Eighteen people were taken to Rotorua Hospital yesterday after inhaling toxic fumes as possum bait burned.

Workers at a Lakeland Helicopters hangar in Murupara, southwest of Rotorua, were preparing the bait for a drop when it caught fire.

Fourteen workers and four firefighters were taken to hospital as a precaution after breathing in the brodifacoum fumes.

The Fire Service said one person showed signs of distress while a Rotorua Hospital spokeswoman said five of the 14 workers required a full medical examination but most were found to have had only minimal exposure to the chemical.

The cause of the fire is unknown but Rotorua's chief fire officer, Wayne Bedford, said it might have started when petrol was decanted.

The flames had spread quickly through 10 100kg bags of brodifacoum, a pesticide also used to kill rodents.

"It's basically a glorified rat poison," Mr Bedford said. "The fumes can be quite toxic."

The workers were able to contain the blaze before firefighters arrived about 20 minutes later

A volunteer brigade at Murupara could not immediately be mobilised, so crews from Kaingaroa and Rotorua attended.

They extinguished the remaining flames and called in a hazardous materials unit from Rotorua.

The regional council, Environment Bay of Plenty, was also alerted.

Mr Bedford said brodifacoum was an anti-coagulant that thinned the blood and could kill humans if they ingested it and started bleeding.

"We don't believe the smoke would do that," he said.

Firefighters remained at the scene last night to decontaminate the hangar, which they planned to flush out with water - the waste would be placed in a secure tanker and taken to a chemical dumpsite. The remains of the bait would be disposed of in the same manner.

Lakeland Helicopters specialises in spraying and pest control. Calls to managers were not returned yesterday.

KILLER TOXIN

* Brodifacoum is a poison that kills by thinning the blood.

* If swallowed or inhaled regularly it could cause bleeding or bruising.

* One-off exposure is not usually a problem.

* If taken in large quantities, it could kill humans.

* An antidote, vitamin K, thickens the blood.

Source: National Poisons Centre