.0018 0.33 70 

8014-95-7 Oleum - based 

on SO3 

80.06 

(SO ) 3 

0.010 3 ERPG-2 30 (SO ) 3 3.5 (SO ) 3 3.4 (SO ) 3 0.0008 0.0007 0.25 93 

Notes:a Toxic endpoints are specified in the Appendix A to 40 CFR part 68 in units of mg/L. See Notes to Exhibit B-1 or B-2 for converting to otb "Buoyant" in the Reference Table column refers to the tables for neutrally buoyant gases and vapors; "Dense" refers to the tables for dense Appendix D, Section D.4.4, for more information on the choice of reference tables. c Hydrochloric acid in concentrations below 37 percent is not regulated. d Use dense gas table if substance is at an elevated temperature. April 15, 1999 B - 7 
Exhibit B-4

Temperature Correction Factors for Liquids Evaporating from Pools at Temperatures o o o o Between 25 C and 50 C (77 F and 122 F) 

CAS 

Number 

Chemical Name Point 

( C) 

Boiling 

o 

Temperature Correction Factor (TCF) 

30 Co 

(86 F) o 

35 C 

(95 F) 

o 

o 

40 C 

(104 F) 

o 

o 

45 C 

(113 F) 

o 

o 

50 C 

(122 F) 

o 

o 

107-02-8 Acrolein 52.69 1.2 1.4 1.7 2.0 2.3 

107-13-1 Acrylonitrile 77.35 1.2 1.5 1.8 2.1 2.5 

814-68-6 Acrylyl chloride 75.00 ND ND ND ND ND 

107-18-6 Allyl alcohol 97.08 1.3 1.7 2.2 2.9 3.6 

107-11-9 Allylamine 53.30 1.2 1.5 1.8 2.1 2.5 

7784-34-1 Arsenous trichloride 130.06 ND ND ND ND ND 

353-42-4 Boron trifluoride compound with 

methyl ether (1:1) 

126.85 ND ND ND ND ND 

7726-95-6 Bromine 58.75 1.2 1.5 1.7 2.1 2.5 

75-15-0 Carbon disulfide 46.22 1.2 1.4 1.6 1.9 LFB 

67-66-3 Chloroform 61.18 1.2 1.5 1.8 2.1 2.5 

542-88-1 Chloromethyl ether 104.85 1.3 1.6 2.0 2.5 3.1 

107-30-2 Chloromethyl methyl ether 59.50 1.2 1.5 1.8 2.1 2.5 

4170-30-3 Crotonaldehyde 104.10 1.3 1.6 2.0 2.5 3.1 

123-73-9 Crotonaldehyde, (E)- 102.22 1.3 1.6 2.0 2.5 3.1 

108-91-8 Cyclohexylamine 134.50 1.3 1.7 2.1 2.7 3.4 

75-78-5 Dimethyldichlorosilane 70.20 1.2 1.5 1.8 2.1 2.5 

57-14-7 1,1-Dimethylhydrazine 63.90 ND ND ND ND ND 

106-89-8 Epichlorohydrin 118.50 1.3 1.7 2.1 2.7 3.4 

107-15-3 Ethylenediamine 36.26 1.3 1.8 LFB LFB LFB 

151-56-4 Ethyleneimine 55.85 1.2 1.5 1.8 2.2 2.7 

110-00-9 Furan 31.35 1.2 LFB LFB LFB LFB 

302-01-2 Hydrazine 113.50 1.3 1.7 2.2 2.9 3.6 

13463-40-6 Iron, pentacarbonyl- 102.65 ND ND ND ND ND 

78-82-0 Isobutyronitrile 103.61 1.3 1.6 2.0 2.5 3.1 

108-23-6 Isopropyl chloroformate 104.60 ND ND ND ND ND 

126-98-7 Methacrylonitrile 90.30 1.2 1.5 1.8 2.2 2.6 

79-22-1 Methyl chloroformate 70.85 1.3 1.6 1.9 2.4 2.9 

60-34-4 Methyl hydrazine 87.50 ND ND ND ND ND 

624-83-9 Methyl isocyanate 38.85 1.2 1.4 LFB LFB LFB 

556-64-9 Methyl thiocyanate 130.00 ND ND ND ND ND 

75-79-6 Methyltrichlorosilane 66.40 1.2 1.4 1.7 2.0 2.4 

April 15, 1999 B - 8 
Exhibit B-4 (continued) 

CAS 

Number 

Chemical Name Point 

( C) 

Boiling 

o 

Temperature Correction Factor (TCF) 

30 Co 

(86 F) o 

35 C 

(95 F) 

o 

o 

40 C 

(104 F) 

o 

o 

45 C 

(113 F) 

o 

o 

50 C 

(122 F) 

o 

o 

13463-39-3 Nickel carbonyl 42.85 ND ND ND ND ND 

7697-37-2 Nitric acid 83.00 1.3 1.6 2.0 2.5 3.1 

79-21-0 Peracetic acid 109.85 1.3 1.8 2.3 3.0 3.8 

594-42-3 Perchloromethylmercaptan 147.00 ND ND ND ND ND 

10025-87-3 Phosphorus oxychloride 105.50 1.3 1.6 1.9 2.4 2.9 

7719-12-2 Phosphorus trichloride 76.10 1.2 1.5 1.8 2.1 2.5 

110-89-4 Piperidine 106.40 1.3 1.6 2.0 2.4 3.0 

107-12-0 Propionitrile 97.35 1.3 1.6 1.9 2.3 2.8 

109-61-5 Propyl chloroformate 112.40 ND ND ND ND ND 

75-55-8 Propyleneimine 60.85 1.2 1.5 1.8 2.1 2.5 

75-56-9 Propylene oxide 33.90 1.2 LFB LFB LFB LFB 

7446-11-9 Sulfur trioxide 44.75 1.3 1.7 LFB LFB LFB 

75-74-1 Tetramethyllead 110.00 ND ND ND ND ND 

509-14-8 Tetranitromethane 125.70 1.3 1.7 2.2 2.8 3.5 

7550-45-0 Titanium tetrachloride 135.85 1.3 1.6 2.0 2.6 3.2 

584-84-9 Toluene 2,4-diisocyanate 251.00 1.6 2.4 3.6 5.3 7.7 

91-08-7 Toluene 2,6-diisocyanate 244.85 ND ND ND ND ND 

26471-62-5 Toluene diisocyanate (unspecified 

isomer) 

250.00 1.6 2.4 3.6 5.3 7.7 

75-77-4 Trimethylchlorosilane 57.60 1.2 1.4 1.7 2.0 2.3 

108-05-4 Vinyl acetate monomer 72.50 1.2 1.5 1.9 2.3 2.7 

Notes: 

ND: No data available. 

LFB: Chemical above boiling point at this temperature; use LFB for analysis. 

April 15, 1999 B - 9 
Appendix B 

Toxic Substances 

B.2 Mixtures Containing Toxic Liquids 

In case of a spill of a liquid mixture containing a regulated toxic substance (with the exception of 

common water solutions, discussed in Section 3.3 in the text), the area of the pool formed by the entire liquid 

spill is determined as described in Section 3.2.2 or 3.2.3. For the area determination, if the density of the 

mixture is unknown, the density of the regulated substance in the mixture may be assumed as the density of 

the entire mixture. 

If the partial vapor pressure of the regulated substance in the mixture is known, that vapor pressure 

may be used to derive a release rate using the equations in Section 3.2. If the partial vapor pressure of the 

regulated toxic substance in the mixture is unknown, it may be estimated from the vapor pressure of the pure 

substance (listed in Exhibit B-2, Appendix B) and the concentration in the mixture, if you assume the mixture 

is an ideal solution, where an ideal solution is one in which there is complete uniformity of cohesive forces. 

This method may overestimate or underestimate the partial pressure for a regulated substance that interacts 

with the other components of a mixture or solution. For example, water solutions are generally not ideal. 

This method is likely to overestimate the partial pressure of regulated substances in water solution if there is 

hydrogen bonding in the solution (e.g., solutions of acids or alcohols in water). 

To estimate partial pressure for a regulated substance in a mixture or solution, use the following 

steps, based on Raoult's Law for ideal solutions: 

� Determine the mole fraction of the regulated substance in the mixture. 

-- The mole fraction of the regulated substance in the mixture is the number of moles 

of the regulated substance in the mixture divided by the total number of moles of all 

substances in the mixture. 

-- If the molar concentration (moles per liter) of each component of the mixture is 

known, the mole fraction may be determined as follows: 

M × V

X � r t 

r n (B-1) � Mi × Vt i�1 

or (canceling out V ): t 

M 

X � r 

r n (B-2) � Mi 

i�1 

April 15, 1999 B - 10 
Appendix B 

Toxic Substances 

where: Xr = Mole fraction of regulated substance in mixture (unitless) 

Mr = Molar concentration of regulated substance in mixture (moles per liter) 

Vt = Total volume of mixture (liters) 

n = Number of components of mixture 

Mi = Molar concentration of each component of mixture (moles per liter) 

For a mixture with three components, this would correspond to: 

M 

Xr � r (B-3) M r � M2

� M3 

where: Xr = Mole fraction of regulated substance in mixture (unitless) 

Mr = Molar concentration of regulated substance (first component) in mixture 

(moles per liter) 

M2 = Molar concentration of second component of mixture (moles per liter) 

M3 = Molar concentration of any other components of mixture (moles per liter) 

-- If the weight of each of the components of the mixture is known, the mole fraction 

of the regulated substance in the mixture may be calculated as follows: 

W r 

MW r X r � (B-4) n Wi

� MWi i�1 

where: Xr = Mole fraction of the regulated substance 

Wr = Weight of the regulated substance 

MW r = Molecular weight of the regulated substance 

n = Number of components of the mixture 

Wi = Weight of each component of the mixture 

MW i = Molecular weight of each component of the mixture 

(Note: Weights can be in any consistent units.) 

For a mixture with three components, this corresponds to: 

W r 

MW r X r � (B-5) W r W2 W3 � �

MW r MW2 MW3 

April 15, 1999 B - 11 
Appendix B 

Toxic Substances 

where: Xr = Mole fraction of the regulated substance 

Wr = Weight of the regulated substance (first component of the mixture) 

MWr = Molecular weight of the regulated substance 

W2 = Weight of the second component of the mixture 

MW2 = Molecular weight of the second component of the mixture 

W3 = Weight of the third component of the mixture 

MW 3 = Molecular weight of the third component of the mixture 

(Note: Weights can be in any consistent units.) 

� Estimate the partial vapor pressure of the regulated substance in the mixture as follows: 

VPm � Xr × VP

p (B-6) 

where: VP m = Partial vapor pressure of the regulated substance in the mixture (millimeters 

of mercury (mm Hg)) 

Xr = Mole fraction of the regulated substance (unitless) 

VP = Vapor pressure of the regulated substance in pure form at the same p o temperature as the mixture (mm Hg) (vapor pressure at 25 C is given in

Exhibit B-1, Appendix B) 

The evaporation rate for the regulated substance in the mixture is determined as for pure substances, 

with VPm as the vapor pressure. If the mixture contains more than one regulated toxic substance, carry out 

the analysis individually for each of the regulated components. The release rate equation is: 

0.0035 × U 0.78 × MW 2/3 × A × VP QR � (B-7) T 

where: QR = Evaporation rate (pounds per minute) 

U = Wind speed (meters per second) 

MW = Molecular weight (given in Exhibit B-2, Appendix B) 

A = Surface area of pool formed by the entire quantity of the mixture (square 

feet) (determined as described in 3.2.2) 

VP = Vapor pressure (mm Hg) (VPm from Equation B-4 above) o o T = Temperature (Kelvin (K); temperature in C plus 273, or 298 for 25 C)

See Appendix D, Section D.2.1 for more discussion of the evaporation rate equation. Equation B-7 

is derived from Equation D-1. 

Worst-case consequence distances to the toxic endpoint may be estimated from the release rate using 

the tables and instructions presented in Chapter 4. 

April 15, 1999 B - 12 
APPENDIX C

FLAMMABLE SUBSTANCES

April 15, 1999 
APPENDIX C FLAMMABLE SUBSTANCES 

C.1 Equation for Estimation of Distance to 1 psi Overpressure for Vapor Cloud 

Explosions 

For a worst-case release of flammable gases and volatile flammable liquids, the release rate is not 

considered. The total quantity of the flammable substance is assumed to form a vapor cloud. The entire 

contents of the cloud is assumed to be within the flammability limits, and the cloud is assumed to explode. 

For the worst-case, analysis, 10 percent of the flammable vapor in the cloud is assumed to participate in the 

explosion (i.e., the yield factor is 0.10). Consequence distances to an overpressure level of 1 pound per 

square inch (psi) may be determined using the following equation, which is based on the TNT-equivalency 

method: 

HC 1/3 

f D � 17 × 0.1 × Wf × (C-1) HCTNT 

where: D = Distance to overpressure of 1 psi (meters) 

Wf = Weight of flammable substance (kilograms or pounds/2.2) 

Hcf = Heat of combustion of flammable substance (kilojoules per kilogram) 

(listed in Exhibit C-1) 

HCTNT = Heat of explosion of trinitrotoluene (TNT) (4,680 kilojoules per kilogram) 

The factor 17 is a constant for damages associated with 1.0 psi overpressures. The factor 0.1 

represents an explosion efficiency of 10 percent. To convert distances from meters to miles, multiply 

by 0.00062. 

Alternatively, use the following equation for quantity in pounds and distance in miles: 

HC 1/3 

f Dmi � 0.0081 × 0.1 × Wlb × (C-2) HCTNT 

where: Dmi = Distance to overpressure of 1 psi (miles) 

Wlb = Weight of flammable substance (pounds) 

These equations were used to derive Reference Table 13 for worst-case distances to the overpressure 

endpoint (1 psi) for vapor cloud explosions. 

C.2 Mixtures of Flammable Substances 

For a mixture of flammable substances, you may estimate the heat of combustion of the mixture from 

the heats of combustion of the components of the mixture using the equation below and then use the equation 

given in the previous section of this appendix to determine the vapor cloud explosion distance. The heat of 

combustion of the mixture may be estimated as follows: 

April 15, 1999 
Appendix C 

Flammable Substances 

W W 

HCm � x × HCx � y × HC

y (C-3) W W m m 

where: HCm = Heat of combustion of mixture (kilojoules per kilogram) 

Wx = Weight of component "X" in mixture (kilograms or pounds/2.2) 

Wm = Total weight of mixture (kilograms or pounds/2.2) 

HCx = Heat of combustion of component "X" (kilojoules per kilogram) 

Wy = Weight of component "Y" in mixture (kilograms or pounds/2.2) 

HCy = Heat of combustion of component "Y" (kilojoules per kilogram) 

Heats of combustion for regulated flammable substances are listed in Exhibit C-1 in the next section 

(Section C.3) of this appendix. 

C.3 Data for Flammable Substances 

The exhibits in this section of Appendix C provide the data needed to carry out the calculations for 

regulated flammable substances using the methods presented in the text of this guidance. Exhibit C-1 

presents heat of combustion data for all regulated flammable substances, Exhibit C-2 presents additional data 

for flammable gases, and Exhibit C-3 presents additional data for flammable liquids. The heats of 

combustion in Exhibit C-1 and the data used to develop the factors in Exhibits C-2 and C-3 are primarily 

from Design Institute for Physical Property Data, American Institute of Chemical Engineers, Physical and 

Thermodynamic Properties of Pure Chemicals, Data Compilation. The derivation of the factors presented 

in Exhibits C-2 and C-3 is discussed in Appendix D. 

April 15, 1999 C - 2 
Exhibit C-1

Heats of Combustion for Flammable Substances

CAS No. Chemical Name State 

Physical 

at 25 C o

Combustion 

Heat of 

(kjoule/kg) 

 75-07-0 Acetaldehyde Gas 25,072 

 74-86-2 Acetylene [Ethyne] Gas 48,222 

 598-73-2 Bromotrifluoroethylene [Ethene, bromotrifluoro-] Gas 1,967 

 106-99-0 1,3-Butadiene Gas 44,548 

 106-97-8 Butane Gas 45,719 

25167-67-3 Butene Gas 45,200*

 590-18-1 2-Butene-cis Gas 45,171 

 624-64-6 2-Butene-trans [2-Butene, (E)] Gas 45,069 

 106-98-9 1-Butene Gas 45,292 

 107-01-7 2-Butene Gas 45,100*

 463-58-1 Carbon oxysulfide [Carbon oxide sulfide (COS)] Gas 9,126 

 7791-21-1 Chlorine monoxide [Chlorine oxide] Gas 1,011*

 590-21-6 1-Chloropropylene [1-Propene, 1-chloro-] Liquid 23,000*

 557-98-2 2-Chloropropylene [1-Propene, 2-chloro-] Gas 22,999 

 460-19-5 Cyanogen [Ethanedinitrile] Gas 21,064 

 75-19-4 Cyclopropane Gas 46,560 

 4109-96-0 Dichlorosilane [Silane, dichloro-] Gas 8,225 

 75-37-6 Difluoroethane [Ethane, 1,1-difluoro-] Gas 11,484 

 124-40-3 Dimethylamine [Methanamine, N-methyl-] Gas 35,813 

 463-82-1 2,2-Dimethylpropane [Propane, 2,2-dimethyl-] Gas 45,051 

 74-84-0 Ethane Gas 47,509 

 107-00-6 Ethyl acetylene [1-Butyne] Gas 45,565 

 75-04-7 Ethylamine [Ethanamine] Gas 35,210 

 75-00-3 Ethyl chloride [Ethane, chloro-] Gas 19,917 

 74-85-1 Ethylene [Ethene] Gas 47,145 

April 15, 1999 C - 3 
Exhibit C-1 (continued) 

CAS No. Chemical Name State 

Physical 

at 25 C o 

Combustion 

Heat of 

(kjoule/kg) 

 60-29-7 Ethyl ether [Ethane, 1,1'-oxybis-] Liquid 33,775 

 75-08-1 Ethyl mercaptan [Ethanethiol] Liquid 27,948 

 109-95-5 Ethyl nitrite [Nitrous acid, ethyl ester] Gas 18,000 

 1333-74-0 Hydrogen Gas 119,950 

 75-28-5 Isobutane [Propane, 2-methyl] Gas 45,576 

 78-78-4 Isopentane [Butane, 2-methyl-] Liquid 44,911 

 78-79-5 Isoprene [1,3-Butadiene, 2-methyl-] Liquid 43,809 

 75-31-0 Isopropylamine [2-Propanamine] Liquid 36,484 

 75-29-6 Isopropyl chloride [Propane, 2-chloro-] Liquid 23,720 

 74-82-8 Methane Gas 50,029 

 74-89-5 Methylamine [Methanamine] Gas 31,396 

 563-45-1 3-Methyl-1-butene Gas 44,559 

 563-46-2 2-Methyl-1-butene Liquid 44,414 

 115-10-6 Methyl ether [Methane, oxybis-] Gas 28,835 

 107-31-3 Methyl formate [Formic acid, methyl ester] Liquid 15,335 

 115-11-7 2-Methylpropene [1-Propene, 2-methyl-] Gas 44,985 

 504-60-9 1,3-Pentadiene Liquid 43,834 

 109-66-0 Pentane Liquid 44,697 

 109-67-1 1-Pentene Liquid 44,625 

 646-04-8 2-Pentene, (E)- Liquid 44,458 

 627-20-3 2-Pentene, (Z)- Liquid 44,520 

 463-49-0 Propadiene [1,2-Propadiene] Gas 46,332 

 74-98-6 Propane Gas 46,333 

 115-07-1 Propylene [1-Propene] Gas 45,762 

 74-99-7 Propyne [1-Propyne] Gas 46,165 

 7803-62-5 Silane Gas 44,307 

April 15, 1999 C - 4 
Exhibit C-1 (continued) 

CAS No. Chemical Name State 

Physical 

at 25 C o 

Combustion 

Heat of 

(kjoule/kg) 

 116-14-3 Tetrafluoroethylene [Ethene, tetrafluoro-] Gas 1,284 

 75-76-3 Tetramethylsilane [Silane, tetramethyl-] Liquid 41,712 

10025-78-2 Trichlorosilane [Silane, trichloro-] Liquid 3,754 

 79-38-9 Trifluorochloroethylene [Ethene, chlorotrifluoro-] Gas 1,837 

 75-50-3 Trimethylamine [Methanamine, N,N-dimethyl-] Gas 37,978 

 689-97-4 Vinyl acetylene [1-Buten-3-yne] Gas 45,357 

 75-01-4 Vinyl chloride [Ethene, chloro-] Gas 18,848 

 109-92-2 Vinyl ethyl ether [Ethene, ethoxy-] Liquid 32,909 

 75-02-5 Vinyl fluoride [Ethene, fluoro-] Gas 2,195 

 75-35-4 Vinylidene chloride [Ethene, 1,1-dichloro-] Liquid 10,354 

 75-38-7 Vinylidene fluoride [Ethene, 1,1-difluoro-] Gas 10,807 

 107-25-5 Vinyl methyl ether [Ethene, methoxy-] Gas 30,549 

*

 Estimated heat of combustion 

April 15, 1999 C - 5 
Exhibit C-2

Data for Flammable Gases

CAS Molecular Specific 

Ratio of 

Limits (Vol %) 

Flammability 

LFL 

(mg/L) 

Factor 

(GF) 

Gas 

g 

Factor 

Boiling 

Liquid 

(LFB) 

Factor 

(Boiling) 

Density 

(DF) 

Reference 

Table a 

Number Chemical Name Weight Heats Lower 

(LFL) 

Upper 

UFL 

75-07-0 Acetaldehyde 44.05 1.18 4.0 60.0 72 22 0.11 0.62 Dense 74-86-2 Acetylene 26.04 1.23 2.5 80.0 27 17 0.12 0.78 Buoyant b 

598-73-2 Bromotrifluoroethylene 160.92 1.11 c 37.0 c 41c 0.25 c 0.29 c Dense 106-99-0 1,3-Butadiene 54.09 1.12 2.0 11.5 44 24 0.14 0.75 Dense 106-97-8 Butane 58.12 1.09 1.5 9.0 36 25 0.14 0.81 Dense 

25167-67-3 Butene 56.11 1.10 1.7 9.5 39 24 0.14 0.77 Dense 

590-18-1 2-Butene-cis 56.11 1.12 1.6 9.7 37 24 0.14 0.76 Dense 624-64-6 2-Butene-trans 56.11 1.11 1.8 9.7 41 24 0.14 0.77 Dense 106-98-9 1-Butene 56.11 1.11 1.6 9.3 37 24 0.14 0.78 Dense 107-01-7 2-Butene 56.11 1.10 1.7 9.7 39 24 0.14 0.77 Dense 463-58-1 Carbon oxysulfide 60.08 1.25 12.0 29.0 290 26 0.18 0.41 Dense 

7791-21-1 Chlorine monoxide 86.91 1.21 23.5 NA 830 31 0.19 NA Dense 

557-98-2 2-Chloropropylene 76.53 1.12 4.5 16.0 140 29 0.16 0.54 Dense 460-19-5 Cyanogen 52.04 1.17 6.0 32.0 130 24 0.15 0.51 Dense 

75-19-4 Cyclopropane 42.08 1.18 2.4 10.4 41 22 0.13 0.72 Dense 

4109-96-0 Dichlorosilane 101.01 1.16 4.0 96.0 160 33 0.20 0.40 Dense 

75-37-6 Difluoroethane 66.05 1.14 3.7 18.0 100 27 0.17 0.48 Dense 

124-40-3 Dimethylamine 45.08 1.14 2.8 14.4 52 22 0.12 0.73 Dense 463-82-1 2,2-Dimethylpropane 72.15 1.07 1.4 7.5 41 27 0.16 0.80 Dense 

74-84-0 Ethane 30.07 1.19 2.9 13.0 36 18 0.14 0.89 Dense 

107-00-6 Ethyl acetylene 54.09 1.11 2.0 32.9 44 24 0.13 0.73 Dense 

75-04-7 Ethylamine 45.08 1.13 3.5 14.0 64 22 0.12 0.71 Dense 

April 15, 1999 C - 6 
Exhibit C-2 (continued) 

CAS Molecular Specific 

Ratio of 

Limits (Vol %) 

Flammability 

LFL 

(mg/L) 

Factor 

(GF) 

Gas 

g 

Factor 

Boiling 

Liquid 

(LFB) 

Factor 

(Boiling) 

Density 

(DF) 

Reference 

Table a 

Number Chemical Name Weight Heats Lower 

(LFL) 

Upper 

UFL 

75-00-3 Ethyl chloride 64.51 1.15 3.8 15.4 100 27 0.15 0.53 Dense 74-85-1 Ethylene 28.05 1.24 2.7 36.0 31 18 0.14 0.85 Buoyant b 

109-95-5 Ethyl nitrite 75.07 1.30 4.0 50.0 120 30 0.16 0.54 Dense 

1333-74-0 Hydrogen 2.02 1.41 4.0 75.0 3.3 5.0 

e e d 

75-28-5 Isobutane 58.12 1.09 1.8 8.4 43 25 0.15 0.82 Dense 74-82-8 Methane 16.04 1.30 5.0 15.0 33 14 0.15 1.1 Buoyant 74-89-5 Methylamine 31.06 1.19 4.9 20.7 62 19 0.10 0.70 Dense 

563-45-1 3-Methyl-1-butene 70.13 1.08 1.5 9.1 43 26 0.15 0.77 Dense 115-10-6 Methyl ether 46.07 1.15 3.3 27.3 64 22 0.14 0.66 Dense 115-11-7 2-Methylpropene 56.11 1.10 1.8 8.8 41 24 0.14 0.77 Dense 463-49-0 Propadiene 40.07 1.16 2.1 2.1 34 21 0.13 0.73 Dense 

74-98-6 Propane 44.10 1.13 2.0 9.5 36 22 0.14 0.83 Dense 

115-07-1 Propylene 42.08 1.15 2.0 11.0 34 21 0.14 0.79 Dense 

74-99-7 Propyne 40.07 1.16 1.7 39.9 28 21 0.12 0.72 Dense 

7803-62-5 Silane 32.12 1.24 c c c 19 c e e Dense 

116-14-3 Tetrafluoroethylene 100.02 1.12 11.0 60.0 450 33 0.29 0.32 Dense 

79-38-9 Trifluorochloroethylene 116.47 1.11 8.4 38.7 400 35 0.26 0.33 Dense 75-50-3 Trimethylamine 59.11 1.10 2.0 11.6 48 25 0.14 0.74 Dense 

689-97-4 Vinyl acetylene 52.08 1.13 2.2 31.7 47 24 0.13 0.69 Dense 

75-01-4 Vinyl chloride 62.50 1.18 3.6 33.0 92 26 0.16 0.50 Dense 75-02-5 Vinyl fluoride 46.04 1.20 2.6 21.7 49 23 0.17 0.57 Dense 75-38-7 Vinylidene fluoride 64.04 1.16 5.5 21.3 140 27 0.22 0.42 Dense 

April 15, 1999 C - 7 
Exhibit C-2 (continued) 

CAS Molecular Specific 

Ratio of 

Limits (Vol %) 

Flammability 

LFL 

(mg/L) 

Factor 

(GF) 

Gas 

g 

Factor 

Boiling 

Liquid 

(LFB) 

Factor 

(Boiling) 

Density 

(DF) 

Reference 

Table a 

Number Chemical Name Weight Heats Lower 

(LFL) 

Upper 

UFL 

107-25-5 Vinyl methyl ether 58.08 1.12 2.6 39.0 62 25 0.17 0.57 Dense 

Notes: NA: Data not availablea "Buoyant" in the Reference Table column refers to the tables for neutrally buoyant gases and vapors; "Dense" refers to the tables for dense Appendix D, Section D.4.4, for more information on the choice of reference tables. b Gases that are lighter than air may behave as dense gases upon release if liquefied under pressure or cold; consider the conditions of releasappropriate table. c Reported to be spontaneously combustible. d Much lighter than air; table of distances for neutrally buoyant gases not appropriate. e Pool formation unlikely. f o Calculated at 298 K (25 C) with the following exceptions:

Acetylene factor at 250 K as reported in TNO, Methods for the Calculation of the Physical Effects of the Escape of Dangerous MEthylene factor calculated at critical temperature, 282 K. Methane factor calculated at critical temperature, 191 K. Silane factor calculated at critical temperature, 270 K. 

g Use GF for gas leaks under choked (maximum) flow conditions. April 15, 1999 C - 8 
Exhibit C-3

Data for Flammable Liquids

CAS Chemical Name Molecular (Vol%) 

Flammability Limit 

(mg/L) 

LFL Liquid Factors 

Factor 

Density 

Factor 

(LLF) 

Liquid Leak 

a 

Number Weight 

Lower 

(LFL) 

Upper 

(UFL) 

Ambient 

(LFA) 

Boiling 

(LFB) 

590-21-6 1-Chloropropylene 76.53 4.5 16.0 140 0.11 0.15 0.52 45 

60-29-7 Ethyl ether 74.12 1.9 48.0 57 0.11 0.15 0.69 34 75-08-1 Ethyl mercaptan 62.14 2.8 18.0 71 0.10 0.13 0.58 40 78-78-4 Isopentane 72.15 1.4 7.6 41 0.14 0.15 0.79 30 78-79-5 Isoprene 68.12 2.0 9.0 56 0.11 0.14 0.72 32 75-31-0 Isopropylamine 59.11 2.0 10.4 48 0.10 0.13 0.71 33 75-29-6 Isopropyl chloride 78.54 2.8 10.7 90 0.11 0.16 0.57 41 

563-46-2 2-Methyl-1-butene 70.13 1.4 9.6 40 0.12 0.15 0.75 31 107-31-3 Methyl formate 60.05 5.9 20.0 140 0.10 0.13 0.50 46 504-60-9 1,3-Pentadiene 68.12 1.6 13.1 44 0.077 0.14 0.72 33 109-66-0 Pentane 72.15 1.3 8.0 38 0.10 0.15 0.78 30 109-67-1 1-Pentene 70.13 1.5 8.7 43 0.13 0.15 0.77 31 646-04-8 2-Pentene, (E)- 70.13 1.4 10.6 40 0.10 0.15 0.76 31 627-20-3 2-Pentene, (Z)- 70.13 1.4 10.6 40 0.10 0.15 0.75 31 

75-76-3 Tetramethylsilane 88.23 1.5 NA 54 0.17 0.17 0.59 40 

10025-78-2 Trichlorosilane 135.45 1.2 90.5 66 0.18 0.23 0.37 64 

109-92-2 Vinyl ethyl ether 72.11 1.7 28.0 50 0.10 0.15 0.65 36 

75-35-4 Vinylidene chloride 96.94 7.3 NA 290 0.15 0.18 0.44 54 

Notes: NA: Data not available.a Use the LLF only for leaks from tanks at atmospheric pressure.b "Dense" in the Reference Table column refers to the tables for dense gases and vapors. See Appendix D, Section D.4.4, for more informatreference tables.April 15, 1999 C - 9 
APPENDIX D

TECHNICAL BACKGROUND

April 15, 1999 
APPENDIX D TECHNICAL BACKGROUND 

D.1 Worst-Case Release Rate for Gases 

D.1.1 Unmitigated Release 

The assumption that the total quantity of toxic gas is released in 10 minutes is the same assumption 

used in EPA's Technical Guidance for Hazards Analysis (1987). 

D.1.2 Gaseous Release Inside Building 

The mitigation factor for gaseous release inside a building is based on a document entitled, Risk 

Mitigation in Land Use Planning: Indoor Releases of Toxic Gases, by S.R. Porter. This paper presented 

three release scenarios and discussed the mitigating effects that would occur in a building with a volume of 

1,000 cubic meters at three different building air exchange rates. There is a concern that a building may not 

be able to withstand the pressures of a very large release. However, this paper indicated that release rates of 

at least 2,000 pounds per minute could be withstood by a building. 

Analyzing the data in this paper several ways, the value of 55 percent emerged as representing the 

mitigation that could occur for a release scenario into a building. Data are provided on the maximum release 

rate in a building and the maximum release rate from a building. Making this direct comparison at the lower 

maximum release rate (3.36 kg/s) gave a release rate from the building of 55 percent of the release rate into 

the building. Using information provided on another maximum release rate (10.9 kg/min) and accounting for 

the time for the release to accumulate in the building, approximately 55 percent emerged again. 

The choice of building ventilation rates affects the results. The paper presented mitigation for three 

different ventilation rates, 0.5, 3, and 10 air changes per hour. A ventilation rate of 0.5 changes per hour is 

representative of specially designed, “gas-tight” buildings, based on the Porter reference. EPA decided that 

this ventilation rate was appropriate for this analysis. A mitigation factor of 55 percent may be used in the 

event of a gaseous release which does not destroy the building into which it is released. This factor may 

overstate the mitigation provided by a building with a higher ventilation rate. 

For releases of ammonia, chlorine, and sulfur dioxide, factors specific to the chemicals, the 

conditions of the release, and building ventilation rates have been developed to estimate mitigation of releases 

in buildings. For information on these factors and estimation of mitigated release rates, see Backup 

Information for the Hazard Assessments in the RMP Offsite Consequence Analysis Guidance, the 

Guidance for Wastewater Treatment Facilities and the Guidance for Ammonia Refrigeration - Anhydrous 

Ammonia, Aqueous Ammonia, Chlorine and Sulfur Dioxide. See also the industry-specific guidance 

documents for ammonia refrigeration and POTWs. 

D.2 Worst-Case Release Rate for Liquids 

D.2.1 Evaporation Rate Equation 

The equation for estimating the evaporation rate of a liquid from a pool is from the Technical 

Guidance for Hazards Analysis, Appendix G. The same assumptions are made for determination of 

April 15, 1999 
Appendix D 

Technical Background 

maximum pool area (i.e., the pool is assumed to be 1 centimeter (0.033 feet) deep). The evaporation rate 

equation has been modified to include a different mass transfer coefficient for water, the reference compound. 

For this document, a value of 0.67 centimeters per second is used as the mass transfer coefficient, instead of 

the value of 0.24 cited in the Technical Guidance for Hazards Analysis. The value of 0.67 is based on 

Donald MacKay and Ronald S. Matsugu, "Evaporation Rates of Liquid Hydrocarbon Spills on Land and 

Water," Canadian Journal of Chemical Engineering, August 1973, p. 434. The evaporation equation 

becomes: 

0.284 × U 0.78 × MW 2/3 × A × VP QR � (D-1) 82.05 × T 

where: QR = Evaporation rate (pounds per minute) 

U = Wind speed (meters per second) 

MW = Molecular weight (given in Exhibits B-1 and B-2, Appendix B, for toxic 

substances and Exhibits C-2 and C-3, Appendix C, for flammable 

substances) 

A = Surface area of pool formed by the entire quantity of the mixture (square 

feet) (determined as described in Section 3.2.2 of the text) 

VP = Vapor pressure (mm Hg) o T = Temperature of released substance (Kelvin (K); temperature in C plus 273, o or 298 for 25 C)

D.2.2 Factors for Evaporation Rate Estimates 

Liquid Factors. The liquid factors, Liquid Factor Ambient (LFA) and Liquid Factor Boiling (LFB), 

used to estimate the evaporation rate from a liquid pool (see Section 3.2 of this guidance document), are 

derived as described in the Technical Guidance for Hazards Analysis, Appendix G, with the following 

differences: 

� The mass transfer coefficient of water is assumed to be 0.67, as discussed above; the value 

of the factor that includes conversion factors, the mass transfer coefficient for water, and the 

molecular weight of water to the one-third power, given as 0.106 in the Technical Guidance 

is 0.284 in this guidance. 

� Density of all substances was assumed to be the density of water in the Technical Guidance; 

the density was included in the liquid factors. For this guidance document, density is not 

included in the LFA and LFB values presented in the tables; instead, a separate Density 

Factor (DF) (discussed below) is provided to be used in the evaporation rate estimation. 

With these modifications, the LFA is: 

0.284 × MW 2/3 × VP LFA � (D-2) 82.05 × 298 

where: MW = Molecular weight 

April 15, 1999 D - 2 
Appendix D 

Technical Background 

VP = Vapor pressure at ambient temperature (mm Hg) o 298 K (25 C) = Ambient temperature and temperature of released substance 

LFB is: 

0.284 × MW 2/3 × 760 LFB � (D-3) 82.05 × BP 

where: MW = Molecular weight 

760 = Vapor pressure at boiling temperature (mm Hg) 

BP = Boiling point (K) 

LFA and LFB values were developed for all toxic and flammable regulated liquids, and LFB values, 

to be used for analysis of gases liquefied by refrigeration, were developed for toxic and flammable gases. 

Density Factor. Because some of the regulated liquids have densities very different from that of 

water, the density of each substance was used to develop a Density Factor (DF) for the determination of 

maximum pool area for the evaporation rate estimation. DF values were developed for toxic and flammable 

liquids at ambient temperature and for toxic and flammable gases at their boiling points. The density factor 

is: 

1 DF � (D-4) d × 0.033 

2 where: DF = Density factor (1/(lbs/ft ))

d = Density of the substance in pounds per cubic foot 

0.033 = Depth of pool for maximum area (feet) 

Temperature Correction Factors. Temperature correction factors were developed for toxic liquids o released at temperatures above 25 C, the temperature used for development of the LFAs. The temperature 

correction factors are based on vapor pressures calculated from the coefficients provided in Physical and 

Thermodynamic Properties of Pure Chemicals, Data Compilation, developed by the Design Institute for 

Physical Property Data (DIPPR), American Institute of Chemical Engineers. The factors are calculated as 

follows: 

VPT × 298 

TCF � T VP298 × T (D-5) 

where: TCFT = Temperature Correction Factor at temperature T 

VPT = Vapor pressure at temperature T 

VP298 = Vapor pressure at 298 K 

T = Temperature (K) of released substance 

o o Factors were developed at intervals of 5 C for temperatures up to 50 C.

April 15, 1999 D - 3 
Appendix D 

Technical Background 

No correction factor was deemed necessary for changes in the density of the regulated toxic liquids 

with changes in temperature, although the density could affect the pool area and release rate estimates. 

Analysis of the temperature dependence of the density of these liquids indicated that the changes in density 

with temperature were very small compared to the changes in vapor pressure with temperature. 

D.2.3 Common Water Solutions and Oleum 

Water solutions of regulated toxic substances must be analyzed somewhat differently from pure toxic 

liquids. Except for solutions of relatively low concentration, the evaporation rate varies with the 

concentration of the solution. At one specific concentration, the composition of the liquid does not change as 

evaporation occurs. For concentrated solutions of volatile substances, the evaporation rate from a pool may 

decrease, very rapidly in some cases, as the toxic substance volatilizes and its concentration in the pool 

decreases. To analyze these changes, EPA used spreadsheets to estimate the vapor pressure, concentration, 

and release rate at various time intervals for regulated toxic substances in water solution evaporating from 

pools. In addition to the spreadsheet analysis, EPA used the ALOHA model with an additional step-function 

feature (not available in the public version). With this step-function feature, changes in the release rate could 

be incorporated and the effects of these changes on the consequence distance analyzed. The results of the 

spreadsheet calculations and the model were found to be in good agreement. The distance results obtained 

from the spreadsheet analysis and the model for various solutions were compared with the results from 

various time averages to examine the sensitivity of the results. An averaging time of 10 minutes was found to 

give reasonable agreement with the step-function model for most substances at various concentrations. The 

spreadsheet analysis also indicated that the first 10 minutes of evaporation was the most important, and the 

evaporation rate in the first 10 minutes likely could be used to estimate the distance to the endpoint. 

Oleum is a solution of sulfur trioxide in sulfuric acid. Sulfur trioxide evaporating from oleum 

exhibits release characteristics similar to those of toxic substances evaporating from water solutions. 

Analysis of oleum releases, therefore, was carried out in the same way as for water solutions. 

NOAA developed a computerized calculation method to estimate partial vapor pressures and release 

rates for regulated toxic substance in solution as a function of concentration, based on vapor pressure data 

from Perry's Chemical Engineers' Handbook and other sources. Using this method and spreadsheet 

calculations, EPA estimated partial vapor pressures and evaporation rates at one-minute intervals over 10 

minutes for solutions of various concentrations. The 10-minute time period was chosen based on the 

ALOHA results and other calculations. For each one-minute interval, EPA estimated the concentration of the 

solution based on the quantity evaporated in the previous interval and estimated the partial vapor pressure 

based on the concentration. These estimated vapor pressures were used to calculate an average vapor 

pressure over the 10-minute period; this average vapor pressure was used to derive Liquid Factor Ambient 

(LFA) values, as described above for liquids. Use of these factors is intended to give an evaporation rate that 

accounts for the decrease in evaporation rate expected to take place as the solution evaporates. 

Density Factors (DF) were developed for solutions of various concentrations from data in Perry's 

Chemical Engineers' Handbook and other sources, as discussed above for liquids. 

Because solutions do not have defined boiling points, EPA did not develop Liquid Factor Boiling 

(LFB) values for solutions. As a simple and conservative approach, the quantity of a regulated substance in a 

solution at an elevated temperatures is treated as a pure substance. The LFB for the pure substance, or the 

April 15, 1999 D - 4 
Appendix D 

Technical Background 

LFA and a temperature correction factor, is used to estimate the initial evaporation rate of the regulated 

substance from the solution. Only the first 10 minutes of evaporation are considered, as for solutions at 

ambient temperatures, because the release rate would decrease rapidly as the substance evaporates and the 

concentration in the solution decreases. This approach will likely give an overestimate of the release rate and 

of the consequence distance. 

D.2.4 Releases Inside Buildings 

If a liquid is released inside a building, its release to the outside air will be mitigated in two ways. 

First, the evaporation rate of the liquid may be much lower inside a building than outside. This is due to wind 

speed, which directly affects the evaporation rate. The second mitigating factor is that the building provides 

resistance to discharge of contaminated air to the outdoors. 

In this method, a conservative wind speed, U, of 0.1 meter per second (m/s) was assumed in the 

building. (See end of text for a justification of this wind speed.) For a release outdoors in a worst-case 

scenario, U is set to 1.5 m/s, and for an alternative scenario, U is set to 3 m/s. The evaporation rate equation 

is: 

QR � U 0.78 × (LFA, LFB)× A (D-6) 

where: QR = Release rate (pounds per minute (lbs/min)) 

U = Wind speed (meters per second (m/s)) 

LFA = Liquid Factor Ambient 

LFB = Liquid Factor Boiling 2 A = Area of pool (square feet (ft ))

As can be seen, if U inside a building is only 0.1, then the evaporation rate inside a building will be much 

lower than a corresponding evaporation rate outside (assuming the temperature is the same). The rate will 

only be (0.1/1.5) 0.78 , about 12 percent of the rate for a worst case, and (0.1/3) 0.78 , about seven percent of the 

rate for an alternative case. 

The evaporated liquid mixes with and contaminates the air in the building. What EPA is ultimately 

interested in is the rate at which this contaminated air exits the building. In order to calculate the release of 

contaminated air outside the building, EPA adapted a method from an UK Health and Safety Executive paper 

entitled, Risk Mitigation in Land Use Planning: Indoor Releases of Toxic Gases, by S.R. Porter. EPA 

assumed that the time for complete evaporation of the liquid pool was one hour. The rate at which 

contaminated air was released from the building during liquid evaporation (based on the paper) was assumed 

to be equal to the evaporation rate plus the building ventilation rate (no pressure buildup in building). The 

building ventilation rate was set equal to 0.5 air changes per hour. This ventilation rate is representative of a 

specially designed, “gas-tight” building. (The mitigation factor developed based on this type of building 

would overstate the mitigation provided by a building with higher ventilation rates.) EPA used a building 3 2 2 with a volume of 1,000 cubic meters (m ) and a floor area of 200 m (2,152 ft ) as an example for this

analysis. EPA assumed that the liquid pool would cover the entire building floor, representing a conservative 

scenario. 

