Employed by Silver City Drilling, which has since had a management change, the man had the task of drilling a borehole to install a dewatering pump to assist the longwall operation further below.
This drilling had been delayed due to water flowing into the hole from a nearby aquifer.
While rotary mud drilling was considered to help overcome this situation, air-rotary hammer-based drilling continued.
This ended up being a key mistake as the 220mm diameter steel pipe used as the air discharge line became part of the chain reaction-like accident which occurred after the driller activated air pressure to lower drill string into the bottom of the borehole.
It was at this time that the New South Wales Mine Safety Investigation Unit said a “large pressure event occurred” with surface casing rising out of the ground to collide with the bottom of the drill rig.
This impact helped make the high-pressure air discharge line break free of its securing system which consisted of some star pickets and fencing wire.
“The supervisor reported that he heard an explosion and he saw the well unload,” the MSIU said.
“He saw the air discharge line shoot up in the air and hit the hinged drilling platform that the driller was standing on. The force of the impact lifted the hinged platform in an upward direction and the driller was forced upwards against the control panel until the air discharge line travelled past the driller’s platform.
“The driller and the platform fell back down with the driller coming to rest with his neck across the drilling platform hand rail. The air discharge line then fell, striking him on the back of the neck.”
The steel pipe of the air discharge line also trapped the driller with ambulance crews needing to use jaws of life gear to cut him free.
Ultimately the man was not airlifted from the scene until about two hours after the incident occurred at around 2pm on August 12, 2012.
“The driller sustained multiple injuries including complete disruption of the spinal column at C4-C6 vertebra, a severed carotid artery and a severe laceration to the back of his head.
“He was flown to Royal North Shore Hospital where he underwent emergency surgery. The driller sustained permanent incapacitating injuries.”
A key contributing factor to the accident was the unusual 90-degree steel elbow connected to the end of the air discharge line pipe.
The MSIU said it had been installed as part of a previous job where it was used to attach to a blowout preventer.
“The installation of the 90-degree elbow on the air discharge line changed the directional forces from horizontal to vertical creating a lifting force on the air discharge line,” the unit said in the conclusion section of its recently released report.
“The air discharge line securing system was inadequate to restrain the air discharge line. The risks involved with the system were not identified or adequately controlled.
“During the application of air to the hole to unload the well, there was a uncontrollable release of water and cuttings from the borehole. These explosive forces escaped the borehole via the air discharge line causing a lifting force and resulted in the air discharge line shooting up in the air and hitting the driller’s platform and then falling onto the driller causing him serious injury.”
A much heavier designed system is now in place to secure air discharge lines at the mine as part of some of the changes since 2012.