Large rubber tires for trucks and heavy equipment have the potential to explode with devastating force as result of a decomposition process, which can occur when the tire overheats or is exposed to a heat source. Workers and others may sustain critical or fatal injuries as a result.


Pyrolysis is a thermochemical decomposition of organic material which can occur at elevated temperatures in the absence of oxygen. This decomposition process only requires the presence of rubber and heat. When heat is applied to the tire or to tire components, hydrocarbon vapours are released inside the tire. As the vapours are released, the air pressure and temperature within the tire increase dramatically. These vapours are highly flammable. If the flammable vapour inside the tire makes contact with oxygen at a temperature in excess of 400 degrees Celsius, auto-ignition can occur, resulting in an explosion.

Once the decomposition process begins, it is irreversible. There is no visual indication that the decomposition process is taking place. Depending on the particular circumstances, an explosion may occur immediately, within minutes or several hours after the exposure to the heat source. In many instances, an explosion can cause the tire and/or wheel components to be thrown great distances, resulting in severe worker injuries and/or fatalities as well as significant property damage.

The following list contains some situations in which pyrolysis can occur:

  • welding
  • heating with a blow torch
  • overheated brakes
  • equipment contact with high voltage power lines
  • tire or equipment fires
  • lightning strike
  • driving long distances with underinflated tires

Locations and sectors

Large rubber tires for trucks and heavy equipment can be found in provincially regulated workplaces. This hazard is of particular concern to workers in the vehicle service sector as well as emergency response services.


  • Brake and tire systems must be maintained in accordance with the manufacturer’s maintenance and operational manuals.
  • Under no circumstances should a rim be heated while the tire is still mounted, such as by welding or the use of cutting torches, or any other procedure that would cause extreme heat. The tire must be removed from the rim before this type of work is conducted.
  • Minimum clearance distances must be maintained when operating equipment in an area where live power lines are present.

In circumstances where pyrolysis is believed to have begun, such as when a piece of equipment has made contact with overhead power lines, the area should be cleared of workers until such time as the hazard no longer exists. The actual length of time may vary depending on the particular circumstances.

Legal requirements

Under section 25 of the Occupational Health and Safety Act (OHSA), the employer must:

  • take every precaution reasonable in the circumstances to protect workers [clause 25(2)(h)]
  • provide information, instruction and supervision to protect the health and safety of the worker [clause 25(2)(a)]
  • ensure the measures and procedures prescribed are carried out in the workplace [clause 25(1)(c)]

Under section 27 of the OHSA, the supervisor must:

  • ensure that a worker works in a manner and with the protective devices, measures and procedures required by the act and its regulations [clause 27(1)(a)]
  • advise a worker of the existence of any potential or actual danger to the health or safety of the worker of which the supervisor is aware [clause 27(2)(a)]
  • take every precaution reasonable in the circumstances for the protection of the worker [clause 27(2)(c)]

Under section 28 of OHSA, a worker must:

  • work in compliance with the provisions of the act and its regulations [clause 28(1)(a)]
  • report to their employer or supervisor the absence of or defect in any equipment or protective device and which may endanger them or another worker [clause 28(1)(c)]

Regulations specific to certain work sectors also apply.

Under the Industrial Establishments Regulation (Regulation 851):

  • section 60 prescribes minimum distance requirements from live power lines
  • section 77 prescribes protection requirements for workers when inflating tires

Under the Construction Projects Regulation (Ontario Regulation 213/91):

  • section 110 prescribes protection requirements for workers when inflating tires
  • section 188 prescribes minimum distance requirements from energized overhead electrical conductors

Under the Mining and Mining Plants Regulation (Regulation 854):

  • section 107.1 prescribes procedure and training requirements for workers in regard to work performed on tire and wheel assemblies
  • subsection 159(2) prescribes minimum distance requirements from energized overhead electric supply lines
  • section 194 prescribes safe welding and cutting operations

Under the Health Care and Residential Facilities Regulation (Ontario Regulation 67/93):

  • subsection 72(1) prescribes minimum distance requirements from energized electrical conductors

For more information

Ontario’s Occupational Health and Safety Partners

This resource does not replace the Occupational Health and Safety Act (OHSA) and its regulations and should not be used as or considered legal advice. Health and safety inspectors apply and enforce these laws based on the facts they find in the workplace.