Dutch Societal Risk Criteria

The curve shows that as the estimated number of fatalities from an event increases, the estimated frequency of the event must decrease accordingly to keep the risk within tolerable bounds (i.e., the risk must remain below the criterion curve shown in Figure 2.10). In other words, the more severe a potential incident is, the more unlikely its occurrence must be.

Type of Risk


(1) the risk to individuals -Individual Risk
(2) the risk to groups of people-Societal Risk


Individual Risk expresses the risk to a single person exposed to a hazard; in other words, an individual in the potential effect zone of an incident or set of incidents.

Societal Risk measures the potential for impacts to a group of people located in the effect zone of an incident or set of incidents.

Consequences Analysis FlowChart [CCPS 2000a]

Basic Steps in QRA Process

How Modern Risk Assessment Evolved

1200 AD-A quantitative approach to answering such questions was developed following disastrous floods in 1953, which killed nearly 2,000 people.

1960s-Bell Telephone Laboratories to address the need for evaluating missile launch control system reliability.

Shuttle program provides a more recent example of the aerospace application The National Aeronautics and Space Administration (NASA) space of QRA. U S . Nuclear Safety Development. The first use of event trees/fault trees for a major QRA in the nuclear industry was the Reactor Safety Study in 1975.

In the early 1990s, the NRC began requiring each nuclear plant licensee to conduct an Individual Plant Examination of External Events (IPEEE), which quantified the risk associated with all analyzed incidents.

Risk

Risk = f(consequence, likelihood)

A simplified version of this relationship, which is often appropriate, expresses risk as the product of the likelihood and the consequences.

(i,e., Risk =Consequence x Likelihood).

Thus, if consequences are expressed in terms of loss per incident, and likelihood as the number of incidents per year, the calculated risk will have the units of losses per year.

This equation shows that a numerically equal value of risk can result from an unlimited number of frequency and consequence pairs (see below).

A single loss every 10 years and 100 losses every 1,000 years yield the same value of risk.