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Potential Consequences of Incidents Involving the Identified Hazardous Materials 29 Table 13. Consequence values. Consequence Population Environmental Value [C] 1 no deaths or serious injuries; only relatively minor injuries less than $1 million 2 1 to 10 deaths or serious injuries $1 million to $10 million 3 11 to 100 deaths or serious injuries over $10 million to $100 million 4 101 to 1,000 deaths or serious injuries over $100 million to $1 billion 5 more than 1,000 deaths or serious injuries over $1 billion Estimating Consequences Each scenario in the hazardous materials portfolio is composed of a specific material, quantity, and location. Potential consequences are dependent on the material itself, the nature of the area around the release, and atmospheric/weather conditions, particularly for human-health effects from an airborne release of toxic materials. Material-specific effects include the nature of danger or hazard the material poses, its chemical and physical properties, the quantities released, how well and how quickly the release is contained, and the rate of a vapor release, if present. The population that might be affected is a function of the specific release location and the population density, the presence of special populations (nursing homes, hospitals, prisons, etc.), the ability to effect a proper evacuation or other miti- gation strategy (such as suitable buildings for sheltering-in-place), and the time available for evacuation or sheltering-in-place. Environmental damage will be determined by land use at the release location and the presence of specific environmentally sensitive features (e.g., reservoirs, waterways, wetlands, parks). Finally, weather conditions can determine how far and at what concentration an airborne toxic plume will travel and be dispersed. These conditions include wind speed and direction, atmospheric stability class, and temperature. While Appendix C contains more details, the following sections outline the general process for estimating potential consequences for a scenario. Estimating Human-Health Consequences The human-health aspect of the consequence term is quantified by estimating the number of individuals that could suffer permanent health effects from a release. This generally involves two steps: (1) determining the potentially affected area and (2) determining how many people inside that area would be killed or seriously injured. In practice, simply measuring the number of people exposed to a hazardous material is often used as a proxy for fatalities and injuries. Determining the affected area is dependent on the type of material involved, its hazards, and how that material behaves when released from its containment or packaging. A great deal of scientific research has gone into estimating impact areas for many types of materials, and you may wish to take advantage of this prior work. The ERG and the companion Argonne Report (Kawprasert and Barkan 2010) provide lists of specific protection action distances for responders that are based on different materials. The Argonne Report is easier to use in this instance because the tables are provided by commodity and the planner does not need to use the guide number, as is the case with the ERG. Although the distances are not specifically correlated to population exposure, they provide reasonable protection distances that could be used for this Guide. Appendix C provides information on some of the modeling tools used by the developers of the ERG that you can use to determine more detailed impact areas for different quantities and concentrations of hazmat.
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30 A Guide for Assessing Community Emergency Response Needs and Capabilities for Hazardous Materials Releases Table 14. Hazard distances used in NRHM Routing Guidelines. Hazmat Category Hazard Distances (miles) Explosives 1 Flammable Gas 0.5 Toxic Gases 5 Flammable/Combustible Liquid 0.5 Flammable Solid, Spontaneously Combustible, 0.5 Dangerous when Wet Oxidizer/Organic Peroxide 0.5 Poisonous (not gas) 5 Corrosive Material 0.5 The use of the ERG specifies protective action distances by commodity for large and small spills and for day and night releases, a total of four different distances. To use this Guide, the hazardous materials portfolio developed in Steps 7 through 9 and described in Table 11 would have to be expanded to include four different scenarios for each of the listed commodities. The users of this Guide could also use a simpler approach that was developed for the Non-Radioactive Hazardous Material Routing Guidelines (NRHM 2007). This guide uses a simpler set of hazard distances shown in Table 14. The table does not specify a distance for infectious substances or radioactive materials. Radioactive materials commonly use a 0.5-mile (800-meter) distance, and this hazard distance would also be reasonable for infectious substances. Once you have a protective, isolation, or evacuation distance, decide how to apply that distance to determine an impact area. For initial isolation distances and for evacuations that are not focused downwind of the release, the impact area can be a circle with a radius equal to the specified distance. For protective actions and evacuations that are directed toward areas downwind of the release, you can use a square area--aligned with the release point--with a side length equal to the specified distance. This is consistent with the methodology in the ERG (2008) (see Figure 2). For a more conservative approach, you can use the larger of the initial isolation and protective action distances. Step 10 Determine the affected area for population impacts from a potential release for each scenario in the hazardous materials portfolio. As shown in Figure 2, the affected area is the protective action distance or hazard distance squared. Sources: ERG (2008); Brown et al. (2009) Figure 2. Protective action area.