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Fire and Emergency said the blaze this past Sunday was most likely accidentally started by one of the children but the polyurethane foam in the sofa escalated it.
The National Fire Investigation Manager, Peter Wilding, said there are about 2500 house fires a year and the foam is a significant contributing factor.
"It would be one of the leading causes of fire spread by quite a long way simply because it burns so quickly," he said.
"I've got photographs even of that house [in South Auckland] and of many other examples as well where there are a lot of other items that will burn in a house that are yet to burn."
"But it's the foam that actually just disappears in the fire."
Mr Wilding said using retardant on the foam is one way to stop it burning up so easily.
A spokesperson for the Minister of Commerce and Consumer Affairs, Kris Faafoi, said an announcement on regulations for the foam is expected to be made soon.