Time-dependent risk modeling of accidental events and responses in process industries

Risk to safety of personnel in process industries is normally modeled in the application of event trees, where the risk is defined as a product of event frequency and its consequences. This method is steady state whilst the actual event is time dependent, comprising, for a gas release, as for example, the size of gas cloud being released, probabilities of ignition, fire or explosion, fatality, escalation to new releases and fire and/or explosion, and the probability of fatality, all varying with time. This Paper presents a method whereby the time-dependent events and the time-dependent probability of fatality are modeled by means of the direct Monte Carlo simulation method. Different accident scenarios are modeled and discussed resulting from event trees analysis. Using the simulation method the modeled scenarios change with relevant probabilities at defined times to configurations with appropriate probabilities of fatalities. Simple sensitivity analysis in dependency on most relevant events is also performed. The Paper uses a realistic example from the offshore industry for which the probability of fatality is quantified by the use of simulation method.