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47 OF 283 
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2dcf?Q-EY\§>- IS 

f ' > 

CONSEQUENCES OF ACCIDENTS INVOLVING 

FLAMMABLE GASES AND LIQUIDS 

July 5, 1990 

££ 
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T, 

11 

TABLE OF CONTENTS (continued) 

Page 

8.0 Modelling Results 13 

8.1 Vapor Cloud Explosion Results 13 

8.2 Vapor Cloud Fire Results 17 

8.3 BLEVE Results 23 

8.4 Pool Fire Results 27 

8.5 Jet Fire Results 32 

9.0 Findings 32 

References 38 

Appendix A Additional Information on Classification Systems and Accident Histories 

for Flammable Chemicals 40 

A l Classification Systems for Flammable Chemicals 41 

A1.1 Definitions Related to Classification of Flammable Substances 41 

A1.2 DOT Classifications 41 

A1.3 NFPA Classifications 42 

A1.4 EEC Indicative Criteria 43 

A2 OSHA Regulations for Service Stations 43 

A3 Additional Information from the Acute Hazardous Events Data Base 43 

Appendix B. Methodologies for Calculation of Consequence Distances 48 

B.1 WHAZAN 49 

B.2 ARCHIE 57 

B3 Yellow Book 67 

B.4 AIChE-Sponsored Course Materials 77 

B.5 Green Book 81 

Appendix C. Hazard Criteria 84 

Cl Explosion Overpressure 85 

Ci.l Damage and Injury from Blast Waves 85 

C1.2 Distance Determination for Different Overpressures 93 

tfl 
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r.> 

1 

TABLE OF CONTENTS 

Page 

1.0 Introduction 1 

2.0 Background 1 

3.0 Existing Classification Systems, Regulations, and Codes 2 

3.1 DOT Classifications 3 

3.2 NFPA Classification Systems 3 

3.3 EEC Classification Scheme 3 

3.4 Regulations and Codes Applicable to Flammable Chemicals 3 

4.0 Past Fire and Explosion Incidents Involving Flammable Chemicals 4 

5.0 Accident Consequence Modelling 4 

5.1 WHAZAN Methodology 5 

5.2 ARCHIE Methodology 5 

53 The "Yellow Book" Methodology 6 

5.4 AIChE-Sponsored Course Materials 6 

5.5 The "Green Book" Methodology 6 

6.0 Consequence Analysis Approach 6 

6.1 Accident Scenarios 7 

6.1.1 Vapor Cloud Explosions 7 

6.1.2 Vapor Cloud Fires 9 

6.1.3 BLEVEs and Fireballs 9 

6.1.4 Pool Fires 10 

6.1.5 Jet Fires 10 

6.2 Chemicals, Quantities, and Conditions Used in Modelling 10 

6.2.1 Chemicals and Quantities Chosen for Modelling 10 

6.2.2 Instantaneous and Prolonged Releases 11 

6.2.3 Initial Conditions Prior to Release 11 

6.14 Meteorology 11 

7.0 Hazard Criteria 12 

7.1 Hazard Criteria for Vapor Cloud Explosions 12 

7.2 Hazard Criteria for Vapor Cloud Fires 12 

7.3 Hazard Criteria for BLEVEs, Pool Fires, and Jet Fires 13 

•p 
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IV 

LIST OF EXHIBITS 

Exhibit Page 

1 Chemicals Known to Have Been Involved in Vapor Cloud Explosions 7 

2 Distances for Vapor Cloud Explosions of Four Liquefied Gases for 

Instantaneous Releases of 1,000 to 180,000 Pounds Determined Using Fraction 

Flashed, WHAZAN Stand-Alone Model 14 

3 Quantity Released Versus Distance for Vapor Qoud Explosions, Instantaneous Releases 16 

4 Distances for Vapor Qoud Fires from Evaporating Pools from Instantaneous Releases, 

Moderate Meteorology, Determined Using WHAZAN 18 

5 Quantity Released Versus Distance for Vapor Qoud Fires, Instantaneous Releases, 

Moderate Meteorology 22 

6 Distances for BLEVEs for Instantaneous Releases of 1,000 to 180,000 Pounds, 

Determined Using WHAZAN 24 

7 Quantity Released Versus Distance for BLEVEs, Instantaneous Releases 26 

8 Distances for Pool Fires for Instantaneous Releases of 1,000 to 180,000 Pounds, 

Determined Using WHAZAN 28 

9 Quantity Released Versus Distance for Pool Fires, Instantaneous Releases 31 

10 Distances for Jet Fires for Prolonged Releases of 10,000 Pounds, Determined Using 

WHAZAN 33 

11 Flammable Gases 34 

12 Flammable, Volatile Liquids 36 

A-1 Fire and Explosion Events Compared to All Events in Acute Hazardous Events Data Base .. 44 

A-2 Flammable Gases and Liquids Reported in In-Plant Fires or Explosions 46 

C-l Human Injuiy Criteria (Includes Injury from Flying Glass and Direa Overpressure Effects) .. 86 

C-2 Property Damage Criteria 88 

C-3 Lethality Curves 91 

C-4 Lethality and Injury Curves 91 

C-5 Air Blast Criteria for Personnel Standing in the Open ..; 92 

C-6 Hazard Criteria Comparison for Vapor Cloud Explosions for Instantaneous Releases 

of 100,000 Pounds 94 

C-7 Hazard Criteria Comparison for Vapor Cloud Fires for Evaporating Pools 

From Instantaneous Releases, Moderate Meteorology 95 

C-8 Human Injury Criteria (Thermal Radiation Effects on Bare Skin) 97 

1 
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Ul 

TABLE OF CONTENTS (continued) 

l_aee 

C2 Flammability Limits 93 

C3 Heat Radiation 96 

C3.1 Heat Radiation Levels Causing Death and Injuiy 96 

C3.2 Distance Determination for Different Heat Radiation Levels 99 

C3.2.1 BLEVEs 99 

C3.2.2 Pool Fires 99 

C4 References 102 

Appendix D. Comparison of Results of Modelling by Different Methods and 

Results of Vaiying Release Scenarios and Meteorological Conditions 103 

D.l Vapor Qoud Explosion Results 104 

D.2 Vapor Qoud Fire Results 104 

D3 BLEVE Results 106 

D.4 Pool Fire Results 106 

D.5 Jet Fire Results 107 

D.6 Instantaneous Release Compared to Prolonged Release 107 

D.7 Moderate Meteorology Compared to Worst Case Meteorology 107 

Appendix E. Inputs for Modelling 108 

^ , 
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V 

UST OF EXHIBITS (continued) 

Exhibit Page 

C-9 Fatality from Heat Exposure 98 

C-10 Hazard Criteria Comparison for BLEVEs, Instantaneous Releases 100 

C-ll Hazard Criteria Comparison for Pool Fires, Instantaneous Releases 101 

D-1 Results of Modelling by All Methods 105 

E-1 Temperatures and Pressures Used in Scenarios 110 

E-2 Chemical Data Used for Models Ill 

E-3 WHAZAN Modelling Data for Instantaneous Releases, Moderate Meteorology 112 

E-4 WHAZAN Modelling Data for Prolonged Releases 113 

E-5 WHAZAN Modelling Data for Instantaneous Releases, Worst Case Meteorology 114 

E-6 ARCHIE Modelling Data 115 

li O 
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CONSEQUENCES OF ACCIDENTS INVOLVING FLAMMABLE GASES AND LIQUIDS 

1.0 Introduction 

When the Emergency Planning and Community Right to Know Act, Title m of the Superfund 

Amendments and Reauthorization Act (SARA), was enacted in 1986, a list of extremely hazardous 

substances (EHSs) (formerly the list of Acutely Toxic Chemicals published in November of 1985) was 

published under Section 302 of Title HL Section 302 requires a fadlity that has an EHS above its 

threshold planning quantity (TPQ) to notify the State Emergency Response Commission (SERC) that it is 

subject to the requirements for emergency planning. 

The original list of EHSs was created using only acute toxidty criteria. The purpose of the list was to 

identify those substances that, if acddentally released, could cause death or serious irreversible health 

effects from toxidty off-site after a short exposure. However, toxidty is not the onty hazard posed by 

chemicals. SARA states that the Administrator may revise the list, but such revisions "shall take into 

account the toxidty, reactivity, volatility, dispersibility, combustibility, or flammability of a substance." 

The purpose of this report is to assess the potential consequences of acddents involving flammable 

chemicals. A particular emphasis is placed on assessing the impacts of acddents on communities 

neighboring industrial facilities. 

The general approach taken in assessing the consequences of potential acddents involving flammable 

chemicals was to identify and evaluate: 1) existing listing and classification systems, along with any 

applicable criteria; 2) existing regulations and codes dealing with flammable materials; and 3) histories of 

acddents involving flammable materials. EPA's evaluation is discussed in Sections 3 and 4. 

None of the above supplied suffident infonnation to serve EPA's specific needs. It was, therefore, dedded 

to model the potential consequences from acddent scenarios involving flammable chemicals to establish 

physical and chemical properties that may be indicative of the hazards associated with these chemicals. 

The results of the consequence modelling were then analyzed. The modelling is discussed in Sections 5 

through 8. EPA's analysis of the modelling results is discussed in Section 9. 

2.0 Background 

EPA originally developed the list of EHSs as part of the Chemical Emergency Preparedness Program 

(CEPP) which was designed to increase public awareness of chemical hazards in communities and to focus 

effort on emergency planning. EPA believed that communities needed a starting point and intended that 

the list draw attention to the substances and facilities that pose the most immediate concern based on 

toxidty from an emergency planning and response perspective. EPA recognized and emphasized that there 

are tens of thousands of compounds and mixtures in commerce that may pose a hazard under specific 

circumstances and that this list addressed lethality and serious irreversible health effects assodated with 

acute toxidty. The Agency chose lethality because it represents the most immediate concern in an 

emergency situation. 

Several commenters on the rulemaking for the EHS list noted that physical/chemical hazards such as 

flammability or explosivity may lead to lethal consequences. In an offidal inquiry to the Agency in 1987, 

Senator Frank Lautenburg also noted concern for hazards other than toxidty and asked that EPA focus on 

other hazards. The Agency agreed and noted its intent to evaluate hazards other than toxidty in the 

future. 

A Physical/Chemical Criteria Workgroup (P/C Workgroup) was formed at EPA to address the concerns 

raised by Senator Lautenburg and others and to focus on the problem of identifying materials which are 

hazardous based upon their physical/chemical properties and could thereby be candidate EHSs. The 

Workgroup initially considered the hazards referred to in the Act and determined that they fell into two 

general categories: hazards related to toxic properties and hazards related to physical/chemical properties. 

The characteristics of reactivity, volatility, dispersibility, combustibility, and flammability, mentioned in the 

)4 
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Act, are related to a variety of physical/chemical properties; the Workgroup chose to focus on the 

physical/chemical properties that lead to the greatest potential hazards to people. Hazards assodated with 

physical/chemical properties are primarily based on two phenomena that can cause serious personal injuiy 

or death. These phenomena are the result of the release of energy from highly reactive or flammable 

chemicals and are identified as overpressures from blast waves and thermal radiation from fires. 

Overpressures result from nearly instantaneous energy release, or detonation, while thermal energy is 

released during combustion, which occurs more slowly. Since explosive chemicals are highly reactive 

substances that can detonate and create overpressures, and flammable chemicals can burn and produce 

thermal radiation, the Workgroup focused on explosives and flammable chemicals as chemicals of concern. 

The P/C Workgroup elected first to investigate what substances might have been identified and what 

criteria might already be in use by other organizations to characterize hazardous chemicals and to 

determine whether these criteria might meet EPA's needs. Criteria were investigated from many 

organizations including the National Fire Protection Assodation (NFPA), the United States Department 

of Transportation (DOT), the Occupational Safety and Health Administration (OSHA), and the European 

Economic Community (EEC). 

The workgroup initially sought to evaluate and possibly use the criteria from these other organizations to 

develop options for adding to the list of EHSs chemicals that are flammable or explosive. The criteria 

from other organizations did not appear to be based on the consequences of an acddent in terms of 

exposure to the community but rather on the consequences that could occur within the facility or during 

shipment of bulk materials or during fire-fighting. For example, an NFPA flammability rating of 4 is 

assigned to materials that will burn readily and that disperse readily or vaporize rapidly or completely at 

ambient conditions. This is important to fire-fighters approaching a fire involving a flammable material 

but gives little indication of the impact on a community from an acddent that takes place inside an 

industrial facility. 

The P/C Workgroup determined that an evaluation of the impacts of acddents involving substances that 

may be hazardous to the community because of certain physical/chemical properties was necessary. Such 

an evaluation would help to develop the criteria that would identify chemicals that should be considered 

extremely hazardous and therefore of concern for community emergency response planning efforts. One 

approach was to model acddents involving flammable chemicals and to analyze the resulting data in order 

to establish a correlation between the severity of acddent consequences to the community and 

physical/chemical properties related to the consequences. 

This approach is similar to the approach taken to establish the TPQs for the Section 302 EHSs listed 

based on toxidty criteria. These TPQs were established by assuming an acddent scenario, a loss of 

containment of a specific toxic chemical, and then estimating the dispersion potential of each chemical. 

An index value based on the dispersion potential and toxidty was used to rank the chemicals, and 

chemicals were assigned to TPQ categories according to their ranking. 

The workgroup elected to segregate the chemicals into separate categories for flammables, explosives, and 

reactives for purposes of analysis and possible regulation even though it was recognized that there may be 

overlap of the consequences; e.g., a detonation of a flammable material may yield the same results as an 

explosion of a commerdal explosive. However, the workgroup wanted to determine what parameters 

distinguish an extremely hazardous flammable substance from all other flammables, extremely hazardous 

explosives from all other explosives, and so on. This report focuses on flammable gases and liquids. 

Separate documents will address the consequences of acddents involving commerdal and non-commerdal 

explosives and reactive chemicals. 

3.0 Existing Classification Systems, Regulations, and Codes 

There are many organizations that have developed lists, definitions, and classifications related to 

flammable chemicals, including DOT, NFPA EEC, OSHA and EPA Some organizations establish their 

classifications with qualitative descriptions but most classifications are based on physical/chemical 

15" 
P.10 

-3-

properties, usually flash point and boiling point None of these classification systems appeared to be 

primarily based on potential hazards to the community from inddents involving releases of flammable 

chemicals from fixed facilities; therefore EPA dedded that none of these systems was appropriate or 

specifically applicable to EPA's regulatory needs. The systems examined are described briefly in the 

following sections; more detail is presented in Appendix A 

3.1 DOT Classifications 

DOT classifies flammable materials for shipping purposes under 49 CFR 172. This regulation lists 

materials DOT regards as hazardous for purposes of transportation and prescribes requirements for 

shipping papers, package marking, labeling, vehicle placarding, and types of containers and safety devices 

that must be used to transport a flammable material. Details of the DOT classifications for flammable 

materials are found in Appendix A 

The DOT hazard classifications are based on maintaining safety during transport, given the range of 

ambient conditions possible. The consequences in terms of "first response" to acddents involving these 

materials are addressed in DOTs Emergency Response Guidebook. This guide details generic isolation 

distances, recommended fire-fighting techniques, and other initial emergency actions for inddents involving 

these substances. However, DOT focuses on transportation safety rather than hazards from fixed sites. 

3.2 NFPA Classification Systems 

The NFPA has a rating scale of 0 to 4, where 0 represents the lowest degree of flammability, for purposes 

of fire-fighting and fire prevention. The ratings are usually noted on Material Safety Data Sheets (MSDSs) 

and are included in a standard that applies to facilities for manufacturing, storage, or use df hazardous 

materials. Approximately 1,500 chemicals have been assigned NFPA ratings. The classifications are 

designed to give "a general idea of the inherent hazards of any material and the order of severity of these 

hazards as they relate to fire prevention, exposure and control" (NFPA 1984). 

NFPA has also developed a code (NFPA 30, Flammable and Combustible Liquids Code) concerning 

flammable and combustible liquids which is part of the National Fire Code and is specifically intended to 

be referenced by public authorities in laws, ordinances, regulations, and administrative orders. It was 

originally written as a model muniripal ordinance for storing, handling, and using flammable liquids at 

fixed facilities. This code includes classifications based on flash point and boiling point The NFPA 

flammability ratings and classifications from the NFPA code are discussed further in Appendix A 

33 EEC Classification Scheme 

The EEC published a Council Directive on June 24,1982, "concerned with the prevention of major 

acddents which might result from certain industrial activities and with the limitation of their consequences 

for man and the environment" (EEC 1982). The directive includes a list of toxic and explosive chemicals 

and several categories of flammable chemicals; the flammable categories are defined by "Indicative 

Criteria." Facilities that have listed chemicals in quantities greater than a specified threshold amount are 

required to report and meet a variety of conditions including performing hazards analyses and preparing 

emergency plans. The thresholds for the flammable categories are 200 metric tons (440,000 pounds) for 

flammable gases and flammable liquids under hazardous processing conditions, and 50,000 metric tons (1.1 

million pounds) for other highly flammable liquids. The indicative criteria related to flammability are 

discussed in Appendix A 

3.4 Regulations and Codes Applicable to Flammable Chemicals 

Several agendes regulate flammable chemicals. OSHA regulates flammable and combustible liquids (29 

CFR 1910.106), with handling and storage requirements and spedfications for storage tanks. Specific 

requirements are included for bulk plants, service stations, processing plants, refineries, chemical plants, 

and distilleries. In addition, there are spedfic regulations dealing with acetylene (29 CFR 1910.101), 
P.11 

hydrogen (29 CFR 1910.102), and liquefied petroleum gases (29 CFR 1910.110). Flammable and 

combustible liquids may also be regulated by state or local governments; e.g., NFPA 30, Flammable and 

Combustible liquids Code (see section 3.2), may be adopted or incorporated into law. DOT regulations 

include shipping requirements for flammable materials (49 CFR 172 and 173). All of these regulations are 

highly specific and deal with containers, pipes, and storage, handling, or transfer conditions in specified 

circumstances; however, none is directly applicable for EPA's purposes. 

Gasoline is a flammable chemical of particular interest because of the high volumes in commerce and the 

many locations where it may be found. Therefore, EPA investigated the regulations for flammable 

chemicals with additional focus on gasoline. Gasoline is not regulated as a special case under any of the 

regulations or codes mentioned above. DOTs requirements for gasoline are similar to those for other 

liquids with similar properties, as are NFPA's recommendations for gasoline. OSHA's regulations fbr 

service stations do not mention gasoline specifically, but refer only to flammable liquids. These 

regulations cover the storage and dispensing of flammable liquids, electrical and heating equipment in 

areas with flammable liquids, waste handling, and fire extinguishers at service stations. Further 

information on the OSHA regulations for flammable liquids may be found in Appendix A EPA's review 

of current regulations indicates gasoline is not considered a spedal case. 

Fuels are not included as hazardous substances under CERCLA; "petroleum, including crude oil or any 

fraction thereof, ...natural gas, natural gas liquids, liquefied natural gas or synthetic gas usable for fuel (or 

mixtures of natural gas and such synthetic gas)" are not included in the definition of hazardous substances 

(40 CFR 300.6). 

4.0 Past Fire and Explosion Inddents Involving Flammable Chemicals 

The Acute Hazardous Events Data Base (AHE/DB) was developed by EPA to provide a historical 

perspective on acddents that involve releases of hazardous substances in the United States (EPA 1988). 

The 1988 version of the data base includes data on 5,827 inddents that occurred between the 1960s and 

1987 (the majority of the inddents appear to have occuned in the 1980s). Information in the data base is 

from the National Response Center, press reports, and several state offices. This data base was reviewed 

to identify acddents specifically involving flammable chemicals and evaluate the consequences of these 

acddents, if possible, in terms of physical/chemical characteristics and the specific hazards posed to the 

surrounding community. 

Fire and explosion inddents account for about 13 percent of the total inddents in the AHE/DB, but they 

account for nearly 92 percent of the deaths and about 36 percent of the injuries reported. However, the 

number of these deaths and injuries that occurred on-site and the number that occuned off-site cannot be 

ascertained from the data base; therefore, the degree of impact these inddents had on the surrounding 

community cannot be accurately determined. Additional details and analyses using the data from the 

AHE/DB may be found in Appendix A Section A3. 

The AHE/DB indicates that flammable chemicals are hazardous; they have been involved in numerous 

acddents that resulted in fires and explosions, and these acddents led to many deaths and injuries. 

However, the data are not suffidently specific to serve as a basis for identifying chemicals that may be 

extremely hazardous based on their physical/chemical properties. 

5.0 Accident Consequence Modelling 

Because classification methods and regulatory approaches used by other organizations did not appear to be 

related to hazards to the community, especially from acddents at fixed facilities, and historical acddent 

data appeared to be inadequate as a basis for identifying and classifying flammable chemicals, EPA dedded 

to use modelling techniques to evaluate potential hazards to the community from inddents involving 

release of flammable liquids and gases from fixed sites. No one hazards analysis model has been 

universally accepted; therefore, two PC-based models and several methods involving manual calculations 

were used for a single release quantity to estimate consequences of acddents involving flammable liquids 

nl 
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-5-

and gases for comparison purposes. As discussed in the following section, the WHAZAN model was 

selected for use in the extensive acddent consequence modelling analysis. 

The models, approach, and results of modelling are discussed in the following sections. EPA did not 

attempt to validate or verify the models used nor to evaluate or estimate their uncertainties; the results 

obtained using the various methods are presented for comparison purposes in Appendix D. In general, the 

various methods show reasonable agreement in predicting consequences for various acddent scenarios and 

hazard criteria levels. Additional information on each of the models is presented in Appendix B. 

Assumptions used in the modelling and the physical/chemical data required as input for the chemicals 

modelled are summarized in Appendix E. 

5.1 WHAZAN Methodology 

The commercially available World Bank Hazard Analysis (WHAZAN) computer system is a group of 

computer programs capable of performing quick estimates of the possible hazardous consequences of 

acddental releases of toxic and/or flammable gases or liquids. It was developed by Technica International 

Ltd. in collaboration with the World Bank. These programs, when combined, comprise models for 

calculating the consequences of different types of chemical releases. The models derive their inputs from a 

data base which contains relevant properties of some hazardous chemicals. The user can add chemicals 

and properties to the data base. A user of WHAZAN can either run one of the models individually for 

calculating the hazardous consequences from a specific type of release (stand-alone models), or can link 

two or more models in a way such that outputs from one model can be used automatically as inputs for 

another model (linked models). The models provide information about four key areas: outflow of the 

chemical from its container, behavior immediately after release, dispersion after release, and fires and 

explosions. 

Many different assumptions are taken into account by WHAZAN when attempting to predict the hazards 

resulting from acddental releases of the chemicals contained within its data base. Assumptions are made 

regarding atmospheric behavior and acddental release rates of various gases and liquids. These assumed 

values, combined with chemical-specific input values, allow WHAZAN to predict the hazardous 

consequences of different types of acddental releases. The WHAZAN model is extensively used by large 

international chemical companies and government agendes. In addition, this model appears to be more 

chemical-specific than the other modelling methods considered and the comparison of WHAZAN results 

with the results using other methods showed reasonable agreement Therefore, WHAZAN was used as 

the primary method of consequence analysis for flammable chemicals. More details on the WHAZAN 

model are found in Appendix B, Section B.l. 

5.2 ARCHIE Methodology 

Acddent hazard assessment and consequence analysis procedures have been incorporated into a program 

developed for the Federal Emergency Management Agency (FEMA), DOT, and EPA, entitled Automated 

Resource for Chemical Hazard Inddent Evaluation (ARCHIE). The primary purpose of ARCHIE is to 

provide emergency personnel with several integrated estimation methods that may be used to assess the 

vapor dispersion, fire, and explosion impacts assodated with episodic discharges of hazardous materials 

into the environment The program is also intended to facilitate a better understanding of the nature and 

sequence of events that may follow an acddent and the resulting consequences. 

The core of the ARCHIE computer program is a set of hazard assessment procedures and models that can 

be sequentially utilized to evaluate consequences of potential discharges of hazardous material and thereby 

assist in the development of a basis for emergency planning. ARCHIE can help emergency planning 

personnel understand: 1) the nature and magnitude of hazards posing a threat to their jurisdiction; 2) the 

sequence of events that must take place for these threats to be realized; and ultimately 3) the nature of 

response actions that may be necessary to mitigate adverse impacts upon the public and its property in the 

event of an emergency. 
P.13 

The system contains numerous models for evaluating different types of releases and their consequences, 

such as pool fires, unconfined vapor doud explosions, fireballs, and tank overpressurization. More details 

about the system are presented in Appendix. B, Section B.2. 

53 The "Yellow Book" Methodology 

The Bureau of Industrial Safety (TNO) of the Netherlands has issued a report, commissioned by the 

Directorate-General of Labour, entitled "Methods for the Calculation of the Effects of the Escape of 

Dangerous Material" (March 9,1980), also known as the "Yellow Book". Equations and calculation 

methods for estimating the effects of several types of acddents involving flammable liquids and gases are 

presented. Some of these methods were used as the basis for models in WHAZAN. The Yellow Book 

indudes calculations for pool fires, vapor cloud fires, and vapor cloud explosions for gases, and pool fires 

and vapor cloud fires for liquids. For gases, two different methodologies are used for vapor doud fires: 

the flash fraction of each gas is modelled as an instantaneous release; the non-flashed fraction is modelled 

as a continuous release from an evaporating pool. In both cases, dispersion as a neutrally buoyant cloud is 

assumed. The flash fraction of each gas is used to calculate the vapor cloud explosion results. Since there 

is no calculated flash fraction for liquids, no vapor cloud explosion results appear for liquids. Appendix B, 

Section B3 presents details of the calculations that were used in this analysis. 

SA AIChE-Sponsored Course Materials 

The American Institute of Chemical Engineers (AIChE) sponsored course material titled, "Methods for 

Calculation of Fire and Explosions Hazards" (1987), presents equations for calculating the effects of 

several types of acddents involving flammable liquids and gases. This material is a compendium of 

methods and algorithms dealing with fires and explosions, not a straightforward approach to determining 

consequences of various acddent scenarios. The equations used in this analysis and details of the 

methodology are presented in Appendix B, Section B.4. 

5.5 The "Green Book" Methodology 

EPA hi conjunction with FEMA and DOT, developed the "Technical Guidance for Hazards Analysis" 

(1987) to provide guidance to local emergency planning committees (LEPCs), local emergency agendes, 

and community groups in assessing hazards related to potential airborne releases of extremely hazardous 

substances listed because of their toxidty under section 302 of SARA Title in. This guidance, known as 

the "Green Book," provides methods for estimating chemical releases and dispersion distances. These 

methods were applied to the airborne dispersion of vapor clouds of flammable liquids and gases to 

estimate distances for vapor cloud fires. See Appendix B, Section B.5 for details of the calculations. 

6.0 Consequence Analysis Approach 

There are many factors that affect the severity of the consequences of an acddent involving a flammable 

chemical. It is impossible to list all of these factors, espedally those that are site-specific (e.g., 

characteristics of terrain, local micrometeorological effects such as slight wind shifts, nearby facilities, and 

population). The inputs to the various hazard analysis models used that may have an impact on acddent 

consequences include the following: 

• Specific physical/chemical propenies of the chemical involved (e.g., volatility and 

heat of combustion); 

• The quantity of the chemical involved; 

• The type of release (instantaneous or prolonged); 
P.14 

• The initial conditions (temperature and pressure) of the chemical just prior to 

release; 

• Meteorology (particularly when modelling scenarios that involve dispersion). 

These factors and their relationship to consequence modelling are discussed below. 

6.1 Acddent Scenarios 

The WHAZAN model (discussed in Section 5.1 and detailed in Appendix B, Section B.1) was applied to 

flammable liquids and gases to determine the distance that might be affeded for various types of acddents, 

using vaiying quantities released and various hazard criteria levels. Among the literature sources 

examined, there appears to be a general consensus regarding the types of acddents in which flammable 

substances typically are involved. The acddents of concern include vapor doud explosions, vapor cloud 

fires, Boiling Liquid Expanding Vapor Explosions (BLEVEs), pool fires, and jet fires. Each of these 

acddent types is described below. 

6.1.1 Vapor Qoud Explosions 

Volatile materials can form vapor clouds when they are released in an uncontrolled manner from 

containment vessels. Materials that are at elevated temperatures and/or pressures are particularly of 

concern. Released volatile, flammable materials can flash directly into the vapor state and/or flow to the 

ground and form a pool of liquid which subsequently evaporates to form a vapor cloud. After a vapor 

cloud is formed, three things can happen: it can disperse and have no fire or explosion impact on 

neighboring communities; it can ignite and burn (vapor cloud fire); or it can detonate or explode and 

cause high pressure shock waves. For a vapor cloud to ignite and burn or explode its concentration in air 

must be within its flammability limits. 

A vapor cloud fire or explosion is more likely if the cloud is confined, by, for example, a building. An 

exemplary list of chemicals that are known to have been involved in vapor cloud explosions is shown in 

Exhibit 1. Note that 12 of the 15 chemicals listed are gases under ambient conditions. 

EXHIBIT 1 - CHEMICALS KNOWN TO HAVE BEEN INVOLVED IN VAPOR CLOUD EXPLOSIONS 

Chemical 

Hydrogen 

Methane/LNG 

Ethylene 

Propylene 

Dimethyl Ether 

Propane 

Vinyl Chloride 

Isobutane 

Isobutylene 

Butadiene 

Ethylene Oxide 

Ethyl Chloride 

Gasoline 

Hexane 

Cyclohexane 

References: R.W. Prugh (1987) 

J. Skarka (1987) 

Boiling Point CO 

-253 

-161 

-102 

-46 

-43 

-42 

-24 

-14 

-12 

- 8 

11 

12 

59 

72 

81 

eP 
P.15 

Chemicals are vaporized much more rapidly by boiling than by evaporation; therefore, chemicals with 

boiling points below ambient temperatures volatilize very rapidly after being spilled and are more likely to 

generate high-mass clouds than chemicals that boil above ambient temperatures. Chemicals that are gases 

at ambient temperatures therefore represent a greater explosion hazard than less volatile chemicals with 

boiling points greater than ambient temperatures (liquids and solids). 

