A fire in a truck hauling gas cylinders was most likely the result of a mechanical failure in the vehicle, says a fire investigator looking into the blaze in Nelson last week .
Nelson-Marlborough specialist fire investigator Craig Piner said it appeared that either excessive heat from the brakes or a failed wheel bearing in the trailer unit caused friction that led to the blaze.
Emergency services, including multiple fire crews, were called to Quarantine Road near the city's airport just after 6am last Monday.
Gas escaping from the cylinders fed the flames and triggered the evacuation of buildings in Quarantine Road within a 500m radius.
Nelson Fire Service assistant area commander Des Irving said the trailer was hauling more than 60 cylinders containing a variety of highly flammable oxyacetylene, LPG and oxygen. He said the gas cylinders had an automatic venting system which prevented them exploding but a couple were jettisoned into nearby buildings by the intense heat.
The truck driver, who was alerted to smoke coming from the vehicle by another motorist, was able to get off the motorway and drive on to Quarantine Road, where he parked and and disconnected his vehicle from the burning trailer unit.
"It could have been a whole lot worse but we're satisfied that the fire was caused by either excessive heat from the brakes or a failed wheel bearing causing friction and catching fire," Mr Piner said.
"In a heavy vehicle that's not uncommon and truck drivers are aware of this possibility but things go wrong and in this case it was just part of a chain of events. Yes, it was unfortunate it happened to be on a truck carrying gas cylinders," Mr Piner said.