The McFarlane's Fibreglass Engineering Ltd manager said he and his colleagues had just finished their afternoon break and had returned to work when a fibreglass boat exploded in the factory behind them.
"It was like spontaneous combustion. We were just talking about what we were going to do tomorrow and it just exploded.
"It was a huge bang."
Mr Lang said they tried to put the fire out using fire extinguishers, but it was too volatile.
"It was too dangerous. The room was full of toxic black smoke in about a minute. We just had to get out."
While fibreglass is generally not flammable, the chemicals used to bind the glass fibres together are. Mr Lang said fibreglass emitted fumes when it was new, and the boat behind them was a new 10m-long vessel.
"So there was a huge surface area of fibreglass. We're still not sure what caused it to catch fire though."
The fire sent plumes of thick black smoke across Dunedin, and traffic was backed up for hundreds of metres either side of the scene in Ravensbourne Rd while firefighters battled the blaze.
A fire safety officer would investigate the cause of the fire today, a New Zealand Fire Service spokesman said.