According to Prugh (1987), the probability ofa vapor cloud exploding appears to depend on the weight of 

flammable vapor in the cloud (Le., the quantity in the cloud above the LFL). Prugh's analysis (based on 

actual vapor Cloud explosion events) indicates that the probability of explosion is 50 percent when the 

weight of flammable vapor is 90,000 kilograms (200,000 pounds); the probability decreases with decreasing 

weight Based on an equation developed by Prugh, for vapor clouds containing less than 10,000 pounds of 

flammable vapor, the probability of explosion becomes relatively low (approximately 7 percent for 10,000 

pounds and less than 1 percent for 1,000 pounds). Prugh's probability analysis considered only the 

likelihood of a vapor doud exploding following a release, not the likelihood that a release might occur. 

The American Petroleum Institute (API) has developed recommended process hazard management 

practices (including such topics as safety reviews, hazards analyses, training, safe practices, and inddent 

investigation) for production and refining departments (API Recommended Practice 750). This document 

has an appendix detailing the application of the recommended practice to facilities that have the potential 

to release five tons of gas or vapor in a period of a few minutes. The five-ton quantity was chosen by API 

as a reasonable threshold on the basis of catastrophic potential and probability of explosion. For a vapor 

cloud containing five tons of hydrocarbon, API considers the probability of explosion to be about 5 

percent, compared to less than 1 percent for one ton or less (API 1990). 

Vapor cloud explosions have occuned at quantities as low as 20 kg, but the damage they have produced 

has been very localized and of little concern regarding injuries and losses. Significant blast effects under 

semi-confined conditions have occuned for quantities as low as 100 kg (220 pounds). Releases as great as 

1,000 metric tons have been identified, but they have usually produced fires or firestorms. The rate of 

discharge has a large influence on air mixing. Rates of discharge lower than about 0.25 metric tons of fuel 

per minute do not seem to be a severe aerial explosion risk (Lewis 1980), probably because inadequate 

mixing keeps the air/chemical concentration below required explosive limits. 

In addition, the presence of objects in the cloud's path appears to affect the likelihood of explosion. 

Wiekema (1984) concludes that, "...when no sizable objects were in the cloud no explosions have been 

recorded, and that in fact, the presence of obstacles and confinement is a necessary condition for an 

explosion to occur." He also notes that, "...an ignition within about one minute after the beginning of the 

release will enhance the possibility of an explosion." Over 60% of the vapor clouds studied ignited within 

100 meters of the release site. A study by Prugh (1987) concludes that the occunence of a vapor cloud 

explosion rather than a vapor cloud fire (both of which occur under similar circumstances) depends upon 

the location of the ignition source and the amount of turbulence or mixing in the cloud. For an 

unconfined vapor cloud explosion to occur, "turbulent mixing of vapor and air, ignition of the cloud at a 

point remote from the source, and (probably) a minimum amount of vapor at concentrations within the 

flammable range (Kletz 1977; Lees 1980) are required." Skarka (1987) concludes that only the central 

zone of the cloud of vapors mixed with air inside the explosion limits can cause and contribute to the 

explosion. 

Many flammable gases have relatively high theoretical TNT equivalents compared to commerdal 

explosives, where the TNT equivalent is the relative weight of trinitrotoluene (TNT) that produces the 

same effect as is produced at a given distance by the material under consideration. Commerdal explosives 

generally have TNT equivalents between roughly 0.3 and 2. The theoretical TNT equivalent for flammable 

gases indicates the explosive potential, assuming the material explodes completely, calculated values 

reported by Prugh (1987) range from 4.5 (for vinyl chloride) to 34 (for hydrogen). For most hydrocarbons, 

the theoretical TNT equivalent is about 12 (Prugh 1987). However, in vapor cloud explosions, it appears 

that only a fraction of the vapor in the cloud explodes. (In contrast, for commerdal explosives, most of 

the explosive material present is expected to be involved in the explosion.) For example, Prugh (1987) 

%* 
P.16 

-9-

reports that for vapor cloud explosions of hydrocarbons, the observed TNT equivalent was 1.0, compared 

to the theoretical TNT equivalent of 12. For modelling the consequences of vapor cloud explosions, a 

"yield factor" is applied to account for the unexploded vapor in the doud. 

Vapor doud explosions are a real concern to communities neighboring industrial Chemical facilities. For 

example, in 1973, a massive vapor cloud explosion occuned in Flixborough, England, following the rupture 

of a pipe carrying cyclohexane at 145°C and 120 psi. Fifty to 60 metric tons of cyclohexane were released. 

The explosion destroyed the chemical plant, killing 29 people (most of them in the plant control room), 

and damaged buildings 1/2 to 3/4 miles away, window breakage was reported up to eight miles from the 

plant (Eisenberg et aL 1975). 

6.1.2 Vapor Qoud Fires 

Vapor cloud fires are similar to vapor cloud explosions except extreme overpressures are not generated. 

Instead, the hazard associated with them is a rapidly moving flame front If a vapor doud or plume 

contacts an ignition source at a point at which its concentration is within the range of its upper and lower 

flammable limits, a wall of flame may flash back towards the source of the gas or vapor (HCHAP 1989). 

These vapor cloud fires are also refened to as flash fires. Following ignition of an over-rich cloud of fuel, 

a diffusion-type flame rolls back across the doud of fuel as air is mixed further with the over-rich cloud 

until all the cloud is burned (Lewis 1980). Individuals engulfed in such a vapor cloud that then ignites 

have a high probability of being killed. However, there were no reported fatalities beyond the actual vapor 

cloud due to radiation effects in a sample of vapor cloud fires examined by Wiekema (1984). He 

concludes that since the area outside of the cloud exposed to intense thermal radiation is small, no 

fatalities due to thermal radiation can be expeaed outside the area engulfed in flame. The size of the 

vapor cloud is determined by the extent to which the released material disperses in the atmosphere before 

ignition. 

6.13 BLEVEs and Fireballs 

Boiling Liquid Expanding Vapor Explosions (BLEVEs) occur when sealed tanks of liquid or gaseous 

hazardous materials are exposed to fire which may cause excessive pressures within the tank combined with 

weakening of tank walls. The sudden failure of the vessel and rapid vaporization and expansion of its 

contents is termed a BLEVE. BLEVEs also generally result in ignition of the vapor cloud when the 

substance is flammable, and a large rising fireball may form, the size of which will vary with the acddent 

conditions and the type and amount of hazardous material present. Although the fireball is generally of 

short duration, the intense thermal radiation generated can cause severe and possibly fatal burns to 

exposed people over relatively considerable distances in a matter of seconds (HCHAP 1989). 

Overpressures and container fragment projectiles also may be generated by BLEVEs but are of less 

concern than the thermal radiation (Nazario 1988). For all major fuel release inddents studied which led 

to BLEVEs, the inddent was accompanied by a major fire inddent (Lewis 1980). 

Lewis (1980) describes BLEVEs for fuels as follows: 

When a pressure vessel containing a liquefied flammable gas or a flammable liquid is 

heated by an external fire which heats the metal wall at the vapor space level, the vessel 

will rupture into a number of large pieces which will rocket considerable distances as fuel 

inside the pieces burns. This is accompanied by a large fireball and some explosive 

pressure effects produced from the liquid rapidly expanding during the propagation of 

fractures as the vessel ruptures. These pressure effects are usually minor compared with 

the fires started by heat radiation. 

The Center for Chemical Process Safety Guidelines for Chemical Process Quantitative Risk Analysis 

(CCPS 1989) describe a fireball as follows: 

^ 
P.17 

-10-

Fireball: The atmospheric burning of a fuel-air cloud in which the energy is mostly 

emitted in the form of radiant heat The inner core of the fuel release consists of almost 

pure fuel whereas the outer layer in which ignition first occurs is a flammable fuel-air 

mixture. As buoyancy forces of the hot gases begin to dominate, the burning cloud rises 

and becomes more spherical in shape. 

Several spectacular acddents have been classified as BLEVEs. One of the most notable was at a Mexico 

Qty liquefied petroleum gas (LPG) site where BLEVEs occurred involving millions of pounds of 

flammable gas and numerous tanks. Hundreds of residents in homes adjacent to the plant were killed. 

A recent article in "Chemical Engineering" suggests a guideline that if 10% of a chemical vaporizes when it 

is released to the atmosphere from a vessel, the chemical has a high potential to BLEVE (Nazario 1988). 

Pentane and lighter hydrocarbons generally satisfy this vaporization criterion when contained in vessels at 

their typical storage temperatures and pressures and released to the atmosphere. Results produced by the 

models for chemicals heavier than pentane have therefore not been considered further in this assessment; 

however, it should be noted that it is not impossible for less volatile chemicals, when subjected to elevated 

temperature and pressure conditions, to result in BLEVEs. 

6.1.4 Pool Fires 

A liquid pool fire is a fire involving a quantity of liquid fuel spilled on the surface of the land or water. 

An ignition source must start the pool fire. Primary hazards of liquid pool fires are to people and 

property involving exposure to thermal radiation and/or toxic or conosive products of combustion 

(HCHAP 1989). 

6.1.5 Jet Fires 

Transportation and storage tanks or pipelines containing compressed or liquefied gases may discharge 

gases at a high speed if somehow punctured or broken during an acddent The gas discharging or venting 

from the hole will form a gas jet that "blows" into the atmosphere in the direction the hole is facing, all 

the while entraining and mixing with air. When the gas is flammable and it encounters an ignition source, 

a flame jet of considerable length may form. For chemicals that are liquid under ambient conditions, no 

gas jet will form; liquid or vapor might leak out through a puncture or break, but will not blow out. 

j 

6.2 Chemicals, Quantities, and Conditions Used in Modelling 

A variety of chemicals were modelled for selected quantities. The chemicals, quantities, and assumptions 

made regarding type of release, temperature and pressure prior to release, and meteorological conditions, 

are discussed below. 

6.2.1 Chemicals and Quantities Chosen for Modelling 

Ten common hydrocarbons, including alkanes, alkenes, and aromatics, of widely vaiying volatility (boiling 

points from -103°C to 137°C) and flammability (as indicated by flash point) were chosen for consequence 

modelling as representative examples of a range of flammable chemicals that may be found in commerce in 

high volumes. Volatility and flammability are important characteristics in determining acddent 

consequences. The selerted chemicals included ethylene, propane, propylene, n-butane, pentane, hexane, 

heptane, toluene, p-xylene, and gasoline. Physical/chemical properties of these chemicals are listed in 

Exhibit E-2, Appendix E. Ethylene, propane, propylene, and n-butane are gases under ambient conditions; 

the other chemicals are liquids. WHAZAN modelling was carried out for releases of 1,000, 2,500, 5,000, 

7,500,10,000, 25,000, 50,000,100,000 and 180,000 pounds of each of the ten hydrocarbons to gain insight 

into the impact of the size of an acddental release on potential consequences. Results of modelling are 

presented in Section 8. 

??> 
-11-

Modelling of 100,000 pound releases of each of the ten hydrocarbons was carried out using the other 

methods discussed in Section 5 to compare the results from other models (PC-based calculation methods 

and others) with WHAZAN. The methods for all the models used are discussed in Appendix B. Results 

of modelling by all methods were found to be in reasonable agreement Eight other organic chemicals, 

including ethylene oxide, ethyl chloride, acetaldehyde, acetone, trichloroethylene, acetic add, benzaldehyde, 

and dimethyl sulfoxide were also modelled for 100,000 pound releases using the WHAZAN model for 

comparison with the hydrocarbons. Some of these chemicals (e.g., trichloroethylene and dimethyl 

sulfoxide) are not considered very flammable; they were included for comparison purposes. Results of 

modelling 100,000 pound releases of the hydrocarbons by all methods and WHAZAN results for the 

additional chemicals are presented in Exhibit D-1, Appendix D. 

622 Instantaneous and Prolonged Releases 

Instantaneous releases are those that take place over a period of time ranging from a few seconds to 

several minutes and then essentially stop. The result of such a release typically is a liquid pool, a puff of 

vapor or gas, or distinct cloud, but can also involve an explosion. A sudden catastrophic vessel failure or 

the failure of a large piping connection can be considered examples of instantaneous releases. 

Instantaneous releases were considered likely to have potentially more severe consequences than prolonged 

releases (see below) and were assumed as the type of release in the comparative modelling using all 

methods. 

Prolonged or continuous releases take place over longer periods of time and, when atmospheric dispersion 

is involved, typically produce plumes stretched out over longer distances. Failure of a small piping 

connection or of a piping gasket are examples of potential prolonged releases. For modelling purposes, 

prolonged releases were assumed to emanate from 1.5 inch diameter holes in containment vessels. This 

simulates the shearing off of a small instrument connection on a vessel or a gasket leak in a larger piece of 

piping. Prolonged releases were modelled using WHAZAN for comparison with instantaneous releases; 

the consequences are, in general, smaller. 

6.23 Initial Conditions Prior to Release 

Flammable chemicals are handled and/or stored at a wide variety of temperatures and pressures at 

industrial facilities. Conditions can range from extremely severe processing conditions (high temperature 

and pressure) to relatively low severity storage conditions. Very volatile chemicals may be stored as liquids 

under pressure and/or at low temperatures. Less volatile chemicals can be stored at ambient temperatures 

and pressures. Acddent consequence modelling is dependent on initial release conditions. Because it is 

not uncommon for storage vessels to be sited closer to plant fencelines and hence neighboring 

communities than processing equipment and because storage vessels generally contain much larger 

volumes of material than processing equipment storage temperatures and pressures that may be found in 

industiy practice were assumed as initial release conditions for modelling purposes. Temperatures and 

pressures used in modelling are listed by chemical in Exhibit E-1, Appendix E. 

6.2.4 Meteorology 

The primary meteorological conditions used for modelling by all methods were 3.0 meters per second wind 

speed and D atmospheric stability, representing average or neutral atmospheric conditions rather than 

worst case situations. More extreme conditions (for dispersion) of 1.5 meters per second wind speed and 

F atmospheric stability were also used for WHAZAN modelling to show the effect of varying 

meteorological conditions on acddent consequences. As explained in the Green Book (Technical 

Guidance 1987), these conditions correspond to stable air and low wind speed, conditions under which 

dispersion results for distances to various hazard criteria levels are generally larger than those calculated 

under conditions usually considered typical 

%^ 
P.19 

-12-

7.0 Hazard Criteria 

The extent and severity of the impacts of an acddent depends on the type of consequence that results. 

Acddents involving flammable substances can result in thermal radiation from fires or blast overpressures 

from explosions, or both. The consequences for various types of acddents have been summarized below: 

Acddent Consequence Units 

Vapor Qoud Explosion Overpressure psi 

BLEVE Thermal radiation kW/m2 

Pool Fire Thermal radiation kW/m2 

Jet Fire Thermal radiation kW/m2 

Vapor Qoud Fire Ignition of fire LFL 

where psi = pounds per square inch, kW/m2 = kilowatts per square meter, and LFL = lower flammable 

limit; these are discussed further below. 

For modelling purposes several hazard criteria levels of overpressure, thermal radiation, or concentration 

associated with each type of acddent consequence were used for modelling. The effects of the hazard 

criteria and the distances resulting from modelling can then be used by EPA in regulatory determinations. 

For a given acddent the WHAZAN model was used to calculate the distance from the acddent site to the 

chosen hazard criteria level. The hazard criteria levels that were used in modelling may have effects that 

range from minor injuiy to humans through various levels of property damage to potentially lethal effects 

on humans (see Appendix C). These are discussed below by type of acddent 

7.1 Hazard Criteria for Vapor Qoud Explosions 

The consequence of greatest concern for vapor cloud explosions is the blast wave. Blast waves from 

acddental explosions can cause damage to people and property by subjecting them to transient crushing 

pressures and winds. Relatively simple concepts have been used to conelate blast wave properties with 

damage. Blast wave damage is primarily a function of either the peak overpressure, the impulse, or some 

combination of these factors. Peak overpressure is most commonly used. For modelling vapor cloud 

explosions, overpressures of 0.3,0.5,1.0, 3.0, and 10.0 psi were considered. At an overpressure of 0.3 psi, 

10 percent of window glass may be broken (Lees 1980). An overpressure level of 0.5 psi can cause 

windows to shatter, with some frame damages (Brasie and Simpson 1968). Overpressure of 1.0 psi can 

cause partial demolition of houses and is the threshold for skin laceration from flying glass (Lees 1980). 

An overpressure level of 3.0 psi can cause steel frame buildings to become distorted and pulled away from 

their foundations (Lees 1980); this overpressure can also hurl a person to the ground (Brasie and Simpson 

1968). An overpressure of 10 psi may totally destroy buildings (Lees 1980) and is the threshold for lung 

hemonhage (U.S. DOT 1988). Appendix C, Section Ci.l, presents additional information on damage and 

injuiy caused by various overpressure levels from explosions. 

7.2 Hazard Criteria for Vapor Cloud Fires 

The minimum concentration of a vapor or gas in air that will ignite and propagate flame is known as its 

lower flammable limit (LFL) concentration or lower explosive limit (LEL) concentration. The words 

flammable and explosive are used interchangeably such that LPL values equal LEL values; the 

concentration of a fuel that will burn in air also can be expeaed to explode under the appropriate 

conditions. Similarly, the maximum concentration of a gas or vapor in air that will ignite and propagate 

flame is known as the upper flammable limit (UFL) or upper explosive limit (UEL) of the fuel (HCHAP 

1989). 

For vapor cloud fires, dispersion modelling was carried out using concentrations equal to 50 percent of the 

LFL, the LFL, and twice the LFL Levels below the LFL are used to account for variability within the 

£5 
-13-

doud from its edge to its center and inaccurades in dispersion modelling. This is based on guidance in 

the WHAZAN manual (WHAZAN 1988) which recommends the following: 

When calculating safe distances from flammable releases, these difficulties [uncertainties 

in concentration] indicate that the analyst should consider concentrations somewhat below 

the LFL. A concentration of LFL/2 or LFL/4 is normally used. 

73 Hazard Criteria for BLEVEs, Pool Fires, and Jet Fires 

The consequence of greatest concern resulting from BLEVEs, pool fires, and jet fires is heat radiation. In 

the case of BLEVEs, injuries and fatalities might also result from overpressures and container fragment 

projectiles, but thermal radiation is considered to be the consequence of greatest concern and is the 

consequence addressed in the modelling. Human injury or fatality from heat radiation from fires is likely 

to occur as a result of direct exposure to a fire rather than as a result of property damage caused by a fire. 

The extent of the injury caused by heat radiation depends both on the heat level and the time of exposure. 

The duration of the fire and the length of time it might take an exposed person to escape or take shelter 

from the fire would be important considerations. 

The WHAZAN model produces results for duration of the fire and distance from the fire for three heat 

radiation levels for BLEVEs, pool fires, and jet fires. For BLEVEs and jet fires, duration and distance 

results are produced for heat radiation levels of 4.0,12.5, and 37.5 kW/mr According to the WHAZAN 

manual, a heat radiation level of 4.0 kW/m2 would lead to a 1 percent probability of fatality after an 

exposure time of 150 seconds. For 12.5 kW/m2 the probability of fatality is 1 percent after a 30 second 

exposure and 50 percent after an exposure time of 80 seconds. For a heat radiation level of 37.5 kW/m2 

the probability of fatality is 1 percent for an 8-second exposure, 50 percent for a 20-second exposure, and 

99 percent for a 50-second exposure (WHAZAN 1988). For pool fires, WHAZAN gives results for 1.6, 

4.0, and 12.5 kW/m2. A heat radiation level of 1.6 kW/m2 would lead to a 1 percent probability of fatality 

after 500 seconds (WHAZAN 1988). Appendix C, Section C3.1, presents additional infonnation on 

thermal radiation. 

8.0 Modelling Results 

WHAZAN modelling was carried out for vapor cloud explosions, vapor cloud fires, BLEVES, pool fires, 

and jet fires of the hydrocarbons using the assumptions discussed above. WHAZAN results are presented 

in the following sections by consequence type. Resulting distances for selected quantities and several 

hazard criteria levels are provided; these results have been considered in making regulatory decisions 

regarding flammable chemicals. The inputs used for the WHAZAN model are presented in detail in 

Exhibit E-3, Appendix E. Results of modelling by other methods and additional WHAZAN results are 

presented in Exhibit D-1, Appendix D. As noted earlier, results from all the methods are in reasonable 

agreement 

8.1 Vapor Cloud Explosion Results 

Exhibit 2 presents WHAZAN modelling results for vapor cloud explosions of four hydrocarbon gases for 

quantities of 1,000 to 180,000 pounds. Ethylene and propane are assumed to be liquefied by refrigeration; 

propylene and n-butane are assumed to be liquefied under pressure. Vapor cloud explosion results could 

not be obtained for liquids under ambient conditions. The exhibit shows the fraction flashed, obtained 

from the linked models, and the quantity assumed to be in the cloud, calculated from the total quantity 

released and the fraction flashed. This quantity was used in the vapor cloud explosion stand-alone model. 

Distances calculated for several overpressure levels are presented. Although the modelling shows distances 

of approximately 100 meters for release quantities as small as about 5,000 pounds at overpressures of 1.0 

psi and lower, the probability of a vapor cloud explosion occurring is relatively low for vapor clouds 

containing quantities smaller than 10,000 pounds (API 1990, Prugh 1987), as noted earlier. Note also that 

the quantity in the cloud is considerably smaller than the quantity released; i.e., a release of 10,000 pounds 

of flammable material would probably result in a cloud containing much less than 10,000 pounds (Exhibit 

So 
P.21 

-14-

Exhibit 2 

DISTANCES FOR VAPOR CLOUD EXPLOSIONS OF FOUR UQUEFIED GASES 

FOR INSTANTANEOUS RELEASES OF LOOO TO 180,000 POUNDS 

DETERMINED USING FRACTION FLASHED, WHAZAN STAND-ALONE MODEL 

Distance in Meters to Various Overpressures 

Chemical 

(Initial 

Conditions) 

Ethylene 

(liquefied by 

refrigeration 

175 K, 1.3 Bars) 

Propylene 

(liquefied under 

pressure 

293 K, 13.3 Bars) 

Propane 

(liquefied by 

refrigeration 

232 K, 1.3 Bars) 

n-Butane 

(liquefied under 

pressure 

293 K, 6.3 Bars) 

Quantity Quantity 

Released Fraction in Cloud 

(lbs) Flashed (lbs) 

1,000 0.023 23 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

58 

115 

173 

230 

575 

1,150 

2,300 

4,140 

1,000 0.329 329 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

823 

1,645 

2,468 

3,290 

8,225 

16,450 

32,900 

59,220 

1,000 0.015 15 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 0 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

38 

75 

113 

150 

375 

750 

1,500 

2,700 

113 113 

283 

565 

848 

1,130 

2,825 

5,650 

11,300 

20,340 

0.3 psi 

(m) 

151 

205 

259 

296 

326 

443 

558 

703 

855 

372 

494 

622 

712 

801 

1,090 

1,370 

1,730 

2,100 

130 

177 

223 

255 

280 

381 

479 

604 

735 

275 

345 

434 

497 

546 

713 

936 

1,180 

1,430 

0.5 psi 

(tn) 

98 

134 

168 

193 

212 

288 

362 

457 

556 

242 

321 

404 

463 

521 

706 

890 

1,121 

1,364 

85 

115 

145 

166 

182 

247 

312 

393 

478 

179 

224 

282 

323 

355 

463 

607 

766 

933 

1.0 psi 

(m) 

57 

77 

97 

111 

122 

166 

209 

263 

321 

139 

185 

233 

267 

300 

408 

513 

647 

787 

49 

66 

83 

96 

105 

143 

180 

227 

276 

103 

129 

163 

186 

205 

267 

350 

442 

538 

3.0 psi 

(tn) 

23 

31 

39 

44 

49 

66 

84 

105 

128 

56 

74 

93 

107 

120 

163 

206 

259 

315 

20 

26 

33 

38 

42 

57 

72 

91 

110 

41 • 

52 

65 

75 

82 

107 

140 

177 

215 

10.0 psi 

(m) 

11 

15 

19 

22 

24 

33 

42 

53 

64 

28 

37 

47 

53 

60 

82 

103 

129 

157 

10 

13 

17 

19 

21 

29 

36 

45 

55 

21 

26 

33 

37 

41 

53 

70 

88 

108 

gn 
P.22 

-15-

2 shows 150 to 3300 pounds in the cloud for a release of 10,000 pounds). Distances for ethylene and 

propane, assumed to be liquefied by refrigeration, are considerably shorter than for propylene and nbutane, assumed to be liquefied under pressure, probably because at reduced temperatures less of the 

ethylene and propane are in the vapor phase to contribute to the amount flashed upon release. For 

propylene and n-butane, modelling results indicate distances greater than 100 meters for an overpressure 

of 1.0 psi for all the quantities modelled. For an overpressure of 1.0 psi, distances for propane range from 

49 meters for a 1,000 pound release to 276 meters for a 180,000 pound release, while for propylene the 

distances are from 139 meters for 1,000 pounds to 787 meters for 180,000 pounds. 

The WHAZAN calculated distances are based on "limit values" to charaderistic damage levels and the 

scaling law of distances, which states that distance is proportional to the cube root of quantity of explosive 

materiaL For TNT, empirical graphs of scaled distance versus overpressure have been derived. It was 

assumed, based on the scaling law, that the WHAZAN limit values would be proportional to the scaled 

distance values for TNT. The limit values were related to a graph of peak overpressure versus scaled 

distance for TNT from Lees (1980), the source dted in the WHAZAN manual; using this relationship and 

the descriptions of the damage levels in the WHAZAN manual, the Yellow Book, and Lees, the 

overpressure related to each limit value was estimated. For an overpressure of 0.5 psi, no limit value was 

provided; therefore, a limit value was estimated from the graph of overpressure and scaled distance and its 

relationship to the limit values. The values for 0.5 psi in Exhibit 2 are based on this estimated limit value. 

To obtain the WHAZAN modelling results presented here, the linked models were used to determine the 

fraction of liquid instantly flashed to vapor, which the model gives only for gases. The fraction flashed was 

used to estimate the flammable mass in the cloud; this quantity was used to run the stand-alone model for 

vapor cloud explosion, rather than the linked models. The linked models were not used for vapor cloud 

explosions because it was found that these models did not produce reasonable results for this type of 

consequence; Le., the quantity apparently assumed to be in the cloud seemed unreasonably high (much 

higher than the quantity that would be immediately flashed into vapor). 

Exhibit 2 shows results for ethylene and propane under low-temperature storage conditions. Ethylene and 

propane were also modelled assuming initial release conditions of higher temperatures and pressures, 

similar to the conditions assumed for propylene and n-butane; under these conditions, distances were 

similar to those found for propylene and n-butane, indicating that gases liquefied by refrigeration may pose 

less potential risk of vapor cloud explosion than gases liquefied under pressure. 

Exhibit 3 shows WHAZAN modelling results as a graph of quantity released versus distance for vapor 

cloud explosions, based on 1.0 psi overpressure. It is assumed that graphs of quantity versus distance for 

other overpressure levels would show similar increases in distance with increasing quantity released. 

Quantities released displayed on the graph range from 1,000 to 50,000 pounds. The curves shown in 

Exhibit 3 illustrate the fact that distance is proportional to the cube root of the quantity of explosive, 

according to the scaling law of distances, which is the basis for WHAZAN modelling of vapor cloud 

explosions. Thus, at a specific hazard criteria level, the smaller the quantity released, the much smaller the 

distance for experiencing the impaa. 

Exhibit C-6, in Section C1.2 of Appendix C, shows WHAZAN modelling results for releases of 100,000 

pounds of ethylene and propylene. Distances to different overpressure levels are displayed graphically. 

These results indicate that the choice of overpressure level has a significant effea on determining the 

affeaed distance, particularly at low overpressures. For example, for propylene the affeaed distance 

decreases from 1,121 meters to 647 meters if an overpressure of 1.0 psi is used rather than 0.5 psi. Similar 

decreases occur for the other chemicals. The graph of distance versus overpressure becomes relatively flat 

between overpressures of 3.0 and 10.0. 

WHAZAN modelling was also carried out using meteorological conditions of 1.5 meters per second wind 

speed and F atmospheric stability. This was done to show the impacts of varying meteorological 

conditions on accident consequences. Results for vapor cloud explosions were identical to those obtained 

using 3.0 meters per second wind speed and D atmospheric stability, indicating that the vapor cloud 

<3fc 
600 

500 

400 

OT 

__ 

O 

o 

^ 300 

o 

c 

(0 

° 200 

100 

- * -

Exhibit 3 

QUANTITY RELEASED VERSUS DISTANCE 

FOR VAPOR CLOUD EXPLOSIONS, INSTANTANEOUS RELEASES 

WHAZAN Modelling for 1,000-50,000 pounds, 1.0 psi Overpressure 

Ethylene41 

Propylene** 

Propane * 

n-Butane ** 

10 20 30 40 

Quantity Released (thousands of pounds) 

50 

* Liquified by refrigeration 

** Liquefied under pressure 
P.24 

-17-

explosion results using WHAZAN are not dependent on meteorological assumptions made. These results 

are presented in Exhibit D-1, Appendix D. 

WHAZAN modelling for a prolonged release was also undertaken to compare the results of assuming an 

instantaneous versus a prolonged release. However, this attempt, which used moderate meteorological 

conditions, produced no vapor cloud explosion results. It was not possible to determine why the model 

produced no vapor doud explosion data for prolonged releases. ARCHIE modelling was then tried for 

modelling prolonged releases (assuming a 1.5-inch hole) of 1,000 to 10,000 pounds of propylene. In the 

case of a liquid release, the results for both instantaneous and prolonged releases were essentially identical; 

therefore, these results are not presented here. If a prolonged gas release was assumed, the model 

calculated the same distances for each different quantity released. Releases of other gases would probably 

provide similar results. These results are not logically consistent and the particular reason(s) for the 

inconsistendes are not known. However, this may be a function of the limitations of the ARCHIE model 

at small release quantities. 

S2 Vapor Qoud Fire Results 

Exhibit 4 displays the results of dispersion modelling using WHAZAN for vapor clouds of flammable 

liquids and gases. The data presented include the downwind and crosswind distances at which the 

concentration in the cloud is equal to 50 percent of the LFL, the LFL, and twice the LFL. The downwind 

distance is the maximum distance at which the specified concentration is reached; the crosswind distance is 

the width of the cloud of flammable vapor at that point The modelled aosswind distances are much 

smaller than the downwind distances, roughly 6 percent, for the chemicals and conditions analyzed. For a 

given downwind distance, the total area (as a function of downwind and aosswind distance) potentially 

affeaed by a vapor cloud fire is likely to be much smaller than the area that might be affeded by a vapor 

cloud explosion; for a fatality to result, a person would have to be located within the limited area covered 

by the vapor cloud and engulfed in the ensuing fire. 

