Asbestos that scores an 11 on a risk scale that tops out at 12 has been found in the ceiling at Auckland's main fire station.
This is despite Fire and Emergency earlier saying none of its stations have high-risk asbestos.
Contractors have been in the ceilings at Auckland City Station, and firefighters fear they have disturbed the dust and brought it down with them, though testing cleared the bedrooms.
The Pitt St station has been shut since last Thursday for tests and decontamination.
The urgent independent survey last weekend commissioned by the firefighters' union found six lots of asbestos in pipe wrapping and insulation debris.
A 2021 FENZ survey found none of that was high risk.
FENZ said it was "unable to comment on matters to do with the investigations until completed".
The union said it did not trust FENZ's data or management of the dangerous material.
"We can't trust FENZ to look out for firefighters," union national secretary Joanne Watson said.
The new survey detected no asbestos in the bedrooms and corridors.
But the surveyors, More Environmental, sounded a warning about workers who had been in the ceiling during renovations several months ago.
"Due to the nature of the ducting works undertaken (cutting through the ceiling tiles to feed ducting to rooms below), the scale of the contamination in the roof void area and the extent of time which has since passed, the historical contamination of this area cannot be excluded," its 42-page survey said.
Firefighters at that time complained of contractors coming down dusty and leaving gear in the laundry, Watson said.
"We won't be allowing members back in until appropriate remedial work is done in loft."
FENZ had allowed workers into the ceiling despite its asbestos management plan, she added.
FENZ did the plan after the 2021 survey it commissioned found asbestos-containing material (ACM) at about 300 properties, including Auckland City station.
"Of the ACM items identified, none were scored as high risk and those that were scored as medium risk were largely at the lower end of the category," FENZ told RNZ last week.
By contrast, the new survey found six lots of high-risk, friable (easy to break up into dust) amosite asbestos in the roof, and recommended:
"Restrict access to void from below."
It also found medium-risk chrysotile asbestos in damaged pipe covers in two bathrooms, and recommended to seal or remove the pipes.
Watson said this raised questions about the 2021 nationwide survey's findings that she would raise with FENZ national management.
"I will tell them we won't allow any renovations in any form to accommodation areas unless they can show they've done the appropriate planning."
Talks between managers and the union continued on Thursday.
"Our people's safety and welfare is always top priority," said deputy chief executive of organisational strategy and capability development Sarah Sinclair in a statement.
She did not directly address questions about why high-risk asbestos was not identified previously, or why contractors were allowed up into the ceiling, or if the contractors had been told of the high-risk findings.
FENZ said it had an asbestos management plan for all stations with asbestos, and each plan was "constantly updated as work is done to identify, confirm and manage" the material.
Sinclair said it would review all the information at Auckland City and work with managers and staff "on next steps".
Martin Campbell, secretary of the northern and Auckland branch of the union, questioned if FENZ had followed its asbestos management plan during the station's renovations.
"Have contractors ... been advised of the recent asbestos findings?" Campbell asked.
RNZ has asked WorkSafe what involvement it has.
In 2021 WorkSafe assessed Auckland fire stations for asbestos and asked for surveys and management plans, but it remains unclear where these checks got to.
FENZ's 2021-22 annual report refers to asbestos once: "We...successfully managed our maintenance and modernisation programmes, which includes...asbestos management."