Fire in vertical lay system moonpool

A member has reported an incident in which there was a fire in the moonpool of a vertical lay system (VLS). A vessel had been involved with the recovery of redundant/damaged 10″ flexible flowlines to on-deck storage reels, and ‘wet storage’ (on the seabed) was being prepared for a previously recovered section of 10″ flowline. (This flowline section had been flushed of hydrocarbons in January 2008.)

Following the recovery of the flowlines to deck, the vessel made several transits totalling approximately 12 kilometres over a 19 hour period. Work was approved to remove some gouges on the VLS moonpool doors utilising a pneumatic grinder. A highly experienced, and competent, boilermaker proceeded to grind out the gouges on the moonpool doors with the grinding sparks directed down and into the moonpool water.

A fire started on the water within the moonpool centraliser and then grew to an above deck height of more than two metres. The person conducting the grinding was using body harness/fall arrest equipment as the moonpool doors had been opened slightly to give him better access. When the fire started, he experienced difficulty in escaping from the area as the fall arrest unit prevented the pay-out of the cable. Fortunately a nearby colleague freed him from the fall arrest cable and they both escaped from the fire area without injury.

The fire alarm was raised and the fire was extinguished within 25 minutes of the alarm being sounded with no persons injured or harmed.

The following were noted:

• The moonpool area, including the area below the VLS doors, was visually checked prior to the grinding, but nevertheless nobody observed or identified the presence of flammable liquids within the moonpool;
• At the earlier onshore hazard identification and risk assessment, the presence of ‘inhibited seawater’ containing very low hydrocarbon levels had been identified, however a fire risk or accumulation of flammable hydrocarbon products within the confines of the moonpool had not been considered as a potential hazard;
• The concentration of hydrocarbon levels found within the 10″ flowline was inconsistent with the hydrocarbon levels expected (‘flushing fluid’ consisting of hydrocarbon < 30mg/ltr (flushed earlier in 2008)). It is possible that there may have been localised concentration of oil in the intervening period through gravity separation of fluids of different densities and/or reintegration of oil trapped in the interstices of the rough bore pipe carcass;
• The application of the permit to work, risk assessment and associated process were not sufficiently robust or effective and several management system improvements have been identified/implemented;
• Competency of the onboard personnel resulted in the fire teams responding very quickly and bringing the fire under control in a timely manner.