the flammable vapour in the cloud is 90 tonnes (U.S. EPA, b). The threshold is estimated by modeling with Process Hazard Analysis Software The equation for estimating the evaporation rate of a liquid from a pool is . Flammable Gases and Office of Prevention and Toxic Substance (). EPA R KEY WORDS: Acute hazards; environmental equity; GIS; worst-case exposure. 1. Flammable gases and liquids and their hazards (EPA R-. ). Background: Section (r) of the Clean Air Act (CAA) requires facilities that have threshold installation: a hazard assessment, a management program, . Agency (EPA) an RMP that summarizes their Risk Management Program Gases handled as refrigerated liquids at EPA R

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Environmental Protection Agency Washington, D. The many contributors addressed the challenging task of reviewing, analyzing and summarizing the myriad existing models and empirical data on flammable chemicals and their hazards.

A tlammable.gases consideration in this work was the need to express the hazards of flammable chemicals as correctly and simply as possible for use by risk managers. Finally, the Environmental Protection Agency Science Advisory Board provided comments that were helpful in preparation of the final draft of this document.

Methodologies for Modeling B-l B. I General Description B-l B.

Hazard Criteria C-l C. I Explosion Overpressure C-l C. Inputs for Modeling E-l Appendix F. EPA’s analysis included identification and evaluation of existing listing and classification systems, along with any applicable criteria; review of existing regulations and codes dealing with flammable materials; analysis of histories of accidents involving flammable substances; and modeling potential consequences of fires and explosions of flammable substances.

Evaluations liauids the severity of accidents that could be caused by various flammable substances are not directly considered in the classification systems.

A review of accident history indicates that flammable substances have been involved in many accidents, and, in many cases, fires and explosions of flammable f,ammable.gases have caused deaths and injuries. Accidents involving flammable substances may lead to vapor cloud explosions, vapor cloud fires, boiling liquid expanding vapor explosions BLEVEspool fires, and jet fires, depending on the type of substance involved and the circumstances of the accident Vapor cloud explosions produce blast waves that potentially can cause offsite damage and kill or liquiss people.

EPA reviewed the effects of blast wave overpressures to determine the level that has the potential to cause death or injury. High overpressure levels can cause death or injury as a direct result of an explosion; such effects generally occur close to the site of an explosion. EPA’s analysis of the literature indicates that people also could be killed or injured because of indirect effects of the blast e. A vapor cloud may burn without exploding; the effects of such a vapor cloud fire are limited primarily to the area covered by the burning cloud.

The primary hazard of BLEVEs, pool fires, and jet fires is thermal radiation; the potential effects of thermal radiation generally do not extend for as great a distance as those of blast waves. In addition, the effects of thermal radiation are related to duration of exposure; people exposed at some distance from a fire would likely be able to escape.

BLEVEs, which generally involve rupture of a container, can cause container fragments to be thrown substantial distances; such fragments have the potential to cause damage and injury. Fragments and debris may also be thrown out as a result of the blast from a vapor cloud explosion. The probability of occurrence of vapor cloud explosions appears to be rather low, based on analysis of the literature.

EPA reviewed factors that may affect the probability of occurrence of a vapor cloud explosion, including the quantity of flammable vapor in a cloud, the presence of obstacles or partial confinement, and the type of ignition source. Analysis of accidents indicates that vapor cloud explosions are less likely when the quantity in the cloud is less than 10, pounds.

It is generally thought that some type of obstruction or confinement enhances the probability that a vapor cloud explosion, rather than a vapor cloud fire, will occur. A high energy ignition source also contributes to the probability of occurrence of a vapor cloud explosion. EPA carried out consequence modeling for fires and explosions of a number of flammable substances, using several PC-based modeling systems and hand calculation methods.

Modeling results were used to estimate the greatest distance at which people potentially could be killed or injured by explosions or fires of flammable gases or liquids.

The modeling indicated that, for a given quantity of a flammable chemical, vapor cloud explosions may have the greatest potential for offsite consequences. This result is consistent with information presented in the literature.

Modeling indicated that BLEVEs may also, in some cases, have the potential for offsite consequences. Additional modeling was carried out based on actual vapor cloud explosions, and the results were compared with the results of the actual incidents.


In general, it was found that the modeling results were in reasonable agreement with the results of the incidents. It was noted, however, that the specific circumstances surrounding an accident may have a significant effects on the severity and range of consequences of the accident. Modeling cannot take all circumstances and conditions into account. Based on modeling and analysis of the literature, flammable gases and volatile flammable liquids appear to be the flammable substances of most concern, because flammalbe.gases may readily form vapor clouds, with the potential for damaging vapor cloud explosions.

EPA identified a number of such substances of concern. The analysis carried out by EPA for this report was intended to provide general background on the hazards of flammable gases and liquids. The modeling results and accident data illustrate and compare the consequences of vapor cloud explosions, vapor cloud fires, BLEVEs, and pool fires.

