Tyre fires, pyrolysis and explosions

Tyres on trucks, cranes and other heavy vehicles may catch fire under a range of circumstances, with the obvious potential for the tyres to then explode. A lesser-known danger arises when the combustion takes place inside the tyre, with no external signs. Whenever excess heat is developed in or applied to a tyre, it can initiate a process within the tyre known as pyrolysis - the decomposition of a substance by heat. This can cause a build-up of flammable gases and pressure within the tyre, which may ultimately rupture or explode.

Enormous amounts of energy can be released by a tyre explosion, often leading to significant equipment damage, serious injuries or fatalities. Pyrolysis related explosions are unpredictable, and have occurred immediately or up to 24 hours after initiation. An explosion can occur where no fire is visible and the danger area can be up to 300 metres from the tyre.

Tyre pyrolysis has occurred from welding on wheel rims, oxyheating wheel nuts, overheating brakes and wheel motor fires. It has also resulted from electrical arcing and current flow when rubber tyred vehicles have been involved in high voltage electrical incidents. Vehicles affected have included rubber tyred cranes and tip trucks, often as a result of collision with overhead supply lines. However, any rubber tyred vehicle involved in an incident where an electrical fault results in discharges or arcing around or through the tyres should be considered as a potential hazard.

Mines have established procedures to follow when personnel suspect there is danger of a tyre explosion, eg after a rubber tyred vehicle has contacted overhead powerlines. These procedures include:

• park the vehicle in an isolation zone, with a minimum 300 metre radius
• remove all personnel from the area, and do not allow anyone to re-enter the isolation zone for 24 hours
• alert fire fighting services.

This hazard must be recognised, and the possibility of tyre pyrolysis and explosions must be considered in the development of a coal mine's safety and health management system, and in the risk management practices and procedures used by metalliferous mines and quarries.

Authorised by Peter Minahan - Chief Inspector of Mines

Contact: minesafetyandhealth@dnrm.qld.gov.au

Issued by Queensland Department of Natural Resources, Mines and Energy