Average individual risk, defined

Average individual risks must be defined in context of the exposed population ... 

Average Individual Risk (total population), defined as the individual risk over a predetermined population, whether or not people are actually exposed to the risk. If the population used is large, this risk measure can be deceiving, as it might depict very low risks while limited portions of the population in fact are exposed to high risks. 

Average Individual Risk— total population Allows risk to a constant population to be compared for several movements allows for the extent of consequence to figure more heavily in risk measure May be significantly misleading with regard to the maximum risk level if this risk is limited to a small portion of the defined oommunity... 

Option 1 had the lowest individual risk, but Option 2 had the lowest soeietal risk and average rate of impact. Since risk criteria were not defined at the operations level in this example, the results were sent baek to management for eomparison to the other facilities transporting pesticide by tank track. 

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. 

Column 3 presents the probable number of cancers of the type defined in column 2, estimated to arise in the future lifetime of a mixed population receiving lO" man-rem (or a population of specific age groups as for thyroid cancer). The risk that an average individual may develop a cancer in the years of life remaining to him is then—for leukemia—50 x 10" per rem received. 

When it comes to public safety, the way judgments about risks are framed are arguably even more important. Do we for instance define risk in terms of loss of hfe, material damage, or their perceived severity When risks are defined in terms of loss of hfe, it could have considerable consequences whether loss of hfe is defined as a total number of hfe years lost or as a number of deaths. As Slovic (1999) put it Whoever controls the defirution of risk controls the rational solution to the problem at hand . The AS/NZS 4360 Risk Management Standard acknowledges this issue by providing only examples of quantitative risk expressions, such as the average individual probabhity of death in an exposed population and the number of new ill-health cases per annum in an exposed population. 

The Dutch major hazards policy deals with the risks to those hving in the vicinity of major industrial hazards, such as chemical plants and LPG-fuelhng stations. The cornerstones of the Dutch major hazards policy are (i) quantitative risk analysis, (ii) individual and societal risk as risk-determining parameters and (iii) quantitative acceptability criteria for evaluating levels of individual and societal risk (Ale 1991, 2002 Bottelberghs 2000). Individual risk is defined as the probability of death of an average, unprotected person that is constantly present at a given location. 

The second risk metric that is being considered by policymakers is individual risk. Individual risk is defined as the probability of death of an average, improtected person that is constantly present at a certain location (note that evacuation could be included in an alternative definition). As levels of individual risk are highly dependent on local flood conditions and topography, it is troublesome to estimate individual risks throughout low-lying regions, without detailed information from flood scenario calculations available. No nationwide estimates are therefore presented for individual risk. 

ABSTRACT Loss of life is not explicitly considered in the current Dutch flood safety poUcy. This paper presents the results of a preliminary study in which the nationwide risks of loss of life were estimated. The risks of loss of life are ejqtressed as individual and societal risk. The first metric is defined as the annual probability of death of an average unprotected person at a predefined location, the second as the cumulative probability of the number of fatalities. This paper covers estimation of societal risks for all flood prone areas (so-called dike rings) in the Netherlands. 

The basic reproductive ratio, Rq, is defined as the average number of secondary cases occurring in a susceptible population. When Rq is greater than 1, the disease is capable of infecting susceptible individuals and the number of cases will therefore increase. Conversely, when Rq is less than 1, the disease will always fail to spread. Estimation of the Rq can help to quantify the risk of a given disease to the population. Comparative examples of Rq values are shown in Table 4.31. 

---