Arson investigators have concluded that last week’s massive fire at a North Knoxville recycling plant started when a piece of machinery backfired.

The fire at Fort Loudon Waste and Recycling started around 1 p.m. Wednesday, according to Knoxville Fire Department spokesman Capt. DJ Corcoran.

Corcoran says a forklift with a propane tank backfired, igniting several pallets of loose paper.

Employees tried to put the fire out themselves and emptied a few fire extinguishers. There was a delay in calling 911, so the fire got a head start on firefighters. Nearby residents called 911 when they spotted the heavy, black smoke.

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It took firefighters more than two days to fully put out the flames. The burning plastic and heavy smoke led to the evacuation of around 100 nearby homes. The fire ultimately consumed two acres of the plant.

The plant owed many thousands in back taxes and OSHA violations.