The electrician was resetting a 400A 1000V circuit breaker in a low voltage switchboard on a mine’s underground 11kV/1000V substation.

The circuit breaker supplied both a 75kW fan starter circuit and a water pump station circuit.

The fan starter’s steel wire armoured cable was damaged by blasting from the mining operation, shorting the three phase conductors to earth.

The circuit breaker had tripped.

The electrician, however, was trying to restore the power supply to the other circuit – the water pump station.

At this mine, different groups of electrical maintenance personnel have their own areas of responsibility and the electrician was unaware of the damaged fan starter circuit as it was the responsibility of another group.

Nor was he fully aware of requirements for arc flash safety clothing and mask during resetting or isolating substation circuit breakers.

It appears he stood in front of the switchboard to reset the circuit breaker. An arc flash and blast then blew the door open.

The circuit breaker was not fitted with phase barriers to avoid arcing between the phases.

Contamination inside the enclosures due to the underground environment was aggravated by high humidity.

“Regular maintenance and inspection of substations and switchboards at the mine must effectively monitor the safety of the electrical installation and its protective features,” the Queensland safety and health manager advised.