The incidents occurred recently when electric cables supplying lights on underground diesel machines were torn from their flameproof light fittings. On each occasion the electrical protection systems fitted to the alternators failed to operate.

In the first incident, a flameproof light on an underground diesel loader was dislodged from its mountings, resulting in the cable supplying the light being torn from the fitting.

In the second incident, the cable supplying a flameproof light on a coal hauler was torn from the light when it contacted a rib bolt while the machine was in motion.

An investigation by the Queensland Mines Inspectorate found the protection systems on the alternators did not operate and later testing showed the protection systems were operational.

There was no evidence of sparking on the light fittings or cables involved.

The inspectorate said testing of alternator protection systems on underground mobile diesel machinery was not occurring, neither on the machines’ introduction to site, nor as part of a scheduled maintenance program.

The inspectorate also found the problem was not an isolated incident, with other sites identifying similar deficiencies.

Mines needed to review maintenance strategies for testing protection systems fitted to alternators on underground mobile diesel machines, the inspectorate said.

If maintenance strategies did not exist, a mine should test all alternators immediately to ensure the correct operation of the protection systems; review maintenance programs to ensure testing occurs on the introduction of machinery to site and as part of a scheduled program; and ensure flameproof light fittings and supply cables on mobile diesel machines are adequately protected.

It also recommended a review with the machine operators is conducted to show the potential severity of incidents resulting from careless operation of underground mobile diesel machines.