April 15, 1999 D - 5 
Appendix D 

Technical Background 

To provide a conservative estimate, EPA calculated the evaporation rate for a spill of a volatile 

liquid, carbon disulfide (CS ), under ambient conditions inside the building: 2 

QR = 0.10.78 × 0.075 × 2,152 = 26.8 pounds per minute (lbs/min) 

3 Next, this evaporation rate was converted to cubic meters per minute (m /min) using the ideal gas

law (the molecular weight of CS is 76.1): 2 

3 3 26.8 lbs/min × 454 grams per pound (g/lb) × 1 mole CS /76.1 g × 0.0224 m /mole = 3.58 m /min. 2 

3 The ventilation rate of the building is 0.5 changes per hour, which equals 500 m per hour, or 8.33

m 3/min. Therefore, during evaporation, contaminated air is leaving the building at a rate of 8.33 + 3.58, or 3 11.9 m /min.

EPA used an iterative calculation for carbon disulfide leaving a building using the above calculated 

parameters. During the first minute of evaporation, 26.8 lbs of pure carbon disulfide evaporates, and EPA 

assumed this evenly disperses through the building so that the concentration of CS in the building air is 2 3 3 0.0268 lbs/m (assuming 1000 m volume in the building). Contaminated air is exiting the building at a rate 3 of 11.9 m /min, so EPA deduced that 11.9 × 0.0268 = 0.319 lbs of carbon disulfide exit the building in the

first minute, leaving 26.5 lbs still evenly dispersed inside. Since this release occurs over one minute, the 

release rate of the carbon disulfide to the outside is 0.319 lbs/min. During the second minute, another 26.8 

lbs of pure carbon disulfide evaporates and disperses, so that the building now contains 26.8 + 26.5 = 53.3 

lbs of carbon disulfide, or 0.0533 lbs/m .

3 Contaminated air is still exiting the building at a rate of 11.9 

m 3/min, so 11.9 × 0.05328 = 0.634 lbs of carbon disulfide are released, leaving 52.6 lbs inside. Again, this 

release occurs over one minute so that the rate of carbon disulfide exiting the building in terms of 

contaminated air is 0.634 lbs/min. EPA continued to perform this estimation over a period of one hour. The 

rate of release of carbon disulfide exiting the building in the contaminated air at the sixty minute mark is 13.7 

lbs/min. This represents the maximum rate of carbon disulfide leaving the building. After all of the carbon 

disulfide is evaporated, there is a drop in the concentration of carbon disulfide in the contaminated air leaving 

the building because the evaporation of carbon disulfide no longer contributes to the overall contamination of 

the air. 

Note that if the same size pool of carbon disulfide formed outside, the release rate for a worst-case 

scenario would be: 

QR = 1.50.78 × 0.075 × 2,152 = 221 lbs/min. 

and for an alternative case: 

QR = 30.78 × 0.075 × 2,152 = 380 lbs/min. 

The maximum release rate of carbon disulfide in the contaminated building air, assuming a 1,000 m3 

building with a building exchange rate of 0.5 air changes per hour, was only about 6 percent (13.7 ÷ 221 

lbs/min x 100) of the worst-case scenario rate, and only about 3.6 percent (13.7 ÷ 380 lbs/min x 100) of the 

alternative scenario rate. EPA set an overall building mitigation factor equal to 10 percent and five percent, 

respectively, in order to be conservative. Please note that (at a constant ventilation rate of 0.5 changes per 

April 15, 1999 D - 6 
Appendix D 

Technical Background 

hour) as the size of the building increases, the maximum rate of contaminated air leaving the building will 

decrease, although only slightly, because of the balancing effect of building volume and ventilation rate. 

Obviously, a higher ventilation rate will yield a higher maximum release rate of contaminated air from the 

building. 

For a release inside a building, EPA assumed a building air velocity of 0.1 m/s. This conservative 

value was derived by setting the size of the ventilation fan equal to 1.0 m .

2 This fan is exchanging air from 3 the building with the outside at a rate of 0.5 changes per hour. For a 1,000 m building, this value becomes 3 3 3 500 m /hour, or 0.14 m /s. Dividing 0.14 m /s by the area of the fan yields a velocity of 0.14 m/s, which was 

rounded down to 0.1 m/s. 

D.3 Toxic Endpoints 

The toxic endpoints for regulated toxic substances, which are specified in the RMP Rule, are 

presented in Appendix B, Exhibits B-1, B-2, and B-3. The endpoints were chosen as follows, in order of 

preference: 

(1) Emergency Response Planning Guideline 2 (ERPG-2), developed by the American Industrial 

Hygiene Association, if available; 

(2) Level of Concern (LOC) derived for extremely hazardous substances (EHSs) regulated 

under section 302 of the Emergency Planning and Community Right-to-Know Act (EPCRA) 

(see the Technical Guidance for Hazards Analysis for more information on LOCs); the 

LOC for EHSs is based on: 

-- One-tenth of the Immediately Dangerous to Life and Health (IDLH) level, 

developed by the National Institute of Occupational Safety and Health (NIOSH), 

using IDLH values developed before 1994, 

or, if no IDLH value is available, 

-- One-tenth of an estimated IDLH derived from toxicity data; the IDLH is estimated 

as described in Appendix D of the Technical Guidance for Hazards Analysis. 

Note that the LOCs were not updated using IDLHs published in 1994 and later, 

because NIOSH revised its methodology for the IDLHs. The EHS LOCs based on 

earlier IDLHs were reviewed by EPA’s Science Advisory Board, and EPA decided 

to retain the methodology that was reviewed. 

ERPG-2 is defined as the maximum airborne concentration below which it is believed nearly all 

individuals could be exposed for up to one hour without experiencing or developing irreversible or other 

serious health effects or symptoms that could impair an individual's ability to take protective action. 

IDLH (pre-1994) concentrations were defined in the NIOSH Pocket Guide to Chemical Hazards as 

representing the maximum concentration from which, in the event of respirator failure, one could escape 

within 30 minutes without a respirator and without experiencing any escape-impairing (e.g., severe eye 

April 15, 1999 D - 7 
Appendix D 

Technical Background 

irritation) or irreversible health effects. (As noted above, LOCs for EHSs were not updated to reflect 1994 

and later IDLHs.) 

The estimated IDLH is derived from animal toxicity data, in order of preferred data, as follows: 

� From median lethal concentration (LC 50) (inhalation): 0.1 x LC 50 

� From lowest lethal concentration (LC LO) (inhalation): 1 x LC LO 

� From median lethal dose (LD 50) (oral): 0.01 x LD 50 

� From lowest lethal dose (LD LO) (oral): 0.1 x LD LO 

The toxic endpoints based on LOCs for EHSs presented in the tables in Appendix B are, in some 

cases, different from the LOCs listed in the Technical Guidance for Hazards Analysis, because some of the 

LOCs were updated based on IDLHs that were published after the development of the LOCs (and before 

1994) or on new or revised toxicity data. 

D.4 Reference Tables for Distances to Toxic and Flammable Endpoints 

D.4.1 Neutrally Buoyant Gases 

Toxic Substances. Reference tables for distances to toxic endpoints for neutrally buoyant gases and 

vapors were derived from the Gaussian model using the longitudinal dispersion coefficients based on work by 

Beals (Guide to Local Diffusion of Air Pollutants, Technical Report 214. Scott Air Force Base, Illinois: 

U.S. Air Force, Air Weather Service, 1971). The reasons for using the Beals dispersion coefficients are 

discussed below. 

Longitudinal dispersion (dispersion in the along-wind direction) is generated mostly by vertical wind 

shear. Wind shear results from the tendency of the wind speed to assume a wind profile—the speed is lowest 

next to the ground and increases with height until it reaches an asymptotic value at approximately a few 

hundred feet above the surface. To account for shear-driven dispersion, any air dispersion model intended for 

modeling short-duration releases must include either (a) a formulation that accounts, either implicitly or 

explicitly, for the height-dependence of wind speed or (b) some type of parameterization that converts shear 

effect into �x, the standard deviation function in the along-wind direction.

Because the standard Gaussian formula does not incorporate �x (it includes only �y and �z, the 

crosswind and horizontal functions), very few alternate ways to formulate �x have been proposed. The 

simplest method was proposed by Turner (Workbook of Atmospheric Dispersion Estimates, Report PB-191 

482. Research Triangle Park, North Carolina: Office of Air Programs, U.S. Environmental Protection 

Agency, 1970), who suggested simply setting �x equal to �y. Textbooks such as that by Pasquill and Smith 

(Atmospheric Diffusion, 3rd ed. New York: Halstead Press, 1983) describe a well-known analytic model. 

However, this model is more complex than a Gaussian model because according to it, dispersion depends on 

wind shear and the vertical variation of the vertical diffusion coefficient. Wilson (Along-wind Diffusion of 

Source Transients, Atmospheric Environment 15:489-495, 1981) proposed another method in which �x is 

April 15, 1999 D - 8 
Appendix D 

Technical Background 

determined as a function of wind shear, but in a form that can then be used in a Gaussian model. However, it 

is now believed that Wilson's formulation gives �x values that are too large. 

To avoid the problems of the analytic method and Wilson's formulation, we chose to include a 

formulation for �x derived from work by Beals (1971). We had three reasons for doing so. First, in terms of 

magnitude, Beals' �x fell in the midrange of the alternative formulations that we reviewed. Second, Beals' �x 

indirectly accounts for wind shear by using (unpublished) experimental data. Third, both the ALOHA and 

DEGADIS models incorporate the Beals methodology. 

When a substance is dispersed downwind, the concentration in the air changes over time. To assess 

the health effects of potential exposure to the substance, the average concentration of the substance over 

some time period is determined. Averaging time is the time interval over which the instantaneous 

concentration of the hazardous material in the vapor cloud is averaged. Averaging time should generally be 

equal to or shorter than either the release duration or cloud duration and, if possible, should reflect the 

exposure time associated with the toxic exposure guideline of interest. The exposure time associated with the 

toxic endpoints specified under the RMP Rule include 30 minutes for the Immediately Dangerous to Life and 

Health (IDLH) level and 60 minutes for the Emergency Response Planning Guideline (ERPG). For the 

neutrally buoyant tables, the 10-minute release scenario was modeled using a 10-minute averaging time. The 

60-minute release scenario was modeled using a 30-minute averaging time to be consistent with the 30-

minute exposure time associated with the IDLH. A 60-minute averaging time may have underpredicted 

consequence distances and, therefore, was not used for development of the distance tables for this guidance. 

Cloud dispersion from a release of finite duration (10 and 60-minute releases) is calculated using an 

equation specified in the NOAA publication ALOHATM 5.0 Theoretical Description, Technical Memorandum 

NOS ORCA 65, August 1992. 

Flammable Substances. The reference tables of distances for vapor cloud fires of neutrally buoyant 

flammable substances were derived using the same model as for toxic substances, as described above. The 

endpoint for modeling was the lower flammability limit (LFL). For flammable substances, an averaging time 

of 0.1 minute (six seconds) was used, because fires are considered to be nearly instantaneous events. 

Distances of interest for flammable substances are generally much shorter than for toxic substance, 

because the LFL concentrations are much larger than the toxic endpoints. For the short distances found in 

modeling the flammable substances, modeling results were found to be the same for 10-minute and longer 

releases; therefore, one table of distances for rural conditions and one table for urban conditions, applicable 

for both 10-minute and longer releases, were developed for flammable substances. 

D.4.2 Dense Gases 

Toxic Substances. The reference tables for dense gases were developed using the widely accepted 

SLAB model, developed by Lawrence Livermore National Laboratory. SLAB solves conservation equations 

of mass, momentum, energy, and species for continuous, finite duration, and instantaneous releases. The 

reference tables were based on the evaporating pool algorithm. 

For the reference tables were developed based on modeling releases of hydrogen chloride (HCl). HCl 

was chosen based on a SLAB modeling analysis of a range of dispersion behavior for releases of regulated 

April 15, 1999 D - 9 
Appendix D 

Technical Background 

dense gases or vapors with different molecular weights. This analysis showed that releases of HCl generally 

provided conservative results under a variety of stability/wind speed combinations, release rates, and toxic 

endpoints. 

Similar to the modeling of neutrally buoyant plumes, the 10-minute release scenario of toxic 

chemicals was modeled using a 10-minute averaging time. The 60-minute release scenario was modeled 

using a 30-minute averaging time to be consistent with the 30-minute exposure time associated with the 

IDLH. 

For all dense gas tables, the reference height for the wind speed was 10 meters. Relative humidity o was assumed to be 50 percent, and the ambient temperature was 25 C. The source area was the smallest 

value that still enabled the model to run for all release rates. The surface roughness factor was one meter for 

urban scenarios and three centimeters for rural scenarios. 

Flammable Substances. For the reference tables for dispersion of dense flammable gases and vapors, 

for analysis of vapor cloud fires, the same model was used as for toxic substances, as described above, and 

the same assumptions were made. For the dispersion of flammable chemicals, averaging time should be very 

small (i.e., no more than a few seconds), because flammable vapors need only be exposed to an ignition 

source for a short period of time to initiate the combustion process. Thus, both the 10-minute and 60-minute 

reference tables for flammable substances use an averaging time of 10 seconds. The 10-minute and 60-

minute tables were combined for flammable substances because the modeling results were found to be the 

same. 

D.4.3 Chemical-Specific Reference Tables 

The chemical-specific reference tables of distances for ammonia, chlorine, and sulfur dioxide were 

developed for EPA’s risk management program guidance for ammonia refrigeration and for POTWs. For 

information on the chemical-specific modeling and development of the chemical-specific reference tables, see 

Backup Information for the Hazard Assessments in the RMP Offsite Consequence Analysis Guidance, the 

Guidance for Wastewater Treatment Facilities and the Guidance for Ammonia Refrigeration - Anhydrous 

Ammonia, Aqueous Ammonia, Chlorine and Sulfur Dioxide. See also the industry-specific guidance 

documents for ammonia refrigeration and POTWs. 

The modeling carried out for aqueous ammonia also is applied in this guidance to ammonia released 

as a neutrally buoyant plume in other situations. The tables of distances derived from this modeling would 

apply to evaporation of ammonia from a water solution, evaporation of ammonia liquefied by refrigeration, or 

ammonia releases from the vapor space of a vessel, because the ammonia would behave as a neutrally 

buoyant plume (or possibly buoyant in some cases). 

D.4.4 Choice of Reference Table for Dispersion Distances 

Gases. Exhibit B-1 of Appendix B indicates whether the reference tables for neutrally buoyant or 

dense gases should be used for each of the regulated toxic gases. Exhibit C-2, Appendix C, provides this 

information for flammable gases. The choice of reference table presented in these exhibits is based on the 

molecular weight of the regulated substance compared to air; however, a number of factors that may cause a 

substance with a molecular weight similar to or smaller than the molecular weight of air to behave as a dense 

April 15, 1999 D - 10 
Appendix D 

Technical Background 

gas should be considered in selecting the appropriate table. For example, a cold gas may behave as a dense 

gas, even if it is lighter than air at ambient temperature. Gases liquefied under pressure may be released as a 

mixture of vapor and liquid droplets; because of presence of liquid mixed with the vapor, a gas that is lighter 

than air may behave as a dense gas in such a release. A gas that polymerizes or forms hydrogen bonds (e.g., 

hydrogen fluoride) also may behave as a dense gas. 

Liquids and Solutions. Exhibits B-2 and B-3, Appendix B, and Exhibit C-3, Appendix C, indicate 

the reference table of distances to be used for each regulated liquid. The methodology presented in this 

guidance for consequence analysis for liquids and solutions assumes evaporation from a pool. All of the 

liquids regulated under CAA section 112(r) have molecular weights greater than the molecular weight of air; 

therefore, their vapor would be heavier than air. However, because the vapor from a pool will mix with air as 

it evaporates, the initial density of the vapor with respect to air may not in all cases indicate whether the vapor 

released from a pool should be modeled as a dense gas or a neutrally buoyant gas. If the rate of release from 

the pool is relatively low, the vapor-air mixture that is generated may be neutrally buoyant even if the vapor is 

denser than air, because the mixture may contain a relatively small fraction of the denser-than-air vapor; i.e., 

it may be mostly air. This may be the case particularly for some of the regulated toxic liquids with relatively 

low volatility. All of the regulated flammable substances have relatively high volatility; the reference tables 

for dense gases are assumed to be appropriate for analyzing dispersion of these flammable liquids. 

To identify toxic liquids with molecular weight greater than air that might behave as neutrally 

buoyant gases when evaporating from a pool, EPA used the ALOHA model for pool evaporation of a number 

of substances with a range of molecular weights and vapor pressures. Modeling was carried out for F 

stability and wind speed 1.5 meters per second (worst-case conditions) and for D stability and wind speed 3.0 

meters per second (alternative-case conditions). Pool spread to a depth of one centimeter was assumed. 

Additional modeling was carried out for comparison assuming different pool areas and depths. The 

molecular weight-vapor pressure combinations at which ALOHA used the neutrally buoyant gas model were 

used to develop the reference table choices given in Exhibit B-2 (for liquids) and B-3 (for solutions) in 

Appendix B. The neutrally buoyant tables should generally give reasonable results for pool evaporation 

under ambient conditions when indicated for liquids. At elevated temperatures, however, evaporation rates 

will be greater, and the dense gas tables should be used. 

The liquids for which the neutrally buoyant table is identified for the worst case probably can be 

expected to behave as neutrally buoyant vapors when evaporating from pools under ambient conditions in 

most situations, but there may be cases when they exhibit dense gas behavior. Other liquids, for which the 

neutrally buoyant tables are not indicated for the worst case, might release neutrally buoyant vapors under o some conditions (e.g., relatively small pools, temperature not much above 25 C). Similarly, the liquids for 

which the neutrally buoyant tables are indicated as appropriate for alternative scenario analysis probably can 

be considered to behave as neutrally buoyant vapors under the alternative scenario conditions in most cases; 

however, there may be cases where they will behave as dense gases, and there may be other liquids that in 

some cases would exhibit neutrally buoyant behavior when evaporating. The reference table choices shown 

in Exhibit B-2 are intended to reflect the most likely behavior of the substances; they will not predict 

behavior of the listed substances evaporating under all conditions. 

April 15, 1999 D - 11 
Appendix D 

Technical Background 

D.4.5 Additional Modeling for Comparison 

Modeling was carried out for two worst-case examples and two alternative-case examples, using two 

different models, for comparison with the results obtained from the methods and distance tables in this 

guidance. This modeling is discussed below. 

ALOHA Model. The Areal Locations of Hazardous Atmospheres (ALOHA) system was developed 

jointly by NOAA and EPA. ALOHA Version 5.2.1 was used for the comparison modeling. The parameters 

for ALOHA modeling were the same as specified in this guidance document for worst-case and alternative 

scenarios. The substances modeled are included in ALOHA’s chemical database, so no chemical data were 

entered for modeling. For consistency with the methodology used to develop the reference tables of distances, 

a wind speed height of 10 meters was selected for ALOHA modeling. 

For all of the substances modeled, the direct source model was chosen for ALOHA modeling, and the 

release rate estimated using the guidance methodology was entered as the release rate for ALOHA. ALOHA 

selected the dense gas model to estimate the distances to the endpoints in all cases. 

WHAZAN Model. The World Bank Hazard Analysis (WHAZAN) system was developed by 

Technica International in collaboration with the World Bank. The 1988 version of WHAZAN was used for 

the comparison modeling. The parameters for atmospheric stability, wind speed, and ambient temperature 

and humidity were the same as specified in this guidance document. For surface roughness, WHAZAN 

requires entry of a “roughness parameter,” rather than a height. Based on the discussion of this parameter in 

the WHAZAN Theory Manual, a roughness parameter of 0.07 (corresponding to flat land, few trees) was 

chosen as equivalent to the surface roughness of 3 centimeters used to represent rural topography in modeling 

to develop the distance tables for this guidance. A roughness parameter of 0.17 (for woods or rural area or 

industrial site) was chosen as equivalent to 1 meter, which was used to develop the urban distance tables. 

Data were added to the WHAZAN chemical database for acrylonitrile and allyl alcohol; ethylene oxide and 

chlorine were already included in the database. 

For WHAZAN modeling of the gases ethylene oxide and chlorine and the liquid acrylonitrile, the 

WHAZAN dense cloud dispersion model was used. For the alternative-case release of allyl alcohol, the 

buoyant plume dispersion model was used for consistency with the guidance methodology. The release rates 

estimated using the guidance methodology were entered as the release rates for all of the WHAZAN 

modeling. 

The WHAZAN dense cloud dispersion requires a “volume dilution factor” as one of its inputs. This 

factor was not explained; it was presumed to account for dilution of pressurized gases with air upon release. 

For the gases modeled, the default dilution factor of 60 was used; for acrylonitrile, a dilution factor of 0 was 

entered. This factor appears to have little effect on the distance results. 

D.5 Worst-Case Consequence Analysis for Flammable Substances 

The equation used for the vapor cloud explosion analysis for the worst case involving flammable 

substances is given in Appendix C. This equation is based on the TNT-equivalency method of the UK Health 

and Safety Executive, as presented in the publication of the Center for Chemical Process Safety of the 

American Institute of Chemical Engineers (AIChE), Guidelines for Evaluating the Characteristics of Vapor 

April 15, 1999 D - 12 
Appendix D 

Technical Background 

Cloud Explosions, Flash Fires, and BLEVEs (1994). The assumption was made for the worst case that the 

total quantity of the released substance is in the flammable part of the cloud. The AIChE document lists this 

assumption as one of a number that have been used for vapor cloud explosion blast prediction; it was chosen 

as a conservative assumption for the worst-case analysis. The yield factor of 10 percent was a conservative 

worst-case assumption, based on information presented in the AIChE document. According to the AIChE 

document, reported values for TNT equivalency for vapor cloud explosions range from a fraction of one 

percent to tens of percent; for most major vapor cloud explosions, the range is one to ten percent. 

The endpoint for the vapor cloud explosion analysis, 1 psi, is reported to cause damage such as 

shattering of glass windows and partial demolition of houses. Skin laceration from flying glass also is 

reported. This endpoint was chosen for the consequence analysis because of the potential for serious injuries 

to people from the property damage that might result from an explosion. 

The TNT equivalent model was chosen as the basis for the consequence analysis because of its 

simplicity and wide use. This model does not take into account site-specific factors and many chemicalspecific factors that may affect the results of a vapor cloud explosion. Other methods are available for vapor 

cloud explosion modeling; see the list of references in Appendix A for some publications that include 

information on other vapor cloud explosion modeling methods. 

D.6 Alternative Scenario Analysis for Gases 

The equation for estimating release rate of a gas from a hole in a tank is based on the equations for 

gas discharge rate presented in the Handbook of Chemical Hazard Analysis Procedures by the Federal 

Emergency Management Agency (FEMA), DOT, and EPA, and equations in EPA's Workbook of Screening 

Techniques for Assessing Impacts of Toxic Air Pollutants. The equation for an instantaneous discharge 

under non-choked flow conditions is: 

m � Cd Ah 2p0

�0 

�

��1 

p1 

p0 

2 

� � p1 

p0 

��1 

� (D-7) 

where: m = Discharge rate (kg/s) 

Cd = Discharge coefficient 2 Ah = Opening area (m ) 

� = Ratio of specific heats 

p0 = Tank pressure (Pascals) 

p1 = Ambient pressure (Pascals) 3 �0 = Density (kg/m ) 

Under choked flow conditions (maximum flow rate), the equation becomes: 

April 15, 1999 D - 13 
Appendix D 

Technical Background 

��1 

m � C 2 ��1 (D-8) d Ah �p0

�0 ��1 

For development of the equation and gas factors presented in this guidance, density (�) was rewritten 

as a function of pressure and molecular weight, based on the ideal gas law: 

p0 MW 

� � (D-9) R Tt 

where: MW = Molecular weight (kilograms per kilomole) 

R = Gas constant (8,314 Joules per degree-kilomole) 

Tt = Tank temperature (K) 

The choked flow equation can be rewritten: 

��1 

1 2 ��1 MW

m � C � (D-10) d Ah p0 

T ��1 8314 t 

To derive the equation presented in the guidance, all the chemical-specific properties, constants, and 

appropriate conversion factors were combined into the "Gas Factor" (GF). The discharge coefficient was 

assumed to have a value of 0.8, based on the screening value recommended in EPA's Workbook of Screening 

Techniques for Assessing Impacts of Toxic Air Pollutants. The GF was derived as follows: 

��1 

2 ��1 MW GF � � (D-11) 132.2 × 6,895 × 6.4516×10�4 × 0.8 

��1 8314 

where: 132.2 = Conversion factor for lbs/min to kg/s 

6,895 = Conversion factor for psi to Pascals (p )0 

6.4516 x 10 -4 = Conversion factor for square inches to square meters (A ) h 

GF values were calculated for all gases regulated under CAA section 112(r) and are listed in 

Appendix B, Exhibit B-1, for toxic gases and Appendix C, Exhibit C-2, for flammable gases. 

April 15, 1999 D - 14 
Appendix D 

Technical Background 

From the equation for choked flow above and the equation for the GF above, the initial release rate 

for a gas from a hole in a tank can be written as: 

QR � HA × Pt × 

1 

Tt 

× GF (D-12) 

where: QR = Release rate (pounds per minute) 

HA = Hole area (square inches) 

Pt = Tank pressure (psia) 

Tt = Tank temperature (K) 

D.7 Alternative Scenario Analysis for Liquids 

D.7.1 Releases from Holes in Tanks 

The equation for estimating release rate of a liquid from a hole in a tank is based on the equations for 

liquid release rate presented in the Handbook of Chemical Hazard Analysis Procedures by FEMA, DOT, 

and EPA and EPA's Workbook of Screening Techniques for Assessing Impacts of Toxic Air Pollutants. 

The equation for the instantaneous release rate is: 

m � A � � hCd �l 2g�l HL Hh � 2 P0 Pa (D-13) 

where: m = Discharge rate (kilograms per second) 

Ah = Opening area (square meters) 

Cd = Discharge coefficient (unitless) 

g = Gravitational constant (9.8 meters per second squared) 

�l = Liquid density (kilograms per cubic meter)

P0 = Storage pressure (Pascals)

Pa = Ambient pressure (Pascals)

HL = Liquid height above bottom of container (meters)

Hh = Height of opening (meters)

A version of this equation is presented in the guidance for use with data found in Appendix B, for 

gases liquefied under pressure. The equation in the text was derived using the conversion factors listed below 

and density factors and equilibrium vapor pressure or tank pressure values listed in Appendix B, Exhibit B-1. 

Equation D-13 becomes: 

QR � 132.2×6.4516×10�4

×0.8×HA 16.018×d×[2×9.8×16.018×d×LH×0.0254�2P

g

×6895] (D-14) 

April 15, 1999 D - 15 
Appendix D 

Technical Background 

where: QR = Release rate (pounds per minute) 

HA = Hole area (square inches) 

132.2 = Conversion factor for kilograms per second to pounds per minute 

6.4516 x 10 -4 = Conversion factor for square inches to square meters (HA) 

0.8 = Discharge coefficient (0.8) 

d = Liquid density (pounds per cubic foot); can derived by using the 

density factor: 1/(DFx0.033) 

16.018 = Conversion factor for pounds per cubic feet to kilograms per cubic 

meters (D) 

9.8 = Gravitational constant (meters per second squared) 

LH = Height of liquid above hole (inches) 

2.54 x 10 -2 = Conversion factor for inches to meters (LH) 

Pg = Gauge pressure in tank (psi) 

6,895 = Conversion factor for psi to Pascals (Pg) 

After combining the conversion factors and incorporating the density factor (DF), this equation becomes: 

0.7 669 QR � HA × 6.82 × LH � × P

g (D-15) DF2 DF 

For liquids stored at ambient pressure, Equation D-13 becomes: 

m � A � hCd�l 2g HL Hh (D-16) 

To derive the equation presented in the guidance for liquids under ambient pressure, all the chemicalspecific properties, constants, and conversion factors were combined into the "Liquid Leak Factor" (LLF). 

The discharge coefficient was assumed to have a value of 0.8, based on the screening value recommended in 

EPA's Workbook of Screening Techniques for Assessing Impacts of Toxic Air Pollutants. The LLF was 

derived as follows: 

LLF � 132.2 × 6.4516 × 10�4 × 0.1594 × 0.8 × 2×9.8× �l (D-17) 

where: LLF = Liquid Leak Factor (pounds per minute-inches2.5) 

132.2 = Conversion factor for kilograms per second to pounds per minute 

(m) 

6.4516 x 10 -4 = Conversion factor for square inches to square meters (Ah) 

0.1594 = Conversion factor for square root of inches to square root of meters 

(HL - Hh) 

0.8 = Discharge coefficient (0.8) 

9.8 = Gravitational constant (meters per second squared) 

�l = Liquid density (kilograms per cubic meter) 

April 15, 1999 D - 16 
Appendix D 

Technical Background 

LLF values were calculated for all liquids regulated under CAA section 112(r) and are listed in 

Appendix B, Exhibit B-2, for toxic liquids and Appendix C, Exhibit C-3, for flammable liquids. 

From the equation for liquid release rate from a hole in a tank at ambient pressure and the equation 

for the LLF, the initial release rate for a liquid from a tank under atmospheric pressure can be written as: 

QRL � HA × LH × LLF (D-18) 

where: QRL = Liquid release rate (pounds per minute) 

HA = Hole area (square inches) 

LH = Height of liquid above hole (inches) 

D.7.2 Releases from Pipes 

The equation used to estimate releases of liquids from pipes is the Bernoulli equation. It assumes 

that the density of the liquid is constant and does not account for losses in velocity due to wall friction. The 

equation follows: 

� � � � � (Pa Pb) g (Za Zb) (Vb 

2 Va 2

) 

(D-19) D gc 2gc 

where: Pa = Pressure at pipe inlet (Pascals) 

Pb = Pressure at pipe outlet (Pascals) 

Za = Height above datum plane at pipe inlet (meters) 

Zb = Height above datum plane at pipe release (meters) 

g = Gravitational acceleration (9.8 meters per second squared) 

gc = Newton's law proportionality factor (1.0) 

Va = Operational velocity (meters per second) 

Vb = Release velocity (meters per second) 

D = Density of liquid (kilograms per cubic meter) 

Isolating V yields: b 

2 g � c (Pa Pb) � � 2 g (Za � Zb) � Va 

2 V (D-20) b D 

To develop the equation presented in the text, conversion factors for English units and constants 

were incorporated as follows: 

April 15, 1999 D - 17 
Appendix D 

Technical Background 

2×6895×(PT�14.7)×DF×0.033 

Vb�197 � (2×9.8×0.3048×(Za �Zb) � 0.005082

×Va 

2 

16.08 (D-21) 

where: Vb = Release velocity (feet per minute) 

197 = Conversion factor for meters per second to feet per minute 

6895 = Conversion factor for psi to Pascals 

PT = Total pipe pressure (psi) 

14.7 = Atmospheric pressure (psi) 

16.08 = Conversion factor for pounds per cubic foot to kilograms per cubic meter 

DF = Density factor (1/(0.033 DF)= density in pounds per cubic foot) 2 9.8 = Gravitational acceleration (meters per second )

0.3048 = Conversion factor for feet to meters 

Z -Z b = Change in pipe elevation, inlet to outlet (feet) a 

0.00508= Conversion factor for feet per minute to meters per second 

V = Operational velocity (feet per minute) a 

D.8 Vapor Cloud Fires 

Factors for leaks from tanks for flammable substances (GF and LLF) were derived as described for 

toxic substances (see above). 

The endpoint for estimating impact distances for vapor cloud fires of flammable substances is the 

lower flammability limit (LFL). The LFL is one of the endpoints for releases of flammable substances 

specified in the RMP Rule. It was chosen to provide a reasonable, but not overly conservative, estimation of 

the possible extent of a vapor cloud fire. 

D.9 Pool Fires 

A factor used for estimating the distance to a heat radiation level from a pool fire that could cause 

second degree burns from a 40-second exposure was developed based on equations presented in the AIChE 

document, Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and 

BLEVEs and in the Netherlands TNO document, Methods for the Determination of Possible Damage to 

People and Objects Resulting from Releases of Hazardous Materials (1992). The AIChE and TNO 

documents present a point-source model that assumes that a selected fraction of the heat of combustion is 

emitted as radiation in all directions. The radiation per unit area received by a target at some distance from 

the point source is given by: 

f m H �

q � 4�x

c 

2 

a (D-22) 

April 15, 1999 D - 18 
Appendix D 

Technical Background 

where: q = Radiation per unit area received by the receptor (Watts per square meter) 

m = Rate of combustion (kilograms per second) 

� = Atmospheric transmissivity a 

Hc = Heat of combustion (Joules per kilogram) 

f = Fraction of heat of combustion radiated 

x = Distance from point source to receptor (meters) 

The fraction of combustion energy dissipated as thermal radiation (f in the equation above) is 

reported to range from 0.1 to 0.4. To develop factors for estimating distances for pool fires, this fraction was 

assumed to be 0.4 for all the regulated flammable substances. The heat radiation level (q) was assumed to be 

5 kilowatts (5,000 Watts) per square meter. This level is reported to cause second degree burns from a 40-

second exposure. One of the endpoints for releases of flammable substances specified in the RMP Rule is 5 

kilowatts per square meter for 40 seconds. It was assumed that people would be able to escape from the heat 

in 40 seconds. The atmospheric transmissivity (�a) was assumed equal to one.

For a pool fire of a flammable substance with a boiling point above the ambient temperature, the 

combustion rate can be estimated by the following empirical equation: 

0.0010 H A c m � Hv � C

p (Tb � Ta) (D-23) 

where: m = Rate of combustion (kilograms per second) 

Hc = Heat of combustion (Joules per kilogram) 

H = Heat of vaporization (Joules per kilogram) v 

C = Liquid heat capacity (Joules per kilogram-degree K) p 

A = Pool area (square meters)

Tb = Boiling temperature (K)

T = Ambient temperature (K) a 

0.0010 = Constant 

Combining Equations D-22 and D-23 (above), and assuming a heat radiation level of 5,000 Watts 

per square meter, gives the following equation for liquid pools of substances with boiling points above 

ambient temperature: 

0.0010 A 

Hv � C

p(Tb �Ta) (D-24) 

x � H 0.4 c 4�q 

or 

April 15, 1999 D - 19 
Appendix D 

Technical Background 

0.0001 A 

x � H c 5,000� (H �v C

p(Tb �Ta)) (D-25) 

where: x = Distance from point source to receptor (meters) 

q = Radiation per unit area received by the receptor = 5,000 Watts per square 

meter 

Hc = Heat of combustion (Joules per kilogram) 

f = Fraction of heat of combustion radiated = 0.4 

Hv = Heat of vaporization (Joules per kilogram) 

Cp = Liquid heat capacity (Joules per kilogram-degree Kelvin) 

A = Pool area (square meters) 

Tb = Boiling temperature (K) 

Ta = Ambient temperature (K) 

0.0010 = Constant 

For a pool fire of a flammable substance with a boiling point below the ambient temperature (i.e., 

liquefied gases) the combustion rate can be estimated by the following equation, based on the TNO 

document: 

0.0010 H A c m � (D-26) H v 

where: m = Rate of combustion (kilograms per second) 

Hv = Heat of vaporization (Joules per kilogram) 

Hc = Heat of combustion (Joules per kilogram) 

A = Pool area (square meters) 

0.0010 = Constant 

Then the equation for distance at which the radiation received equals 5,000 Watts per square meter becomes: 

0.0001 A 

x � H (D-27) c 5,000� Hv 

where: x = Distance from point source to receptor (meters) 

5,000 = Radiation per unit area received by the receptor (Watts per square meter) 

Hc = Heat of combustion (Joules per kilogram) 

Hv = Heat of vaporization (Joules per kilogram) 

A = Pool area (square meters) 

0.0001 = Derived constant (see equations D-20 and D-21) 

April 15, 1999 D - 20 
Appendix D 

Technical Background 

A "Pool Fire Factor" (PFF) was calculated for each regulated flammable liquid and gas (to be applied 

to gases liquefied by refrigeration) to allow estimation of the distance to the heat radiation level that would 

lead to second degree burns. For the derivation of this factor, ambient temperature was assumed to be 298 K o (25 C). Other factors are discussed above. The PFF for liquids with boiling points above ambient 

temperature was derived as follows: 

0.0001 PFF � H c 5,000� [H � � v C

p(Tb 298)] (D-28) 

where: 5,000 = Radiation per unit area received by the receptor (Watts per square meter) 

Hc = Heat of combustion (Joules per kilogram) 

Hv = Heat of vaporization (Joules per kilogram) 

Cp = Liquid heat capacity (Joules per kilogram-degree K) 

Tb = Boiling temperature (K) 

298 = Assumed ambient temperature (K) 

0.0001 = Derived constant (see above) 

For liquids with boiling points below ambient temperature, the PFF is derived as follows: 

0.0001 PFF � H (D-29) c 5,000� Hv 

where: 5,000 = Radiation per unit area received by the receptor (Watts per square meter) 

Hc = Heat of combustion (Joules per kilogram) 

Hv = Heat of vaporization (Joules per kilogram) 

0.0001 = Derived constant (see above) 

Distances where exposed people could potentially suffer second degree burns can be estimated as the 

PFF multiplied by the square root of the pool area (in square feet), as discussed in the text. 

D.10 BLEVEs 

Reference Table 30, the table of distances for BLEVEs, was developed based on equations presented 

in the AIChE document, Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash 

Fires, and BLEVEs. The Hymes point-source model for a fireball, as cited in the AIChE document, uses the 

following equation for the radiation received by a receptor: 

2.2 �a R Hc mf 

0.67 

q � (D-30) 

4�L 2 

where: q = Radiation received by the receptor (Watts per square meter) 

mf = Mass of fuel in the fireball (kg) 

April 15, 1999 D - 21 
Appendix D 

Technical Background 

�a = Atmospheric transmissivity

H = Heat of combustion (Joules per kilogram) c 

R = Radiative fraction of heat of combustion

L = Distance from fireball center to receptor (meters)

� = 3.14 

Hymes (as cited by AIChE) suggests the following values for R: 

R = 0.3 for vessels bursting below relief valve pressure

R = 0.4 for vessels bursting at or above relief valve pressure

For development of Reference Table 30, the following conservative assumptions were made: 

R = 0.4 

�a = 1 

The effects of radiant heat on an exposed person depend on both the intensity of the radiation and the 

duration of the exposure. For development of the table of distances for BLEVEs, it was assumed that the 

time of exposure would equal the duration of the fireball. The AIChE document gives the following 

equations for duration of a fireball: 

t

c � 0.45 mf 

1/3 for mf < 30,000 kg (D-31) 

and 

t

c � 2.6 mf 

1/6 for mf > 30,000 kg (D-32) 

where: mf = Mass of fuel (kg) 

tc = Combustion duration (seconds) 

According to several sources (e.g., Eisenberg, et al., Vulnerability Model, A Simulation System for 

Assessing Damage Resulting from Marine Spills; Mudan, Thermal Radiation Hazards from Hydrocarbon 

Pool Fires (citing K. Buettner)), the effects of thermal radiation are generally proportional to radiation 

intensity to the four-thirds power times time of exposure. Thus, a thermal "dose" can be estimated using the 

following equation: 

Dose � tq 4/3 (D-33) 

where: t = Duration of exposure (seconds) 

2 q = Radiation intensity (Watts/m )

The thermal "dose" that could cause second-degree burns was estimated assuming 40 seconds as the 

duration of exposure and 5,000 Watts/m2 as the radiation intensity. The corresponding dose is 3,420,000 

(Watts/m )

2 4/3

-second. 

April 15, 1999 D - 22 
Appendix D 

Technical Background 

For estimating the distance from a fireball at which a receptor might receive enough thermal radiation 

to cause second degree burns, the dose estimated above was substituted into the equation for radiation 

received from a fireball: 

3 

3,420,000 4 q � (D-34) 

t 

3/4 2.2 �a R Hc mf 

0.67 3,420,000 � (D-35) 

t 4�L 2 

2.2 �a R Hc mf 

0.67 

L � 3/4 (D-36) 3,420,000 4�

t 

where: L = Distance from fireball center to receptor (meters) 

q = Radiation received by the receptor (Watts per square meter) 

mf = Mass of fuel in the fireball (kg) 

� = Atmospheric transmissivity (assumed to be 1) a 

H = Heat of combustion (Joules per kilogram) c 

R = Radiative fraction of heat of combustion (assumed to be 0.4) 

t = Duration of the fireball (seconds) (estimated from the equations above); 

assumed to be duration of exposure 

Equation D-36 was used to develop the reference table for BLEVEs presented in the text (Reference 

Table 30). 

D.11 Alternative Scenario Analysis for Vapor Cloud Explosions 

According to T.A. Kletz, in "Unconfined Vapor Cloud Explosions" (Eleventh Loss Prevention 

Symposium, sponsored by AIChE, 1977), unconfined vapor cloud explosions almost always result from the 

release of flashing liquids. For this reason, the quantity in the cloud for the alternative scenario vapor cloud 

explosion in this guidance is based on the fraction flashed from the release of a flammable gas liquefied under 

pressure. The guidance provides a method to estimate the quantity in the cloud from the fraction flashed into 

vapor plus the quantity that might be carried along as aerosol. The recommendation to use twice the quantity 

flashed as the mass in the cloud (so long as it does not exceed the total amount of flammable substance 

available) is based on the method recommended by the UK Health and Safety Executive (HSE), as cited in the 

AIChE document, Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, 

and BLEVEs. The factor of two is intended to allow for spray and aerosol formation. 

April 15, 1999 D - 23 
Appendix D 

Technical Background 

The equation for the flash fraction, for possible use in for the alternative scenario analysis, is based 

on the Netherlands TNO document, Methods for the Calculation of the Physical Effects of the Escape of 

Dangerous Material (1980), Chapter 4, "Spray Release." The following equation is provided: 

Tb TbCl Tl X � X � ln 

vap (D-37) ,a vap,b Tl hv Tb 

where: X = Weight fraction of vapor after expansion vap,a 

Xvap,b = Weight fraction of vapor before expansion (assumed to be 0 for calculation 

of the flash fraction) 

Tb = Boiling temperature of gas compressed to liquid (K) 

Tl = Temperature of stored gas compressed to liquid (K) 

Cl = Specific heat of gas compressed to liquid (Joules/kilogram-K) 

h = Heat of evaporation of gas compressed to liquid (Joules/kilogram) v 

To develop a Flash Fraction Factor (FFF) for use in consequence analysis, compressed gases were o assumed to be stored at 25 C (298 K) (except in cases where the gas could not be liquefied at that

temperature). The equation for FFF is: 

TbCl 298 FFF � ln (D-38) hv Tb 

where: Tb = Boiling temperature of gas compressed to liquid (K) 

Cl = Specific heat of gas compressed to liquid (Joules/kilogram-K) 

h = Heat of evaporation of gas compressed to liquid (Joules/kilogram) v 

298 = Temperature of stored gas compressed to liquid (K) 

The recommendation to use a yield factor of 0.03 for the alternative scenario analysis for vapor cloud 

explosions also is based on the UK HSE method cited by AIChE. According to the AIChE document, this 

recommendation is based on surveys showing than most major vapor cloud explosions have developed 

between 1 percent and 3 percent of available energy. 