The largest modelled downwind distance results (approximately 1,800 meters) were for a release of 180,000 

pounds of ethylene; a 1,000 pound release of p-xylene showed the smallest downwind distance (about 20 

meters) results. Ethylene also provided the largest downwind distance and p-xylene the smallest at the 

other hazard criteria levels analyzed for vapor cloud fires. 

Vapor cloud fires were modelled using WHAZAN by running the linked WHAZAN models to obtain the 

pool evaporation rate, which is also shown in Exhibit 4. The pool evaporation rate was used as the release 

rate for the stand-alone buoyant plume dispersion model. Note that the fraction flashed cannot be used 

with the buoyant plume dispersion model; therefore, the results shown here do not include the quantity of 

gas immediately flashed into vapor on release, but only the quantity that evaporates from a pool. For 

propylene and n-butane, gases assumed to be liquefied under pressure, the fraction flashed is appredable 

(33 percent for propylene, 11 percent for n-butane), indicating the calculated distances for these materials 

may be understated. 

Exhibit 5 presents WHAZAN vapor cloud fire results as a graph of quantity released versus distance for 

instantaneous releases, assuming moderate meteorological conditions and modelling to a concentration 

equal to 50 percent of the LFL. Distances are clearly not linearly related to the quantity released; Le., 

inaeasing the quantity released by a faaor of ten increases the distance by a faaor of approximately two 

and one-half for the chemicals modelled. 

Exhibit C-7, in Section C2 of Appendix C is a graphical presentation of results based on 50 percent of the 

LFL, the LFL, and twice the LFL for vapor cloud fires for two hydrocarbons. This analysis was done to 

determine the sensitivity of the model results to changes in the flammable limit level. Using the LFL 

rather than 50 percent of the LFL for 100,000 pounds of ethylene lowers the affeaed distance, as would be 

expeaed, but by much less than a faaor of two. The effea of changing from the LFL to twice the LFL is 

even smaller. The data presented in Exhibit 4 show there is little difference in distance based on varying 

the hazard criteria levels for the other chemicals analyzed. 

qo 
Exhibit 4 

DISTANCES FOR VAPOR CLOUD FIRES FROM EVAPORATING POOLS 

FROM INSTANTANEOUS RELEASES, MODERATE METEOROLOGY*, 

DETERMINED USING WHAZAN 

Distance in Meters to Three Concentrations 

1/2 LFL LFL 2 LFL 

Chemical 

(Initial 

Conditions) 

Ethylene 

(liquefied by 

refrigeration 

175 K, 1.3 Bars) 

Propylene 

(liquefied under 

pressure 

293 K, 13.3 Bars* 

Propane 

(liquefied by 

refrigeration 

232 K, 1.3 Bars) 

Quantity 

Released 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

i 7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

Evaporation 

Rate 

(Ib/s) 

60 

115 

190 

254 

313 

611 

1,012 

1,678 

2,580 

20 

42 

68 

90 

110 

214 

353 

587 

900 

24 

49 

79 

108 

132 

260 

430 

712 

1,091 

Downwind 

Distance 

(m) 

203 

294 

391 

462 

522 

768 

1,030 

1,390 

1,810 

106 

158 

207 

242 

270 

394 

527 

705 

905 

112 

162 

214 

254 

285 

417 

557 

747 

959 

Crosswind 

Distance 

(m) 

13 

18 

24 

28 

31 

45 

58 

77 

97 

7 

10 

13 

15 

17 

24 

31 

41 

52 

7 

10 

13 

16 

18 

25 

33 

43 

54 

Downwind 

Distance 

(n) 

138 

199 

264 

311 

351 

514 

688 

925 

1.190 

74 

107 

141 

164 

184 

266 

354 

473 

605 

TT 

110 

145 

172 

193 

282 

375 

500 

640 

Crosswind 

Distance 

(m) 

9 

13 

16 

19 

21 

31 

40 

53 

67 

5 

7 

9 

10 

12 

17 

22 

28 

36 

5 

7 

9 

11 

12 

17 

23 

30 

38 

Downwind 

Distance 

(m) 

95 

135 

179 

211 

237 

346 

462 

618 

793 

60 

87 

112 

131 

147 

212 

281 

375 

479 

55 

77 

99 

117 

131 

191 

253 

337 

430 

Crosswind 

Distance 

(m) 

6 

9 

11 

13 

15 

21 

28 

36 

46 

4 

6 

7 

9 

9 

13 

17 

23 

29 

4 

5 

7 

8 

9 

12 

16 

21 

26 

9° 

ja 

* Wind speed 3.0 meters per second, atmospheric stability class D. 
-

X> 

9X> 

Chemical 

(Initial 

Conditions) 

n-Butane 

(liquefied under 

pressure 

293 K, 6.3 Bars) 

Pentane 

(293 K, 

2.74 Bars) 

Gasoline 

(293 K, 

1.013 Bars) 

-

Quantity 

Released 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25.000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

* Wind speed 3.0 meters per 

Exhibit 4 

DISTANCES FOR VAPOR CLOUD FIRES FROM EVAPORATING POOLS 

FROM INSTANTANEOUS RELEASES, MODERATE METEOROLOGY", 

Evaporation 

Rate 

(Ib/s) 

11 

24 

40 

53 

64 

126 

209 

346 

534 

7 

15 

24 

33 

40 

77 

128 

212 

326 

7 

13 

22 

29 

35 

71 

117 

194 

298 

second, atmospher 

DETERMINED USING WHAZAN 

(continued] 1 

Distance in Meters to Three Concentrations 

1/2 LFL 

Downwind 

Distance 

(m) 

73 

103 

135 

159 

178 

259 

345 

460 

588 

53 

81 

101 

120 

133 

193 

256 

341 

435 

55 

78 

100 

115 

132 

191 

254 

338 

431 

ic stability 

Crosswind 

Distance 

(m) 

5 

7 

9 

10 

11 

16 

21 

28 

35 

4 

5 

7 

8 

9 

12 

16 

21 

26 

4 

5 

7 

8 

9 

12 

16 

21 

26 

class D. 

LFL 

Downwind 

Distance 

(m) 

49 

73 

93 

108 

120 

175 

233 

309 

396 

38 

57 

72 

84 

92 

131 

173 

230 

294 

39 

55 

71 

81 

89 

130 

172 

228 

290 

Crosswind 

Distance 

(m> 

3 

5 

6 

7 

8 

11 

15 

19 

24 

3 

4 

5 

6 

6 

9 

11 

14 

18 

3 

4 

5 

5 

6 

8 

11 

14 

18 

**• 

2 LFL 

Downwind 

Distance 

. (m) 

35 

52 

66 

76 

84 

119 

158 

209 

267 

27 

41 

51 

59 

65 

90 

118 

156 

199 

28 

39 

50 

57 

63 

89 

117 

155 

196 

Crosswind 

Distance 

(m) 

2 

3 

4 

5 

6 

8 

10 

13 

17 

2 

•• 3 

3 

4 

4. 

6 

8 

10 

13 

2 

3 

3 

4 

4 

6 

8 

10 

12 

-

-

-

i 

£ 

• 
Exhibit 4 

DISTANCES FOR VAPOR CLOUD FIRES FROM EVAPORATING POOLS 

FROM INSTANTANEOUS RELEASES, MODERATE METEOROLOGY*, 

DETERMINED USING WHAZAN 

(continued) 

Distance in Meters to Three Concentrations 

1/2 LFL LFL 2 LFL 

Chemical 

(Initial 

Conditions) 

Hexane 

(293 K, 

1.013 Bars) 

Heptane 

(293 K, 

1.013 Bars) 

Toluene 

(293 K, 

1.013 Bars) 

Quantity 

Released 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

Evaporation 

Rate 

(lb/s) 

4 

9 

13 

18 

22 

44 

73 

121 

185 

2 

4 

i 9 

11 

13 

26 

42 

71 

108 

2 

4 

7 

9 

9 

20 

33 

53 

82 

Downwind 

Distance 

(m) 

41 

58 

71 

82 

91 

133 

176 

233 

297 

29 

41 

58 

65 

71 

99 

130 

173 

219 

31 

43 

53 

61 

64 

89 

117 

154 

196 

Crosswind 

Distance 

(m) 

3 

4 

5 

5 

6 

9 

11 

15 

18 

2 

3 

4 

4 

5 

7 

9 

11 

14 

2 

3 

4 

4 

4 

6 

8 

10 

12 

Downwind 

Distance 

(m) 

29 

41 

50 

58 

65 

91 

119 

158 

201 

21 

29 

41 

46 

50 

71 

89 

118 

150 

22 

31 

37 

43 

43 

64 

83 

105 

134 

Crosswind 

Distance 

(m) 

2 

3 

3 

4 

4 

6 

8 

10 

13 

1 

2 

3 

3 

3 

5 

6 

8 

10 

1 

2 

2 

3 

3 

4 

6 

7 

9 

Downwind 

Distance 

(m) 

21 

29 

36 

41 

46 

65 

83 

108 

136 

15 

21 

29 

33 

36 

50 

63 

82 

101 

16 

22 

27 

31 

31 

46 

59 

74 

92 

Crosswind 

Distance 

(m) 

1 

2 

2 

3 

3 

4 

6 

7 

9 

1 

1 

2 

2 

2 

3 

4 

5 

7 

1 

1 

2 

2 

2 

3 

4 

5 

6 

s 

LP 

Wi-nd speed 3.0 meters per second, atmospheric stability class D. 
Exhibit 4 

DISTANCES FOR VAPOR CLOUD FIRES FROM EVAPORATING POOLS 

FROM INSTANTANEOUS RELEASES, MODERATE METEOROLOGY*, 

DETERMINED USING WHAZAN 

(continued) 

Distance in Meters to Three Concentrations 

1/2 LFL LFL 2 LFL 

Chemical 

(Initial 

Conditions) 

p-Xylene 

(293 K, 

1.013 Bars) 

Quantity 

Released 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000-

100,000 

180,000 

Evaporation 

Rate 

(tb/s) 

1 

2 

4 

4 

7 

11 

20 

31 

49 

Downwind 

01 stance 

(m) 

21 

30 

42 

42 

48 

67 

86 

111 

141 

Crosswind 

Distance 

(m) 

1 

2 

3 

3 

3 

4 

6 

7 

9 

Downwind 

Distance 

(m) 

15 

21 

30 

30 

36 

47 

63 

78 

97 

Crosswind 

Distance 

(m) 

1 

1 

2 

2 

2 

3 

4 

5 

7 

Downwind 

Distance 

(m) 

11 

15 

21 

21 

26 

33 

44 

55 

69 

Crosswind 

Distance 

(m) 

1 

1 

1 

1 

2 

2 

3 

4 

5 

S> 

* Wind speed 3.0 meters per second, atmospheric stability class D. 
1200 

1000 — 

8 00 

CA 

k. 

o 

a> 

E 

**^ 

9 

O 

c 

(0 

w 

Q 

600 — 

4 00 

2 00 

Exhibit 5 

QUANTITY RELEASED VERSUS DISTANCE 

FOR VAPOR CLOUD FIRES, INSTANTANEOUS 

RELEASES, MODERATE METEOROLOGY 

WHAZAN Modelling for 1,000-50,000 Pounds, 50% LFL 

10 

* Llqu.fl.d by -•frlgtration 

** Liqu*fi*d undar pr*(*ur• 

fe 

20 30 40 

Quantity Released (thousands of pounds) 

50 
-23-

WHAZAN modelling was also carried out for the ten chemicals shown in Exhibit 4 using additional 

meteorological conditions of wind speed of 1.5 meters per second and F atmospheric stability as inputs, for 

comparison with the results obtained using the average meteorological conditions. The WHAZAN results 

for vapor doud fires appear to be strongly dependent on the meteorological assumptions made, with 

distances determined using worst case meteorology being much greater than those resulting from 

modelling using moderate meteorology. Distances for a concentration equal to 50 percent of the LFL 

under worst case meteorological conditions extend from 1,790 to 6350 meters for gases, compared to 460 

to 1^90 meters under moderate conditions. These results are presented in Exhibit D-1, Appendix D. 

Exhibit D-1, Appendix D, also includes results of WHAZAN modelling for prolonged releases of ten 

chemicals, where release was assumed to take place from 1.5 inch diameter holes in 12 foot diameter 

tanks. Distances to the 50 percent of the LFL level for vapor cloud fires are much smaller (18 to 79 

meters) than for instantaneous releases, indicating that using instantaneous release conditions is, in 

general, more conservative than using prolonged release conditions. 

83 BLEVE Results 

Exhibit 6 presents WHAZAN modelling results for BLEVEs of gases (ethylene, propylene, propane, and 

n-butane) and for pentane, a volatile liquid assumed to be stored under pressure, for release quantities of 

1,000 pounds to 180,000 pounds. Distances for three levels of heat radiation and the duration of the 

BLEVEs are shown. These data are all important components in analyzing the consequences of BLEVEs, 

which are a function- of exposure to heat radiation levels for the duration of the resulting fireball. As 

noted in Section 6.13, pentane and lighter hydrocarbons have charaaeristics (Le., 10 percent of the 

chemical vaporizes when it is released to the atmosphere from a vessel) that give them a high potential to 

be involved in BLEVEs (Nazario 1988). While heavier hydrocarbons may be subjea to BLEVEs under 

some conditions, the likelihood of occurrence of a BLEVE is much smaller for such chemicals; therefore, 

WHAZAN BLEVE results for hydrocarbons heavier than pentane are not included in Exhibit 6. 

The most volatile of the chemicals analyzed, ethylene, shows the greatest distances, and the least volatile, 

pentane, the smallest; however, distances do not vary greatly from chemical to chemical. For release 

quantities of less than 10,000 pounds, at a heat radiation level of 12.5 kW/m2, distances for ethylene vary 

from 82 meters for 1,000 pounds to 179 meters for 10,000 pounds. For pentane, the range is 56 meters for 

1,000 pounds to 120 meters for 10,000 pounds. 

The duration of a BLEVE as estimated by WHAZAN appears to depend only on the quantity released; it 

does not vary by chemical. For release quantities of 10,000 pounds or less, WHAZAN shows the BLEVE 

duration to range from 8 seconds for 1,000 pounds to 17 seconds for 10,000 pounds. As noted earlier, the 

WHAZAN manual (WHAZAN 1988) suggests that at a heat radiation level of 12.5 kW/m2, there would 

be a 1 percent probability of fatality for a 30 second exposure. Therefore, for BLEVEs lasting less than 30 

seconds, as is the case for BLEVEs involving quantities less than 10,000 pounds, a higher heat radiation 

level might be of greater interest (e.g., 37.5 kW/m2 rather than 12.5 kW/m2), as exposure could not last 

longer than 20 seconds. For a heat radiation level of 37.5 kW/m2, distances for ethylene are 39 meters for 

a 1,000 pound release and 103 meters for a 10,000 pound release. 

Exhibit 7 shows WHAZAN results, presented graphically, for BLEVEs of 1,000 to 50,000 pounds of 

hydrocarbons. The graph of released quantity versus distance indicates that distance is proportional to the 

cube root of quantity, as was the case for vapor cloud explosions. 

Exhibit C-10, in Section C3.2 of Appendix C, presents BLEVE results, in graphical form, from WHAZAN 

modelling of two hydrocarbons for three heat radiation levels, to test the model results for sensitivity to 

vaiying hazard criteria levels. For ethylene and propylene, using 37.5 kW/m2 rather than 12.5 kW/m2 

appears to have a relatively small effea on results; using 4 kW/m2 rather than 12.5 kW/m2 appears to have 

a greater effea. 

% 
P.31 

-24-

Exhlbit6 

DISTANCES FOR BLEVES 

FOR INSTANTANEOUS RELEASES OF 1,000 TO 180,000 POUNDS 

DETERMINED USING WHAZAN 

Distance in Meters to Three Heat Radiation Levels 

Chemical 

(Initial 

Conditions) 

Ethylene 

(liquefied by 

refrigeration 

175 K, 1.3 Bars) 

Propylene 

(liquefied under 

pressure 

293 K, 13.3 Bars) 

Propane 

(liquefied by 

refrigeration 

232 K, 1.3 Bars) 

n-Butane 

(liquefied under 

pressure 

293 K, 6.3 Bars) 

Quantity 

Released 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

Distance to 

4.0 kW/m2 

(m) 

146 

198 

250 

287 

316 

430 

543 

685 

835 

108 

147 

185 

212 

234 

318 

402 

508 

618 

104 

142 

179 

206 

227 

308 

389 

492 

599 

101 

137 

173 

199 

219 

298 

376 

475 

579 

Distance to 

12.5 kU/m2 

(m) 

82 

112 

141 

162 

179 

243 

307 

388 

472 

61 

83 

105 

120 

132 

180 

227 

287 

350 

59 

80 

102 

116 

128 

174 

220 

278 

339 

57 

78 

98 

112 

124 

169 

213 

269 

328 

Distance to 

37.5 kU/«2 

(m) 

47 

65 

82 

94 

103 

140 

177 

224 

273 

35 

48 

60 

69 

76 

104 

131 

166 

202 

34 

46 

59 

67 

74 

101 

127 

161 

196 

33 

45 

57 

65 

72 

97 

123 

155 

189 

BLEVE 

Duration 

(sec) 

8 

11 

14 

16 

17 

23 

29 

36 

44 

8 

11 

14 

16 

17 

23 

29 

36 

44 

8 

11 

14 

16 

17 

23 

29 

36 

44 

8 

11 

14 

16 

17 

23 

29 

36 

44 

qn 
P.32 

-25-

Exhlbit 6 

DISTANCES FOR BLEVES 

FOR INSTANTANEOUS RELEASES OF 1,000 TO 180,000 POUNDS 

DETERMINED USING WHAZAN 

Distance in Meters to Three Heat Radiation Levels 

(continued) 

Chemical 

(initial 

Conditions) 

Pentane 

(293 K, 

2.74 Bars) 

Quantity 

Released 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

Distance to 

4.0 kW/m2 

On) 

101 

137 

173 

199 

219 

298 

376 

475 

579 

Distance to 

12.5 kU/m2 

(m) 

57 

78 

98 

112 

124 

169 

213 

269 

328 

Distance to 

37.5 kW/m2 

(m) 

33 

45 

57 

65 

72 

97 

123 

155 

189 

BLEVE 

Duration 

(sec) 

8 

11 

14 

16 

17 

23 

29 

36 

44 

tfc 
350 

300 

250 

(0 

o 

u c 

(0 •#•" 

(0 

5 

200 

150 

100 

50 

Exhibit 7 

QUANTITY RELEASED VERSUS DISTANCE 

FOR BLEVES, INSTANTANEOUS RELEASES 

WHAZAN Modelling for 1,000-50,000 Pounds, 12-5 kW/m2 

-H-- Ethylene 

-0 Propylene 

-B Propane* 

-A n-Butane* 

¥ 

10 20 30 40 

Quantity Released (thousands of pounds) 

50 

* Liquefied by refrigeration 

** Liquefied undar preaeure 
-27-

WHAZAN modelling was also carried out for BLEVEs using worst case meteorological conditions. 

Vaiying the meteorological conditions appeared to have no effea; results obtained were identical to the 

results obtained using moderate meteorological conditions, indicating that meteorological conditions would 

be expeaed to have little impaa on the consequences of BLEVEs. Results are presented in Exhibit D-1, 

Appendix D. 

WHAZAN modelling assuming a prolonged release for a BLEVE gave results identical to those assuming 

an instantaneous release, as shown in Exhibit D-1, Appendix D. As BLEVEs result from sudden vessel 

failure, they would always be essentially instantaneous; therefore, it is not clear that any distinction can be 

made between instantaneous versus prolonged release input in modelling BLEVEs. 

8.4 Pool Fire Results 

Exhibit 8 presents WHAZAN modelling results for pool fires resulting from releases of 1,000 to 180,000 

pounds of ten hydrocarbons. Distances are given for three levels of heat radiation. The initial quantity in 

the pool and the duration of the fire are also provided. 

For all the chemicals shown in Exhibit 8, distances for releases smaller than 10,000 pounds are less than 

100 meters. The distance results for pool fires do not vary greatly by chemical, possibly because all of the 

chemicals shown here are hydrocarbons, and all have similar heats of combustion. (WHAZAN produced 

somewhat smaller distances for a given quantity of several organic chemicals with differing heats of 

combustion; see Exhibit D-1, Appendix D.) Ethylene and propane, the two gases assumed liquefied by 

refrigeration, show greater distances than propylene and n-butane, gases assumed to be liquefied under 

pressure. Larger quantities of the pressurized gases flash into vapor on release than for the refrigerated 

gases; therefore, the quantity in the pool would be larger for the refrigerated gases, and the greater 

distances would be expeaed. 

The pool fire duration data range from about 20 seconds for 1,000 pounds of propylene to approximately 2 

minutes for 180,000 pounds of p-xylene. After that time the material in the pool is consumed, 

extinguishing the pool fire. The data for a specific quantity and hazard criteria level are fairly consistent 

from chemical to chemical. 

The WHAZAN pool fire results are presented graphically in Exhibit 9 for releases of 1,000 to 50,000 

pounds. The graph of quantity released versus distance indicates that distance is proportional to the cube 

root of the quantity released, as was the case for vapor cloud explosions and BLEVEs. 

Exhibit C-ll, in Section C3.2 of Appendix C, presents WHAZAN modelling results, in graphical form, for 

ethylene and propylene, showing the effea of using different heat radiation levels. As was the case for 

BLEVEs, using a different heat radiation level appears to have a greater effea on distance at lower levels 

than at higher levels. The graph indicates that basing results on 10 kW/m2, as in ARCHIE modelling (see 

Exhibit D-1, Appendix D), rather than 12.5 kW/m2, probably does not have a great effea on the results. 

WHAZAN modelling of pool fires for ten chemicals using worst case meteorology gave results identical to 

those obtained using moderate meteorology, indicating that meteorological conditions probably do not 

have much effea on pool fire consequences. These results are presented in Exhibit D-1, Appendix D. 

WHAZAN pool fire results for prolonged releases (assuming release from a hole with a diameter of 1.5 

inches) of 100,000 pounds of ten chemicals are presented in Exhibit D-1, Appendix D; results for 

instantaneous releases are also included for comparison. Distances for prolonged releases are much 

smaller (9 to 23 meters compared to 152 to 182 meters) than for instantaneous releases, again indicating 

that the input of instantaneous release type is more conservative than assuming a prolonged release. 

\5D 
-28-

Exhlbit8 

DISTANCES FOR POOL FIRES 

FOR INSTANTANEOUS RELEASES OF 1,000 TO 180,000 POUNDS 

DETERMINED USING WHAZAN 

Distance in Meters to Three Heat Radiation Levels 

Chemical 

(Initial 

Conditions) 

Ethylene 

(liquefied by 

refrigeration 

(175 K, 1.3 Bars) 

Propylene 

(liquefied under 

pressure 

293 K, 13.3 Bars) 

Propane 

(liquefied by 

refrigeration 

232 K, 1.3 Bars) 

n-Butane 

(liquefied under 

pressure 

(293 K, 6.3 Bars) 

Quantity 

Released 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

Quantity 

In Pool 

(lbs) 

977 

2,448 

5,000 

7,321 

9,768 

24,476 

46,526 

97,682 

175,739 

650 

1,678 

3,352 

5,027 

6,483 

16,229 

32,414 

64,827 

116,865 

986 

2,470 

4,917 

7,387 

9,856 

24,696 

49,172 

98,564 

177,282 

858 

2,227 

5,005 

6,659 

8,577 

21,433 

42,777 

85,775 

154,350 

Poolfire 

Radius 

(m) 

11 

15 

19 

23 

25 

36 

46 

60 

74 

9 

13 

17 

20 

21 

30 

39 

51 

64 

10 

15 

19 

22 

25 

35 

45 

58 

73 

10 

14 

18 

21 

23 

32 

42 

54 

67 

Distance to 

1.6 kW/m2 

(m) 

112 

151 

190 

217 

238 

321 

403 

506 

614 

100 

136 

170 

194 

211 

284 

356 

447 

542 

114 

153 

192 

219 

241 

324 

407 

511 

620 

110 

150 

188 

214 

232 

313 

393 

493 

598 

Distance to 

4.0 kW/tn2 

(tn) 

72 

96 

120 

137 

150 

203 

255 

320 

388 

63 

86 

108 

123 

133 

180 

225 

283 

343 

72 

97 

121 

139 

152 

205 

257 

323 

392 

70 

95 

119 

135 

147 

198 

249 

312 

378 

Distance to 

12.5 kW/m2 

(m) 

40 

54 

68 

TT 

85 

115 

144 

181 

220 

36 

49 

61 

69 

75 

102 

128 

160 

194 

41 

55 

69 

78 

86 

116 

146 

183 

222 

39 

54 

67 

77 

83 

112 

141 

176 

214 

Poolfire 

Duration 

(sec) 

26 

32 

38 

42 

45 

57 

68 

81 

94 

22 

28 

33 

36 

39 

49 

58 

69 

80 

25 

31 

37 

41 

44 

55 

65 

78 

90 

23 

29 

35 

38 

41 

51 

61 

73 

84 

101 
-29-

Exhlbit8 

DISTANCES FOR POOL FIRES 

FOR INSTANTANEOUS RELEASES OF 1,000-180,000 POUNDS 

DETERMINED USING WHAZAN 

Distance in Meters to Three Heat Radiation Levels 

(continued) 

Chemical 

(Initial 

Conditions) 

Pentane 

(293 K, 

2.74 Bars) 

Gasoline 

(293 K, 

1.013 Bars) 

Hexane 

(293 K, 

1.013 Bars) 

Heptane 

(293 K, 

1.013 Bars) 

Quantity 

Released 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5.000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

Quantity 

In Pool 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

Poolfire 

Radius 

(m) 

10 

14 

19 

22 

24 

34 

45 

58 

72 

10 

14 

18 

22 

24 

34 

44 

57 

71 

11 

15 

19 

22 

25 

35 

46 

59 

74 

11 

15 

20 

23 

26 

36 

47 

61 

76 

Distance to 

1.6 kW/m2 

(m) 

114 

153 

192 

219 

240 

324 

406 

510 

618 

109 

146 

184 

209 

230 

310 

389 

488 

592 

108 

146 

183 

209 

229 

309 

388 

488 

592 

104 

140 

175 

200 

220 

297 

373 

469 

569 

Distance to 

4.0 kW/m2 

(m) 

72 

97 

121 

138 

152 

205 

257 

322 

391 

69 

93 

116 

132 

145 

196 

246 

309 

375 

69 

92 

116 

132 

145 

196 

246 

308 

374 

66 

88 

11 

127 

139 

188 

236 

297 

360 

Distance to 

12.5 kV/m2 

(m) 

41 

55 

69 

78 

86 

116 

145 

182 

221 

39 

52 

66 

75 

82 

111 

139 

175 

212 

39 

52 

65 

75 

82 

111 

139 

174 

212 

37 

50 

63 

72 

79 

106 

134 

168 

204 

Poolfire 

Duration 

(sec) 

25 

31 

37 

41 

44 

55 

66 

78 

91 

26 

33 

39 

43 

46 

58 

69 

82 

95 

27 

34 

40 

44 

48 

60 

71 

85 

98 

29 

36 

43 

48 

52 

65 

77 

92 

106 

. 0 ^ 
-30-

Exhlbit8 

DISTANCES FOR POOL FIRES 

FOR INSTANTANEOUS RELEASES OF 1,000-180,000 POUNDS 

DETERMINED USING WHAZAN 

Distance in Meters to Three Heat Radiation Levels 

(continued) 

Chemical 

(Initial 

Conditions) 

Toluene 

(293 K, 

1.013 Bars) 

p-Xylene 

(293 K, 

1.013 Bars) 

Quantity 

Released 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

Quantity 

In Pool 

(lbs) 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

1,000 

2,500 

5,000 

7,500 

10,000 

25,000 

50,000 

100,000 

180,000 

Poolfire 

Radius 

(m) 

11 

15 

20 

23 

26 

36 

47 

60 

75 

11 

15 

20 

23 

26 

37 

47 

61 

76 

Distance to 

1.6 kW/m2 

(m) 

95 

128 

160 

183 

201 

272 

338 

429 

520 

94 

127 

159 

181 

199 

269 

338 

425 

517 

Distance to 

4.0 kW/m2 

(m) 

60 

81 

101 

116 

127 

172 

214 

271 

329 

59 

80 

101 

115 

126 

170 

214 

269 

327 

Distance to 

12.5 kW/m2 

(m) 

34 

46 

57 

65 

72 

97 

121 

153 

186 

34 

45 

57 

65 

71 

96 

121 

152 

185 

Poolfire 

Duration 

(sec) 

32 

40 

48 

53 

57 

71 

87 

100 

117 

33 

41 

49 

54 

58 

73 

87 

103 

119 

\C3 
150 

125 

100 — 

co 

_. 

a> 

0) 

E 

o 

c 

n 

_£ 

Q 

75 

50 

25 

Exhibit 9 

QUANTITY RELEASED VERSUS DISTANCE 

FOR POOL FIRES, INSTANTANEOUS RELEASES 

WHAZAN Modelling for 1,000-50,000 Pounds, 12.5 kW/m2 

10 20 30 40 

Quantity Released (thousands of pounds) 

— ^-^^^^^xX^ 

— Wj 

I I I 

* 

-r- Ethylene 

** 

O Propylene 

* 

D Propane 

<^-i n-Butane 

• Pentane 

• Gasoline 

-^ Hexane 

I I 

50 

t*> 

* Liquefied by refrigeration 

** Liquefied under pressure 
-32-

8.5 Jet Fire Results 

Exhibit 10 presents WHAZAN results for jet fires, which are defined by the model as prolonged releases. 

Results were obtained only for two gases (propylene and n-butane) assumed to be stored under pressure at 

ambient temperature. Results for releases of 10,000 pounds and three heat radiation levels are shown 

along with the duration of the jet fire. Distances for 10,000 pound releases of n-butane were less than 25 

meters for a all three heat radiation levels modelled. For propylene, the distances ranged from 35 meters 

at 37.5 kW/m2 to 51 meters at 4.0 kW/m2. The duration of the release (and presumably of the jet fire) 

would be approximately one hour for the n-butane jet fire and about 15 minutes for the propylene jet fire. 

