Understanding Major Accident Hazards

Frequency Determination – How likely is it to happen ?

The purpose of frequency analysis is to determine the likelihood of each of the undesired events or accident scenarios identified at the hazard identification stage.  There are two basic approaches which are commonly employed in trying to estimate event frequencies.  These are:

• To use relevant historical data
• To synthesise event frequencies using techniques such as Fault Tree Analysis and Event Tree Analysis

The two approaches are in fact complementary, each having strengths where the other has weaknesses and hence, wherever possible, it is useful to pursue both approaches.  In this way, the two approaches can be used as independent checks on one another and hence, hopefully, serve to increase confidence in the results.