Effect of full-bore natural gas release on fire and individual risks: A case study for an LNG-Fueled ship

This study investigated the significance of categorizing and selecting representative leak sizes in Quantitative Risk Assessment (QRA) for estimating natural gas fire risks. In most fire QRA procedures, the full-bore sizes of leaks have been overlooked even though they causes the catastrophic consequences with relatively high frequencies. So, in the present study, the effect of particular leak sizes on the individual risks (IRs) were investigated through the fire risk assessment. As case studies, LNG (Liquefied Natural Gas) fuel gas supply system for a large ship were considered with three different approaches. Approach 1 considers only three categories of leak sizes; small, medium, and large. Approach 2 includes the full-bore leak in addition to categories of Approach 1, and Approach 3 reflects more categories of leak sizes with every 1 mm increment in diameter. Compared with the total IR of Approach 3, the total IR of Approach 1 was two times lower, whereas Approach 2 resulted in the comparable total IR with an approximately 4% deviation. Admitting that Approach 3 should be close to the exact solution, Approach 2 gave acceptable results, whereas Approach 1 unsatisfactorily underestimated the total IR. The results indicated that full-bore leak accidents are critically important scenarios and omission of them can lead to misjudgment in the risk-informed decision-making process. Taking the full-bore accidents into additional account to the conventional simplified QRA can reduce the time and effort for estimating the leak-related risks without a significant loss of accuracy in the estimated risks.