NSW Resources Regulator investigates “unplanned” explosion at BHP Billiton’s Mt Arthur coal mine in Hunter

Explosives which may have sat live for three months after failing to detonate during a planned mine explosion have blasted a hole nearly two metres deep – and hurled large rocks 100 metres away – after being disturbed by a dozer.

The resources regulator is investigating the "unplanned initiation" of explosives at Mt Arthur coal mine in the Hunter Valley after an dozer set off explosives on August 20, 2024 that had failed to detonate during planned explosions three months earlier. Picture: NSW Resources Regulator.

An investigation has been launched into how live explosives, which had sat at the state’s largest coal mine for three months after an apparent misfire, were set off by a bulldozer driver conducting routine work.

The huge explosion, which rocked Mt Arthur South coal mine in the Hunter Valley on August 20, produced a crater almost two metres deep and three-and-a-half metres wide and hurled large rocks and parts of the dozer about 100 metres away.

Despite the force of the explosion smashing machinery windows and creating the enormous hole, no one was injured during what has been called an “unplanned initiation”.

The NSW Resources Regulator has taken over the investigation into the early morning blast at the open cut mine, owned by BHP Billiton just outside of Muswellbrook.

A preliminary investigation by the regulator said the Caterpillar D11T dozer driver was operating in the mine’s Roxburgh pit about 7.30am.

The force of the explosion ripped off part of the dozer’s blade (see bottom right and inset top right). Picture: NSW Resources Regulator

The dozer was operating on a “bench” – or a narrow strip of land cut into the side of an open-pit mine – and near a Leibherr R-996 excavator, which was loading a 793D haul truck.

The bench being excavated had been “fired, in accordance with a planned shot”, or explosion, on May 20.

Rocks were found to be been blown 100 metres away from the explosion. Picture: NSW Resources Regulator

“While the dozer operator was pushing blast waste material on the lower bench, an unplanned initiation of explosives occurred,” the preliminary report stated.

“ The explosion caused multiple pieces of fly rock and parts from the dozer blade to be projected about 100m from the incident site.

“The location of the explosion left a crater measuring 1.8m deep, and about 3.5m in width.”

While the operator was not physically injured, the dozer was significantly damaged, with glass blown out of the cabin entry door and rear window, while the front window was shattered.

A section of the dozer blade was also blown away.

More damage from the explosion. Picture: NSW Resources Regulator.

Shattered glass throughout the machine’s cabin. Picture: NSW Resources Regulator.

Inspectors and investigators from the Resources Regulator attended the mine and commenced an investigation to determine the cause and circumstances of the incident.

“During an examination of the area, an amount of material believed to be emulsion and detonation wire was observed. Samples

of the emulsion were seized,” the report said.

Part of the dozer blade found blown away from the explosion. Picture: NSW Resources Regulator.

Included in the investigation will be the planning and detonation of the May 20 “shot”, the mine’s explosion control plans and safety issues arising from misfires.

A spokeswoman for Thiess, which conducts the mining operations in the Ayredale and Roxburgh pits, replied to questions on Wednesday.

“The safety of our people is our priority,” the spokeswoman said in a statement.

“ An investigation into the incident that occurred at our Mt Arthur South operation on the morning of 20 August 2024 is ongoing.

“ While this is underway, we are unable to provide any further comment.”

BHP Billiton, which owns the mine, has also been contacted for comment.

Originally published as NSW Resources Regulator investigates “unplanned” explosion at BHP Billiton’s Mt Arthur coal mine in Hunter