Workers at Wellington Hospital described having "burning lungs" and feeling dizzy after being exposed to exhaust fumes from a diesel heater.
One man said he was still feeling disorientated months later and wants an apology from Capital and Coast District Health Board – now Health NZ.
Worksafe has warned health officials to better manage the risks of diesel exhaust emissions following the incident, which happened in a temporary Covid-screening tent structure during the Omicron wave.
The heater was in use from February 15 and was removed on April 2 when a staff member "was assessed as experiencing symptoms that could possibly be associated with fume inhalation", documents provided to the Herald under the Official Information Act show.
An assessment revealed the heater's flue had become dislodged by the wind, the DHB's chief financial officer Matthew Parr said.
"Our assessment found no indication that the detector and alarm triggered at any stage, and testing did not find meaningful levels of carbon monoxide or sufficient output to have caused symptoms."
Despite this, several workers did report symptoms, which led to the DHB discovering the fault in the heater.
Worksafe was notified of the incident on April 6 and two days later ordered the hospital not to use it anymore.
Security guard Aaron Gittoes, 26, had been working at the site intermittently since December 2021 and first noticed symptoms on April 1.
"On the day that exhaust fumes came out, I felt sleepy, I felt dizzy, I nearly passed out but I didn't connect the two," he told NZME.
"Me and another colleague at work, the screener that was in there from the DHB side … we couldn't stop laughing at random things, we were delirious.
He said he turned up for work the following day and could taste and smell the diesel.
"My lungs were burning, and my eyes were itchy."
He alerted his boss and the DHB on April 2.
Gittoes said he didn't receive a blood and oxygen test, and was told simply to go home and get fresh air.
Three months on, he is concerned the symptoms could be permanent and is seeking an apology from health authorities.
But the DHB said they hadn't received any reports of staff or contractors experiencing ongoing effects or symptoms.
An email from Health and Safety Adviser Leigh McLachlan on April 11 referred to a call from an ED staff member, who was concerned about "harmful effects from exposure to carbon monoxide".
The staff member was also worried about the lack of communication about the hazard and the "lack of concern by the employer for the health and welfare of employees."
The staff member said she "experienced symptoms including feeling fatigued, and headachy in the mornings following the shift".
She was also worried about reprisals from work if she reported it, the email read.
Parr told NZME the DHB took health and safety for everyone onsite "extremely seriously" and followed best practice to ensure everyone on campus remained "safe and supported".
Carbon monoxide is produced by the combustion of fossil fuels such as diesel, gas, coal, wood and oil.
Medical officer of health Denise Barnfather said carbon monoxide was a particular problem in areas where appliances had been used or installed incorrectly and there was no ventilation.
She said the failure of the DHB's testing to pick up any carbon monoxide in the environment did not necessarily mean there was nothing to detect.
Dizziness and headaches were normal reactions to carbon monoxide poisoning but the presence of diesel could create additional symptoms.
"It produces a lot of aggravating toxins that can irritate the eyes, nose, mouth, lungs," said Barnfather.
She had not before encountered a case where symptoms lasted months after exposure, but said every reaction could be different.
"It's really the dose that makes the poison – how long have people been exposed, and to how much have they been exposed, and the vulnerabilities of the people exposed."
A WorkSafe spokesperson said they sent an improvement notice requiring Te Whatu Ora, Health New Zealand Capital, Coast and Hutt Valley to "better manage the risks associated with diesel exhaust emissions".
"This includes developing a process to identify hazards and apply appropriate controls. Ongoing monitoring, maintenance, and review of the controls also needs to be demonstrated to WorkSafe."
The man will appear in Kaikohe District Court on Monday, May 26.