For both of these gases, the other types of accidents modelled gave much greater distances than jet fires. 

As detailed in Exhibit D-1, Appendix D, jet fires for 100,000 pound releases of n-butane and propylene 

produce distance results almost identical to the results for 10,000 pound releases. However, the duration 

of the jet fires for the 100,000 pound releases was much greater. Note that for an instantaneous release of 

these gases, the possible result would be a vapor cloud explosion or fire, not a jet fire. 

9.0 Findings 

Based on the results of modelling flammable hazards using the WHAZAN model and analysis of the 

literature, a clear distinction can be made between the results for flammable substances that boil at higher 

temperatures than pentane and flammable substances that boil at lower temperatures than pentane. This 

would suggest a distinction exists at roughly 310°K - 315°K (37°C - 42°C). Analysis of other classification 

schemes and regulations (see Seaion 3) shows that flammable gases and volatile flammable liquids appear 

to be the flammable materials considered of greatest concern by agencies and organizations such as DOT, 

NFPA and EEC The temperature at which clear distinctions in consequences can be made corresponds 

to the temperature at which DOT and NFPA have made distinctions in categories of flammable materials 

(boiling point below 38°C and flash point below 23°C for NFPA flammability rating 4; boiling point below 

35°C and flash point below 23°C for DOT Packing Group I). This temperature also corresponds to very 

high ambient temperatures (38°C is roughly 100°F); it is possible for substances with boiling points less 

than 37°C - 42°C to be gases under ambient conditions. Therefore, flammable gases and very volatile 

flammable liquids (including substances that boil at temperatures less than about 42°C) appear to be the 

most likely candidates for further consideration. 

Exhibit 11 identifies 69 flammable gases (boiling point at or below 20°C). This list includes most 

flammable gases currently in commerce. Eight of these substances are regulated as extremely hazardous 

substances (EHSs) on the basis of toxicity and are indicated in the exhibit by an asterisk. The substances 

in this exhibit are gases that have NFPA flammability ratings of 4 (NFPA 1984) or are listed by DOT as 

flammable gases in cunent DOT regulations (U.S. DOT 1984) or in DOTs proposed rule (U.S. DOT 

1987). (Note that there are discrepancies in the ratings of a few chemicals, e.g., vinyl bromide is listed as a 

flammable gas by DOT but considered non-flammable by the NFPA) Liquids that boil close to ambient 

temperature may vaporize readily and also may form vapor clouds. If the flash points of such liquids are 

at or below ambient temperature, the vapor may ignite under ambient conditions and vapor cloud fires or 

explosions may occur. Exhibit 12 shows 28 liquids that boil below 38°C and have flash points lower than 

23°C (i.e., their flash points are at or below normal ambient temperature). Three of them (indicated by an 

asterisk in the exhibit) are listed as EHSs because of toxicity. The substances in this exhibit have NFPA 

flammability ratings of 4 (NFPA 1984) or appear to meet the criteria for this rating on the basis of flash 

point and boiling point. 

Chemicals with higher boiling points (38°C and above) with flash points at or below ambient temperature 

will not vaporize readily under ambient conditions, but may ignite and burn. For these chemicals, pool 

fires are a more likely event than vapor cloud fires and explosions. Modelling indicates that pool fires are 

less hazardous than vapor cloud fires and explosions, based on the distance results. Over 350 liquids with 

boiling points of 38°C or higher and flash points below 23°C have been identified, including many 

common, high-volume substances such as gasoline, benzene, toluene, and the xylenes. 

\Q5 
P.40 

-33-

Exhlbit 10 

DISTANCES FOR JET FIRES 

FOR PROLONGED RELEASES OF 10,000 POUNDS 

DETERMINED USING WHAZAN 

Distance in Meters to Three Heat Radiation Levels 

Chemical 

(Initial 

Conditions) 

Propylene 

(liquefied under 

pressure 

293 K, 13.3 Bars) 

Quantity 

Released 

(lbs) 

10,000 

Distance to 

4.0 kU/m2 

(a) 

51 

Distance to 

12.5 kW/m2 

(m) 

40 

Distance to 

37.5 kW/m2 

(m) 

35 

Jet Fire 

Duration 

(min) 

15 

n-Butane 10,000 

(liquefied under 

pressure 

293 K, 6.3 Bars) 

25 19 17 60 

\0k 
EHS 

P.41 

-34-

Exhlbit 11 

FLAMMABLE GASES 

CAS# Chemical 

74-86-2 ACETYLENE 

7784-42-1 ARSINE* 

598-73-2 BROMOTRIFLUORETHYLENE 

75-63-8 BROMOTRIFLUOROMETHANE 

106494) 1,3-BUTADIENE 

75-28-5 ISOBUTANE 

106-97-8 BUTANE 

590-18-1 2-BUTENE-CIS 

624-64-6 2-BUTENE-TRANS 

10648-9 ALPHA-BUTYLENE 

107-01-7 BETA-BUTYLENE 

25167-67-3 BUTYLENE 

630-08-0 CARBON MONOXIDE 

463-58-1 CARBON OXYSULFIDE 

7791-21-1 CHLORINE MONOXIDE 

460-19-5 CYANOGEN 

506-77-4 CYANOGEN CHLORIDE 

287-23-0 CYCLOBUTANE 

75-19^1 CYCLOPROPANE 

778i394> DEUTERIUM 

19287-45-7 DIBORANE* 

4109-96-0 DICHLOROSILANE 

75-68-3 DIFLUORO-1-CHLOROETHANE 

75-37-6 DIFLUOROETHANE 

124-40-3 DIMETHYLAMINE 

463-82-1 2^-DIMETHYLPROPANE 

74-84-0 ETHANE 

107-00-6 ETHYL ACETYLENE 

75-04-7 ETHYLAMINE 

75-00-3 ETHYL CHLORIDE 

74-85-1 ETHYLENE 

75-21-8 ETHYLENE OXIDE* 

353-36-6 ETHYL FLUORIDE 

540-67-0 ETHYL METHYL ETHER 

109-95-5 ETHYL NITRITE 

50-00-0 FORMALDEHYDE* 

7782-65-2 GERMANE 

1333-74-0 HYDROGEN 

77834)7-5 HYDROGEN SELENIDE* 

77834)6-4 HYDROGEN SULFIDE* 

64741-48-6 UQUEFIED NATURAL GAS 

68476*5-7 UQUEFIED PETROLEUM GAS 

74-82-8 METHANE 

74-89-5 METHYLAMINE 

563-45-1 3-METHYL-l-BUTENE 

74-87-3 METHYL CHLORIDE 

Boiline Point CO 

-83 

-63 

-59 

-4.4 

-12 

-0_5 

3.7 

0.9 

-6.5 

1.0 

-63 

-192 

-50 

4 

-21 

13 

13 

-33 

-250 

-93 

83 

-9 

-25 

7 

9.5 

-89 

17 

12 

-104 

11 

-38 

11 

17 

-20 

-88 

-253 

^»1 

-60 

-159 

•40 

-162 

-63 

20 

-24 

Kft 
P.42 

-35-

Exhlbit 11 

FLAMMABLE GASES (continued) 

CAS# Chemical 

115-10-6 METHYL ETHER 

593-53-3 METHYL FUJORIDE 

74-93-1 METHYL MERCAPTAN* 

115-11-7 2-METHYLPROPENE 

8006-14-2 NATURAL GAS 

68476-26-6 OIL GAS 

504-60-9 13-PENTADIENE 

7803-51-2 PHOSPHINE* 

463-49-0 PROPADIENE 

74-98-6 PROPANE 

115-07-1 PROPYLENE 

74-99-7 PROPYNE 

7803-62-5 SILANE 

116-14-3 TETRAFLUOROETHYLENE 

79-38-9 TRIFLUOROCHLOROETHYLENE 

42<M6-2 1,1,1-TRIFLUOROETHANE 

75-50-3 TRIMETHYLAMINE 

689-97-4 VINYL ACETYLENE 

593-60-2 VINYL BROMIDE 

75-01-4 VINYL CHLORIDE 

75-02-5 VINYL FLUORIDE 

75-38-7 VINYLIDENE FLUORIDE 

107-25-5 VINYL METHYL ETHER 

Boiline Point CO 

-24 

6 

-7 

-43 

-88 

-35 

-42 

-48 

-23 

-111 

-76 

-28 

-48 

3 

5 

16 

-13 

-72 

-83 

12 

EHS 

Sources: NFPA 1984, U.S. DOT 1984, U.S. DOT 1987. 

\0% 
-36-

Exhibitl2 

FLAMMABLE, VOLATILE UQUIDS 

CAS •# Chemical 

75-07-0 ACETALDEHYDE 

627-20-3 AMYLENE, beta-,cis 

646-04-8 AMYLENE, beta-,trans 

7S-91-2 TERT-BUTYL HYDROPEROXIDE 

503-17-3 2-BUTYHE 

SS7-98-2 2-CHLOROPROP_l__HE 

590-21-6 1-CHLOROPROPYLEHE 

75-18-3 DIMETHYL SULFIDE 

60-29-7 ETHYL ETHER 

7S-08-1 ETHYL MERCAPTAN 

110-00-9 FURAN* 

74-90-8 HYDROGEN CYANIDE* 

78-79-5 ISOPRENE 

ISOPROPENYL ACETYLENE 

563-46-2 2-METHYL-I-BUTENE 

563-45-1 3-METHYL-l-BUTEHE 

107-31-3 METHYL FORMATE 

78-78-4 ISOFENTANE 

109-66-0 PENTANE 

109-67-1 1-PENTENE 

8030-30-6 PETROLEUM NAPHTHA 

7S-31-0 ISOPROPYLAMINE 

7S-29-6 ISOPROPYL CHLORIDE 

75-56-9 PROPYLENE OXIDE* 

7S-76-3 TETRAMETHYLSILANE 

1002S-78-2 TRICHLQROSILANE 

109-92-2 VINYL ETHYL ETHER 

75-35-4 VINYLIDENE CHLORIDE 

Boiling Point 

C O 

20 

37 

36 

35 

27 

23 

33 

37 

35 

34 

32 

26 

34 

33 

31 

37 

32 

28 

36 

30 

35 

32 

36 

34 

26 

32 

36 

32 

Flash Point 

rc-

-36 

<-20 

<-20 

<27 

<-20 

<-20 

<-6 

-38 

-45 

-18 

-18 

-54 

<-7 

<-7 

<-7 

-32 

-57 

-49 

-18 

-18 

-26 

-32 

-37 

-14 

-46 

-28 

EHS 

Sources: NFPA 1984, U.S. DOT 1984, U.S. DOT 1987. 

p9 
-37-

For vapor cloud explosions, BLEVEs, and pool fires, the distance for a given hazard criterion level is 

proportional to the cube root of the quantity released (Le, doubling the quantity of chemical used in the 

analysis does not double the distance, but increases it by a faaor of about 1.26, the cube root of 2). For 

vapor cloud fires, the distance is not directly proportional to quantity, the exact relationship is not known, 

but the quantity versus distance curve (see Exhibit 5) is similar in shape to the curves showing the cube 

root relationship (see Exhibits 3,7, and 9). 

For a given quantity of a flammable chemical, distances for all types of accidents depend on the hazard 

criterion level chosen for use in the analysis; Le, the overpressure level (for vapor cloud explosions), 

concentration (for vapor doud fires), or heat radiation level (for BLEVEs, pool fires, and jet fires). The 

greatest distances calculated using the WHAZAN model resulted from vapor cloud explosions and vapor 

cloud fires of gases and very volatile liquids. Vapor cloud explosions have been described as unlikely for 

douds containing less than 10,000 pounds of flammable gas (API 1990). As noted earlier, the effects of 

vapor doud fires are likely to be limited to a much smaller cross-sectional area than the effects of vapor 

cloud explosions, since persons would have to be in the path of the engulfing fire for fatalities to occur. 

The vapor doud explosion results vaiy depending on the overpressure considered; at overpressures of 3.0 

psi and higher, modelling showed greater distances for BLEVEs than for vapor cloud explosions. Pool 

fires appear to produce more localized consequences than vapor cloud explosions, vapor cloud fires, and 

BLEVEs. 

The consequence analysis results do not take into account the likelihood that a particular type of 

consequence, such as a vapor doud explosion, will result from a particular acddent The specific 

circumstances surrounding an acddent (e.g., amount of material involved; release type, such as storage, 

processing, transfer, transport) and the specific conditions (e.g., time of day, local meteorology and climate, 

proximity and type of population) at the time of an acddent may have significant effects on the severity 

and range of consequences. Modelling cannot take all circumstances and conditions into account. 

The modelling also indicates that meteorological conditions can have a major effect on the consequences 

of vapor cloud fires, based on the dispersion of the flammable cloud, which impacts both distance travelled 

and concentration. Storage temperatures of liquefied gases may have a significant effect on consequence ' 

results for gas releases; at extremely cold storage temperatures, much less of the gas will flash on release. 

Based on the results for prolonged releases under the conditions modelled, it appears that instantaneous 

releases have consequences at greater distances than prolonged releases. 

The greatest distance overall calculated using the WHAZAN model for an instantaneous release of 10,000 

pounds was for a vapor cloud explosion of propylene liquefied under pressure. The distance for an 

overpressure of 0.3 psi was 800 meters; however, this overpressure is probably too low to cause serious 

injuiy. For an overpressure of 1.0 psi, modelling produced a distance of 300 meters for a 10,000 pound 

release of propylene. Note, however, that a 10,000 pound release under the conditions modelled would 

produce a cloud containing approximately 3300 pounds of propylene, a quantity that would have a low 

probability of exploding (Prugh 1987). Vapor cloud fire results for a 10,000 pound release of ethylene, 

based on dispersion to a concentration equal to 50 percent of the LFL, indicated a downwind distance of 

550 meters, which is greater than the vapor cloud explosion distance of 300 meters for 1.0 psi; however, 

the area within which the vapor cloud would be flammable (and hence fatal to anyone in the fire zone) is 

much smaller than the area that would be subjeaed to an overpressure of 1.0 psi or greater in case of a 

vapor cloud explosion. 

110 
-38-

References 

AIChE. 1987. American Institute of Chemical Engineers. Methods for Calculation of Fire and Explosions 

Hazards. New York: AIChE 

APL 1990. American Petroleum Institute. Management of Process Hazards. Production and Refining 

Departments. .API Recommended Practice 750. Washington, D.C: API 

ASTM. 1969. American Sodety for Testing and Materials. Standard Method of Test for Flash Point of 

Volatile Flammable Materials by Tag Open-Cup Apparatus. 

Bureau for Industrial Safety (TNO). 1980. Methods for the Calculation of the Physical Effects of the 

Escape of Dangerous MateriaL Rijswijk, Netherlands: TNO (Commissioned by: Directorate-General of 

Labour). 

Brasie W., Simpson, D. 1968. "Guidelines For Estimating Damage Explosion," AICHE Symposium on 

Loss Prevention in the Process Industries, February 18-23,1968. 

CCPS. 1989. Center for Chemical Process Safety of the American Institute of Chemical Engineers. New 

York: American Institute of Chemical Engineers. 

EEC 1982. European Economic Community. Official Journal of the European Communities, Volume 

25, L230. Council Directive of 24 June 1982 on the major acddent hazards of certain industrial activities. 

Eichler T., Napadensky, H. 1977. "Acddental Vapor Phase Explosions on Transportation Routes Near 

Nuclear Plants," ITT Research Institute, Prepared for Argonne National Laboratory. April 1977. 

Eisenberg NA et al. 1975. Vulnerability Model. A Simulation System for Assessing Damage Resulting 

from Marine Spills. NTIS AD-A015-245. Springfield, VA 

Grelecki C "Fundamentals of Fire and Explosion Hazards Evaluation," C Grelecki, Hazards Research 

Corp., AICHE Today Series. 

HCHAP. 1989. Handbook of Chemical Hazard Analysis Procedures. Federal Emergency Management 

Agency, U.S. Department of Transportation, U.S. Environmental Protection Agency. 

Lewis DJ. 1980. Unconfined Vapor-Cloud Explosions-Historical Perspective and Predictive Method 

Based on Inddent Records. Prog. Energy Comb. Sd., Vol. 6. Great Britain: Pergamon Press Ltd. 

McRae T. 1984. "The Effects of Large Scale LNG/Water RPT Explosions," McRae, T.G., etaL, Lawrence 

Livermore National Laboratory. April 27,1984. 

MHiAT. 1985. Manual of Industrial Hazard Assessment Techniques. Office of Environmental and 

Sdentific Affairs, The World Bank. 

Mudan KS. 1984. Thermal Radiation Hazards from Hydrocarbon Pool Fires. Prog. Energy. Combust. 

Sd. 1984, Vol. 10. Great Britain: Pergamon Press Ltd. 

Nazario NN. 1988. Preventing or Surviving Explosions. Chemical Engineering, August 15,1988. 

NFPA "Fire Proteaion Handbook," 16th edition, National Fire Proteaion Assodation (NFPA). 

NFPA 1984. National Fire Protection Assodation. Fire Protection Guide on Hazardous Materials, 8th 

ed. Quincy, MA NFPA 

HI 
-39-

Prugh RW. 1987. Evaluation of Unconfined Vapor Qoud Explosion Hazards, International Conference 

on Vapor Qoud Modelling, Cambridge, MA November 2-4,1987. 

Richmond D. 1968. "The Relationship Between Seleaed Blast-Wave Parameters and the Response of 

Mammals Exposed to Air Blast" Richmond DR, Damon EG, Fletcher ER, Bowen IG, White CS., Ann. 

N.Y. Acad. ScL, 1968. 

Sax NI, Lewis RJ. 1987. Hawley's Condensed Chemical Dictionary, llth ed. New York: Van Nostrand 

Reinhold Co. 

SkarkaJ. 1987. Considerations of Maximum Hazard limits Originating from LPC Processing and 

Handling, International Conference on Vapor Qoud Modelling, Cambridge, MA November 2-4,1987. 

Technical Guidance. 1987. Technical Guidance for Hazards Analysis, Emergency Planning for Extremely 

Hazardous Substances. U.S. Environmental Protection Agency, Federal Emergency Management Agency, 

U.S. Department of Transportation. 

U.S. Air Force 1983. "Explosives Safety Standards," AF Regulation 127-100,20 May 1983. 

U.S. DOT 1984. Hazardous Materials Table. 49 CFR 172,101. 

U.S. DOT 1987. Proposed Rulemaking. 52 FR 42787-42931, November 6,1987. 

U.S. DOT 1988. "Hazard Analysis of Commercial Space Transportation," Office of Commercial Space 

Transportation Licensing Programs Division, U.S. Department of Transportation. May 1988. 

USEPA 1988. U.S. Environmental Protection Agency. Acute hazardous events data base (1988). Draft 

final report Prepared by Industrial Economics, Inc. EPA Contraa No. 68-W8-0038. 

WHAZAN. 1988. WHAZAN User Guide. Technica International Ltd. 

Wiekema BJ. 1984. Vapor Qoud Explosions - An Analysis Based on Acddents, Parts I and II, Journal of 

Hazardous Materials, 8 (1984). 

\\lm 
P.47 

APPENDIX A 

ADDITIONAL INFORMATION ON CLASSIFICATION SYSTEMS 

AND ACCIDENT HISTORIES FOR FLAMMABLE CHEMICALS 

\ & 
-41-

Appendix A. Additional Information on Classification Systems and Acddent Histories 

for Flammable Chemicals 

A l Classification Systems for Flammable Chemicals 

A.1.1 Definitions Related to Classification of Flammable Substances 

A flammable material is "any solid, liquid, vapor or gas that will ignite easily and burn rapidly. Flammable 

gases are ignited very easily, the flame and heat propagation rate is so great as to resemble an explosion, 

especially if the gas is confined. Flammable gases are extremely dangerous fire hazards and require 

precisely regulated storage conditions" (Sax and Lewis 1987). 

The flash point of a chemical is "the temperature at which a liquid or volatile solid gives off a vapor 

suffident to form an ignitable mixture with the air near the surface of the liquid or within the test vessel" 

(NFPA as dted by Sax and Lewis 1987). There are many different methods to measure a chemical's flash 

point Examples are the Cleveland Open Cup (COC) and Pensky-Martens methods. Most flash point 

tests pass a flame just above the surface of the material being tested. The material is heated slowly and 

the flash point is defined as the temperature at which the vapor generated above the material ignites. 

Note that because ignition is the test end point, flash point tests can be used as a criterion for determining 

whether a material is flammable or not Hash point is also related to a chemical's volatility. 

Unfortunately, most flash point tests are relatively inaccurate, particularly when applied to viscous liquids 

(their precision is generally ±3°F (ASTM 1969)). 

The boiling point of a chemical is "the temperature of a liquid at which its vapor pressure is equal to or 

very slightly greater than the atmospheric pressure of the environment" (Sax and Lewis 1987). Boiling 

point is an indicator of a chemical's volatility. Boiling point tests are relatively accurate and simple to run. 

A.1.2 DOT Classifications 

Current DOT classifications for flammable materials are as follows (49 CFR 172): 

Flammable Liquid: Any liquid having a flash point below 100°F (37.8°C). 

Combustible Liquid: Liquid with flash point of 100°F (37.8°C) or greater, and less than 200°F 

(93°C). 

Flammable Solid: Any solid material, other than an explosive, which under normal transportation 

conditions is liable to cause fires through friction or retained heat, or which 

can be ignited readily and burns so vigorously and persistently as to aeate a 

serious transportation hazard. 

Flammable Gas: Compressed gas is defined as a material having pressure greater than 40 psia at 

70°F, or pressure greater than 104 psia at 130°F, or a flammable liquid, vapor 

pressure greater than 40 psia at 100°F; a compressed gas is classed as 

flammable if mixture of 13% or less by volume with air forms flammable 

mixture or flammable range is wider than 12%, or it is shown to be explosive 

or flammable by one of several test procedures. 

DOT published a proposed rule on November 6,1987 to reclassify chemicals consistent with United 

Nations (UN) International standards. The proposed flammable classifications are: 

Hazard Class 2.1 Gases, ignitable when in a mixture of 13 percent or less by volume with air, or have a 

flammable range with air of at least 12 percent regardless of the lower flammable limit A gas is defined 

as a substance with a normal boiling point of 20°C (68°F) or less at one atmosphere pressure. Flammable 

gases are not assigned to packing groups. 

H-i-
P.49 

-42-

t * 

Hazard Class 3 Liquids, with flash points of 60.5°C (141°F) or lower. Packing groups are assigned 

according to flash point and boiling point 

Hazard Qass 3 Packing Groups 

Packing Group I - Boiling point less than 35°C (95°F). 

Packing Group II - Flash point less than 23°C (73°F) and boiling point greater than 35°C (95°F). 

Packing Group m - Flash point between 23°C (73°F) and 60.5°C (171°F) and boiling point 

greater than 35°C (95°F). 

A U NFPA Classifications 

NFPA ratings for flammability are as follows (NFPA 1984): 

NFPA 4 Assigned to materials that will burn readily and'are readily dispersed in air or will 

vaporize rapidly or completely at atmospheric pressure and normal ambient 

temperature. Gases and cryogenic materials are included, as well as liquids or 

liquefied gases with flash points below 22.8°C (73°F) and boiling points below 37.8°C 

(100T). 

NFPA 3 Assigned to liquids and solids that can be ignited under almost all ambient 

temperature conditions. Liquids with flash points below 22.8°C (73°F) and boiling 

points at or above 37.8°C (100°F), or flash points at or above 22.8°C (73°F) and below 

37.8°C (100°F). 

NFPA 2 Assigned to materials that must be moderately heated or exposed to relatively high 

ambient temperatures before ignition can occur. Would not under normal conditions 

form hazardous atmospheres with air. Liquids with flash points greater than 37.8°C 

(100°F) and less than or equal to 93.4°C (200°F). 

NFPA 1 Assigned to materials that must be preheated before ignition can occur. Considerable 

preheating required under all ambient temperature conditions. Liquids, solids, and 

semi-solids with flash point greater than 93.4°C (200°F). 

NFPA 0 Assigned to materials that will not burn. 

The classifications in NFPA 30 are: 

Flammable Liquid Flash Point < 100°F (37.8°C) 

Vapor Pressure < 40 psia @ 100°F (37.8°C) 

Class IA Flash Point < 73°F (22.8°C) 

Boiling Point < 100°F (37.8°C) 

Qass IB Flash Point < 73°F (22.8°C) 

Boiling Point __ 100°F (37.8°C) 

Class IC Flash Point > 73°F (22.8°C) and < 100°F (37.8°C) 

Combustible Liquid Flash Point £ 100°F (37.8°C) 

Qass II 100°F (37.8°C) __ Hash Point < 140°F (60°C) 

Qass IIIA 140°F (60°C) < Hash Point < 200°F (93°C) 

115 
P.50 

-43-

f 

Class HIB Flash Point > 200°F (93°C) 

NFPA 704 gives Qass IA liquids a flammability rating of 4 and Qass IB and IC liquids a flammability 

rating of 3. 

A.L4 EEC Indicative Criteria 

The Indicative Criteria related to flammability are as follows (EEC 1982): 

Flammable Gases: Substances which in the gaseous state at normal pressure and mixed with air 

become flammable and the boiling point of which at normal pressure is 20°C 

or below. 

Highly Flammable Substances which have a flash point lower than 21°C and the boiling point of 

Liquids: which at normal pressure is above 20°C 

Flammable Liquids: Substances which have a flash point lower than 55°C and which remain liquid 

under pressure, where particular processing conditions, such as high pressure 

and high temperature, may aeate major-acddent hazards. 

A2 OSHA Regulations for Service Stations 

Some of the specific requirements for flammable liquids (e.g., gasoline) included in OSHA's regulations for 

service stations are the following: 

• Aboveground tanks in a bulk plant may be conneaed by piping to service station 

underground tanks if a valve is instaUed within control of service station personnel; 

• Hammable liquids can be dispersed from tank vehicles in non-public areas if the 

vehicle, hose, and nozzle meet requirements; 

• Qass I (flammable) liquids cannot be stored in a basement or pit unless there is 

ventilation; 

• Electrical and heating equipment must meet certain standards when installed in areas 

where flammable liquids are stored or handled; 

• No smoking or open flames in areas used for fueling or servicing, and motors must be 

shut off during fueling. 

A3 Additional Information from the Acute Hazardous Events Data Base 

The Acute Hazardous Events Data Base (AHE/DB) includes information on 773 inddents for which one 

of the end effects (up to four end effects may be listed) was fire or explosion. Most of the explosion 

inddents involved flammable chemicals rather than explosives and, therefore, were included in this analysis 

of flammable chemical acddents. The first (or primary) end effea was listed as fire or explosion in 542 

(70 percent) of such inddents; for most of the others, spill or vapor release was listed as the first end 

effect, and fire or explosion was second. Of the 773 fire or explosion inddents, 652 (84 percent) took 

place at a fixed location, while 121 (16 percent) occurred during transportation. 

A total of 431 deaths was reported resulting from 88 of the fire or explosion inddents, and 4,195 injuries 

were reported from 286 inddents. Fire and explosion inddents account for about 13 percent of the total 

inddents in the AHE/DB, but they account for nearly 92 percent of the deaths and about 36 percent of the 

injuries reported. Exhibit A-1 graphically presents fire and explosion events and deaths and injuries in fire 

and explosion events compared to the total in the AHE/DB. 

\ll_ 
P.51 

Exhibit A-1 

FIRE AND EXPLOSION EVENTS COMPARED TO ALL 

EVENTS IN ACUTE HAZARDOUS EVENTS DATA BASE 

Fire and Explosion Events Compared to Total Events 

Deaths in Fire and Explosion Events Compared to Total Deaths 

Injuries in Fire and Explosion Events Compared to Total Injuries 

in 
-45-

Specific flammable chemicals that the AHE/DB reports as having been involved in two or more in-plant 

fire or explosion inddents are presented in Exhibit A-2. Number of inddents versus boiling point (as an 

indication of volatility) is shown; the DOT hazard class and packing group that would be assigned based 

on flash point and boiling point is also indicated for each chemical (see key). In the case of some fuel 

chemicals (gasoline, propane, butane, natural gas/methane) the number of in-plant inddents was estimated 

from the number reported in the 1985 version of the AHE/DB, as fuels have been deleted from the 1988 

version, by assuming that the number of inddents would have inaeased by a faaor of 2. The total number 

of inddents in the 1988 version of the data base was approximately double the number in the 1985 version; 

therefore, it was assumed that the number of fuel inddents probably also would have approximately 

doubled. 

As Exhibit A-2 shows, a number of flammable gases were reported involved in in-plant fires or explosions, 

as were several liquids in DOT Packing Group I/NFPA Flammability Rating 4 (Le., the most flammable 

and volatile categories). There were also a number of flammable chemicals that fall into DOT packing 

groups n and HI and several chemicals that are considered merely combustible rather than flammable by 

DOT and NFPA standards. There does not appear to be any clear correlation between physical/chemical 

properties (flash point and boiling point) and the number of fire and explosion inddents reported for 

chemicals in the AHE/DB. The severity of the inddents, as indicated by the number of deaths and injuries 

that resulted, was also considered in relation to the flash points and boiling points of the chemicals. There 

did not appear to be a clear correlation between the properties of the chemicals and the severity of the 

inddents. Acddents and resulting consequences are dependent not only upon the physical/chemical 

properties of the chemicals involved, but also on faaors such as location, time, weather, amount, other 

chemicals nearby, and release conditions; little information on these faaors is provided in the AHE/DB. 

Production volume for the flammable and combustible chemicals shown in Exhibit A-2 was considered as a 

possible faaor related to the number of inddents reported. Although several high-volume chemicals were 

involved in relatively large numbers of in-plant inddents (toluene in 17 inddents, gasoline in an estimated 

13 inddents, vinyl chloride in 7 inddents), there appears to be no clear correlation between number of 

inddents and production volume. 

In addition to the specific chemicals shown in Exhibit A-2, there were many unknown chemicals and nonspecific materials involved in inddents reported in the AHE/DB. A large number of inddents (61) 

involved unknown substances. Chemical types or categories listed include the following: 

Alcohol: 3 

Explosives: 14 

Fertilizer: 4 

Hammable chemicals, gas, liquid, or material: 7 

Hazardous waste or industrial waste: 12 

Paint: 7 

Pestidde: 29 

Petroleum products or petroleum refining slurry: 6 

Plastics: 7 

Rubber, rubber hose or tires: 8 

Solvents: 13 

Various other non-specific listings also are included, such as several kinds of oil and fuel, and nonchemical materials such as insulated wire. 

