The following photos shows a logging truck. Unfortunately, while tying down a load of logs, the truck’s driver hooked a high-voltage power line with a steel cable:
Version 1 – Photos of incinerated logging truck
Version 2 – Photos of incinerated logging truck
The conventional wisdom says:
1) Tires are made of rubber
2) Rubber is a good insulator
3) Voltage from the logging cable should go nowhere
4) Therefore no fire
But the reality is that tires are conductive:
Tires are electrical conductors, not insulators. It is true that you are safe in your vehicle when a live wire falls on it. But that’s because electricity always seeks the easiest path to the ground. If you remain in the vehicle, the path of the electricity will be on the outside of the vehicle; through the tires, and into the ground. As long as we do not provide a path to the ground through our body the electricity will not enter it. So when an electrical wire falls on your vehicle, stay in your vehicle until help arrives and the power is shut off by PSE&G. If you have to get out of your car because of a life threatening situation, jump out with both feet together, making sure that you are not touching any part of the vehicle when your feet hit the ground and hop or shuffle at least 30 feet away.
See also: Do Rubber Car Tires Protect Me From Lightning?
The reason why tires are conductive is that the rubber in tires contains about 50% carbon black. Carbon black can be conductive, especially at high voltages:
Insights on conductive plastics
For ESD performance, carbon black is frequently used as the active agent and conductivity is achieved by forming conductive bridges through a “conduction zone” of overlapping electronic structures enabling nearest-neighbor transfer of electrons. Consequently, to achieve conductivity using carbon black, there needs to be sufficient carbon black present so as to form conductive bridges for the electrons.
So, once the steel logging cable connected to the power line (which was not insulated), the tires started to act like filaments in a light bulb. Like this tree branch:
The tires would heat up rapidly, then ignite. Once the tires start burning it’s all over, as pointed out in version 2…
Tire fires are hot. Often fire departments can not put out scrap tire pile fires. So a few duals get lit up, the aluminum fuel tanks boil over, and that’s the end for Mr. Logging Truck!
In the following video you can see pairs of tires burning, and how much heat they generate:
Moral: Be cautious around high voltage overhead power lines. And going back to the “electrical safety myths” article above, if a high-voltage wire falls on your car, you need to get out of the car fast if the tires start burning.
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Filed under: BrainStuff Tagged: High Voltage, Logging truck, mistakes, Tire fire, tires
