Tulsa firefighters said the blaze erupted early Saturday morning at an auto repair shop.
Authorities said the unidentified man was sleeping inside the vehicle and using the heater to keep the truck warm. The heater was attached to an extension cord that ran to another building.
The fire broke out around 2:30 a.m. and spread to another vehicle.
Firefighters said the owner of the lot told them he was letting the homeless man sleep on the property.
The blaze was among several firefighters worked overnight as a strong cold front sent temperatures plummeting.
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