Mar 302015
 

It’s the little things that catch you out. On the Shell-managed, Australia-flagged liquefied natural gas, LNG, tanker Northwest Stormpetrel the cargo engineer followed the rules as he checked the LNG forcing vaporiser’s steam trap to resolve drainage issues but thanks to a missing safety clip still got a painful face-full of steam that required him to be evacuated from the ship for treatment says a report from Australia’s Transport Safety Bureau, ATSB.An LNG forcing vaporiser utilises steam to generate LNG vapour for consumption in the ship’s boilers when there is insufficient natural boil-off from LNG in the cargo tanks. There was excess time available in the vessel’s schedule for its journey to Japan so it was decided to include the forcing vaporiser among items to be checked as the vessel took advantage of the slack time.

On the morning of 8 November, Northwest Stormpetrel’s engineers discussed the planned task. The cryogenic engineer – cargo engineer – routinely carried out vaporiser-related maintenance and was familiar with its systems and the task.

At 0800, the cargo engineer and the integrated rating assigned to assist him met on the ship’s main deck. They discussed the task, reviewed its risk assessment and completed a toolbox talk. The cargo engineer then went to the cargo machinery room, CMR, on the starboard side of the main deck where the vaporiser was located to isolate the system before work on it started. Meanwhile, the integrated rating  fabricate a new gasket for the steam trap in the engine room.

petrelfvIn the CMR, the cargo engineer isolated and locked out the forcing vaporiser’s steam supply, outlet, drain and bypass valves. After checking that the system was depressurised, he completed the permit to work with the chief engineer, who authorised the work. The cargo engineer then returned to the CMR and started dismantling the steam trap located below the vaporiser.

At about 0900, the integrated rating came to the CMR with the new gasket for the dismantled and cleaned steam trap. The cargo engineer discussed the remaining work with him before re-assembling the trap. The system then needed to be de-isolated and returned to its normal operational condition.

Shortly before 1000, the cargo engineer walked around the vaporiser to check if everything was in order for de-isolating the system. Satisfied with the checks, he removed all the valve lock outs.

clippetrelThe cargo engineer then began carefully opening and closing steam valves, regularly checking if everything was normal. The IR stood by and kept watch for abnormal signs. After the vaporiser’s steam supply valve had been fully opened, the regulator was set to its normal working pressure.

At about 1000, the cargo engineer decided to fully open the steam trap’s inlet valve that he had earlier cracked open. He had turned the hand wheel of the valve about one turn when the valve’s bonnet came away from the valve body. A jet of steam erupted from the top of the valve’s open body, scalding the cargo engineer’s hands, forehead and neck before he could move clear. After getting clear of the steam, he took off his gloves, safety glasses and hardhat. The integrated rating helped him out of the CMR and, once outside, his boots and overalls were removed. They then hurried to the nearest safety shower and began cooling the cargo engineer’s burns.

The IR called Northwest Stormpetrel’s navigation bridge and reported the incident. The ship’s master initiated an emergency response and a shipboard medical team was tasked to attend the injured cargo engineer. The master then notified authorities ashore of the incident and asked for a medical evacuation to be arranged and then requested medical advice.

Investigations found that the bonnet locking clip on the steam valve was missing which allowed the bonnet to unscrew and come away from the valve body. The missing clip was not found, nor could it be established when or how it had been lost.

The steam valve’s bonnet had several threads and unscrewing it to the point of release would have required turning it several times. However, it was reported that the bonnet came away after the valve’s hand wheel was turned only one turn to open. It is likely that when the cargo engineer began to fully open the valve, the bonnet was already partially unscrewed and being held by very little thread. The nearly unscrewed bonnet and its missing locking clip may have been more readily apparent visually and by touchor feel, had the valve’s location been less confined, the lighting been better and greater vigilance been exercised.

Qarns the ATSB: “Work on pressurised shipboard systems can potentially have a high risk of serious injury. Familiarity with repetitive tasks on these systems can sometimes reduce the perception of that risk. Therefore, it is important that the associated risk controls, such as risk assessments and permits to work, are periodically reviewed and carefully completed to effectively identify and mitigate all risks – including the presence of defective system components”.

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