Lifeboat Launch Simulation and Its Application to Safety Assessment

ABSTRACT: The paper deals with the motion simulation of lifeboats launched from fixed or floating platforms and its application to collision risk assessment. The mathematical model of the Davit launch system is presented. By solving the motion differential equations, the three dimensional motion responses of the lifeboat and the platform are simulated in the time domain and the clearance between the lifeboat and platform structural members are monitored. Numerical examples are given and key parametric effects are investigated through deterministic and probabilistic analyses. It is demonstrated that the motion simulation combined with probabilistic analysis techniques can provide an effective tool for quantitative risk assessment of offshore emergency evacuations using lifeboats. 1. INTRODUCTION During an emergency evacuation from offshore fixed or floating platforms, it is of vital importance that lifeboats can be successfully launched and disconnected from the platform. This is actually one of the recommendations made in Cullen's Report [1] into the Piper Alpha disaster which states: "Operators should be required by regulation to submit to the regulatory body for its acceptance an evacuation, escape and rescue analysis in respect of each of its installations". Aimed at improving the understanding of thebehaviour of lifeboats during launch and assessing the risk involved due to possible collisions with platform structural members, the lifeboat launch operation is studied using response simulation techniques. The current study focuses on the traditional Davit launch of lifeboat system for TEMPSC (Totally Enclosed Motor Propelled Survival Craft) whereby the lifeboats are lowered vertically from winches on two cables (see Fig.1). It addressee the following main issues:Motion responses of lifeboats during descending from floating or fixed platformsLifeboat movements during turning and sailawayKey parameters and their effects on motionand risk of collisionProbabilistic analysis as a tool for safetyassessment For lifeboats launched from floating structures Such as semisubmersible units, the lifeboat motion response caused by environmental loading and the platform motion is mathematically modelled. The motion equations are solved numerically to simulate the lifeboat and platform responses and monitor the occurrence of collision in the time domain. Impact velocity can be computed if collision occurs to determine the extent of damage. Investigations of key parametric effects are carried out. The main parameters studied are the types of platforms, severity of environment, vertical descent speed, disconnection time and lifeboat heading. Useful results are obtained which will help the development of appropriate evacuation procedures. It is also demonstrated in the paper thatprobabilistic techniques can be incorporated into the analysis to obtain a quantitative indicator of the risk level of lifeboat launch. The results canbe valuable for aseessing the adequacy of evacuation procedures using lifeboats.