A number of chemicals reported to have been involved in fires or explosions are not flammable or are only 

slightly flammable (e.g., chlorine (23 inddents), ammonia (19 inddents), hydrochloric add (12 inddents), 

nitric add (11 inddents)). These chemicals were not included in Exhibit 2; their involvement in fires and 

explosions may be related to their reactivities and other chemicals involved in the inddents rather than to 

flammability. 

ua 
Exhibi

t A-2 

FLAMMABLE GASES AND LIQUIDS 

REPORTED IN IN-PLANT FIRES OR EXPLOSIONS 

2 0 

c 

V •o •J — 

o _c 

c 

o 

'n 

Q 

a. 

X UJ \ I) L. II L. 

U 

JD 

E _} 

z 

19 -

18 -

17 -

16 -

15 14 - 13 - 12 - 11 10 H 

9 8 - 7 - 6 -

5 4 - 3 - 2 - 1 -

0 

TOLUENE 

o 

GASOLINE 

O 

PROPANE 

D 

HYOR06EN 

D 

* 

ETHYLENE 

D 

HY0R06EN 

SULFIDE • 

METHANE 

P 

SHANE ACETYLENE 

P P 

PHOSPHINE 

D 

VINYL CHLORIDE 

D 

BUTANE 

a 

ETHYLENE 0X10E 

P 

ISOBUTANE P HYDROGEN CYANIO

C O O 

ETHYL ETHER a.b.e.d 

++• o «*»< o 

Mttantic 

HEXME 

"TMJL KTHYI ipm. 

BUTADIENE 

a CARR

M OISULFIK 

KROLEIN 

ACETONE 

STYRENE 

A 

XYLENE 

o 

KEROSENE 

o 

NAPHTHA 

*'"

1

 ^ ^. r 

KTHKt*UK ACNYUYE 

O A A tTlf, L

 MRPHOLINE ACETATE TM rnuL, "

t 

CREOSOTE 

A 

NITROBENZENE 

XX X 

OIKTHYl TOLUENE 

SULFOXIDE OIISOCYANATE 

-300 

1 

-10 0 0 100 300 

mS> 

\ 

I 

Boiling Point (degrees C) 

• VINYL ACETATE 

b TRICHLOROETHANE c BENZENE d TRICHLOROETHYLENE 

Ico 
P.54 

-47-

KEY FOR EXHIBIT A-2 

O Flammable gases (Boiling point <.20°C) 

DOT Hazard Qass 2.1 (23 for flammable and poison) 

NFPA Flammability Rating 4 

+ Flammable liquids, DOT Packing Group I or equivalent 

DOT Hazard Qass 3, Packing Group I: Boiling point <35°C 

NFPA Flammability Rating 4: Boiling point <38°C, Flash point <23°C 

° Flammable liquids, DOT Packing Group II or equivalent 

DOT Hazard Qass 3, Packing Group II: Boiling point >35°C, Flash point <23°C 

NFPA Flammability Rating 3: Boiling point >38°C, Flash point <23°C, 

or Flash point <38°C and Flash point >23°C 

A Flammable liquids, DOT Packing Group HI or equivalent 

DOT Hazard Qass 3, Packing Group HI: Boiling point >35°C, Flash point >23°C, 

Flash point <60.5°C 

NFPA Flammability Rating 2: Flash point >38°C, Flash point <93°C 

X Combustible liquids 

No applicable DOT Hazard Qass 

NFPA Flammability Rating 2 or 1 (NFPA 1: Flash point >93°C) 

I ID-
P.55 

APPENDIX B 

METHODOLOGIES FOR MODELLING 

\%\ 
P.56 

-49-

B.1 WHAZAN (World Bank Hazard Analysis) 

B.1.1 General Description 

WHAZAN consists of a series of 13 consequence models (along with a database of chemical properties for 

a selection of important hazardous chemicals) which can be run individually or linked together. The 

consequence models consist of 4 release/evaporation models, 5 dispersion models, and 4 models dealing 

with fires and explosions. For this analysis, the linked model for instantaneous and prolonged releases was 

used. This model produces outputs which indude pool fires, jet fires, vapor doud explosions, 

fireballs/BLEVEs, evaporation rates for pools, and flashed fractions for liquified gases. The evaporation 

rate was input into the individual (stand-alone) vapor doud dispersion model to determine the maximum 

distance to 50 percent of the LFL. Similarly, flashed fraction was input into the vapor doud explosion 

stand-alone model to determine distances for vapor cloud explosions of liquified gases. The equations 

used in this report are described below. The models can be run on an IBM PC and most likely on other 

compatible systems. 

B.L2 WHAZAN Pressurized Release Outflow 

For liquid stored in a refrigerated or pressurized container, WHAZAN calculates liquid outflow using the 

Bernoulli equation. The equation assumes the driving force for outflow may be the liquid head or 

difference between the storage pressure and the atmospheric pressure. 

W = CDARDLPITVP^/DL + 2gH]% 

where: 

W = release rate (kg/sec) 

CQ = coeffident of discharge 

A% = area of release (m2) 

DL = density of the liquid (kg/m3) 

Pj = initial (storage) pressure (N/m2) 

PA = atmospheric pressure (N/m2) 

g = gravitational acceleration (m/s2) 

H = liquid head (m) 

The fraction of liquid that flashes once the fluid has reached atmospheric pressure is given by: 

Fv = CPLCTI - T^/H^ 

where: 

Fv = fraction flashed to vapor 

CpL = liquid specific heat (J/kg/K) 

T-. = storage temperature (K) 

TB = boiling point (K) 

Hya-s heat of evaporation (J/kg) 

B.L3 WHAZAN Two-Phase Outflow 

For a two-phase outflow (liquid and gas) of a flashing liquid, the release rate of the liquid is given by: 

W = ARCQ (2Dm(Ps-Pc)),A 

19& 
-50-

where: 

Dm = density of two-phase mixture (kg/m3) 

Pg = saturated pressure (N/rn2) 

Pc -= choked pressure (N/m2) 

The density of the 2-phase mixture at the exit plane is given by: 

Dm = l/(TyDv) + (l-Fv)(D-j 

where: 

Dv = density of the vapor (kg/m3) 

The fraction of the release that has flashed to vapor at the exit plane, F v is given by: 

Fy = CpLCTi-T^/H^p 

where: 

CpL = Liquid specific heat (J/kg/K) 

Ts = Saturation Temperature (K) 

B.1.4 WHAZAN Gas Outflow 

These equations may be applied to the discharge of toxic and flammable gases from large vessels or pipes. 

This model assumes reversible adiabatic expansion and ideal gas behavior. To calculate gas outflow rates, 

WHAZAN uses the following: 

W = YCDARPi[MG(2/(G+l))(G+1>

/

(

G

-

1

)/RTl1/2 

where 

W = gas outflow (kg/fc) 

Y = coefficient in gas outflow model 

CQ = coeffident of discharge 

AR = area of release (m2) 

Pa = initial (storage) pressure (N/m2) 

M = molecular weight 

G = ratio of vapor specific heats at constant volume and at constant pressure 

R = universal gas constant (Nm/K-mole) 

T = temperature (K) 

In most cases of interest, flow will be critical because upstream pressure exceeds: 

PA(2/(G+1))(G/1-

G

> 

In these cases Y = 1.0. In the event that the upstream pressure is less than that given by the above 

expression, then: 

Y = (PA/P1)

1/G[1-(PA/P1)(G

-

1

)

/G]1/2[2((G+1)/2)(G+1)/

(

G1>/(G-1)]1/2 

\lZ> 
P.58 

-51-

, B.L5 WHAZAN Adiabatic Expansion Outflow 

These equations describe the initial behavior of an instantaneous pressurized release. The outflow may be 

used for subsequent dispersion calculations. The model assumes a core of uniform concentration 

containing 50% of the released mass surrounded by a peripheral zone charaaerized by a Gaussian 

distribution of concentration. For the estimation of the rapid adiabatic expansion experienced during the 

instantaneous release of a flashing liquid or pressurized vapor, WHAZAN uses a simple two zone 

hemispherical modeL The expansion process is considered to have two stages: 

(1) In the first stage, gas expands down to atmospheric pressure or liquid flashes (as 

appropriate). 

The change in internal energy is: 

Uj-U^C/iyTz ) 

The energy of expansion is: 

E = C^-T^ -PAO^ ) 

where 

V*. = Initial internal energy (J/kg) 

U2 = final internal energy (J/kg) 

Cy = vapor specific heat at constant volume (J/kg/K) 

Tj = storage temperature (K) 

T2 = temperature after initial expansion (k) 

E = energy of expansion (J) 

PA = atmospheric pressure (N/m2) 

Vj = initial volume (m3) 

V2 = final volume (m3) 

(2) In the second stage, the kinetic energy developed by the initial expansion drives the turbulent 

mixing of air into the cloud as the cloud spreads outward. 

Once the expansion energy, E, has been determined, the expression for the turbulent coeffident is: 

Kj, = 0.0137E1/2VGO

1/3[tE%/VGO1/3]-1/4 

and the expression for the core radius as a function of time is: 

rc = 136(4KDt)^ 

where 

KD = turbulent diffusion coeffident (m2/sec) 

E = expansion energy (J) 

VGO = volume of a unit gas at standard conditions (kg/m3) 

t = time (sec) 

rc = radius of cloud core (m) 

The equation for the concentration in the core is: 

j c = 0.0478VGO/((4KDt)3>

2

) 

yk 
P.59 

-52-

The following are expressions for the core concentration and radius at the end of the mixing: 

j c = 172.95E-°-9ppm 

rc = 0.08837E°*3VGO

W 

It was found (Ulden 1974) that the end of the initial expansion occurred at a doud radius, r, such that r/rc 

= 1.456. At this value of r/r^ 91% pf the released material is still within the doud. 

B.1.6 WHAZAN Evaporation from liquid Pool 

For an instantaneous spill, if the atmospheric temperature is less than the normal boiling point of the 

liquid, evaporation is calculated by: 

d*1* _ a(P-W/j? r ) £7<2-»>/(a*n)r(4*n)/<2*j>) 

where 

dm 

dt = change of mass with time (kg/sec) 

Ps = saturated pressure (N/m2) 

M = molecular weight 

R = universal gas constant (Nm/K-mole) 

TA = atmospheric temperature (K) 

U = wind speed (m/s) 

= radius of pool (m) 

= 4.785xl0"3 neutral atmospheric stability 

= 0.25 (the midpoint of the observed range) 

r 

If the atmospheric temperature > normal boiling point of the chemical, two alternative models 

apply. If the dominant means of transfer of heat to the pool is wind, the previous equation is appropriate. 

If the dominant heat transfer mechanism is conduction through the ground, the appropriate model is as 

follows: 

dm = nr

2K(T.-TB) I (H^t*'2

) 

where 

K = 6.68x10s to represent an average soil 

B.1.7 WHAZAN Pool Fires 

To describe a pool fire phenomenon, WHAZAN uses equations governing pool spread and burning rate. 

In pool spread, the liquid is assumed to form a drcular pool of uniform height. For an instantaneous 

spill, the pool radius is given by: 

T5 
P.60 

-53-

. r = (t//3)% 

where: 

0 = (irDL/8 gm)* 

where: 

DL = density of liquid (kg/m3) 

g = gravitational acceleration = 9.8 m/s2 

m = released mass in cloud/pool (kg) 

For continuous spills: 

r = (t/fl* 

where: 

0 = (97rDL/32gW)1/3 

To calculate burning rate for liquids having boiling points above ambient temperature: 

dm 0.00 1 H, 

c 

dt ICPL{TB-TK) +fl v v ] 

where: 

Hc = heat of combustion (J/kg) 

CpL = liquid specific heat (J/kg/K) 

Hyap = heat of evaporation (J/kg) 

TB = boiling point (k) 

TA = atmospheric temperature (K) 

dm/dt = pool spread 

For liquids having boiling points below ambient temperature: 

dm 0.001HC 

dt = Hyp 

The heat released is calculated as: 

(itr2 + 2nrfl) (-^)nHc 

(72 (45) 0*

6 1

 + 1) eft 

\7Jo 
P.61 

-54-

where: 

r = radius of pool (m) 

The effidency faaor n has been shown by tests to have a value up to around 035. 

The flame height is calculated as: 

if = 84 r 

(1 — ) dt' 

D. (2gr)V* 

0.61 

where: 

g = gravitational acceleration (m/s2) 

Numeric input data requirements for the "instantaneous" case are as follows: 

Parameter Valid Range Default 

Spill size 10 - 107kg 

Bund area 0 - 106m

2

 0 

.Ambient temperature 200 - 400°K 68°F 

Effidency faaor 0.01 -1 0.35 

For the continuous case, the spill size is replaced by the spill rate and duration. 

B.L8 WHAZAN Jet Fires 

The flame length is given by: 

L = 18.5 W041 

where: 

W = release rate (kg/s) 

L = length (m) 

.Alternatively the flame length can be based on the distance to the lower flammability limit (LFL) as given 

by the jet dispersion model. To calculate jet dispersion, the envelope within which the concentration of a 

turbulent jet is above a specified level, j c , is represented by a major axis of length: 

A = 

<2>1+jb2) 

*>Jc * A-a-i 

DjD^2/(0.220^) 

and a minor axis of length: 

xim-r 
P.62 

-55-

B = A-{l/b2) log, 

The shape parameters are given by 

bj = 503 + 482 DTO - 9.9SD^ 

b2 = 23.0 + 41.0 DTO 

where: 

Dyg = gas density relative to air at the same conditions, 

Dv l = gas density after initial expansion (relative to air at ambient conditions), 

j c = specified level of a turbulent jet - the envelope of concentrations of a turbulent jet is above 

this level (ppm), 

D: = diameter of jet once expanded to atmospheric pressure (m). 

The jet shape is symmetrical about the major axis. D: is calculated assuming adiabatic expansion. 

B.1.9 WHAZAN Vapor Cloud Explosions (based on Buoyant Plume Dispersion) 

WHAZAN model expresses vapor cloud explosions in terms of overpressure versus distance. 

Overpressurization is related to the dispersion concentration of the gas and assumptions about its 

explosive yield. WHAZAN uses the standard Gaussian model of plume dispersion to calculate the 

ground-level concentration of a buoyant release (where the release point can be at ground-level or at 

height, h): 

C = W exp ( -y2

 h2 \ 

[2oy

2

 20/J (UOyO,) 

where: 

W = release rate (kg/sec) 

Y = crosswind distance (m) 

h = release height (m) 

U = wind speed (m/sec) 

oyoz = standard deviation of plume concentration profile 

Then WHAZAN uses results of studies by Lees to relate the explosive yield of the gas concentration with 

the overpressurization waves distributed over distances. 

B.1.10 WHAZAN Fireballs/BLEVEs 

WHAZAN uses empirical correlations to calculate the size, duration, and radiant intensity of fireballs of 

flammable liquid and/or vapor. 

•7& 
P.63 

-56-

The maximum fireball radius is given by this model as: 

rm = 2.665 m*327 

where: 

' m = released mass in cloud (kg) 

and the duration by. 

t = 1.089 nr327 

The energy released by combustion at effidency is 

Q = Hf-mn 

where: 

Hc = heat of combustion (J/kg) 

n = effidency of combustion 

where n is found to vary with the saturated vapor pressure of the material stored, as 

n = 0.27 Ps

3 2 

where: 

Ps = saturated pressure (MN/m2) 

The heat flux at a given distance from the fireball center is calculated assuming an inverse square-law 

relationship. 

.•v* 
P.64 

B.2 ARCHIE (Automated Resource for Chemical Hazard Inddent Evaluation) 

B.2.1 General Description 

In a combined effort, FEMA, U.S. DOT, and U.S. EPA sponsored the development of a handbook and 

computer program entitled ARCHIE to provide emergency planning personnel with the tools necessary to 

evaluate the nature and magnitude of chemical release threats from potentially hazardous facilities. 

A core part of the program estimates the downwind dispersion of a chemical release given a diversity of 

release scenarios. The program operates on an IBM personal computer or other compatible system. 

ARCHIE is capable of addressing a wide variety of common acddent scenarios. The scenarios include 

nine methods to estimate discharge rate and duration of a gas or liquid release from a tank or pipeline, 

seven methods to estimate size of the liquid pool, two methods to estimate the rate at which a liquid pool 

will evaporate or boil, seven methods dealing with explosions and fires, and one method to estimate 

downwind chemical concentrations and hazard zones. 

ARCHIE finds the downwind length of the hazard zone at the discharge height of the vapor, the peak 

concentration expeaed at ground level, and the length of the hazard zone at ground level. The vapor 

dispersion model contains a finite duration equation validated by Palazzi using the experimental data of 

De Raven. The model uses Pasquill-Gifford dispersion coeffidents. 

B22 ARCHIE Pressurized liquid Release 

The release scenario consists of pressurized liquid release from a spherical tank with a 15 foot diameter. 

For a given liquid height and vapor space pressure, the instantaneous liquid release rate from a tank is 

given by the equation: 

m = AhCd jo* \.2gPl [HL - Hh) + 2 [P0 - Pa) J 

where: 

m = Discharge rate (kg/s) 

g = Gravitational constant = 9.8 m/s2 

p. = Liquid density (kg/m3) 

P0 = Storage pressure (N/m2) 

Pa = Ambient pressure (N/m2) 

HL = Liquid height above bottom of container (m) 

Hh = Height of discharge opening (m) 

Aj, = Area of discharge opening (m2) 

Cd = Discharge coeffident 

This assumes the tank is full. An average release rate for the tank may be obtained by computing the time 

(Te) required to empty a tank. For a spherical tank: 

Te = 

16 Z),.25 

T 

15 D2 fig Cd 

\1P 
P.65 

-58-

where: 

D T = Tank diameter (m) 

D Q = Opening diameter (m) 

Te = Time to empty (sec) 

B23 ARCHIE Estimating Pool Size 

ARCHIE estimates pool size for instantaneous releases of boiling liquids in absence of frictional resistance 

during spreading. The liquid pool is assumed to be circular and the pool is not bounded by secondary 

containment The maximum diameter of the pool is: 

1.7766 V-A 

E

2 

1/8 

where: 

--'max

 = maximum diameter of pool (m) 

V = total liquid volume (m3) 

A = effective gravity (same as gravitational constant (g) for spills 

on land) (m/s2) 

Ey = vaporization flux (kg/m2/s) 

The time needed to reach maximum diameter, t^-p is calculated as follows: 

t___. = 0.6966 

B.2.4 ARCHIE Volatilization of liquid Pool 

A_?„ 

ARCHIE assumes the volatile liquid is near ambient temperature when discharged. Evaporative flux of 

volatile liquids as developed by U.S. Air Force Engineering and Services Laboratory is: 

Ev = 4.66xl0-«a v

0

-

7 5 T*l°M

" 

P

8h 

where: 

Ey = Evaporation flux (lbs/min/ft2) 

Uw = Wind speed (m/h) 

Ps = Vapor pressure of chemical (mm Hg) 

Psh = Vapor pressure of hydrazine (mm Hg) 

My, = Molecular weight of chemical 

TF = Spill temperature correction faaor 

\3( 
P.66 

-59-

The spill temperature correction faaor is defined as follows: 

T F =1T<0» C 2 

TF = 1 + A3 x HTTp Tp > 0°C 

where Tp is the pool temperature in degrees C The vapor pressure of hydrazine is given by the following 

equation: 

ln(P) = 65.3319 -

 724 ^ ' 2

 - 8.221n(T) + 6.1557XlO** T 

where T is in kelvins and P is in atmospheres. 

Overall volatilization rate: 

Vw = Ey • A 

where 

A = pool area (m2) 

Vw = volatilization rate (kg/s) 

Ey ---vaporization flux (kg/m2/s) 

B.2.5 ARCHIE Gas Discharge from Pressurized Vessel 

For gas discharge from pressurized vessel under non-choke flow conditions, the mass flow rate is calculated 

from: 

-4-iMter-terir 

Under choked flow conditions, the mass flow rate is calculated from: 

/ _____y 

where: 

m = Discharge rate (kg/s) 

Ab = Opening area (m2) 

7 = Ratio of specific heats 

p0 = Tank pressure (Pascals) 

p2 = Ambient pressure (Pascals) 

pQ = Density (kg/m3) 

["him 
P.67 

-60-

This equation ignores deaeases in discharge rate due to thermodynamic cooling. Also, this equation 

assumes the discharge is adiabatic and that the wall friction effects are negligible. 

B.2.6 ARCHIE Vapor Qoud Fire Model 

The length and width dimensions of a doud or plume of flammable vapor is determined by ARCHIE'S 

model of toxic vapor dispersion. Either a neutrally buoyant or heavy gas model could be used to predia 

cloud dimensions. For neutrally buoyant gases, ARCHIE considers releases as point sources at ground 

level The emission rate is constant Ambient temperature was assumed to be 20°C The model assumes 

steady state unless the release duration is significantly smaller than the charaaeristic travel time. 

Relatively short-duration releases were assumed to be instantaneous. ARCHIE uses the finite duration 

model validated by Palazzi to predia gas dispersion. According to the model, the finite concentration (Cf) 

at any location is given by: 

*£ Lrf( 2L- ) -erf { X~

U

f ) 1 when f. tx 

2 [ ((2)V*ox) ({2)^2oxj\ 

*-§ * erf f-^^ ) -erf ( X~^ ) 1 when t * tK ( (2)^0 , j ((2)i'2

ox)\ * 

where: 

Cc = centerline concentration given as: 

^ _> 2oy 

'

c

 2noyoxUw 

e

2

°y x exp - -J -j— + exp - — -?— 

2o2 * 2o2 

Here, tR is the duration of release in seconds. The maximum concentration is given by the following 

equation: 

(•max r* H^M^)]"^ 

«u --^ M-^&r-U » "^ 

(23 
P.68 

-61-

The parameters used in the above equations are defined as follows: 

Cggx = Maximum centerline concentration (kg/m3) 

Q = Continuous source release rate (kg/sec) 

Uw = Wind speed (m/sec) 

z = Vertical distance (m) 

y = Crosswind distance (m) 

x = Downwind distance (m) 

H = Source height (m) 

a- = Longitudinal standard deviation (m) 

oy = Lateral standard deviation (m) 

az -s Vertical standard deviation (m) 

The dispersion distances for neutrally buoyant gases are generally 2 to 5 times larger than those for heavy 

gases. 

B.2.7 ARCHIE Unconfined Vapor Cloud Explosion 

ARCHIE uses the TNT-equivalent model for use in evaluating the vapor cloud explosion scenario. The 

amount of combustion energy in the cloud is compared with the equivalent amount of TNT. Considering 

that only a fraction of the energy in the cloud will contribute to the explosion and referring to the TNT 

explosion/overpressurization data, enables the model to calculate the pressurization at distances from the 

explosion. The fraction of energy in the cloud assumed to contribute to the explosion ranges from 2 to 20 

percent Other assumptions include: 

• Ambient temperature is 20°C; 

• Effects of terrain, buildings, obstacles have not been considered. 

The equation is stated as: 

% r 

AH. 

1155 •"cloud

 x

 - - - - X Yi 

where: 

mTNT = TNT equivalent mass (lbs) 

AHC = Lower heat of combustion (kcal/kg) 

m

cioud

 = Mass m doud (lbs) 

Yf = Yield faaor 

Distance to a given overpressurization is then calculated from the equation: 

X = m^3 exp (3.503 1 - 0.724 1 l n (Op) + 0.0398 (lnOp )

2

 ) 

where: 

X = distance to given overpressure (ft) 

Op = Peak overpressure (psi) 

\7A> 
-62-

. B.2.8 ARCHIE Tank Overpressurization Explosion Model 

This model assumes that the pressurization waves aeated by an exploding tank will propagate omnidirectionally in a hiemispherical field at ground level. The computational algorithm proceeds as follows: 

1. Calculate the ratio Pj/Pa where Pa is the absolute ambient pressure and Pj is the absolute 

internal gas pressure at which the tank is expeaed to rupture. 

2. Compute the ratio T/Ta where Ta is the absolute ambient air temperature and Tj is the 

absolute temperature of the gas in the tank. 

3. Determine the initial overpressure ratio, P^ by solving the following equation by trial and 

error. 

f = o in(^ ) P

" ln( l + P,0) 

-

2 Y i l n 

1-Yi .-*, 

l-(Yi-DP T O 

^fVY- 3 + 0.5 Y a (Ya 

+

 D Peo 

where .7 is the ratio of specific heat at constant pressure to that at constant volume. 

4. Compute the nondimensional starting distance R0 from: 

lUH 

ti -1 

1/3 

Compute the value of R from: 

ftd" 

Yi " 1 

where: 

V -= Volume of the gas in the tank (ft3) 

r = Distance from the center of the tank at which the side-on overpressure is desired (ft) 

6. Locate the point assodated with P^ and R0 on an overpressurization graph. 

7. Follow the nearest curve for Ps vs. R to the R value computed in step 5. Read the Ps value 

assodated with this R value. If the gas vessel is on the ground and/or close to a reflecting 

surface, inaease Ps by 100% for R less than 1 and by 10% for R greater than 1. 

\"b5 
P.70 

-63-

8. The side-on overpressure is determined by multiplying the above resultant value of Ps by the 

absolute value ambient atmospheric pressure Pa. 

B_2.9 ARCHIE Fireball Model 

In calculating the maximum diameter and height the fireball attains, as well as the safe separation 

distances for fatality and injury, ARCHIE makes the following assumptions: 

Fuel is propane 

Ambient temperature is 20°C 

Atmospheric absorption of thermal radiation is negligible 

Fraction of combustion energy radiated = 0.2 

Observer is at ground level 

Minimum fatality zone is equal to half the maximum diameter calculated 

Based on a series of experiments: 

D__ax = 1CTJ 

Z = 26.3W1/n 3 

T = 2.23W1A5 

where: 

W = Mass in vessel (lbs) 

Djug- = Maximum diameter of fireball (ft) 

Z = Maximum height of fireball (ft) 

T = Duration of fireball (s) 

The safe separation distance for fatality, XF, in feet, was found to be: 

XF = 1.48W0-

56

 W > 2000 lbs 

XF = 8.0W0*

33

 W < 2000 lbs 

For injury, the safe separation distance, XI, in feet, is: 

XI = 4.53W0-

52 

B.2.10 ARCHIE liquid Pool Fire Model 

ARCHIE calculates various pool fire faaors to determine the radius in which injuries and fatalities are 

expeaed from the fire. These faaors include burning velodty, maximum pool diameter, flame height, 

effective emissive power, inddent flux, and view faaor (fraction of flame seen by a given observer). In 

calculating these faaors, there are several simplifying assumptions: 

• Pool area is circular 

• Observer is at ground level 

• Ambient temperature is 20°C 

• Atmospheric absorption of thermal radiation is negligible 

• Negligible wind in the vicinity of the flame; thus, uniform thermal radiation field radially and 

no flame tilt 

• Pool ignites shortly after release 

• Burning rate equals spill rate 

The scenario chosen to model is an instantaneous Uquid hydrocarbon release in the absence of friaional 

resistance during spreading. The equation to estimate the burning velodty is: 

lit. 
P.71 

-64-

92.6e-0-

0043r 'Aff. IP' 7 

P 6 

where: 

y «= Burning velodty (m/s) 

MW = Molecular weight (kg/kmol) 

p = Liquid specific gravity 

TB = Normal boiling point (°F) 

In the pool fire scenario, the radius of the pool inaeases until all the material is consumed by the fire. 

The maximum diameter and time to reach maximum diameter are given by. 

= 1.7766 V

3A 1/8 

tW = 0.6966 

Ay2 

i / « 

where: 

V = Total liquid volume (m3) 

y = Burning velodty (m/s) 

A = Effeaive gravity (same as gravitational constant (g) for spills on land) (m/fc2) 

The time averaged pool diameter is obtained by dividing the maximum diameter by the square root of two. 

The mean visible flame height is based on equations correlated with data from laboratory fires. Visible 

flame height, Hflame, is expressed as: 

Bfum = "D , 

•BVp 

Pa*/£^ 

0.61 

where: 

H

name =

 Flam e

 -^-g1" (TM) 

p = Liquid density (kg/m3) 

pa = Air density at ambient temperature (kg/m3) 

Dp = Pool diameter (m) 

g = Gravitational acceleration -= 9.8 m/s2 

Effective emissive power of the flame accounts for the inddent flux shielding by surrounding layers of 

smoke for liquid hydrocarbon fires. Based on literature data and correlated to the normal boiling point, 

effective emissive power is defined as: 

IX) 
P.72 

-65-

, Ep = -0313 TB + 117 

where: 

Ep = Effective emissive power (kW/m2) 

TB = Normal boiling point (°F) 

The inddent flux at any given location is given by the equation: 

Qincident-EpXrxVF 

where: 

^incident =

 Indden t flux (*W/m2

) 

T = Transmissivity 

VF = Geometric view faaor 

r, the transmissivity coeffident is mainly a function of the path-length (distance from observer to flame 

surface), relative humidity, and the flame temperature. For the calculation scheme in ARCHIE, r has 

been set to 1, and the attenuation of thermal flux due to atmospheric absorption is not taken into account 

This assumption provides a conservative hazard estimate, since the presence of water and carbon dioxide 

tends to reduce the inddent flux at any given location. 

The view faaor defines the fraction of flame that is seen by a given observer. This geometric term has 

been calculated as a function of distance from the flame center for an upright flame approximated by a 

cylinder. It has also been assumed that the optimum orientation between observer and flame that yields a 

maximum view faaor prevails. The resulting equation is as follows: 

VF = 1.143 3> 

X 

11.757 

where: 

X = Distance from flame center (m) 

Rp = Pool radius (m) 

For fatality, the inddent flux level is set to 10 kW/m2. For injuiy, the corresponding level is 5 kW/m2. 

These levels are based on analysis of numerous sources of experimental burn data (Mudan, 1984). 

