Burning computer had been shut down

A Whangarei business owner has been left baffled by a freak fire sparked in a computer that was turned off.

Even firefighters are grappling for a take home message from the Rathbone St blaze, which they were called to at about 6.45pm on Thursday following a sprinkler activation and 111 call from a passerby.

The fire gutted the offending computer, leaving a large black scorch mark on the carpet. The response from the Fire Service and sprinkler system saw the office filled with about 6cm of water.

Whangarei Fire Service senior station officer Brad Cunningham said the fire was a "tricky one".

"In an ideal world every electrical appliance would be turned off at the wall. But we've got hard drives running right now at the fire station. It's pretty unusual, but these things do happen."

Sterling Building Consultants' seven staff had been forced out of the company's premises for the time being due to moderate water and smoke damage.

Fire risk management officer Craig Bain said he could not recall another incident where a shut down computer had caused a fire.

"It's rare ... but it also depends on how clean and tidy it is. Has it got dust all through it? Or is it the multi box it's plugged into?"

Company director Geoff Cockery said staff were in the habit of shutting down their computers overnight to conserve power. Mr Cockery said he had previously worried about using multi boxes - the machine that caused the fire was plugged straight into the wall and was only seven months old.

"Even though it does seem to be quite bizarre, it makes you a lot more conscious around leaving stuff plugged in or on stand by," Mr Cockery said.

Local computer engineer Vince Cocurullo said even when a computer was shut down, there was still power flowing to it. "There's a transformer inside the computer. I have heard of the transformers getting hot and catching fire. It's possible but really, really unlikely."

He said most computer fires could be prevented by installing power surge protectors, making sure power cords were in good condition and storing computers in well-ventilated and dust-free areas away from paper.