Mr McKeagg said it was unclear if a leaking butane canister had been left in the fridge or if it had vapourised off the alcohol during the night. The butane vapour would have eventually reached its explosive limit and been ignited when the thermostat kicked in and started the motor, he said.
Most fridges had a protective layer between the motor and the storage space but this could get worn down in older appliances, Mr McKeagg said.
Under normal circumstances that would not be a problem as most people do not keep volatile substances in their kitchen fridge, he said.
Mr McKeagg had never heard of people mixing butane and alcohol and had only seen one similar explosion during his 30 years in the fire service.
"In the first one the lid of a sample bottle in a laboratory had been left slightly ajar. Volatile vapour escaped and when the fridge engine clicked on it blew the hell out of the fridge and the lab.''