A wooden rake mistakenly left in a duct and metal tubing lying directly against wood contributed to a blaze that gutted the kitchen of one of Auckland's most popular eateries.
The kitchens of Al Brown's restaurants Federal Delicatessen and Depot, at 86 Federal St, were damaged in a fire on April 9 - the same day the kitchen ventilation system was due for a clean.
A fire report obtained by NZME. News Service under the Official Information Act shows the accidental blaze was sparked by coal dust igniting behind the pizza oven in the Depot kitchen.
Flames quickly spread throughout the ducting to the ceiling above Federal Delicatessen, gutting the kitchen.
Parts of the ducting lying against timber with no air gap exacerbated the fire and a wooden-handled rake, which was mistakenly left in the chute when it was last cleaned in January, may have added to the fuel, the report showed.
Specialist fire investigator Russell Dickson said a couple of factors exacerbated what was a relatively common duct fire.
Precautions such as an air gap or heat wrap were advisable for ducting passing through timber and regulations often prevented the occurrence, he said.
It was also not advisable to use coal dust because it could ignite very easily, he said.
"An unfortunate fact in some ways is that it was due to be cleaned that day, Murphy's Law. But there's things they're going to look at.
"I think we're all well aware of timber being quite close to the ducting and that, I'm sure, won't happen again. But like everything it's always a learning curve, and unfortunately sometimes learning curves can be quite expensive."
Mr Dickson said the kitchen had a rigorous cleaning regime but fire in kitchen ducting was not uncommon. A number of people including engineers and legal experts were examining the situation, he said.
"Ducting fires are not uncommon, and in some cases very hard to get everything cleaned. They had a good cleaning regime but it was just a couple of hiccups that created the whole issue."
The general manager of Al Brown and Company, Stuart Robertson, said the affected restaurants had now been reopened.
"We are thrilled that SkyCity were able to mobilise their contractors to get the repairs under way so quickly and that both restaurants are back open and cranking," he said.
A council spokesman refused to comment because its building control staff were not investigating.
The spokesman told NZME. News Service in May a council inspection manager inspected the site and thought the fire was probably caused by a lack of cleaning of the kitchen ventilation.
Skycity said fire safety measures would be checked in its other restaurants to ensure they were safe.
"Skycity has addressed the matters in the Fire Service report in the repairs to Depot and Federal Delicatessen.
"This includes fire wrapping and separation of the ducting and timber. As a further precaution, Skycity is re-assessing the ducting in its other restaurants," a spokesperson said.