An incident in which a dozer fell into a water-filled test hole at Rio Tinto’s Bengalla mine is being investigated by the Mine Safety Investigation Unit.
The unit is looking into why and how a D11 dozer slid into 5 metre deep water-filled test hole in November 2013.
It is the fourth accident involving a dozer in Hunter Valley coal mines in the last four years.
Described as a “high potential incident” it was found the hole had been dug two days earlier into a 5 metre thick overburden bench in an active mining area to determine the depth to coal before being filled with rain.
On the day of the incident, the dozer driver approached the pooled water on the northern end of the bench in reverse. He stopped to test the water depth using the ripper blade.
As the ripper blade was lowered the ground beneath the dozer slumped and the dozer slid backwards into the deep water and test hole.
Water filled the cabin to head height and the driver was able to escape the cabin by levering the right hand door handle with his foot.
The unit says four inspections prior to the incident failed to identify the hazard and safeguards in place did not apply to the scenario.
Rio Tinto conducted an internal investigation and has taken a number of steps to prevent the accident happening again.
These include installing guide posts and a reference beacon around the void and a requirement that test holes are reported to the supervisor for recording in the shift statutory inspection book.
The unit said the accident highlighted the importance of an “effective risk management program concerning the excavation of test holes on benches and dozers operating in wet and unconsolidated ground conditions.”
In 2011 there were three incidents involving dozers falling into water.
On two of these occasions dozer cabins were submerged in water.
A spokesperson for Coal & Allied said the safety of its workers is a top priority.
“While the driver of this dozer was fortunate not to have been injured, the safety of our people is our number one priority and we regard this as an unacceptable incident.
“We have worked with the NSW Government’s Chief Inspector for the mining industry and the Mines Investigation Unit to ensure it was thoroughly investigated and procedures have been introduced that greatly reduce the risk that a similar incident could occur again."