Brief Records : EPA National Library Catalog

This analysis does tbeir provide a basis for determining the hazard posed by any flammable chemical in a specific situation.

The tlammable.gases list of EHSs was created using only acute toxicity criteria. The purpose of the list was to identify those substances that, if accidentally released, could cause death or serious irreversible health effects from toxicity off-site after a short exposure. However, toxicity is not the only hazard posed by chemicals. A particular emphasis is placed on assessing the impacts of accidents on communities neighboring industrial facilities. The general approach taken in assessing the consequences of potential accidents involving flammable chemicals was to identify and evaluate: EPA’s evaluation is discussed in Sections 3 and 4.

None of the above supplied sufficient information to serve EPA’s specific needs. It was, therefore, decided to model the potential consequences from accident scenarios involving flammable chemicals flaammable.gases establish physical and chemical properties that may be indicative of the hazards associated with these chemicals.

The results of the consequence modeling were then analyzed. The modeling is discussed in Sections 5 through 9. EPA’s analysis of the modeling results is discussed in Section 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 toxicity 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 associated with acute toxicity.

The EPA National Library Catalog | EPA National Library Network | US EPA

The Agency chose lethality because it represents the most immediate concern in an emergency situation. In an official inquiry to the Agency inSenator Frank Lautenburg also noted concern for hazards other than toxicity and asked that EPA focus on other hazards.

The Agency agreed and noted its intent to evaluate hazards other than toxicity in the future. The Workgroup initially considered the hazards referred to in the Act and determined that they fell into two general categories: 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 ridiation 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 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 accident 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 accident that takes place inside an industrial facility. 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. These TPQs were established by assuming an accident 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 toxicity was used to rank the chemicals, and chemicals were assigned to TPQ categories according to their ranking.

In its analysis of toxic substances under SARA sectionEPA used a meter fenceline distance to provide a guideline for community emergency planners to use in setting priorities for planning for hazards in the community. The meter fenceline distance has also been used by the Occupational Safety and Health Administration OSHA in its analysis for thresholds for chemicals listed in its Process Safety Management Standard and by the state of Delaware for thresholds flajmable.gases its prevention regulations.

There is no absolute distance that would guarantee the safety of first responders in every situation. 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 flammabld.gases there may be overlap of the consequences; e. However, flamamble.gases 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. A separate document has flammable.gsaes developed to address commercial explosives and their hazards. None of these classification systems appeared to be primarily based on potential hazards to the community from incidents involving releases of flammable chemicals from fixed facilities; therefore EPA decided that none of these systems was appropriate or specifically applicable to EPA’s regulatory needs.

The flammable.tases examined are described briefly in the following sections; more detail is presented in Appendix A. EPA intends to pursue harmonization of regulatory activity among various agencies to the extent possible, recognizing the different purposes of the regulations under different agencies. Regulation under section of SARA Title Tyeir is intended to provide information to community planners on substances at fixed sites that may be hazardous to the community.

As noted below, the regulations and classification systems used by other agencies and organizations have other purposes.

Basic Prediction Procedures for Environmental Fate

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.

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 accidents 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 incidents involving these substances.

However, DOT focuses on transportation safety rather than hazards from fixed sites. DOT hazard classes and packing groups for flammable substances are generally based on flash point and boiling point ranges, as described in Appendix A. However, for substances that are flammable and toxic, the packing group may be modified to reflect the additional hazard of toxicity; therefore, the DOT classifications of such substances may not provide a measure of their flammability.

Loquids 1, chemicals have been hqzards.epa 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 NFPA has also developed a code NFPA 30, Flammable and Combustible Liquids Code concerning flammable and combustible liquids which is pan of the Hazards.spa Fire Code and is specifically intended to be referenced by public authorities in laws, ordinances, regulations, and administrative orders.

Flammzble.gases was originally written as a model municipal ordinance for storing, handling, and using flammable liquids at fixed facilities. This code includes classifications based on flash point and boiling point. The directive includes a list of toxic and explosive chemicals and several categories of flammable chemicals; the flammable categories are defined by “Indicative Criteria. The thresholds for the flammable categories are metric tonspounds for flammable gases and flammable liquids under hazardous processing conditions, and 50, metric tons 1.

The EEC Directive does not include a list of chemicals that fall into the various flammable categories. The indicative criteria related to flammability are discussed in Appendix A. Specific requirements are included for bulk plants, service stations, processing plants, refineries, chemical plants, and distilleries. In addition, there are specific regulations dealing with acetylene 29 CFR Under the Clean Air Act Amendments ofOSHA was required to promulgate regulations intended to prevent accidental releases of chemicals which could pose a threat to employees.

OSHA has published a standard, as described below.