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Fire investigators say leaking propane gas is high on the list of flammable gases that may have caused the fatal Icepak Coolstore fire but it will take weeks to prove - or disprove - the theory.
Waikato Fire Commander Roy Breeze said characteristics of the fire indicate that it was caused by a flammable gas.
Because propane - an odourless and flammable gas - was used as a refrigerant in the Tamahere coolstore, it is high on the list of possible causes for the explosion that killed Derek Lovell and injured six other firefighters.
However, Mr Breeze said the investigation was far from complete so it was too early to eliminate other possibilities.
"We do agree that the type of explosion was most likely a flammable gas leak in the building of some sort and we know that the refrigerant used in the building was a propane or butane based type gas.
However it is purely one of the options we are looking at."
Mr Breeze said firefighters have now gathered all the evidence from the scene and will spend the next couple of weeks trying to establish what kind of gas leak caused the fire.
"For example there's an option there could have been some chemicals in the building that released some flammable gas or there could have been portable LPG cylinders that released gas," said Mr Breeze.
Mr Breeze said five Fire Service investigators would work through the various possible scenarios for the explosion, using information they gathered at the scene and from witnesses, to try to prove what happened.
"They will combine all those possible options of what was in the building, what the witnesses said, the actual physical proof of the way the building burnt and they will be able to zoom in very closely to an area of where the fire started. In addition to that they have to prove of disprove some theory."
Mr Breeze said an example would be if they were considering a leaking LPG cylinder the investigators would have to see if it could actually generate enough gas to cause the kind of explosion that occurred a week ago.
Meanwhile, injured firefighter Alvan Walker was discharged from Waikato Hospital yesterday. His wife, Jenny Love, said he would need to "take it easy" for a while but was enjoying being home.
Another of the injured firefighters, Brian Halford, was yesterday moved back into the hospital's high-dependency unit for monitoring.
Adrian Brown, Dennis Wells and David Beanland are on wards in Waikato Hospital and Merv Neil is still in a critical condition in Middlemore Hospital's burns unit.
