The Court of Inquiry – a formal military fact-finding process – took almost 21 months after the November 2022 incidents in Wellington Harbour to begin gathering evidence, the Herald has found.
The eventual inquiry document, recently released to the Herald under the Official Information Act (OIA), said the time elapsed meant some witnesses’ memories lacked detail or conflicted with statements taken immediately after the events.
The HMNZS Te Mana. Photo / New Zealand Defence Force
The inquiry investigated three carbon monoxide detections in a machinery compartment on Te Mana while the frigate was in Wellington between November 23 and 25, 2022.
It found the carbon monoxide most likely came from the ship’s aft (rear) sewage-treatment plant and made its way into the affected compartment 3M through deck drains.
The report identified a conflict between the sailors’ reports of their experience and expert evidence that found the recorded concentrations and duration of exposure were unlikely to have been harmful.
The two sailors later reported continuing health problems, although the inquiry concluded those were unlikely to have been caused directly by the recorded carbon monoxide exposure.
It accepted both sailors had suffered temporary impairment and said there was no evidence of “malingering”.
The two sailors, positioned in compartment 3M for aft-steering duties, twice detected a rotten-egg smell. They left the compartment and reported it, then returned carrying a portable gas detector.
Carbon monoxide was subsequently detected at 14 parts per million.
The sailors left again but were instructed to return to the compartment, open hatches and remain close to the exit while maintaining communications. The detector continued to show carbon monoxide.
When visiting the sick bay later that day, they were assessed as being “okay”, but a Navy medic told the inquiry no actual observations were carried out “because they were still walking around” and the parts-per-million reading on the detector was considered low.
The most serious of the three incidents came the next day, on November 24, after the same sailors returned to the compartment while Te Mana was manoeuvring to berth at Wellington’s Queen’s Wharf in winds gusting about 40 knots.
They later said they regained consciousness about 2.45pm when their portable detector was alarming. It recorded carbon monoxide reaching 48ppm. A subsequent entry by personnel wearing breathing apparatus produced a peak reading of 68ppm.
A WorkSafe table reproduced by the inquiry said exposure to 35ppm could cause headaches and dizziness after six to eight hours, while 100ppm could cause headaches after two to three hours. At 800ppm, it listed headache, dizziness, nausea and convulsions within 45 minutes and unconsciousness within two hours.
Royal NZ Navy’s HMNZS Te Mana at Wynyard Quarter, Auckland in 2016.
Having become aware of the gas incident, a machinery-control watchkeeper considered broadcasting a toxic-gas warning – in line with procedures – then decided against it.
The officer told the inquiry the ship was close to the berth, with a pilot and tugs involved, and a toxic-gas alarm could create confusion.
There were also about 30 civilian and military guests aboard after a Navy “shop window” demonstration of the frigate’s capabilities, with concern voiced that sounding a toxic-gas alarm could cause panic.
The commanding officer was not informed until the ship had berthed. The court found this meant the captain had not been given the opportunity to decide how the ship should respond.
The two sailors underwent an initial medical assessment. Their blood-oxygen readings were within normal limits and oxygen was not administered.
They later developed headaches. About 9pm, a duty medic returned to the ship and gave them paracetamol but carried out no further medical examination and took no consultation notes. The court found New Zealand Defence Force (NZDF) medical protocols were not followed.
It said the sailors’ report that they had been unconscious should have been considered a significant factor in deciding their treatment.
Higher medical attention was not obtained until more than 24 hours after the incident, when the sailors continued reporting symptoms.
The sailors reported severe headaches and feeling “spacey” immediately after the incident, followed by ongoing headaches, disrupted sleep, poor concentration, anxiety and poor general wellbeing.
The inquiry, though, said it was more likely the impact the sailors experienced was the result of a neurofunctional disorder or post-traumatic stress disorder associated with what they genuinely believed had been a harmful exposure.
It said factors included their belief they had been exposed to dangerous carbon monoxide levels and their concerns about the Navy’s initial medical response and subsequent care.
NZDF has told the Herald both sailors had since been offered and undergone further neuropsychological assessment as recommended by the inquiry.
The NZ Navy’s Sea Sprite helicopter in 2020 – testing an air-to-surface missile (top) and returning to the frigate Te Mana.
The court also found that failing to broadcast a toxic-gas incident meant the ship did not move into its trained heightened response, affecting actions including the medical response.
The inquiry found there was no deficiency in the toxic-gas training Te Mana had received. The ship had been assessed as “Safe” in a readiness exercise two months before the incidents. It recommended training be expanded because compartment 3M had not been regarded as an area in which toxic gas was expected.
The inquiry also examined a toxic-gas incident aboard sister frigate Te Kaha in 2002, finding new pipes had been installed to stop gas from the aft sewage-treatment plant entering accommodation areas.
The same engineering solution was not installed aboard Te Mana, the inquiry found, because there had been no previous report of toxic gas in Te Mana’s toilets or bathrooms.
After the 2022 incidents, a large U-bend was installed in Te Mana’s main gravity line to the aft sewage-treatment plant in the 2023/24 financial year.
The Court of Inquiry had initially been ordered by then-Maritime Component Commander Commodore Garin Golding in October 2023, almost 11 months after the incidents. It convened five days later but received no evidence.
A July 2024 minute released through the OIA said the president and another inquiry member had been sitting on a separate Court of Inquiry. The inquiry into the Te Mana leak began taking evidence in August 2024 through to November 2024, and the report was completed in July 2025.
The court said the delay meant some witnesses’ recollections were lacking in detail or inconsistent, and it generally relied on interviews conducted immediately after the 2022 incidents where accounts conflicted.
An NZDF spokesperson said all recommendations had now been completed. Toxic-gas training covering all ship compartments was completed across the fleet between September 2025 and June this year.
It also reviewed whether the same toxic-gas risk existed on other Navy vessels but did not say what the review found.
Other changes included new standard operating procedures to ensure appropriate information is provided when medical assessments and treatment are outsourced. It also found one sailor missed correspondence sent to his Defence email while on parental leave and later had to arrange his own rehabilitation logistics.
NZDF said there had been no unexplained toxic-gas detections aboard Navy ships since the 2022 incidents.
David Fisher is based in Northland and has worked as a journalist for more than 30 years, winning multiple journalism awards including being twice named Reporter of the Year and being selected as one of a small number of Wolfson Press Fellows to Wolfson College, Cambridge. He first joined the Herald in 2004.
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