ERPGs^TM

Emergency Response Planning Guidelines (ERPGs) are values developed by the AIHA Guideline Foundation’s Emergency Response Planning Guideline Working Group (ERPG WG) to assist emergency response personnel in planning for accidental or intentional catastrophic chemical releases to the community. ERPGs are developed to meet the need for community emergency exposure planning guidelines, particularly for chemicals that have high potential for uncontrolled releases and those that might pose particular hazards because of their volatility and toxicity.

The primary focus of the ERPGs is to provide guideline levels for once-in-a-lifetime, short-term (typically 1-hour) exposures to airborne concentrations of acutely toxic, high-priority chemicals. Users may include industrial hygienists, emergency planners, and emergency responders. In order to develop ERPGs, acute toxicity data are the primary source of information used. Other information may be used when high-quality, robust, acute inhalation toxicity data are not available. As the focus is on data from acute studies, the ERPGs should not be used in situations where exposure could be frequent, such as in a work place, or as a consequence of frequent chemical releases.

ERPGs are intended to be used by persons trained in emergency response planning as planning tools for assessing the adequacy of incident prevention and containment measures undertaken for chemical releases, for transportation emergency planning, and for developing facility site and community emergency response plans. The levels are not to be used to determine safe limits for routine operations, as definitive delineators between safe and unsafe exposure conditions, or as a basis for quantitative risk assessment.

Use and Application

Emergency response planning programs generally include accidental release scenarios in which air dispersion models determine concentration isopleths. Programs designed to protect the public from transportation incidents involving chemical materials also use the ERPG values.

ERPGs also are important for compliance with the U.S. Environmental Protection Agency’s (EPA) Emergency Planning and Community Right-to-know Act (EPCRA).

Those who use ERPG values include:

• Community emergency planners
• Emergency responders
• Air dispersion modelers
• Industrial process safety engineers
• Community Action Emergency Response (CAER) participants
• Local Emergency Planning Committees (LEPCs)
• State Emergency Response Commissions (SERCs)
• Industrial hygienists
• Toxicologists
• Transportation safety engineers
• Fire protection specialists
• Process safety engineers and professionals
• Government agencies
• Risk assessors and risk managers
• Resource Conservation and Recovery Act (RCRA) managers

ERPGs are commonly used by regulators, industry, and consultants in process safety consequence modeling for episodic releases and is referenced in American Institute for Chemical Engineers, Center for Chemical Process Safety. ERPGs can be used with dispersion models, together with other information such as inventory storage volumes and atmospheric conditions, to provide computerized estimates of the potential spread and airborne concentration in case of a release. From these estimates, action plans can be developed. The plans may vary for any given emergency depending on such things as population density, type of population (e.g., schools, elderly), terrain, weather conditions, and the nature of the release. Using estimated release rates, the physical and chemical properties of the products released, and meteorological data, the dispersion modeling methods generate estimated distances and time of arrival for ERPG concentrations. Such information can be used when making the determination to evacuate or shelter-in-place for a potentially exposed population.

Many documents can be of assistance in conducting a risk analysis. Risk analysis in transportation settings is outlined in the U.S. Department of Transportation’s (U.S. DOT) Community Teamwork: Working Together to Promote Hazardous Materials Safety, a Guide for Local Officials (NRT-1). In conjunction with the U.S. Federal Emergency Management Agency (FEMA) and US DOT, the U.S. Environmental Protection Agency (U.S. EPA) published a supplement to NRT-1 in December 1987. This document, entitled Technical Guidance for Hazards Analysis and often referred to as the Green Book, provides technical assistance to LEPCs in assessing the lethal hazards associated with potential airborne releases of extremely hazardous substances and provides a technical applications basis for using community exposure limits.

Most dispersion models, as related to accidental releases of toxic chemicals, have their roots from assumptions established in the Green Book. Consistent with the Green Book and with other emergency planning guidance, ERPGs can be used to calculate where protective actions are needed, such as evacuation, sheltering-in-place, and isolation zones. It is important to note that during the planning process, the potential impact of an accidental or intentional release in the community can be characterized before any release takes place by calculating a modeled air dispersion value and comparing it with the ERPG.

Various air dispersion models, both proprietary and in the public domain, are used to model emergency response scenarios. Each model poses numerous variables that require the modeler or investigator to make custom assessments of each possible scenario. Each facility and each model is unique. The model should be carefully chosen to best meet the chemical, topographical, meteorological, and population characteristics of the facility in question. The AIHA Guideline Foundation does not recommend any air dispersion model over another.

Under the authority of section 112(r) of the U.S. EPA’s Clean Air Act, the Chemical Accident Prevention Provisions require facilities that produce, handle, process, distribute, or store certain chemicals to develop a Risk Management Program and prepare a Risk Management Plan (RMP). ERPGs also can be useful in developing RMPs, site-specific ranking schemes, prioritized lists of chemicals, more detailed process hazard analyses, and process safety programs.

ERPGs vs. OELs

Occupational exposure limits (OELs), guidelines, and standards exist to protect healthy adult workers from the effects of exposures over their working lifetime, whereas ERPGs are developed to protect the general public from rare, unanticipated, short-term chemical exposures.

Rationales and Interpretations

The technical supporting documentation for each ERPG includes a rationale that discusses the basis for the ERPG value. The rationale is part of the comprehensive ERPG documentation for that chemical and summarizes the data used to support the respective ERPG value. ERPG values are intended to provide estimates of concentration ranges above which a person could reasonably anticipate adverse health effects as a consequence of exposure to that specific chemical. ERPGs are approximate threshold values above which there would be an unacceptable likelihood of observing the defined adverse effects. Technical supporting documentation is available for purchase from AIHA for each chemical with an ERPG.

Human responses do not occur at precise exposure levels but can extend over a wide range of concentrations. In all populations, there are sensitive individuals who will experience adverse health effects at exposure concentrations far below levels at which most individuals normally would respond. The ERPG values should not be expected to protect everyone but should be applicable to most individuals in the general public.

ERPGs are emergency planning and response guidelines, not occupational exposure guidelines. ERPGs and occupational exposure guidelines differ because they are intended for different populations, different durations of exposure, and different frequency of exposures. Users of the ERPG values should review the documentation carefully before applying these values.