The Queensland Mines Inspectorate issued a safety alert to all Queensland coal mines.

Regional inspector of mines Michael Downs said in normal start-up, the spring-loaded pump start switch is turned to the “start” position, then released to the “run” position as the pump operates. The hydraulic brake pressure increases and operates the traction switch that allows the foot pedal to move the shuttle car.

A rapid response function gives the ability for the car to be driven immediately in an emergency. The pump start switch is held in the start position and the foot pedal operated; immediately the car is able to move, independent of the hydraulic brake circuit.

An investigation revealed a broken foot pedal return spring that allowed sagging of the foot pedal providing a signal to move the car.

“A combination of the foot pedal depressed, the car in emergency [rapid response] mode and the pump switch held in the start position caused the lunge forward of the car,” Downs said.

He said the foot pedal spring was replaced on the shuttle car, but the possibility of re-occurrence was not completely removed.

“The need for the rapid response function was questioned. As a trial, the rapid response circuit has been disabled and may become a permanent modification.”

As a result of the incident, the following recommendations have been made:

• Examine the foot pedal operation of shuttle cars of this model to ensure that at rest, the traction switch is in a neutral position;
• Examine the integrity of the foot pedal springs ie length and strength;
• Risk assess the need for a rapid response function;
• Ensure shuttle car operators, mechanics and electricians are aware of the possibility of unplanned movement – as in this incident; and
• Ensure the maintenance system includes routine inspection of the foot pedal spring and traction switch neutral position adjustment.

Joy’s director engineering Mick Sams told ILN that the OEM agreed with the recommendations set out by the inspectorate.

“We would also encourage that mines risk assess whether they need that rapid response function, which is no longer used on newer Joy shuttle car models,”he said.

Sams said Joy will release a service bulletin to customers outlining the correct procedure for disabling the rapid response function of the car.

“If they are going to disable it, they need to know how to do it properly,” he said.