Diver exposed to unplanned release of production gas

During saturation diving activities at 65m water depth, from a Diving Support Vessel (DSV), a diver was exposed to a sudden and unplanned release of hydrocarbon gas under pressure (estimated pressure >150bar). The pressure release resulted in ejection of a stuck blind stab and the diver being pushed backwards by the force of the gas. The diver was unharmed. Our member considered the incident to be a very high potential near miss.

Nearing the end of the bell run, saturation divers were working on a subsea skid when they identified incorrect tagging. Work was stopped and the divers were then instructed by the Diving Supervisor to proceed with a dummy stab removal at the same location, using hand tools (T-Bar and hammer). During initial hammering of the dummy stab, a discharge of gas bubbles was observed coming from the receptacle, followed by a larger one. At this time, both divers were instructed to stop working for ten minutes to allow for the gas to discharge. Diver 1 was instructed to return to the bell and Diver 2 was subsequently instructed to restart tapping the blind stab with the hammer. Suddenly the dummy stab ejected and trapped production gas was released. Diver 2 was positioned just outside the line of fire, but he was pushed backwards by the force of the gas release, though he remained on the top of the skid.

• Unlike the isolation in place for previous work, the isolation of this skid could not be demonstrated because of  the configuration of the pipework and because there was no way to vent the void behind the blind stab.
• Dummy stab removal with diver and hand tools was a deviation from procedure. There was no time out taken to discuss the change in task or initiate a Management of Change procedure;
• The Dive Supervisor had previously used divers to remove blind stabs, which created a normalisation of this way of working.
• The task Specific Risk Assessment was not adequately reviewed at the Toolbox Talk.
• ROV tooling developed for blind stab removal was available and ought to have been used as per the task specific Risk Assessment but was not used.
• Specific task plans were not developed for diver dummy stab removal.
• Several people could have intervened and stopped the job but did not. Only one person – the Pre-Commissioning Engineer had a concern and highlighted the non-compliance with procedures, but did not exercise stop work authority.
• The divers continued with dummy stab removal despite the gas bubble release without challenging the ‘as-found’ condition.