Xylene can also cause headaches, dizziness, confusion, loss of muscle coordination, and in high doses, death.
The lab worker spoken to by the Chronicle said that after the container of xylene was retrieved from the freezer it was opened on a table inside the lab where the liquid, which by now had mostly turned into gas, escaped.
The remnants of the substance left in the container were transferred to a smaller container, which was placed back in the freezer.
Those in the room then began to feel ill and noticed a smell, the worker said.
They left the room and warned others there was likely a substance that had escaped - later identified as the frozen xylene.
Medlab says it was then that the substance was removed and destroyed.
A member of the lab team said there was a second chemical exposure four days later on Tuesday, April 20.
After that exposure, where gas again spilled from a frozen container, a worker then took a number of days off work feeling ill, the lab worker told the Chronicle.
Medlab Central chief executive Dr Cynric Temple-Camp accepted that a number of staff were exposed to xylene in the first instance.
He said it was the result of a staff member accidentally placing the wrong chemical in the freezer and later retrieving it.
However, Temple-Camp said the second exposure was ethanol, and not xylene.
"What happened on the Friday is the xylene was placed in the freezer. When this was realised, the substance was removed and destroyed.
"A senior scientist then put the correct chemical in the freezer."
Medlab did not alert WorkSafe to the xylene incident, nor the second exposure.
Temple-Camp said that decision was made after using the government department's online tool.
"I guess the question is whether it's a serious incident, or whether it's an exposure to one of the accepted substances," Temple-Camp said.
"When you've had an exposure you may not have been seriously at risk - that's a matter of judgement."
At the time of the incident, Temple-Camp said the company was not aware that a staff member had suffered an illness as a result of the exposure, but was later informed.
Temple-Camp said immediately after the incident a "very thorough" review was done to determine the cause of the exposure.
WorkSafe has subsequently confirmed to the Chronicle that it was notified of the incident late last week and is looking into the matter.
The facility is operated by Medlab Central on behalf of the Whanganui DHB, which contracts the company to provide laboratory-level testing services.
The DHB did not say if it had been alerted to the incident.
"Whanganui DHB is in discussion with Medlab about the incident and has no comment to make at this stage," a spokesperson said.
Dr Deborah Powell, the national secretary for Apex - the union that represents New Zealand's scientific and technical employees, said laboratories were inherently risky places.
"We use a lot of chemicals, and there are biological hazards as well as chemical hazards. We're actually pretty damn good at our health and safety with respect to these matters."
Powell said the union had been working alongside employees affected by the exposure, and that while a review was completed, it was clear staff were unhappy with its contents.
