Background
Some mining operators rely on tyre inflation cages to control the risk of a tyre burst when inflating (and testing) newly assembled light vehicle tyres and on-highway type truck tyres (up to 24 inch rim diameter). Many of these cages are of unproven or uncertified design, and lack comprehensive instructions.
There is no Australian or international standard for the design, manufacture or testing of tyre inflation cages for any size of tyre. However, tyre inflation cages are commercially available in Australia, for tyres with rim diameters less than 24 inches, that are engineer-designed, third-party tested and certified to manufacturer’s standards.
Summary of hazard
The sudden depressurisation of a tyre can release a large amount of energy as a percussive shock wave. For tyre assemblies that have split wheels or multi-piece rims these components can become projectiles following a sudden depressurisation.
The risk of a tyre burst is particularly high during the first inflation of a tyre after assembly or mounting i.e. components (e.g. the bead) fail to engage properly, or the wheel or rim is not correctly assembled. This initial inflation is often undertaken in a workshop or maintenance area. The percussive shock wave and projectiles generated can damage equipment and be potentially lethal to
personnel in the “line of fire”.
Contributory factors
Many tyre inflation cages are purchased or manufactured without comprehensive designer or manufacturer instructions for their installation, operation, inspection and maintenance.
During installation, this can lead to mining operators:
bolting tyre inflation cages to concrete floors or other structures. The bolts and nuts used, the concrete floor or support structure are usually not designed to withstand the forces generated during a tyre burst, and therefore may generate projectiles.
over-restraining the cage structure which reduces the capacity of the tyre inflation cage to deflect or deform and adsorb the energy of the tyre burst . Most tyre inflation cages are more effective if they are free-standing and should not be bolted down without consulting the manufacturer.
During use, this can lead to mining operators assuming that tyre inflation cages provide some degree of protection and will restrain projectiles if a tyre assembly fails catastrophically. This belief may:
- mislead personnel into having a false sense of security
- affect the perception of risk, which can lead to decisions that increase exposure to harm (e.g. reduce the size of exclusion zones, pneumatic pressure testing of tyres).