Fatal accident rate, defined

The hazard analysis of any industrial process impacts on risk assessment. Risk assessment involves the estimation of the frequency and consequences of a range of hazard scenarios and of individual and societal risk. The risk assessment process is shown in Figure 3.1. The risk criterion used in hazard analysis is the fatal accident rate (FAR). The FAR is defined as the number of fatalities per 108h exposure. The actual FAR in the U.K. was 3.5 in the chemical industry in 1975. No doubt the ideal FAR value should be zero, which is difficult to achieve in practice. 

Table 5.1 sutmnarizes a number of risk measures defined in the Guidelines for Chemical Process Quantitative Risk Analysis, Second Edition (CCPS, 1989) and illustrates the advantages and disadvantages when used for transportation risk analyses. Since measures such as the fatal accident rate (FAR) are geared toward estimating risk to employees at fixed facilities, this measure has not been included as it does not generally apply to transportation risk analysis. 

Only in a limited number of countries have individual risk limit values courageously been defined. One famous definition is the British Fatal Accident Rate (FAR). Operations with a FAR of less than 0.4 are regarded as safe. The FAR is defined as the number of fatalities per 1000 employees in their average working life time of 25 years. The answer to the question whether those relatives who have just lost a loved one find consolation in the statement that the probability for one worker in a company with 1000 employees to die fi om the consequences of a process is once in 30000 years can easily be found by the reader. 

Individual Hazard Index (IHI) The Fatal Accident Rate (FAR) for a particular hazard, with the exposure time defined as the actual time that a person is exposed to a hazard of concern. 

This is one method of setting a tolerable risk level. If a design team is prepared to define what is considered to be a target fatal accident rate for a particular situation it becomes possible to define a numerical value for the tolerable risk. Whilst it seems a bit brutal to set such targets the reality is that certain industries have historical norms and also have targets for improving those statistical results. 

One approach is to compare the risks, calculated from a hazard analysis, with risks that are generally considered acceptable such as, the average risks in the particular industry, and the kind of risks that people accept voluntarily. One measure of the risk to life is the Fatal Accident Frequency Rate (FAFR), defined as the number of deaths per 108 working hours. This is equivalent to the number of deaths in a group of 1000 men over their working lives. The FAFR can be calculated from statistical data for various industries and activities some of the published values are shown in Tables 9.8 and 9.9. Table 9.8 shows the relative position of the chemical industry compared with other industries Table 9.9 gives values for some of the risks that people accept voluntarily. 

The second view is macroscopic. In case more than one event is evaluated, an aggregation of the single events is possible in order to assess the overall effects. If the sample under investigation happens to contain accident and non-accident events, an accident rate or prevention rate can be calculated as ratio of frequency of accidents (or one minus accidents) with a measure by frequency of accidents without the measure. Summary statistics can also be computed in non-accident events by statistically evaluating the indicators defined on the physical level. In comparison to a baseline without measure the change due to a specific safety measure can be evaluated at the desired level of detail. Within the accident group, rates for specific injury severities as well as a fatality rate can be estimated. 

Societal risks are usually given as fatal accident frequency rates (FAFRs). The fatal accident frequency rate is defined as the number of fatal injury accidents in a group of 1000 in a working lifetime (10 hours). 

The output from Stage (c) may be expressed in the form of individual risk or of societal risk. Individual risk is tiie probability of death to an individual within a year (e.g. 1 in 10 per year). Societal risk is the probability of death to a group of people - either employees or members of the general public - within a year (e.g. a risk of 500 or more deaths of 10 per year). Societal risks are usually given as fatal accident frequency rates (FAFRs). The fatal accident frequency rate is defined as the number of fatal injury accidents in a group of 1000 in a working lifetime (10 hours). 

The average accident fatality rate in the U.S. is approximately 5x10" per individual per year, so the quantitative value for the first goal is 5 x 10 per individual per year. The "vicinity of a nuclear power plant" is defined to be the area within one mile (1.6 km) of the plant site boundary. The average U.S. cancer fatality rate is approximately 2 x 10 per year, so the quantitative value for the second goal is 2 x 10 per average individual per year. The population "near a nuclear power plant" is defined as the population within ten miles (16 km) of the plant site. 

The safety record of the smaller railroads can be investigated using FRA data. Table 15.3 shows accident and fatality-rate data for the years 1994-96 for three different sizes of railroads the large Class I railroads, the medium-size Class II railroads, and the small Class III railroads who are defined as having less than 400,000 employee-hours per year. In rough terms. Class III would be equivalent to those railroads shown in table 15.1 as moving less than 40,000 carloads a year. 

---