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Once you have determined which hazmat are present in your jurisdiction, either at fixed facilities or along transportation corridors, you need to assess the potential consequences that would result from an incidental or intentional release of those materials. Since you have an idea of the quantities present in each location, you can use this information to help determine the potential impacts from a complete release. The Guide builds on the hazardous materials portfolio and adds columns to address potential consequences. Defining Consequences The potential consequences term is a measure of the potential impacts to the population or environment from a release of hazmat. There are many factors to consider when estimating these impacts. Since consequences to people and the environment are typically measured in different ways, this Guide uses the CARVER method to assign a relative value for the two differ- ent types of consequences. (CARVER is an acronym for criticality, accessibility, recuperability, vulnerability, effect, and recognizability and is employed by the U.S. Department of Defense.) The CARVER method uses a range of values that approximate a logarithmic scale for each measure that needs to be estimated. For both population and environmental consequences, this Guide uses values from 1 to 5 as defined in Table 13. The next section will help you determine the consequence value for each scenario in the hazardous materials portfolio. The method of assessing consequences should be consistent with the capability of the emer- gency response planner or planning team. For many areas, the emergency response teams commonly use plume modeling to identify areas where precautions to protect against the release should be directed. Others might only have the most current version of the ERG (2008). The hazard distances in the ERG can be used in lieu of modeling the release, and a realistic fraction of the people exposed to the release could be expected to require medical treatment. This number can be used in conjunction with the consequence scale to conservatively estimate impacts. The following paragraphs discuss some of the approaches to addressing the consequence term. The approach selected should be the one that best matches the capability of the emergency response planning team. These consequences are measured assuming no effective emergency response (identified above as potential unmitigated consequences). This enables the effectiveness of the emergency response to be captured in the response time and emergency response capability terms in the risk equation. For each scenario in the risk portfolio, both population and environmental consequences will be estimated and the maximum of the two estimates will be used in the risk equation. 28 C H A P T E R 5 Potential Consequences of Incidents Involving the Identified Hazardous Materials
Potential Consequences of Incidents Involving the Identified Hazardous Materials 29 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. Consequence Value [C] Population Environmental 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 Table 13. Consequence values.
30 A Guide for Assessing Community Emergency Response Needs and Capabilities for Hazardous Materials Releases Sources: ERG (2008); Brown et al. (2009) Figure 2. Protective action area. 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 areaâaligned with the release pointâwith 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. Hazmat Category Hazard Distances (miles) Explosives 1 Flammable Gas 0.5 Toxic Gases 5 Flammable/Combustible Liquid 0.5 Flammable Solid, Spontaneously Combustible, Dangerous when Wet 0.5 Oxidizer/Organic Peroxide 0.5 Poisonous (not gas) 5 Corrosive Material 0.5 Table 14. Hazard distances used in NRHM Routing Guidelines.
Potential Consequences of Incidents Involving the Identified Hazardous Materials 31 Determining how many people might fall within that impact area can be done in several ways. If you have detailed population data in a geographic information system, you can overlay that impact area over the population data and automatically count the population inside it. You should be aware of differences in residential (nighttime) and employment (daytime) population for the specific area. Another approach is to use average population density figures for the area (determined from Census data) and combine that with the area of potential exposure. For example, if there is a population density of 1,500 people per square mile and the protective action area or hazard area is 0.5 mile on a side, then the number of affected people would be 1,500 Ã 0.25 mi2, or 375 people. For fires, it is more appropriate to use the initial isolation zone as the impacted area, so in that case the number of affected people would be 1,500 Ã Ï Ã (50 m/1000)2 or 4 individuals. Again, all of these people would not be killed or seriously injured, but this provides an estimate of potentially affected population. Step 11 Use population density estimates or a geographic information system with population data layers to determine the potential population exposure for a potential release for each scenario. Using Table 13, specify the CARVER scale value based on the estimated number of potentially exposed individuals. Counting all the potentially exposed individuals as fatalities is very con- servative, but is appropriate for this type of assessment. Estimating Environmental Consequences Environmental consequences can include property damage as well as land and aquatic contamination and remediation. For most hazmat incidents, the impact on the