Several firefighters involved in fighting the Nelson fires have experienced symptoms of carbon monoxide poisoning, the NZ firefighters union says.
The New Zealand Professional Firefighters Union has also accused Fire and Emergency New Zealand of failing to provide crews with adequate care.
The union has subsequently demanded that monitoring for carbon monoxide levels be mandatory for Nelson firefighters although Fire and Emergency says there is no evidence to indicate the incidents were caused by exposure to the gas.
Three firefighters involved in fighting the relentless Nelson blaze presented with dizziness, nausea and vomiting.
Fire and Emergency claims however that the incidences were caused by heat stress and dehydration.
Despite high levels of CO being detected, the union says not enough monitoring is being done and is calling for mandatory measures to be taken for members currently deployed.
They have advised that all crews must be equipped with a gas detector as well as commit to seeing a doctor if they experience symptoms of CO poisoning.
The union says Fire and Emergency has failed to provide a duty of care by neglecting to monitor CO levels properly and adequately advising firefighters of proper medical protocol.