Controlling Hydrocarbon Fires in Offshore Structures

Abstract

Abstract This paper reviews improvements in the understanding of fire hazards and protection in offshore structures since the Piper Alpha disaster in 1988. Important new knowledge on fire development, spread and escalation have come about through a number of industry sponsored initiatives, which have also demonstrated how to control and mitigate fire hazards by good design and effective protection. The most notable gains in knowledge have been in the areas of unconfined two-phase hydrocarbon jet fires, confined jet and pool fires (compartment fires), and understanding the value of area deluge for fire mitigation. Background The Piper Alpha disaster was a tragic milestone in influencing the Safety Case regime [1]. Since then there have been a number of Industry sponsored initiatives, which have contributed to significant advances in the science and understanding of the consequences of accidental hydrocarbon fires in offshore structures and the engineering of safe design. While some uncertainties remain, the application of this knowledge, via a Hazards and Effects Management Process or appropriate Standard (e.g. ISO 13702:1999), is normally sufficient to improve design and operation of plant in a cost efficient way. A short review of the fire hazard aspects of the Piper Alpha disaster helps to focus on credible scenarios. Next to each event are some pertinent questions asked of the main fire hazards and the effectiveness of possible protective barriers that could be brought to bear in safety studies and design:The initial blast ruptured oil lines in the adjacent module. How severe was the resulting fire? To what extent does the surrounding congestion and confinement affect the severity? How toxic is the smoke?The Tartan riser failed on the outboard side of the emergency shut-off valve resulting is a full-bore jet fire. What protection should be applied to risers and valves? Is passive fire protection (PFP) adequate? Will PFP age with time and then be less effective against fires? Is a sub-sea isolation valve effective against rise fires? How close to the platform should it be located?The water deluge system did not operate. How effective are water-based systems in controlling different types of fire?How effective are blowdown systems against different types of fire? What strategies should be adopted? The Blast and Fire Engineering for Topside Structures (BFETS) Project [2,3] started in 1990 was the first major initiative to provide interim guidance on how to reduce the potential for such disasters. This project also identified gaps in knowledge and recognized the need for full-scale experiments and further guidance, which have been addressed in numerous follow-up studies and other Joint Industry Projects. In this paper I review the considerable progressmade to address the questions raised above. Fire Hazards An accidental release of flammable hydrocarbon results in a variety of fire consequences, dependent on the type and initial state of the hydrocarbon.