Ineffective risk management programs have been blamed for a drill rig accident which left a 26-year old man with permanent spinal injuries.
The man was working for Silver City Drilling at Ashton Coal mine in 2012, contracted to drill two large diameter surface to seam boreholes for dewatering ICRA Ashtons longwall operations.
At about 2pm on August 12 the driller was operating an air rotary hammer drill at a borehole when a large pressure event occurred due to the surface casing pushing out of the ground and making contact with the bottom of the drill rig.
This caused the air discharge line (a 220mm, 5 meter long steel pipe) to break free of its securing system and travel in an upwards arc, hitting the driller’s platform.
The force of the impact lifted the platform upwards and then it fell, with the driller coming to rest with his neck across the platform rail guard.
The driller sustained multiple injuries, including complete disruption of the spinal column at C4 and C6 vertebra, a severed artery and a sever laceration to the back of his head.
He was flown to Royal North Shore Hospital where he underwent emergency surgery.
The man sustained permanent incapacitating injuries.
An investigation into the accident by NSW Department of Trade and Investment has found that discussions were held that day about excessive water in the borehole, which caused drilling delays prior to the incident as water had to be pumped out of the bore by two water cartage trucks assigned to the task.
The report says that suggestions about changing the drilling method to rotary mud were made, to alleviate safety concerns that using weighted, water-based mud would be a safer method of drilling rather than using compressed air.
Despite these concerns, the rotary air hammer drilling method was continued, which resulted in the incident.
The report lists contributing factors as insufficient installation depth of the conductor to isolate alluvials; excessive water in the borehole creating hazardous conditions; the design of the air discharge line and drill pad such that the line had to pass under the drill platform; failure to use mud drilling altrernative; poor risk management processes, in relation to identification of risk and failure to change systems of work.
The report says that supervisors did not ensure that workers conformed with the agreed work system stipulated by Ashton Coal Operations.
This incident has since highlighted the importance of effective risk management, including ensuring that unconsolidated ground is identified and controlled, that appropriate drilling methods are used, and clear reporting lines and supervisory arrangements are in place.
The rig in question was a Schramm T130XD, capable of 130,000 pounds of pull back pressure with head travel of 15 metres, with three air compressors that run in parallel configuration achieving from 2400-3100kPa.
The rig’s air discharge line had previously been a straight run (on the first borehole), however discharge of material outside the tailings dam had resulted in the drill crew taping a spade to the end of the discharge pipe to redirect the waste water and tailings into the excavated dam, then a 90 degree elbow was attached to direct the flow downwards.
This shifted the direction of pressure upwards, rather than back towards the rig, which resulted in the pipe striking the driller’s platform.