Shipping statistics from a range of

Shipping statistics from a range of sources were studied to establish credible frequencies for fires on ferries. The fire statistics published by the Marine Accident Investigation Branch of the Department of Transport were finally selected as the basis for calculating the frequency of fires on the rail deck and in adjacent compartments of the ferry. These were the initiating fire frequencies from which event trees were developed. An event tree consists of an initiating event - in this case the initiating fire - and a series of branches, each denoting a possible outcome of a chain of subsequent events. A series of event trees were drawn to investigate under which circumstances an initiating fire could develop into a "severe fire". The frequency of these "severe fires" was calculated by assigning probabilities to each of the branches of the event trees.