The Risk Management Tool Box Blog

Pyrolosis in Truck Tyres

Graham Marshall - Friday, July 19, 2013

Coming into contact with overhead power lines when driving can cause the tyres on trucks, cranes and other heavy vehicles to catch fire and explode.

Five workers have been killed by exploding tyres in Australia in recent years and many more injured as excessive heat developing in tyres has led to the unpredictable phenomenon known as pyrolysis.

Pyrolysis can occur when excess heat is applied to a tyre.

Often it is a result of electrical arcing and current flow when rubber tyred vehicles have been involved in high voltage electrical incidents.

The heat decomposes the rubber and other compounds used to manufacture the tyre, creating a ready fuel source.

The ratio of this fuel to the air used to inflate the tyres can then reach flammable or LEL (explosive) levels.

The explosive energy released during a tyre explosion can lead to serious injuries or fatalities and significant equipment damage.

Because of the amount of kinetic energy released, a danger area up to 300 metres away is typically required to be established.

Pyrolysis related explosions are unpredictable, sometimes happening immediately, sometimes up to 24 hours after the heat was applied to the tyres.

And the explosion can happen with no visible signs of a fire on the outside of the tyre before it explodes.

Besides electrical heat sources, other sources of heat that lead to pyrolysis in tyres include welding (e.g., on wheel rims), oxy/acetylene heating wheel nuts, overheating brakes and wheel motor fires.

Tyre explosions predominantly occur with split rim configurations, but can happen with all types of tyres.

Any pneumatic rubber tyred vehicle involved in an incident where an electrical fault results in discharges or arcing around or through the tyres should be considered a potential hazard.

Procedures to follow when there is a danger of a tyre explosion, such as when a rubber tyred vehicle has contacted overhead power lines include:

+ Parking the vehicle in an isolation zone, with a minimum 300 metre radius;

+ Removing everyone from the area, and not allowing anyone to re-enter the isolation zone for 24 hours; and

+ Alerting fire fighting services to the potential hazard.

It should be noted that if pneumatic tyres are filled with nitrogen instead of air, it reduces, if not eliminates the risk of pyrolyic tyre explosion.

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