The engineers entered the ship to investigate the source of the liquid and collapsed.

The second engineer regained enough consciousness to crawl to safety while the superintendent and second mate put on breathing apparatus and rescued the chief engineer, the report said.

All affected were hospitalised with symptoms of hydrogen sulphide exposure and later recovered, the commission said.

‘Unpleasant odour’

The report, led by Chief Commissioner David Clarke and supported by Deputy Chief Commissioner Stephen Davies Howard, plus commissioners Paula Rose and Bernadette Roka Arapere, said the “unpleasant odour” and its effect on people meant the presence of hydrogen sulphide was suspected.

The colourless, flammable and highly toxic gas, which was a byproduct of decaying fish, was known for its characteristic “rotten egg smell” at lower concentrations.

All four affected suffered irritation to their upper airways, while the chief engineer also suffered mild hypoxia. All were discharged from the hospital the same day, Taic said.

The commission has included the owner of the fishing vessel and the Lyttelton Port Company in a set of recommendations aimed at improving safety systems on and off ships in port.

The acting chief investigator of accidents, Tahlia Fisher, said while the immediate cause was the accidental starting of an offal pump, the investigation found four broader safety issues which affected industries beyond the marine sector.

Australian-owned Southern Ocean vessel

The Australian-flagged Antarctic Discovery was a longline fishing vessel which commonly operated in the Southern Ocean.

It was owned by Australian Longline Fishing, which bought the vessel in 2015 while it was being modified to meet conservation requirements.

The modification included installing an offal chute in the factory deck where the fish were processed. From there, the offal was minced and then pumped forward along the factory deck through a flexible line and then into a steel pipe into a tank.

On February 21 2025, the vessel was in dry dock at Lyttelton.

The two apprentice fitters climbed down into the ship to work on pipe components tucked behind a tank which held a mixture of decaying fish offal and seawater.

The pipework was right next to the control panel for the offal pump, Taic said.

The report said it was “about as likely as not” that one of the fitters accidentally pressed the pump’s start button, releasing the tank’s contents.

“Foul-smelling” toxic hydrogen sulphide gas began building up. Taic said the fitters had no option but to climb the ladder through the falling liquid to escape to the open air.

The vessel superintendent went below to investigate and was briefly overcome by the gas.

Combination of failures

The commission found that a combination of procedural failures, design shortcomings and inadequate oversight contributed to the accident.

The offal pump had not been isolated nor locked and “tagged out”, which left it active during maintenance.

A suction valve at the front of the ship remained open and the temporary flexible red hose, installed after a previous valve failure, was not capped.

Four people were rushed to hospital after being overcome by toxic gas from rotting fish waste while working on the Antarctic Discovery fishing vessel. Photo / George Heard

The space where the apprentices worked had “many of the characteristics associated with an enclosed and confined space” but had not been identified as such, meaning the risk assessment for work permitted in the space was not in line with good industry practice, the commission said.

“This accident demonstrates how routine maintenance in complex environments can escalate when overlapping responsibilities and weak procedural controls coincide,” the commissioners noted.

The Transport Accident Investigation Commission is an independent Crown entity and a standing commission of inquiry.

It investigates selected maritime, aviation and rail accidents and incidents and makes recommendations aimed at helping the transport sector improve safety.

Tracy Neal is a Nelson-based Open Justice reporter at NZME. She was previously RNZ’s regional reporter in Nelson-Marlborough and has covered general news, including court and local government for the Nelson Mail.

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