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APPENDIX E Estimating Emergency Response Times For community-wide hazmat emergency response assessments or where planning agencies have limited funds to support more detailed analysis, a representative response time can provide a qualitative measure to incorporate in planning activities. For example, the 85th percentile of response times across the jurisdiction could be estimated (i.e., the time within which appropriate response could reach 85 percent of the jurisdiction). Where resources permit, a five-step geospatial approach is desired: 1. Create a geospatial layer of responder location(s) for the jurisdiction. For higher response Tiers, the responders are probably dispersed and the planners need to determine how to define the critical mass. One option is to measure initial response time from the location of the hazmat response vehicle(s). 2. Create geospatial layer of hazard locations. a. For facilities, this is a point layer with the type of business, hazardous material, hazmat class, isolation distance, etc. Each jurisdiction can determine which facilities are included. b. For transportation networks, this is a road/rail/pipe/waterway centerline layer(s) with the class of network link (freeway, arterial road, mainline rail, etc.) and a measure of expected hazmat flow (high, medium, low). 3. Perform a network "service area" analysis as shown in Figure E-1. a. The bands reflect impedance values, typically distance, which can be converted to response times based on posted speed limits or a related factor. b. Traditional "shortest path" routing algorithms can be used to determine the expected travel time from each capability to any other point in the transportation network. For a relatively small number of hazard sites, this can be done using on-line mapping tools such as Google Maps or MapQuest. For large areas, a GIS software package is desirable. c. Response time values corresponding to the different bands are based on policy and should reflect the type of jurisdiction (urban, suburban, rural, or remote). 4. Use the adjusted consequence value from Step 14 in the risk equation instead of the previ- ously determined value. Note: These are representative values and not based on any analyses. 5. Figure E-1 can help identify facilities that exist outside a set response time for a more detailed evaluation to determine if additional mitigation strategies should be implemented for those locations. Color-coding them by hazard class would give a quick prioritization for this evaluation. Figure E-2 provides a representative map showing response times to link segments for materials transported through a jurisdiction. The process is similar to that defined in Figure E-1, except that the response time is added as an attribute to each transportation link. As response times along each road segment can be stored as network attributes in a GIS, a planner can visually exam- ine all network segments (with color-coded highlighting) to see where the response times for a E-1
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Figure E-1. Network service area analysis. Figure E-2. Example network response time display.
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Estimating Emergency Response Times E-3 Table E-1. Continued development of the risk metric equation, adding the Response Time Factor [RTF]. Vulner- Consequence Response Hazard [H] Capability Risk ability [C]* Time [ERC] Metric Facility or Route Description [V] Pop. Env. [RTF] Facility Z Fire (ethylene) 3 4 2 1 1 Roads x, y Fire (gasoline) 3 2 1 4 1 Facility Z Explosion (ethylene) 2 3 2 1 1 Railroad s BLEVE (ethylene) 4 2 1 4 1 Facility Z Toxic Gas (chlorine) (L) 3 4 1 3 5 Facility Z Toxic Gas (chlorine) (S) 4 2 2 1 1 Railroad s Toxic Gas (chlorine) (L) 3 5 1 3 5 Railroad s Toxic Gas (chlorine) (S) 4 3 1 1 1 Roads x, w Toxic Gas (ammonia) (L) 1 4 2 4 5 Roads x, w Toxic Gas (ammonia) (S) 2 2 1 4 1 Roads x, u Toxic Liquid (37% HCl) (L) 2 2 2 4 1 Roads x, u Toxic Liquid (37% HCl) (S) 3 1 1 4 1 (S) small release; (L) large release. specific capability level exceed a threshold value such as that defined in Chapter 6 based on juris- dictional characteristics. The assignment of a value for the Response Time Factor [RTF] uses the performance objectives in Step 5 with the actual response times for each of the four target outcomes--Assess, Manage, Rescue, and Control--shown in Table 18. For each scenario, the ratio of the actual average response time to the goal response time for each target outcome is calculated and the value for the RTF is assigned using Table 19. For each scenario the maximum value for RTF is entered in the Risk Metric Table. The result of this calculation is shown in Table E-1. The final step is to multiply all the values for each scenario, using the maximum of the con- sequence estimate, to get the Risk Metric for each scenario. This is shown in Table 21 in the main body of the report.