Before determining the cause of the explosion, the Coroner's Inquest had to first try to establish the cause of the fire.
Evidence was given that the business' partners, Messrs Benge and Pratt had left the premises at 9:30 pm on Saturday evening after they shut off the gas and locked up the premises. At around 10 pm., Mr. Benge thought he saw a light in the upstairs storey of the building above the grocery. He returned to the building and inspected the upstairs floor but found no sign of anything out of the ordinary. Benge testified that he had used one or two matches when upstairs but the Coroner concluded that the lapse of an hour and a half or more until the first signs of the fire were discovered discounted these matches as being the cause of the fire.
In his verdict, the Coroner, Mr W G Riddell, S.M., noted that matches were stored in the upper room or south front upper room as it was identified in evidence where the fire was likely to have started. He observed that it was "not an uncommon thing for rats to cause a fire by getting at the matches". Given the uncertainty of the facts, he concluded that it was impossible to say from the evidence what the real cause of the fire was.
Nevertheless, Mr Riddell, concluded the building was old - one of the oldest in Upper Hutt at the time - it was wooden and of two storeys, yet there was no fire hose, extinguishers, or other fire fighting equipment on the premises. Furthermore, the Coroner observed that no efforts were taken to put the fire out. News reports of the time show that Upper Hutt did not have a fire brigade then and had only recently installed a high pressure water system. The one fire hose owned by the town had been locked up and only belatedly was taken to the scene of the fire.
Had effective fire fighting capabilities existed and been put to use, the Coroner concluded, the ensuing explosion might have been prevented.