Fatigued crew sprayed boat boiler that hadn't cooled before explosion - TAIC

An explosion on a ship berthed in Bluff that injured three people occurred when crew were cleaning a boiler that hadn't cooled, the Transport Accident Investigation Commission (TAIC) says.

Three crew members were injured in the accident on board the Malta-flagged M.V Olivia, which happened in May last year.

All three of the injured were taken to Invercargill's Kew Hospital - two received serious burns and the third received bruising.

TAIC released its final report into the accident on Friday.

The team of engineering crew members were cleaning air blasting soot from inside the boiler when a blowback explosion occurred.

"It is likely that the boiler initially flamed out and failed to restart because of a combination of the following issues. Malfunction of the burner's air-intake flap, the faulty ignition transformer and buildup of soot inside the boiler," the report said.

When the Olivia arrived in Bluff a month earlier, the port stay was scheduled to be only five days.

Urgent maintenance and repair work on all the ship's generators extended the stay in Bluff indefinitely, the report said.

The commission said the crew considered that cleaning the boiler was a routine and regular activity and the boiler was usually cleaned a few days before arriving at a port.

"Although the activity was familiar, the conditions were not. Cleaning the boiler at sea, after it had cooled for several days, differed materially from cleaning it after repeated ignition attempts and an earlier blowback while the furnace remained hot," the report said.

Chief investigator of accidents Louise Cook said it was likely that disturbed heated soot ignited residual fuel as the air lance was withdrawn.

"Before internal cleaning, a boiler furnace needs to be isolated and verified as safely cooled. Blowing compressed air into that hot furnace with unburned fuel was a recipe for a blowback," she said.

The investigation identified two safety issues; inadequate implementation of the vessel's safety management system, and a lack of guidance for managing crew during sustained intensive work periods.

The report said it was "very likely" that senior engineering officers were fatigued as they sought to complete the generator repairs, which adversely affected their decision-making.

TAIC said it was very likely that the severity of the injuries would have been reduced if the crew members had worn appropriate face protection.

"The decision to not use any face or eye protection was further indication that the crew did not appreciate the risk," the report said.

There were also no senior engineering officers on duty overnight which meant that there was nobody authorised to oversee work that carried a higher risk than the cleaning and preparation work planned for the night shift.

"Long repair programmes need continuing attention to workloads, rest and supervision. If an unexpected job is beyond people's capability, it should be a straightforward decision to stop and get the right support," Cook said.

The ship's operator, Fleet Management Limited, had taken several steps to address both issues identified, including reviewing procedures, protective equipment and fleet training.

As a result, the commission did not issue any new recommendations.