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8 A Guide for Assessing Community Emergency Response Needs and Capabilities for Hazardous Materials Releases As with all formulations of risk, the fundamental components are the frequency of some event happening combined with the potential consequences of that event. The consequence considers the mitigating effects of response capability and its proximity to potential incidents, as shown in Equation 2: C = C u ERC RTF (2) where C = consequence, Cu = potential consequences (unmitigated), ERC = emergency response capability, and RTF = response time [factor]. To be most effective, you should compute the risk metric for each hazard and location, although there may be opportunities to group certain elements together. Each element in the risk equation is discussed in more detail in the following sections and in subsequent chapters. Hazard For this Guide, hazard is a yes/no variable that indicates whether there is a threat or hazard that could be realized in the region. While there are clearly differences in the relative "hazard" posed by different materials, those differences are primarily captured in the consequence term in the risk equation. Hazards (or threats when considering security issues) can be defined for both fixed facilities and transportation. The quantity of a hazardous material present in one location at any time will also affect the potential consequences. In general, the types of hazards posed by hazmat can be arranged into the following seven categories of Incident Release Type: Fires; Explosions or BLEVEs (boiling liquid expanding vapor explosion); Toxic gas releases; Toxic liquid releases; Corrosives; Radioactive materials releases; and Releases of biologically active materials. In the section where these categories are explained in more detail, it will be shown how all the U.S.DOT HM classes and divisions can be related to these seven categories. These are the seven categories that will be carried through the rest of this Guide. Vulnerability 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 consider vulnerability. One approach considers potential release probabilities based on historical or scientific data, while the other approach considers the quantity and frequency of materials present in a given time period, usually 1 year. In this assessment, the hazards present at fixed facilities or along a transport route will be considered. The details of the approach are presented in Chapter 7.