April 15, 1999 D - 24 
APPENDIX E

WORKSHEETS FOR OFFSITE CONSEQUENCE ANALYSIS

Using the Methods in this Guidance

April 15, 1999 
WORKSHEET 1

WORST-CASE ANALYSIS FOR TOXIC GAS

1. Select Scenario (defined by rule for worst case as release of largest quantity 

over 10 minutes) 

Guidance 

Reference 

� Identify toxic gas Name: 

CAS number: - -

Chapter 2 

Section 3.1 

� Identify largest quantity in 

largest vessel or pipeline 

Quantity (pounds): 

� Identify worst-case 

meteorological conditions 

Atmospheric stability class: F 

Wind speed: 1.5 m/s 

Ambient temperature: 25 C

o 

Relative humidity: 50% 

2. Determine Release Rate 

� Estimate release rate 

Quantity/10 min, except 

gases liquefied by 

refrigeration in some cases 

Release rate (lbs/min): 

Will release always take place in enclosure? 

(If yes, go to next step) 

Section 3.1.1 

� Revise release rate to 

account for passive mitigation 

(enclosure) 

Can release cause failure of enclosure? 

(If yes, use unmitigated release rate) 

Factor to account for enclosure: 0.55 

Mitigated release rate (lbs/min): 

Section 3.1.2 

3. Determine Distance to the Endpoint Specified by Rule 

� Identify endpoint Endpoint (mg/L): Exhibit B-1 

� Determine gas density 

Consider conditions (e.g., 

liquefied under pressure) 

Dense: 

Neutrally buoyant: 

Exhibit B-1 

� Determine site topography 

Rural and urban defined by 

rule 

Rural: 

Urban: 

Section 2.1 

� Determine appropriate 

reference table of distances 

Use 10-minute tables 

Reference table used (number): Chapter 4 

Reference 

Tables 1-12 

� Find distance on reference 

table 

Release rate/endpoint (neutrally buoyant): 

Distance to endpoint (mi): 

Chapter 4 

Reference 

Tables 1-12 

April 15, 1999 E - 1 
WORKSHEET 2

WORST-CASE ANALYSIS FOR TOXIC LIQUID

1. Select Scenario (defined by rule for worst case as release of largest quantity to 

form an evaporating pool) 

Guidance 

Reference 

� Identify toxic liquid 

� Identify concentration for 

solutions or mixtures 

Name: 

CAS number: - -

Concentration in solution or mixture (wt %): 

Chapter 2 

Section 3.2 

Section 3.2.4 

for mixtures � Identify largest quantity in 

largest vessel or pipeline 

Quantity (pounds): 

Quantity of regulated substance in mixture: 

� Identify worst-case 

meteorological conditions 

Atmospheric stability class: F 

Wind speed: 1.5 m/s 

Ambient temperature: 25 C

o 

Relative humidity: 50% 

2. Determine Release Rate 

� Determine temperature of 

spilled liquid 

Must be highest maximum 

daily temperature or process 

temperature, or boiling point 

for gases liquefied by 

refrigeration 

Temperature of liquid (C): o Section 3.2 

Section 3.1.3 

� Determine appropriate 

liquid factors for release rate 

estimation 

LFA: 

LFB: 

DF: 

TCF: 

Section 3.2, 

Exhibits B-2, 

B-4 

Section 3.3, 

Exhibit B-3 

for water 

solutions 

Estimate Maximum Pool Area 

� Estimate maximum pool 

area 

Spilled liquid forms pool 1 

cm deep 

Maximum pool area (ft ): 2 Section 3.2.3 

Equation 3-6 

April 15, 1999 E - 2 
WORKSHEET 2 (continued) 

Estimate Pool Area for Spill into Diked Area 

� Estimate diked area 

Consider failure of dikes or 

overflow of diked area 

Diked area (ft ): 2 

Is diked area smaller than maximum area? ____ 

(If no, use maximum area to estimate release rate) 

Diked volume (ft ): 3 

Spilled volume (ft ): 3 

Is spilled volume smaller than diked volume?___ 

(If no, estimate overflow) 

Overflow volume (ft ): 3 

Overflow area (ft ): 2 

Section 3.2.3 

� Choose pool area for release 

rate estimation 

Maximum area, diked area, 

or sum of diked area and 

overflow area 

Pool area (ft ): 2 Section 3.2.3 

Estimate Release Rate from Pool 

� Estimate release rate for 

undiked pool (maximum pool 

area) 

Based on quantity spilled, 

LFA or LFB, and DF 

Release rate (lbs/min): Section 3.2.2 

Section 3.2.4 

(mixtures) 

Equation 3-3 

or 3-4 

� Estimate release rate for 

diked pool (use pool area 

from previous section) 

Based on pool area and LFA 

or LFB 

Release rate (lbs/min): Section 3.2.2 

Section 3.2.4 

(mixtures) 

Equation 3-7 

or 3-8 

� Revise release rate for 

release in building 

Apply factor to release rate 

Release rate if outside (lbs/min) 

(Use release rate for undiked or diked pool) 

Factor to account for enclosure: 0.1 

Revised release rate (lbs/min): 

Section 3.2.3 

Equations 3-9, 

3-10 

� Revise release rate for 

temperature 

Apply appropriate TCF to 

release rate 

Revised release rate (lbs/min): Section 3.2.5 

Equation 3-11 

� Estimate duration of release Release duration (min): Section 3.2.2 

Equation 3-5 

April 15, 1999 E - 3 
WORKSHEET 2 (continued) 

3. Determine Distance to the Endpoint 

� Identify endpoint 

Specified by rule 

Endpoint (mg/L): Exhibit B-2 

� Determine vapor density Dense: 

Neutrally buoyant: 

Exhibit B-2 

� Determine site topography 

Rural and urban defined by 

rule 

Rural: 

Urban: 

Section 2.1 

� Determine appropriate 

reference table of distances 

Based on release duration, 

vapor density, topography 

Reference table used (number): Chapter 4 

Reference 

Tables 1-12 

� Find distance on reference 

table 

Release rate/endpoint (neutrally buoyant): 

Distance to endpoint (mi): 

Chapter 4 

Reference 

Tables 1-12 

April 15, 1999 E - 4 
WORKSHEET 3

WORST-CASE ANALYSIS FOR FLAMMABLE SUBSTANCE

1. Select Scenario (defined by rule for worst case as vapor cloud explosion of 

largest quantity) 

Guidance 

Reference 

� Identify flammable 

substance 

Name: 

CAS number: - -

Chapter 2 

Section 3.1 

� Identify largest quantity in 

largest vessel or pipeline 

Consider total quantity of 

flammable substance, 

including non-regulated 

substances in flammable 

mixtures 

Quantity (pounds): 

2. Determine Distance to the

yield factor assumed to be 

Endpoint (endpoint specified by the rule as 1 psi ov

10% for TNT-equivalent model) 

erpressure; 

� Estimate distance to 1 psi 

using Reference Table 

Find quantity, read distance 

from table 

Distance to 1 psi (mi): Chapter 5 

Reference 

Table 13 

� Alternatively, estimate 

distance to 1 psi using 

equation

For pure substance: 

Heat of combustion (kJ/kg): 

For mixture: 

Heat of combustion of major component 

(kJ/kg): 

Heats of combustion of other components 

(kJ/kg): , , 

Distance to 1 psi (mi). 

Chapter 5 

Appendix C.1 

 Appendix C.2 

Exhibit C-1 

April 15, 1999 E - 5 
WORKSHEET 4

ALTERNATIVE SCENARIO ANALYSIS FOR TOXIC GAS

1. Select Scenario Guidance 

Reference 

� Identify toxic gas Name: 

CAS number: - -

Chapter 6 

Chapter 7 

Section 7.1 � Identify conditions of 

storage or processing of toxic 

gas 

Treat gases liquefied by 

refrigeration as liquids 

Non-liquefied pressurized gas: 

Gas liquefied under pressure: 

In tank: 

In pipeline: 

Other (describe): 

� Develop alternative 

scenario 

� More likely than worst 

case 

� Should reach endpoint 

off site 

Describe scenario: 

� Identify average 

meteorological conditions 

Atmospheric stability class: D 

Wind speed: 3.0 m/s 

Ambient temperature: 25 C

o 

Relative humidity: 50% 

2. Determine Release Rate 

� Estimate gas release rate 

from hole in tank (choked/ 

maximum flow) for 

� Pressurized gas 

� Gas liquefied under 

pressure released from vapor 

space 

Hole area (in ): 2 

Tank pressure (psia): 

Tank temperature (K): 

GF: 

Release rate (lbs/min): 

Section 7.1.1 

Equation 7-1 

Exhibit B-1 

� Estimate flashing liquid 

release rate from hole in tank 

� Gas liquefied under 

pressure released from liquid 

space 

Hole area (in ): 2 

Tank pressure (psig): 

DF: 

Liquid height above hole (in): 

Release rate (lbs/min): 

Section 7.1.2 

Equation 7-2 

Exhibit B-1 

April 15, 1999 E - 6 
WORKSHEET 4 (continued) 

� Estimate flashing liquid 

release rate from break in 

long pipeline 

� Gas liquefied under 

pressure completely filling 

pipeline 

Initial flow rate (lbs/min): 

DF: 

Initial flow velocity (ft/min): 

Pipe pressure (psi): 

Change in pipe elevation (ft): 

Cross-sectional pipe area (ft ): 2 

Release rate (lbs/min): 

Sections 7.1.1 

and 7.2.1 

Exhibit B-1 

� Estimate release duration Time to stop release (min): 

Time to empty tank or pipe (min): 

Default release duration: 60 min 

Section 7.1.1 

� Revise release rate for 

passive mitigation (enclosure) 

Release rate if outside (lbs/min): 

Factor to account for enclosure: 0.55 

Revised release rate (lbs/min): 

Section 7.1.2 

Section 3.1.2 

� Revise release rate for 

active mitigation 

Active mitigation technique used: 

Time to stop release using active technique 

(min): 

Fractional release rate reduction by active 

technique: 

Revised release rate (lb/min): 

� Estimate release duration 

(mitigated release) 

Release duration (min): Section 7.1.2 

� Other release rate 

estimation 

Release rate (lb/min): 

Method of release rate estimation (describe): 

Release duration (min): 

3. Determine Distance to the Endpoint 

� Identify endpoint 

Specified by rule 

Endpoint (mg/L): Exhibit B-1 

� Determine gas density 

Consider conditions (e.g., 

liquefied under pressure, 

refrigeration) 

Dense: 

Neutrally buoyant: 

Exhibit B-1 

� Determine site topography 

Rural and urban defined by 

rule 

Rural: 

Urban: 

Section 2.1 

April 15, 1999 E - 7 
WORKSHEET 4 (continued) 

� Determine appropriate 

reference table of distances 

Based on release duration, 

vapor density, and 

topography 

Reference table used (number): Chapter 8 

Reference 

Tables 14-25 

� Find distance on reference 

table 

Release rate/endpoint (neutrally buoyant): 

Distance to endpoint (mi): 

Chapter 8 

Reference 

Tables 14-25 

April 15, 1999 E - 8 
WORKSHEET 5

ALTERNATIVE SCENARIO ANALYSIS FOR TOXIC LIQUID

1. Select Scenario Guidance 

Reference 

� Identify toxic liquid Include 

gases liquefied by 

refrigeration 

� Identify concentration for 

solutions or mixtures 

Name: 

CAS number: - -

Concentration in solution or mixture (wt %): 

Chapter 6 

Chapter 7 

Section 7.2 

� Identify conditions of 

storage or processing of toxic 

liquid 

Atmospheric tank: 

Pressurized tank: 

Pipeline: 

Other (describe): 

� Develop alternative 

scenario 

� More likely than worst 

case 

� Should reach endpoint 

off site 

Describe scenario: 

� Identify meteorological 

conditions 

Atmospheric stability class: F 

Wind speed: 3.0 m/s 

Ambient temperature: 25 C

o 

Relative humidity: 50% 

2. Determine Release Rate 

Determine Liquid Release Rate and Quantity Released into Pool 

� Estimate liquid release rate 

from hole in atmospheric tank 

Hole area (in ): 2 

LLF: 

Liquid height above hole (in): 

Liquid release rate (lbs/min): 

Section 7.2.1 

Equation 7-4 

Exhibit B-2 

� Estimate liquid release rate 

from break in long pipeline 

Initial flow rate (lbs/min): 

DF: 

Initial flow velocity (ft/min): 

Pipe pressure (psi): 

Change in pipe elevation (ft): 

Cross-sectional pipe area (ft ): 2 

Liquid release rate (lbs/min): 

Section 7.2.1 

Equations 7-5 

- 7-7 

Exhibit B-2 

� Estimate liquid release 

duration 

Time to stop release (min): 

Time to empty tank to level of hole (min): 

Section 7.2.1 

April 15, 1999 E - 9 
WORKSHEET 5 (continued) 

� Revise liquid release 

duration for active mitigation 

Active mitigation technique (describe): 

Time to stop release (min): 

Section 7.2.2 

� Estimate quantity of liquid 

released into pool 

Liquid release rate times 

duration 

Quantity of liquid released (lbs): Sections 7.2.1, 

7.2.2, 7.2.3 

Determine Pool Area and Evaporation Rate from Pool 

� Determine temperature of 

spilled liquid 

Temperature of liquid ( C): o Section 7.2.3 

� Determine appropriate 

liquid factors for release rate 

estimation 

LFA: 

LFB: 

DF: 

TCF: 

Sections 7.2.3, 

3.2, and 

Exhibits B-2, 

B-4 

Section 3.3 

and Exhibit B3 for water 

solutions 

Estimate Maximum Pool Area 

� Estimate maximum pool 

area 

Spilled liquid forms pool 1 

cm deep 

Maximum pool area (ft ): 2 Section 7.2.3, 

3.2.3 Equation 

3-6 

Estimate Pool Area for Spill into Diked Area 

� Estimate diked area 

Consider possibility of failure 

of dikes or overflow of diked 

area 

Diked area (ft ): 2 

Is diked area smaller than maximum area? ____ 

(If no, use maximum area to estimate release rate) 

Diked volume (ft ): 3 

Spilled volume (ft ): 3 

Is spilled volume smaller than diked volume?___ 

(If no, estimate overflow) 

Overflow volume (ft ): 3 

Overflow area (ft ): 2 

Section 7.2.3, 

3.2.3 

� Choose pool area for 

evaporation rate estimation 

Maximum area, diked area, 

or sum of diked area and 

overflow area 

Pool area (ft ): 2 Section 7.2.3, 

3.2.3 

April 15, 1999 E - 10 
WORKSHEET 5 (continued) 

Estimate Release Rate from Pool 

� Estimate release rate for 

undiked pool 

Based on quantity spilled, 

LFA or LFB, and DF 

Release rate (lbs/min): Section 7.2 3 

Section 3.2.4 

(mixtures) 

Equation 7-8 

or 7-9 

� Estimate release rate for 

diked pool (use pool area 

from previous section) 

Based on pool area and LFA 

or LFB 

Release rate (lbs/min): Sections 7.2.3, 

3.2.2 

Section 3.2.4 

(mixtures) 

Equation 7-10 

or 7-11 

� Revise release rate for 

temperature 

Apply appropriate TCF to 

release rate 

Revised release rate (lbs/min): Sections 7.2.3, 

3.2.5 

Equation 3-11 

� Revise release rate for 

release in building 

Apply factor to release rate 

Release rate if outside (lbs/min): 

Factor to account for enclosure: 0.05 

Revised release rate (lbs/min): 

Sections 7.2.3, 

3.2.3 

� Revise release rate for 

active mitigation technique 

Active mitigation technique used: 

Fractional release rate reduction by active 

technique: 

Revised release rate (lb/min): 

Section 7.2.3 

� Compare liquid release rate 

and pool evaporation rate 

� Choose smaller release rate 

as release rate for analysis 

Release rate (lb/min): Section 7.2.3 

3. Determine Distance to the Endpoint 

� Identify endpoint 

Specified by rule 

Endpoint (mg/L): Exhibit B-2 

� Determine vapor density Dense: 

Neutrally buoyant: 

Exhibit B-2 

� Determine site topography 

Rural and urban defined by 

rule 

Rural: 

Urban: 

Section 2.1 

April 15, 1999 E - 11 
WORKSHEET 5 (continued) 

� Determine appropriate 

reference table of distances 

Based on release duration, 

vapor density, and 

topography 

Reference table used (number): Chapter 8 

Reference 

Tables 14-25 

� Find distance on reference 

table 

Release rate/endpoint (neutrally buoyant): 

Distance to endpoint (mi): 

Chapter 8 

Reference 

Tables 14-25 

April 15, 1999 E - 12 
WORKSHEET 6

ALTERNATIVE SCENARIO ANALYSIS FOR FLAMMABLE SUBSTANCE

1. Select Scenario Guidance 

Reference 

� Identify flammable 

substance 

Name: 

CAS number: - -

Chapter 6 

� Identify conditions of 

storage or processing of 

flammable substance 

Treat gases liquefied by 

refrigeration as liquids 

Non-liquefied pressurized gas: 

Gas liquefied under pressure: 

Gas liquefied by refrigeration: 

Liquid under atmospheric pressure: 

Liquid under pressure greater than atmospheric: 

Other (describe): 

� Identify appropriate 

scenario 

� Vapor cloud fire 

� Pool fire 

� BLEVE/fireball 

� Vapor cloud explosion 

� Other (not covered by 

OCA Guidance) 

(describe): 

Alternative scenario/type of fire or explosion 

2. Determine Release Rate 

Determine Release Rate for Vapor Cloud Fire 

� For gas releases and 

flashing liquid releases, see 

Worksheet 4 

Release rate (lbs/min): Section 9.1 

Section 7.1 

Equations 7-1, 

7-2, 7-3 

Exhibit C-2 

� For liquid releases (nonflashing), see Worksheet 5 

Liquid release rate (lbs/min): 

Liquid release duration (min): 

Quantity in pool (lbs): 

Release rate to air (lbs/min): 

Section 9.2 

Section 7.2 

Equations 7-4-

7-12 

Exhibit C-3 

Determine Pool Area for Pool Fire 

Estimate pool area: See 

Worksheet 5 

Quantity in pool (lbs): 

Pool area (ft ): 2 

Sections 10.2 

Section 7.2 

Exhibits C-2, 

C-3 

April 15, 1999 E - 13 
WORKSHEET 6 (continued) 

Determine Quantity for BLEVE 

Determine quantity in tank Quantity (lbs): Section 10.3 

Determine Quantity for Vapor Cloud Explosion 

Determine quantity in tank Quantity (lbs): Section 10.4 

3. Determine Distance to the Endpoint 

� Identify endpoint suitable 

for scenario 

� LFL 

� 5 kW/m for 40 2 

seconds 

� 1 psi overpressure 

Endpoint: Chapter 6 

Exhibits C-2, 

C-3 

Determine Distance to LFL for Vapor Cloud Fire 

� Determine vapor density Dense: 

Neutrally buoyant: 

Exhibit B-2 

� Determine site topography 

Rural and urban defined by 

rule 

Rural: 

Urban: 

Section 2.1 

� Determine appropriate 

reference table of distances 

Based on vapor density and 

topography 

Reference table used (number): Section 10.1 

Reference 

Tables 26-29 

� Find distance on reference 

table 

Release rate/endpoint (neutrally buoyant): 

Distance to LFL (mi): 

Section 10.1 

Reference 

Tables 26-29 

Determine Distance to Heat Radiation Endpoint for Pool Fire 

� Calculate distance to 5 

kW/m 2 

PFF: 

Pool area (ft ): 2 

Distance (ft): 

Section 10.2 

Equation 10-1 

April 15, 1999 E - 14 
WORKSHEET 6 (continued) 

Determine Distance to Heat Radiation Endpoint for BLEVE 

Determine distance for 

radiation from fireball 

equivalent to 5 kW/m for 40 2 

seconds 

Quantity (lbs): 

Distance (mi): 

Section 10.3 

Reference 

Table 30 

Determine Distance to Overpressure Endpoint For Vapor Cloud Explosion 

Determine distance to 1 psi 

Quantity in cloud can be 

less than total quantity 

Yield factor can be less 

than 10% 

FFF: 

Quantity flashed: 

Yield factor: 

Distance to 1 psi (mi): 

Section 10.4 

Exhibit C-2 

Reference 

Table 13 

April 15, 1999 E - 15 
APPENDIX F

CHEMICAL ACCIDENT PREVENTION PROVISIONS

As codified at 40 CFR part 68 as of July 1, 1998
Pt. 67, App. A 

local agent, any noncompliance penalties owed by the source owner or operator shall be paid to the State or 

local agent. 

APPENDIX A TO PART 67—TECHNICAL 

SUPPORT DOCUMENT 

NOTE: EPA will make copies of appendix A 

available from: Director, Stationary Source 

Compliance Division, EN–341, 401 M Street, 

SW., Washington, DC 20460. 

[54 FR 25259, June 20, 1989] 

APPENDIX B TO PART 67—INSTRUCTION 

MANUAL 

NOTE: EPA will make copies of appendix B 

available from: Director, Stationary Source 

Compliance Division, EN–341, 401 M Street, 

SW., Washington, DC 20460. 

[54 FR 25259, June 20, 1989] 

APPENDIX C TO PART 67—COMPUTER 

PROGRAM 

NOTE: EPA will make copies of appendix C 

available from: Director, Stationary Source 

Compliance Division, EN–341, 401 M Street, 

SW., Washington, DC 20460. 

[54 FR 25259, June 20, 1989] 

PART 68—CHEMICAL ACCIDENT


PREVENTION PROVISIONS


Subpart A—General 

Sec. 

68.1 Scope. 

68.2 Stayed provisions. 

68.3 Definitions. 

68.10 Applicability. 

68.12 General requirements. 

68.15 Management. 

Subpart B—Hazard Assessment 

68.20 Applicability. 

68.22	 Offsite consequence analysis parameters. 

68.25 Worst-case release scenario analysis. 

68.28 Alternative release scenario analysis. 

68.30 Defining offsite impacts—population. 

68.33	 Defining offsite impacts—environment. 

68.36 Review and update. 

68.39 Documentation. 

68.42 Five-year accident history. 

Subpart C—Program 2 Prevention Program 

68.48 Safety information. 

68.50 Hazard review. 

68.52 Operating procedures. 

40 CFR Ch. I (7–1–98 Edition) 

68.54 Training. 

68.56 Maintenance. 

68.58 Compliance audits. 

68.60 Incident investigation. 

Subpart D—Program 3 Prevention Program 

68.65 Process safety information. 

68.67 Process hazard analysis. 

68.69 Operating procedures. 

68.71 Training. 

68.73 Mechanical integrity. 

68.75 Management of change. 

68.77 Pre-startup review. 

68.79 Compliance audits. 

68.81 Incident investigation. 

68.83 Employee participation. 

68.85 Hot work permit. 

68.87 Contractors. 

Subpart E—Emergency Response 

68.90 Applicability. 

68.95 Emergency response program. 

Subpart F—Regulated Substances for


Accidental Release Prevention


68.100 Purpose. 

68.115 Threshold determination. 

68.120 Petition process. 

68.125 Exemptions. 

68.130 List of substances. 

Subpart G—Risk Management Plan 

68.150 Submission. 

68.155 Executive summary. 

68.160 Registration. 

68.165 Offsite consequence analysis. 

68.168 Five-year accident history. 

68.170 Prevention program/Program 2. 

68.175 Prevention program/Program 3. 

68.180 Emergency response program. 

68.185 Certification. 

68.190 Updates. 

Subpart H—Other Requirements 

68.200 Recordkeeping. 

68.210	 Availability of information to the 

public. 

68.215	 Permit content and air permitting 

authority or designated agency requirements. 

68.220 Audits. 

APPENDIX A TO PART 68—TABLE OF TOXIC 

ENDPOINTS 

AUTHORITY: 42 U.S.C. 7412(r), 7601(a)(1), 

7661–7661f. 

SOURCE: 59 FR 4493, Jan. 31, 1994, unless 

otherwise noted. 

36

Environmental Protection Agency 

Subpart A—General 

§ 68.1 Scope. 

This part sets forth the list of regulated substances and thresholds, the 

petition process for adding or deleting 

substances to the list of regulated substances, the requirements for owners or 

operators of stationary sources concerning the prevention of accidental 

releases, and the State accidental release prevention programs approved 

under section 112(r). The list of substances, threshold quantities, and accident prevention regulations promulgated under this part do not limit in 

any way the general duty provisions 

under section 112(r)(1). 

§ 68.2 Stayed provisions. 

(a) Notwithstanding any other provision of this part, the effectiveness of 

the following provisions is stayed from 

March 2, 1994 to December 22, 1997. 

(1) In Sec. 68.3, the definition of ‘‘stationary source,’’ to the extent that 

such definition includes naturally occurring hydrocarbon reservoirs or 

transportation subject to oversight or 

regulation under a state natural gas or 

hazardous liquid program for which the 

state has in effect a certification to 

DOT under 49 U.S.C. 60105; 

(2) Section 68.115(b)(2) of this part, to 

the extent that such provision requires 

an owner or operator to treat as a regulated flammable substance: 

(i) Gasoline, when in distribution or 

related storage for use as fuel for internal combustion engines; 

(ii) Naturally occurring hydrocarbon 

mixtures prior to entry into a petroleum refining process unit or a natural 

gas processing plant. Naturally occurring hydrocarbon mixtures include any 

of the following: condensate, crude oil, 

field gas, and produced water, each as 

defined in paragraph (b) of this section; 

(iii) Other mixtures that contain a 

regulated flammable substance and 

that do not have a National Fire Protection Association flammability hazard rating of 4, the definition of which 

is in the NFPA 704, Standard System 

for the Identification of the Fire Hazards of Materials, National Fire Protection Association, Quincy, MA, 1990, 

available from the National Fire Pro­

§ 68.2 

tection Association, 1 Batterymarch 

Park, Quincy, MA 02269–9101; and 

(3) Section 68.130(a). 

(b) From March 2, 1994 to December 

22, 1997, the following definitions shall 

apply to the stayed provisions described in paragraph (a) of this section: 

Condensate means hydrocarbon liquid 

separated from natural gas that condenses because of changes in temperature, pressure, or both, and remains 

liquid at standard conditions. 

Crude oil means any naturally occurring, unrefined petroleum liquid. 

Field gas means gas extracted from a 

production well before the gas enters a 

natural gas processing plant. 

Natural gas processing plant means 

any processing site engaged in the extraction of natural gas liquids from 

field gas, fractionation of natural gas 

liquids to natural gas products, or 

both. A separator, dehydration unit, 

heater treater, sweetening unit, compressor, or similar equipment shall not 

be considered a ‘‘processing site’’ unless such equipment is physically located within a natural gas processing 

plant (gas plant) site. 

Petroleum refining process unit means 

a process unit used in an establishment 

primarily engaged in petroleum refining as defined in the Standard Industrial Classification code for petroleum 

refining (2911) and used for the following: Producing transportation fuels 

(such as gasoline, diesel fuels, and jet 

fuels), heating fuels (such as kerosene, 

fuel gas distillate, and fuel oils), or lubricants; separating petroleum; or separating, cracking, reacting, or reforming intermediate petroleum streams. 

Examples of such units include, but are 

not limited to, petroleum based solvent 

units, alkylation units, catalytic 

hydrotreating, catalytic hydrorefining, 

catalytic hydrocracking, catalytic reforming, catalytic cracking, crude distillation, lube oil processing, hydrogen 

production, isomerization, polymerization, thermal processes, and blending, 

sweetening, and treating processes. Petroleum refining process units include 

sulfur plants. 

Produced water means water extracted from the earth from an oil or 

natural gas production well, or that is 

37

§ 68.3 

separated from oil or natural gas after 

extraction. 

[59 FR 4493, Jan. 31, 1994, as amended at 61 

FR 31731, June 20, 1996] 

§ 68.3 Definitions. 

For the purposes of this part: 

Accidental release means an unanticipated emission of a regulated substance or other extremely hazardous 

substance into the ambient air from a 

stationary source. 

Act means the Clean Air Act as 

amended (42 U.S.C. 7401 et seq.) 

Administrative controls mean written 

procedural mechanisms used for hazard 

control. 

Administrator means the administrator of the U.S. Environmental Protection Agency. 

AIChE/CCPS means the American Institute of Chemical Engineers/Center 

for Chemical Process Safety. 

API means the American Petroleum 

Institute. 

Article means a manufactured item, 

as defined under 29 CFR 1910.1200(b), 

that is formed to a specific shape or design during manufacture, that has end 

use functions dependent in whole or in 

part upon the shape or design during 

end use, and that does not release or 

otherwise result in exposure to a regulated substance under normal conditions of processing and use. 

ASME means the American Society 

of Mechanical Engineers. 

CAS means the Chemical Abstracts 

Service. 

Catastrophic release means a major 

uncontrolled emission, fire, or explosion, involving one or more regulated 

substances that presents imminent and 

substantial endangerment to public 

health and the environment. 

Classified information means ‘‘classified information’’ as defined in the 

Classified Information Procedures Act, 

18 U.S.C. App. 3, section 1(a) as ‘‘any 

information or material that has been 

determined by the United States Government pursuant to an executive 

order, statute, or regulation, to require 

protection against unauthorized disclosure for reasons of national security.’’ 

Condensate means hydrocarbon liquid 

separated from natural gas that condenses due to changes in temperature, 

40 CFR Ch. I (7–1–98 Edition) 

pressure, or both, and remains liquid at 

standard conditions. 

Covered process means a process that 

has a regulated substance present in 

more than a threshold quantity as determined under § 68.115. 

Crude oil means any naturally occurring, unrefined petroleum liquid. 

Designated agency means the state, 

local, or Federal agency designated by 

the state under the provisions of 

§ 68.215(d) . 

DOT means the United States Department of Transportation. 

Environmental receptor means natural 

areas such as national or state parks, 

forests, or monuments; officially designated wildlife sanctuaries, preserves, 

refuges, or areas; and Federal wilderness areas, that could be exposed at 

any time to toxic concentrations, radiant heat, or overpressure greater than 

or equal to the endpoints provided in 

§ 68.22(a) , as a result of an accidental 

release and that can be identified on 

local U. S. Geological Survey maps. 

Field gas means gas extracted from a 

production well before the gas enters a 

natural gas processing plant. 

Hot work means work involving electric or gas welding, cutting, brazing, or 

similar flame or spark-producing operations. 

Implementing agency means the state 

or local agency that obtains delegation 

for an accidental release prevention 

program under subpart E, 40 CFR part 

63. The implementing agency may, but 

is not required to, be the state or local 

air permitting agency. If no state or 

local agency is granted delegation, 

EPA will be the implementing agency 

for that state. 

Injury means any effect on a human 

that results either from direct exposure to toxic concentrations; radiant 

heat; or overpressures from accidental 

releases or from the direct consequences of a vapor cloud explosion 

(such as flying glass, debris, and other 

projectiles) from an accidental release 

and that requires medical treatment or 

hospitalization. 

Major change means introduction of a 

new process, process equipment, or regulated substance, an alteration of process chemistry that results in any 

change to safe operating limits, or 

38

Environmental Protection Agency 

other alteration that introduces a new 

hazard. 

Mechanical integrity means the process of ensuring that process equipment 

is fabricated from the proper materials 

of construction and is properly installed, maintained, and replaced to 

prevent failures and accidental releases. 

Medical treatment means treatment, 

other than first aid, administered by a 

physician or registered professional 

personnel under standing orders from a 

physician. 

Mitigation or mitigation system means 

specific activities, technologies, or 

equipment designed or deployed to capture or control substances upon loss of 

containment to minimize exposure of 

the public or the environment. Passive 

mitigation means equipment, devices, 

or technologies that function without 

human, mechanical, or other energy 

input. Active mitigation means equipment, devices, or technologies that 

need human, mechanical, or other energy input to function. 

NFPA means the National Fire Protection Association. 

Natural gas processing plant (gas plant) 

means any processing site engaged in 

the extraction of natural gas liquids 

from field gas, fractionation of mixed 

natural gas liquids to natural gas products, or both, classified as North American Industrial Classification System 

(NAICS) code 211112 (previously Standard Industrial Classification (SIC) code 

1321). 

Offsite means areas beyond the property boundary of the stationary source, 

and areas within the property boundary to which the public has routine and 

unrestricted access during or outside 

business hours. 

OSHA means the U.S. Occupational 

Safety and Health Administration. 

Owner or operator means any person 

who owns, leases, operates, controls, or 

supervises a stationary source. 

Petroleum refining process unit means 

a process unit used in an establishment 

primarily engaged in petroleum refining as defined in NAICS code 32411 for 

petroleum refining (formerly SIC code 

2911) and used for the following: Producing transportation fuels (such as 

gasoline, diesel fuels, and jet fuels), 

heating fuels (such as kerosene, fuel 

§ 68.3 

gas distillate, and fuel oils), or lubricants; Separating petroleum; or Separating, cracking, reacting, or reforming intermediate petroleum streams. 

Examples of such units include, but are 

not limited to, petroleum based solvent 

units, alkylation units, catalytic 

hydrotreating, catalytic hydrorefining, 

catalytic hydrocracking, catalytic reforming, catalytic cracking, crude distillation, lube oil processing, hydrogen 

production, isomerization, polymerization, thermal processes, and blending, 

sweetening, and treating processes. Petroleum refining process units include 

sulfur plants. 

Population means the public. 

Process means any activity involving 

a regulated substance including any 

use, storage, manufacturing, handling, 

or on-site movement of such substances, or combination of these activities. For the purposes of this definition, any group of vessels that are 

interconnected, or separate vessels 

that are located such that a regulated 

substance could be involved in a potential release, shall be considered a single process. 

Produced water means water extracted from the earth from an oil or 

natural gas production well, or that is 

separated from oil or natural gas after 

extraction. 

Public means any person except employees or contractors at the stationary source. 

Public receptor means offsite residences, institutions (e.g., schools, hospitals), industrial, commercial, and office buildings, parks, or recreational 

areas inhabited or occupied by the public at any time without restriction by 

the stationary source where members 

of the public could be exposed to toxic 

concentrations, radiant heat, or overpressure, as a result of an accidental 

release. 

Regulated substance is any substance 

listed pursuant to section 112(r)(3) of 

the Clean Air Act as amended, in 

§ 68.130. 

Replacement in kind means a replacement that satisfies the design specifications. 

RMP means the risk management 

plan required under subpart G of this 

part. 

39

§ 68.10 

SIC means Standard Industrial Classification. 

Stationary source means any buildings, structures, equipment, installations, or substance emitting stationary 

activities which belong to the same industrial group, which are located on 

one or more contiguous properties, 

which are under the control of the 

same person (or persons under common 

control), and from which an accidental 

release may occur. The term stationary source does not apply to transportation, including storage incident to 

transportation, of any regulated substance or any other extremely hazardous substance under the provisions of 

this part. A stationary source includes 

transportation containers used for 

storage not incident to transportation 

and transportation containers connected to equipment at a stationary 

source for loading or unloading. Transportation includes, but is not limited 

to, transportation subject to oversight 

or regulation under 49 CFR parts 192, 

193, or 195, or a state natural gas or 

hazardous liquid program for which the 

state has in effect a certification to 

DOT under 49 U.S.C. section 60105. A 

stationary source does not include naturally occurring hydrocarbon reservoirs. Properties shall not be considered contiguous solely because of a 

railroad or pipeline right-of-way. 

Threshold quantity means the quantity specified for regulated substances 

pursuant to section 112(r)(5) of the 

Clean Air Act as amended, listed in 

§ 68.130 and determined to be present at 

a stationary source as specified in 

§ 68.115 of this part. 

Typical meteorological conditions 

means the temperature, wind speed, 

cloud cover, and atmospheric stability 

class, prevailing at the site based on 

data gathered at or near the site or 

from a local meteorological station. 

Vessel means any reactor, tank, 

drum, barrel, cylinder, vat, kettle, 

boiler, pipe, hose, or other container. 

Worst-case release means the release 

of the largest quantity of a regulated 

substance from a vessel or process line 

failure that results in the greatest distance to an endpoint defined in 

§ 68.22(a). 

[59 FR 4493, Jan. 31, 1994, as amended at 61 

FR 31717, June 20, 1996; 63 FR 644, Jan. 6, 1998] 

40 CFR Ch. I (7–1–98 Edition) 

§ 68.10 Applicability. 

(a) An owner or operator of a stationary source that has more than a 

threshold quantity of a regulated substance in a process, as determined 

under § 68.115, shall comply with the requirements of this part no later than 

the latest of the following dates: 

(1) June 21, 1999; 

(2) Three years after the date on 

which a regulated substance is first 

listed under § 68.130; or 

(3) The date on which a regulated 

substance is first present above a 

threshold quantity in a process. 

(b) Program 1 eligibility requirements. A covered process is eligible for 

Program 1 requirements as provided in 

§ 68.12(b) if it meets all of the following 

requirements: 

(1) For the five years prior to the 

submission of an RMP, the process has 

not had an accidental release of a regulated substance where exposure to the 

substance, its reaction products, overpressure generated by an explosion involving the substance, or radiant heat 

generated by a fire involving the substance led to any of the following offsite: 

(i) Death; 

(ii) Injury; or 

(iii) Response or restoration activities for an exposure of an environmental receptor; 

(2) The distance to a toxic or flammable endpoint for a worst-case release 

assessment conducted under Subpart B 

and § 68.25 is less than the distance to 

any public receptor, as defined in 

§ 68.30; and 

(3) Emergency response procedures 

have been coordinated between the stationary source and local emergency 

planning and response organizations. 

(c) Program 2 eligibility requirements. A covered process is subject to 

Program 2 requirements if it does not 

meet the eligibility requirements of either paragraph (b) or paragraph (d) of 

this section. 

(d) Program 3 eligibility requirements. A covered process is subject to 

Program 3 if the process does not meet 

the requirements of paragraph (b) of 

this section, and if either of the following conditions is met: 

40

Environmental Protection Agency 

(1) The process is in SIC code 2611, 

2812, 2819, 2821, 2865, 2869, 2873, 2879, or 

2911; or 

(2) The process is subject to the 

OSHA process safety management 

standard, 29 CFR 1910.119. 

(e) If at any time a covered process 

no longer meets the eligibility criteria 

of its Program level, the owner or operator shall comply with the requirements of the new Program level that 

applies to the process and update the 

RMP as provided in § 68.190. 

(f) The provisions of this part shall 

not apply to an Outer Continental 

Shelf (‘‘OCS’’) source, as defined in 40 

CFR 55.2. 

[61 FR 31717, June 20, 1996, as amended at 63 

FR 645, Jan. 6, 1998] 

§ 68.12 General requirements. 

(a) General requirements. The owner 

or operator of a stationary source subject to this part shall submit a single 

RMP, as provided in §§ 68.150 to 68.185. 

The RMP shall include a registration 

that reflects all covered processes. 

(b) Program 1 requirements. In addition to meeting the requirements of 

paragraph (a) of this section, the owner 

or operator of a stationary source with 

a process eligible for Program 1, as provided in § 68.10(b), shall: 

(1) Analyze the worst-case release 

scenario for the process(es), as provided 

in § 68.25; document that the nearest 

public receptor is beyond the distance 

to a toxic or flammable endpoint defined in § 68.22(a); and submit in the 

RMP the worst-case release scenario as 

provided in § 68.165; 

(2) Complete the five-year accident 

history for the process as provided in 

§ 68.42 of this part and submit it in the 

RMP as provided in § 68.168; 

(3) Ensure that response actions have 

been coordinated with local emergency 

planning and response agencies; and 

(4) Certify in the RMP the following: 

‘‘Based on the criteria in 40 CFR 68.10, 

the distance to the specified endpoint 

for the worst-case accidental release 

scenario for the following process(es) is 

less than the distance to the nearest 

public receptor: [list process(es)]. Within the past five years, the process(es) 

has (have) had no accidental release 

that caused offsite impacts provided in 

the risk management program rule (40 

§ 68.12 

CFR 68.10(b)(1)). No additional measures are necessary to prevent offsite 

impacts from accidental releases. In 

the event of fire, explosion, or a release 

of a regulated substance from the process(es), entry within the distance to 

the specified endpoints may pose a danger to public emergency responders. 

Therefore, public emergency responders should not enter this area except as 

arranged with the emergency contact 

indicated in the RMP. The undersigned 

certifies that, to the best of my knowledge, information, and belief, formed 

after reasonable inquiry, the information submitted is true, accurate, and 

complete. [Signature, title, date 

signed].’’ 

(c) Program 2 requirements. In addition to meeting the requirements of 

paragraph (a) of this section, the owner 

or operator of a stationary source with 

a process subject to Program 2, as provided in § 68.10(c), shall: 

(1) Develop and implement a management system as provided in § 68.15; 

(2) Conduct a hazard assessment as 

provided in §§ 68.20 through 68.42; 

(3) Implement the Program 2 prevention steps provided in §§ 68.48 through 

68.60 or implement the Program 3 prevention steps provided in §§ 68.65 

through 68.87; 

(4) Develop and implement an emergency response program as provided in 

§§ 68.90 to 68.95; and 

(5) Submit as part of the RMP the 

data on prevention program elements 

for Program 2 processes as provided in 

§ 68.170. 

(d) Program 3 requirements. In addition to meeting the requirements of 

paragraph (a) of this section, the owner 

or operator of a stationary source with 

a process subject to Program 3, as provided in § 68.10(d) shall: 

(1) Develop and implement a management system as provided in § 68.15; 

(2) Conduct a hazard assessment as 

provided in §§ 68.20 through 68.42; 

(3) Implement the prevention requirements of §§ 68.65 through 68.87; 

(4) Develop and implement an emergency response program as provided in 

§§ 68.90 to 68.95 of this part; and 

(5) Submit as part of the RMP the 

data on prevention program elements 

41

§ 68.15 

for Program 3 processes as provided in 

§ 68.175. 

[61 FR 31718, June 20, 1996] 

§ 68.15 Management. 

(a) The owner or operator of a stationary source with processes subject 

to Program 2 or Program 3 shall develop a management system to oversee 

the implementation of the risk management program elements. 

(b) The owner or operator shall assign a qualified person or position that 

has the overall responsibility for the 

development, implementation, and integration of the risk management program elements. 

(c) When responsibility for implementing individual requirements of 

this part is assigned to persons other 

than the person identified under paragraph (b) of this section, the names or 

positions of these people shall be documented and the lines of authority defined through an organization chart or 

similar document. 

[61 FR 31718, June 20, 1996] 

Subpart B—Hazard Assessment 

SOURCE: 61 FR 31718, June 20, 1996, unless 

otherwise noted. 

§ 68.20 Applicability. 

The owner or operator of a stationary source subject to this part shall 

prepare a worst-case release scenario 

analysis as provided in § 68.25 of this 

part and complete the five-year accident history as provided in § 68.42. The 

owner or operator of a Program 2 and 3 

process must comply with all sections 

in this subpart for these processes. 