Applying these two damage criteria, the above equations were rearranged to solve for hazard distances X10 

and Xo5 for fatality and injuiy, respectively: 

[2& 
-66-

^••°- 3 0 -0^5i8

 E^ 

X„K = 0.4 3 * £0.5 7 

05

 0.3048

 p 

where: 

X10 = Radius for expeaed fatalities (ft) 

XQS = Radius for expeaed injuries (ft) 

[2ft 
P.74 

B3 Yellow Book 

B3.1 General Description 

The Yellow Book indudes calculations for pool fires, vapor doud fires, and vapor doud explosions for 

gases; and pool fires and vapor doud fires for liquids. For gases, two different methodologies are used for 

vapor doud fires: the flash fraction of each gas is modeled as an instantaneous release and the nonflashed fraction is modeled as a continuous release from an evaporating pooL In both cases, dispersion as 

a neutrally buoyant doud is assumed. The flash fraction of each gas is used to calculate the vapor cloud 

explosion results. Since there is no calculated flash fraction for liquids, no vapor doud explosion results 

are calculated for liquids. 

B32 Vapor Qoud Explosion Calculations for Gases 

Reference: Yellow Book, Chapter 4, "Spray Release," p. 44; Chapter 7, "Dispersion," pp. 25-27, and 

Appendix 2, p. 52; Chapter 8, "Vapor Qoud Explosion," pp. 24-25. 

For gases, the flash fraction for a spray release is calculated. This fraction is then multiplied by the total 

quantity to obtain the quantity instantaneously in the air. The ma-rimnm fraction of this quantity that is 

between the upper and lower flammability limits is calculated. Damage circles for the resulting quantity 

can then be determined. 

Equations: 

Mass Flashed (Chapter 4, p. 44) 

w

vap

 = **vap,a " s 

where 

W ^ = mass flashed (kg) 

X^p^ = flash fraction 

Wg = mass stored (kg) 

The flash fraction is calculated from the following equation (Chapter 4, p. 16, equation (3)): 

Xvap.a Xvap,b -**T

 + -***£- * J* -jr 

where: 

Xygpt, = weight fraction of vapor before expansion (assumed to be 0 for calculation of the flash 

fraction) 

Tb = boiling temperature (K) 

Tj = temperature of stored gas compressed to liquid (K) 

C} = specific heat of gas compressed to liquid (J/kg-K) 

hy = heat of evaporation of gas compressed to liquid (J/kg) 

Flash fractions for selected gases are listed in Chapter 4, p.44, Table 1. 

1^0 
P.75 

-68-

B3.2.1 Quantity of Vapor Contributing to Explosion (Chapter 7, pp. 25-26). 

The equation in this section estimates the amoimt of gas in the explosive range. This amount develops as 

the dispersion progresses. Initially, and dose to the source, the concentration in a large part of the cloud 

will be greater than the upper explosive limit; Mg, (the amount of gas in the explosive range) will then be 

small. As the dispersion progresses, Mg, inaeases to a maximum concentration that is reached when the 

nr^-rimi-m concentration is a little above the upper explosive limit After this Mg, will gradually drop 

again. 

( % | = ERF ty/vi) - ERF {*fc) - -^ P EXP (-v2) + 1&, EXP (-v j 

V

 M /max V" i/fl 

where 

Mg_ = amount of gas in explosive range (kg) 

M = total amount of gas which has escaped (kg) 

ERF(x) =s error function = 

- | : f EXP (-t2)dt 

(These values are listed in Appendix 2 on p 52.) 

where 

v = Pj/P^Vj-LnOMv2-!) 

= ^ln(v ) 

2

 v2-l 

and 

Px = upper explosive limit (UEL) 

P2 = lower explosive limit (LEL) 

B3.22 Determination of Damage Circles (Chapter 8, p. 25) 

For the limit value of certain types of damage(s) the relation is expressed below: 

R(S) = C(S) x (nE)1/3 

i4l 
-69-

, R(S) = the radius of a damage circle (m) 

C(S) = constant for characteristic type of damage (mJ"1/3) 

A constant C(S) goes with each charaaeiistic damage (S), listed on p.25. For glass damage causing injuiy, 

C(S) = .15 (a corresponding overpressure is not given). 

Only part of the total combustion energy in the explosive part of the cloud is available for shock wave 

propagation. This fraction is symbolized by the yield faaor, n. This yield faaor can be divided into two 

independent faaors nc and n^, in which n = nc x r^. nc indicates the yield loss as a result of the nonstoichiometry of a cloud with a continuous development of fuel concentration in the explosive pan of the 

doud; it is put at 30%. n,,, gives the mechanical yield of the combustion. Depending slightly on the type 

of gas, i^ is calculated as follows: 

a. Isochoric combustion: i*^ - approx. 33% 

b. Isobaric combustion: nm = approx. 18% 

Where a gas cloud explosion occurs, there is probably some form of confinement which would result in 

isochoric combustion and a probable value for i^ of 33%. n would then equal approximately 10%. 

To determine E, the energy content of the explosive pan of the vapor cloud, an equation is given as an 

example on p. 26: 

E = mass x hc 

where 

hc = heat of combustion (J/kg) 

B33 Yellow Book Vapor Cloud Fire Calculations for Gases 

Reference: Yellow Book, Chap. 5, "Evaporation," and Chap. 7, "Dispersion." 

The evaporation rate for the pool left following the flash of an instantaneous release of a chemical is 

calculated using the following: 

Wygp = mass flashed 

The quantity remaining is: 

where 

w — w w 

"pool "store "vap 

W,,,,,, = mass in pool (kg) 

W ^e = mass stored (kg) 

The total volume of the chemical in the pool is calculated using the equation on page 42 of the Yellow 

Book: 

« • i 

'» " T, 

+•2-
P.77 

-70-

, where 

Vj 0 = volume (m3) 

W| = mass in pool (kg) 

Pj = density (kg/m3) 

The pool of liquid will spread out until the minimum layer thickness is reached. The time, te, at which 

this takes place is best calculated using iterations of the equation on page 23: 

*i,o ~2 x 

(n x e

2

 x C" x g x Vli0 x t\) 

P i' 

16 *^xitxC"xgx (-2-) x *1#Bin x tj 

-2 x (n x C" x g x V1/0 x o1>nin

2

 x t2)

1/2 + * C" x g x 6XtaUl2

 x t2 = 0 

where 

^l o = volume 

e ' = rsx (Ts - Tb) /hyX (-rxas)

1/2

 [p. 16] 

Ts = ambient temperature = 293°K 

Tb = boiling point of the chemical (°K) 

as = thermal diffusivity of substrate = 1.0 x IO"6 m2/s for conaete 

C = constant for spreading liquids = 2 

g = acceleration due to gravity = 9.8 m/s2 

te = time for minimum pool thickness to be attained (to be iterated) (s) 

px = density of the chemical (kg/m3) 

5limin = minimum thickness = 0.01 m 

TS = coeffident of heat conduaion of substrate = 1.1 w/mk 

This equation is used reiteritively to compute values of te until a minimum positive value is found. 

The evaporation rate at the minimum pool thickness is calculated as follows: 

Mp = 4 x {it x e

2

 x C" x g x V1#0 x te)

1/2

 - (8/3) xnxC"xgxex &1§min x tt 

3/2 

where 

Mp = the evaporation rate at the minimum pool thickness (kg/m2s) 

and all other variables are as defined above. 

A dispersion distance to 50% of the lower flammability limit is calculated using the equation on page 15 

of the Dispersion section of the Yellow Book (where y, z, and h all equal 0): 

1*6 
P.78 

-71-

C(x, y, z) m 

[2 x it x Uv x oy(x) x ox(x) ] 

where 

C(x, y, z) = 

m = 

ay(x) 

concentration at coordinate x, y, z -= 50% of LFL (kg/m3) 

evaporation rate at minimum pool thickness (as described above) (kg/sec) 

aXb = 0.128X0905 and a2(x) = cX*1 = 0.2X076 

(using values in the table on page 10 for neutral conditions) 

B.3.4 Vapor Qoud Fire Calculations for Gases (Based on Fraction Flashed, 50% LFL) 

Reference: Yellow Book, Chapter 4, "Spray Release," pp. 36,44; Chapter 7, "Dispersion," p. 23. 

The following equations estimate the consequence distance for a vapor cloud fire for gases, assuming that 

a percentage of the total amount released is immediately vaporized; this vaporized quantity is assumed to 

be available for the vapor cloud fire. The quantity evaporating from the pool that remains after flashing is 

not considered in this calculation. 

The flashed mass is calculated as follows (Chapter 4, p 44): 

Wf = Xy^W. 

Wf = mass flashed (kg) 

Xy^p^ = flash fraction (see Section B.3.2 for calculation) 

Ws = mass stored (kg) 

The quantity Wf is then used as an instantaneous source using equation 23 (p. 24 in "Dispersion" section), 

where the concentration at a point (x, y, z) at time t is given as: 

C(x,y, z, t) = m 

(2 ir)3/2oXIo„oZI 

EXP 

(x-Vvt)-

2°*r 2 EXP - -21 

2 o, 

EXP (z-hY-

+ EXP (z+h)2 

2oZI

2 

where: 

m = 

x -= 

y = 

z = 

h = 

source strength for an instantaneous release (kg) 

coordinate in wind direction (m) 

coordinate at right angles to wind direaion (m) 

coordinate in vertical direaion (m) 

wind speed (m/s) 

source height (m) 

144-
P.79 

-72-

a

xi

 aYi a z i = standard deviations in x, y, and z directions for an instantaneous source 

We assume that y, z, and h = 0, and that x = Uyt where uw is wind speed, to determine the distance the 

doud has traveled in the x direction only: 

c(x, 0,0 , t) -

 m 

(2it) 3 / 2 oxza„oZI 

From 

when 

From 

p. 23, CTjg, ffyi* 

aXI = e I *** 

a ^ = aj xb* 

(jja = c, x * 

*

 ai» ty, Cj, dj, ej, 

page 24: 

e! = .13 

aj = a/2 

Cj = c 

and a

n are described 

and f- are constants 

f, = l 

bj = b 

dI = d 

by these equations: 

From Table 10 on page 10, a = .128, b = .905, c = .20. 

Therefore: 

a

xi

 = •**•* x 

aXI 

^Zl 

C 

m 

C = 

Solve for x: 

= .064x-905 

= .2 x *76 

= concentration 

= w8 

ws 

(2 rr)3/2 (.064)(.2)(.13) x 2.665 

X = w. 

(2*) 3/

2

 (.13) (.064) (.13)C 

l/2-«5 , _ , 0-3 „ 

[ .01703CJ 

145 
P.80 

-73-

, B3rS Pool Fire Calculations for Gases and liquids 

Reference: Chapter 4, "Spray Release," p. 44; Chapter 6, "Heat Radiation," pp. 8-14,19-35. 

To determine the heat radiation into the environment the radiating surface (the flame from the burning 

pool) is seen as an upright cylinder with diameter D and length L. The radiation load q per unit area 

exposed which is experienced at a distance r from the center of the fire is (Ch. 6, p. 8): 

q^ = fjxFx E 

where 

qr = radiation load (q) at a distance r from the center of the fire (kW/m2) 

r1 = atmospheric coeffident of transmission 

F = geometric view faaor 

E = average intensity of radiation (kW/m2) 

B.3.5.1 Atmospheric Coefficient of Transmission 

Pan of the radiated heat is absorbed by the air between the objea exposed to radiation and the fire. This 

reduction is taken into account by r-., the coeffident of transmission. The size of this coeffident is 

dependent upon the amount of water vapor between the flame and the objea, the air temperature, and the 

relevant distance (r) between the objea and the center of the fire. 

The relevant distance (r) is the unknown variable for the purposes of this study, q,, the radiation load, is 

assumed to be 12.5 kw/m2, the intensity that corresponds to one percent probability of fatality for a 30 

second exposure. Figure 2 on p. 35 gives r-. as a function of the produa of vapor pressure and relevant 

distance. The vapor pressure is determined by multiplying the relative humidity by the saturated vapor 

pressure (given in Table 1, p.19) at a prevailing temperature. To be conservative, a value of 10 percent 

was used for relative humidity. 

To estimate the relevant distance, an iterative process, including calculations and estimates of ra 

(atmospheric coeffident of transmission) and F (geometric view faaor) from B.3.5.1, B.3.5.2, and B.3.5.3, 

was used. Assuming a relevant distance and multiplying that estimate by the vapor pressure yields an 

estimate for t, using the table on page 35. This value for t can then be used in calculating the view faaor 

(F), as described in B.3.5.2 and B.3.5.3. The estimate for F is used to determine another estimate for the 

relevant distance. This new assumed distance is used to estimate another value for t, and the steps above 

are reiterated. This reiterative process is used until the relevant distance approaches a single value. 

B.3.5.2 The Geometric View Factor F 

The effea of the geometrical shape of the flame and the place and orientation of the exposed objea are 

incorporated in the view faaor F. The size of the view faaor is determined by the length to diameter 

ratio of the flame (Chapter 6, p. 9). 

r r // V " 

hi. =4 2

 m 

\^o 
P.81 

-74-

where 

Lf = length of the flame (m) 

d = diameter of the flame (m) 

m" = rate of evaporation (kg/m**s) 

g = acceleration due to gravity = 9.8 m/s 

p = density of air (at 18°C = 1.213 kg/m3) 

2 

The diameter of the flame is assumed equal to the diameter of the pool The diameter of the pool is 

calculated from the volume of propane in the pool, assuming the pool spreads out to a thickness of .01 m. 

The calculation for the rate of evaporation (m") is dependent upon whether the stored material is a liquid 

with a boiling point below the ambient temperature or above the ambient temperature. 

Liquids with a boiling point below ambient temperature are gases stored under high pressure conditions. 

The equation is given in Chapter 6, p. 10: 

xn" = -rr- • IO"3 kg/m2 sec hv 

where 

hc = heat of combustion (J/kg) 

hy = heat of vaporization (J/kg) 

For liquids with a boiling point above ambient temperature (Ch. 6, p.ll): 

^ . 10"3 

CpAT + hv 

where 

Cp = specific heat or heat capadty at constant pressure (J/kg.K) 

AT = boiling temperature - ambient temperature (K) 

The value of the view faaor (not the size) can be determined by solving the initial equation for radiation 

load for F: 

q^. = fjxFx E 

F *= q^xE ) 

B.3.5.3 Intensity of Radiation of the Fire 

The value for E, the average intensity of radiation (W/m2), is dependent on both the type of fuel and on 

the diameter of the pool. The magnitude of the average intensity of radiation is given on Table 3, p. 21 

for four gases: butane, propane, ethylene, and propylene. The value for the other substances is calculated 

using the equation in Chapter 6, Appendix 2, p. 32 for liquids: 

m 
P.82 

-75-

0.35 f

 b° 

C„AT+hv • 

72 1 „ . fe . . IO3 

[ CpA T + hv 

IO3 

.61 

bc 

+ 1 

where 

E = radiation intensity (W/m2) 

hj. = heat of combustion (J/kg) 

Cp = heat capadty (J/kg-K) 

hy = heat of vaporization (J/kg) 

AT = boiling point - ambient temperature (°K) 

The length to diameter ratio can then be determined using the equation in Chapter 6, p. 9: 

Lf _ 42 M" 

PaVff^ 

Table 1 on p. 24 gives view faaors between a vertical upright cylinder and a surface on the ground. The 

table lists the view faaors as coordinates between the ratio of flame length to radius and the ratio of the 

distance of the objea from the fire to radius. These ratios are diagrammed in Appendix L Using the 

section of the table that gives maximum view faaors, the ratio a/b is assumed to be the length to radius 

ratio and is taken to be twice the flame length to diameter ratio. Using the known ratio a/b and the view 

faaor F, the ratio c/b can be estimated and the relevant distance (c) to the objea receiving radiation can 

be determined. Using this new assumed distance, a new value for T1 can be estimated in a reiteration of 

the process, until the distance approaches a single value. 

B3.6 Vapor Cloud Fire for liquids (Dispersion Distance to 50% LFL) 

Reference: Yellow Book, Chapter 5, "Evaporation," Pp. 29-38; Chapter 7, "Dispersion," Pp. 15-16. 

The calculations in this section model the consequence distance in a vapor cloud fire when the material 

evaporates from a pool on the ground rather than flashing into a vapor state after an instantaneous 

release. The consequence distance to a concentration that is 50% of the lower flammability limit (LFL) is 

modeled. The 50% LFL figure is a conservative level that accounts for uncertainties like the uneven 

dispersion within the cloud and the estimated value of the lower flammability limit To determine the 

mass flux of evaporating non-boiling liquids, the following equation is used (Chapter 5, P. 33): 

'4*. 
P.83 

-76-

j& = 2.10- 3 tf;Z* rk£.c -g- (P, - 2-H for: PK < 2x10* Pa 

* * * 

where 

n 

mm, = mass flux of evaporating liquid (kg/m**) 

Uw 10 = wind speed at 10 meters = 3 m/s 

rpooi,c = radius of circular pool = 46.8 in 

M = molecular weight 

R = molar gas constant = 83X103 J/kmol-K 

Tnb = temperature of non-boiling liquid = ambient temperature -= 293 K 

Pw = saturated vapor pressure of liquid (Pa) 

Pm = partial vapor pressure in surroundings = 0 for liquid (Pa) 

In order to calculate the dispersion to 50% LFL, the equation for the concentration for a continuous 

source on p. 15 of Chapter 7 is used: 

C(x,y,z) *- 0 __ ^ , . EXPJ £—\ .\EXP(- <z:

h)2) + EXp(- {z:h)2)) 

2nUv{x)ox(x) ( 2oy

2

(x)j [ { 2o2 U) J ( 2o2 (x) j J 

with y, z, and h = 0, this equation reduces to: 

C(x) =

 rt 

2n Uvoy (x) o z (x) 

where 

C(x) = concentration as a function of x only (kg-m'3) 

m = source strength (leg's"1) 

Uw = wind speed at 10 m height (m/s) 

h = source height (m) 

ffy(x) = aXb and a2(x) = cX*1, 

(see p. 10 for practical formulae for oy and c-_) 

To calculate m, the source strength, we multiply m^, (kg/m2 sec) the mass flux of the evaporating 

liquid, by the area of the pool (m2). The equation is then solved for X, the distance to the 50% LFL 

concentration. 

WR 
P.84 

BA AIChE-Sponsored Course Materials 

B4.1 General Description 

The American Institute of Chemical Engineers (AIChE) course material indudes calculations for pool 

fires and vapor doud fires for gases and liquids. For vapor doud fires for gases, the flash fraction of each 

gas is modeled as an instantaneous release; the AICHE material explains that the consequence distance 

produced by the initial flash fraction doud is so much larger than the consequence distance for the 

remaining non-flashed pan that it dominates in assessing the hazard area. The calculations for vapor 

doud explosions and BLEVES appear incomplete and cannot be used as methodologies. 

BA2 Vapor Cloud Fire Calculation for Gases 

Reference: AIChE Pp. B-65 and B-85; D-9 - D-10. 

The fraction of liquified gas vaporized (v) is given on p. D-9: 

v = fraction of liquid vaporized 

v = l-expiCp/hyCT,, - Ta)} 

where 

Cp = specific heat (Btu/lb°F) 

hy = latent heat of vaporization (Btu/lb) 

Tb = normal boiling point (°F) 

Tx = temperature of liquid stream (°F) 

We then multiply the fraction of the liquid vaporized by the quantity released to determine the amoimt of 

vaporized material (Q). 

To determine the distance to 50% LFL, the equation on p. B-84 is used: 

(Ut)°-2x

2

+y2 + z

2 

*<*- y> *• c> - ,v» <?(%)«/»*«/»e x p C2 

-V. 0> 0 t) = 1310/(Ut)2-

62

 for neutral conditions 

where 

X = concentration at the center of the cloud (assume 50% LFL) at time t (kg/m3) 

U = wind speed (m/s) 

t = time (s) 

Ut = distance (m) 

The equation is solved for U t the distance, by including the 50% LFL concentration as X and the quantity 

of vaporized material, Q. 

ISO 
P.85 

-78-

, B.43 Vapor Qoud Fire Calculations for liquids 

Reference: AIChE Pp. D-2 - D-5, D-9 - D-10. 

To determine the rate of evaporation from a circular pool, the area of the pool must first be determined. 

This is calculated by dividing the total volume of liquid by the thickness of the pool, which is estimated for 

different surface types in Table I on p. D-4. The radius of the pool is then determined and used in the 

following equation for evaporation (p. D-2): 

E = K,U^n)

/P+n¥4+I1><2+n> (kg/isec) 

where 

K* = a"U0 D2n/<

2+I0 -jj-n/P+n) 

° ~

 s

 = vapor density (kg/m3) 

RT 

Ps -= saturated vapor pressure (N/m2) 

M = molecular weight (kg/kmol) 

R = universal gas constant (8314.3 J/mol K) 

T = ambient temperature, K 

Values of n, a", K'/U0 are given in Table II (using neutral stability). 

The distance that a vapor cloud disperses from a liquid pool is given by the equation on p. D-9: 

&.. = {(36.8)(Q)/(U)(CL)}0'

552

 (m) 

where 

d1 = distance at which cloud is diluted to LFL (m) 

Q = source strength or volumetric vapor escape rate (m3/sec) 

U = wind velodty (m/sec) 

C^ = lower explosive limit (vol^n^/vol^) 

(used 50% LEL versus LEI,) 

The volumetric vapor escape rate (Q) is calculated from the Evaporation rate using the Ideal Gas Law. 

The evaporation rate (kg/s) is convened to moles using the molecular weight, moles are convened to liters 

at the prevailing temperature, and liters may then be convened to m3. 

B.4.4 Pool Fire Calculations for liquid and Gases 

Reference: AIChE Pp. D-16 - D-29. 

The AIChE methodology does not distinguish between liquids and gases in the calculation of the thermal 

flux at a specified distance from a burning pool. To determine the liquid burning rate (v), the following 

equation is used (P. D-17): 

v = vw {l-exp(-kxd)} (for a pool of diameter d) 

where 

-kj = attenuation coeffident 

v = liquid burning rate (lbs/s) 

151 
P.86 

-79-

va = liquid infinite pool burning rate = .0030 h,Jh\ 

d = pool diameter (ft) 

hc = heat of combustion (Btu/lb) 

h'v = sensible heat of vaporization (Btu/lb) = sensible heat + latent heat 

The mass burning rate can then be calculated (p. D-17): 

M = vp 

where 

M = mass burning rate (lb/ft2 sec) 

v = liquid burning rate (in/min) 

p = density of the liquid (lb/ft3) 

The mass burning rate is then used to estimate the ratio of flame height (h) to pool diameter (d) (p. D18): 

4 =42 a 

m 

Pa (gd) s 

where 

m = mass burning rate (kg/m2 sec) 

pa = density ambient air (1.206 kg/m3) 

g = acceleration of gravity = 9.8 m/sec2 

d = pool diameter (in) 

Thermal flux is calculated by dividing the total heat (Q) by the surface area of the flame envelope (S). 

Total heat available during the pool fire is: 

Q =(hc)(m)(A) (Btu/sec) 

where 

hc = heat of combustion (Btu/lb or cal/g) 

m = mass burning rate (lb/ft2 sec) 

A = pool area (fr or nr) 

Pool area is determined by dividing the total volume of the liquid by the thickness of the pool. 

Thicknesses for spreading pools over different surfaces are listed in Table I, page D-4. 

Only a fraction of the total heat is radiated from the surface of the flame envelope. These fractions may 

be read from Table II, page D-5. The surface heat flux (q0) can then be determined (p. D-19). 

q0 = Q/S (Btu/ft2hr) 

where 

S = surface area of cylindrical flame = 2-rh + -rr2 

Q = total heat 

IS* 
P.87 

19): 

-80-

The heat absorbed (q,.) by a receiver at various distances (x) from the pool center is given by (p. Dwhere 

q0 = heat flux at flame surface (Btu/ft2 hr) 

E^. = receiver surface absorptivity (from Table IH, D-25 - assumed to be 1, all heat absorbed) 

Tx = atmospheric transmissivity at distance X = 1-E„ 

Fx = view fador from receiver to flame 

E^, = emissivity of water in air 

The atmospheric transmissivity is estimated as a function of distance (x) from the center of the flame to 

the receiver times the partial pressure of water. Ew is read from a graph of emissivity versus the partial 

pressure of water (atm) times the distance (ft) found on p. D-26, assuming the partial pressure is .0024 for 

worst case winter conditions. 

The view faaor (F) is read from tables on pp. D-27 - D-29. It is plotted as a function of distance (D) 

from the flame centerline to the receiver flame radius and the plots are arranged by the flame height/pool 

diameter ratio. 

The distance is initially assumed to find a value for E^ and q_ is equal to 12.5 kw/m2. The equation is 

then solved for Fr and the distance "D" can be determined. Successive approximations of the calculations 

for the value of Fx are then calculated using the new values for the distance until one value is approached. 

IS3> 
P.88 

B.5 Green Book 

The Technical Guidance for Hazards Analysis ("Green Book") contains calculations for the consequence 

distances for Vapor Qoud Hres, where 50% of the lower flammability limit (LFL) or another fraction of 

the LFL may be used as concentration level. 

Reference: Green Book, Appendix G, "Equations Used for Estimation of Vulnerable Zones." 

The rate of release of a chemical is needed for calculation of the distance for a specific concentration. It 

is dependent on the quantity of chemical released, the nature of the release scenario (i.e., pool of liquid), 

and the properties of the chemical released. For spilled pools of chemicals, the rate of release is usually 

taken to be the evaporation rate (rate of volatilization). Using the assumptions presented above; the 

following equation is used to calculate the rate of release to air for liquids (in lbs/min): 

OR (60 sec/min x MW x K x A x VP x (929 cm2

/ft2) 

Rx (Tl+273) x (760mmHg/atm) xlSAg/lb 

where 

QR = rate of release to air (lbs/min) 

MW = molecular weight (g/g mole) 

K = gas phase mass transfer coeffident (cm/sec) 

A = surface area of spilled material (ft2) 

VP = vapor pressure of material at temperature Tl (mm Hg) 

R = 82.05 atm cm3/g mole K, and 

Tl = temperature at which the chemical is stored (°C) 

The equation for the evaporation rate (rate of volatilization) can be rewritten as follows: 

0R B 0.16 2 XMWX KxA X VP 

J?(Tl+273) 

K can be estimated based on a known value for a reference compound as follows: 

K = Krefx(MWreJ^vTW)1/3 

Using water as the reference compound: 

K-xrf = Kwatcr = 0.25x(U)078 

where: U = windspeed (m/sec) 

Combining the two equations above: 

K = 0.25 (U)078 x (18/MW)1/3 

Combining equations for QR and K yields the following equations (Green Book p. G-2): 

s*V 
P.89 

OR 

-82-

0.16 2 x 0.2 5 x (D) 0-

7 8

 x (18) 1 / 3 x Mff2/3 x A X VP 

RX (Tl+273) 

QR _. 0.106 x (P)0

*

78

 xMH2'

3

 xAxVP 

W

 RX {Tl+273) 

Calculation of the surface area (A) of the spilled material is carried out as described below. 

The following assumptions are used to calculate the surface area of the spill: 

Density = 62.4 lb/ft3 (Le., all liquids are assumed to have the same density as water) 

Depth of pool is 0.033 ft (1 cm) 

The surface area of the spilled liquid (ft2) is (Green Book p G-3): 

e5JI__£) 0.49X05 

62.4 lb/ft 3 x 0.033f t 

where 

QS = quantity spilled (lbs) and 

A = surface area (ft2) 

Substituting for A in the above equation for release rate, the quantity released to air per minute (QR) can 

be estimated as follows: 

0 „ = 0.106 JC (P) 0 7 8

 xMti2'

3

 X 0.49 X QS x VP 

82.0 5 x (Tl+273) 

For gases, it is assumed (Green Book p. 3-3) that the entire mass is released in the ten minutes: 

QS (lbs) 

QR = 

10 minutes 

where 

QS = quantity spilled (lbs) 
P.90 

-83-

, The following equation was used to derive the distance to a concentration (C). The concentration 

downwind of a release is given by (Green Book p. G-4): 

OR 

1mOyOzU 

for a ground level release with no effective plume risk where: 

C = airborne concentration (g/m3) (assumed 50% LFL) 

QR = rate of release to air (g/sec) 

it = 3.141 

ay x az = dispersion deviation, horizontal (y), and vertical (z) 

U = windspeed (m/sec) 

This equation is then solved for the produa oy av the dispersion deviation. 

a o 2? 

y

 * iitf (50% LFL) 

To determine the downwmd distance (d), Exhibit G-1 on p. G-6 lists oy and az as functions of d, using the 

stability category D for open-country conditions: 

Oy = .08 d (1 + .0001 d)"1/2 

oz = .06 d (1 + .0015 d)"1/2 

d = downwind distance, for 102<d<104 (m) 

However, the produa of ay and oz derived from the downwind concentration equation cannot be used to 

solve the produa of ay (d) and oz (d). The value from these successive approximations was then 

compared to the numerical value of the OyOz produa from the concentration equation to estimate the 

distance (d). 

ISQ 
P.91 

APPENDKC 

HAZARD CRITERIA 

ffft 
P.92 

-85-

Appendix C 

Hazard Criteria 

C l Explosion Overpressure 

C1.1 Damage and Injury from Blast Waves 

Blast waves from acddental explosions can cause damage to people and property by subjecting them to 

transient crushing pressures and winds. Relatively simple concepts have been used to quite effectively 

correlate blast wave properties with damage. The concept states that damage is primarily a function of 

either the peak overpressure, the impulse or some combination of these faaors. Peak overpressure is 

most commonly used. 

Criteria for peak overpressures causing personal injury are given in Exhibit C-l, including injury from 

direa blast effects and from flying glass. Guidelines for peak overpressures required to produce property 

damage are presented in Exhibit C-2. These data are largely based on empirical observations. There 

seems to be general agreement between sources on the data presented in Exhibit C-2; however, the same is 

not true for the data presented in Exhibit C-l. According to Exhibit C-l, lung damage may occur at 

overpressures of 10 psi. According to other sources, threshold lung damage may not occur until peak 

overpressures reach 30 to 40 psi (Grelecki, Richmond 1968). The values for corresponding fatalities also 

vary. According to the Exhibit, the lowest overpressure dted for fatality from direa blast effects is 14.5 

psi. According to another source, a 1% mortality rate is probable at 27.0 psi. Others dte values in the 

range of 35 to 120 psi as the threshold overpressure value for fatalities, 20.5 to 180 psi for a 50% fatality 

rate, and 29 to 250 psi for a 99% fatality rate (Grelecki, Richmond 1968, Lees 1980). 

