Risk mapping in quantitative risk analysis for oil and gas facilities

When applying Quantitative RiskAnalysis (QRA) methodologies to estimate the risk for workers of large oil & gas plants, the total number of events to be taken into account may be very high, therefore it is necessary to adopt a proper procedure to evaluate the risk in a systematic way. In this paper, a Risk Mapping approach is applied to a large onshore oil & gas facility, with the aim to discuss the possibility of neglecting the accidental events causing smaller damage area, which are usually produced by smaller leak sizes, and to evaluate the influence on risk results of different ignition probability models. The main scope of the work is to discuss the most critical phases of a Risk Mapping approach, and to provide the analysts with a tool to estimate when it is possible to simplify the analysis by neglecting events or using simplified models, and when this is not advisable from the point of view of risk.