A subsea pipeline transporting gas in Malaysia has a smal l leak at its subsea flange at 70m water depth, located 140m away from the processing platform. The flange has undergone three rectification works; however, the repair works were unsuccessful to achieve zero leak. A Quant itative Pipeline Risk Assessment (QPiRATM) fire and dispersion analysis has been conducted to analyze the potential hazards from the leak to assets and environment and the consequence of the release to human safety. The result from this study can be used by the operator to manage risk by introducing a modification to the operation procedure or applying a mitigation measure, if required.

A process hazard analysis software, PHAST 6.7 has been utilized to per form fire and dispersion study for t he identified leak flow. This paper will present the method of conduct ing the study by establishing the leak size from the given flow rate, calculating the subsea and sea surface rel ease rates, and performing sensitivity analyses for different leak cases should the leak flow rate increases over the operation time. The concentr ation of the gas release from the current leak size to the environment is calculated for the potent ial of fire and explosion and it s possibility of human fatality within the heat radiation zone.