Exhibits C-3 and C-4 show how lethality and injuiy vary with both overpressure and the duration of the 

blast wave. Exhibit C-5 shows similar data as a function of both pounds of TNT and range in feet 

Exhibits C-3 through C-5 present potential injury levels resulting from direa exposure to blast 

overpressures in an open area. They do not take into account injuries resulting from property damage 

presented in Exhibit C-2. For example, substantial injury and possible deaths may result from the 

shattering of conaete walls at 2.0 to 3.0 psi. In planning with regard to injuiy to personnel, the following 

guidelines have been recommended (Brasie and Simpson 1968): 

• Personnel in areas subjea to overpressures greater than about 2 psi are 

likely casualties from fragmentation or self-impaa against objects. 

• Personnel beyond the under 1 psi overpressure range should be 

reasonably safe inside a reinforced struaure away from windows or, if 

outdoors, lying on the ground. 

Nazario (1988) recommends that all personnel in open terrain be evacuated if the potential of 0.3 psi 

overpressure exists and recommends evacuating personnel in buildings that might experience an 

overpressure exceeding 1.0 psi (0.25 psi overpressure if the building has windows). 

According to the AIChE (1987), the usual procedure for control room design for plants where there may 

be the potential for explosions is to design the control room for a peak overpressure on the order of 1 to ~ 

3 psi. 

[S«? 
-86-

EXHHUTC-1. HUMAN IN JURY CRITERIA 

(Indudes Injury from Flying Glass and Direct Overpressure Effects) 

Overpressure 

(psi) 

0.6 

1.0 - 2.0 

1.5 

2.0 - 3.0 

2.4 

2.8 

3.0 

3.4 

4.0 - 5.0 

5.8 

6.3 

Injury 

Threshold for injuiy 

from flying glass* 

Threshold for skin 

laceration from flying glass 

Threshold for multiple 

skin penetrations from 

flying glass (bare skin)* 

Threshold for serious wounds 

from flying glass 

Threshold for eardrum rupture 

10% probability of eardrum 

rupture 

Overpressure will hurl 

a person to the ground 

1% eardrum rupture 

Serious wounds from flying 

glass near 50% probability 

Threshold for body-wall 

penetration from 

flying glass (bare skin)* 

50% probability of eardrum 

rupture 

Comments 

Based on studies 

using sheep and dogs 

Based on Army data 

Based on studies 

using sheep and dogs 

Based on Army data 

Conflicting data on 

eardrum rupture 

Conflicting data on 

eardrum rupture 

One source suggested an 

overpressure of 1.0 psi 

for this effea 

Not a serious lesion 

Based on Army data 

Based on studies 

using sheep and dogs 

Conflicting data on 

eardrum rupture 

Source 

(Fletcher, Richmond, 

and Yelvenon 1980) 

(Lees 1980) 

(Fletcher, Richmond, 

and Yelvenon 1980) 

(Lees 1980) 

(Lees 1980) 

(Lees 1980) 

(Brasie and Simpson 

1968) 

(U.S. DOT 1988) 

(Lees 1980) 

(Fletcher, Richmond, 

and Yelvenon 1980) 

(Lees 1980) 

Interpretation of tables of data presented in reference. 

UaO 
-87-

EXHIBITC-1. HUMAN INJURY CRITERIA 

(Indudes Injury from Flying Glass and Direct Overpressure Effects) 

(continued) 

Overpressure 

(psi) 

Injury Comments Source 

7.0 - 8.0 Serious wounds from flying 

glass near 100% probability 

10.0 Threshold lung 

hemonhage 

Based on Army data 

Not a serious lesion 

(applies to a blast of 

long duration (over 50 

msec); 20-30 psi required 

for 3 msec duration waves) 

(Lees 1980) 

(U.S. DOT 1988) 

14.5 

16.0 

17.5 

20.5 

25.5 

27.0 

29.0 

Fatality threshold for 

direa blast effects 

50% eardrum 

rupture 

10% probability of fatality 

from direa blast effects 

50% probability of fatality 

from direa blast effects 

90% probability of fatality 

from direa blast effects 

1% Mortality 

99% probability of fatality 

from direa blast effects 

Fatality primarily from 

lung hemonhage 

Some of the ear injuries 

would be severe 

Conflicting data on 

mortality 

Conflicting data on 

mortahty 

Conflicting data on 

mortality 

A high inddence of severe 

lung injuries (applies to a 

blast of long duration (over 

50 msec); 60-70 psi required 

for 3 msec duration waves) 

Conflicting data on 

mortality 

(Lees 1980) 

(U.S. DOT 1988) 

(Lees 1980) 

(Lees 1980) 

(Lees 1980) 

(U.S. DOT 1988) 

(Lees 1980) 

l-l 
-88-

EXHIBIT C-2. PROPERTY DAMAGE CRITERIA 

Overpressure (psi) Damage Source(s) 

0.03 

0.04 

0.10 

0.15 

0.30 

0.4 

0.5 - 1.0 

0.7 

1.0 

1.0 - ZO 

1.3 

Occasional breaking of large glass 

windows already under strain 

Loud noise (143dB). Sonic boom 

glass failure 

Breakage of windows, small, under strain 

Typical pressure for glass failure 

"Safe distance" (probability 0.95 no 

serious damage beyond this value). Missile 

limit Some damage to house ceilings. 

10% window glass broken. 

Minor struaural damage 

Shattering of glass windows, occasional 

damage to window frames. One source 

reported glass failure at 0.147 psi 

Minor damage to house structures 

Partial demolition of houses, made 

uninhabitable 

Shattering of corrugated asbestos siding 

Failure of corrugated aluminum/steel paneling 

Failure of wood siding panels (standard 

housing construction) 

Steel frame of clad building slightly 

distorted 

(Lees 1980) 

(Lees 1980) 

(Lees 1980) 

(Lees 1980) 

(Lees 1980) 

(McRae 1984, Lees 

1980) 

(Brasie and Simpson 

1968, .Air Force 1983, 

U.S. DOT 1988, 

Lees 1980) 

(Lees 1980) 

(Lees 1980) 

(Brasie and Simpson 

1968, Air Force 1983, 

U.S. DOT 1988, 

Lees 1980) 

(Lees 1980) 

2.0 Partial collapse of walls and roofs of houses (Lees 1980) 

SSlr 
-89-

EXHIBIT C-2. PROPERTY DAMAGE CRITERIA 

(continued) 

Overpressure (psi) Damage Source(s) 

2.0 - 3.0 

13 

2-5 

3.0 

3.0 - 4.0 

4.0 

4.8 

5.0 

5.0 - 7.0 

7.0 

7.0 - 8.0 

Shattering of non-reinforced conaete or cinder 

block wall panels (1.5 psi according to 

another source) 

Lower limit of serious struaural damage 

50% destruction of brickwork of house 

Steel frame building distorted and 

pulled away from foundations 

Collapse of self-framing steel panel buildings 

Rupture of oil storage tanks 

Snapping failure - wooden utility tanks 

Cladding of light industrial buildings 

ruptured 

Failure of reinforced conaete struaures 

Snapping failure - wooden utility poles 

Nearly complete destruction of houses 

Loaded train wagons overturned 

Shearing/flexure failure of brick wall panels 

(8-12 inches thick, not reinforced) 

Sides blown in of steel frame buildings 

Overturning of loaded rail cars 

(Brasie and Simpson 

1968, jAir Force 1983, 

U.S. DOT 1988, 

Lees 1980) 

(Lees 1980) 

(Lees 1980) 

(Lees 1980) 

(Brasie and Simpson 

U.S. DOT 1988, 

Lees 1980) 

(Lees 1980) 

(McRae 1984) 

(Brasie and Simpson 

1968, Lees 1980) 

(Lees 1980) 

(Lees 1980) 

(Brasie and Simpson 

1968, Air Force 1983, 

U.S. DOT 1988, 

Lees 1980) 

(Air Force 1983) 

(Brasie and Simpson 

1968, U.S. DOT 1988) 

MUS) 
P.97 

-90-

EXHIBIT C-2. PROPERTY DAMAGE CRITERIA 

(continued) 

Overpressure (psi) Damage Source(s) 

9.0 Loaded train box-cars completely demolished (Lees 1980) 

10.0 Probable total destruction of buildings (Lees 1980) 

30.0 Steel towers blown down (Brasie and Simpson 

1968, Air Force 1983) 

88.0 Crater damage (McRae 1984) 

{.iA 
-91-

EXfflBITC-3. LETraALTTY CURVES 

(For a 154 lb Person in Free Stream Situations) 

kPa PU 

Maximum 

incident 

overpressure 

10.000 

5,000 

2.000 

1.000 

SOO 

200 

619 

9 9 * lathality 

50% lethality — - - — 

I H lathality 

0.2 0.4 1.0 2 « 710 20 40 100 200 1000 

Ouration ef poaitive ina**m ovorpreMure. rmac 

SOOO 

EXHIBIT C-4. LETHALITY AND INJURY CURVES 

(For a 154 Ib Person in Free Stream Situations) 

kPa 

10* 

103 

Maximum 

incident 

overpressura 

IO* 

10 

0.1 

I H Lethality 

P* 

1.000 

100 

10 

0.1 • 

0.01 

Threshold lung dameoa -»«*«•*•« 

S0% Eardrum rupture • -

9SH Eardrum protection with muffs =^ = 

95S Eardrum protection w/o muffs — . _ . _ 

-f- •+• 

0.2 1.0 10 100 

Ouration of positive incident ovarpranur 

Notes: msec = milliseconds 

kPa = kilopascals = 6.895 psi 

psi = pounds per square inch = 0.1450 kPa 

Source: U.S. DOT 1988, Kokinakis and Rudolph 1982. 

— I — 

1000 

.msec 

10.000 

Itf 
-92-

EXHHHT C-5. AIR-BLAST CRITERIA FOR PERSONNEL STANDING IN THE OPEN 

P.99 

100 

RANGE IN FEET 

10,000 

Source: U.S. DOT 1988, Richmond and Fletcher 1971. 

*\A\C 
p.1 

-93-

Note that although glass is reported to shatter at an overpressure level of 0.5 psi (see Exhibit C-2), there is 

evidence that human injuiy from flying glass is unlikely at this level. Lees (1980) dtes a report stating that 

risk of injury from frying window glass is negligible for an explosion that gives a peak overpressure of 0.6 

psi or less. Lees also dtes a report giving the skin laceration threshold for flying glass as 1-2 psi and the 

serious wound threshold as 2-3 psi (see Exhibit C-l). Fletcher, Richmond, and Yelverton (1980) carried 

out experiments on the effects on sheep and dogs of glass fragments from windows shattered by various 

blast overpressures. Their results (briefly dted in Exhibit C-l) appear to agree reasonably well with the 

data reported by Lees. Their data indicate that the threshold for injury from flying glass is about 0.6 psi. 

Multiple injuries from skin penetration (i.e., ten or more) may occur for bare skin at overpressures of 1.5 

psi or higher. Flying glass may penetrate the body-wall at 5.8 psi or higher if the skin is bare. The 

authors point out that the skin and body-wall thickness of men and sheep are approximately the same 

(Fletcher, Richmond, and Yelverton 1980); therefore, the data reported should be roughly applicable to 

humans. 

C.L2 Distance Determination for Different Overpressures 

To determine the effea on distance of modelling to different overpressures for vapor cloud explosion, the 

WHAZAN model was run for several different overpressures for vapor doud explosions of ethylene and 

propylene. Exhibit C-6 shows explosion overpressure versus consequence distance for 100,000 pound 

releases of ethylene and propylene. The curves are not linear, a relatively small change in overpressure at 

the lower end of the scale results in a relatively large change in the consequence distance, while a relatively 

small change in overpressure at the upper end of the scale results in relatively small change in 

consequence distance. However, increasing the overpressure at the upper end of the overpressure scale 

appears to have a much smaller effea on the consequence distance. 

C2 Flammability limits 

As noted in the text (Section 5.3.2.2), the lower flammable limit (LFL) of a vapor or gas is the minimum 

concentration in air that will ignite and propagate flame. Using 50 percent of the LFL to estimate 

consequence distances for vapor cloud fires accounts for variability within the cloud from its edge to its 

center and inaccurades in dispersion modelling. 

To determine the effea of using different concentrations to estimate the consequence distance for vapor 

cloud fires, two representative chemicals, ethylene and propylene, were modelled using WHAZAN at 

10,000 pounds and 100,000 pounds. Moderate meteorology (wind speed 3.0 meters per second and 

atmospheric stability D) was assumed. The model was run for three concentrations, at 50% of the lower 

flammable limit at the lower flammable limit and at 200% of the lower flammable limit The results of 

modelling are shown graphically in Exhibit C-7. The results curves for both quantities and both chemicals 

modelled are basically similar in shape but of differing magnitudes. The results curves clearly are not 

linear: the change in magnitude between the consequence distance obtained at 50% of the lower 

flammabile limit and that at the lower flammable limit is clearly greater than the change between the 

lower flammable limit and 200% of the lower flammable limit for all four curves. 

ib"! 
Exhibit C-6 

HAZARD CRITERIA COMPARISON FOR VAPOR CLOUD EXPLOSIONS 

FOR INSTANTANEOUS RELEASES OF 100,000 POUNDS 

1750 

1500 

1250 ^** 

(0 

o 

o 

E 

g 1000 

c 

to 

n 

O 

750 

500 

250 

Ethylene 

Propylene 

* 

4 5 6 

Overpressure (psi) 

8 9 10 

ho 
Exhibit C-7 

HAZARD CRITERIA COMPARISON FOR VAPOR CLOUD FIRES 

FOR EVAPORATING POOLS FROM INSTANTANEOUS RELEASES, MODERATE METEOROLOGY 

(Wind speed 3.0 meters per second, atmospheric stability class D) 

1500 

1250 

1000 

(D 

O 

C 

D 

in 

750 -

500 -

250 

0 

• Ethylene (100,000 lbs.) 

A Propylene (100.000 lbs.) 

* Ethylene (10,000 lbs.) 

O Propylene (10.000 Iba.) 

vO xj\ 

1 

50% LFL LFL 2LFL 

-8> 

Concentration 

CO 
P.4 

-96-

C3 Heat Radiation 

C3.1 Heat Radiation Levels Causing Death and Injury 

Human injury or fatality from heat radiation from fires is likely to occur as a result of direa exposure to a 

fire rather than as a result of property damage caused by a fire. The extent of the injury caused by heat 

radiation depends both on the heat level and the time of exposure. Exhibit C-8 presents heat radiation 

levels and exposure times required to produce various human effects or injuries. There are few data on 

fatalities from heat radiation; the fatality data shown in Exhibit C-8 have been calculated or estimated. 

Both the WHAZAN (1988) and Mudan (1984) fatality data appear to be based on data on the relation 

between thermal radiation intensity and burn injury for nuclear explosions at different yields (Eisenberg et 

aL 1975, as dted by Mudan 1984). According to Mudan (1984), exposure times for nuclear explosions are 

typically very short and interpretation of the data is "somewhat subjective." 

In a review of fire hazards by Takata in 1970 for the Armed Services Explosive Safety Board, estimates are 

presented of critical radiant exposure necessary to ignite or damage several types of targets, including 

people. As reported in VoL I of the CPIA "Hazards of Rockets and Propellants," minimum critical 

exposures necessary to ignite or damage people range from 94.6 kW/m2 for a 10-second exposure time to 

35.1 kW/m2 for a 60-second exposure and 27.8 kW/m2 for a 190-second exposure. 

The WHAZAN manual includes a table for fatality based upon exposure to heat Exhibit C-9 presents the 

lethality of heat flux as presented in the manual. 

The exposure times given for the fatality levels are calculated from a Probit equation (indicating statistical 

probability based on deviations from the mean of normal distribution), as follows: 

Probit = -14.9 + 2.56 logg (t x Q4/3 x IO"4) 

where Q is in watts per square meter and t is in seconds 

The WHAZAN model uses radiation levels of 12.5 to 37.5 kW/m2 in its output, based on the likelihood 

that people would be able to "shelter" from the fire within 30 seconds to one minute. For this period of 

time, the probability of fatality ranges from 1 percent at 12.5 kW/m2 for 30 seconds to 99 percent at 37.5 

for 50 seconds (see Exhibit C-9). 

Mudan (1984) estimated a slightly lower fatality threshold of 10 kW/m2 for a 40-second exposure time. 

Mudan estimated this level from the data of Eisenberg et al (1975, as dted by Mudan 1984). A plot of 

thermal radiation versus time for injuries and fatalities shows that 1 percent fatalities may occur at 10 

kW/m2 at a time of 40 seconds. The 10 kW/m3 radiation level suggested by Mudan, which is used in the 

ARCHIE model to determine the zone for fatalities from pool fires, agrees quite well with the 12.5 

kW/m2 level. 

Nazario (1988) indicates that all personnel should be evacuated from areas where the radiant heat is likely 

to exceed one-half of the threshold value for second degree burns to bare skin (5,000 Btu/hr-ft2, or 16 

kW/m2, for an exposure of about 5 seconds). 

^0 
P.5 

-97-

EXHIB_TC-8 

HUMAN INJURY CRITERIA 

(Thermal Radiation Effects on Bare Skin) 

Thermal 

Radiation 

fkW/m«_ 

1.75 

6.4 

10 

12_5 

37.5 

Time of Exposure 

(Seconds') 

60 

27 

92 

15 

13 

40 

8 

20 

40 

30 

80 

200 

8 

20 

50 

Injury or Effect 

Pain threshold reached 

Severe pain 

Second degree burn 

Pain threshold reached 

"Unbearable" pain 

Second degree burn 

(injury threshold) 

Pain Uireshold reached 

Second degree bum 

Fatality threshold 

1% fatality 

50% fatality 

99% fatality 

1% fatality 

50% fatality 

99% fatality 

Source 

WHAZAN 1988 

Buettner 1951 

Hardy et aL 1953 

Stoll and Greene 1959 

Bigelow et aL 1945 

HCHAP 1989 

WHAZAN 1988 

Mudan 1984 

Mudan 1984 

WHAZAN 1988 

WHAZAN 1988 

Mudan 1984 

WHAZAN 1988 

WHAZAN 1988 

WHAZAN 1988 

WHAZAN 1988 

WHAZAN 1988 

WHAZAN 1988 

ru 
P.6 

Thermal Radiation 

(kW/m2) 

1.6 

4.0 

12^ 

37.5 

-98-

Exhibit C-9 

FATALITY FROM HEAT EXPOSURE 

Seconds 

1% 

500 

150 

30 

8 

exposure for % fatality 

50% 

1300 

370 

80 

20 

99% 

3200 

930 

200 

50 

Reference: WHAZAN Handbook (1988) 

t"|V 
P.7 

-99-

C32 Distance Determination for Different Heat Radiation Levels 

Modelling was carried out using the WHAZAN model to determine the effea of heat radiation level on 

consequence distances for BLEVEs and pool fires. 

C3.2.1 BLEVES 

For BLEVEs, ethylene and propylene were modelled at 10,000 pounds and 100,000 pounds. The model 

was run for three heat flux consequence levels, 4 kW/m2,12.5 kW/m2, and 37.5 kW/m2. The relationship 

between the consequence distance results for ethylene and propylene and other hydrocarbon results for 

BLEVEs can be seen by examining Exhibit C-10. The results curves for both quantities and both 

hydrocarbons modelled are basically similar in shape but of differing magnitudes. The results curves 

dearly are not linear: the change in magnitude between the consequence distance obtained at 4 kW/m2 

and that at 12-5 kW/m2 is dearly greater than the change between 12.5 kW/m2 and 37.5 kW/m2 for all four 

curves. Results for other hydrocarbons studied are approximately the same as the results for propylene. 

C322 Pool Fires 

For pool fires, ethylene and propylene were modelled at 10,000 pounds and 100,000 pounds. The 

WHAZAN model was run for three heat flux consequence levels, 1.6 kW/m2,4 kW/m2, and 12.5 kW/m2. 

Modelling results are presented in Exhibit C-ll. The results curves for both quantities and both chemicals 

modelled are basically similar in shape but of only slightly differing magnitudes. The results curves clearly 

are not linear: the change in magnitude between the consequence distance obtained at 1.6 kW/m2 and that 

at 4 kW/m2 is dearly greater than the change between 4 kW/m2 and 12.5 kW/m2 for all four curves. 

Results for other hydrocarbons studied are approximately the same as the results for ethylene and 

propylene. 

\"B 
Exhibit C-10 

HAZARD CRITERIA COMPARISON FOR BLEVES, 

INSTANTANEOUS RELEASES 

O 

c 

a 

+-> 

m 

S <I___JJ * 

Q 

800 

700 H 

600 -

500-

400 -

300 -

200 -

100 -

0 

0 

£ 

• Ethylene (100.000 lbs.) 

A Propylene (100.000 lbs.) 

* Ethylene (10.000 Iba.) 

O Propylene (10.000 lbs.) 

12.5 37.5 

BLEVE Heat Flux (kW/m2) 

Tl 

00 
Exhibit C-ll 

HAZARD CRITERIA COMPARISON FOR POOL FIRES, 

INSTANTANEOUS RELEASES 

CD 

<_> 

C 

o 

600 

500 -

400 -

300 -

^ 200 -

100 -

0 

_3 Poolfire Heat Flux (kW/m2) 

to 
P.10 

-102-

CA References 

AIChE. 1987. American Institute of Chemical Engineers. Methods for Calculation of Fire and Explosions 

Hazards. New York: AIChE, 

Brasie, W., Simpson, D. 1968. "Guidelines For Estimating Damage Explosion," AICHE Symposium on 

Loss Prevention in the Process Industries, February 18-23,1968. 

CPIA 1984. Hazards of Chemical Rockets and Propellants, Volume I, Safety, Health, and the 

Environment CPIA Publication 394, September 1984. Laurel, MD: Johns Hopkins University. 

Eichler, T., Napadensky, H. 1977. "Acddental Vapor Phase Explosions on Transportation Routes Near 

Nuclear Plants," HT Research Institute, Prepared for Argonne National Laboratory. April 1977. 

Eisenberg R A et al. 1975. Vulnerability Model. A Simulation System for Assessing Damage Resulting 

from Marine Spills. NTIS AD-A015-245. Springfield, VA 

Fletcher E.R., Richmond D.R., Yelverton J.T. 1980 (May 30). "Glass Fragment Hazard from Windows 

Broken by Airblast" Washington, D.C:Defense Nuclear Agency. Report Number DNA 5593T. 

Grelecki, C "Fundamentals of Fire and Explosion Hazards Evaluation," C Grelecki, Hazards Research 

Corp., AICHE Today Series. 

HCHAP. 1989. Handbook of Chemical Hazard Analysis Procedures. Federal Emergency Management 

Agency, U.S. Department of Transportation, U.S. Environmental Protection Agency. 

Kokinakis W., Rudolph R. 1982. An Assessment of the Cunent State-of-the-Art of Incapadtation by Air 

Blast Minutes of the 20th Explosives Safety Seminar, August 1982. 

Lees, F.P. 1980. Loss Prevention in the Process Industries, Vol. 1. London: Butterworths. 

McRae, T. 1984. "The Effects of Large Scale LNG/Water RPT Explosions," McRae, T.G., etal., Lawrence 

Livermore National Laboratory. April 27,1984. 

Mudan K.S. 1984. Thermal Radiation Hazards from Hydrocarbon Pool Fires. Prog. Energy. Combust 

Sd. 1984, Vol. 10. Great Britain: Pergamon Press Ltd. 

Nazario N.N. 1988. Preventing or Surviving Explosions. Chemical Engineering, August 15,1988. 

NFPA "Fire Protection Handbook," 16th edition, National Fire Protection Association (NFPA). 

Richmond, D. 1968. "The Relationship Between Seleaed Blast-Wave Parameters and the Response of 

Mammals Exposed to Air Blast." Richmond DR, Damon E.G., Fletcher E.R., Bowen I.G., White CS., 

Ann. N.Y. Acad. ScL, 1968. 

Richmond D.R., Fletcher E.R. 1971. Blast Criteria for Personnel in Relation to Quantity-Distance. 

Minutes of the 13th ASESB Seminar, 401-419. 

U.S. Air Force 1983. "Explosives Safety Standards," AF Regulation 127-100, 20 May 1983. 

U.S. DOT 1988. "Hazard Analysis of Commerdal Space Transportation," Office of Commerdal Space 

Transportation Licensing Programs Division, U.S. Department of Transportation. May 1988. 

WHAZAN. 1988. WHAZAN User Guide. Technica International Ltd. 

Wiekema, B. J. 1984. "Vapor Cloud Explosions - An Analysis Based on Acddents," Journal of Hazardous 

Materials, 8 (1984). 

^ 
P.11 

APPENDIX D 

COMPARISON OF RESULTS OF MODELLING BY DIFFERENT METHODS AND 

RESULTS OF VARYING RELEASE SCENARIOS AND METEOROLOGICAL CONDITIONS 

in 
-104-

Appendix D. Comparison of Results of Modelling by Different Methods and 

Results of Varying Release Scenarios and Meteorology 

D.l Vapor Cloud Explosion Results 

Exhibit D-1 presents the results of modelling using several methods for vapor cloud explosions based on 

0.5 psi overpressure. This exhibit shows the maximum distance at which the models indicate that the 

chosen overpressure would be reached. For releases of 100,000 pounds of gases, distances of 326 to 1,165 

meters were calculated. 

The distances obtained from WHAZAN, the Yellow Book, and ARCHIE at each overpressure level agree 

quite well with each other, although the WHAZAN and Yellow Book distances for vapor cloud explosions 

for ethylene and propane are significantly lower than the distances obtained from ARCHIE. These two 

gases are assumed to be stored at reduced temperatures. The WHAZAN and Yellow Book vapor cloud 

explosion calculations are based on the quantity of gas immediately flashed into vapor on release, and this 

quantity depends on the difference between the temperature of the released gas and its boiling point As 

ethylene and propane are assumed to be stored at temperatures not far above their boiling points, the 

fraction calculated to be immediately flashed into vapor (i.e., the quantity that may be involved in a vapor 

cloud explosion) is relatively small. ARCHIE, on the other hand, assumes that all the material in a 

container of pressurized gas is released to the air as a gas-aerosol mixture unless the storage temperature 

is more than 10°C below the boiling point of the gas. For ethylene and propane, the assumed storage 

temperature, though below ambient temperature, is greater than the boiling point; therefore, ARCHIE, 

unlike WHAZAN and the Yellow Book, does not yield consequence distances for these two gases that are 

significantly lower than those for the other gases. If the storage temperature is more than 10°C below the 

boiling point, ARCHIE assumes the material is released as a liquid, and, therefore, no vapor doud 

explosion results are obtained. 

ARCHIE produced vapor cloud explosion results for the liquids modelled; however, a disclaimer was 

provided in the accompanying manual and on the output results pointing out that "inddents involving 

tanks that are designed to operate at atmospheric pressure are very rare." An additional disclaimer stated 

that clouds or plumes containing less than 1,000 pounds of vapor or gas are very unlikely to explode when 

completely unconfined; modelling indicated that for heptane, toluene, and p-xylene, there would be less 

than 1,000 pounds of vapor released. Because of these disclaimers, the ARCHIE vapor cloud explosion 

results for the liquids modelled are not included in Exhibit D-1. 

D.2 Vapor Qoud Fire Results 

Exhibit D-1 includes vapor cloud fire results calculated by five methods for releases of 100,000 pounds. 

