Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 63


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 62
APPENDIX B Estimating Vulnerability Detailed Discussion Regarding the techniques used to evaluate the vulnerability term, it is possible to develop some rough, order-of-magnitude estimates of the vulnerability level to be assigned to each scenario in the hazardous materials risk portfolio. For a rail line that transports 20 rail cars of ethylene per week, there would be approximately 1,000 rail cars per year. The total distance in the region trav- eled by these cars can probably be estimated by just watching the trains as they come into the region. The cars might travel 20 miles in the region on their way to a classification yard, where they are bro- ken out of the train and then transported an additional 10 miles from the classification yard to the facility, which means that the loaded cars will travel a total of 30,000 rail car miles per year. A com- modity flow survey might find that there are an additional 500 cars of ethylene per year that are transported through the region with a total shipment distance of 20 miles. These rail cars represent another 10,000 rail car miles per year. Therefore, the region is exposed to 80,000 rail car miles per year. The Bureau of Transportation Statistics (BTS 2008) publishes an annual report, the latest of which is titled "2008 National Transportation Statistics." In that report, based on the number of incidents and train miles of travel, the frequency of an incident is 3 10-6 per train mile. Assum- ing 60 cars per train, obtainable from the AAR report titled "Train Facts," and based on statistics published by the FRA, there are 6 to 10 rail cars involved in a typical train incident. Thus, the prob- ability of an incident per rail car mile is 3 10-6 incidents/train mile 60 cars/train 10 damaged cars or 5 10-7 per car mile. If there are 80,000 car miles of ethylene being transported per year, a conservative estimate, then the probability of an ethylene rail car being involved in an incident is 4 10-2 per year. Looking at the rail car incident statistics for the years 1997 through 2004, there were 37 rail cars of ethylene involved in an incident and there was one fire and one explosion, assumed to be a BLEVE. Thus, the approximate estimate for a BLEVE involving ethylene traveling on the rail line through the region is approximately 1 10-3 per year. Based on this rather approx- imate analysis, the vulnerability level for a BLEVE involving ethylene is "moderate," or in numer- ical terms, is assigned a value of 3. Since the frequency estimate is exactly mid-range for "moderate" (see Table 20), it is probably quite accurate. For the truck mode, if there is one or more major interstate highways traversing the jurisdiction, each with truck average annual daily traffic (AADT) above 10,000, then the vulnerability level should be set at "high," unless it can be shown that the sum of all the hazmat shipments in the region is less than 100 per day, which would justify a "moderate" rating. The rationale for assign- ing "high" to the vulnerability is based on the recognition that if there are 10,000 daily truck ship- ments over a roadway 30 to 40 miles long, then there are hundreds of millions of truck miles annually and, as a result, there will be more than 10 serious truck incidents each year and there will probably be one hazardous material release every few years. Based on the information in Table 20, the likelihood of a hazardous material release would be in the "high" range for commonly shipped flammables and combustible materials, the most commonly shipped hazmat. For materials that B-1

OCR for page 62
B-2 A Guide for Assessing Community Emergency Response Needs and Capabilities for Hazardous Materials Releases make up only a small percentage of the shipments, like toxic liquids and gases, the vulnerability level might be assigned "low," and even less commonly shipped materials can reasonably be assigned a level of "very low." All these assignments are based on traffic flow data and a reasonably complete picture of the hazardous material flows through the region. For rail transport, if the typical train consist contains several cars carrying the same flamma- ble material, say alcohol or propane, the common practice would be to place these cars together. In an incident, when the consist derails and forms an accordion type configuration, which is common, then all the flammable cars are in proximity to each other. If one of the cars is rup- tured and a fire breaks out, then the possibility of a BLEVE is quite high. This configuration sel- dom occurs for truck transport. About 5 percent of the truck incidents involve multiple trucks, and if only 5 percent of the trucks carry hazmat, then the probability that two hazmat trucks would be involved in an incident is less than 0.3 percent. The probability that both will be car- rying flammable materials reduces that probability to less than 0.2 percent and the probability of a fire involving one of them reduces the probability to less than 0.05 percent. Thus, if the vul- nerability of a fire in a region is considered "moderate" for truck transport, it would be reason- able to assign the vulnerability of an explosion to be "low." If pipelines traverse the region, then the vulnerabilities are more difficult to characterize because the risk appears to be very low. The data in the "2008 National Transportation Statis- tics" report published by BTS can be used to obtain the annual risk of a pipeline incident to be 1.8 10-9 per mile of pipeline. This is a generic number obtained by taking the total number of pipeline incidents (404 in 2007) and dividing by the total miles of liquid and gas pipelines (229,962 million miles). This is an unreasonably low number because it is certainly much higher in earthquake-prone areas and in urban areas where ground disturbance is much more likely. If the region has product or gas pipelines but is not in an earthquake-prone area and is not urban, then it would be reasonable to assign a vulnerability level of "very low" to the pipeline. If it were in an urban area, then it would be reasonable to assign a vulnerability level of "moderate" to the pipeline. In a region with significant earthquake risk, it would be reasonable to assign a vulner- ability level of "high." A vulnerability level of "very high" may be reasonable if the region has an active fault and the pipeline crosses the fault. For one final example, consider a hypothetical facility with a large quantity of ethylene. The facil- ity would fall under both OSHA and EPA regulations governing the handling of highly hazardous chemicals. One of the EPA requirements is that the facility's ERP estimates the consequences for their most limiting hazardous material incident, which is assumed here to be an explosion of a ves- sel containing ethylene. While the plan is not required to estimate the probability of that limiting incident, the safety officer at the facility must list the company's past incident history and should be knowledgeable of incidents at similar facilities. From these incidents, which may not include an explosion of an ethylene vessel, the safety office will likely be able to identify near-miss incidents that can be used to estimate the vulnerability term for an explosion of an ethylene vessel at the facil- ity. If that vulnerability--based on the most limiting incident--was judged to be "low," it might be reasonable to raise the vulnerability for the entire facility to "moderate." Example Risk Metric Evaluation of the Vulnerability Term This appendix will work through the process of evaluating the terms in the risk metric equa- tion. The example shown here is more exact, and order-of-magnitude estimates similar to those shown in the body of the report could be substituted for some of the semi-quantitative estimates shown here.