§ 68.22 Offsite consequence analysis 

parameters. 

(a) Endpoints. For analyses of offsite 

consequences, the following endpoints 

shall be used: 

(1) Toxics. The toxic endpoints provided in appendix A of this part. 

(2) Flammables. The endpoints for 

flammables vary according to the scenarios studied: 

(i) Explosion. An overpressure of 1 

psi. 

(ii) Radiant heat/exposure time. A radiant heat of 5 kw/m2 for 40 seconds. 

40 CFR Ch. I (7–1–98 Edition) 

(iii) Lower flammability limit. A 

lower flammability limit as provided in 

NFPA documents or other generally 

recognized sources. 

(b) Wind speed/atmospheric stability 

class. For the worst-case release analysis, the owner or operator shall use a 

wind speed of 1.5 meters per second and 

F atmospheric stability class. If the 

owner or operator can demonstrate 

that local meteorological data applicable to the stationary source show a 

higher minimum wind speed or less stable atmosphere at all times during the 

previous three years, these minimums 

may be used. For analysis of alternative scenarios, the owner or operator 

may use the typical meteorological 

conditions for the stationary source. 

(c) Ambient temperature/humidity. 

For worst-case release analysis of a 

regulated toxic substance, the owner or 

operator shall use the highest daily 

maximum temperature in the previous 

three years and average humidity for 

the site, based on temperature/humidity data gathered at the stationary 

source or at a local meteorological station; an owner or operator using the 

RMP Offsite Consequence Analysis 

Guidance may use 25°C and 50 percent 

humidity as values for these variables. 

For analysis of alternative scenarios, 

the owner or operator may use typical 

temperature/humidity data gathered at 

the stationary source or at a local meteorological station. 

(d) Height of release. The worst-case 

release of a regulated toxic substance 

shall be analyzed assuming a ground 

level (0 feet) release. For an alternative 

scenario analysis of a regulated toxic 

substance, release height may be determined by the release scenario. 

(e) Surface roughness. The owner or 

operator shall use either urban or rural 

topography, as appropriate. Urban 

means that there are many obstacles in 

the immediate area; obstacles include 

buildings or trees. Rural means there 

are no buildings in the immediate area 

and the terrain is generally flat and 

unobstructed. 

(f) Dense or neutrally buoyant gases. 

The owner or operator shall ensure 

that tables or models used for dispersion analysis of regulated toxic substances appropriately account for gas 

density. 

42

Environmental Protection Agency 

(g) Temperature of released substance. For worst case, liquids other 

than gases liquified by refrigeration 

only shall be considered to be released 

at the highest daily maximum temperature, based on data for the previous three years appropriate for the 

stationary source, or at process temperature, whichever is higher. For alternative scenarios, substances may be 

considered to be released at a process 

or ambient temperature that is appropriate for the scenario. 

§ 68.25 Worst-case release scenario 

analysis. 

(a) The owner or operator shall analyze and report in the RMP: 

(1) For Program 1 processes, one 

worst-case release scenario for each 

Program 1 process; 

(2) For Program 2 and 3 processes: 

(i) One worst-case release scenario 

that is estimated to create the greatest 

distance in any direction to an endpoint provided in appendix A of this 

part resulting from an accidental release of regulated toxic substances 

from covered processes under worstcase conditions defined in § 68.22; 

(ii) One worst-case release scenario 

that is estimated to create the greatest 

distance in any direction to an endpoint defined in § 68.22(a) resulting from 

an accidental release of regulated flammable substances from covered processes under worst-case conditions defined in § 68.22; and 

(iii) Additional worst-case release 

scenarios for a hazard class if a worstcase release from another covered process at the stationary source potentially 

affects public receptors different from 

those potentially affected by the worstcase release scenario developed under 

paragraphs (a)(2)(i) or (a)(2)(ii) of this 

section. 

(b) Determination of worst-case release 

quantity. The worst-case release quantity shall be the greater of the following: 

(1) For substances in a vessel, the 

greatest amount held in a single vessel, 

taking into account administrative 

controls that limit the maximum quantity; or 

(2) For substances in pipes, the greatest amount in a pipe, taking into ac­

§ 68.25 

count administrative controls that 

limit the maximum quantity. 

(c) Worst-case release scenario—toxic 

gases. (1) For regulated toxic substances that are normally gases at ambient temperature and handled as a gas 

or as a liquid under pressure, the owner 

or operator shall assume that the 

quantity in the vessel or pipe, as determined under paragraph (b) of this section, is released as a gas over 10 minutes. The release rate shall be assumed 

to be the total quantity divided by 10 

unless passive mitigation systems are 

in place. 

(2) For gases handled as refrigerated 

liquids at ambient pressure: 

(i) If the released substance is not 

contained by passive mitigation systems or if the contained pool would 

have a depth of 1 cm or less, the owner 

or operator shall assume that the substance is released as a gas in 10 minutes; 

(ii) If the released substance is contained by passive mitigation systems 

in a pool with a depth greater than 1 

cm, the owner or operator may assume 

that the quantity in the vessel or pipe, 

as determined under paragraph (b) of 

this section, is spilled instantaneously 

to form a liquid pool. The volatilization rate (release rate) shall be calculated at the boiling point of the substance and at the conditions specified 

in paragraph (d) of this section. 

(d) Worst-case release scenario—toxic 

liquids. (1) For regulated toxic substances that are normally liquids at 

ambient temperature, the owner or operator shall assume that the quantity 

in the vessel or pipe, as determined 

under paragraph (b) of this section, is 

spilled instantaneously to form a liquid 

pool. 

(i) The surface area of the pool shall 

be determined by assuming that the 

liquid spreads to 1 centimeter deep unless passive mitigation systems are in 

place that serve to contain the spill 

and limit the surface area. Where passive mitigation is in place, the surface 

area of the contained liquid shall be 

used to calculate the volatilization 

rate. 

(ii) If the release would occur onto a 

surface that is not paved or smooth, 

the owner or operator may take into 

43

§ 68.28 

account the actual surface characteristics. 

(2) The volatilization rate shall account for the highest daily maximum 

temperature occurring in the past 

three years, the temperature of the 

substance in the vessel, and the concentration of the substance if the liquid spilled is a mixture or solution. 

(3) The rate of release to air shall be 

determined from the volatilization rate 

of the liquid pool. The owner or operator may use the methodology in the 

RMP Offsite Consequence Analysis 

Guidance or any other publicly available techniques that account for the 

modeling conditions and are recognized 

by industry as applicable as part of 

current practices. Proprietary models 

that account for the modeling conditions may be used provided the owner 

or operator allows the implementing 

agency access to the model and describes model features and differences 

from publicly available models to local 

emergency planners upon request. 

(e) Worst-case release scenario— 

flammables. The owner or operator shall 

assume that the quantity of the substance, as determined under paragraph 

(b) of this section, vaporizes resulting 

in a vapor cloud explosion. A yield factor of 10 percent of the available energy released in the explosion shall be 

used to determine the distance to the 

explosion endpoint if the model used is 

based on TNT-equivalent methods. 

(f) Parameters to be applied. The owner 

or operator shall use the parameters 

defined in § 68.22 to determine distance 

to the endpoints. The owner or operator may use the methodology provided 

in the RMP Offsite Consequence Analysis Guidance or any commercially or 

publicly available air dispersion modeling techniques, provided the techniques 

account for the modeling conditions 

and are recognized by industry as applicable as part of current practices. 

Proprietary models that account for 

the modeling conditions may be used 

provided the owner or operator allows 

the implementing agency access to the 

model and describes model features and 

differences from publicly available 

models to local emergency planners 

upon request. 

(g) Consideration of passive mitigation. 

Passive mitigation systems may be 

40 CFR Ch. I (7–1–98 Edition) 

considered for the analysis of worst 

case provided that the mitigation system is capable of withstanding the release event triggering the scenario and 

would still function as intended. 

(h) Factors in selecting a worst-case scenario. Notwithstanding the provisions 

of paragraph (b) of this section, the 

owner or operator shall select as the 

worst case for flammable regulated 

substances or the worst case for regulated toxic substances, a scenario based 

on the following factors if such a scenario would result in a greater distance 

to an endpoint defined in § 68.22(a) beyond the stationary source boundary 

than the scenario provided under paragraph (b) of this section: 

(1) Smaller quantities handled at 

higher process temperature or pressure; and 

(2) Proximity to the boundary of the 

stationary source. 

§ 68.28 Alternative release scenario 

analysis. 

(a) The number of scenarios. The 

owner or operator shall identify and 

analyze at least one alternative release 

scenario for each regulated toxic substance held in a covered process(es) and 

at least one alternative release scenario to represent all flammable substances held in covered processes. 

(b) Scenarios to consider. (1) For each 

scenario required under paragraph (a) 

of this section, the owner or operator 

shall select a scenario: 

(i) That is more likely to occur than 

the worst-case release scenario under 

§ 68.25; and 

(ii) That will reach an endpoint offsite, unless no such scenario exists. 

(2) Release scenarios considered 

should include, but are not limited to, 

the following, where applicable: 

(i) Transfer hose releases due to 

splits or sudden hose uncoupling; 

(ii) Process piping releases from failures at flanges, joints, welds, valves 

and valve seals, and drains or bleeds; 

(iii) Process vessel or pump releases 

due to cracks, seal failure, or drain, 

bleed, or plug failure; 

(iv) Vessel overfilling and spill, or 

overpressurization and venting through 

relief valves or rupture disks; and 

44

Environmental Protection Agency 

(v) Shipping container mishandling 

and breakage or puncturing leading to 

a spill. 

(c) Parameters to be applied. The 

owner or operator shall use the appropriate parameters defined in § 68.22 to 

determine distance to the endpoints. 

The owner or operator may use either 

the methodology provided in the RMP 

Offsite Consequence Analysis Guidance 

or any commercially or publicly available air dispersion modeling techniques, provided the techniques account for the specified modeling conditions and are recognized by industry as 

applicable as part of current practices. 

Proprietary models that account for 

the modeling conditions may be used 

provided the owner or operator allows 

the implementing agency access to the 

model and describes model features and 

differences from publicly available 

models to local emergency planners 

upon request. 

(d) Consideration of mitigation. Active and passive mitigation systems 

may be considered provided they are 

capable of withstanding the event that 

triggered the release and would still be 

functional. 

(e) Factors in selecting scenarios. 

The owner or operator shall consider 

the following in selecting alternative 

release scenarios: 

(1) The five-year accident history 

provided in § 68.42; and 

(2) Failure scenarios identified under 

§ 68.50 or § 68.67. 

§ 68.30 Defining offsite impacts—population. 

(a) The owner or operator shall estimate in the RMP the population within 

a circle with its center at the point of 

the release and a radius determined by 

the distance to the endpoint defined in 

§ 68.22(a). 

(b) Population to be defined. Population shall include residential population. The presence of institutions 

(schools, hospitals, prisons), parks and 

recreational areas, and major commercial, office, and industrial buildings 

shall be noted in the RMP. 

(c) Data sources acceptable. The owner 

or operator may use the most recent 

Census data, or other updated information, to estimate the population potentially affected. 

§ 68.39 

(d) Level of accuracy. Population shall 

be estimated to two significant digits. 

§ 68.33 Defining offsite impacts—environment. 

(a) The owner or operator shall list in 

the RMP environmental receptors 

within a circle with its center at the 

point of the release and a radius determined by the distance to the endpoint 

defined in § 68.22(a) of this part. 

(b) Data sources acceptable. The 

owner or operator may rely on information provided on local U.S. Geological Survey maps or on any data source 

containing U.S.G.S. data to identify 

environmental receptors. 

68.36 Review and update. 

(a) The owner or operator shall review and update the offsite consequence analyses at least once every 

five years. 

(b) If changes in processes, quantities 

stored or handled, or any other aspect 

of the stationary source might reasonably be expected to increase or decrease the distance to the endpoint by 

a factor of two or more, the owner or 

operator shall complete a revised analysis within six months of the change 

and submit a revised risk management 

plan as provided in § 68.190. 

§ 68.39 Documentation. 

The owner or operator shall maintain 

the following records on the offsite 

consequence analyses: 

(a) For worst-case scenarios, a description of the vessel or pipeline and 

substance selected as worst case, assumptions and parameters used, and 

the rationale for selection; assumptions shall include use of any administrative controls and any passive mitigation that were assumed to limit the 

quantity that could be released. Documentation shall include the anticipated effect of the controls and mitigation on the release quantity and rate. 

(b) For alternative release scenarios, 

a description of the scenarios identified, assumptions and parameters used, 

and the rationale for the selection of 

specific scenarios; assumptions shall 

include use of any administrative controls and any mitigation that were assumed to limit the quantity that could 

45

§ 68.42 

be released. Documentation shall include the effect of the controls and 

mitigation on the release quantity and 

rate. 

(c) Documentation of estimated 

quantity released, release rate, and duration of release. 

(d) Methodology used to determine 

distance to endpoints. 

(e) Data used to estimate population 

and environmental receptors potentially affected. 

§ 68.42 Five-year accident history. 

(a) The owner or operator shall include in the five-year accident history 

all accidental releases from covered 

processes that resulted in deaths, injuries, or significant property damage on 

site, or known offsite deaths, injuries, 

evacuations, sheltering in place, property damage, or environmental damage. 

(b) Data required. For each accidental 

release included, the owner or operator 

shall report the following information: 

(1) Date, time, and approximate duration of the release; 

(2) Chemical(s) released; 

(3) Estimated quantity released in 

pounds; 

(4) The type of release event and its 

source; 

(5) Weather conditions, if known; 

(6) On-site impacts; 

(7) Known offsite impacts; 

(8) Initiating event and contributing 

factors if known; 

(9) Whether offsite responders were 

notified if known; and 

(10) Operational or process changes 

that resulted from investigation of the 

release. 

(c) Level of accuracy. Numerical estimates may be provided to two significant digits. 

Subpart C—Program 2 Prevention

Program 

SOURCE: 61 FR 31721, June 20, 1996, unless 

otherwise noted. 

§ 68.48 Safety information. 

(a) The owner or operator shall compile and maintain the following up-todate safety information related to the 

40 CFR Ch. I (7–1–98 Edition) 

regulated substances, processes, and 

equipment: 

(1) Material Safety Data Sheets that 

meet the requirements of 29 CFR 

1910.1200(g); 

(2) Maximum intended inventory of 

equipment in which the regulated substances are stored or processed; 

(3) Safe upper and lower temperatures, pressures, flows, and compositions; 

(4) Equipment specifications; and 

(5) Codes and standards used to design, build, and operate the process. 

(b) The owner or operator shall ensure that the process is designed in 

compliance with recognized and generally accepted good engineering practices. Compliance with Federal or state 

regulations that address industry-specific safe design or with industry-specific design codes and standards may be 

used to demonstrate compliance with 

this paragraph. 

(c) The owner or operator shall update the safety information if a major 

change occurs that makes the information inaccurate. 

§ 68.50 Hazard review. 

(a) The owner or operator shall conduct a review of the hazards associated 

with the regulated substances, process, 

and procedures. The review shall identify the following: 

(1) The hazards associated with the 

process and regulated substances; 

(2) Opportunities for equipment malfunctions or human errors that could 

cause an accidental release; 

(3) The safeguards used or needed to 

control the hazards or prevent equipment malfunction or human error; and 

(4) Any steps used or needed to detect 

or monitor releases. 

(b) The owner or operator may use 

checklists developed by persons or organizations knowledgeable about the 

process and equipment as a guide to 

conducting the review. For processes 

designed to meet industry standards or 

Federal or state design rules, the hazard review shall, by inspecting all 

equipment, determine whether the 

process is designed, fabricated, and operated in accordance with the applicable standards or rules. 

46

Environmental Protection Agency 

(c) The owner or operator shall document the results of the review and ensure that problems identified are resolved in a timely manner. 

(d) The review shall be updated at 

least once every five years. The owner 

or operator shall also conduct reviews 

whenever a major change in the process occurs; all issues identified in the 

review shall be resolved before startup 

of the changed process. 

§ 68.52 Operating procedures. 

(a) The owner or operator shall prepare written operating procedures that 

provide clear instructions or steps for 

safely conducting activities associated 

with each covered process consistent 

with the safety information for that 

process. Operating procedures or instructions provided by equipment manufacturers or developed by persons or 

organizations knowledgeable about the 

process and equipment may be used as 

a basis for a stationary source’s operating procedures. 

(b) The procedures shall address the 

following: 

(1) Initial startup; 

(2) Normal operations; 

(3) Temporary operations; 

(4) Emergency shutdown and operations; 

(5) Normal shutdown; 

(6) Startup following a normal or 

emergency shutdown or a major change 

that requires a hazard review; 

(7) Consequences of deviations and 

steps required to correct or avoid deviations; and 

(8) Equipment inspections. 

(c) The owner or operator shall ensure that the operating procedures are 

updated, if necessary, whenever a 

major change occurs and prior to startup of the changed process. 

§ 68.54 Training. 

(a) The owner or operator shall ensure that each employee presently operating a process, and each employee 

newly assigned to a covered process 

have been trained or tested competent 

in the operating procedures provided in 

§ 68.52 that pertain to their duties. For 

those employees already operating a 

process on June 21, 1999, the owner or 

operator may certify in writing that 

the employee has the required knowl­

§ 68.56 

edge, skills, and abilities to safely 

carry out the duties and responsibilities as provided in the operating procedures. 

(b) Refresher training. Refresher 

training shall be provided at least 

every three years, and more often if 

necessary, to each employee operating 

a process to ensure that the employee 

understands and adheres to the current 

operating procedures of the process. 

The owner or operator, in consultation 

with the employees operating the process, shall determine the appropriate 

frequency of refresher training. 

(c) The owner or operator may use 

training conducted under Federal or 

state regulations or under industryspecific standards or codes or training 

conducted by covered process equipment vendors to demonstrate compliance with this section to the extent 

that the training meets the requirements of this section. 

(d) The owner or operator shall ensure that operators are trained in any 

updated or new procedures prior to 

startup of a process after a major 

change. 

§ 68.56 Maintenance. 

(a) The owner or operator shall prepare and implement procedures to 

maintain the on-going mechanical integrity of the process equipment. The 

owner or operator may use procedures 

or instructions provided by covered 

process equipment vendors or procedures in Federal or state regulations or 

industry codes as the basis for stationary source maintenance procedures. 

(b) The owner or operator shall train 

or cause to be trained each employee 

involved in maintaining the on-going 

mechanical integrity of the process. To 

ensure that the employee can perform 

the job tasks in a safe manner, each 

such employee shall be trained in the 

hazards of the process, in how to avoid 

or correct unsafe conditions, and in the 

procedures applicable to the employee’s job tasks. 

(c) Any maintenance contractor shall 

ensure that each contract maintenance 

employee is trained to perform the 

maintenance procedures developed 

under paragraph (a) of this section. 

47

§ 68.58 

(d) The owner or operator shall perform or cause to be performed inspections and tests on process equipment. 

Inspection and testing procedures shall 

follow recognized and generally accepted good engineering practices. The frequency of inspections and tests of process equipment shall be consistent with 

applicable manufacturers’ recommendations, industry standards or 

codes, good engineering practices, and 

prior operating experience. 

§ 68.58 Compliance audits. 

(a) The owner or operator shall certify that they have evaluated compliance with the provisions of this subpart at least every three years to verify that the procedures and practices 

developed under the rule are adequate 

and are being followed. 

(b) The compliance audit shall be 

conducted by at least one person 

knowledgeable in the process. 

(c) The owner or operator shall develop a report of the audit findings. 

(d) The owner or operator shall 

promptly determine and document an 

appropriate response to each of the 

findings of the compliance audit and 

document that deficiencies have been 

corrected. 

(e) The owner or operator shall retain 

the two (2) most recent compliance 

audit reports. This requirement does 

not apply to any compliance audit report that is more than five years old. 

§ 68.60 Incident investigation. 

(a) The owner or operator shall investigate each incident which resulted in, 

or could reasonably have resulted in a 

catastrophic release. 

(b) An incident investigation shall be 

initiated as promptly as possible, but 

not later than 48 hours following the 

incident. 

(c) A summary shall be prepared at 

the conclusion of the investigation 

which includes at a minimum: 

(1) Date of incident; 

(2) Date investigation began; 

(3) A description of the incident; 

(4) The factors that contributed to 

the incident; and, 

(5) Any recommendations resulting 

from the investigation. 

(d) The owner or operator shall 

promptly address and resolve the inves40 CFR Ch. I (7–1–98 Edition) 

tigation findings and recommendations. Resolutions and corrective actions shall be documented. 

(e) The findings shall be reviewed 

with all affected personnel whose job 

tasks are affected by the findings. 

(f) Investigation summaries shall be 

retained for five years. 

Subpart D—Program 3 Prevention

Program 

SOURCE: 61 FR 31722, June 20, 1996, unless 

otherwise noted. 

§ 68.65 Process safety information. 

(a) In accordance with the schedule 

set forth in § 68.67, the owner or operator shall complete a compilation of 

written process safety information before conducting any process hazard 

analysis required by the rule. The compilation of written process safety information is to enable the owner or operator and the employees involved in operating the process to identify and understand the hazards posed by those processes involving regulated substances. 

This process safety information shall 

include information pertaining to the 

hazards of the regulated substances 

used or produced by the process, information pertaining to the technology of 

the process, and information pertaining to the equipment in the process. 

(b) Information pertaining to the 

hazards of the regulated substances in 

the process. This information shall 

consist of at least the following: 

(1) Toxicity information; 

(2) Permissible exposure limits; 

(3) Physical data; 

(4) Reactivity data: 

(5) Corrosivity data; 

(6) Thermal and chemical stability 

data; and 

(7) Hazardous effects of inadvertent 

mixing of different materials that 

could foreseeably occur. 

NOTE TO PARAGRAPH (b): Material Safety 

Data Sheets meeting the requirements of 29 

CFR 1910.1200(g) may be used to comply with 

this requirement to the extent they contain 

the information required by this subparagraph. 

(c) Information pertaining to the 

technology of the process. 

48

Environmental Protection Agency 

(1) Information concerning the technology of the process shall include at 

least the following: 

(i) A block flow diagram or simplified 

process flow diagram; 

(ii) Process chemistry; 

(iii) Maximum intended inventory; 

(iv) Safe upper and lower limits for 

such items as temperatures, pressures, 

flows or compositions; and, 

(v) An evaluation of the consequences 

of deviations. 

(2) Where the original technical information no longer exists, such information may be developed in conjunction with the process hazard analysis 

in sufficient detail to support the analysis. 

(d) Information pertaining to the 

equipment in the process. 

(1) Information pertaining to the 

equipment in the process shall include: 

(i) Materials of construction; 

(ii) Piping and instrument diagrams 

(P&ID’s); 

(iii) Electrical classification; 

(iv) Relief system design and design 

basis; 

(v) Ventilation system design; 

(vi) Design codes and standards employed; 

(vii) Material and energy balances for 

processes built after June 21, 1999; and 

(viii) Safety systems (e.g. interlocks, 

detection or suppression systems). 

(2) The owner or operator shall document that equipment complies with 

recognized and generally accepted good 

engineering practices. 

(3) For existing equipment designed 

and constructed in accordance with 

codes, standards, or practices that are 

no longer in general use, the owner or 

operator shall determine and document 

that the equipment is designed, maintained, inspected, tested, and operating 

in a safe manner. 

§ 68.67 Process hazard analysis. 

(a) The owner or operator shall perform an initial process hazard analysis 

(hazard evaluation) on processes covered by this part. The process hazard 

analysis shall be appropriate to the 

complexity of the process and shall 

identify, evaluate, and control the hazards involved in the process. The owner 

or operator shall determine and document the priority order for conducting 

§ 68.67 

process hazard analyses based on a rationale which includes such considerations as extent of the process hazards, 

number of potentially affected employees, age of the process, and operating 

history of the process. The process hazard analysis shall be conducted as soon 

as possible, but not later than June 21, 

1999. Process hazards analyses completed to comply with 29 CFR 

1910.119(e) are acceptable as initial 

process hazards analyses. These process 

hazard analyses shall be updated and 

revalidated, based on their completion 

date. 

(b) The owner or operator shall use 

one or more of the following methodologies that are appropriate to determine and evaluate the hazards of the 

process being analyzed. 

(1) What-If; 

(2) Checklist; 

(3) What-If/Checklist; 

(4) Hazard and Operability Study 

(HAZOP); 

(5) Failure Mode and Effects Analysis 

(FMEA); 

(6) Fault Tree Analysis; or 

(7) An appropriate equivalent methodology. 

(c) The process hazard analysis shall 

address: 

(1) The hazards of the process; 

(2) The identification of any previous 

incident which had a likely potential 

for catastrophic consequences. 

(3) Engineering and administrative 

controls applicable to the hazards and 

their interrelationships such as appropriate application of detection methodologies to provide early warning of 

releases. (Acceptable detection methods might include process monitoring 

and control instrumentation with 

alarms, and detection hardware such as 

hydrocarbon sensors.); 

(4) Consequences of failure of engineering and administrative controls; 

(5) Stationary source siting; 

(6) Human factors; and 

(7) A qualitative evaluation of a 

range of the possible safety and health 

effects of failure of controls. 

(d) The process hazard analysis shall 

be performed by a team with expertise 

in engineering and process operations, 

and the team shall include at least one 

employee who has experience and 

knowledge specific to the process being 

49

§ 68.69 

evaluated. Also, one member of the 

team must be knowledgeable in the 

specific process hazard analysis methodology being used. 

(e) The owner or operator shall establish a system to promptly address the 

team’s findings and recommendations; 

assure that the recommendations are 

resolved in a timely manner and that 

the resolution is documented; document what actions are to be taken; 

complete actions as soon as possible; 

develop a written schedule of when 

these actions are to be completed; communicate the actions to operating, 

maintenance and other employees 

whose work assignments are in the 

process and who may be affected by the 

recommendations or actions. 

(f) At least every five (5) years after 

the completion of the initial process 

hazard analysis, the process hazard 

analysis shall be updated and revalidated by a team meeting the requirements in paragraph (d) of this section, 

to assure that the process hazard analysis is consistent with the current 

process. Updated and revalidated process hazard analyses completed to comply with 29 CFR 1910.119(e) are acceptable to meet the requirements of this 

paragraph. 

(g) The owner or operator shall retain process hazards analyses and updates or revalidations for each process 

covered by this section, as well as the 

documented resolution of recommendations described in paragraph (e) of this 

section for the life of the process. 

§ 68.69 Operating procedures. 

(a) The owner or operator shall develop and implement written operating 

procedures that provide clear instructions for safely conducting activities 

involved in each covered process consistent with the process safety information and shall address at least the 

following elements. 

(1) Steps for each operating phase: 

(i) Initial startup; 

(ii) Normal operations; 

(iii) Temporary operations; 

(iv) Emergency shutdown including 

the conditions under which emergency 

shutdown is required, and the assignment of shutdown responsibility to 

qualified operators to ensure that 

40 CFR Ch. I (7–1–98 Edition) 

emergency shutdown is executed in a 

safe and timely manner. 

(v) Emergency operations; 

(vi) Normal shutdown; and, 

(vii) Startup following a turnaround, 

or after an emergency shutdown. 

(2) Operating limits: 

(i) Consequences of deviation; and 

(ii) Steps required to correct or avoid 

deviation. 

(3) Safety and health considerations: 

(i) Properties of, and hazards presented by, the chemicals used in the 

process; 

(ii) Precautions necessary to prevent 

exposure, including engineering controls, administrative controls, and personal protective equipment; 

(iii) Control measures to be taken if 

physical contact or airborne exposure 

occurs; 

(iv) Quality control for raw materials 

and control of hazardous chemical inventory levels; and, 

(v) Any special or unique hazards. 

(4) Safety systems and their functions. 

(b) Operating procedures shall be 

readily accessible to employees who 

work in or maintain a process. 

(c) The operating procedures shall be 

reviewed as often as necessary to assure that they reflect current operating practice, including changes that result from changes in process chemicals, 

technology, and equipment, and 

changes to stationary sources. The 

owner or operator shall certify annually that these operating procedures 

are current and accurate. 

(d) The owner or operator shall develop and implement safe work practices to provide for the control of hazards during operations such as lockout/ 

tagout; confined space entry; opening 

process equipment or piping; and control over entrance into a stationary 

source by maintenance, contractor, 

laboratory, or other support personnel. 

These safe work practices shall apply 

to employees and contractor employees. 

§ 68.71 Training. 

(a) Initial training. (1) Each employee 

presently involved in operating a process, and each employee before being involved in operating a newly assigned 

process, shall be trained in an overview 

50

Environmental Protection Agency 

of the process and in the operating procedures as specified in § 68.69. The 

training shall include emphasis on the 

specific safety and health hazards, 

emergency operations including shutdown, and safe work practices applicable to the employee’s job tasks. 

(2) In lieu of initial training for those 

employees already involved in operating a process on June 21, 1999 an owner 

or operator may certify in writing that 

the employee has the required knowledge, skills, and abilities to safely 

carry out the duties and responsibilities as specified in the operating procedures. 

(b) Refresher training. Refresher training shall be provided at least every 

three years, and more often if necessary, to each employee involved in 

operating a process to assure that the 

employee understands and adheres to 

the current operating procedures of the 

process. The owner or operator, in consultation with the employees involved 

in operating the process, shall determine the appropriate frequency of refresher training. 

(c) Training documentation. The owner 

or operator shall ascertain that each 

employee involved in operating a process has received and understood the 

training required by this paragraph. 

The owner or operator shall prepare a 

record which contains the identity of 

the employee, the date of training, and 

the means used to verify that the employee understood the training. 

§ 68.73 Mechanical integrity. 

(a) Application. Paragraphs (b) 

through (f) of this section apply to the 

following process equipment: 

(1) Pressure vessels and storage 

tanks; 

(2) Piping systems (including piping 

components such as valves); 

(3) Relief and vent systems and devices; 

(4) Emergency shutdown systems; 

(5) Controls (including monitoring 

devices and sensors, alarms, and interlocks) and, 

(6) Pumps. 

(b) Written procedures. The owner or 

operator shall establish and implement 

written procedures to maintain the ongoing integrity of process equipment. 

§ 68.73 

(c) Training for process maintenance 

activities. The owner or operator shall 

train each employee involved in maintaining the on-going integrity of process equipment in an overview of that 

process and its hazards and in the procedures applicable to the employee’s 

job tasks to assure that the employee 

can perform the job tasks in a safe 

manner. 

(d) Inspection and testing. (1) Inspections and tests shall be performed on 

process equipment. 

(2) Inspection and testing procedures 

shall follow recognized and generally 

accepted good engineering practices. 

(3) The frequency of inspections and 

tests of process equipment shall be consistent with applicable manufacturers’ 

recommendations and good engineering 

practices, and more frequently if determined to be necessary by prior operating experience. 

(4) The owner or operator shall document each inspection and test that has 

been performed on process equipment. 

The documentation shall identify the 

date of the inspection or test, the name 

of the person who performed the inspection or test, the serial number or 

other identifier of the equipment on 

which the inspection or test was performed, a description of the inspection 

or test performed, and the results of 

the inspection or test. 

(e) Equipment deficiencies. The owner 

or operator shall correct deficiencies in 

equipment that are outside acceptable 

limits (defined by the process safety information in § 68.65) before further use 

or in a safe and timely manner when 

necessary means are taken to assure 

safe operation. 

(f) Quality assurance. (1) In the construction of new plants and equipment, 

the owner or operator shall assure that 

equipment as it is fabricated is suitable for the process application for 

which they will be used. 

(2) Appropriate checks and inspections shall be performed to assure that 

equipment is installed properly and 

consistent with design specifications 

and the manufacturer’s instructions. 

(3) The owner or operator shall assure that maintenance materials, spare 

parts and equipment are suitable for 

the process application for which they 

will be used. 

51

§ 68.75 

§ 68.75 Management of change. 

(a) The owner or operator shall establish and implement written procedures 

to manage changes (except for ‘‘replacements in kind’’) to process chemicals, technology, equipment, and procedures; and, changes to stationary 

sources that affect a covered process. 

(b) The procedures shall assure that 

the following considerations are addressed prior to any change: 

(1) The technical basis for the proposed change; 

(2) Impact of change on safety and 

health; 

(3) Modifications to operating procedures; 

(4) Necessary time period for the 

change; and, 

(5) Authorization requirements for 

the proposed change. 

(c) Employees involved in operating a 

process and maintenance and contract 

employees whose job tasks will be affected by a change in the process shall 

be informed of, and trained in, the 

change prior to start-up of the process 

or affected part of the process. 

(d) If a change covered by this paragraph results in a change in the process 

safety information required by § 68.65 of 

this part, such information shall be updated accordingly. 

(e) If a change covered by this paragraph results in a change in the operating procedures or practices required by 

§ 68.69, such procedures or practices 

shall be updated accordingly. 

§ 68.77 Pre-startup review. 

(a) The owner or operator shall perform a pre-startup safety review for 

new stationary sources and for modified stationary sources when the modification is significant enough to require a change in the process safety information. 

(b) The pre-startup safety review 

shall confirm that prior to the introduction of regulated substances to a 

process: 

(1) Construction and equipment is in 

accordance with design specifications; 

(2) Safety, operating, maintenance, 

and emergency procedures are in place 

and are adequate; 

(3) For new stationary sources, a 

process hazard analysis has been performed and recommendations have 

40 CFR Ch. I (7–1–98 Edition) 

been resolved or implemented before 

startup; and modified stationary 

sources meet the requirements contained in management of change, 

§ 68.75. 

(4) Training of each employee involved in operating a process has been 

completed. 

§ 68.79 Compliance audits. 

(a) The owner or operator shall certify that they have evaluated compliance with the provisions of this section 

at least every three years to verify 

that the procedures and practices developed under the standard are adequate and are being followed. 

(b) The compliance audit shall be 

conducted by at least one person 

knowledgeable in the process. 

(c) A report of the findings of the 

audit shall be developed. 

(d) The owner or operator shall 

promptly determine and document an 

appropriate response to each of the 

findings of the compliance audit, and 

document that deficiencies have been 

corrected. 

(e) The owner or operator shall retain 

the two (2) most recent compliance 

audit reports. 

§ 68.81 Incident investigation. 

(a) The owner or operator shall investigate each incident which resulted in, 

or could reasonably have resulted in a 

catastrophic release of a regulated substance. 

(b) An incident investigation shall be 

initiated as promptly as possible, but 

not later than 48 hours following the 

incident. 

(c) An incident investigation team 

shall be established and consist of at 

least one person knowledgeable in the 

process involved, including a contract 

employee if the incident involved work 

of the contractor, and other persons 

with appropriate knowledge and experience to thoroughly investigate and 

analyze the incident. 

(d) A report shall be prepared at the 

conclusion of the investigation which 

includes at a minimum: 

(1) Date of incident; 

(2) Date investigation began; 

(3) A description of the incident; 

(4) The factors that contributed to 

the incident; and, 

52

Environmental Protection Agency 

(5) Any recommendations resulting 

from the investigation. 

(e) The owner or operator shall establish a system to promptly address and 

resolve the incident report findings and 

recommendations. Resolutions and corrective actions shall be documented. 

(f) The report shall be reviewed with 

all affected personnel whose job tasks 

are relevant to the incident findings including contract employees where applicable. 

(g) Incident investigation reports 

shall be retained for five years. 

§ 68.83 Employee participation. 

(a) The owner or operator shall develop a written plan of action regarding the implementation of the employee participation required by this 

section. 

(b) The owner or operator shall consult with employees and their representatives on the conduct and development of process hazards analyses and 

on the development of the other elements of process safety management in 

this rule. 

(c) The owner or operator shall provide to employees and their representatives access to process hazard analyses 

and to all other information required 

to be developed under this rule. 

§ 68.85 Hot work permit. 

(a) The owner or operator shall issue 

a hot work permit for hot work operations conducted on or near a covered 

process. 

(b) The permit shall document that 

the fire prevention and protection requirements in 29 CFR 1910.252(a) have 

been implemented prior to beginning 

the hot work operations; it shall indicate the date(s) authorized for hot 

work; and identify the object on which 

hot work is to be performed. The permit shall be kept on file until completion of the hot work operations. 

§ 68.87 Contractors. 

(a) Application. This section applies 

to contractors performing maintenance 

or repair, turnaround, major renovation, or specialty work on or adjacent 

to a covered process. It does not apply 

to contractors providing incidental 

services which do not influence process 

safety, such as janitorial work, food 

§ 68.87 

and drink services, laundry, delivery or 

other supply services. 

(b) Owner or operator responsibilities. 

(1) The owner or operator, when selecting a contractor, shall obtain and 

evaluate information regarding the 

contract owner or operator’s safety 

performance and programs. 

(2) The owner or operator shall inform contract owner or operator of the 

known potential fire, explosion, or 

toxic release hazards related to the 

contractor’s work and the process. 

(3) The owner or operator shall explain to the contract owner or operator 

the applicable provisions of subpart E 

of this part. 

(4) The owner or operator shall develop and implement safe work practices consistent with § 68.69(d), to control the entrance, presence, and exit of 

the contract owner or operator and 

contract employees in covered process 

areas. 

(5) The owner or operator shall periodically evaluate the performance of 

the contract owner or operator in fulfilling their obligations as specified in 

paragraph (c) of this section. 

(c) Contract owner or operator responsibilities. (1) The contract owner or operator shall assure that each contract 

employee is trained in the work practices necessary to safely perform his/ 

her job. 

(2) The contract owner or operator 

shall assure that each contract employee is instructed in the known potential fire, explosion, or toxic release 

hazards related to his/her job and the 

process, and the applicable provisions 

of the emergency action plan. 

(3) The contract owner or operator 

shall document that each contract employee has received and understood the 

training required by this section. The 

contract owner or operator shall prepare a record which contains the identity of the contract employee, the date 

of training, and the means used to verify that the employee understood the 

training. 

(4) The contract owner or operator 

shall assure that each contract employee follows the safety rules of the 

stationary source including the safe 

work practices required by § 68.69(d). 

(5) The contract owner or operator 

shall advise the owner or operator of 

53

§ 68.90 

any unique hazards presented by the 

contract owner or operator’s work, or 

of any hazards found by the contract 

owner or operator’s work. 

Subpart E—Emergency Response 

SOURCE: 61 FR 31725, June 20, 1996, unless 

otherwise noted. 

§ 68.90 Applicability. 

(a) Except as provided in paragraph 

(b) of this section, the owner or operator of a stationary source with Program 2 and Program 3 processes shall 

comply with the requirements of § 68.95. 

(b) The owner or operator of stationary source whose employees will not 

respond to accidental releases of regulated substances need not comply with 

§ 68.95 of this part provided that they 

meet the following: 

(1) For stationary sources with any 

regulated toxic substance held in a 

process above the threshold quantity, 

the stationary source is included in the 

community emergency response plan 

developed under 42 U.S.C. 11003; 

(2) For stationary sources with only 

regulated flammable substances held in 

a process above the threshold quantity, 

the owner or operator has coordinated 

response actions with the local fire department; and 

(3) Appropriate mechanisms are in 

place to notify emergency responders 

when there is a need for a response. 

§ 68.95 Emergency response program. 

(a) The owner or operator shall develop and implement an emergency response program for the purpose of protecting public health and the environment. Such program shall include the 

following elements: 

(1) An emergency response plan, 

which shall be maintained at the stationary source and contain at least the 

following elements: 

(i) Procedures for informing the public and local emergency response agencies about accidental releases; 

(ii) Documentation of proper first-aid 

and emergency medical treatment necessary to treat accidental human exposures; and 

40 CFR Ch. I (7–1–98 Edition) 

(iii) Procedures and measures for 

emergency response after an accidental 

release of a regulated substance; 

(2) Procedures for the use of emergency response equipment and for its 

inspection, testing, and maintenance; 

(3) Training for all employees in relevant procedures; and 

(4) Procedures to review and update, 

as appropriate, the emergency response 

plan to reflect changes at the stationary source and ensure that employees 

are informed of changes. 

(b) A written plan that complies with 

other Federal contingency plan regulations or is consistent with the approach in the National Response 

Team’s Integrated Contingency Plan 

Guidance (‘‘One Plan’’) and that, 

among other matters, includes the elements provided in paragraph (a) of this 

section, shall satisfy the requirements 

of this section if the owner or operator 

also complies with paragraph (c) of this 

section. 

(c) The emergency response plan developed under paragraph (a)(1) of this 

section shall be coordinated with the 

community emergency response plan 

developed under 42 U.S.C. 11003. Upon 

request of the local emergency planning committee or emergency response 

officials, the owner or operator shall 

promptly provide to the local emergency response officials information 

necessary for developing and implementing the community emergency response plan. 

Subpart F—Regulated Substances

for Accidental Release Prevention 

SOURCE: 59 FR 4493, Jan. 31, 1994, unless 

otherwise noted. Redesignated at 61 FR 31717, 

June 20, 1996. 

§ 68.100 Purpose. 

This subpart designates substances 

to be listed under section 112(r)(3), (4), 

and (5) of the Clean Air Act, as amended, identifies their threshold quantities, and establishes the requirements 

for petitioning to add or delete substances from the list. 

§ 68.115 Threshold determination. 

(a) A threshold quantity of a regulated substance listed in § 68.130 is 

54

Environmental Protection Agency 

present at a stationary source if the 

total quantity of the regulated substance contained in a process exceeds 

the threshold. 

(b) For the purposes of determining 

whether more than a threshold quantity of a regulated substance is present 

at the stationary source, the following 

exemptions apply: 

(1) Concentrations of a regulated toxic 

substance in a mixture. If a regulated 

substance is present in a mixture and 

the concentration of the substance is 

below one percent by weight of the 

mixture, the amount of the substance 

in the mixture need not be considered 

when determining whether more than a 

threshold quantity is present at the 

stationary source. Except for oleum, 

toluene 2,4-diisocyanate, toluene 2,6­

diisocyanate, and toluene diisocyanate 

(unspecified isomer), if the concentration of the regulated substance in the 

mixture is one percent or greater by 

weight, but the owner or operator can 

demonstrate that the partial pressure 

of the regulated substance in the mixture (solution) under handling or storage conditions in any portion of the 

process is less than 10 millimeters of 

mercury (mm Hg), the amount of the 

substance in the mixture in that portion of the process need not be considered when determining whether more 

than a threshold quantity is present at 

the stationary source. The owner or operator shall document this partial pressure measurement or estimate. 

