Fire risk analysis procedure based on temperature approximation for determination of failed area of offshore structure: Living quarters on semi-drilling rig

Fire risk analysis (FRA), one of the dedicated safety studies in offshore risk assessment, aims at determining the potential fire scenarios that threaten the offshore plants and its associated facilities. In the detailed design stage, there is a routine FRA procedure that is conducted to probabilistically determine the safety of the topside structure. This procedure, however, lacks a direct probabilistic risk analysis for determination of the design accidental load (DAL) or of the necessary insulated protection applied to the critical targets on offshore plants. This paper conceptually proposes a quantitative-probabilistic FRA procedure for calculating the design temperature distribution and probable failed areas of critical targets. The proposed procedure considers a full combination of blowout scenarios that can possibly take place on a semi-submersible drilling rig. In scenario identification, the probability distributions of random variables related to fire events are taken into consideration. In consequence analysis, a CFD-based fire simulation (KFX, 2010) in conjunction with a heat transfer analysis (FAHTS, 2010) is carried out to calculate the temperature distribution at the wall surface of living quarters (LQ). In response to the heavy computational CFD simulation, this paper also introduces an approximation method to reduce the time cost of analysis, which depends on the number of input scenarios. Lastly, in risk evaluation, the failed area of LQ is predicted using 2 different risk analysis methods: cumulative failure frequency (CFF) and temperature exceedance curve (TEC).