Hamersley Iron Pty Ltd has been fined $75,000 after a worker was fatally injured when the truck he was driving crashed at the company's Channar iron ore mine in August 2018.
Hamersley Iron, a Rio Tinto subsidiary, pleaded guilty in the South Hedland Magistrates Court to causing the death of an employee.
On the day of the incident, the worker was driving down ramp 84E that has a gradient mostly between 8 and 10 per cent and is around 1.2km long.
During the descent, the fully loaded truck gained excessive speed and was estimated to be travelling at more than 100kph before colliding with a windrow at the bottom of the ramp.
The maximum speed for any truck descending a ramp at the mine was 20kph.
Open pit operations usually require trucks to carry loads uphill. Due to natural features in the area, trucks at Channar travel downhill from elevated pits to nearby processing facilities.
The worker was driving an electric drive truck where the vehicle's speed is controlled by electric brakes or a hydraulically powered service brake.
Above a certain speed, payload and gradient, the truck's momentum will exceed the retarding capability of the electric braking system. In these circumstances, the driver must apply the service brake to slow and stop the vehicle.
An investigation determined the fatally injured worker appeared to lose control of the vehicle and had not activated the service brake during his descent of ramp 84E.
Given the length and gradient of the ramps at Channar, the risk of trucks gaining excessive speed and getting out of control was well known.
While the company installed devices to detect truck speeds and report non-compliance, those mounted on ramp 84E had been deactivated in 2016 for unknown reasons.
Acting WorkSafe Chief Inspector Mines Christina Folley said the tragic incident should not have happened.
"Between February 2014 and August 2018, there had been a number of incidents involving excessive speed on ramps at Channar," Ms Folley said.
"There had also been excessive speed and braking incidents at other Rio Tinto operations in the area during that period.
"Hamersley Iron needed to have more control over the speed descent hazard at Channar and more effective policies in place to deal with downhill haulage."
Following the incident, Hamersley Iron and other Rio Tinto mines in the area made a number of changes to improve safety. This included developing a risk-based classification for haulage ramps, additional signage and demarcation, and over-speed alerts delivered to drivers via audible in-cab alarms.
Channar is located around 350km inland from Port Hedland in the Pilbara and is one of three adjoining leases that form Rio Tinto's Greater Paraburdoo operations.