environment will be measurable but not excessively high. The emergency response planner or planning team may judge that many scenarios pose little environmental risk. These scenarios do not need to be assessed. As with population exposure, environmental consequences are determined through two steps: (1) determining the impact area and (2) determining the consequences within that area. The impact area can be determined in the same manner as human-health consequences, by using the impact distances in the ERG. Appendix C provides additional approaches for obtaining more detailed estimates of environmental exposure areas. Step 12 Determine the affected area for environmental impacts from a potential release for each scenario in the hazardous materials portfolio using the same methods used to estimate the affected area for population impacts. Environmental consequences are divided into two types: property damage and land and aquatic contamination. For most materials, one of these two will be the dominant consequence category. Property damage can be assessed for hazards that have the capability of totally destroying a structureâflash fires, fires (flammable gas clouds should be considered here in addition to flammable liquids and solids), and BLEVEs or explosionsâby using per-acre land values that consider the number and type of structures typically found. A fire, if not prevented from spreading, can involve nearby structures and do extensive damage. An explosion or BLEVE can do a lot of structural damage, resulting in replacement of the structure as part of the damage estimate. The hazard distance specified in the NRHM Routing Guidelines (2007) or the protective action distance specified using the ERG would provide too large an area. The initial isolation distance specified in the ERG would be more representative of the damage area from a fire or explosion. The circular area specified by this radius is the suggested area to be used to estimate damage to nearby structures. Alternatively, the dispersion code in the Areal Location of Hazardous Atmospheres model (ALOHA 2007) has an option to estimate the damage radius from fires and BLEVEs. The user only has to specify the material and the quantity present.
32 A Guide for Assessing Community Emergency Response Needs and Capabilities for Hazardous Materials Releases For land and aquatic contamination, impacts are a concern if the released material kills plants and trees, or forms a toxic particulate that is deposited on the ground. Preventing human exposure by confiscating crops or decontaminating land or buildings would result in the greatest costs. It would be very conservative to assume that the same area used for estimating population impacts experienced some damage from the release event. The extent of land impacts is also sensitive to the type of hazard. Ammonia will do a lot of damage to a wetland because of its aquatic toxicity, but it is a beneficial fertilizer on farmland. To estimate the potentially affected area, the hazard distance from the NRHM Routing Guidelines (2007) could be used to determine the extent of the potentially affected zone and, within that zone, to estimate the fraction of the area where environmental damage could occur. Table 15 shows representative values for different types of land use. The values shown were developed initially for a security-related assessment for another project, to estimate economic losses on a per-acre basis when the structures or habitat are essentially destroyed. These are place- holders, and you could develop your own set of land-use values for your region. Where structures would not be entirely destroyed, it might be appropriate to use 10 percent of the replacement value. This would represent replacement of windows and repair of minor structural damage. Similarly, a reasonable estimate for land and wetland contamination might also be 10 percent. Depending on the incident release type and the size of the potential incident, you may wish to adjust the percentage to a value other than 10 percent. Step 13 Use the per-acre damage estimates in Table 15 or a geographic information system with environmental data layers to determine the potential environmental consequences for each scenario. If the risk assessment tool is used, scenarios judged to present minimal risk to structures or the environment can be shown as having a zero or low impact. Selecting the Consequence Value Again, the mitigating effects of emergency response coverage are not considered when determining these potential consequences. Comparing the potential population exposure and the environmental costs measured in economic terms to the values in Table 13 provides the appropriate consequence value to use. Remember to take the higher of the population and environmental values. Step 14 For each scenario: (1) determine the consequence value in Table 13 for the potential population impacts determined in Step 11, (2) determine the consequence value in Table 13 for the potential environmental impacts determined in Step 13, and (3) record the larger value as the consequences for the scenario. If the assessment tool is being used, this step is performed automatically. An example of the calculation sequence that begins with Step 10 and concludes with Step 14 is shown in Appendix C. Area Type Structure Environment Residential Commercial Industrial Land Use Farm Land Wetland Rural $ 150,000 $ 1.2 million $ 2.4 million Fallow $ 200 $ 50,000 Suburban $ 1.2 million $ 12 million $ 24 million Low-value crop $ 1,000 $ 100,000 Urban $ 8 million $ 50 million $ 80 million High-value crop $ 400,000 $ 400,000 Table 15. Estimated per-acre values.
