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Machine Design

Truck Fire Started By a Dropped Cigarette

A fire destroyed the cab of a delivery truck and severely damaged the engine compartment while the truck was in the shop for repairs. The fire was discovered after work hours and was confined to the vehicle, so no one was hurt.

The truck had been outside the garage all day awaiting service. At 4 p.m., before the shop was closed for the night, mechanics moved the truck into the garage so they could start working on it first thing in the morning.

Employees of the company that owned the truck came around 5 p.m. to clear out extra equipment. The garage foreman walked within 10 ft of the truck while locking up for the night at 6 p.m. without noticing anything amiss. The fire was reported at 6:30 p.m.

Investigators determined the fire had burned at a relatively low temperature because materials in the cab and engine compartment didn’t burn completely. There was also a substantial buildup of black ashes and soot. Such high concentrations of carbon indicate a cool, smoky fire.

They also ruled out an electrical fire. Although some wiring bundles had been damaged, wire insulation had burned or melted from the outside rather than from overheated conductors.

The cargo area behind the cab sustained some smoke damage but was otherwise untouched; the fire had stayed within the cab and engine compartment. Because the truck’s tires were also intact, investigators concluded the fire started in the cab rather than closer to the engine.

Within a wide V-shape that extended over the back of both seats, nonmetallic seat parts burned away completely, leaving bare metal. Outside the V, there were more soot markings and incompletely burned seat foam. Inside the cab, a similar pattern marked the “doghouse” between and in front of the seats.

The vertices of both Vs pointed to foam between the seats, a strong indication the fire started there. The foam there also had a hole burned in it through which one could see the floor of the truck.

Both accessories and trash found in the truck indicated that the cab was an area of frequent cigarette smoking. This, along with the evidence of a low-temperature fire and the way the ignition point burned a hole through the seat foam, led investigators to conclude that the fire was caused by someone dropping a still-smoldering cigarette butt.

This month’s safety violation comes from the files of Lanny Berke, a registered professional engineer and Certified Safety Professional involved in forensic engineering since 1972. Got a safety violation to share? Send your images and explanations to [email protected].

© 2011 Penton Media, Inc.

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