In February 2020, a haul truck arrived at a workshop for maintenance with no tyres fitted in position 4 or 5. The position 6 tyre casing blew out 15 days later. Four workers were working on the haul truck in close proximity to the tyre. One worker was thrown backwards by the percussive shock wave and knocked unconscious. Two other workers received minor injuries (ringing in ears and light bruises). The workshop walls were damaged and projectile shrapnel was found up to 17 metres from the position 6 tyre.
During the 15 days, the truck had not moved and the tyres were cold. The tyre casing that failed was a 46/90R57 size, of steel radial construction and with only 2,000 hours of recorded service.
Direct causes
The direct (physical) cause was cut damage on the outside edge of a tread lug of the tyre. This exposed the steel reinforcing layers to air and moisture resulting in progressive corrosion and separation damage that reduced the integrity of the tyre casing to resist internal pressure.
Contributory causes
- The tyre was not disposed of when it was removed from service in October 2018. It had a large cut caused by a rock during operation which, over time, allowed moisture to enter the steel cord area causing corrosion.
- The tyre was stored in the elements for 16 months before being fitted to transport the truck to the workshop.
- The decision to return the discarded defective tyre to service was not based on an inspection and assessment by a suitably competent person.
- The site did not have a safe system of work for the inspection of tyres used for transportation purposes.
- The damage to the tyre was not obvious due to the steel cord corrosion being internal.
- Persons in the workshop were working in close proximity to fully inflated tyres.