The five people killed when their boat capsized in 2022 had their chances of survival reduced by petrol leaking into the air pocket they were in.

The Transport Accident Investigation Commission (TAIC) revealed part of its preliminary report into the Kaikōura boat tragedy today as it found “urgent” safety issues which need to be addressed.

In September 2022, 11 people were on board a commercial vessel on a bird-watching trip. The sea was flat and calm, but disaster struck when a whale reportedly surfaced directly underneath the boat, capsizing it.

The skipper and five other passengers were rescued from atop the boat - but five others were found deceased in an air-pocket beneath it.

TAIC has revealed the boat had leaked petrol into the air-pocket and this had likely reduced the chances of survival for those who had been inside it.

“All of the deceased showed symptoms of petrol exposure consistent with inhalation”.

Being exposed to petrol in a confined space such as an air-pocket reduces survivability as petrol attacks the cardiac and central nervous systems.

“In low concentration levels, people can experience the smell and irritation of the eyes and upper respiratory tract. High levels of exposure can rapidly lead to confusion loss of consciousness and sudden death,” the report read.

When the boat capsized, two people were ejected from the vessel entirely and eight others were initially under the hull in the air-pocket.

The skipper and two others swam out immediately, but one other person surfaced under the hull and tried to tell the others under it to swim out. In doing this, they noticed the air “did not feel good” and swam out from under the boat.

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The police dive squad, who entered the air-pocket sometime after the vessel had capsized noticed a “very strong” smell of petrol within it.

Chief investigator of accidents Naveen Kozhuppakalam said the petrol had almost certainly leaked from flaws in the fuel system of the boat.

“A pipe connected to the secondary fuel tank vent hose had a hole that was the main source of leaked fuel. It presented a hazard that risked fire or explosion if the fuel leaked when filling the tank, or risked fumes in the air-pocket if the boat overturned.”

As well as this, the secondary vent hose did not vent to outside air, and instead vented into a sealed metal tube fitted to the rear of a boat.

There was also a second leak from the primary fuel tank vent hose where it joined the fuel tank - and this should have been sealed with a hose clamp.

TAIC is now calling on Maritime New Zealand to urgently address this problem, saying that there are hundreds of boats just like 1-Catcher in the commercial fleet, and tens of thousands more in the recreational fleet.

They say Maritime NZ does not adequately assess the integrity and safety of fuel systems on boats because the rules don’t require the entire fuel system to be inspected.

Chief Commissioner Jane Meares said the issue goes further than just the i-Catcher.

“It’s nation and system-wide. Everyone on board a boat deserves to be safe.”

Kozhuppakalam said the vessel had been inspected by five different marine surveyors and not one report shows an inspection of the fuel system below the deck plate.

“Surveyors are more likely to discover deficiencies if they are required to inspect the whole fuel system as a critical item - not just the parts that are easy to get to.”

Vita Molyneux is a Wellington-based journalist who covers breaking news and stories from the capital. She has been a journalist since 2018 and joined the Herald in 2021.