A report from the NSW Department of Resources and Energy has highlighted the importance of procedural controls in preventing haul truck collisions with light vehicles.
On August 12 this year at the Ashton Coal Handling and Preparation Plant, a Komatsu 730E haul truck rolled onto and crushed the front of a light vehicle, causing an employee to have to flee from the passenger seat.
The truck had been parked for the purpose of inspecting an oil leak on the left-hand rear wheel, and after the mechanic has ascertained that the truck should be taken out of service and left the scene, the operator returned to move the truck.
The operator discovered that the truck would not start, but could not get a hold of the mechanic due to radio issues, and instead phoned his supervisor.
The mechanic and an electrician returned to the truck to carry out a restart, and parked their light vehicle close to the front of the truck in order to connect jumper cables from the light vehicle to the trucks battery.
The electrician remained in the passenger seat of the vehicle while the mechanic attempted to start the truck.
The jump start was unsuccessful, however the truck did start when the mechanic tested the first starter motor.
While returning to the cab via stairs the mechanic noticed the truck was rolling forward, and he shouted to alert the operator, and they both attempted to stop the truck using the brake/retard pedal.
Meanwhile the electrician also noticed the truck rolling forward, and attempted to exit the vehicle.
The door of the vehicle had locked, so the electrician was forced to quickly climb out of the passenger window.
The electrician was not harmed during the incident.
The truck was stopped, but not before the front right tyre had rolled onto and crushed the front of the light vehicle.
Barring “minor defects”, extensive testing did not reveal any faults in the braking system, despite the operator reporting he had the park brake and dump brake before shutting down the truck.
The report stated “tests confirmed that shutting down the truck engine automatically applied the park brake, regardless of the park brake switch position, as the park brakes are spring-applied and rely on hydraulic pressure generated while the engine is running to keep them released”.
When the starter motor test circuit was examined, it was found that the circuit bypassed all interlocks, including the park brake switch interlock.
The report said the bypass of the park brake interlock was critical to the incident, because if the park brake switch was in the off position while the starter motor was tested, this would allow hydraulic pressure to build in the park brake circuit, disengaging the park brake and allowing to truck to roll forward.
It was found that parking procedures had not been followed, including the need to park the truck in a “fundamentally stable” position, meaning the vehicle should not be able to move even if the parking brake is not applied, made possible on ramps through use of wheel chocks.
Also, the vehicle had not been isolated before the inspection took place, and the light vehicle had not been parked in line of sight of the truck’s operator, failing site procedures.
The report highlighted that knowledge of the importance of continuing the task of emptying waste bins had influenced the behaviour of the mechanic and the operator.
It was also suggested that in the absence of observable mechanical faults, it was possible the operator had overlooked applying the park brake, or he may have engaged the dump brake by mistake.
In addition, no record of a risk assessment or change management process was evidenced, meaning that the risk control applied to the starter motor test circuit was ineffective and other risk controls were not given sufficient consideration.
The report also indicated “the importance of using appropriate investigative techniques to avoid attributing an incident to a single causal factor, if an investigation is to achieve its intended outcome of preventing future recurrence of an incident”.