(2) Concentrations of a regulated flammable substance in a mixture. (i) General 

provision. If a regulated substance is 

present in a mixture and the concentration of the substance is below 

one percent by weight of the mixture, 

the mixture need not be considered 

when determining whether more than a 

threshold quantity of the regulated 

substance is present at the stationary 

source. Except as provided in paragraph (b)(2) (ii) and (iii) of this section, 

if the concentration of the substance is 

one percent or greater by weight of the 

mixture, then, for purposes of determining whether a threshold quantity is 

present at the stationary source, the 

entire weight of the mixture shall be 

treated as the regulated substance unless the owner or operator can demonstrate that the mixture itself does 

§ 68.115 

not have a National Fire Protection 

Association flammability hazard rating of 4. The demonstration shall be in 

accordance with the definition of flammability hazard rating 4 in the NFPA 

704, Standard System for the Identification of the Hazards of Materials for 

Emergency Response, National Fire 

Protection Association, Quincy, MA, 

1996. Available from the National Fire 

Protection Association, 1 

Batterymarch Park, Quincy, MA 02269– 

9101. This incorporation by reference 

was approved by the Director of the 

Federal Register in accordance with 5 

U.S.C. 552(a) and 1 CFR part 51. Copies 

may be inspected at the Environmental 

Protection Agency Air Docket (6102), 

Attn: Docket No. A–96–O8, Waterside 

Mall, 401 M. St. SW., Washington DC; 

or at the Office of Federal Register at 

800 North Capitol St., NW, Suite 700, 

Washington, DC. Boiling point and 

flash point shall be defined and determined in accordance with NFPA 30, 

Flammable and Combustible Liquids 

Code, National Fire Protection Association, Quincy, MA, 1996. Available 

from the National Fire Protection Association, 1 Batterymarch Park, Quincy, MA 02269–9101. This incorporation 

by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR 

part 51. Copies may be inspected at the 

Environmental Protection Agency Air 

Docket (6102), Attn: Docket No. A–96– 

O8, Waterside Mall, 401 M. St. SW., 

Washington DC; or at the Office of Federal Register at 800 North Capitol St., 

NW., Suite 700, Washington, DC. The 

owner or operator shall document the 

National Fire Protection Association 

flammability hazard rating. 

(ii) Gasoline. Regulated substances in 

gasoline, when in distribution or related storage for use as fuel for internal 

combustion engines, need not be considered when determining whether 

more than a threshold quantity is 

present at a stationary source. 

(iii) Naturally occurring hydrocarbon 

mixtures. Prior to entry into a natural 

gas processing plant or a petroleum refining process unit, regulated substances in naturally occurring hydrocarbon mixtures need not be considered 

when determining whether more than a 

55

§ 68.120 

threshold quantity is present at a stationary source. Naturally occurring 

hydrocarbon mixtures include any 

combination of the following: condensate, crude oil, field gas, and produced 

water, each as defined in § 68.3 of this 

part. 

(3) Articles. Regulated substances contained in articles need not be considered when determining whether more 

than a threshold quantity is present at 

the stationary source. 

(4) Uses. Regulated substances, when 

in use for the following purposes, need 

not be included in determining whether 

more than a threshold quantity is 

present at the stationary source: 

(i) Use as a structural component of 

the stationary source; 

(ii) Use of products for routine janitorial maintenance; 

(iii) Use by employees of foods, drugs, 

cosmetics, or other personal items containing the regulated substance; and 

(iv) Use of regulated substances 

present in process water or non-contact 

cooling water as drawn from the environment or municipal sources, or use 

of regulated substances present in air 

used either as compressed air or as part 

of combustion. 

(5) Activities in laboratories. If a regulated substance is manufactured, processed, or used in a laboratory at a stationary source under the supervision of 

a technically qualified individual as defined in § 720.3(ee) of this chapter, the 

quantity of the substance need not be 

considered in determining whether a 

threshold quantity is present. This exemption does not apply to: 

(i) Specialty chemical production; 

(ii) Manufacture, processing, or use 

of substances in pilot plant scale operations; and 

(iii) Activities conducted outside the 

laboratory. 

[59 FR 4493, Jan. 31, 1994. Redesignated at 61 

FR 31717, June 20, 1996, as amended at 63 FR 

645, Jan. 6, 1998] 

§ 68.120 Petition process. 

(a) Any person may petition the Administrator to modify, by addition or 

deletion, the list of regulated substances identified in § 68.130. Based on 

the information presented by the petitioner, the Administrator may grant or 

deny a petition. 

40 CFR Ch. I (7–1–98 Edition) 

(b) A substance may be added to the 

list if, in the case of an accidental release, it is known to cause or may be 

reasonably anticipated to cause death, 

injury, or serious adverse effects to 

human health or the environment. 

(c) A substance may be deleted from 

the list if adequate data on the health 

and environmental effects of the substance are available to determine that 

the substance, in the case of an accidental release, is not known to cause 

and may not be reasonably anticipated 

to cause death, injury, or serious adverse effects to human health or the 

environment. 

(d) No substance for which a national 

primary ambient air quality standard 

has been established shall be added to 

the list. No substance regulated under 

title VI of the Clean Air Act, as amended, shall be added to the list. 

(e) The burden of proof is on the petitioner to demonstrate that the criteria 

for addition and deletion are met. A petition will be denied if this demonstration is not made. 

(f) The Administrator will not accept 

additional petitions on the same substance following publication of a final 

notice of the decision to grant or deny 

a petition, unless new data becomes 

available that could significantly affect the basis for the decision. 

(g) Petitions to modify the list of 

regulated substances must contain the 

following: 

(1) Name and address of the petitioner and a brief description of the organization(s) that the petitioner represents, if applicable; 

(2) Name, address, and telephone 

number of a contact person for the petition; 

(3) Common chemical name(s), common synonym(s), Chemical Abstracts 

Service number, and chemical formula 

and structure; 

(4) Action requested (add or delete a 

substance); 

(5) Rationale supporting the petitioner’s position; that is, how the substance meets the criteria for addition 

and deletion. A short summary of the 

rationale must be submitted along 

with a more detailed narrative; and 

56

Environmental Protection Agency 

(6) Supporting data; that is, the petition must include sufficient information to scientifically support the request to modify the list. Such information shall include: 

(i) A list of all support documents; 

(ii) Documentation of literature 

searches conducted, including, but not 

limited to, identification of the database(s) searched, the search strategy, 

dates covered, and printed results; 

(iii) Effects data (animal, human, and 

environmental test data) indicating 

the potential for death, injury, or serious adverse human and environmental 

impacts from acute exposure following 

an accidental release; printed copies of 

the data sources, in English, should be 

provided; and 

(iv) Exposure data or previous accident history data, indicating the potential for serious adverse human 

health or environmental effects from 

an accidental release. These data may 

include, but are not limited to, physical and chemical properties of the substance, such as vapor pressure; modeling results, including data and assumptions used and model documentation; 

and historical accident data, citing 

data sources. 

(h) Within 18 months of receipt of a 

petition, the Administrator shall publish in the FEDERAL REGISTER a notice 

either denying the petition or granting 

the petition and proposing a listing. 

§ 68.125 Exemptions. 

Agricultural nutrients. Ammonia used 

as an agricultural nutrient, when held 

by farmers, is exempt from all provisions of this part. 

§ 68.130 List of substances. 

(a) Regulated toxic and flammable 

substances under section 112(r) of the 

Clean Air Act are the substances listed 

in Tables 1, 2, 3, and 4. Threshold quantities for listed toxic and flammable 

substances are specified in the tables. 

(b) The basis for placing toxic and 

flammable substances on the list of 

regulated substances are explained in 

the notes to the list. 

§ 68.130 

TABLE 1 TO § 68.130.—L IST OF REGULATED 

TOXIC SUBSTANCES AND THRESHOLD QUANTITIES FOR ACCIDENTAL RELEASE PREVENTION 

[Alphabetical Order—77 Substances] 

Chemical name CAS No. 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

Acrolein [2­ 107–02–8 5,000 b 

Propenal]. 

Acrylonitrile [2­ 107–13–1 20,000 b 

Propenenitrile]. 

Acrylyl chloride [2­ 814–68–6 5,000 b 

Propenoyl chloride]. 

Allyl alcohol [2­ 107–18–61 15,000 b 

Propen-l-ol]. 

Allylamine [2­ 107–11–9 10,000 b 

Propen-l-amine]. 

Ammonia (anhy­ 7664–41–7 10,000 a, b 

drous). 

Ammonia (conc 7664–41–7 20,000 a, b 

20% or greater). 

Arsenous tri­ 7784–34–1 15,000 b 

chloride. 

Arsine .................. 7784–42–1 1,000 b 

Boron trichloride 10294–34–5 5,000 b 

[Borane, 

trichloro-]. 

Boron trifluoride 7637–07–2 5,000 b 

[Borane, 

trifluoro-]. 

Boron trifluoride 353–42–4 15,000 b 

compound with 

methyl ether 

(1:1) [Boron, 

trifluoro [oxybis 

[metane]]-, T-4-. 

Bromine ............... 7726–95–6 10,000 a, b 

Carbon disulfide .. 75–15–0 20,000 b 

Chlorine ............... 7782–50–5 2,500 a, b 

Chlorine dioxide 10049–04–4 1,000 c 

[Chlorine oxide 

(ClO2)]. 

Chloroform [Meth­ 67–66–3 20,000 b 

ane, trichloro-]. 

Chloromethyl 542–88–1 1,000 b 

ether [Methane, 

oxybis[chloro-]. 

Chloromethyl 107–30–2 5,000 b 

methyl ether 

[Methane, 

chloromethoxy-]. 

Crotonaldehyde 4170–30–3 20,000 b 

[2-Butenal]. 

Crotonaldehyde, 123–73–9 20,000 b 

(E)- [2-Butenal, 

(E)-]. 

Cyanogen chlo­ 506–77–4 10,000 c 

ride. 

Cyclohexylamine 108–91–8 15,000 b 

[Cyclohexanamine]. 

Diborane .............. 19287–45–7 2,500 b 

Dimethyldichloros­ 75–78–5 5,000 b 

ilane [Silane, 

dichlorodimethyl-]. 

1,1­ 57–14–7 15,000 b 

Dimethylhydrazine [Hydrazine, 

1,1-dimethyl-]. 

57

§ 68.130 40 CFR Ch. I (7–1–98 Edition) 

TABLE 1 TO § 68.130.—L IST OF REGULATED TABLE 1 TO § 68.130.—L IST OF REGULATED 

TOXIC SUBSTANCES AND THRESHOLD QUAN- TOXIC SUBSTANCES AND THRESHOLD QUANTITIES FOR ACCIDENTAL RELEASE PREVEN- TITIES FOR ACCIDENTAL RELEASE PREVENTION—Continued TION—Continued 

[Alphabetical Order—77 Substances] [Alphabetical Order—77 Substances] 

Chemical name CAS No. 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

Epichlorohydrin 106–89–8 20,000 b 

[Oxirane, 

(chloromethyl)-]. 

Ethylenediamine 107–15–3 20,000 b 

[1,2­

Ethanediamine]. 

Ethyleneimine 151–56–4 10,000 b 

[Aziridine]. 

Ethylene oxide 75–21–8 10,000 a, b 

[Oxirane]. 

Fluorine ............... 7782–41–4 1,000 b 

Formaldehyde 50–00–0 15,000 b 

(solution). 

Furan ................... 110–00–9 5,000 b 

Hydrazine ............ 302–01–2 15,000 b 

Hydrochloric acid 7647–01–0 15,000 d 

(conc 37% or 

greater). 

Hydrocyanic acid 74–90–8 2,500 a, b 

Hydrogen chloride 7647–01–0 5,000 a 

(anhydrous) 

[Hydrochloric 

acid]. 

Hydrogen fluoride/ 7664–39–3 1,000 a, b 

Hydrofluoric 

acid (conc 50% 

or greater) 

[Hydrofluoric 

acid]. 

Hydrogen sele­ 7783–07–5 500 b 

nide. 

Hydrogen sulfide 7783–06–4 10,000 a, b 

Iron, 13463–40–6 2,500 b 

pentacarbonyl­

[Iron carbonyl 

(Fe(CO)5), (TB5-11)-]. 

Isobutyronitrile 78–82–0 20,000 b 

[Propanenitrile, 

2-methyl-]. 

Isopropyl 108–23–6 15,000 b 

chloroformate 

[Carbonochloridic acid, 1­

methylethyl 

ester]. 

Methacrylonitrile 126–98–7 10,000 b 

[2­

Propenenitrile, 

2-methyl-]. 

Methyl chloride 74–87–3 10,000 a 

[Methane, 

chloro-]. 

Methyl 79–22–1 5,000 b 

chloroformate 

[Carbonochloridic acid, 

methylester]. 

Methyl hydrazine 60–34–4 15,000 b 

[Hydrazine, 

methyl-]. 

Methyl isocyanate 624–83–9 10,000 a, b 

[Methane, 

isocyanato-]. 

Chemical name CAS No. 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

Methyl mercaptan 74–93–1 10,000 b 

[Methanethiol]. 

Methyl 556–64–9 20,000 b 

thiocyanate 

[Thiocyanic 

acid, methyl 

ester]. 

Methyltrichlorosil­ 75–79–6 5,000 b 

ane [Silane, 

trichloromethyl-]. 

Nickel carbonyl .... 13463–39–3 1,000 b 

Nitric acid (conc 7697–37–2 15,000 b 

80% or greater). 

Nitric oxide [Nitro­ 10102–43–9 10,000 b 

gen oxide (NO)]. 

Oleum (Fuming 8014–95–7 10,000 e 

Sulfuric acid) 

[Sulfuric acid, 

mixture with 

sulfur trioxide] 1. 

Peracetic acid 79–21–0 10,000 b 

[Ethaneperoxoic 

acid]. 

Perchloromethyl­ 594–42–3 10,000 b 

mercaptan 

[Methanesulfenyl chloride, 

trichloro-]. 

Phosgene [Car­ 75–44–5 500 a, b 

bonic dichloride]. 

Phosphine ........... 7803–51–2 5,000 b 

Phosphorus 10025–87–3 5,000 b 

oxychloride 

[Phosphoryl 

chloride]. 

Phosphorus tri­ 7719–12–2 15,000 b 

chloride [Phosphorous trichloride]. 

Piperidine ............ 110–89–4 15,000 b 

Propionitrile 107–12–0 10,000 b 

[Propanenitrile]. 

Propyl 109–61–5 15,000 b 

chloroformate 

[Carbonochloridic acid, 

propylester]. 

Propyleneimine 75–55–8 10,000 b 

[Aziridine, 2­

methyl-]. 

Propylene oxide 75–56–9 10,000 b 

[Oxirane, methyl-]. 

Sulfur dioxide (an­ 7446–09–5 5,000 a, b 

hydrous). 

Sulfur tetrafluoride 7783–60–0 2,500 b 

[Sulfur fluoride 

(SF4), (T-4)-]. 

Sulfur trioxide ...... 7446–11–9 10,000 a, b 

Tetramethyllead 75–74–1 10,000 b 

[Plumbane, 

tetramethyl-]. 

Tetranitromethane 509–14–8 10,000 b 

[Methane, 

tetranitro-]. 

58

Environmental Protection Agency § 68.130 

TABLE 1 TO § 68.130.—L IST OF REGULATED TABLE 1 TO § 68.130.—L IST OF REGULATED 

TOXIC SUBSTANCES AND THRESHOLD QUAN- TOXIC SUBSTANCES AND THRESHOLD QUANTITIES FOR ACCIDENTAL RELEASE PREVEN- TITIES FOR ACCIDENTAL RELEASE PREVENTION—Continued TION—Continued 

[Alphabetical Order—77 Substances] [Alphabetical Order—77 Substances] 

Chemical name CAS No. 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

Titanium tetra­ 7550–45–0 2,500 b 

chloride [Titanium chloride 

(TiCl4) (T-4)-]. 

Toluene 2,4­ 584–84–9 10,000 a 

diisocyanate 

[Benzene, 2,4­

diisocyanato-1­

methyl-] 1. 

Toluene 2,6­ 91–08–7 10,000 a 

diisocyanate 

[Benzene, 1,3­

diisocyanato-2­

methyl-] 1. 

Toluene 26471–62–5 10,000 a 

diisocyanate 

(unspecified 

isomer) [Benzene, 1,3­

diisocyanatomethyl-] 1. 

Chemical name CAS No. 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

Trimethylchlorosil­ 75–77–4 10,000 b 

ane [Silane, 

chlorotrimethyl-]. 

Vinyl acetate 108–05–4 15,000 b 

monomer [Acetic acid ethenyl 

ester]. 

1 The mixture exemption in § 68.115(b)(1) does not apply to 

the substance. 

NOTE: Basis for Listing: 

a Mandated for listing by Congress. 

b On EHS list, vapor pressure 10 mmHg or greater. 

c Toxic gas. 

d Toxicity of hydrogen chloride, potential to release hydrogen chloride, and history of accidents. 

e Toxicity of sulfur trioxide and sulfuric acid, potential to 

release sulfur trioxide, and history of accidents. 

TABLE 2 TO § 68.130.—L IST OF REGULATED TOXIC SUBSTANCES AND THRESHOLD QUANTITIES FOR


ACCIDENTAL RELEASE PREVENTION


[CAS Number Order—77 Substances]


CAS No. Chemical name 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

50–00–0 ..................... 

57–14–7 ..................... 

60–34–4 ..................... 

67–66–3 ..................... 

74–87–3 ..................... 

74–90–8 ..................... 

74–93–1 ..................... 

75–15–0 ..................... 

75–21–8 ..................... 

75–44–5 ..................... 

75–55–8 ..................... 

75–56–9 ..................... 

75–74–1 ..................... 

75–77–4 ..................... 

75–78–5 ..................... 

75–79–6 ..................... 

78–82–0 ..................... 

79–21–0 ..................... 

79–22–1 ..................... 

91–08–7 ..................... 

106–89–8 ................... 

107–02–8 ................... 

107–11–9 ................... 

107–12–0 ................... 

107–13–1 ................... 

107–15–3 ................... 

107–18–6 ................... 

107–30–2 ................... 

108–05–4 ................... 

108–23–6 ................... 

108–91–8 ................... 

109–61–5 ................... 

110–00–9 ................... 

110–89–4 ................... 

123–73–9 ................... 

Formaldehyde (solution) .................................................................................... 

1,1-Dimethylhydrazine [Hydrazine, 1,1-dimethyl-] ............................................. 

Methyl hydrazine [Hydrazine, methyl-] .............................................................. 

Chloroform [Methane, trichloro-] ........................................................................ 

Methyl chloride [Methane, chloro-] .................................................................... 

Hydrocyanic acid ............................................................................................... 

Methyl mercaptan [Methanethiol] ...................................................................... 

Carbon disulfide ................................................................................................. 

Ethylene oxide [Oxirane] ................................................................................... 

Phosgene [Carbonic dichloride] ......................................................................... 

Propyleneimine [Aziridine, 2-methyl-] ................................................................ 

Propylene oxide [Oxirane, methyl-] ................................................................... 

Tetramethyllead [Plumbane, tetramethyl-] ......................................................... 

Trimethylchlorosilane [Silane, chlorotrimethyl-] ................................................. 

Dimethyldichlorosilane [Silane, dichlorodimethyl-] ............................................ 

Methyltrichlorosilane [Silane, trichloromethyl-] .................................................. 

Isobutyronitrile [Propanenitrile, 2-methyl-] ......................................................... 

Peracetic acid [Ethaneperoxoic acid] ................................................................ 

Methyl chloroformate [Carbonochloridic acid, methylester] .............................. 

Toluene 2,6-diisocyanate [Benzene, 1,3-diisocyanato-2-methyl-]1 ................... 

Epichlorohydrin [Oxirane, (chloromethyl)-] ........................................................ 

Acrolein [2-Propenal] ......................................................................................... 

Allylamine [2-Propen-1-amine] .......................................................................... 

Propionitrile [Propanenitrile] ............................................................................... 

Acrylonitrile [2-Propenenitrile] ............................................................................ 

Ethylenediamine [1,2-Ethanediamine] ............................................................... 

Allyl alcohol [2-Propen-1-ol] ............................................................................... 

Chloromethyl methyl ether [Methane, chloromethoxy-] ..................................... 

Vinyl acetate monomer [Acetic acid ethenyl ester] ........................................... 

Isopropyl chloroformate [Carbonochloridic acid, 1-methylethyl ester] .............. 

Cyclohexylamine [Cyclohexanamine] ................................................................ 

Propyl chloroformate [Carbonochloridic acid, propylester] ................................ 

Furan .................................................................................................................. 

Piperidine ........................................................................................................... 

Crotonaldehyde, (E)- [2-Butenal, (E)-] ............................................................... 

15,000 

15,000 

15,000 

20,000 

10,000 

2,500 

10,000 

20,000 

10,000 

500 

10,000 

10,000 

10,000 

10,000 

5,000 

5,000 

20,000 

10,000 

5,000 

10,000 

20,000 

5,000 

10,000 

10,000 

20,000 

20,000 

15,000 

5,000 

15,000 

15,000 

15,000 

15,000 

5,000 

15,000 

20,000 

b 

b 

b 

b 

a 

a, b 

b 

b 

a, b 

a, b 

b 

b 

b 

b 

b 

b 

b 

b 

b 

a 

b 

b 

b 

b 

b 

b 

b 

b 

b 

b 

b 

b 

b 

b 

b 

59

§ 68.130 40 CFR Ch. I (7–1–98 Edition) 

TABLE 2 TO § 68.130.—L IST OF REGULATED TOXIC SUBSTANCES AND THRESHOLD QUANTITIES FOR


ACCIDENTAL RELEASE PREVENTION—Continued


[CAS Number Order—77 Substances]


CAS No. Chemical name 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

126–98–7 ................... 

151–56–4 ................... 

302–01–2 ................... 

353–42–4 ................... 

506–77–4 ................... 

509–14–8 ................... 

542–88–1 ................... 

556–64–9 ................... 

584–84–9 ................... 

594–42–3 ................... 

624–83–9 ................... 

814–68–6 ................... 

4170–30–3 ................. 

7446–09–5 ................. 

7446–11–9 ................. 

7550–45–0 ................. 

7637–07–2 ................. 

7647–01–0 ................. 

7647–01–0 ................. 

7664–39–3 ................. 

7664–41–7 ................. 

7664–41–7 ................. 

7697–37–2 ................. 

7719–12–2 ................. 

7726–95–6 ................. 

7782–41–4 ................. 

7782–50–5 ................. 

7783–06–4 ................. 

7783–07–5 ................. 

7783–60–0 ................. 

7784–34–1 ................. 

7784–42–1 ................. 

7803–51–2 ................. 

8014–95–7 ................. 

10025–87–3 ............... 

10049–04–4 ............... 

10102–43–9 ............... 

10294–34–5 ............... 

13463–39–3 ............... 

13463–40–6 ............... 

19287–45–7 ............... 

26471–62–5 ............... 

Methacrylonitrile [2-Propenenitrile, 2-methyl-] ................................................... 

Ethyleneimine [Aziridine] ................................................................................... 

Hydrazine ........................................................................................................... 

Boron trifluoride compound with methyl ether (1:1) [Boron, 

trifluoro[oxybis[methane]]-, T-4-. 

Cyanogen chloride ............................................................................................. 

Tetranitromethane [Methane, tetranitro-] ........................................................... 

Chloromethyl ether [Methane, oxybis[chloro-] ................................................... 

Methyl thiocyanate [Thiocyanic acid, methyl ester] ........................................... 

Toluene 2,4-diisocyanate [Benzene, 2,4-diisocyanato-1-methyl-]1 ................... 

Perchloromethylmercaptan [Methanesulfenyl chloride, trichloro-] ..................... 

Methyl isocyanate [Methane, isocyanato-] ........................................................ 

Acrylyl chloride [2-Propenoyl chloride] .............................................................. 

Crotonaldehyde [2-Butenal] ............................................................................... 

Sulfur dioxide (anhydrous) ................................................................................. 

Sulfur trioxide ..................................................................................................... 

Titanium tetrachloride [Titanium chloride (TiCl4) (T-4)-] ................................... 

Boron trifluoride [Borane, trifluoro-] ................................................................... 

Hydrochloric acid (conc 37% or greater) ........................................................... 

Hydrogen chloride (anhydrous) [Hydrochloric acid] .......................................... 

Hydrogen fluoride/Hydrofluoric acid (conc 50% or greater) [Hydrofluoric acid] 

Ammonia (anhydrous) ....................................................................................... 

Ammonia (conc 20% or greater) ....................................................................... 

Nitric acid (conc 80% or greater) ...................................................................... 

Phosphorus trichloride [Phosphorous trichloride] .............................................. 

Bromine .............................................................................................................. 

Fluorine .............................................................................................................. 

Chlorine .............................................................................................................. 

Hydrogen sulfide ................................................................................................ 

Hydrogen selenide ............................................................................................. 

Sulfur tetrafluoride [Sulfur fluoride (SF4), (T-4)-] .............................................. 

Arsenous trichloride ........................................................................................... 

Arsine ................................................................................................................. 

Phosphine .......................................................................................................... 

Oleum (Fuming Sulfuric acid) [Sulfuric acid, mixture with sulfur trioxide]1 ....... 

Phosphorus oxychloride [Phosphoryl chloride] ................................................. 

Chlorine dioxide [Chlorine oxide (ClO2)] ........................................................... 

Nitric oxide [Nitrogen oxide (NO)] ..................................................................... 

Boron trichloride [Borane, trichloro-] .................................................................. 

Nickel carbonyl .................................................................................................. 

Iron, pentacarbonyl- [Iron carbonyl (Fe(CO)5), (TB-5-11)-] ............................... 

Diborane ............................................................................................................ 

Toluene diisocyanate (unspecified isomer) [Benzene, 1,3-diisocyanatomethyl1]1. 

10,000 

10,000 

15,000 

15,000 

10,000 

10,000 

1,000 

20,000 

10,000 

10,000 

10,000 

5,000 

20,000 

5,000 

10,000 

2,500 

5,000 

15,000 

5,000 

1,000 

10,000 

20,000 

15,000 

15,000 

10,000 

1,000 

2,500 

10,000 

500 

2,500 

15,000 

1,000 

5,000 

10,000 

5,000 

1,000 

10,000 

5,000 

1,000 

2,500 

2,500 

10,000 

b 

b 

b 

b 

c 

b 

b 

b 

a 

b 

a, b 

b 

b 

a, b 

a, b 

b 

b 

d 

a 

a, b 

a, b 

a, b 

b 

b 

a, b 

b 

a, b 

a, b 

b 

b 

b 

b 

b 

e 

b 

c 

b 

b 

b 

b 

b 

a 

1 The mixture exemption in § 68.115(b)(1) does not apply to the substance. NOTE: Basis for Listing: a Mandated for listing by Congress. b On EHS list, vapor pressure 10 mmHg or greater. c Toxic gas. d Toxicity of hydrogen chloride, potential to release hydrogen chloride, and history of accidents. e Toxicity of sulfur trioxide and sulfuric acid, potential to release sulfur trioxide, and history of accidents. 

TABLE 3 TO § 68.130.—L IST OF REGULATED FLAMMABLE SUBSTANCES AND THRESHOLD QUANTITIES


FOR ACCIDENTAL RELEASE PREVENTION


[Alphabetical Order—63 Substances]


Chemical name CAS No. 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

Acetaldehyde .................................................................................................................. 

Acetylene [Ethyne] .......................................................................................................... 

Bromotrifluorethylene [Ethene, bromotrifluoro-] .............................................................. 

1,3-Butadiene .................................................................................................................. 

Butane ............................................................................................................................. 

1-Butene ......................................................................................................................... 

2-Butene ......................................................................................................................... 

Butene ............................................................................................................................. 

75–07–0 

74–86–2 

598–73–2 

106–99–0 

106–97–8 

106–98–9 

107–01–7 

25167–67–3 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

g 

f 

f 

f 

f 

f 

f 

f 

60

Environmental Protection Agency § 68.130 

TABLE 3 TO § 68.130.—L IST OF REGULATED FLAMMABLE SUBSTANCES AND THRESHOLD QUANTITIES


FOR ACCIDENTAL RELEASE PREVENTION—Continued


[Alphabetical Order—63 Substances]


Chemical name CAS No. 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

2-Butene-cis .................................................................................................................... 

2-Butene-trans [2-Butene, (E)] ....................................................................................... 

Carbon oxysulfide [Carbon oxide sulfide (COS)] ........................................................... 

Chlorine monoxide [Chlorine oxide] ............................................................................... 

2-Chloropropylene [1-Propene, 2-chloro-] ...................................................................... 

1-Chloropropylene [1-Propene, 1-chloro-] ...................................................................... 

Cyanogen [Ethanedinitrile] .............................................................................................. 

Cyclopropane .................................................................................................................. 

Dichlorosilane [Silane, dichloro-] .................................................................................... 

Difluoroethane [Ethane, 1,1-difluoro-] ............................................................................. 

Dimethylamine [Methanamine, N-methyl-] ..................................................................... 

2,2-Dimethylpropane [Propane, 2,2-dimethyl-] ............................................................... 

Ethane ............................................................................................................................. 

Ethyl acetylene [1-Butyne] .............................................................................................. 

Ethylamine [Ethanamine] ................................................................................................ 

Ethyl chloride [Ethane, chloro-] ...................................................................................... 

Ethylene [Ethene] ........................................................................................................... 

Ethyl ether [Ethane, 1,1’-oxybis-] ................................................................................... 

Ethyl mercaptan [Ethanethiol] ......................................................................................... 

Ethyl nitrite [Nitrous acid, ethyl ester] ............................................................................. 

Hydrogen ........................................................................................................................ 

Isobutane [Propane, 2-methyl] ....................................................................................... 

Isopentane [Butane, 2-methyl-] ...................................................................................... 

Isoprene [1,3-Butadinene, 2-methyl-] ............................................................................. 

Isopropylamine [2-Propanamine] .................................................................................... 

Isopropyl chloride [Propane, 2-chloro-] .......................................................................... 

Methane .......................................................................................................................... 

Methylamine [Methanamine] ........................................................................................... 

3-Methyl-1-butene ........................................................................................................... 

2-Methyl-1-butene ........................................................................................................... 

Methyl ether [Methane, oxybis-] ..................................................................................... 

Methyl formate [Formic acid, methyl ester] .................................................................... 

2-Methylpropene [1-Propene, 2-methyl-] ........................................................................ 

1,3-Pentadinene .............................................................................................................. 

Pentane ........................................................................................................................... 

1-Pentene ....................................................................................................................... 

2-Pentene, (E)­ ............................................................................................................... 

2-Pentene, (Z)­ ............................................................................................................... 

Propadiene [1,2-Propadiene] .......................................................................................... 

Propane .......................................................................................................................... 

Propylene [1-Propene] .................................................................................................... 

Propyne [1-Propyne] ....................................................................................................... 

Silane .............................................................................................................................. 

Tetrafluoroethylene [Ethene, tetrafluoro-] ....................................................................... 

Tetramethylsilane [Silane, tetramethyl-] ......................................................................... 

Trichlorosilane [Silane, trichloro-] ................................................................................... 

Trifluorochloroethylene [Ethene, chlorotrifluoro-] ............................................................ 

Trimethylamine [Methanamine, N,N-dimethyl-] .............................................................. 

Vinyl acetylene [1-Buten-3-yne] ...................................................................................... 

Vinyl chloride [Ethene, chloro-] ....................................................................................... 

Vinyl ethyl ether [Ethene, ethoxy-] ................................................................................. 

Vinyl fluoride [Ethene, fluoro-] ........................................................................................ 

Vinylidene chloride [Ethene, 1,1-dichloro-] ..................................................................... 

Vinylidene fluoride [Ethene, 1,1-difluoro-] ...................................................................... 

Vinyl methyl ether [Ethene, methoxy-] ........................................................................... 

590–18–1 

624–64–6 

463–58–1 

7791–21–1 

557–98–2 

590–21–6 

460–19–5 

75–19–4 

4109–96–0 

75–37–6 

124–40–3 

463–82–1 

74–84–0 

107–00–6 

75–04–7 

75–00–3 

74–85–1 

60–29–7 

75–08–1 

109–95–5 

1333–74–0 

75–28–5 

78–78–4 

78–79–5 

75–31–0 

75–29–6 

74–82–8 

74–89–5 

563–45–1 

563–46–2 

115–10–6 

107–31–3 

115–11–7 

504–60–9 

109–66–0 

109–67–1 

646–04–8 

627–20–3 

463–49–0 

74–98–6 

115–07–1 

74–99–7 

7803–62–5 

116–14–3 

75–76–3 

10025–78–2 

79–38–9 

75–50–3 

689–97–4 

75–01–4 

109–92–2 

75–02–5 

75–35–4 

75–38–7 

107–25–5 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

f 

f 

f 

f 

g 

g 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

g 

g 

f 

f 

f 

g 

g 

g 

g 

f 

f 

f 

g 

f 

g 

f 

f 

g 

g 

g 

g 

f 

f 

f 

f 

f 

f 

g 

g 

f 

f 

f 

a, f 

g 

f 

g 

f 

f 

NOTE: Basis for Listing:


a Mandated for listing by Congress.


f Flammable gas.


g Volatile flammable liquid.


61 
§ 68.130 40 CFR Ch. I (7–1–98 Edition) 

TABLE 4 TO § 68.130.—L IST OF REGULATED FLAMMABLE SUBSTANCES AND THRESHOLD QUANTITIES


FOR ACCIDENTAL RELEASE PREVENTION


[CAS Number Order—63 Substances]


CAS No. Chemical name CAS No. 

Threshold 

quantity 

(lbs) 

Basis for 

listing 

60–29–7 ..................... 

74–82–8 ..................... 

74–84–0 ..................... 

74–85–1 ..................... 

74–86–2 ..................... 

74–89–5 ..................... 

74–98–6 ..................... 

74–99–7 ..................... 

75–00–3 ..................... 

75–01–4 ..................... 

75–02–5 ..................... 

75–04–7 ..................... 

75–07–0 ..................... 

75–08–1 ..................... 

75–19–4 ..................... 

75–28–5 ..................... 

75–29–6 ..................... 

75–31–0 ..................... 

75–35–4 ..................... 

75–37–6 ..................... 

75–38–7 ..................... 

75–50–3 ..................... 

75–76–3 ..................... 

78–78–4 ..................... 

78–79–5 ..................... 

79–38–9 ..................... 

106–97–8 ................... 

106–98–9 ................... 

196–99–0 ................... 

107–00–6 ................... 

107–01–7 ................... 

107–25–5 ................... 

107–31–3 ................... 

109–66–0 ................... 

109–67–1 ................... 

109–92–2 ................... 

109–95–5 ................... 

115–07–1 ................... 

115–10–6 ................... 

115–11–7 ................... 

116–14–3 ................... 

124–40–3 ................... 

460–19–5 ................... 

463–49–0 ................... 

463–58–1 ................... 

463–82–1 ................... 

504–60–9 ................... 

557–98–2 ................... 

563–45–1 ................... 

563–46–2 ................... 

590–18–1 ................... 

590–21–6 ................... 

598–73–2 ................... 

624–64–6 ................... 

627–20–3 ................... 

646–04–8 ................... 

689–97–4 ................... 

1333–74–0 ................. 

4109–96–0 ................. 

7791–21–1 ................. 

7803–62–5 ................. 

10025–78–2 ............... 

25167–67–3 ............... 

Ethyl ether [Ethane, 1,1′-oxybis-] ........................................... 

Methane ................................................................................. 

Ethane .................................................................................... 

Ethylene [Ethene] ................................................................... 

Acetylene [Ethyne] ................................................................. 

Methylamine [Methanamine] .................................................. 

Propane .................................................................................. 

Propyne [1-Propyne] .............................................................. 

Ethyl chloride [Ethane, chloro-] .............................................. 

Vinyl chloride [Ethene, chloro-] .............................................. 

Vinyl fluoride [Ethene, fluoro-] ................................................ 

Ethylamine [Ethanamine] ....................................................... 

Acetaldehyde .......................................................................... 

Ethyl mercaptan [Ethanethiol] ................................................ 

Cyclopropane ......................................................................... 

Isobutane [Propane, 2-methyl] ............................................... 

Isopropyl chloride [Propane, 2-chloro-] .................................. 

Isopropylamine [2-Propanamine] ........................................... 

Vinylidene chloride [Ethene, 1,1-dichloro-] ............................ 

Difluoroethane [Ethane, 1,1-difluoro-] .................................... 

Vinylidene fluoride [Ethene, 1,1-difluoro-] .............................. 

Trimethylamine [Methanamine, N, N-dimethyl-] ..................... 

Tetramethylsilane [Silane, tetramethyl-] ................................. 

Isopentane [Butane, 2-methyl-] .............................................. 

Isoprene [1,3,-Butadiene, 2-methyl-] ...................................... 

Trifluorochloroethylene [Ethene, chlorotrifluoro-] ................... 

Butane .................................................................................... 

1-Butene ................................................................................. 

1,3-Butadiene ......................................................................... 

Ethyl acetylene [1-Butyne] ..................................................... 

2-Butene ................................................................................. 

Vinyl methyl ether [Ethene, methoxy-] ................................... 

Methyl formate [Formic acid, methyl ester] ........................... 

Pentane .................................................................................. 

1-Pentene ............................................................................... 

Vinyl ethyl ether [Ethene, ethoxy-] ......................................... 

Ethyl nitrite [Nitrous acid, ethyl ester] .................................... 

Propylene [1-Propene] ........................................................... 

Methyl ether [Methane, oxybis-] ............................................. 

2-Methylpropene [1-Propene, 2-methyl-] ............................... 

Tetrafluoroethylene [Ethene, tetrafluoro-] .............................. 

Dimethylamine [Methanamine, N-methyl-] ............................. 

Cyanogen [Ethanedinitrile] ..................................................... 

Propadiene [1,2-Propadiene] ................................................. 

Carbon oxysulfide [Carbon oxide sulfide (COS)] ................... 

2,2-Dimethylpropane [Propane, 2,2-dimethyl-] ...................... 

1,3-Pentadiene ....................................................................... 

2-Chloropropylene [1-Propene, 2-chloro-] ............................. 

3-Methyl-1-butene .................................................................. 

2-Methyl-1-butene .................................................................. 

2-Butene-cis ........................................................................... 

1-Chloropropylene [1-Propene, 1-chloro-] ............................. 

Bromotrifluorethylene [Ethene, bromotrifluoro-] ..................... 

2-Butene-trans [2-Butene, (E)] ............................................... 

2-Pentene, (Z)- ....................................................................... 

2-Pentene, (E)- ....................................................................... 

Vinyl acetylene [1-Buten-3-yne] ............................................. 

Hydrogen ................................................................................ 

Dichlorosilane [Silane, dichloro-] ............................................ 

Chlorine monoxide [Chlorine oxide] ....................................... 

Silane ..................................................................................... 

Trichlorosilane [Silane,trichloro-] ............................................ 

Butene .................................................................................... 

60–29–7 

74–82–8 

74–84–0 

74–85–1 

74–86–2 

74–89–5 

74–98–6 

74–99–7 

75–00–3 

75–01–4 

75–02–5 

75–04–7 

75–07–0 

75–08–1 

75–19–4 

75–28–5 

75–29–6 

75–31–0 

75–35–4 

75–37–6 

75–38–7 

75–50–3 

75–76–3 

78–78–4 

78–79–5 

79–38–9 

106–97–8 

106–98–9 

106–99–0 

107–00–6 

107–01–7 

107–25–5 

107–31–3 

109–66–0 

109–67–1 

109–92–2 

109–95–5 

115–07–1 

115–10–6 

115–11–7 

116–14–3 

124–40–3 

460–19–5 

463–49–0 

463–58–1 

463–82–1 

504–60–9 

557–98–2 

563–45–1 

563–46–2 

590–18–1 

590–21–6 

598–73–2 

624–64–6 

627–20–3 

646–04–8 

689–97–4 

1333–74–0 

4109–96–0 

7791–21–1 

7803–62–5 

10025–78–2 

25167–67–3 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

10,000 

g 

f 

f 

f 

f 

f 

f 

f 

f 

a, f 

f 

f 

g 

g 

f 

f 

g 

g 

g 

f 

f 

f 

g 

g 

g 

f 

f 

f 

f 

f 

f 

f 

g 

g 

g 

g 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

f 

g 

f 

g 

f 

g 

f 

f 

g 

g 

f 

f 

f 

f 

f 

g 

f 

Note: Basis for Listing: a Mandated for listing by Congress. f Flammable gas. g Volatile flammable liquid. 

[59 FR 4493, Jan. 31, 1994. Redesignated at 61 FR 31717, June 20, 1996, as amended at 62 FR 45132, 

Aug. 25, 1997; 63 FR 645, Jan. 6, 1998] 

62 
Environmental Protection Agency 

Subpart G—Risk Management


Plan


SOURCE: 61 FR 31726, June 20, 1996, unless 

otherwise noted. 

§ 68.150 Submission. 

(a) The owner or operator shall submit a single RMP that includes the information required by §§ 68.155 through 

68.185 for all covered processes. The 

RMP shall be submitted in a method 

and format to a central point as specified by EPA prior to June 21, 1999. 

(b) The owner or operator shall submit the first RMP no later than the 

latest of the following dates: 

(1) June 21, 1999; 

(2) Three years after the date on 

which a regulated substance is first 

listed under § 68.130; or 

(3) The date on which a regulated 

substance is first present above a 

threshold quantity in a process. 

(c) Subsequent submissions of RMPs 

shall be in accordance with § 68.190. 

(d) Notwithstanding the provisions of 

§§ 68.155 to 68.190, the RMP shall exclude classified information. Subject to 

appropriate procedures to protect such 

information from public disclosure, 

classified data or information excluded 

from the RMP may be made available 

in a classified annex to the RMP for review by Federal and state representatives who have received the appropriate security clearances. 

§ 68.155 Executive summary. 

The owner or operator shall provide 

in the RMP an executive summary that 

includes a brief description of the following elements: 

(a) The accidental release prevention 

and emergency response policies at the 

stationary source; 

(b) The stationary source and regulated substances handled; 

(c) The worst-case release scenario(s) 

and the alternative release scenario(s), 

including administrative controls and 

mitigation measures to limit the distances for each reported scenario; 

(d) The general accidental release 

prevention program and chemical-specific prevention steps; 

(e) The five-year accident history; 

§ 68.165 

(f) The emergency response program; 

and 

(g) Planned changes to improve safety. 

§ 68.160 Registration. 

(a) The owner or operator shall complete a single registration form and include it in the RMP. The form shall 

cover all regulated substances handled 

in covered processes. 

(b) The registration shall include the 

following data: 

(1) Stationary source name, street, 

city, county, state, zip code, latitude, 

and longitude; 

(2) The stationary source Dun and 

Bradstreet number; 

(3) Name and Dun and Bradstreet 

number of the corporate parent company; 

(4) The name, telephone number, and 

mailing address of the owner or operator; 

(5) The name and title of the person 

or position with overall responsibility 

for RMP elements and implementation; 

(6) The name, title, telephone number, and 24-hour telephone number of 

the emergency contact; 

(7) For each covered process, the 

name and CAS number of each regulated substance held above the threshold quantity in the process, the maximum quantity of each regulated substance or mixture in the process (in 

pounds) to two significant digits, the 

SIC code, and the Program level of the 

process; 

(8) The stationary source EPA identifier; 

(9) The number of full-time employees at the stationary source; 

(10) Whether the stationary source is 

subject to 29 CFR 1910.119; 

(11) Whether the stationary source is 

subject to 40 CFR part 355; 

(12) Whether the stationary source 

has a CAA Title V operating permit; 

and 

(13) The date of the last safety inspection of the stationary source by a 

Federal, state, or local government 

agency and the identity of the inspecting entity. 

§ 68.165 Offsite consequence analysis. 

(a) The owner or operator shall submit in the RMP information: 

63

§ 68.168 

(1) One worst-case release scenario 

for each Program 1 process; and 

(2) For Program 2 and 3 processes, 

one worst-case release scenario to represent all regulated toxic substances 

held above the threshold quantity and 

one worst-case release scenario to represent all regulated flammable substances held above the threshold quantity. If additional worst-case scenarios 

for toxics or flammables are required 

by § 68.25(a)(2)(iii), the owner or operator shall submit the same information 

on the additional scenario(s). The 

owner or operator of Program 2 and 3 

processes shall also submit information 

on one alternative release scenario for 

each regulated toxic substance held 

above the threshold quantity and one 

alternative release scenario to represent all regulated flammable substances held above the threshold quantity. 

