Investigators have found that spontaneously combusting tempura flakes were responsible for causing fires in seven sushi restaurants in the US.
The deep-fried tempura flakes known as "tenkasu" in Japan but colloquially known as “crunch” are made with a type of oil that self-heats and can create the environment for fires to occur.
In a statement issued by the City of Madison, Wisconsin it was claimed that fires at Madison restaurants Sumo Steakhouse and Sushi Bar on April 5, and at Takara Japanese Restaurant on May 10, were categorically caused by the tempura flake mixture.
In released security footage from a fire at the Sumo Steakhouse and Sushi Bar a timeline can be seen where tempura that was made at 4pm and left in the fridge overnight, catches flame about ten hours later at 2.26am. Within 20 minutes the fridge is completely engulfed in flames. Luckily the sprinkler system is set of by the fire before the restaurant burns to the ground, but not before significant damage is done to the kitchen and restaurant. The estimated cost of the damage for the two Madison fires combined was $575,000.
Five other fires were reportedly caused by the combusting tempura in Wisconsin, Minnesota, Virginia, as well as Canada. A report by the Madison Fire Department said “After being deep-fried, the flour is left to drain and cool for a day."
"The oil will combine with the oxygen in the air and in that chemical process, it releases heat."
The two most common oils to create this reaction are vegetable oil and canola oil.