Auckland Airport says it has fixed a problem with fumes which contributed to disruption and long queues of passengers through security screening at the international terminal earlier this year.
It investigated quickly and thoroughly, using external experts, it told RNZ on Wednesday.
A briefing shows hundreds of crew and staff had to be re-routed through passenger screening in February and March, when the bulk duty free screening point was shut due to unknown fumes.
"An airport-related health and safety issue created fumes and staff sickness in the bulk duty-free screening area," said the briefing, part of a weekly one from the Civil Aviation Authority (CAA) in March to the transport minister.
This led to 640 staff and crew being unable to use their usual, dedicated screening area, and instead "taking up one lane that would have otherwise been used to facilitate passenger screening", in a busier than usual period due to the Taylor Swift concert in Sydney.
Paramedics were called in when a CAA staff member became unwell, the briefing said.
The airport said it shut the staff-only area for a month, during which external experts did 24/7 air monitoring.
This showed a "very low risk to the health of airport workers and there was no evidence of fumes above safe levels in the area", said an airport spokesperson in a statement.
WorkSafe also investigated what the CAA briefing dubbed "the fume incident".
"The safety of airport workers is our priority and workers only returned to the area on 14 March following the testing and extensive collaboration and consultation," the airport spokesperson said.
"However, recognising that fumes can be unpleasant, we took several steps to reduce odour in the BDF [bulk duty-free], including installing fans, increasing air flow and installing ongoing monitoring."
The bulk duty-free screening point has since been shifted to a new area as part of building work.
The Civil Aviation briefing said there were possibly two causes, one related to the construction work going on as the airport does an upgrade, and one "likely to be related to aircraft fuel vapours".
"We have some questions about their [the airport's] capacity to actively manage the size and complexity of the on-site construction projects, and their impact," it said.
The airport rejected that in its statement to RNZ.
"We don't accept any suggestion that the oversight of construction contractors is not being well managed, and we work with our airport partners, including AVSEC, on health and safety planning for each upcoming phase of work."
The airport said it identified two sources for the fumes: aircraft on the airfield, and truck exhaust.
"We discovered small gaps in the building around service pipe work, enabling [aircraft] fumes to access the building, so we sealed these gaps."
A truck with its engine idling near some open roller doors was also pinpointed, so the airport got trucks to switch off during deliveries and put in four fans to push the fumes away.