(b) The owner or operator shall submit the following data: 

(1) Chemical name; 

(2) Physical state (toxics only); 

(3) Basis of results (give model name 

if used); 

(4) Scenario (explosion, fire, toxic gas 

release, or liquid spill and vaporization); 

(5) Quantity released in pounds; 

(6) Release rate; 

(7) Release duration; 

(8) Wind speed and atmospheric stability class (toxics only); 

(9) Topography (toxics only); 

(10) Distance to endpoint; 

(11) Public and environmental receptors within the distance; 

(12) Passive mitigation considered; 

and 

(13) Active mitigation considered (alternative releases only); 

§ 68.168 Five-year accident history. 

The owner or operator shall submit 

in the RMP the information provided 

in § 68.42(b) on each accident covered by 

§ 68.42(a). 

§ 68.170 Prevention program/Program

2. 

(a) For each Program 2 process, the 

owner or operator shall provide in the 

RMP the information indicated in 

paragraphs (b) through (k) of this sec40 CFR Ch. I (7–1–98 Edition) 

tion. If the same information applies to 

more than one covered process, the 

owner or operator may provide the information only once, but shall indicate 

to which processes the information applies. 

(b) The SIC code for the process. 

(c) The name(s) of the chemical(s) 

covered. 

(d) The date of the most recent review or revision of the safety information and a list of Federal or state regulations or industry-specific design 

codes and standards used to demonstrate compliance with the safety information requirement. 

(e) The date of completion of the 

most recent hazard review or update. 

(1) The expected date of completion 

of any changes resulting from the hazard review; 

(2) Major hazards identified; 

(3) Process controls in use; 

(4) Mitigation systems in use; 

(5) Monitoring and detection systems 

in use; and 

(6) Changes since the last hazard review. 

(f) The date of the most recent review 

or revision of operating procedures. 

(g) The date of the most recent review or revision of training programs; 

(1) The type of training provided— 

classroom, classroom plus on the job, 

on the job; and 

(2) The type of competency testing 

used. 

(h) The date of the most recent review or revision of maintenance procedures and the date of the most recent 

equipment inspection or test and the 

equipment inspected or tested. 

(i) The date of the most recent compliance audit and the expected date of 

completion of any changes resulting 

from the compliance audit. 

(j) The date of the most recent incident investigation and the expected 

date of completion of any changes resulting from the investigation. 

(k) The date of the most recent 

change that triggered a review or revision of safety information, the hazard 

review, operating or maintenance procedures, or training. 

64

Environmental Protection Agency 

§ 68.175 Prevention program/Program

3. 

(a) For each Program 3 process, the 

owner or operator shall provide the information indicated in paragraphs (b) 

through (p) of this section. If the same 

information applies to more than one 

covered process, the owner or operator 

may provide the information only 

once, but shall indicate to which processes the information applies. 

(b) The SIC code for the process. 

(c) The name(s) of the substance(s) 

covered. 

(d) The date on which the safety information was last reviewed or revised. 

(e) The date of completion of the 

most recent PHA or update and the 

technique used. 

(1) The expected date of completion 

of any changes resulting from the PHA; 

(2) Major hazards identified; 

(3) Process controls in use; 

(4) Mitigation systems in use; 

(5) Monitoring and detection systems 

in use; and 

(6) Changes since the last PHA. 

(f) The date of the most recent review 

or revision of operating procedures. 

(g) The date of the most recent review or revision of training programs; 

(1) The type of training provided— 

classroom, classroom plus on the job, 

on the job; and 

(2) The type of competency testing 

used. 

(h) The date of the most recent review or revision of maintenance procedures and the date of the most recent 

equipment inspection or test and the 

equipment inspected or tested. 

(i) The date of the most recent 

change that triggered management of 

change procedures and the date of the 

most recent review or revision of management of change procedures. 

(j) The date of the most recent prestartup review. 

(k) The date of the most recent compliance audit and the expected date of 

completion of any changes resulting 

from the compliance audit; 

(l) The date of the most recent incident investigation and the expected 

date of completion of any changes resulting from the investigation; 

(m) The date of the most recent review or revision of employee participation plans; 

§ 68.190 

(n) The date of the most recent review or revision of hot work permit 

procedures; 

(o) The date of the most recent review or revision of contractor safety 

procedures; and 

(p) The date of the most recent evaluation of contractor safety performance. 

§ 68.180 Emergency response program. 

(a) The owner or operator shall provide in the RMP the following information: 

(1) Do you have a written emergency 

response plan? 

(2) Does the plan include specific actions to be taken in response to an accidental releases of a regulated substance? 

(3) Does the plan include procedures 

for informing the public and local 

agencies responsible for responding to 

accidental releases? 

(4) Does the plan include information 

on emergency health care? 

(5) The date of the most recent review or update of the emergency response plan; 

(6) The date of the most recent emergency response training for employees. 

(b) The owner or operator shall provide the name and telephone number of 

the local agency with which the plan is 

coordinated. 

(c) The owner or operator shall list 

other Federal or state emergency plan 

requirements to which the stationary 

source is subject. 

§ 68.185 Certification. 

(a) For Program 1 processes, the 

owner or operator shall submit in the 

RMP the certification statement provided in § 68.12(b)(4). 

(b) For all other covered processes, 

the owner or operator shall submit in 

the RMP a single certification that, to 

the best of the signer’s knowledge, information, and belief formed after reasonable inquiry, the information submitted is true, accurate, and complete. 

§ 68.190 Updates. 

(a) The owner or operator shall review and update the RMP as specified 

in paragraph (b) of this section and 

submit it in a method and format to a 

65

§ 68.200 

central point specified by EPA prior to 

June 21, 1999. 

(b) The owner or operator of a stationary source shall revise and update 

the RMP submitted under § 68.150 as 

follows: 

(1) Within five years of its initial submission or most recent update required 

by paragraphs (b)(2) through (b)(7) of 

this section, whichever is later. 

(2) No later than three years after a 

newly regulated substance is first listed by EPA; 

(3) No later than the date on which a 

new regulated substance is first 

present in an already covered process 

above a threshold quantity; 

(4) No later than the date on which a 

regulated substance is first present 

above a threshold quantity in a new 

process; 

(5) Within six months of a change 

that requires a revised PHA or hazard 

review; 

(6) Within six months of a change 

that requires a revised offsite consequence analysis as provided in § 68.36; 

and 

(7) Within six months of a change 

that alters the Program level that applied to any covered process. 

(c) If a stationary source is no longer 

subject to this part, the owner or operator shall submit a revised registration 

to EPA within six months indicating 

that the stationary source is no longer 

covered. 

Subpart H—Other Requirements 

SOURCE: 61 FR 31728, June 20, 1996, unless 

otherwise noted. 

§ 68.200 Recordkeeping. 

The owner or operator shall maintain 

records supporting the implementation 

of this part for five years unless otherwise provided in subpart D of this part. 

§ 68.210 Availability of information to

the public. 

(a) The RMP required under subpart 

G of this part shall be available to the 

public under 42 U.S.C. 7414(c). 

(b) The disclosure of classified information by the Department of Defense 

or other Federal agencies or contractors of such agencies shall be con40 CFR Ch. I (7–1–98 Edition) 

trolled by applicable laws, regulations, 

or executive orders concerning the release of classified information. 

§ 68.215 Permit content and air permitting authority or designated 

agency requirements. 

(a) These requirements apply to any 

stationary source subject to this part 

68 and parts 70 or 71 of this chapter. 

The 40 CFR part 70 or part 71 permit for 

the stationary source shall contain: 

(1) A statement listing this part as 

an applicable requirement; 

(2) Conditions that require the source 

owner or operator to submit: 

(i) A compliance schedule for meeting the requirements of this part by 

the date provided in § 68.10(a) or; 

(ii) As part of the compliance certification submitted under 40 CFR 

70.6(c)(5), a certification statement 

that the source is in compliance with 

all requirements of this part, including 

the registration and submission of the 

RMP. 

(b) The owner or operator shall submit any additional relevant information requested by the air permitting 

authority or designated agency. 

(c) For 40 CFR part 70 or part 71 permits issued prior to the deadline for 

registering and submitting the RMP 

and which do not contain permit conditions described in paragraph (a) of this 

section, the owner or operator or air 

permitting authority shall initiate permit revision or reopening according to 

the procedures of 40 CFR 70.7 or 71.7 to 

incorporate the terms and conditions 

consistent with paragraph (a) of this 

section. 

(d) The state may delegate the authority to implement and enforce the 

requirements of paragraph (e) of this 

section to a state or local agency or 

agencies other than the air permitting 

authority. An up-to-date copy of any 

delegation instrument shall be maintained by the air permitting authority. 

The state may enter a written agreement with the Administrator under 

which EPA will implement and enforce 

the requirements of paragraph (e) of 

this section. 

(e) The air permitting authority or 

the agency designated by delegation or 

agreement under paragraph (d) of this 

section shall, at a minimum: 

66

Environmental Protection Agency 

(1) Verify that the source owner or 

operator has registered and submitted 

an RMP or a revised plan when required by this part; 

(2) Verify that the source owner or 

operator has submitted a source certification or in its absence has submitted a compliance schedule consistent 

with paragraph (a)(2) of this section; 

(3) For some or all of the sources subject to this section, use one or more 

mechanisms such as, but not limited 

to, a completeness check, source audits, record reviews, or facility inspections to ensure that permitted sources 

are in compliance with the requirements of this part; and 

(4) Initiate enforcement action based 

on paragraphs (e)(1) and (e)(2) of this 

section as appropriate. 

§ 68.220 Audits. 

(a) In addition to inspections for the 

purpose of regulatory development and 

enforcement of the Act, the implementing agency shall periodically 

audit RMPs submitted under subpart G 

of this part to review the adequacy of 

such RMPs and require revisions of 

RMPs when necessary to ensure compliance with subpart G of this part. 

(b) The implementing agency shall 

select stationary sources for audits 

based on any of the following criteria: 

(1) Accident history of the stationary 

source; 

(2) Accident history of other stationary sources in the same industry; 

(3) Quantity of regulated substances 

present at the stationary source; 

(4) Location of the stationary source 

and its proximity to the public and environmental receptors; 

(5) The presence of specific regulated 

substances; 

(6) The hazards identified in the 

RMP; and 

(7) A plan providing for neutral, random oversight. 

(c) Exemption from audits. A stationary source with a Star or Merit ranking under OSHA’s voluntary protection 

program shall be exempt from audits 

under paragraph (b)(2) and (b)(7) of this 

section. 

(d) The implementing agency shall 

have access to the stationary source, 

supporting documentation, and any 

§ 68.220 

area where an accidental release could 

occur. 

(e) Based on the audit, the implementing agency may issue the owner 

or operator of a stationary source a 

written preliminary determination of 

necessary revisions to the stationary 

source’s RMP to ensure that the RMP 

meets the criteria of subpart G of this 

part. The preliminary determination 

shall include an explanation for the 

basis for the revisions, reflecting industry standards and guidelines (such as 

AIChE/CCPS guidelines and ASME and 

API standards) to the extent that such 

standards and guidelines are applicable, and shall include a timetable for 

their implementation. 

(f) Written response to a preliminary determination. (1) The owner or operator 

shall respond in writing to a preliminary determination made in accordance with paragraph (e) of this section. 

The response shall state the owner or 

operator will implement the revisions 

contained in the preliminary determination in accordance with the timetable included in the preliminary determination or shall state that the 

owner or operator rejects the revisions 

in whole or in part. For each rejected 

revision, the owner or operator shall 

explain the basis for rejecting such revision. Such explanation may include 

substitute revisions. 

(2) The written response under paragraph (f)(1) of this section shall be received by the implementing agency 

within 90 days of the issue of the preliminary determination or a shorter 

period of time as the implementing 

agency specifies in the preliminary determination as necessary to protect 

public health and the environment. 

Prior to the written response being due 

and upon written request from the 

owner or operator, the implementing 

agency may provide in writing additional time for the response to be received. 

(g) After providing the owner or operator an opportunity to respond under 

paragraph (f) of this section, the implementing agency may issue the owner 

or operator a written final determination of necessary revisions to the stationary source’s RMP. The final determination may adopt or modify the revisions contained in the preliminary 

67

§ 68.220 

determination under paragraph (e) of 

this section or may adopt or modify 

the substitute revisions provided in the 

response under paragraph (f) of this 

section. A final determination that 

adopts a revision rejected by the owner 

or operator shall include an explanation of the basis for the revision. A 

final determination that fails to adopt 

a substitute revision provided under 

paragraph (f) of this section shall include an explanation of the basis for 

finding such substitute revision unreasonable. 

(h) Thirty days after completion of 

the actions detailed in the implementation schedule set in the final determination under paragraph (g) of this 

section, the owner or operator shall be 

40 CFR Ch. I (7–1–98 Edition) 

in violation of subpart G of this part 

and this section unless the owner or 

operator revises the RMP prepared 

under subpart G of this part as required 

by the final determination, and submits the revised RMP as required 

under § 68.150. 

(i) The public shall have access to the 

preliminary determinations, responses, 

and final determinations under this 

section in a manner consistent with 

§ 68.210. 

(j) Nothing in this section shall preclude, limit, or interfere in any way 

with the authority of EPA or the state 

to exercise its enforcement, investigatory, and information gathering authorities concerning this part under 

the Act. 

68

Environmental Protection Agency Pt. 68, App. A 

APPENDIX A TO PART 68—T ABLE OF 

TOXIC ENDPOINTS 

[As defined in § 68.22 of this part]

CAS No. Chemical name Toxic end­ point (mg/L) 

107–02–8 ..........................................107–13–1 ..........................................814–68–6 ..........................................107–18–6 ..........................................107–11–9 ..........................................7664–41–7 ........................................7664–41–7 ........................................7784–34–1 ........................................7784–42–1 ........................................10294–34–5 ......................................7637–07–2 ........................................353–42–4 ..........................................7726–95–6 ........................................75–15–0 ............................................7782–50–5 ........................................10049–04–4 ......................................67–66–3 ............................................542–88–1 ..........................................107–30–2 ..........................................4170–30–3 ........................................123–73–9 ..........................................506–77–4 ..........................................108–91–8 ..........................................19287–45–7 ......................................75–78–5 ............................................57–14–7 ............................................106–89–8 ..........................................107–15–3 ..........................................151–56–4 ..........................................75–21–8 ............................................7782–41–4 ........................................50–00–0 ............................................110–00–9 ..........................................302–01–2 ..........................................7647–01–0 ........................................74–90–8 ............................................7647–01–0 ........................................7664–39–3 ........................................7783–07–5 ........................................7783–06–4 ........................................13463–40–6 ......................................78–82–0 ............................................108–23–6 ..........................................126–98–7 .......................................... 

Acrolein [2-Propenal] ....................................................................................................................................................................................Acrylonitrile [2-Propenenitrile] .......................................................................................................................................................................Acrylyl chloride [2-Propenoyl chloride] .........................................................................................................................................................Allyl alcohol [2-Propen-1-ol] .......................................................................................................................................................................... Allylamine [2-Propen-1-amine] ...................................................................................................................................................................... Ammonia (anhydrous) ................................................................................................................................................................................... Ammonia (conc 20% or greater) ..................................................................................................................................................................Arsenous trichloride ......................................................................................................................................................................................Arsine ............................................................................................................................................................................................................Boron trichloride [Borane, trichloro-] ............................................................................................................................................................. Boron trifluoride [Borane, trifluoro-] ..............................................................................................................................................................Boron trifluoride compound with methyl ether (1:1) [Boron, trifluoro[oxybis[methane]]-, T-4 ......................................................................Bromine ......................................................................................................................................................................................................... Carbon disulfide ............................................................................................................................................................................................Chlorine ......................................................................................................................................................................................................... Chlorine dioxide [Chlorine oxide (ClO2)] ......................................................................................................................................................Chloroform [Methane, trichloro-] ...................................................................................................................................................................Chloromethyl ether [Methane, oxybis[chloro-] ..............................................................................................................................................Chloromethyl methyl ether [Methane, chloromethoxy-] ................................................................................................................................ Crotonaldehyde [2-Butenal] ..........................................................................................................................................................................Crotonaldehyde, (E)-, [2-Butenal, (E)-] ......................................................................................................................................................... Cyanogen chloride ........................................................................................................................................................................................Cyclohexylamine [Cyclohexanamine] ...........................................................................................................................................................Diborane ........................................................................................................................................................................................................ Dimethyldichlorosilane [Silane, dichlorodimethyl-] ........................................................................................................................................ 1,1-Dimethylhydrazine [Hydrazine, 1,1-dimethyl-] ........................................................................................................................................Epichlorohydrin [Oxirane, (chloromethyl)-] ...................................................................................................................................................Ethylenediamine [1,2-Ethanediamine] ..........................................................................................................................................................Ethyleneimine [Aziridine] ............................................................................................................................................................................... Ethylene oxide [Oxirane] ............................................................................................................................................................................... Fluorine .........................................................................................................................................................................................................Formaldehyde (solution) ...............................................................................................................................................................................Furan ............................................................................................................................................................................................................. Hydrazine ......................................................................................................................................................................................................Hydrochloric acid (conc 37% or greater) ...................................................................................................................................................... Hydrocyanic acid ........................................................................................................................................................................................... Hydrogen chloride (anhydrous) [Hydrochloric acid] .....................................................................................................................................Hydrogen fluoride/Hydrofluoric acid (conc 50% or greater) [Hydrofluoric acid] ........................................................................................... Hydrogen selenide ........................................................................................................................................................................................Hydrogen sulfide ...........................................................................................................................................................................................Iron, pentacarbonyl- [Iron carbonyl (Fe(CO)5), (TB–5–11)-] ........................................................................................................................ Isobutyronitrile [Propanenitrile, 2-methyl-] ....................................................................................................................................................Isopropyl chloroformate [Carbonochloride acid, 1-methylethyl ester] ..........................................................................................................Methacrylonitrile [2-Propenenitrile, 2-methyl-] .............................................................................................................................................. 

0.0011 

0.076 

0.00090 0.036 0.0032 

0.14 

0.14 

0.010 

0.0019 

0.010 0.028 0.023 

0.0065 0.16 0.0087 

0.0028 

0.49 

0.00025 0.0018 

0.029 

0.029 0.030 0.16 

0.0011 0.026 

0.012 

0.076 0.49 

0.018 0.090 0.0039 0.012 

0.0012 

0.011 

0.030 

0.011 0.030 0.016 0.00066 

0.042 

0.00044 

0.14 

0.10 0.0027 

69

Pt. 68, App. A 40 CFR Ch. I (7–1–98 Edition) 

70


APPENDIX A TO PART 68—T ABLE OF 

TOXIC ENDPOINTS—Continued

[As defined in § 68.22 of this part]

CAS No. Chemical name Toxic end­ point (mg/L) 

74–87–3 ............................................79–22–1 ............................................60–34–4 ............................................624–83–9 ..........................................74–93–1 ............................................556–64–9 ..........................................75–79–6 ............................................13463–39–3 ......................................7697–37–2 ........................................10102–43–9 ......................................8014–95–7 ........................................79–21–0 ............................................594–42–3 ..........................................75–44–5 ............................................7803–51–2 ........................................10025–87–3 ......................................7719–12–2 ........................................110–89–4 ..........................................107–12–0 ..........................................109–61–5 ..........................................75–55–8 ............................................75–56–9 ............................................7446–09–5 ........................................7783–60–0 ........................................7446–11–9 ........................................75–74–1 ............................................509–14–8 ..........................................7750–45–0 ........................................584–84–9 ..........................................91–08–7 ............................................26471–62–5 ......................................75–77–4 ............................................108–05–4 .......................................... 

Methyl chloride [Methane, chloro-] ...............................................................................................................................................................Methyl chloroformate [Carbonochloridic acid, methylester] .......................................................................................................................... Methyl hydrazine [Hydrazine, methyl-] .........................................................................................................................................................Methyl isocyanate [Methane, isocyanato-] ...................................................................................................................................................Methyl mercaptan [Methanethiol] .................................................................................................................................................................. Methyl thiocyanate [Thiocyanic acid, methyl ester] ...................................................................................................................................... Methyltrichlorosilane [Silane, trichloromethyl-] .............................................................................................................................................Nickel carbonyl .............................................................................................................................................................................................. Nitric acid (conc 80% or greater) .................................................................................................................................................................. Nitric oxide [Nitrogen oxide (NO)] ................................................................................................................................................................. Oleum (Fuming Sulfuric acid) [Sulfuric acid, mixture with sulfur trioxide] .................................................................................................... Peracetic acid [Ethaneperoxoic acid] ...........................................................................................................................................................Perchloromethylmercaptan [Methanesulfenyl chloride, trichloro-] ................................................................................................................ Phosgene [Carbonic dichloride] .................................................................................................................................................................... Phosphine .....................................................................................................................................................................................................Phosphorus oxychloride [Phosphoryl chloride] ............................................................................................................................................. Phosphorus trichloride [Phosphorous trichloride] .........................................................................................................................................Piperidine ......................................................................................................................................................................................................Propionitrile [Propanenitrile] .......................................................................................................................................................................... Propyl chloroformate [Carbonochloridic acid, propylester] ........................................................................................................................... Propyleneimine [Aziridine, 2-methyl-] ...........................................................................................................................................................Propylene oxide [Oxirane, methyl-] ..............................................................................................................................................................Sulfur dioxide (anhydrous) ............................................................................................................................................................................ Sulfur tetrafluoride [Sulfur fluoride (SF4), (T-4)-] .......................................................................................................................................... Sulfur trioxide ................................................................................................................................................................................................Tetramethyllead [Plumbane, tetramethyl-] .................................................................................................................................................... Tetranitromethane [Methane, tetranitro-] ......................................................................................................................................................Titanium tetrachloride [Titanium chloride (TiCl4) (T-4)-] ..............................................................................................................................Toluene 2,4-diisocyanate [Benzene, 2,4-diisocyanato-1-methyl-] ................................................................................................................ Toluene 2,6-diisocyanate [Benzene, 1,3-diisocyanato-2-methyl-] ................................................................................................................ Toluene diisocyanate (unspecified isomer) [Benzene, 1,3-diisocyanatomethyl-] ......................................................................................... Trimethylchlorosilane [Silane, chlorotrimethyl-] ............................................................................................................................................Vinyl acetate monomer [Acetic acid ethenyl ester] ...................................................................................................................................... 

0.82 

0.0019 

0.0094 0.0012 0.049 0.085 0.018 0.00067 0.026 

0.031 

0.010 0.0045 0.0076 

0.00081 

0.0035 0.0030 

0.028 

0.022 

0.0037 

0.010 0.12 0.59 0.0078 

0.0092 0.010 

0.0040 0.0040 0.020 0.0070 0.0070 

0.0070 0.050 0.26 

[61 FR 31729, June 20, 1996, as amended at 62 FR 45132, Aug. 25, 1997] 
federal register
Wednesday 

January 6, 1999 

Part IV 

Environmental 

Protection Agency 

40 CFR Part 68 

Accidental Release Prevention 

Requirements; Risk Management 

Programs Under Clean Air Act Section 

112(r)(7), Amendments; Final Rule 
964 Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 68 

[FRL–6214–9] 

RIN 2050–AE46 

Accidental Release Prevention 

Requirements; Risk Management 

Programs Under Clean Air Act Section 

112(r)(7); Amendments 

AGENCY: Environmental Protection


Agency (EPA).


ACTION: Final rule.


SUMMARY: This action modifies the 

chemical accident prevention rule 

codified in 40 CFR Part 68. The 

chemical accident prevention rule 

requires owners and operators of 

stationary sources subject to the rule to 

submit a risk management plan (RMP) 

by June 21, 1999, to a central location 

specified by EPA. In this action, EPA is 

amending the rule to: add four 

mandatory and five optional RMP data 

elements, establish specific procedures 

for protecting confidential business 

information when submitting RMPs, 

adopt the government’s use of a new 

industry classification system, and make 

technical corrections and clarifications 

to Part 68. However, as stated in the 

proposed rule for these amendments, 

this action does not address issues 

concerning public access to offsite 

consequence analysis data in the RMP. 

DATES: The rule is effective February 5, 

1999. 

ADDRESSES: Supporting material used in 

developing the proposed rule and final 

rule is contained in Docket A–98–08. 

The docket is available for public 

inspection and copying between 8:00 

a.m. and 5:30 p.m., Monday through 

Friday (except government holidays) at 

Room 1500, 401 M Street SW, 

Washington, DC 20460. A reasonable fee 

may be charged for copying. 

FOR FURTHER INFORMATION CONTACT: Sicy 

Jacob or John Ferris, Chemical 

Emergency Preparedness and 

Prevention Office, Environmental 

Protection Agency (5104), 401 M Street 

SW, Washington, DC 20460, (202) 260– 

7249 or (202) 260–4043, respectively; or 

the Emergency Planning and 

Community Right-to-Know Hotline at 

800–424–9346 (in the Washington, DC 

metropolitan area, (703) 412–9810). You 

may wish to visit the Chemical 

Emergency Preparedness and 

Prevention Office (CEPPO) Internet site, 

at www.epa.gov/ceppo. 

SUPPLEMENTARY INFORMATION: 

Regulated Entities 

Entities potentially regulated by this 

action are those stationary sources that 

have more than a threshold quantity of 

a regulated substance in a process. 

Regulated categories and entities 

include: 

Category Examples of regulated entities 

Chemical Manufacturers ..................................... Basic chemical manufacturing, petrochemicals, resins, agricultural chemicals, pharmaceuticals, 

paints, cleaning compounds. 

Petroleum ............................................................ Refineries. 

Other Manufacturing ........................................... Paper, electronics, semiconductors, fabricated metals, industrial machinery, food processors. 

Agriculture ........................................................... Agricultural retailers. 

Public Sources .................................................... Drinking water and waste water treatment systems. 

Utilities ................................................................. Electric utilities. 

Other ................................................................... Propane retailers and users, cold storage, warehousing, and wholesalers. 

Federal Sources .................................................. Military and energy installations. 

This table is not meant to be 

exhaustive, but rather provides a guide 

for readers to indicate those entities 

likely to be regulated by this action. The 

table lists entities EPA is aware of that 

could potentially be regulated by this 

action. Other entities not listed in the 

table could also be regulated. To 

determine whether a stationary source is 

regulated by this action, carefully 

examine the provisions associated with 

the list of substances and thresholds 

under § 68.130 and the applicability 

criteria under § 68.10. If you have 

questions regarding applicability of this 

action to a particular entity, consult the 

hotline or persons listed in the 

preceding FOR FURTHER INFORMATION 

CONTACT section. 

Table of Contents 

I. Introduction and Background 

A. Statutory Authority 

B. Background 

II. Summary of the Final Rule 

III. Discussion of Issues 

A. NAICS Codes 

B. RMP Data Elements 

C. Prevention Program Reporting 

D. Confidential Business Information 

E. Other Issues 

F. Technical Corrections 

IV. Section-by-Section Discussion of the 

Final Rule 

V. Judicial Review 

VI. Administrative Requirements 

A. Docket 

B. Executive Order 12866 

C. Executive Order 12875 

D. Executive Order 13045 

E. Executive Order 13084 

F. Regulatory Flexibility 

G. Paperwork Reduction 

H. Unfunded Mandates Reform Act 

I. National Technology Transfer and


Advancement Act


J. Congressional Review Act 

I. Introduction and Background 

A. Statutory Authority 

These amendments are being 

promulgated under sections 112(r) and 

301(a)(1) of the Clean Air Act (CAA) as 

amended (42 U.S.C. 7412(r), 7601(a)(1)). 

B. Background 

The 1990 CAA Amendments added 

section 112(r) to provide for the 

prevention and mitigation of accidental 

chemical releases. Section 112(r) 

mandates that EPA promulgate a list of 

‘‘regulated substances,’’ with threshold 

quantities. Processes at stationary 

sources that contain a threshold 

quantity of a regulated substance are 

subject to accidental release prevention 

regulations promulgated under CAA 

section 112(r)(7). EPA promulgated the 

list of regulated substances on January 

31, 1994 (59 FR 4478) (the ‘‘List Rule’’) 

and the accidental release prevention 

regulations creating the risk 

management program requirements on 

June 20, 1996 (61 FR 31668) (the ‘‘RMP 

Rule’’). Together, these two rules are 

codified as 40 CFR Part 68. EPA 

amended the List Rule on August 25, 

1997 (62 FR 45132), to change the listed 

concentration of hydrochloric acid. On 

January 6, 1998 ( 63 FR 640), EPA 

amended the List Rule to delist Division 

1.1 explosives (classified by DOT), to 

clarify certain provisions related to 

regulated flammable substances and to 

clarify the transportation exemption. 

Part 68 requires that sources with 

more than a threshold quantity of a 

regulated substance in a process 

develop and implement a risk 

management program that includes a 

five-year accident history, offsite 

consequence analyses, a prevention 
Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 965 

program, and an emergency response 

program. In Part 68, processes are 

divided into three categories (Programs 

1 through 3). Processes that have no 

potential impact on the public in the 

case of accidental releases have minimal 

requirements (Program 1). Processes in 

Programs 2 and 3 have additional 

requirements based on the potential for 

offsite consequences associated with the 

worst-case accidental release and their 

accident history. Program 3 is also 

triggered if the processes are subject to 

OSHA’s Process Safety Management 

(PSM) Standard. By June 21, 1999, 

sources must submit to a location 

designated by EPA, a risk management 

plan (RMP) that summarizes their 

implementation of the risk management 

program. 

When EPA promulgated the risk 

management program regulations, it 

stated that it intended to work toward 

electronic submission of RMPs. The 

Accident Prevention Subcommittee of 

the CAA Advisory Committee convened 

an Electronic Submission Workgroup to 

examine technical and practical issues 

associated with creating a national 

electronic repository for RMPs. Based 

on workgroup recommendations, EPA is 

in the process of developing two 

systems, a user-friendly PC-based 

submission system (RMP*Submit) and a 

database of RMPs (RMP*Info). 

The Electronic Submission 

Workgroup also recommended that EPA 

add some mandatory and optional data 

elements to the RMP and asked EPA to 

clarify how confidential business 

information (CBI) submitted in the RMP 

would be handled. Based on these 

recommendations and requests for 

clarifications, EPA proposed 

amendments to Part 68 on April 17, 

1998 (63 FR 19216). These amendments 

proposed to replace the use of Standard 

Industrial Classification (SIC) codes 

with the North American Industry 

Classification System (NAICS) codes, 

add four mandatory data elements to the 

RMP, add five optional data elements to 

the RMP, establish specific 

requirements for submission of 

information claimed CBI, and make 

technical corrections and clarifications 

to the rule. EPA received 47 written 

comments on the proposed rule. 

Today’s rule reflects EPA’s 

consideration of all comments; major 

issues raised by commenters and EPA’s 

responses are discussed in Section III of 

this preamble. A summary of all 

comments submitted and EPA’s 

responses can be found in a document 

entitled, Accidental Release Prevention 

Requirements; Risk Management 

Programs Under Clean Air Act Section 

112(r)(7); Amendments: Summary and 

Response to Comments, in the Docket 

(see ADDRESSES). 

II. Summary of the Final Rule 

NAICS Codes 

On January 1, 1997, the U.S. 

Government, in cooperation with the 

governments of Canada and Mexico, 

adopted a new industry classification 

system, the North American Industry 

Classification System (NAICS), to 

replace the Standard Industrial 

Classification (SIC) codes (April 9, 1997, 

62 FR 17288). The applicability of some 

Part 68 requirements (i.e., Program 3 

prevention requirements) is determined, 

in part, by SIC codes, and Part 68 also 

requires the reporting of SIC codes in 

the RMP. Therefore, EPA is revising Part 

68 to replace all references to ‘‘SIC 

code’’ with ‘‘NAICS code.’’ In addition, 

EPA is replacing, as proposed, the nine 

SIC codes subject to Program 3 

prevention program requirements with 

ten NAICS codes, as follows: 

NAICS Sector 

32211 Pulp mills 

32411 Petroleum refineries 

32511 Petrochemical manufacturing 

325181 Alkalies and chlorine 

325188 All other inorganic chemical 

manufacturing 

325192 Other cyclic crude and intermediate 

manufacturing 

325199 All other basic organic chemical 

manufacturing 

325211 Plastics and resins 

325311 Nitrogen fertilizer 

32532 Pesticide and other agricultural 

chemicals 

NAICS codes are either five or six digits, 

depending on the degree to which the 

sector is subdivided. 

RMP Data Elements 

As proposed, EPA is adding four new 

data elements to the RMP: latitude/ 

longitude method and description, CAA 

Title V permit number, percentage 

weight of a toxic substance in a liquid 

mixture, and NAICS code for each 

process that had an accidental release 

reported in the five-year accident 

history. EPA is also adding five optional 

data elements: local emergency 

planning committee (LEPC) name, 

source or parent company e-mail 

address, source homepage address, 

phone number at the source for public 

inquiries, and status under OSHA’s 

Voluntary Protection Program (VPP). 

Prevention Program Reporting 

EPA is not revising Sections 68.170 

and 68.175 as proposed. Prevention 

program reporting, therefore, will not be 

changed to require a prevention 

program for each portion of a process for 

which a Process Hazard Analysis (PHA) 

or hazard review was conducted. 

Instead, EPA plans to create functions 

within RMP*Submit to provide 

stationary sources with a flexible way of 

explaining the scope and content of 

each prevention program they 

implement at their facility. 

Confidential Business Information 

EPA is clarifying how confidential 

business information (CBI) submitted in 

the RMP will be handled. EPA has 

determined that the information 

required by certain RMP data elements 

does not meet the criteria for CBI and 

therefore may not be claimed as such. 

The Agency is also requiring submission 

of substantiation at the time a CBI claim 

is filed. 

Finally, EPA is promulgating several 

of the technical corrections and 

clarifications, as proposed in the 

Federal Register, April 17, 1998 (63 FR 

19216). 

III. Discussion of Issues 

EPA received 47 comments on the 

proposed rule. The commenters 

included chemical manufacturers, 

petroleum refineries, environmental 

groups, trade associations, a state 

agency, and members of the public. The 

major issues raised by commenters are 

addressed briefly below. The Agency’s 

complete response to comments 

received on this rulemaking is available 

in the docket (see ADDRESSES). The 

document is titled Accidental Release 

Prevention Requirements; Risk 

Management Programs Under Clean Air 

Act Section 112(r)(7); Amendments: 

Summary and Response to Comments. 

A. NAICS Codes 

Two commenters asked that sources 

be given the option to use either SIC 

codes or NAICS codes, or both, in their 

initial RMP because the NAICS system 

is new and may not be familiar to 

sources. EPA disagrees with this 

suggestion. EPA intends to provide 

several outreach mechanisms to assist 

sources in identifying their new NAICS 

code. RMP*Submit will provide a ‘‘pick 

list’’ that will make it easier for sources 

to find the appropriate code. Also, 

selected NAICS codes are included in 

the General Guidance for Risk 

Management Programs (July 1998) and 

in the industry-specific guidance 

documents that EPA is developing. EPA 

will also utilize the Emergency Planning 

and Community Right-to-Know Hotline 

at 800–424–9346 (or 703–412–9810) and 

its web site at www.epa.gov/ceppo/, to 

assist sources in determining the 

source’s NAICS codes. EPA also notes 

that the Internal Revenue Service is 

planning to require businesses to 
966 Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 

provide NAICS-based activity codes on 

their 1998 tax returns, so many sources 

will have become familiar with their 

NAICS codes by the June 1999 RMP 

deadline. 

EPA believes it is necessary and 

appropriate to change from SIC codes to 

NAICS codes at this time. EPA 

recognizes that NAICS codes were 

developed for statistical purposes by the 

Office of Management and Budget 

(OMB). In the notice of April 9, 1997 (62 

FR 17288) OMB stated that the ‘‘[u]se of 

NAICS for nonstatistical purposes (e.g., 

administrative, regulatory, or taxation) 

will be determined by the agency or 

agencies that have chosen to use the SIC 

for nonstatistical purposes.’’ EPA has 

determined that NAICS is appropriate in 

this rule for several reasons. First, the 

reason the SIC codes were replaced by 

NAICS codes is because the SIC codes 

no longer accurately represent today’s 

industries. The SIC codes will become 

more obsolete over time because OMB 

will no longer be supporting the SIC 

codes; therefore, no new or modified 

SIC codes will be developed to reflect 

future changes in industries. Second, as 

the SIC codes become obsolete, most 

users of SIC codes will likely change to 

NAICS codes over time, so future data 

sharing and consistency will be 

enhanced by use of NAICS codes in the 

RMP program. Third, through this 

rulemaking process, EPA has analyzed 

specific conversions of SIC codes to 

NAICS codes for the RMP program and 

was able to identify NAICS codes that 

were applicable to fulfilling the 

purposes of this rule. Finally, because 

the RMP reporting requirement is new, 

it is reasonable to begin the program 

with NAICS codes now rather than 

converting to them later. 

Three commenters expressed support 

for the ten NAICS codes that EPA 

proposed to use in place of the nine SIC 

codes referenced in section 68.10(d)(1) 

of Part 68 and one commenter partially 

objected. Section 68.10(d)(1) provides 

that processes in the referenced codes 

are subject to Program 3 requirements (if 

not eligible for Program 1). One 

commenter objected to EPA’s proposal 

to replace the SIC code for pulp and 

paper mills with only the NAICS code 

for pulp mills that do not also produce 

paper or paperboard. The commenter 

asked EPA to reexamine the accident 

history of paper and paperboard mills. 

As discussed in the preamble of the 

proposed rule, EPA reviewed the 

accident history data prior to proposing 

the new NAICS codes. Neither facilities 

that classify themselves as paper mills 

(NAICS Code 322121) nor paperboard 

mills (NAICS code 32213) met the 

accident history criteria that EPA used 

to select industrial sectors for Program 

3. 

EPA notes that a pulp process at a 

paper or a paperboard mill may still be 

subject to Program 3 as long as the 

process contains more than a threshold 

quantity of a regulated substance and is 

not eligible for Program 1. Section 

68.10(d)(1) uses industrial codes to 

classify processes, not facilities as a 

whole. Since section 68.10(d)(1) will 

continue to list the code for pulp mills, 

pulpmaking processes will continue to 

be subject to Program 3. In addition, 

under section 68.10(d)(2), paper 

processes will be in Program 3 (unless 

eligible for Program 1) if they are subject 

to OSHA’s Process Safety Management 

(PSM) standard. Most pulp and paper 

processes are, in fact, subject to this 

standard. 

One commenter objected to assigning 

NAICS codes to a process rather than 

the source as a whole. EPA first notes 

that the requirement to assign a SIC 

code to a process was adopted in the 

original RMP rulemaking two years ago. 

Today’s rule does not change that 

requirement except to substitute NAICS 

for SIC codes. In any event, EPA is 

today modifying Part 68 to clarify that 

sources provide the NAICS code that 

‘‘most closely corresponds to the 

process.’’ EPA believes that assigning an 

industry code to a process will help 

implementing agencies and the public 

understand what the covered process 

does; using the code makes it possible 

to provide this information without 

requiring a detailed explanation from 

the source. In addition, the primary 

NAICS code for a source as a whole may 

not reflect the activity of the covered 

process. 

B. RMP Data Elements 

EPA proposed to add, as optional 

RMP data elements: local emergency 

planning committee (LEPC), source (or 

parent company) E-mail address, source 

homepage address, phone number at the 

source for public inquiries, and OSHA 

Voluntary Protection Program (VPP) 

status. EPA also proposed to add, as 

mandatory data elements: method and 

description of latitude/longitude, Title 

V permit number, percent weight of a 

toxic substance in a liquid mixture, and 

NAICS code (only in the five-year 

accident history section). 

Commenters generally supported the 

new optional data elements. One 

commenter requested that the optional 

elements be made mandatory. EPA 

disagrees with this comment. While the 

elements are useful, many sources 

covered by this rule will not have e-mail 

addresses or home pages. The RMP will 

provide both addresses and phone 

numbers so that the public will have 

methods to reach the source. EPA has 

learned that in some areas there are no 

functioning LEPCs, therefore, at this 

time, EPA will not add this as a 

mandatory data element. However, in 

most cases, the LEPC for an area can be 

determined by contacting the local 

government or the State Emergency 

Response Commission (SERC) for which 

the area is located. Therefore, reporting 

these data elements will remain 

optional at this time. 

One commenter supported adding the 

listing of local emergency planning 

committee in the RMP data elements as 

an optional data element. The 

commenter stated that, although it is an 

optional data element, this listing will 

enhance the ability of local responders 

and emergency planners to adequately 

prepare and train for emergency events. 

Of the data elements that were 

proposed to be mandatory, one 

commenter objected to the addition of 

latitude/longitude method and 

description. The commenter stated that 

it was not clear in the proposal why the 

method and description information is 

needed. EPA is seeking latitude/ 

longitude method and description in 

accordance with its Locational Data 

Policy. Several EPA regulations require 

sources to provide their latitude and 

longitude, so that EPA can more readily 

locate facilities and communicate data 

between Agency offices. Sharing of data 

between EPA offices reduces 

duplication of information. Latitude/ 

longitude method and description 

provides information needed by EPA 

offices, and other users of the data, to 

rectify discrepancies that may appear in 

the latitude and longitude information 

provided by the source under various 

EPA requirements. Documentation of 

the method by which the latitude and 

longitude are determined and a 

description of the location point 

referenced by the latitude and longitude 

(e.g., administration building) will 

permit data users to evaluate the 

accuracy of those coordinates, thus 

addressing EPA data sharing and 

integration objectives. 

EPA believes this information will 

also facilitate EPA-State coordination of 

environmental programs, including the 

chemical accident prevention rule. The 

State/EPA Data Management Program is 

a successful multi-year initiative linking 

State environmental regulatory agencies 

and EPA in cooperative action. The 

Program’s goals include improvements 

in data quality and data integration 

based on location identification. 

Therefore, as proposed, the latitude/ 

longitude method and description will 

be added to the existing RMP data 
Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 967 

elements. RMP*Submit will provide a 

list of methods and descriptions from 

which sources may choose. 

EPA also proposed to require that 

sources report the percentage weight 

(weight percent) of a toxic substance in 

a mixture in the offsite consequence 

analysis (OCA) and the accident history 

sections of the RMP. This information is 

necessary for users of RMP data to 

understand how worst case and 

alternative release scenarios have been 

modeled. EPA has decided to require 

reporting of the weight percent of toxic 

substance in a liquid mixture because 

this information is necessary to 

understand the volatilization rate, 

which determines the downwind 

dispersion distance of the substance. 

The volatilization rate is affected by the 

vapor pressure of the substance in the 

mixture. For example, a spill of 70 

percent hydrofluoric acid (HF) will 

volatilize more quickly than a spill of 

the same quantity of HF in a 50 percent 

solution; consequently, over a 10­

minute period, the 70 percent solution 

will travel further. Reviewers of the 

RMP data, including local emergency 

planning committees, need to know the 

weight percent to be able to evaluate the 

results reported in the offsite 

consequence analysis and the impacts 

reported in the accident history. 

Without knowing the weight percent of 

the substance in the mixture, users of 

the data may compare scenarios or 

incidents that appear to involve the 

same chemical in the same physical 

state, but in fact involve the same 

chemical held in a different physical 

state. 