OCR for page 62
Estimating Vulnerability B-3 A typical analysis will start with a map of the region (Figure B-1) that shows the location of the major facilities, highways, and railroads where hazmat are likely to be encountered in the region being evaluated. This analysis will consider a plant, labeled Facility Z, which uses coal and water to generate low-molecular-weight hydrocarbons using the Fischer-Tropsch process. From the low- molecular-weight hydrocarbons produced, some propane is separated out and the remaining straight-chain hydrocarbons are cracked to produce ethylene and vinyl. The ethylene is then con- verted to ethylene oxide, which is shipped offsite by railroad. Some of the propane is cracked to form vinyl, which is then reacted with chlorine to produce vinyl chloride monomer. The process also produces approximately 37 percent HCl, a byproduct of the vinyl chloride production for use in a facility in the neighboring community, labeled City K. The vinyl chloride monomer is used onsite to produce vinyl chloride plastic components. To produce the vinyl chloride monomer, rail cars of chlorine are shipped to the facility. The facility has sufficient inventories of highly hazardous chemicals to fall under both the OSHA regulations for Process Safety Management of Highly Hazardous Chemicals (29 CFR 1910.119) and the EPA regulations for Chemical Accident Protec- tion Provisions (40 CFR Part 68). To meet the EPA regulations, the facility emergency response organization must coordinate with the local emergency responders as it develops its Emergency Response Program. It is through this coordination that the local community emergency respon- ders are made aware of the worst case incident that could occur at Facility Z. Assume that the worst- case incident has been found to be an explosion of a large tank of ethylene oxide. In addition to the facility, hazardous chemicals are transported on the area roadways, shown in Figure B-1. The process of evaluating the risk metric for the region depicted in Figure B-1 requires some form of survey to identify the types and number of shipments on the region's transportation Figure B-1. Map showing Facility Z and the surrounding transport corridors.

OCR for page 62
B-4 A Guide for Assessing Community Emergency Response Needs and Capabilities for Hazardous Materials Releases networks. Ideally, it would be a formal commodity flow survey, but if the resources are not avail- able for such a survey, tabulations of hazardous material shipments can be made by setting up observation points on each of the highways, not necessarily at the same time, to tabulate hazmat flows. Discussions with local railroad managers, particularly at the sorting yard, might be suffi- cient to identify the flow of hazmat on the railroad. Once information is available on the types of hazmat present at Facility Z, the next step is to estimate the types of hazards that might be present and then the likelihood that these hazards will be realized. The Risk Management Plan developed to meet EPA regulations identified an ethyl- ene oxide fire and explosion and chlorine release as the limiting accidents at the facility. The chlo- rine release was divided into a small release and a large release because of the different emergency response situations they present. To an emergency responder, a small release has the potential for continuing for a long time, taxing the resources of the emergency response community. Through discussions with the safety staff at the facility, the frequency of these accidents was roughly esti- mated and is shown in the fourth column in Table B-1. Since the vulnerability levels represent accident or release frequencies that differ by factors of 100, it is often easy to estimate the vulner- ability level by recalling similar accidents at other facilities. For example, a keen observer might recall that there seems to be an explosion at a petrochemical plant several times a year. If there were only 100 petrochemical facilities in the country, then the hazard from an explosion at those facilities would be quite high, probably a 4 or a 3 on the vulnerability scale. Note that there would have to be 10,000 or more such facilities to justify assigning a 2 as the vulnerability level, indicat- ing the estimated accident frequency for the facility to be between 10-4 and 10-6 per year. The fire frequency for ethylene oxide was assigned a vulnerability value of 4 largely because the material is highly flammable; its flammable range is between 3 and 100 percent. The frequency of leaks in the case of small chlorine or ethylene oxide leaks followed by fires was considered to be 1 per 10 years because both chlorine and ethylene oxide tank cars must be connected and disconnected almost 100 times per year. The probability of a single human error will be a significant factor in the accident frequency for those activities. Table B-1. Facility vulnerability assessment. Accident Y/N Vulnerability Facility or Route Hazard Frequency [H] 1/year [V] Facility Z Fire (Ethylene Oxide) 1 1.00E-01 4 Facility Z Explosion (Ethylene Oxide) 1 1.00E-05 2 Facility Z Toxic Gas (Chlorine) (L) 1 1.00E-03 3 Facility Z Toxic Gas (Chlorine) (S) 1 1.00E-01 4