The distances given are downwind distances for dispersion to a concentration equal to 50 percent of the 

LFL. For the Yellow Book, results for gases were calculated based on both the quantity of gas 

immediately flashed into vapor upon release and on the remaining liquefied gas evaporating from a pool 

after flashing; note that the distances obtained using the quantity flashed into vapor are significantly larger 

than those calculated using the evaporating pool, except in the cases of the two gases assumed'to be stored 

at reduced temperatures. For these two gases, ethylene and propane, the distances calculated based on the 

evaporating pool are greater than the distances based on the quantity flashed. Results from the AIChE 

course material for gases are based only on the quantity flashed, as recommended. The distances 

calculated for ethylene and propane, the gases assumed stored at reduced temperatures, are considerably 

lower than the distances for the two gases assumed stored at ambient temperature. Distances obtained for 

gases using the Green Book methodology are generally lower than those found by the other methods, 

probably because the Green Book recommends assuming total release of the gas over a ten minute period, 

while the other methods assume an instantaneous release. The distances calculated using the Green Book 

n<8 
Exhibit D-1 

RESULTS OF MODELLING BY ALL METHODS 

WHAZAN Modelling Results for Instantaneous Releases, Moderate and Worst Case Meteorology, and 

Prolonged Releases, Moderate Meteorology (100,000 pounds) 

Chemical 

Ethylene 

Propylene 

Propane 

Butane 

Ethylene Oxide 

Ethyl Chloride 

Acetaldehyde 

Pentane 

Acetone 

Gasoline 

Hexane 

Trichloroethylene 

Heptane 

Toluene 

Acetic Acid 

p-Xylene 

Benzaldehyde 

Dimethyl Sulfoxide 

Boiling 

Point 

(K) 

171 

227 

229 

275 

282 

286 

293 

313 

329 

332 

345 

360 

375 

383 

391 

410 

452 

462 

INSTANTANEOUS RELEASE 

MODERATE METEOROLOGY 

Distance (meters) 

VCE VCF BLEVE 

(0.5 psi) (50X LFL) <12.5kW/m2) 

457 1390 388 

1121 706 287 

392 747 278 

766 460 269 

443 338 206 

268 262 178 

130 451 200 

** 341 269 

•• 214 ** 

** 338 ** 

•* 233 •* 

#* jj ** 

*• 173 *• 

*• 154 *• 

** 98 ** 

** 110 ** 

** 30 ** 

** 41 •« 

Pool 

Fire 

(12.5kw/m2) 

181 

160 

183 

176 

109 

97 

107 

182 

116 

175 

174 

** 

168 

153 

** 

152 

109 

86 

VCE 

INSTANTANEOUS RELEASE 

WORST CASE METEOROLOGY 

Distance (meters) 

VCF BLEVE 

(0.5 psi) (SOX LFL) (12.5kw.m2) 

457 

1121 

392 

766 

* 

* 

* 

** 

* 

## 

•* 

* 

** 

** 

* 

•• 

* 

* 

Pool 

Fire 

(12.5kU/m2) 

6350 388 

2900 287 

3100 278 

1790 269 

• * 

» * 

• * 

1280 269 

* * 

1270 ** 

842 *• 

• • 

604 ** 

535 *• 

• * 

374 ** 

• • 

• * 

181 

160 

183 

176 

• 

* 

* 

182 

• 

175 

174 

» 

168 

153 

* 

152 

• 

• 

VCF 

(50X LFL) 

79 

18 

73 

20 

* 

« 

* 

21 

• 

64 

56 

« 

57 

67 

* 

65 

• 

* 

PROLONGED RELEASE 

MODERATE METEOROLOGY 

Distance (meters) 

BLEVE Pool 

(12.5lcU/m2) Fire 

(12.5kv/n*2)(12 

388 17 

287 15 

278 17 

269 9 

• • 

• * 

• • 

269 23 

• • 

** 16 

•• 15 

• • 

*• 15 

*« 16 

• • 

** 16 

• • 

• * 

Jet 

Fin 

.5M 

*» 

42 

•• 

21 

• 

• 

* 

** 

• 

*• 

•_ 

• 

•_ 

#* 

• 

** 

• 

• 

* Analysis was not carried out 

** No results were obtained from analysis, or results were not Included, based on evaluation. 

VCE = Vapor Cloud Explosion 

VCF « Vapor Cloud Fire 

n. Modelling Results Using Other Methods for Instantaneous Releases, Moderate Meteorology 

(100,000 pounds) 

8 

Chemical 

Ethylene 

Propylene 

Propane 

Butane 

Pentane 

Gasoline 

Hexane 

Heptane 

Toluene 

p-Xylene 

Boiling 

Point 

(K> 

171 

227 

229 

275 

313 

332 

345 

375 

383 

410 

ARCHIE Results 

Distance (meters) 

VCE VCF 

(0.5 psi) (50X LFL) 

867 770 

682 751 

683 733 

680 712 

•• 453 

» M 7 

** 160 

«* 112 

** 97 

** 0 

BLEVE 

285 

285 

285 

285 

*# 

** 

** 

«» 

** 

*« 

Pool 

Fire 

(10kV/rri_> 

** 

** 

** 

** 

151 

137 

151 

153 

150 

144 

VCE 

(0.5 psi) 

415 

932 

326 

635 

** 

*« 

** 

** 

*» 

** 

Yellow Book Results 

Distance (meters) 

VCF (Gases) VCF (All) 

Flash Pool 

Fraction Evaporation 

(50X LFL) (50% LFL) 

330 922 

862 554 

261 586 

547 242 

•* 239 

** 216 

** 115 

" 60 

•* 42 

** 22 

Pool 

Fire 

(12.5kU.m2) 

134 

112 

137 

120 

120 

107 

112 

106 

86 

86 

AIChE Manual Results 

Distance (meters) 

VCF (Gases) VCF (Liquids) 

Flash Pool 

Pool 

Fire 

Fraction Evaporation (12.5k_/m2) 

(SOX LFL) (50X LFL) 

452 •• 

1165 *• 

355 *« 

720 ** 

** 187 

** 170 

** 95 

** 53 

*« 38 

** 21 

299 

188 

225 

190 

221 

213 

206 

202 

169 

166 

Green Book 

Distance 

VCF 

(SOX LFL) 

371 

350 

332 

310 

165 

163 

86 • 

50 • 

44 • 

28 • 

* Analysis was not carried out. 

** No results were obtained from 

VCE « Vapor Cloud Explosion 

VCF » Vapor Cloud Fire 

analysis, or results were not Included, based on evaluation. 

• Method Is not valid 

for distances less 

than 100 meters. 

^ 3 

_Z2 

TJ 
P.14 

-106-

method, whidi does not take storage temperature into account are higher than other results only in the 

cases of the Yellow Book results for the flashed fraction of ethylene and propane (the gases assumed 

stored at reduced temperatures). 

Results for chemicals that are liquids at ambient temperatures are based on evaporating pools for all the 

models (see Appendix B for details). Distances to a concentration equal to 50 percent of the LFL for 

vapor doud fires range from 261 to 1,390 meters for gases; distances are generally smaller for liquids, 

although significant distances result for volatile liquids (e.g., distances calculated by the various methods 

range from 165 to 453 meters for pentane). Distances obtained using the Green Book dispersion 

modelling calculations are not valid for less than 100 meters; therefore, the Green Book results for four 

relatively non-volatile liquids should be disregarded. It is possible that distances less than 100 meters 

obtained from some of the other methods may also be invalid, as similar methods appear to be used in the 

calculations. 

D3 BLEVE Results 

Exhibit D-1 presents the results obtained using WHAZAN and ARCHIE to model BLEVEs for 100,000 

pound releases. WHAZAN results are shown for a heat radiation level of 12.5 kW/m2 for WHAZAN. 

The distance reported as the "fatality distance" on the ARCHIE output results is presented in this exhibit 

BLEVEs are not modelled in ARCHIE; however, since fireballs are generally associated with BLEVEs, 

these results from the ARCHIE model are presented in Exhibit D-1 for comparison to WHAZAN 

BLEVE results. The other models used for consequence analysis did not include methods for analyzing 

BLEVEs. 

ARCHIE results are based on fireball size and heat radiation (see Appendix C, Section ALIO). 

According to the ARCHIE manual, the fatality level corresponds to a heat flux in excess of 160 kilojoules 

per square meter (kJ/m2). Using the fireball duration of 15 seconds to convert the heat radiation level 

from kJ/m2 to kW/m2 indicates that the ARCHIE fatality level is about 11 kW/m2, which is veiy dose to 

12.5 kW/m2, used by WHAZAN. Note, however, that WHAZAN gives a BLEVE duration of 36 seconds 

while ARCHIE gives a duration of 15 seconds for a 100,000 pound release. 

The ARCHIE model gives a fatality distance of 285 meters for all the chemicals modelled; the lack of 

variation by chemical is probably due to the faa that, according to the ARCHIE manual, ARCHIE 

assumes that the chemical modelled is propane or has similar charaaeristics. WHAZAN consequence 

distances range from 178 meters to 387 meters for a heat radiation level of 12.5 kW/m2. 

D.4 Pool Fire Results 

Results of modelling using different methods for pool fires, showing the maximum distance at which a heat 

radiation level of 12.5 kW/m2 (10 kW/m2 for ARCHIE) is reached, are presented in Exhibit D-1. The 

WHAZAN model indicated that the pool fires of the chemicals modelled would last 60 seconds or more; 

as stated in the WHAZAN manual, it might be possible to "shelter" from the fire within about 30 seconds 

to one minute. 

Differences between chemicals modelled by each method are relatively small. The distances calculated by 

different methods are in reasonably good agreement with each other. The calculations based on the 

AIChE-sponsored materials gave the greatest distances (166 to 299 meters), while the Yellow Book 

method gave the smallest (86 to 134 meters). The ARCHIE model does not give pool fire results for 

gases. The other models allow the calculation of results for gases; the results for gases differ little from 

the results for liquids. The distances found for pool fires for 100,000 pound releases of gases for a heat 

radiation level of 12.5 kW/m2 are smaller than the distances for vapor cloud explosions for the same 

quantity modelled at 3.0 psi or lower, except for gases assumed stored at reduced temperatures. Vapor 

cloud fire results (for 50 percent of the LFL) and BLEVE results (for 12.5 kW/m2) for gases are larger 

than the pool fire results. For relatively volatile liquids (e.g., pentane), vapor cloud fire distances are 

generally greater than pool fire distances; for less volatile liquids, distances calculated by most of the 

methods are greater for pool fires. 

\Q) ,0 
P.15 

JJ 

-107-

D.5 Jet Fire Results 

Jet fire results, which are, by definition, prolonged releases, were obtained only for propylene and butane, 

the two gases assumed to be liquefied under pressure. For jet fires, the release was assumed to take place 

from a 1.5 inch hole in a tank 12 feet in diameter. Results are shown for 100,000 pound releases in 

Exhibit D-1 for a heat flux level of 123 kW/m2. Jet fires of propylene and butane under these conditions 

gave distances that are smaller than any of the distances for any other acddent type resulting from 

instantaneous releases. Distances for jet fires are somewhat greater, however, than for vapor cloud fires or 

pool fires resulting from prolonged releases under the same conditions. 

D.6 Instantaneous Release Compared to Prolonged Release 

Ten hydrocarbons studied were modelled using the prolonged release scenario in the WHAZAN linked 

model for comparison with the modelling results for instantaneous release. The WHAZAN linked model 

(prolonged release) was run for 100,000 pounds of each chemical assuming the same meteorological 

conditions (3.0 meters per second wind speed and D wind stability), and storage conditions as for the 

instantaneous release. To simulate a prolonged release, a 1.5 inch hole in a 12 foot diameter tank was 

assumed. The average evaporation rate for the pool, as determined in the linked model, was then used to 

run the WHAZAN stand-alone model for buoyant plume dispersion (see Appendix B.1 for more 

information). 

Exhibit D-1 shows results of WHAZAN modelling for prolonged releases of ten chemicals, where release 

was assumed to take place from 13 inch diameter holes in 12 foot diameter tanks. Distances to 50 

percent of the LFL for vapor cloud fires are much smaller (18 to 79 meters) than for instantaneous 

releases. 

For pool fires, prolonged releases also result in much smaller consequence distances than instantaneous 

releases. As was the case for instantaneous releases, the consequence distance varies little from chemical 

to chemical. The magnitude of the results curve is much smaller for prolonged releases than for 

instantaneous releases, and all of the prolonged release consequence distances are less than 25 meters. 

WHAZAN did not produce vapor cloud explosion results for prolonged releases. As shown in Exhibit D1, WHAZAN produced BLEVE results for prolonged releases that are identical to the results for 

instantaneous releases. It is not clear what these results mean, since BLEVEs seem to be instantaneous 

releases by definition (see Section 7.13). 

D.7 Moderate Meteorology Compared to Worst Case Meteorology 

Ten hydrocarbons were modelled using WHAZAN to determine the effea on consequence distances of 

using worst case meteorology rather than moderate meteorology. The WHAZAN linked model 

(instantaneous release) was run for 100,000 pounds of each chemical using the same storage temperatures 

and pressures as used with moderate meteorology. Worst case meteorological conditions (1.5 meters per 

second wind speed and F wind stability) were used rather than moderate meteorological conditions (3.0 

meters per second wind speed and D wind stability). The average evaporation rate for the pool, as 

determined in the linked model, was used to run the WHAZAN stand-alone model for buoyant plume 

dispersion. Various other default values were used in the model; these values are summarized in Appendix 

E. 

Exhibit D-1 includes vapor cloud fire results from WHAZAN for ten chemicals using worst case 

meteorological conditions of wind speed of 1.5 meters per second and F atmospheric stability. The 

WHAZAN results appear to be strongly dependent on the meteorological assumptions made, with 

distances determined using worst case meteorology being much greater than those resulting from 

modelling using moderate meteorology. As shown in Exhibit D-1, distances under worst case 

meteorological conditions extend from 1,790 to 6350 meters for gases, compared to 460 to 1390 meters 

under moderate conditions. For the other consequence types, the results were the same for both 

meteorological conditions, indicating that varying meteorological conditions probably have little effea on 

the potential consequences of vapor cloud explosions, BLEVEs, and pool fires. 

\<t* 
P.16 

APPENDIX E 

INPUTS FOR MODELLING 

\<&-
P.17 

-109-

Appendix E. Inputs for Modelling 

This appendix presents the inputs for the consequence analyses. Temperatures and pressures assumed as 

storage conditions for each of the chemicals modelled are listed in Exhibit E-1. Exhibit E-2 presents the 

physical/chemical property data used for modelling. The data shown were used for WHAZAN modelling, 

which required more data than the other methods. The same data were used as required for modelling by 

the other methods; in some cases the methods required conversion of the data to different units. Exhibit 

E-3 shows the assumptions used for WHAZAN modelling for instantaneous releases and moderate 

meteorology. The same meteorological assumptions were used in modelling by the other methods. 

Assumptions for WHAZAN modelling of prolonged releases are shown in Exhibit E-4, and assumptions 

for WHAZAN modelling under worst-case meteorological conditions are shown in Exhibit E-5. Modelling 

for prolonged releases and for worst-case meteorology was done only with WHAZAN. Exhibit E-6 

presents the data and assumptions used for ARCHIE modelling. 

\<& 
P.18 

-110-

Exhibit E-1 

Temperatures and Pressures Used in Scenarios 

Chemical 

Gases 

Ethylene 

Propylene 

Propane 

Butane 

Ethylene oxide 

Ethyl chloride 

Liquids 

Acetaldehyde 

Pentane 

Gasoline 

Hexane 

Heptane 

Toluene 

p-Xylene 

Acetone 

Trichloroethylene 

Acetic add 

Benzaldehyde 

Dimethyl sulfoxide 

Storage 

Temo.(°K) 

175 

293 

232 

293 

293 

288 

293 

293 

293 

293 

293 

293 

293 

293 

293 

293 

293 

293 

Conditions 

Press.(Bars) 

13 

133 

13 

63 

6.18 

13 

1.013 

2.74 

1.013 

1.013 

1.013 

1.013 

1.013 

1.013 

1.013 

1.013 

1.013 

1.013 

\&*. 
<? 

o^ 

PROPERTIES 

CAS Nunber 

Liquid Heat Capacity (J/kg/K) 

Liquid Density (kg/cube m) 

Gamma Ratio of Specific Heat 

Heat of Evaporation (J/kg) 

Heat of Combustion (J/kg) 

Lower Flamnablllty Limit (fract.) 

Upper Flamnablllty Limit (fract.) 

Soiling Point at 1 Atmos. (K) 

Molecular Veight 

Vapor Heat Capacity (J/kg/K) 

Critical Temperature (K) 

Saturated Vapor Pressure (Bara) 

Liquid Enthalpy (J/kg) 

Vapor Enthalpy (J/kg) 

Vapor Entropy (J/kg/K) 

Saturated Vapor Temperature (K) 

Vapor Density (kg/cube m) 

PROPERTIES 

CAS Number 

Liquid Heat Capacity (J/kg/K) 

Liquid Density (kg/cube m) 

Garnna Ratio of Specific Heat 

Heat of Evaporation (J/kg) 

Heat of Combustion (J/kg) 

Lower Flamnablllty Limit (fract.) 

Upper Flamnablllty Limit (fract.) 

Boiling Point at 1 Atmos. (K) 

Molecular Weight 

Vapor Heat Capacity (J/kg/K) 

Critical Temperature (K) 

Saturated Vapor Pressure (Bara) 

Liquid Enthalpy (J/kg) 

Vapor Enthalpy (J/kg) 

Vapor Entropy (J/kg/K) 

Saturated Vapor Temperature (K) 

Vapor Density (kg/cube m) 

ETHYLENE 

74851 

2750.0 

569.0 

1.255 

4.83E+05 

-4.72E+07 

0.027 

0.286 

170.828 

28.05 

700.0 

283.1 

— -6.69E+05 

-396000 

-131.1 

171.049 

1.163 

ACETALDEHYDE 

75070 

2483.09 

783.4 

1.182 

5.69E+05 

-2.51E+07 

0.016 

0.104 

293.55 

44.053 

946.63 

461.0 

1.198 

7.40E+05 

282237 

5679.52 

298.15 

PROPYLENE 

115071 

2500.0 

520.0 

1.152 

4.38E+05 

-4.58E+07 

0.020 

0.111 

227.423 

42.08 

1000.0 

365.0 

11.717 

-4.35E+05 

-65000 

-131.7 

227.71 

1.744 

ACETONE 

67641 

2176.0 

789.9 

1.127 

5.11E+05 

-2.86E+07 

0.026 

0.128 

329.44 

58.08 

1296.7 

0.306 

513671 

2.84E+05 

5085.23 

298.15 

Exhibit E-2 

Chemical Data Used for Models 

PROPANE 

74986 

2400.0 

590.0 

1.13 

4.26E+05 

-4.60E+07 

0.021 

0.095 

229.273 

44.09 

1100.0 

369.8 

9.622 

-4.33E+05 

-62000 

-144.2 

229.575 

1.828 

DIMETHYL 

SULFOXIDE 

67685 

1957.63 

1095.4 

6.03E+05 

-1.98E+07 

0.026 

0.285 

462.15 

78.129 

459.88 

726 0 

0.000812 

5.84E+05 

137113 

3920.06 

298.15 

BUTANE 

75285 

2500.0 

600.0 

1.092 

3.90E+05 

-4.54E+07 

0.018 

0.084 

274.843 

58.12 

1200.0 

425.0 

2.282 

-4.37E+05 

-81000 

-54.4 

275.183 

2.409 

TRICHLOROETHYLENE 

79016 

946.58 

1464.2 

1 116 

2.40E+04 

-6.58E+06 

0.125 

0.90 

360.1 

131.389 

390.38 

571.0 

0.0983 

2.82E+05 

116392 

2474.73 

298.15 

PENTANE 

109660 

2207.0 

626.0 

1.086 

3.67E+05 

-4.54E+07 

0.015 

0.078 

312.669 

72.15 

1547.0 

469.7 

0.593 

4.33E+05 

-40400 

-157.0 

313.056 

ETHYL 

CHLORIDE 

75003 

1616.98 

897.8 

1.155 

3.79E+05 

-1.99E+07 

0.038 

0.154 

285.42 

64.514 

970.9 

460.35 

1.588 

3.42E+05 

205523 

4274.73 

298.15 

2.87 

GASOLINE 

8006619 

2056.0 

732.0 

1.054 

3.20E+05 

-4.35E+07 

0.014 

0.074 

332.226 

72.00 

1234.0 

787.0 

0.501 

0.00E+00 

390000 

-1429.0 

332.952 

ETHYLENE 

OXIDE 

75218 

1979.0 

869.0 

1.212 

5.80E+05 

-2.67E+07 

0.03 

1.00 

261.814 

44.05 

1006.0 

469.0 

1.699 

-6.29E+05 

-26400 

-100.8 

282.118 

1.826 

-

HEXANE 

110543 

2456.19 

659.0 

1.063 

3.35E+05 

-4.48E+07 

0.014 

0.074 

344.589 

86.17 

1819.0 

507.4 

0.175 

-4.25E+05 

-40200 

-171.6 

344.995 

ACETIC 

ACID 

64197 

2048.2 

1042.9 

1.145 

4.05E+05 

-1.31E+07 

0.054 

0.16 

391.05 

60.052 

1114.0 

592.71 

0.016 

4.72E+05 

226460 

4197.53 

294.30 

HEPTANE 

142825 

2605.74 

683.8 

1.045 

3.17E+05 

-4.46E+07 

0.012 

0.067 

374.557 

100.21 

1992.26 

540.7 

0.055 

-4.23E+05 

-40200 

-203.3 

374.993 

BENZALOEHYDE 

100527 

1676.3 

1041.5 

1.10 

3.62E+05 

-3.20E+07 

0.015 

0.10 

452.2 

106.124 

981.8 

694.8 

0.0009 

5.00E+0S 

292724 

297.00 

TOLUENE 

108883 

1738.0 

867.0 

1.089 

3.61E+05 

-4.06E+07 

0.012 

0.070 

383.111 

92.00 

1122.0 

592.0 

0.039 

3.17E+05 

746000 

-2732 6 

383.553 

P-XYLENE 

106423 

1750.0 

861 0 

1.071 

3.40E+05 

-4 08E+07 

' 0.011 

0.070 

410.05 

106.00 

1193 0 

616^2 

0.012 

0.00E+00 

417000 

-1527.5 

410.509 

-, 

-w 

• 

>-* 

i 
Exhibit E-3 

WHAZAN Modelling Data for Instantaneous Releases, Moderate Meteorology 

Data Inputs Ethylene 

Storage Temperature (K) 175.0 

Storage Pressure (Bar) 1.3 

Anfelent Temperature (K) 293.0 

Stored Mass (kg) 45360 

Bund Area (m2) 0.000 

Wind Speed (m/s) 3.000 

Max Time of Interest (s) 100000 

BUOYANT PLUME DISPERSION 

Effective Release Height (m) 0.000 

Release Rate (kg/s) 761.0 

Min. Cone, of Interest (ppm) 13500 

Wind Speed (m/s) 3.000 

Anbient Temperature (K) 293.0 

Surface Roughness Parameter 000.1 

Atmospheric Stability Category D 

Propylene Propane 

293.0 

13.3 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

265.7 

10000 

3.000 

293.0 

000.1 

D 

232.0 

1.3 

293.0 

45360 

0.000 

3.00 

100000 

0.000 

244.5 

10500 

3.00 

293.0 

000.1 

D 

Butane 

293.0 

6.3 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

157.4 

9000 

3.000 

293.0 

000.1 

D 

Pentane 

293.0 

2.74 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

96.25 

7500 

3.000 

293.0 

000.1 

D 

Gasoline 

293.0 

1.013 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

88.25 

7000 

3.000 

293.0 

000.1 

D 

Hexane 

293.0 

1.013 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

54.81 

7000 

3.000 

293.0 

000.1 

D 

Heptane 

293.0 

1.013 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

31.94 

6000 

3.000 

293.0 

000.1 

D 

Toluene 

293.0 

1.013 

293.0 

45360 

0.000 

3.0 

100000 

0.000 

24.04 

6000 

3.000 

293.0 

000.1 

D 

p-Xylene 

293.0 

1.013 

293.0 

45360 

0.000 

3.0 

100000 

0.000 

14.11 

5500 

3.000 

293.0 

000.1 

D 

to 

Oata Inputs 

Storage Temperature (K) 

Storage Pressure (Bar) 

Ant>i ent Temperature (K) 

Stored Mass (kg) 

Bund Area (m2) 

Wind Speed (m/s) 

Max Time of Interest (s) 

BUOYANT PLUME DISPERSION 

Effective Release Height (m) 

Release Rate (kg/s) 

Min. Cone, of Interest (ppm) 

Wind Speed (m/s) 

Anfeient Temperature (K) 

Surface Roughness Parameter 

Atmospheric Stability Category 

Ethylene Oxide 

293.0 

6.18 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

109.6 

15000 

3.000 

293.0 

0.100 

D 

Ethyl Chloride 

288.0 

1.3 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

137.4 

19000 

3.000 

293.0 

0.100 

D 

Acetaldehyde 

293.0 

1.013 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

102.5 

8000 

3.000 

293.0 

0.100 

D 

Acetone 

293.0 

1.013 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

44.51 

13000 

3.000 

293.0 

0.100 

D 

Trichloroethylene 

293.0 

1.013 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

44.52 

62500 

3.000 

293.0 

0.100 

D 

Acetic Acid 

293.0 

1.013 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

30.84 

27000 

3.000 

293.0 

0.100 

0 

Benzaldehyde 

293.0 

1.013 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

1.38 

7500 

3.000 

293.0 

0.100 

D 

Dfmeth) 

293.0 

1.013 

293.0 

45360 

0.000 

3.000 

100000 

0.000 

3.357 

13000 

3.000 

293.0 

0.100 

D 
Exhibit E-4 

WHAZAN Modelling Data for Prolonged Releases 

Data Inputs Ethylene Propylene Propane Butane 

Storage Temperature (K) 175.0 293.0 232.0 293.0 

Storage Pressure (Bar) 1.3 13.3 1.3 6.3 

Anfcient Temperature (K) 293.0 293.0 293.0 293.0 

Stored Mass (kg) 45360 45360 45360 45360 

Release Area (m2) 0.001 0.001 0.001 0.001 

Discharge Coefficient 0.600 0.600 0.600 0.600 

Liquid Head (ra) 4.33 4.33 4.33 4.33 

Bund Area (m2) 0.000 0.000 0.000 0.000 

Wind Speed (m/s) 3.000 3.000 3.00 3.000 

Max Time of Interest (s) 100000 100000 100000 100000 

BUOYANT PLUME DISPERSION 

Effective Release Height (m) 0.000 0.000 0.000 0.000 

Release Rate (kg/s) 4.728 0.271 4.853 0.386 

Hln. Cone, of Interest (ppm) 13500 10000 10500 9000 

Wind Speed (m/s) 3.000 3.000 3.000 3.000 

Ambient Temperature (K) 293.0 293.0 293.0 293.0 

Surface Roughness Parameter 000.1 000.1 000.1 000.1 

Atmospheric Stability Category D D D D 

Pentane 

293.0 

2.74 

293.0 

45360 

0.001 

0.600 

4.33 

0.000 

3.0 

100000 

0.000 

0.454 

7500 

3.000 

293.0 

000.1 

D 

Gasoline 

293.0 

1.013 

293.0 

45360 

0.001 

0.600 

4.33 

0.000 

3.0 

100000 

0.000 

4.132 

7000 

3.000 

293.0 

000.1 

D 

Hexane 

293.0 

1.013 

293.0 

45360 

0.001 

0.600 

4.33 

0.000 

3.000 

100000 

0.000 

3.729 

7000 

3.000 

293.0 

000.1 

D 

Heptane 

293.0 

1.013 

293.0 

45360 

0.001 

0.600 

4.33 

0.000 

3.000 

100000 

0.000 

3.866 

6000 

3.000 

293.0 

000.1 

D 

Toluene 

293.0 

1.013 

293.0 

45360 

0.001 

0.600 

4.33 

0.000 

3.000 

100000 

0.000 

4.879 

6000 

3.000 

293.0 

000.1 

D 

p-Xylene 

293.0 

1.013 

293.0 

45360 

0.001 

0.600 

4.33 

0.000 

3.000 

100000 

0.000 

4.846 

5500 

3.000 

293.0 

000.1 

0 

TJ 
. Exhibit E-5 

WHAZAN Modelling Data for Instantaneous Releases, Worst Case Meteorology 

Data Inputs Ethylene 

Storage Temperature (K) 175.0 

Storage Pressure (Bar) 1.3 

Ambient Temperature (K) 293.0 

Stored Mass (kg) 45360 

Bund Area (m2) 0.000 

Wind Speed (m/s) 1.500 

Max Time of Interest (s) 100000 

BUOYANT PLUME DISPERSION 

Effective Release Height (m) 0.000 

Release Rate (kg/s) 576.7 

Min. Cone, of Interest (ppm) 13500 

Wind Speed (m/s) 1.500 

Ambient Temperature (K) 293.0 

Surface Roughness Parameter 0.100 

Atmospheric Stability Category F 

Propylene 

293.0 

13.3 

293.0 

45360 

0.000 

1.500 

100000 

0.000 

201.4 

10000 

1.500 

293.0 

0.100 

F 

Propane 

232.0 

1.3 

293.0 

45360 

0.000 

1.500 

100000 

0.000 

244.5 

10500 

1.500 

293.0 

0.100 

F 

Butane 

293.0 

6.3 

293.0 

45360 

0.000 

1.500 

100000 

0.000 

119.3 

9000 

1.500 

293.0 

0.100 

F 

Pentane 

293.0 

2.74 

293.0 

45360 

0.000 

1.500 

100000 

0.000 

72.95 

7500 

1.500 

293.0 

0.100 

F 

Gasoline 

293.0 

1.013 

293.0 

45360 

0.000 

1.500 

100000 

0.000 

66.88 

7000 

1.500 

293.0 

0.100 

F 

Hexane 

293.0 

1.013 

293.0 

45360 

0.000 

1.500 

100000 

0.000 

41.54 

7000 

1.500 

293.0 

0.100 

F 

Hcpt8n6 

293.0 

1.013 

293.0 

45360 

0.000 

1.500 

100000 

0.000 

41.54 

6000 

1.500 

293.0 

0.100 

F 

Toluene 

293.0 

1.013 

293.0 

45360 

0.000 

1.500 

100000 

0.000 

18.22 

6000 

1.500 

293.0 

0.100 

F 

p-Xylene 

293.0 

1.013 

293.0 

45360 

0.000 

1.500 

100000 

0.000 

10.70 

5500 

1.500 

293.0 

0.100 

F 
Exhibit E-6 

ARCHIE Modelling Data 

CAS Number 

PHYSIOCHEMICAL PROPERTIES OF MATERIAL 

Normal Boiling Point (deg F) 

Molecular Weight 

Liquid Specific Gravity 

Vapor Pressure at Container Temp (psia) 

Vapor Pressure at Ambient Temperature (psia) 

Lower Flammable Limit (volX) 

Lower Heat of Combustion (Btu/lb) 

Gas Explosion Yield Factor 

CONTAINER CHARACTERISTICS 

Total Weight of Contents (lbs) 

Temperature of Container Contents (deg F) 

Tank Contents During Fireball (lbs) 

ENVIRONMENTAL/LOCATION CHARACTER ISTICS 

Ambient Temperature (deg F) 

Wind Velocity (mph) 

ETHYLENE 

74851 

-151.91 

28.05 

18.90 

2.7 

20292 

0.06 

100000 

-144.0 

100000 

68.0 

11.9 

PROPYLENE 

115071 

-50.039 

42.08 

192.90 

2.0 

19690 

0.03 

100000 

68.0 

100000 

68.0 

11.9 

PROPANE 

74986 

-46.71 

44.CIlS. 85 

2.1 

19776 

0.03 

100000 

-42.0 

100000 

68.0 

11.9 

BUTANE 

75285 

35.32 

58.12 

91.34 

1.8 

19519 

0.03 

100000 

68.0 

100000 

68.0 

11.9 

PENTANE 

109660 

103.404 

72.15 

0.626 

7.12 

7.12 

1.5 

19519 

0.03 

100000 

68.0 

100000 

68.0 

11.9 

6AS0LINE 

8006619 

138.607 

72.00 

0.732 

6.49 

6.49 

1.4 

18702 

0.03 

100000 

68.0 

100000 

68.0 

11.9 

HEXANE 

110543 

160.86 

86.17 

0.659 

2.05 

2.05 

1.4 

19261 

0.03 

100000 

68.0 

100000 

68.0 

11.9 

HEPTANE 

142825 

214.803 

100.21 

0.6838 

0.62 

0.62 

1.2 

19175 

0.03 

100000 

68.0 

68.0 

11.9 

TOLUENE 

108883 

230.2 

92.00 

0.867 

0.44 

0.44 

1.2 

17455 

0.03 

100000 

68.0 

68.0 

11.9 

P-XYLENE 

106423 

278.69 

106.0 

0.861 

0.13 

0.13 

1.1 

17541 

0.03 

100000 

68.0 

68.0 

11.9 

cn 

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