One commenter stated that for gas 

mixtures, percentage by volume (or 

volume percent) should be required to 

be reported rather than weight percent. 

In this final rule, EPA does not require 

reporting of the weight percent (or 

volume percent) of a regulated 

substance in a gas mixture. If a source 

handles regulated substances in a 

gaseous mixture (e.g., chlorine with 

hydrogen chloride), the quantity of a 

particular regulated substance in the 

mixture is what is reported in the RMP, 

since that is what would be released 

into the air. Its percentage weight in the 

mixture is irrelevant. 

Another commenter objected to this 

data element, claiming that it could 

result in reverse engineering and create 

a competitive disadvantage. EPA does 

not believe that this requirement would 

create a competitive disadvantage, since 

similar information is available to the 

public under Emergency Planning and 

Community Right-to-Know Act (EPCRA) 

of 1986. Even so, if it were to have such 

an effect, sources can claim this element 

as CBI if it can meet the criteria for CBI 

claims in 40 CFR Part 2. Another 

commenter stated that the public would 

be concerned if the percentages did not 

add to 100, in the event that the source 

handles both regulated and nonregulated substances. EPA believes that 

because a source must model only one 

substance in a release scenario, the 

source need not report the percentages 

of the other substances in the mixture. 

Therefore, it is expected that the weight 

percent for mixtures would not always 

add up to 100, because the mixture 

could contain non-regulated substances. 

A third commenter suggested that 

requiring sources to report percentage 

weight of a toxic substance in a liquid 

mixture would create confusion with 

the reporting of mixtures containing 

flammable regulated substances. 

In the January 6, 1998 rule (63 FR 

640), EPA clarified that flammable 

regulated substances in mixtures are 

only covered by the RMP rule if the 

entire mixture meets the National Fire 

Protection Association (NFPA) criteria 

of 4, thus the entire mixture becomes 

the regulated substance. As a result, the 

percentage of flammables in a mixture is 

not relevant under the rule and the 

requirement to report the percentage 

weight will only apply to toxic 

substances in a liquid mixture. 

Finally, in the Federal Register notice 

of June 20, 1996 (61 FR 31688), EPA 

clarified the relationship between the 

risk management program and the air 

permit program under Title V of the 

CAA for sources subject to both 

requirements. Under section 

502(b)(5)(A), permitting authorities 

must have the authority to assure 

compliance by all covered sources with 

each applicable CAA standard, 

regulation or requirement, including the 

regulations implementing section 

112(r)(7). Requiring sources covered by 

Title V and section 112(r) to provide 

their Title V permit number will help 

Title V permitting authorities assure 

that each source is complying with the 

RMP rule. 

In summary, with the exception of 

adding the phrase ‘‘that most closely 

corresponds to the process’’ in sections 

68.42(b)(4), 68.160(b)(7), 68.170(b), and 

68.175(b), EPA has decided to finalize 

the optional and mandatory data 

elements as they were proposed. 

C. Prevention Program Reporting 

The final RMP rule, issued June 20, 

1996 (61 FR 31668), requires sources to 

report their prevention program for each 

‘‘process.’’ Because the applicable 

definition of ‘‘process’’ is broad, 

multiple production and storage units 

might be a single, complex ‘‘process.’’ 

However, the Agency realizes that some 

elements of a source’s prevention 

program for a process may not be 

applicable to every portion of the 

process. In such a situation, reporting 

prevention program information for the 

process as a whole could be misleading 

without an explanation of which 

prevention program element applies to 

which part of the process. In order to get 

more specific information on which 

prevention program practices apply to 

different production and storage units 

within a process, EPA proposed to 

revise the rule to require prevention 

program reporting for each part of the 

process for which a separate process 

hazard analysis (PHA) or hazard review 

was conducted. EPA further proposed 

deleting the second sentence from both 

sections 68.170(a) and 68.175(a), which 

presently states that, ‘‘[i]f the same 

information applies to more than one 

covered process, the owner or operator 

may provide the information only once, 

but shall indicate to which process the 

information applies.’’ 

A number of industry commenters 

objected to the proposed revisions as 

wrongly assuming that a one-to-one 

relationship exists between a prevention 

program and a PHA. The commenters 

asserted that EPA’s proposed revision 

did not reflect how facilities conduct 

PHAs or implement prevention 

measures and would cause significant 

duplicate reporting, creating 

unnecessary extra work for facility 

personnel. One commenter explained 

that depending on a source’s 

circumstances, it might conduct a PHA 

for each production line, including all 

of its different units, or it might conduct 

a PHA for each common element of its 

different production lines. Accordingly, 

the commenters claimed that EPA’s 

proposal to require the owner/operator 

to submit separate prevention program 

information for every portion of a 

process covered by a PHA would result 

in multiple submissions of much of the 

same material, and would add no value 

to process safety or accidental release 

prevention. Commenters also opposed 

the deletion of the second sentence in 

sections 68.170(a) and 68.175(a). One 

commenter noted that many of the 

elements of the prevention program will 

not only be common to a process, but 

will be common to an entire stationary 

source. Thus commenters argued that 

EPA’s proposals would result in 

redundant submittals and place an 

unjustified burden on the regulated 

community. 

EPA acknowledges that PHAs do not 

necessarily determine the scope of 

prevention program measures. 

Moreover, EPA agrees that duplicative 
968 Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 

reporting should be reduced as much as 

possible. At the same time, EPA, 

implementing agencies, and other users 

of RMP data need to have information 

that is detailed enough to understand 

the hazards posed by, and the safety 

practices used for, particular parts of 

processes and equipment. EPA 

recognizes that some aspects of 

prevention programs are likely to be 

implemented facility-wide, rather than 

on a process or unit basis, whereas other 

aspects may apply to a particular 

process or only to particular units 

within a process. For example, most 

sources are likely to develop an 

employee participation plan and a 

system for hot work permits facilitywide, rather than on a process or unit 

basis. For sources having processes that 

include several units (e.g., multiple 

reactors or purification systems), the 

hazards, process controls, and 

mitigation systems may vary among the 

individual units. For example, one may 

have a deluge fire control system while 

another may have a runaway reaction 

quench system. 

EPA has concluded that its proposed 

changes to prevention program 

reporting would not lead sources to 

prepare RMPs that accurately and 

efficiently communicate the hazards 

posed by different aspects of covered 

processes and the safety practices used 

to address those hazards. The Agency 

now believes that no rule changes are 

necessary to ensure that RMPs convey 

that information. The current rule 

already requires prevention program 

reporting, and the issue has been how 

to efficiently convey that information in 

sufficient detail. EPA believes that its 

electronic program for submitting RMPs 

can be designed to provide for sufficient 

specificity in prevention program 

reporting without requiring duplicative 

reporting. In particular, the Agency 

plans to create a comment/text field in 

RMP*Submit for specifying which parts 

of a prevention program apply to which 

portions of a particular process. For 

example, if a deluge system only applies 

to a certain part of the overall process, 

the source would indicate in the 

comment/text screen the portions of the 

process to which the deluge system 

applies. 

To reduce the burden of reporting, 

EPA also plans to create a function in 

RMP*Submit which will allow a source 

to automatically copy prevention 

program data previously entered for one 

process to fill blank fields in another 

process’s prevention program. The 

source could then edit any of the data 

elements that are different. For example, 

where the prevention programs for two 

processes are identical (e.g., two 

identical storage tanks that are 

considered separate processes), the 

source could copy the data entered for 

one to fill in the blank field for the 

other. If some of the data elements vary 

between the prevention programs, the 

source will be able to autofill and 

change only those items that vary 

among processes or units. 

Although the autofill option will 

minimize the burden of reporting 

common data elements for those sources 

filing electronically, EPA has decided 

not to delete the sentence, in both 

sections 68.170(a) and 68.175(a), which 

states, ‘‘[i]f the same information applies 

to more than one covered process, the 

owner or operator may provide the 

information only once, but shall 

indicate to which processes the 

information applies ’’, as proposed. 

D. Confidential Business Information 

(CBI) 

1. Background 

A central element of the chemical 

accident prevention program as 

established by the Clean Air Act and 

implemented by Part 68 is providing 

state and local governments and the 

public with information about the risk 

of chemical accidents in their 

communities and what stationary 

sources are doing to prevent such 

accidents. As explained in the preamble 

to the final RMP rule (61 FR 31668, June 

20, 1996), every covered stationary 

source is required to develop and 

implement a risk management program 

and provide information about that 

program in its RMP. Under CAA section 

112(r)(7)(B)(iii), a source’s RMP must be 

registered with EPA and also submitted 

to the Federal Chemical Safety and 

Hazard Investigation Board (‘‘the 

Board’’), the state in which the source 

is located, and any local entity 

responsible for emergency response or 

planning. That section also provides 

that RMPs ‘‘shall be available to the 

public under section 114(c)’’ of the 

CAA. Section 114(c) gives the public 

access to information obtained under 

the Clean Air Act except for information 

(other than emission data) that would 

divulge trade secrets. 

As noted previously, in the final RMP 

rule EPA announced its plan to develop 

a centralized system for submitting 

electronic versions of RMPs that would 

reduce the paperwork burden on both 

industry and receiving agencies and 

provide ready public access to RMP 

data. Under the system, a covered 

source would submit its RMP on 

computer diskette, which would be 

entered into a central database that all 

interested parties could access 

electronically. The system would thus 

make it possible for a single RMP 

submission to reach all interested 

parties, including those identified in 

section 112(r)(7)(B)(iii).1 

An important assumption underlying 

the Agency’s central submission plan 

was that RMPs would rarely, if ever, 

contain confidential business 

information (CBI). Following 

publication of the final rule, concerns 

were raised that at least some of the 

information required to be reported in 

RMPs could be CBI in the case of 

particular sources. While the June 20, 

1996 rule provided for protection of CBI 

under section 114(c) (see section 

68.210(a)), EPA was asked to address 

how CBI would be protected in the 

context of the electronic programs being 

developed for RMP submission and 

public access. 

In the April 17, 1998 proposal to 

revise the RMP rule, EPA made several 

proposals concerning protection of CBI. 

It first reviewed the information 

requirements for RMPs (sections 

68.155–185) and proposed to find that 

certain required data elements would 

not entail divulging information that 

could meet the test for CBI set forth in 

the Agency’s comprehensive CBI 

regulations at 40 CFR Part 2.2 

Information provided in response to 

those requirements could not be 

claimed CBI. EPA also requested 

comment on whether some information 

that might be claimed as CBI (e.g., 

worst-case release rate or duration) 

would be ‘‘emission data’’ and thus 

publicly available under section 114(c) 

even if CBI. 

EPA administers a variety of statutes 

pertaining to the protection of the 

environment, each with its own data 

collection requirements and 

requirements for disclosure of 

information to the public. In the 

implementation of these statutes, the 

Agency collects emission, chemical, 

process, waste stream, financial, and 

other data from facilities in many, if not 

most, sectors of American business. 

Companies may consider some of this 

information vital to their competitive 

1 It is important to note that, as discussed in 

Section III. E of this preamble, this rule does not 

address issues concerning public access to offsite 

consequence analysis data in the RMP. 

2 Information is CBI if (1) the business has 

asserted a claim which has not expired, been 

waived, or been withdrawn; (2) the business has 

shown that it has taken and will continue to take 

reasonable steps to protect the information from 

disclosure; (3) the information is not and has not 

been reasonably obtainable by the public (other 

than governmental bodies) by use of legitimate 

means; (4) no statute requires disclosure of the 

information; and (5) disclosure of the information 

is likely to cause substantial harm to the business’ 

competitive position. 40 CFR section 2.208. 
Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 969 

position, and claim it as confidential 

business information (CBI). 

In the course of implementing 

statutes, the Agency may have a need to 

communicate some or all of the 

information it collects to the public as 

the basis for a rulemaking, to its 

contractors, or in response to requests 

pursuant to the Freedom of Information 

Act (FOIA). Information found to be CBI 

is exempt from disclosure under FOIA. 

To manage both CBI claims and FOIA 

requests, EPA has promulgated in 40 

CFR Part 2, Subpart B a set of 

procedures for reviewing CBI claims, 

releasing information found not to be 

CBI, and where authorized, disclosing 

CBI. Subpart B lists the criteria that 

information must meet in order to be 

considered CBI, as well as the special 

handling requirements the Agency must 

follow when disclosing CBI to 

authorized representatives. 

For RMP requirements that might 

entail divulging CBI, EPA proposed that 

a source be required to substantiate a 

CBI claim to EPA at the time that it 

makes the claim. Under EPA’s Part 2 

regulations, a source claiming CBI 

generally is required to substantiate the 

claim only when EPA needs to make the 

information public as part of some 

proceeding (e.g., a rulemaking) or EPA 

receives a request from the public (e.g., 

under the Freedom of Information Act 

(FOIA)) for the information. In view of 

the public information function of RMPs 

and the interest already expressed by 

members of the public in them, EPA 

proposed ‘‘up-front substantiation’’ of 

CBI claims to ensure that information 

not meeting CBI criteria would be made 

available to the public as soon as 

possible. This approach of requiring upfront substantiation is the same as that 

used for trade secret claims filed under 

the Emergency Planning and 

Community Right-to-Know Act (EPCRA) 

of 1986.3 

3 Section 302 of EPCRA (codified in 40 CFR Part 

355) requires any facility having more than a 

threshold planning quantity of an extremely 

hazardous substance (EHS) to notify its state 

emergency response commission (SERC) and local 

emergency planning committee (LEPC) that the 

facility is subject to emergency planning. The vast 

majority of toxic substances listed in 40 CFR 

Section 68.130 were taken from the EHS list. 

Section 303 of EPCRA requires LEPCs to prepare an 

emergency response plan for the community that is 

under their jurisdiction. Section 303 of EPCRA also 

requires that facilities subject to section 302 shall 

provide any information required by their LEPC 

necessary for developing and implementing the 

emergency plan. Section 304 of EPCRA requires an 

immediate notification of a release of an EHS or 

Hazardous Substances listed in 40 CFR Section 

302.4 above a reportable quantity to state and local 

entities. Section 304 also requires a written followup which includes among other things, the 

chemical name, quantity released and any known 

or anticipated health risks associated with the 

In addition, EPA proposed that any 

source claiming CBI submit two 

versions of its RMP: (1) a redacted 

(‘‘sanitized’’), electronic version, which 

would become part of RMP*Info, and (2) 

an unsanitized (unredacted) paper copy 

of the RMP (see proposed section 

68.151(c)). The electronic database of 

RMPs would contain only the redacted 

version unless and until EPA ruled 

against all or part of the source’s CBI 

claim, in keeping with the Part 2 

procedures. In this way, the public 

would have access only to the non-CBI 

elements of sources’ RMPs. EPA further 

stated that state and local agencies 

could receive the unredacted RMPs by 

requesting them from EPA under the 

Part 2 regulations. Those regulations 

authorize EPA to provide CBI to an 

agency having implementation 

responsibilities under the CAA if the 

agency either demonstrates that it has 

the authority under state or local law to 

compel such information directly from 

the source or that it will ‘‘provide 

adequate protection to the interests of 

affected businesses’’ (40 CFR 

2.301(h)(3)). 

The following sections of this 

preamble summarize and respond to the 

comments EPA received on the CBIrelated aspects of its proposal. At the 

outset, however, EPA wants to 

emphasize that it does not anticipate 

many CBI claims being made in 

connection with RMPs. The Agency 

developed the RMP data elements with 

the issue of CBI in mind. It sought to 

define data elements that would provide 

basic information about a source’s risk 

management program without requiring 

it to reveal CBI. To have done otherwise 

would have risked creating RMPs that 

were largely unavailable to the public. 

EPA continues to believe that the 

required RMP data elements will rarely 

require that a business divulge CBI. The 

Agency will carefully monitor the CBI 

claims made. If it appears that the 

number of claims being made is 

jeopardizing the public information 

release. Sections 311 and 312 of EPCRA (codified 

in 40 CFR Part 370) require facilities that are subject 

to OSHA Hazard Communication Standard (HCS), 

to provide information to its SERC, LEPC and local 

fire department. This information includes the 

hazards posed by its chemicals, and inventory 

information, including average daily amount, 

maximum quantity and general location. Section 

313 of EPCRA (codified in 40 CFR Part 372) 

requires certain facilities that are in specific 

industries (including chemical manufacturers) and 

that manufacture, process, or otherwise use a toxic 

chemical above specified threshold amounts to 

report, among other things, the annual quantity of 

the toxic chemical entering each environmental 

medium. Most facilities covered by CAA 112(r) are 

covered by one or more of these sections of EPCRA. 

Section 322 of EPCRA (codified in Part 350) allows 

facilities to claim only the chemical identity as 

trade secret. 

objective of the chemical accident 

prevention program, EPA will consider 

ways of revising RMPs, including 

further rulemakings or revising the 

underlying program, to ensure that 

important health and safety information 

is available to the public. 

2. RMP Data Elements Found Not CBI 

Fifteen commenters representing 

environmental groups and members of 

the public opposed allowing some or all 

RMP data to be claimed as CBI in light 

of the public’s interest in the 

information RMPs will provide. A 

number of commenters urged EPA not 

to allow the following RMP data 

elements (and supporting documents) to 

be claimed as CBI: 

• Mitigation measures considered by 

the firm in its offsite consequence 

analysis, 

• Major process hazards identified by 

the firm, 

• Process controls in use, 

• Mitigation systems in use, 

• Monitoring and detection systems 

in use, and 

• Changes since the last hazard 

review. 

In addition, one commenter 

contended that even chemical identity 

and quantity should be ineligible for 

CBI protection, since the requirement to 

submit an RMP only applies to facilities 

using a few well-known, extremely 

hazardous chemicals, and the public’s 

right to know should always outweigh 

a company’s claim to CBI. 

Along the same lines, a number of 

commenters urged EPA to develop a 

‘‘corporate sunshine rule’’ that would 

allow confidentiality concerns to be 

overridden if the protected information 

is needed by the public and experts to 

understand and assess safety issues. 

Another commenter recommended that 

a business claiming a chemical’s 

identity as CBI should be required to 

provide the generic name of the 

chemical and information about its 

adverse health effects so the public can 

determine the potential risks. 

One commenter argued that some of 

the RMP data that EPA suggested could 

reveal CBI, (e.g., release rate), were not 

‘‘emission data,’’ because the worst case 

scenario data are theoretical estimates, 

and do not represent any real emissions, 

past or present. 

Representatives of the chemical and 

petroleum industries disagreed with 

EPA’s proposal to list the data elements 

that EPA believed could not reveal CBI 

in any case. These commenters asserted 

that EPA could not anticipate all the 

ways in which information required by 

a data element might reveal CBI, and 

accordingly urged the Agency to make 
970 Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 

case-by-case determinations on CBI 

claims. They also contended that 

‘‘emission data’’ under section 114(c) 

does not extend to data on possible, as 

opposed to actual, emissions, and thus 

that RMP information concerning 

potential accidental releases would not 

qualify as ‘‘emission data,’’ which must 

be made available to the public. As pointed out above, an important 

purpose of the chemical accident 

prevention program required by section 

112(r) is to inform the public of the risk 

of accidents in their communities and 

the methods sources are employing to 

reduce such risks. EPA therefore 

believes that as much RMP data as 

possible should be available to the 

public as soon as possible. However, 

section 112(r)(7)(B)(iii) requires that 

RMPs be made ‘‘available to the public 

under section 114(c),’’ which provides 

for protection of trade secret 

information (other than emission data). 

Given the statute’s direction to protect 

whatever trade secret information is 

contained in an RMP, EPA is not 

authorized to release such information 

even when the public’s need for such 

information arguably outweighs a 

business’ interest in its confidentiality. 

The Agency also cannot issue a 

‘‘corporate sunshine rule’’ that conflicts 

with existing law requiring EPA (and 

other agencies) to protect trade secret 

information. 

As explained above (and in more 

detail in the proposed rule), EPA 

examined each RMP data element to 

determine which would require 

information that might, depending on a 

business’ circumstances, meet the CBI 

criteria set forth in EPA’s regulations 

implementing section 114(c) and other 

information-related legal requirements. 

The point of this exercise was to both 

protect potential trade secret 

information and promote the public 

information purpose of RMPs by 

identifying which RMP information 

might reveal CBI in a particular case and 

by precluding CBI claims for 

information that could not reveal CBI in 

any case. EPA presented the results of 

its analysis and an explanation of why 

certain data elements could entail the 

reporting of CBI depending on a 

business’ circumstances and why others 

could not. No commenter provided any 

specific examples or explanations that 

contradicted the Agency’s rationale for 

its determinations of which data 

elements could or could not result in 

reporting of CBI. However, EPA is deleting from the list 

of 40 CFR Part 68.151(b)(1) the reference 

to 40 CFR Part 68.160(b)(9), to allow for 

the possibility of the number of fulltime employees at the stationary source 

to be claimed as CBI. Upon further 

review, EPA was unable to determine 

that providing the number of employees 

at the stationary source could never 

entail divulging information that could 

meet the test for CBI set forth in the 

Agency’s comprehensive CBI 

regulations at 40 CFR Part 2. Therefore, 

EPA has removed this element from the 

list of data elements that can not be 

claimed CBI in Part 68. With this 

exception, EPA is promulgating the list 

of RMP data elements for which CBI 

claims are precluded, as proposed 

(Section 68.151(b)).

EPA’s justifications for its specific CBI 

findings appear in an appendix to this 

preamble. A more detailed analysis of 

all RMP data elements and CBI 

determinations is available in the docket 

(see ADDRESSES). The Agency continues 

to find no reasonable basis for 

anticipating that the listed elements will 

in any case require a business to reveal 

CBI that is not ‘‘emission data.’’ The 

information required by each of the 

listed data elements either fails to meet 

the criteria for CBI set forth in EPA’s 

CBI regulations at Part 2 or meets the 

Part 2 definition of ‘‘emission data.’’ In 

many cases, the information is available 

to the public through other reports filed 

with EPA, states, or local agencies (e.g., 

reports required by Emergency Planning 

and Community Right-to-Know Act 

(EPCRA) sections 312 and 313 provide 

general facility identification 

information and reports of most 

accidental releases are available through 

several Federal databases including 

EPA’s Emergency Release Notification 

System and Accidental Release 

Information Program databases). In order to preclude CBI claims for 

other data elements, the Agency would 

have to show that the information 

required by a data element either was 

‘‘emission data’’ under section 114(c) or 

could not, under any circumstances, 

reveal CBI. As explained below, EPA 

does not believe such a showing can be 

made for any of the data elements not 

on the list. Therefore, CBI claims made 

for information required by data 

elements not on the list will be 

evaluated on a case-by-case basis 

according to the procedures contained 

in 40 CFR Part 2 (except that 

substantiation will have to accompany 

the claims, as discussed below).

The Agency agrees with the 

commenters who argued that 

information about potential accidental 

releases is not ‘‘emission data’’ under 

section 114(c). EPA’s existing policy 

statement (see 56 FR 7042, Feb. 21, 

1991) on what information may be 

considered ‘‘emission data’’ was 

developed to implement sections 110 

and 114(a) of the CAA, which the 

Agency generally invokes when it seeks 

to gather technical data from a source 

about its actual emissions to the air. 

While the policy is not explicitly 

limited in its scope, EPA believes it 

would be inappropriate to apply it to 

RMP data elements concerning 

hypothetical, as opposed to actual, 

releases to the air. Under the definition 

of ‘‘emission data’’ contained in Part 2, 

information is ‘‘emission data’’ if it is (1) 

‘‘necessary to determine the identity, 

amount, frequency, concentration, or 

other characteristics * * * of any 

emission which has been emitted by the 

source,’’ (2) ‘‘necessary to determine the 

identity, amount, frequency, 

concentration, or other characteristics 

* * * of the emissions which, under an 

applicable standard or limitation, the 

source was authorized to emit;’’ or (3) 

general facility identification 

information regarding the source which 

distinguishes it from other sources (40 

CFR section 2.301(a)(2)(i) (emphasis 

added)). Under these criteria, EPA has 

concluded that only the RMP data 

elements relating to source-level 

registration information (sections 

68.160(b)(1)–(6), (8)–(13)) and the fiveyear accident history (section 68.168) 

are ‘‘emission data.’’ Of the RMP data 

elements, only the five-year accident 

history involves actual, past emissions 

to the environment; the other data 

elements would not, therefore, qualify 

as ‘‘emission data’’ under the first prong 

of the Part 2 definition. Moreover, the 

data elements relating to a source’s 

offsite consequence analysis, prevention 

program and emergency response 

program do not attempt to identify or 

otherwise reflect ‘‘authorized’’ 

emissions; the data elements instead 

reflect the source’s potential for 

accidental releases. Accordingly, these 

data elements would not be ‘‘emission 

data’’ under the second prong of the 

definition. As for the third prong, some 

of the source-level data are ‘‘emission 

data’’ because they help identify a 

source. Most other RMP data elements 

are reported on a process level and are 

not generally used to distinguish one 

source from another. 

The Agency believes it is unable to 

show that the remaining data elements 

could not, under any circumstances, 

reveal CBI. EPA continues to believe 

that it is theoretically possible for the 

remaining data elements (the elements 

not listed in section 68.151(b)) to reveal 

CBI either directly or through reverse 

engineering, depending on the 

circumstances of a particular case. At 

the same time, EPA believes that, in 

practice, the remaining data elements 

will rarely reveal CBI. The purpose of 
Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 971 

the data in the RMP is for a source to 

articulate its hazards, and the steps it 

takes to prevent accidental releases. In 

general, the kinds of information 

specifying the source’s hazards and risk 

management program are not likely to 

be competitively sensitive. 

In particular, covered processes at the 

vast majority of stationary sources 

subject to the RMP rule are too common 

and well-known to support a CBI claim 

for information related to such 

processes. For example, covered public 

drinking water and wastewater 

treatment plants generally use common 

regulated substances in standard 

processes (i.e., chlorine used for 

disinfection). Also, covered processes at 

many sources involve the storage of 

regulated substances that the sources 

sell (e.g., propane, ammonia), so the 

processes are already public knowledge. 

Other covered processes involve the use 

of well-known combinations of 

regulated substances such as 

refrigerants. RMP information regarding 

these types of processes should not 

include CBI. 

Even in the case of unusual or unique 

processes, it is generally unlikely that 

RMP information could be used to 

reveal CBI through reverse engineering. 

To begin with, required RMP 

information is general enough that it is 

unlikely to provide a basis for reverse 

engineering a process. For example, a 

source must report in its RMP whether 

overpressurization is a hazard and 

whether relief valves are used to control 

pressure, but it is not required to report 

information on actual pressures used, 

flow rates, chemical composition, or the 

configuration of equipment. Moreover, 

while RMP information may provide 

some data that could be used in an 

attempt to discover CBI information 

through reverse engineering, it typically 

will not provide enough data for such 

an attempt to succeed, because the 

source is not required to provide a 

detailed description of the chemistry or 

production volume of the process. 

Businesses claiming CBI based on the 

threat of reverse engineering will be 

required to show how reverse 

engineering could in fact succeed with 

the information that the RMP would 

otherwise make public, together with 

other publicly available information. A 

business unable to do so will have its 

claim denied. 

While EPA is requiring that a source 

claiming a chemical’s identity as CBI 

provide the generic category or class 

name of the chemical, the RMP does not 

require sources to provide information 

about the adverse health effects of the 

chemical. Chemicals were included in 

the section 112(r) program because they 

are acutely toxic or flammable; health 

effects related to chronic exposure were 

not considered because they are 

addressed by other rules (see List Rule 

at 59 FR 4481). EPA believes that 

generic names are sufficient to indicate 

the general health concerns from shortterm exposures. Should a member of the 

public desire more information, EPA 

encourages the use of EPCRA section 

322(h), which provides a means for the 

public to obtain information about the 

adverse health effects of a chemical 

covered by that statute, where the 

chemical’s identity has been claimed a 

trade secret. The public will find this 

provision of EPCRA useful because most 

sources subject to the RMP rule are also 

subject to EPCRA. 

3. Up-front Substantiation of CBI Claims 

One commenter supported the 

proposal to require CBI claims to be 

substantiated at the time they are made. 

Another commenter stated that there is 

no compelling need to require up-front 

substantiation. The commenter stated 

that up-front substantiation would place 

a sizable burden on both industry and 

EPA and would be in direct conflict 

with the Paperwork Reduction Act. The 

commenter claimed that, with the 

exception of EPCRA, where a submitter 

is allowed to claim only one data 

element—chemical identity—as CBI, it 

is EPA’s standard procedure not to 

require submitters to provide written 

substantiation unless a record has been 

requested. Further, the commenter 

stated that the Agency has not shown 

any reason for departing from that 

procedure in this rule. 

EPA believes that requiring up-front 

substantiation of CBI claims made for 

RMP data has ample precedent, is fully 

consistent with the Agency’s CBI 

regulations and the Paperwork 

Reduction Act, and is critical to 

achieving the public information 

purposes of the accident prevention 

program. EPCRA is not the only 

example of an up-front substantiation 

requirement. The Agency has also 

required up-front substantiation in 

several other regulatory contexts, 

including those where, like here, 

providing the public with health and 

safety information is an important 

objective [see e.g., 40 CFR section 

725.94, 40 CFR section 710.38, and 40 

CFR section 720.85 (regulations 

promulgated under Toxic Substances 

Control Act)]. 

Even under its general CBI 

regulations, the Agency need not wait 

for a request to release data to require 

businesses to substantiate their CBI 

claims. When EPA expects to get a 

request to release data claimed 

confidential, the Agency is to initiate 

‘‘at the earliest practicable time’’ the 

regulations’’ procedures for making CBI 

determinations (40 CFR section 

2.204(a)(3)). Those procedures include 

calling on affected businesses to 

substantiate their claims (see 40 CFR 

section 2.204(e)). Since state and local 

agencies, environmental groups, 

academics and others have already 

indicated their interest in obtaining 

complete RMP data (see comments 

received on this rulemaking, available 

in the DOCKET), EPA fully expects to 

get requests for RMP data claimed CBI. 

Consequently, even if EPA did not 

establish an up-front substantiation 

requirement in this rule, under the 

Agency’s general CBI regulations it 

could require businesses claiming CBI 

for RMP data to substantiate their claims 

without first receiving a request to 

release the data. Establishing an upfront requirement in this rule will 

simply allow EPA to obtain 

substantiation of CBI claims without 

having to request it in every instance. 

Requiring up-front substantiation for 

RMP CBI claims is consistent with the 

Paperwork Reduction Act. Any burden 

posed by this requirement has already 

been evaluated as part of the 

Information Collection Request (ICR) 

associated with this rulemaking. EPA 

disagrees that up-front substantiation 

will impose a substantial or undue 

burden. As noted above, under EPA’s 

current CBI regulations, a source 

claiming CBI could and probably would 

be required to provide substantiation for 

its claim, in view of the public interest 

in RMP information. A requirement to 

submit substantiation with the claim 

should thus make little difference to the 

source. Moreover, a source presumably 

does not make any claim of CBI lightly. 

Before filing a CBI claim, the source 

must first determine whether the claim 

meets the criteria specified in 40 CFR 

section 2.208. Up-front substantiation 

only requires that the source document 

that determination at the time it files its 

claim. Since it would be sensible for a 

source to document the basis of its CBI 

claim for its own purposes (e.g., in the 

case of a request for substantiation), 

EPA expects that many sources already 

prepare documentation for their CBI 

claims by the time they file them. Also, 

submitting substantiation at the time of 

claim reduces any additional burden 

later, such as reviewing the Agency’s 

request, retrieving the relevant 

information, etc. Therefore, providing 

documentation at the time of filing 

should impose no additional burden. 

In view of the public information 

function of RMPs, EPA believes that upfront substantiation is clearly warranted 
972 Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 

for CBI claims made for RMP data. Upfront substantiation will ensure that 

sources filing claims have carefully 

considered whether the data they seek 

to protect in fact meets the criteria for 

protection. Given the public interest 

already expressed in RMP data, EPA 

expects that CBI claims for RMP data 

will have to be substantiated at some 

point. Up-front substantiation will save 

EPA and the public time and resources 

that would otherwise be required to 

respond to each CBI claim with a 

request for substantiation. EPA is 

therefore promulgating the up-front 

substantiation requirement as proposed. 

4. State and Local Agency Access to 

Unredacted RMPs 

One commenter objected to EPA’s 

statement in the proposal that it would 

provide unredacted (unsanitized) 

versions of the RMPs to a state and local 

agency only upon meeting the criteria 

required by the EPA’s CBI rules at 40 

CFR Part 2.4 The commenter, an 

association of fire fighters, argued that 

the Agency’s position was inconsistent 

with CAA section 112(r)(7)(B)(iii), 

which provides that RMPs ‘‘shall . . . be 

submitted to the Chemical Safety and 

Hazard Investigation Board [a federal 

agency], to the State in which the 

stationary source is located, and to any 

local agency or entity having 

responsibility for planning for or 

responding to accidental releases which 

may occur at such source . . . .’’ The 

commenter claimed that this provision 

entitles the specified entities, including 

local fire departments, to receive 

unredacted RMPs without having to 

make the showings required by EPA’s 

CBI regulations. 

EPA is not resolving this issue today. 

The Agency has reviewed the relevant 

statutory text and legislative history, as 

well as analogous provisions of EPCRA, 

and believes that arguments can be 

made on both sides of this issue. While 

section 112(r)(7)(B)(iii) calls for RMPs to 

be submitted to states, local entities and 

the Board, it is not clear that Congress 

intended CBI contained in RMPs to be 

provided to those entities without 

ensuring appropriate protection of CBI. 

4 Section 2.301(h)(3) provides that a State or local 

government may obtain CBI from EPA under two 

circumstances: (1) it provides EPA a written 

opinion from its chief legal officer or counsel 

stating that the State or local agency has the 

authority under applicable State or local law to 

compel the business to disclose the information 

directly; or (2) the businesses whose information is 

disclosed are informed and the State or local 

government has shown to a EPA legal office’s 

satisfaction that its disclosure of the information 

will be governed by State or local law and by 

‘‘procedures which will provide adequate 

protection to the interests of affected businesses.’’ 

At stake in resolving this issue are two 

important interests—local responders’ 

interest in unrestricted access to 

information that may be critical to their 

safety and effectiveness in responding to 

emergencies and businesses’ interest in 

protecting sensitive information from 

their competitors. Before making a final 

decision on this issue, EPA believes it 

would benefit from further public input. 

Because EPA stated that it would not 

provide unredacted RMPs to states and 

local agencies, those interested in 

protecting CBI may not have considered 

it necessary to lay out the legal and 

policy arguments supporting their 

views. State and local agencies, many of 

which in the past have expressed 

concern about the potential 

administrative burden of receiving 

RMPs directly from sources, also did not 

comment on the issue. EPA has 

therefore decided to accept additional 

comments on this issue alone. 

(Additional comments on any other 

issues addressed in this rulemaking will 

not be considered or addressed, since 

the Agency is taking final action on 

them here.) Comments should be mailed 

to the persons listed in the preceding 

FOR FURTHER INFORMATION CONTACT 

section. In the meantime, unredacted 

RMPs will be available to states, local 

agencies and the Board under the terms 

of the Agency’s existing CBI regulations 

at 40 CFR section 2.301(h)(3) (for state 

and local agencies) and 40 CFR section 

2.209(c) (for the Board). 

Section 112(r)(7)(B)(iii) states in 

relevant part: 

[RMPs] shall also be submitted to the 

Chemical Safety and Hazard Investigation 

Board, to the State in which the stationary 

source is located, and to any local agency or 

entity having responsibility for planning for 

or responding to accidental releases which 

may occur at such source, and shall be 

available to the public under section 114(c) 

of [the Act]. 

Section 114(c) provides for the public 

availability of any information obtained 

by EPA under the Clean Air Act, except 

for information (other than emissions 

data) that would divulge trade secrets. 

From a public policy perspective, 

there are some obvious advantages to 

reading section 112(r)(7)(B)(iii) in the 

way the commenter suggests. Local fire 

departments and other local responders 

are typically the first to arrive at the 

scene of chemical accidents in their 

jurisdictions. RMP information that first 

responders could find helpful include 

chemical identity, chemical quantity, 

and potential source of an accident. 

Under EPA’s regulations, however, any 

or all of this information could be 

claimed CBI. In addition, state and local 

authorities are often in the best position 

to assess the adequacy of a source’s risk 

management program and to initiate a 

dialogue with the facility should its 

RMP indicate a need for improvement. 

However, state and local authorities’ 

ability to provide this contribution to 

community safety would be impeded to 

the extent a source claimed key 

information as CBI. While states and 

local agencies may obtain information 

claimed CBI under EPA’s CBI 

regulations (assuming they can make the 

requisite showing), the time required to 

obtain the necessary authority or 

findings from state or local and EPA 

officials could be substantial. 

At the same time, there are also public 

policy reasons for ensuring protection of 

CBI contained in RMPs. Congress has in 

many statutes, including the CAA and 

EPCRA, provided for the protection of 

trade secrets to safeguard the 

competitive position of private 

businesses. Businesses’ ability to 

maintain the confidentiality of trade 

secrets helps ensure competition in the 

U.S. economy and U.S. businesses’ 

competitive position in the world 

economy. Protection of trade secrets 

also encourages innovation, which is an 

important contributor to economic 

growth. 

A reading of section 112(r)(7)(B)(iii) 

that demands submission of unredacted 

RMPs to states, local entities, and the 

Board may lead to widespread public 

access to information claimed CBI. For 

purposes of section 112(r)(7)(B)(iii), 

‘‘any local agency or entity having 

responsibility for planning for or 

responding to accidental releases’’ 

includes local emergency planning 

committees (LEPCs) established under 

EPCRA. Section 301(c) of EPCRA 

provides that LEPCs must include 

representatives from both the public and 

private sectors, including the media and 

facilities subject to EPCRA 

requirements. Submission of an 

unredacted RMP to an LEPC would thus 

entail release of CBI to some members 

of the public and potentially even 

competitors.5 More generally, local 

agencies may not be subject to any legal 

requirement to protect CBI and may lack 

the knowledge and resources to address 

CBI claims. Arguably, it would be 

5 EPA does not believe that submission of an RMP 

containing CBI to the statutorily specified entities 

would defeat a source’s ability to claim information 

as CBI for purposes of section 114(c) and EPA’s CBI 

regulations. Under those regulations, information 

that has been released to the public cannot be 

claimed CBI. Release of a RMP containing CBI to 

the entities specified by section 112(r)(7)(B)(iii), 

including LEPCs, would not constitute such a 

release. EPCRA similarly provides that disclosure of 

trade secret information to an LEPC does not 

prevent a facility from claiming the information 

confidential (see EPCRA section 322(b)(1)). 
Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 973 

anomalous for Congress to require EPA 

to protect trade secrets contained in 

RMPs against release to the public only 

to risk divulging the same information 

by requiring submission of unredacted 

RMPs to a broad range of entities that 

may not have the need or capacity to 

protect CBI themselves. It would also 

appear inconsistent with the approach 

Congress took to protecting trade secrets 

in EPCRA, where Congress did not 

provide for release of trade secret 

chemical identity information to local 

agencies. 

Relatedly, many state and local 

agencies objected to EPA’s original 

proposal in the RMP proposed 

rulemaking (58 FR 54190, October 20, 

1993) that sources submit RMPs directly 

to States, local agencies, and the Board, 

as well as EPA. They noted that 

managing the information contained in 

RMPs would be difficult without a 

significant expenditure of typically 

scarce resources. Many states and local 

agencies thus supported EPA’s final 

decision to develop an electronic 

submission and distribution system that 

would allow covered sources to submit 

their RMPs to EPA, which would make 

them available to states, local agencies, 

and the Board, as well as the general 

public. If the statute is read to require 

submission of RMP information to state 

and local agencies, and the Board, to the 

extent it is claimed as CBI, the resource 

concerns raised by State and local 

agencies commenters likely would be 

raised to that extent again. 

EPA also questions the extent to 

which states, local entities and the 

Board would be disadvantaged if they 

did not receive unredacted RMPs 

without making the showings required 

by EPA’s CBI regulations. As noted 

earlier, EPA expects that relatively little 

RMP information will be CBI. RMP data 

will only rarely contain CBI, and the upfront substantiation will minimize the 

number of CBI claims it receives by 

ensuring that sources carefully examine 

the basis for any claims before 

submitting them. Consequently, the 

Agency believes that a state or local 

agency will rarely confront a redacted 

RMP. 

Moreover, EPCRA provides state and 

local entities, including fire 

departments, with access to much of the 

pertinent data already. EPA’s 

regulations under EPCRA cover a 

universe of sources and chemicals that 

includes most, if not all, the sources and 

substances covered by the RMP rule. 

The EPCRA regulations require 

reporting of some of the same 

information required by the RMP rule, 

including chemical identity. EPCRA 

withholds from public release only 

chemical identities that are trade secrets 

and the location of specific chemicals 

where a facility so requests. In practice, 

relatively few facilities have requested 

trade secret protection for a chemical’s 

identity. 

Additionally, EPCRA section 312(f) 

empowers local fire departments to 

conduct on-site inspections at facilities 

subject to EPCRA section 312(a) and 

obtain information on chemical 

location. Most facilities subject to 

EPCRA section 312(a) are also subject to 

the RMP rule. On-site inspections could 

also provide information on hazards and 

mitigation measures. In addition, 

EPCRA section 303(d)(3) authorizes 

LEPCs, which include representatives of 

fire departments, to request from 

facilities covered by EPCRA section 

302(b) such information as may be 

necessary to prepare an emergency 

response plan and to include such 

information in the plan as appropriate. 

Some sources subject to the RMP rule 

are also covered by EPCRA section 

302(b). 

In light of the points made above, EPA 

questions whether section 

112(r)(7)(B)(iii) should be interpreted to 

require submission of unredacted RMPs 

containing CBI to the statutorily 

specified entities without provision 

being made for protecting CBI. EPA 

invites the public to provide any 

additional comment or information 

relevant to interpreting the submission 

requirement of section 112(r)(7)(B)(iii). 

5. Other CBI Issues 

Two commenters disagreed with 

EPA’s statement that a source cannot 

make a CBI claim for information 

available to the public under EPCRA or 

another statute. They claimed that a 

request for information under EPCRA 

cannot supersede the CBI provisions 

applicable to data collected under the 

authorities of the CAA or Toxic 

Substances Control Act or any other 

regulatory program. 

EPA does not agree with this 

comment. Claims of CBI may not be 

upheld if the information is properly 

obtainable or made public under other 

statutes or authorities. For example, 

chemical quantity on site is available to 

the public under EPCRA Tier II 

reporting. In addition, under EPCRA 

section 303(d)(3), LEPCs have the 

authority to request any information 

they need to develop and implement 

community emergency response plans. 

If information obtained through such a 

request is included in the community 

plan, it will become available to the 

public under EPCRA section 324. 

Information obtainable or made public 

under EPCRA would not be eligible for 

CBI protection under 40 CFR section 

2.208, which specifically excludes from 

CBI protection information already 

available to the public. Filing a CBI 

claim under the CAA or another statute 

does not protect information if it is 

legitimately requested and made public 

under other federal, state, or local law. 

Information obtainable or made public 

(through proper means) under existing 

statutes cannot be CBI under EPA’s CBI 

regulations. 

