Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 38


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 37
CHAPTER 7 Aligning Hazardous Materials with Varying Levels of Capability This chapter brings together your prior work on filling out the hazardous materials portfolio to develop a risk metric that reflects how well your emergency response capability is aligned with the hazmat present in your jurisdiction. A new term, vulnerability, is added to support calculation of the risk metric. Adding Risk to the Hazardous Materials Portfolio Until this point, the various incident scenarios that could occur in the region have been iden- tified and the consequences assessed without regard to likelihood or frequency. The vulnerability term, which will be discussed next, provides a way of assigning a risk level to each scenario. The measure of risk described in Chapter 1 was called the risk metric because it is not a quantitative measure of risk, for example, the risk of an incident occurring involving a hazardous material being released on a local rail line or highway. The risk metric provides a way of prioritizing the emergency response shortfalls. Given that resources are always going to be limited, it is wise to fix the shortfalls that result in the greatest reduction in risk. Addressing shortfalls that would result in only slight reductions in risk might not be worth the cost, even if funds were available. The vulnerability term is a measure of the likelihood that the population or environment will be exposed to threats produced by an incident. There are two ways to address vulnerability: (1) consider potential release probabilities based on historical or scientific data, and (2) consider the quantity and frequency of materials present. In both cases, vulnerability is expressed on an annual basis. Table 20 shows the range of values used in this Guide for the vulnerability term for both of these approaches (based on likelihood of release and based on frequency of presence). These approaches apply to both fixed facilities and transportation. The frequency approach addresses how often the materials are present in sufficient quantities to be of concern at the facility, whereas the transportation approach refers to the frequency of shipments along a particular transportation corridor or through the community. These values could be assigned to Freight Analysis Framework (FAF 2010) truck volume levels and the Commodity Flow Survey (CFS 2007) hazmat percentage of truck tonnage. The vulnerability levels for a particular scenario can often be estimated from experience. For example, the history of hazmat responses can be used to assign an overall vulnerability level for the region. Typically, that level will be high or very high. If a CFS is available, assuming the same incident rate for all transport on each mode, then the vulnerability level by hazmat class and division can be obtained by multiplying the overall likelihood of a hazmat incident in the area by the class/division distribution of shipments from the CFS. If you desire to factor in the likelihood or probability of a package breach given an incident for hazmat like gasoline, the likelihood can be reduced by an order of magnitude (i.e., by a factor of 10), and for other bulk commodities the likelihood can be reduced by two orders of magnitude (i.e., by a factor of 100). The likelihood of a fire or BLEVE is at least two orders of 37

OCR for page 37
38 A Guide for Assessing Community Emergency Response Needs and Capabilities for Hazardous Materials Releases Table 20. Vulnerability levels. Vulnerability Level Approximate Range Value Description Likelihood of Release Frequency of Presence 5 Very High > 1 per year many times per day -2 4 High 1 to 10 per year several times per week to daily -2 -4 3 Moderate 10 to 10 per year a few times per month -4 -6 2 Low 10 to 10 per year a few times per year 1 Very Low < 10-6 per year < a few times per year magnitude--one vulnerability level--below the vulnerability level assigned using the estimated incident frequency from historical data. For estimating the likelihood of a release at a fixed facility, you must rely on estimates obtained through discussions with the companies that have inventories of hazmat. LEPCs will have access to the company's safety officer and planning documents for any facility that falls under EPA or Occupational Safety and Health Administration (OSHA) regulations, because hazmat are present above the prescribed threshold values. In some cases, these planning documents will include a discussion of the likelihood of a release requiring non-company emergency response support. If the documents do not include that discussion, you can estimate the likelihood based on discussions with the safety officer. The safety officer will be familiar with process upsets and near-misses, serious incident scenarios that were stopped by the intervention of safety systems or trained operators at the local facility and other similar facilities operating around the United States. The vulnerability level for a serious incident will be one or, in a few cases, two. Thus, if several facilities of similar design have been operating for a total of 1,000 plant years and there was only one known near-miss, then the vulnerability level is probably "low" because there are typically several near-misses before there is an actual release. For purposes of this example, the vulnerability will be judged as "moderate," somewhere in the range of 10-2 to 10-4 per year (or 1 in every 100 to 10,000 years). There might be more than one type of hazardous material present at a facility, and the vulnerability term could be adjusted upwards accordingly. The size and nature of the facility matters as well. If the facility was the only producer of a key product in a region or had another similar characteristic, the vulnerability level probably should be set higher from a security perspective. The vulnerability term would also be used if the major threat was viewed to be security rather than safety. The vulnerability would be associated with iconic targets or critical infrastructure, and the fraction of the time a material could damage the targets or infrastructure would be used to assign a value to the vulnerability term. Based on the last column in Table 20, the vulnerability term would be assigned as "low" if the hazardous material that could damage the iconic structure or the critical infrastructure were present in the area only a few times a year. When you consider vulnerability from the safety perspective, the term for a transport corridor has several components: number of vehicles carrying the hazardous material, incident rate for those vehicles, hazmat involvement, and hazmat release. While an individual skilled in risk assessment might not have any difficulty assigning values to those terms, a simpler alternative might be to just focus on traffic volume. Consider each mode separately. If the region is traversed by a Class 1 railroad, with 25 or more trains a day traversing the region, a "high" vulnerability should be assigned for all the hazards believed to be present in the area. From an incident perspective, if there were 25 trains traversing the area every day, then there are millions of rail car miles per year passing through the region, and there could be several train incidents per year. It follows