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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.
