KEY POINTS:
Firefighters will this morning start scouring through the ruins of the Onehunga Mitre 10 expo centre, confident they will discover what started the fire that devastated the building and a storage shed this week.
More than 80 firefighters battled the blaze, which started shortly after 5pm on Monday, sending smoke so high it was seen from the North Shore and stopped traffic on the Southwestern Motorway during rush hour.
Manukau District Chief Fire Officer Larry Cocker told the Herald that no one had been able to access the site yesterday because it was still smouldering and firefighters had to deem it safe before allowing people in.
Mr Cocker said investigators had an idea of what caused the blaze, but it was too soon to say what it was.
More would be known later today.
He said the fire in the 50m by 30m building began on the inside of an external wall of a storage area.
Two nearby power transformers also caught fire and powerlines were seen falling down, leaving 579 customers without power.
Mr Cocker said investigators were not yet certain whether the transformer fires were caused by the fire, or if they might have caused it.
"The fire investigator guys have got a couple of leads that they're working on and I think they need to talk to Vector, the power engineers, and they've just got to eliminate some other bits and pieces before they can narrow it down."
The fire was complex for firefighters because it was fuelled by smaller gas bottles, and larger bottles full of LPG which customers can buy in exchange for empty ones.
Mr Cocker defended criticism of the length of time firefighters took to arrive, saying it took them just under seven minutes, within the seven-minute timeframe firefighters aimed to attend urban incidents in.
There was also no cause for concern over roofing which contained asbestos because the asbestos was wet and therefore would not produce dust that can cause health problems including lung cancer, he said.
Mr Cocker said the Fire Service advised having sprinklers in large buildings - something also noted in media reports when the Mitre 10 Mega store on Te Irirangi Drive caught fire in February this year and after an earlier fire in Johnsonville in September 1998.
Mitre 10 chief executive Craig Wilson defended the company's fire safety standards.
"As a responsible retailer committed to the safety of our customers and staff, we are uncompromising [with] store safety," he said.
"Given the nature of the products that we sell, some of which are flammable, we cannot afford to be complacent. We are 100 per cent confident that the buildings in question will be found to be fully compliant."
The six staff from the expo centre would work at other branches until the future of the site was known.
The company's nearby retail outlet was not involved in the fire and remains open.
