Titel_SS06

Number of events per year

Number of fatalities per event

Figure 13.1: Farmer diagram (or F-N diagram) with indication of acceptable risks, the ALARP zone
and non-acceptable risks.

On the x-axis the consequences are given, typically in terms of the number of fatalities, but in
principle any other type of consequences could be considered. On the y-axis the probability of
occurrence of the corresponding events are given. The Farmer diagrams may be applied to
illustrate the risk profile for a specific activity or for specific types of hazards. In this way e.g.
the risk profile for different types of natural hazards may be compared national wise and
regional wise. However, by such comparisons the scale dependency problem must be taken
into account, as the probability of occurrences will depend on the area of the considered
region as well as the time horizon of the considered activity.

Several variants of Farmer diagrams, e.g. risk matrixes have been developed in different
application areas. Their common feature is, however, that they depict the relationship between
consequences and probability of events with consequences. Typically risk matrixes may be
defined where consequences and probabilities are indicated in ranges or even fully subjective
in linguistic terms, see Figure 13.2.

Probability of event

Consequence of eventsmall

moderate

significant

large

small moderate significant large

Figure 13.2: Risk matrix with indication of acceptable (green), ALARP (yellow) and non-acceptable
(red) regions.