6. Actions Taken 

In summary, the Agency is adding 

two sections (68.151 and 68.152) to Part 

68. Section 68.151 sets forth the 

procedures for a source to follow when 

asserting a CBI claim and lists data 

elements that can not be claimed as CBI. 

This section also requires sources filing 

CBI claims to provide the information 

claimed confidential, in a format to be 

specified by EPA, instead of the 

unsanitized paper copy of the RMP as 

discussed in the proposal. Section 

68.152 sets forth the procedures for 

substantiating CBI claims. Sources 

claiming CBI are required to submit 

their substantiation of their claims at the 

same time they submit their RMPs. 

E. Other Issues 

Two commenters asked why EPA had 

proposed to drop the phrase ‘‘if used’’ 

in section 68.165(b)(3) where the rule 

asks for the basis of the offsite 

consequence analysis results. EPA has 

decided to retain the language, since 

sources will have a choice of using 

either EPA’s RMP guidance documents 

or a model. Where a model is used, the 

source will have to provide the name of 

the model. These commenters also 

asked why EPA proposed to drop 

(alternative releases only) from section 

68.165(b)(13). EPA has also decided to 

retain the parenthetical language. 

One commenter stated that EPA 

should allow sources to submit RMPs 

either electronically or in hard copy. 

The commenter stated that not allowing 

hard copy submissions will be 

burdensome on many sources who have 

never filed an electronic report to the 

government before. As stated in the 

April proposal, EPA is allowing sources 

to submit RMPs on paper. Paper 

submitters are asked to fill out a simple 

paper form to tell EPA why they are 

unable to file electronically. 

Two commenters objected to placing 

offsite consequence analysis (OCA) data, 

particularly worst-case release 

scenarios, on the Internet, for security 

reasons. Issues related to public access 

to OCA data are beyond the scope of 

this rulemaking, as this action is limited 

to the issues discussed above. It does 
974 Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 

not include decisions regarding how the 

public will access the OCA data 

elements of the RMPs. Statements in the 

preamble about EPA providing public 

access to RMP data are not intended to 

address which portions of the RMP data 

will be electronically available. 

A number of commenters were 

concerned about a statement EPA made 

in the preamble to the proposed rule 

regarding the definition of ‘‘process’’, 

and stated that EPA’s interpretation of 

‘‘process’’ is not consistent with the 

interpretation the Occupational Safety 

and Health Administration (OSHA) uses 

in its process safety management (PSM) 

standard (29 CFR 1910.119). In this 

rulemaking, EPA did not propose any 

changes to the definition of process nor 

is it adopting any changes to the 

definition. As EPA stated in the 

preamble to the final RMP rule, it will 

interpret ‘‘process’’ consistently with 

OSHA’s interpretation of that term (29 

CFR 1910.119). Therefore, if a source is 

subject to the PSM rule, the limits of its 

process(es) for purposes of OSHA PSM 

will be the limits of its process(es) for 

purposes of RMP (except in cases 

involving atmospheric storage tanks 

containing flammable regulated 

substances, which are exempt from PSM 

but not RMP). If a source is not covered 

by OSHA PSM and is complicated from 

an engineering perspective, it should 

consider contacting its implementing 

agency for advice on determining 

process boundaries. EPA and OSHA are 

coordinating the agencies’ approach to 

common issues, such as the 

interpretation of ‘‘process’’. 

F. Technical Corrections 

When Part 68 was promulgated, the 

text of section 68.79(a), was drawn from 

the OSHA PSM standard, but it was not 

revised to reflect the different structure 

of EPA’s rule. The OSHA PSM standard 

is contained in a single section; EPA’s 

Program 3 prevention program is 

contained in a subpart. Rather than 

referencing ‘‘this section,’’ the 

paragraph should have referenced the 

‘‘subpart.’’ Therefore, as proposed, EPA 

is changing ‘‘section’’ to ‘‘subpart’’ in 

section 68.79(a). 

Under section 68.180(b), EPA 

intended that all covered sources report 

the name and telephone number of the 

agency with which they coordinate 

emergency response activities, even if 

the source is not required to have an 

emergency response plan. However, the 

rule refers only to coordinating the 

emergency plan. In this action, EPA is 

revising this section to refer to the local 

agency with which emergency response 

activities and the emergency response 

plan is coordinated. 

IV. Section-by-Section Discussion of the 

Final Rule 

In Section 68.3, Definitions, the 

definition of SIC is removed and 

replaced by the definition of NAICS. 

Section 68.10, Applicability, is 

revised to replace the SIC codes with 

NAICS codes, as discussed above. 

Section 68.42, Five-Year Accident 

History, is revised to require the 

percentage concentration by weight of 

regulated toxic substances released in a 

liquid mixture and the five- or six-digit 

NAICS code that most closely 

corresponds to the process that had the 

release. The phrase ‘‘five- or six-digit’’ 

has been added before the NAICS code 

to clarify the level of detail required for 

NAICS code reporting. 

Section 68.79, Compliance Audits, the 

word ‘‘section’’ in paragraph (a) is 

replaced by ‘‘subpart.’’ 

Section 68.150, Submission, is revised 

by adding a paragraph to state that 

procedures for asserting CBI claims and 

determining the sufficiency of such 

claims are provided in new Sections 

68.151 and 68.152. 

Section 68.151 is added to set forth 

the procedures to assert a CBI claim and 

list data elements that may not be 

claimed as CBI, as discussed above. 

Section 68.152 is added to set forth 

procedures for substantiating CBI 

claims, as proposed. 

Section 68.160, Registration, is 

revised by adding the requirements to 

report the method and description of 

latitude and longitude, replacing SIC 

codes with five- or six-digit NAICS 

codes, and adding the requirement to 

report Title V permit number, when 

applicable. This section is also revised 

to include optional data elements. The 

phrase ‘‘five- or six-digit’’ has been 

added before NAICS code to clarify the 

level of detail required for NAICS code 

reporting. 

Section 68.165, Offsite Consequence 

Analysis, is revised by adding the 

requirement that the percentage weight 

of a regulated toxic substance in a liquid 

mixture be reported. 

Section 68.170, Prevention Program/ 

Program 2, is revised to replace SIC 

codes with five- or six-digit NAICS 

codes, as is Section 68.175. 

Section 68.180, Emergency Response 

Program, is revised to clarify that 

paragraph (b) covers both the 

coordination of response activities and 

plans, as proposed. 

V. Judicial Review 

The proposed rule amending the 

accidental release prevention 

requirements; under section 112(r)(7) 

was proposed in the Federal Register on 

April 17, 1998. This Federal Register 

action announces EPA’s final decision 

on the amendments. Under section 

307(b)(1) of the CAA, judicial review of 

this action is available only by filing a 

petition for review in the U.S. Court of 

Appeals for the District of Columbia 

Circuit on or before March 8, 1999. 

Under section 307(b)(2) of the CAA, the 

requirements that are the subject of 

today’s action may not be challenged 

later in civil or criminal proceedings 

brought by EPA to enforce these 

requirements. 

VI. Administrative Requirements 

A. Docket 

The docket is an organized and 

complete file of all the information 

considered by the EPA in the 

development of this rulemaking. The 

docket is a dynamic file, because it 

allows members of the public and 

industries involved to readily identify 

and locate documents so that they can 

effectively participate in the rulemaking 

process. Along with the proposed and 

promulgated rules and their preambles, 

the contents of the docket serve as the 

record in the case of judicial review. 

(See section 307(d)(7)(A) of the CAA.) 

The official record for this 

rulemaking, as well as the public 

version, has been established for this 

rulemaking under Docket No. A–98–08 

(including comments and data 

submitted electronically). A public 

version of this record, including 

printed, paper versions of electronic 

comments, which does not include any 

information claimed as CBI, is available 

for inspection from 8:00 a.m. to 5:30 

p.m., Monday through Friday, excluding 

legal holidays. The official rulemaking 

record is located at the address in 

ADDRESSES at the beginning of this 

document. 

B. Executive Order 12866 

Under Executive Order (E.O.) 12866, 

[58 FR 51,735 (October 4, 1993)], the 

Agency must determine whether the 

regulatory action is ‘‘significant’’, and 

therefore subject to OMB review and the 

requirements of the E.O. The Order 

defines ‘‘significant regulatory action’’ 

as one that is likely to result in a rule 

that may: 

(1) Have an annual effect on the 

economy of $100 million or more or 

adversely affect in a material way the 

economy, a sector of the economy, 

productivity, competition, jobs, the 

environment, public health or safety, or 

state, local or tribal government or 

communities; 
Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 975 

(2) Create a serious inconsistency or 

otherwise interfere with an action taken 

or planned by another agency; 

(3) Materially alter the budgetary 

impact of entitlements, grants, user fees, 

or loan programs or the rights and 

obligations of recipients thereof; or 

(4) Raise novel legal or policy issues 

arising out of legal mandates, the 

President’s priorities, or the principles 

set forth in the E.O. 

Pursuant to the terms of Executive 

Order 12866, OMB has notified EPA 

that it considers this a ‘‘significant 

regulatory action’’ within the meaning 

of the Executive Order. EPA has 

submitted this action to OMB for 

review. Changes made in response to 

OMB suggestions or recommendations 

will be documented in the public 

record. 

C. Executive Order 12875 

Under Executive Order 12875, EPA 

may not issue a regulation that is not 

required by statute and that creates a 

mandate upon a State, local or tribal 

government, unless the Federal 

government provides the funds 

necessary to pay the direct compliance 

costs incurred by those governments, or 

EPA consults with those governments. If 

EPA complies by consulting, Executive 

Order 12875 requires EPA to provide to 

the Office of Management and Budget a 

description of the extent of EPA’s prior 

consultation with representatives of 

affected State, local and tribal 

governments, the nature of their 

concerns, copies of any written 

communications from the governments, 

and a statement supporting the need to 

issue the regulation. In addition, 

Executive Order 12875 requires EPA to 

develop an effective process permitting 

elected officials and other 

representatives of State, local and tribal 

governments ‘‘to provide meaningful 

and timely input to the development of 

regulatory proposals containing 

significant unfunded mandates.’’ 

EPA has concluded that this rule may 

create a nominal mandate on State, local 

or tribal governments and that the 

Federal government will not provide the 

funds necessary to pay the direct costs 

incurred by these governments in 

complying with the mandate. 

Specifically, some public entities may 

be covered sources and will have to add 

the new data elements to their RMP. In 

developing this rule, EPA consulted 

with state, local and tribal governments 

to enable them to provide meaningful 

and timely input in the development of 

this rule. Even though this rule revises 

Part 68 in a way that does not 

significantly change the burden 

imposed by the underlying rule, EPA 

has taken efforts to involve state and 

local entities in this regulatory effort. 

Specifically, much of the rule responds 

to issues raised by the Electronic 

Submission Workgroup discussed 

above, which includes State and local 

government stakeholders. In addition, 

EPA has recently conducted seminars 

with tribal governments; however, there 

were no concerns raised on any issues 

that are covered in this rule. EPA 

discussed the need for issuing this 

regulation in sections II and III in this 

preamble. Also, EPA provided OMB 

with copies of the comments to the 

proposed rule. 

D. Executive Order 13045 

Executive Order 13045: ‘‘Protection of 

Children from Environmental Health 

Risks and Safety Risks’’ (62 FR 19885, 

April 23, 1997) applies to any rule that: 

(1) is determined to be ‘‘economically 

significant’’ as defined under E.O. 

12866, and (2) concerns an 

environmental health or safety risk that 

EPA has reason to believe may have a 

disproportionate effect on children. If 

the regulatory action meets both criteria, 

the Agency must evaluate the 

environmental health or safety effects of 

the planned rule on children, and 

explain why the planned regulation is 

preferable to other potentially effective 

and reasonably feasible alternatives 

considered by the Agency. 

This final rule is not subject to the 

E.O. 13045 because it is not 

‘‘economically significant’’ as defined in 

E.O. 12866, and because it does not 

involve decisions based on 

environmental health or safety risks. 

E. Executive Order 13084 

Under Executive Order 13084, EPA 

may not issue a regulation that is not 

required by statute, that significantly or 

uniquely affects the communities of 

Indian tribal governments, and that 

imposes substantial direct compliance 

costs on those communities, unless the 

Federal government provides the funds 

necessary to pay the direct compliance 

costs incurred by the tribal 

governments, or EPA consults with 

those governments. If EPA complies by 

consulting, Executive Order 13084 

requires EPA to provide to the Office of 

Management and Budget, in a separately 

identified section of the preamble to the 

rule, a description of the extent of EPA’s 

prior consultation with representatives 

of affected tribal governments, a 

summary of the nature of their concerns, 

and a statement supporting the need to 

issue the regulation. In addition, 

Executive Order 13084 requires EPA to 

develop an effective process permitting 

elected and other representatives of 

Indian tribal governments ‘‘to provide 

meaningful and timely input in the 

development of regulatory policies on 

matters that significantly or uniquely 

affect their communities.’’ 

Today’s rule does not significantly or 

uniquely affect the communities of 

Indian tribal governments. Two of the 

amendments made by this rule, the 

addition of RMP data elements and the 

conversion of SIC codes to NAICS 

codes, impose only minimal burden on 

any sources that may be owned or 

operated by tribal governments, such as 

drinking water and waste water 

treatment systems. The third 

amendment made by this rule addresses 

the procedures for submission of 

confidential business information in the 

RMP. The sources that are mentioned 

above handle chemicals that are known 

to public (e.g., chlorine for use of 

disinfection, propane used for fuel, etc.). 

EPA does not, therefore, expect RMP 

information on these types of processes 

to include CBI, so any costs related to 

CBI will not fall on Indian tribal 

governments. Accordingly, the 

requirements of section 3(b) of 

Executive Order 13084 do not apply to 

this rule. 

Notwithstanding the non-applicability 

of E. O. 13084, EPA has recently 

conducted seminars with the tribal 

governments. However, there were no 

concerns raised on any issues that are 

covered in this rule. 

F. Regulatory Flexibility 

EPA has determined that it is not 

necessary to prepare a regulatory 

flexibility analysis in connection with 

this final rule. EPA has also determined 

that this action will not have a 

significant economic impact on a 

substantial number of small entities. 

Two of the amendments made by this 

rule, the addition of RMP data elements 

and the conversion of SIC codes to 

NAICS codes, impose only minimal 

burden on small entities. Moreover, 

those small businesses that claim CBI 

when submitting the RMP will not face 

any costs beyond those imposed by the 

existing CBI regulations. Even 

considering the costs of CBI 

substantiation, however, there is no 

significant economic impact on a 

substantial number of small entities. 

EPA estimates that very few small 

entities (approximately 500) will claim 

CBI and that these few entities represent 

a small fraction of the small entities 

(less than 5 percent) affected by the 

RMP rule. Finally, EPA estimates that 

those small businesses filing CBI will 

experience a cost which is significantly 

less than one percent of their annual 

sales. For a more detailed analysis of the 
976 Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 

small entity impacts of CBI submission, 

see Document Number, IV-B–02, 

available in the docket for this 

rulemaking (see ADDRESSES section). 

G. Paperwork Reduction 

1. General 

The information collection 

requirements in this rule have been 

submitted for approval to the Office of 

Management and Budget (OMB) under 

the Paperwork Reduction Act, 44 U.S.C. 

3501 et seq. An Information Collection 

Request (ICR) document has been 

prepared by EPA (ICR No. 1656.05) and 

a copy may be obtained from Sandy 

Farmer, by mail at Office of Policy, 

Regulatory Information Division, U.S. 

Environmental Protection Agency 

(2137), 401 M St, SW, Washington, DC 

20460, by e-mail at 

farmer.sandy@epamail.epa.gov or by 

calling (202) 260–2740. A copy may also 

be downloaded off the Internet at http:/ 

/www.epa.gov/icr. The information 

requirements are not effective until 

OMB approves them. 

The submission of the RMP is 

mandated by section 112(r)(7) of the 

CAA and demonstrates compliance with 

Part 68 consistent with section 114(c) of 

the CAA. The information collected also 

will be made available to state and local 

governments and the public to enhance 

their preparedness, response, and 

prevention activities. Certain 

information in the RMP may be claimed 

as confidential business information 

under 40 CFR Part 2 and Part 68. 

This rule will impose very little 

burden on affected sources. First, EPA 

estimates that the new data elements 

will require only a nominal burden, .25 

hours for a typical source, because 

latitude and longitude method and 

description will be selected from a list 

of options, the Title V permit number is 

available to any source to which Title V 

applies, and the percentage weight of a 

toxic substance in a liquid mixture is 

usually provided by the supplier of the 

mixture. Second, the NAICS code 

provision is simply a change from one 

code to another.6 Third, as discussed 

above in the preamble, EPA believes 

that the CBI provisions of this rule will 

add no additional burden beyond what 

sources otherwise would face in 

6 EPA intends to provide several outreach 

mechanisms to assist sources in identifying their 

new NAICS code. RMP*Submit will provide a 

‘‘pick list’’ that will make it easier for sources to 

find the appropriate code. Also, selected NAICS 

codes are included in the General Guidance for Risk 

Management Programs (July 1998) and in the 

industry-specific guidance documents that EPA is 

developing. EPA will also utilize the Emergency 

Planning and Community Right-to-Know Hotline at 

800–424–9346 (or 703–412–9810) to assist sources 

in determining the source’s NAICS codes. 

complying with the CBI rules in 40 CFR 

Part 2. The Agency has calculated the 

burden of substantiations made for 

purposes of this rule below. 

Burden means the total time, effort, or 

financial resources expended by persons 

to generate, maintain, retain, or disclose 

or provide information to or for a 

Federal agency. This includes the time 

needed to review instructions; develop, 

acquire, install, and utilize technology 

and system for the purposes of 

collecting, validating, and verifying 

information, processing and 

maintaining information, and disclosing 

and providing information; adjust the 

existing ways to comply with any 

previously applicable instructions and 

requirements; train personnel to be able 

to respond to a collection of 

information; search data sources; 

complete and review the collection of 

information; and transmit or otherwise 

disclose the information. 

An agency may not conduct or 

sponsor, and a person is not required to 

respond to a collection of information 

unless it displays a currently valid OMB 

control number. The OMB control 

numbers for EPA’s regulations are listed 

in 40 CFR Part 9 and 48 CFR Chapter 

15. 

2. CBI Burden 

In the Notice of Proposed Rulemaking 

for these amendments, EPA proposed to 

amend existing 40 CFR Part 68 to add 

two sections which would clarify the 

procedures for submitting RMPs that 

contain confidential business 

information (CBI). As proposed, CBI 

would be handled in much the same 

way as it presently is under other EPA 

programs, except that EPA would 

require sources claiming CBI to submit 

documentation substantiating their CBI 

claims at the time such claims were 

made and EPA also would not permit 

CBI claims for certain data elements 

which clearly are not CBI. Aside from 

these procedural changes, however, the 

proposed rule was substantively 

identical to the existing rules governing 

the substantiation of CBI claims, 

presently codified in 40 CFR Part 2. 

At the time it proposed these 

amendments, EPA estimated the public 

reporting burden for CBI claims to be 15 

hours for chemical manufacturers with 

Program 3 processes, the only kinds of 

facilities that EPA expects to be able to 

claim CBI for any RMP data elements. 

This estimate was premised upon EPA’s 

assessment that it would require 8.5 

hours per claim to develop and submit 

the CBI substantiation and 6.5 hours to 

complete an unsanitized version of the 

RMP, for a total of 15 hours. EPA also 

estimated that approximately 20 percent 

of the 4000 chemical manufacturers (out 

of 64,200 stationary sources estimated to 

be covered by the RMP rule) may file 

CBI claims (800 sources). The 800 

sources represent a conservative 

projection based on the Agency’s 

experience under EPCRA program. 

Consequently, the total annual public 

reporting burden for filing CBI claims 

was estimated to be approximately 

12,000 hours over three years (800 

facilities multiplied by an average 

burden of 15 hours), or an annual 

burden of 4,000 hours (Information 

Collection Request No. 1656.04). 

a. Comment received. EPA received 

one comment on the ICR developed for 

the proposed rule, opposing up-front 

substantiation of any CBI claims. The 

commenter stated that ‘‘[t]his is a major 

departure from standard EPA procedure, 

and would impose a substantial and 

unjustified burden for several years.’’ 

The commenter further added that upfront substantiation would significantly 

increase the burden of this rule, and that 

up-front substantiation unnecessarily 

increases the volume and potential loss 

of CBI documents. The commenter also 

stated that the estimate of 15 hours for 

chemical manufacturers ‘‘seems 

unreasonably low,’’ and cited the EPA 

burden estimate of 27.7 to 33.2 hours 

per claim (with an average of 28.8) 

under the trade secret provisions of 

EPCRA. 

In the preamble to the proposed rule, 

EPA estimated that 20 percent of the 

4,000 chemical manufacturers will file a 

CBI claim. The commenter contends 

that ‘‘[t]he EPA analysis * * * excludes 

facilities in other industries that will 

need to file CBI claims.’’ 

Finally, the commenter stated that 

claiming multiple data elements as CBI 

will increase reporting burden. 

b. EPA response. Burden Estimates: 

EPA disagrees with these comments. As 

pointed out above, the requirement to 

submit up-front substantiation of CBI 

claims imposes no additional burden. In 

addition, the total burden of the CBI 

provisions of this rule are not 

understated. EPA has re-examined its 

analysis in light of the commenter’s 

concerns and has determined—contrary 

to the commenter’s claim—that its 

initial estimate of the total burden 

associated with preparing and claiming 

CBI was likely too conservative. As 

explained below, the Agency’s best 

available information indicates that the 

process of documenting and submitting 

a claim of CBI should impose a burden 

of approximately 9.5 hours per CBI 

claimant. 

First, EPA believes that the 

requirement to submit, at the time a 

source claims information as CBI, 
Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 977 

substantiation demonstrating that the 

material truly is CBI imposes no burden 

on sources beyond that which presently 

exists under EPA’s CBI regulations in 

Part 2. In order to decide whether they 

might properly claim CBI for a given 

piece of information, a source must 

determine if the criteria stated in section 

2.208 of 40 CFR Part 2 are satisfied. 

Naturally, a source goes through this 

process before a CBI claim is made. EPA 

agrees that most programs do not 

require the information that forms the 

basis for the substantiation to be 

submitted at the time of the claim; 

however, a facility must still determine 

whether or not a claim can be 

substantiated. Because existing rules 

require sources to formulate a legitimate 

basis for claiming CBI, even if those 

rules do not require immediate 

documentation, and because the Agency 

fully expects requests for RMP 

information which will necessitate 

sources’ submitting such 

documentation, EPA believes that upfront submission will not increase the 

burden of the regulation. 

Second, in response to the 

commenter’s claim that the Agency had 

underestimated the total burden 

associated with CBI claims, EPA 

undertook a review of recent 

information collection requests (ICRs) 

covering data similar to that required to 

be submitted in an RMP. Initially, EPA 

examined the ICR prepared for Part 2 

itself (ICR No. 1665.02, OMB Control 

No. 2020–0003). Under an analysis 

contained in the Statement of Support 

for the ICR, the Agency estimated that 

it takes approximately 9.4 hours to 

substantiate claims of CBI, prepare 

documentation, and submit such 

documentation to EPA. Next, the 

Agency reviewed a survey conducted by 

the Agency (under Office of 

Management and Budget clearance 

#2070–0034), to present the average 

burden associated with indicating 

confidential business information 

claims for certain data elements under 

the proposed inventory update rule 

(IUR) amendment under TSCA section 

8. This survey specifically asked 

affected industry how long it would take 

to prepare CBI claims for two data 

elements—chemical identity and 

production volume range information. 

Part 68 also requires similar information 

(e.g., chemical identity and maximum 

quantity in a process) to be included in 

a source’s RMP and, indeed, EPA 

anticipates that they will be the data 

elements most likely to be claimed CBI. 

The average burden estimates for 

chemical identity were between 1.82 

and 3.13 hours, and the average burden 

estimates for production volume in 

ranges were between 0.87 and 2.08 

hours. Thus, assuming that the average 

source claims both chemical identity 

and the maximum quantity in a process 

as CBI, a conservative estimate for the 

reporting burden would be 5.21 hours. 

Finally, EPA examined the burden 

estimate upon which it relied at 

proposal. That estimate predicted that 

the average CBI claim would take 15 

hours, of which 8.5 would be 

developing and submitting the CBI 

claim, and 6.5 would be completing an 

unsanitized version of the RMP. In view 

of EPA’s current plan not to require a 

source claiming CBI to submit a full, 

unsanitized RMP, but instead to submit 

only the particular elements claimed as 

CBI, the Agency expects the latter 

burden to decrease to 1 hour, for a total 

burden of 9.5 hours. 

In light of its extensive research of the 

burden hours involved in preparing and 

submitting CBI claims, EPA believes 

that the total burden estimate was not 

understated in the April proposal. 

Rather, other ICRs and the ICR proposal, 

combined with the changes to the 

method of documenting CBI claims, 

indicate that a burden estimate between 

5.21 and 9.5 hours is appropriate for 

this final rule. EPA has selected the 

most conservative of these, 9.5 hours, in 

its ICR for this final rule. 

EPA rejected one ICR’s burden 

estimate as being inapplicable to the 

present rulemaking. Although the 

commenter urged the Agency to adopt 

the estimate associated with trade secret 

claims under EPCRA (28 hours), EPA 

believes that the estimates discussed 

above are more accurate for several 

reasons. First, the EPCRA figures are 

based upon a survey with a very small 

sample size, as compared to the TSCA 

survey cited previously. Second, most 

(if not all) of the facilities submitting 

RMPs are likely to already be reporting 

under sections 311 and 312 or section 

313 of EPCRA, and many of the 

manufacturers submitting an RMP are 

subject to TSCA reporting requirements; 

thus, most sources likely to claim CBI 

for an RMP data element will have 

already done some analysis of whether 

or not such information would reveal 

legitimately confidential matter. 

Other Facilities Can Claim CBI: The 

Agency does not agree with the 

commenter’s claim that facilities other 

than chemical manufacturers might be 

expected to claim CBI for information 

contained in their RMPs. The other 

industries affected by the RMP rule (e.g., 

propane retailers, publicly owned 

treatment works) will not be disclosing 

in the RMP information that is likely to 

cause substantial harm to the business’s 

competitive position. For example, 

covered public drinking water and 

wastewater treatment plants generally 

use common regulated substances in 

standard processes (i.e., chlorine used 

for disinfection). Also, covered 

processes at many sources involve the 

storage of regulated substances that the 

sources sell (e.g., propane, ammonia), so 

the processes are already public 

knowledge. Other covered processes 

involve the use of well-known 

combinations of regulated substances 

such as refrigerants. Therefore, it is not 

likely that these businesses would claim 

information as CBI. 

As a point of comparison, EPA notes 

that of the 869,000 facilities that are 

estimated to be required to report under 

sections 311 and 312 of EPCRA, 

approximately 58 facilities have 

submitted trade secret claims for under 

those sections. For this reason, EPA 

believes the estimate of 800 sources 

may, in fact, be an overestimate of the 

number of sources claiming CBI. 

Reporting Multiple Data Elements: 

The Agency disagrees with the 

commenters assertion that it has 

underestimated the reporting burden on 

sources’ claiming multiple data 

elements as CBI. The burden figures 

stated above are based on the Agency’s 

estimates of the average number of data 

elements that a typical source will likely 

claim CBI. 

Public reporting of the new RMP data 

elements is estimated to require an 

average of .25 hours for all sources 

(64,200 sources) and substantiating CBI 

claims is estimated to take 

approximately 9.5 hours for certain 

chemical manufacturing sources (800 

sources). The aggregate increase in 

burden over that estimated in the 

previous Information Collection Request 

(ICR) for part 68 is estimated to be about 

23,650 hours over three years, or an 

annual burden of 7,883 hours for the 

three years covered by the ICR. 

H. Unfunded Mandates Reform Act 

Title II of the Unfunded Mandates 

Reform Act of 1995 (UMRA), P.L. 104– 

4, establishes requirements for Federal 

agencies to assess the effects of their 

regulatory actions on State, local, and 

tribal governments and the private 

sector. Under section 202 of the UMRA, 

EPA generally must prepare a written 

statement, including a cost-benefit 

analysis, for proposed and final rules 

with ‘‘Federal mandates’’ that may 

result in expenditures to State, local, 

and tribal governments, in the aggregate, 

or to the private sector, of $100 million 

or more in any one year. Before 

promulgating an EPA rule for which a 

written statement is needed, section 205 
978 Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 

of the UMRA generally requires EPA to 

identify and consider a reasonable 

number of regulatory alternatives and 

adopt the least costly, most costeffective or least burdensome alternative 

that achieves the objectives of the rule. 

The provisions of section 205 do not 

apply when they are inconsistent with 

applicable law. Moreover, section 205 

allows EPA to adopt an alternative other 

than the least costly, most cost-effective 

or least burdensome alternative if the 

Administrator publishes with the final 

rule an explanation why that alternative 

was not adopted. Before EPA establishes 

any regulatory requirements that may 

significantly or uniquely affect small 

governments, including tribal 

governments, it must have developed 

under section 203 of the UMRA a small 

government agency plan. The plan must 

provide for notifying potentially 

affected small governments, enabling 

officials of affected small governments 

to have meaningful and timely input in 

the development of EPA regulatory 

proposals with significant Federal 

intergovernmental mandates, and 

informing, educating, and advising 

small governments on compliance with 

the regulatory requirements. 

EPA has determined that this rule 

does not contain a Federal mandate that 

may result in expenditures of $100 

million or more for state, local, and 

tribal governments, in the aggregate, or 

the private sector in any one year. The 

EPA has determined that the total 

nationwide capital cost for these rule 

amendments is zero and the annual 

nationwide cost for these amendments 

is less than $1 million. Thus, today’s 

rule is not subject to the requirements 

of sections 202 and 205 of the Unfunded 

Mandates Act. 

EPA has determined that this rule 

contains no regulatory requirements that 

might significantly or uniquely affect 

small governments. Small governments 

are unlikely to claim information 

confidential, because sources owned or 

operated by these entities (e.g., drinking 

water and waste water treatment 

systems), handle chemicals that are 

known to public. The new data 

elements and the conversion of SIC 

codes to NAICS codes impose only 

minimal burden on these entities. 

I. National Technology Transfer and 

Advancement Act 

Section 12(d) of the National 

Technology Transfer and Advancement 

Act of 1995 (‘‘NTTAA’’), Pub L. 104– 

113, section 12(d)(15 U.S.C. 272 note), 

directs EPA to use voluntary consensus 

standards in its regulatory activities 

unless to do so would be inconsistent 

with applicable law or otherwise 

impractical. Voluntary consensus 

standards are technical standards (e.g., 

materials specifications, test methods, 

sampling procedures, business 

practices) that are developed or adopted 

by voluntary consensus standards 

bodies. The NTTAA requires EPA to 

provide Congress, through OMB, 

explanations when the Agency decides 

not to use available and applicable 

voluntary consensus standards. 

This action does not involve technical 

standards. Therefore, EPA did not 

consider the use of any voluntary 

consensus standards. 

J. Congressional Review Act 

The Congressional Review Act, 5 

U.S.C. section 801 et seq., as added by 

the Small Business Regulatory 

Enforcement Fairness Act of 1996, 

generally provides that before a rule 

may take effect, the agency 

promulgating the rule must submit a 

rule report, which includes a copy of 

the rule, to each House of the Congress 

and to the Comptroller General of the 

United States. EPA will submit a report 

containing this rule and other required 

information to the U.S. Senate, the U.S. 

House of Representatives, and the 

Comptroller General of the United 

States prior to publication of the rule in 

the Federal Register. This action is not 

a ‘‘major rule’’ as defined by 5 U.S.C. 

section 804(2). This rule will be 

effective February 5, 1999. 

APPENDIX TO PREAMBLE—D ATA ELEMENTS THAT MAY NOT BE CLAIMED AS CBI 

Rule element 

68.160(b)(1) Stationary source name, street, 

city, county, state, zip code, latitude, and longitude, method for obtaining latitude and longitude, and description of location that latitude and longitude represent. 

68.160(b)(2) Stationary source Dun and Bradstreet number. 

68.160(b)(3) Name and Dun and Bradstreet 

number of the corporate parent company. 

68.160(b)(4) The name, telephone number, and 

mailing address of the owner/operator. 

68.160(b)(5) The name and title of the person 

or position with overall responsibility for RMP 

elements and implementation. 

68.160(b)(6) The name, title, telephone number, 

and 24-hour telephone number of the emergency contact. 

68.160(b)(7) Program level and NAICS code of 

the process. 

68.160(b)(8) The stationary source EPA identifier. 

68.160(b)(10) Whether the stationary source is 

subject to 29 CFR 1910.119. 

68.160(b)(11) Whether the stationary source is 

subject to 40 CFR Part 355. 

68.160(b)(12) If the stationary source has a 

CAA Title V operating permit, the permit number. 

Comment 

This information is filed with EPA and other agencies under other regulations and is made 

available to the public and, therefore, does not meet the criteria for CBI claims. It is also 

available in business and other directories. 

This information provides no information that would affect a source’s competitive position. 

This information is filed with state and local agencies under EPCRA and is made available to 

the public and, therefore, does not meet the criteria for CBI claims. 

This information provides no information that would affect a source’s competitive position. 

This information provides no information that would affect a source’s competitive position. 

This information provides no information that would affect a source’s competitive position. 

Sources are required to notify the state and local agencies if they are subject to this rule; this 

information is available to the public and, therefore, does not meet the criteria for CBI 

claims. 

This information will be known to state and federal air agencies and is available to the public 

and, therefore, does not meet the criteria for CBI claims. 
Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 979 

APPENDIX TO PREAMBLE—D ATA ELEMENTS THAT MAY NOT BE CLAIMED AS CBI—Continued 

Rule element 

68.160(b)(13) The date of the last safety inspection and the identity of the inspecting entity. 

68.165(b)(4) Basis of the results (give model 

name if used). 

68.165(b)(9) Wind speed and atmospheric stability class (toxics only). 

68.165(b)(10) Topography (toxics only) ............. 

68.165(b)(11) Distance to an endpoint ............... 

68.165(b)(12) Public and environmental receptors within the distance. 

68.168 Five-year accident history .......................


68.170(b), (d), (e)(1), and (f)–(k) 

68.175(b), (d), (e)(1), and (f)–(p) 

NAICS code, prevention program compliance dates and information. 

68.180 Emergency response program ...............


Comment 

This information provides no information that would affect a source’s competitive position. 

Without the chemical name and quantity, this reveals no business information. 

This information provides no information that would affect a source’s competitive position. 

Without the chemical name and quantity, this reveals no business information. 

By itself, this information provides no confidential information. Other elements that would reveal chemical identity or quantity may be claimed as CBI. 

By itself, this information provides no confidential information. Other elements that would reveal chemical identity or quantity may be claimed as CBI. 

Sources are required to report most of these releases and information (chemical released, 

quantity, impacts) to the federal, state, and local agencies under CERCLA and EPCRA; 

these data are available to the public and, therefore, do not meet the criteria for CBI claims. 

Much of this information is also available from the public media. 

NAICS codes and the prevention program compliance dates and information provide no information that would affect a source’s competitive position. 

This information provides no information that would affect a source’s competitive position. 

List of Subjects in 40 CFR Part 68 

Environmental protection, 

Administrative practice and procedure, 

Air pollution control, Chemicals, 

Hazardous substances, 

Intergovernmental relations, Reporting 

and recordkeeping requirements. 

Dated: December 29, 1998. 

Carol M. Browner, 

Administrator. 

For the reasons set out in the 

preamble, title 40, chapter I, subchapter 

C, part 68 of the Code of Federal 

Regulations is amended to read as 

follows: 

PART 68—CHEMICAL ACCIDENT 

PREVENTION PROVISIONS 

1. The authority citation for Part 68 

continues to read as follows: 

Authority: 42 U.S.C. 7412(r), 7601(a)(1), 

7661–7661f. 

2. Section 68.3 is amended by 

removing the definition of SIC and by 

adding in alphabetical order the 

definition for NAICS to read as follows: 

§ 68.3 Definitions. 

* * * * * 

NAICS means North American 

Industry Classification System. 

* * * * * 

3. Section 68.10 is amended by 

revising paragraph (d)(1) to read as 

follows: 

§ 68.10 Applicability. 

* * * * * 

(d) * * * 

(1) The process is in NAICS code 

32211, 32411, 32511, 325181, 325188, 

325192, 325199, 325211, 325311, or 

32532; or 

* * * * * 

4. Section 68.42 is amended by 

revising paragraph (b)(3), redesignating 

paragraphs (b)(4) through (b)(10) as 

paragraphs (b)(5) through (b)(11) and by 

adding a new paragraph (b)(4) to read as 

follows: 

§ 68.42 Five-year accident history. 

* * * * * 

(b) * * * 

(3) Estimated quantity released in 

pounds and, for mixtures containing 

regulated toxic substances, percentage 

concentration by weight of the released 

regulated toxic substance in the liquid 

mixture; 

(4) Five- or six-digit NAICS code that 

most closely corresponds to the process; 

* * * * * 

5. Section 68.79 is amended by 

revising paragraph (a) to read as follows: 

§ . 68.79 Compliance audits. 

(a) The owner or operator shall certify 

that they have evaluated compliance 

with the provisions of this subpart at 

least every three years to verify that 

procedures and practices developed 

under this subpart are adequate and are 

being followed. 

* * * * * 

6. Section 68.150 is amended by 

adding paragraph (e) to read as follows: 

§ 68.150 Submission. 

* * * * * 

(e) Procedures for asserting that 

information submitted in the RMP is 

entitled to protection as confidential 

business information are set forth in 

§§ 68.151 and 68.152. 

7. Section 68.151 is added to read as 

follows: 

§ 68.151 Assertion of claims of 

confidential business information. 

(a) Except as provided in paragraph 

(b) of this section, an owner or operator 

of a stationary source required to report 

or otherwise provide information under 

this part may make a claim of 

confidential business information for 

any such information that meets the 

criteria set forth in 40 CFR 2.301. 

(b) Notwithstanding the provisions of 

40 CFR part 2, an owner or operator of 

a stationary source subject to this part 

may not claim as confidential business 

information the following information: 

(1) Registration data required by 

§ 68.160(b)(1) through (b)(6) and (b)(8), 

(b)(10) through (b)(13) and NAICS code 

and Program level of the process set 

forth in § 68.160(b)(7); 

(2) Offsite consequence analysis data 

required by § 68.165(b)(4), (b)(9), (b)(10), 

(b)(11), and (b)(12). 

(3) Accident history data required by 

§ 68.168; 

(4) Prevention program data required 

by § 68.170(b), (d), (e)(1), (f) through (k); 

(5) Prevention program data required 

by § 68.175(b), (d), (e)(1), (f) through (p); 

and 

(6) Emergency response program data 

required by § 68.180. 

(c) Notwithstanding the procedures 

specified in 40 CFR part 2, an owner or 

operator asserting a claim of CBI with 

respect to information contained in its 

RMP, shall submit to EPA at the time it 

submits the RMP the following: 

(1) The information claimed 

confidential, provided in a format to be 

specified by EPA; 
980 Federal Register / Vol. 64, No. 3 / Wednesday, January 6, 1999 / Rules and Regulations 

(2) A sanitized (redacted) copy of the 

RMP, with the notation ‘‘CBI’’ 

substituted for the information claimed 

confidential, except that a generic 

category or class name shall be 

substituted for any chemical name or 

identity claimed confidential; and 

(3) The document or documents 

substantiating each claim of confidential 

business information, as described in 

§ 68.152. 

8. Section 68.152 is added to read as 

follows: 

§ 68.152 Substantiating claims of 

confidential business information. 

(a) An owner or operator claiming that 

information is confidential business 

information must substantiate that claim 

by providing documentation that 

demonstrates that the claim meets the 

substantive criteria set forth in 40 CFR 

2.301. 

(b) Information that is submitted as 

part of the substantiation may be 

claimed confidential by marking it as 

confidential business information. 

Information not so marked will be 

treated as public and may be disclosed 

without notice to the submitter. If 

information that is submitted as part of 

the substantiation is claimed 

confidential, the owner or operator must 

provide a sanitized and unsanitized 

version of the substantiation. 

(c) The owner, operator, or senior 

official with management responsibility 

of the stationary source shall sign a 

certification that the signer has 

personally examined the information 

submitted and that based on inquiry of 

the persons who compiled the 

information, the information is true, 

accurate, and complete, and that those 

portions of the substantiation claimed as 

confidential business information 

would, if disclosed, reveal trade secrets 

or other confidential business 

information. 

9. Section 68.160 is amended by 

revising paragraphs (b)(1), (b)(7), and 

(b)(12) and adding paragraphs (b)(14) 

through (b)(18) to read as follows: 

§ 68.160 Registration. 

* * * * * 

(b) * * * 

(1) Stationary source name, street, 

city, county, state, zip code, latitude and 

longitude, method for obtaining latitude 

and longitude, and description of 

location that latitude and longitude 

represent; 

* * * * * 

(7) For each covered process, the 

name and CAS number of each 

regulated substance held above the 

threshold quantity in the process, the 

maximum quantity of each regulated 

substance or mixture in the process (in 

pounds) to two significant digits, the 

five- or six-digit NAICS code that most 

closely corresponds to the process, and 

the Program level of the process; 

* * * * * 

(12) If the stationary source has a CAA 

Title V operating permit, the permit 

number; and 

* * * * * 

(14) Source or Parent Company E-Mail 

Address (Optional); 

(15) Source Homepage address 

(Optional) 

(16) Phone number at the source for 

public inquiries (Optional); 

(17) Local Emergency Planning 

Committee (Optional); 

(18) OSHA Voluntary Protection 

Program status (Optional); 

10. Section 68.165 is amended by 

revising paragraph (b) to read as follows: 

§ 68.165 Offsite consequence analysis. 

* * * * * 

(b) The owner or operator shall 

submit the following data: 

(1) Chemical name; 

(2) Percentage weight of the chemical 

in a liquid mixture (toxics only); 

(3) Physical state (toxics only); 

(4) Basis of results (give model name 

if used); 

(5) Scenario (explosion, fire, toxic gas 

release, or liquid spill and evaporation); 

(6) Quantity released in pounds; 

(7) Release rate; 

(8) Release duration; 

(9) Wind speed and atmospheric 

stability class (toxics only); 

(10) Topography (toxics only); 

(11) Distance to endpoint; 

(12) Public and environmental 

receptors within the distance; 

(13) Passive mitigation considered; 

and 

(14) Active mitigation considered 

(alternative releases only); 

11. Section 68.170 is amended by 

revising paragraph (b) to read as follows: 

§ 68.170 Prevention program/Program 2. 

* * * * * 

(b) The five- or six-digit NAICS code 

that most closely corresponds to the 

process. 

* * * * * 

12. Section 68.175 is amended by 

revising paragraph (b) to read as follows: 

§ 68.175 Prevention program/Program 3. 

* * * * * 

(b) The five- or six-digit NAICS code 

that most closely corresponds to the 

process. 

* * * * * 

13. Section 68.180 is amended by 

revising paragraph (b) to read as follows: 

§ 68.180 Emergency response program. 

* * * * * 

(b) The owner or operator shall 

provide the name and telephone 

number of the local agency with which 

emergency response activities and the 

emergency response plan is 

coordinated. 

* * * * *


[FR Doc. 99–231 Filed 1–5–99; 8:45 am]


BILLING CODE 6560–50–P