Probabilistic fire risk analysis and structural safety assessment of FPSO topside module

•A proper evaluation of structural safety is difficult with the existing fire risk assessment.•This paper proposes a new concept of cumulative failure frequency to topside module of FPSO.•The cumulative failure frequency methods allow for a proper probabilistic evaluation.

An offshore platform normally is exposed to flammable oil and gas in the course of its operation. Uncontrolled hydrocarbon leaks or accumulated flammable gas clouds present very dire threats, due to the probability of resultant fire and explosion. Fire accident represents a major part of the total risk to offshore platforms. Nevertheless, existing procedures of fire risk analysis (FRA) are still not comprehensive enough to systematically evaluate the risks to topside structure safety. As reported in this paper, a new FRA procedure is established to overcome the deficiencies of existing ones.Prior to introducing the new FRA procedure, this paper reviews two types of existing FRA procedures and points out a common problem, namely the difficult application of design accidental loads (DALs) to structural consequence analysis. In this regard, the new procedure includes an extended structural consequence analysis rather than follow the conventional means of determining specific DALs. Moreover, the new procedure offers a new concept of cumulative failure frequency for assessment of topside module structure safety. The role of cumulative failure frequency is to probabilistically identify failed members of objective structures. The key advantages of the new FRA procedure are twofold: first, effective structural consequence analysis without the need for DALs, and second, probabilistic safety assessment of topside structure subjected to a certain number of prescribed fire-accident scenarios. The cumulative failure frequency, in fact, becomes useful information for determination of risk mitigation measures (e.g. passive fire protection (PFP), deluge systems, etc.). This paper not only presents a detailed description of the new FRA procedure but also demonstrates an example using a real FPSO separation module.