Static shock hazards

WHILE an electrostatic zap from a vehicle door or a metal doorframe in an office may seem harmless, a recent incident on a Bowen Basin drill rig has shown an electrostatic shock in a mining environment has the potential to cause severe injuries.
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The PVC pipe involved in the electrostatic shock on a Bowen Basin drill rig.

Angie Tomlinson

In certain circumstances electrostatic charges can build up on materials that when touched by a person can cause immediate pain and a potential reaction leading to further injuries.

In a recent incident in Queensland, a drill rig operator received a severe electrostatic shock from a PVC pipe.

As the operator was climbing onto the driller’s operating platform, he had one foot on the platform and the other on or near the PVC pipe. He felt the shock through his legs and it caused him to fall over.

According to the Queensland Mines Inspectorate safety bulletin, the magnitude of the shock caused the operator severe pain, he felt ill, and was taken to hospital and put under observation for several hours.

The equipment being used by the drill operator included a GD1400 truck mounted drill rig fitted with a 700cfm/250psi compressor, 6m by 100mm PVC pipe Class PN 9 pipe to AS/NZS 1477, and “Washington” diverter.

A dry drilling process was being used to drill into previously grouted ground, and a large volume of compressed air was being used to clear the drill cuttings, which were mostly fine dry material.

The PVC pipe was raised off the ground on a piece of rusty bore casing, and the drill rig was supported on wooden blocks. Three drill rods were in the ground at the time of the incident.

The diverter was coupled to the borehole case with a Victaulic coupling using a rubber seal.

The build-up of electrostatic charge on the pipe was repeatable, 24 hours later.

Whilst the Mines Inspectorate said the potential to cause a fatality from electrostatic shock in the above situation was unknown, the incident did have high potential to cause a person severe injuries due to a fall as a result of a shock.

It said there was also potential to cause an ignition of methane upon such an energy discharge.

The inspectorate issued the following recommendation to prevent similar incidents in the future:

Use anti-static pipes/hoses for the attachments to the Washington diverter;

Use earthing strap/cables between the pipes and rig and ground;

Use metallic pipes;

Where possible, avoid using dry drilling; and

Be aware of the possibility of electrostatic charge build-up in low humidity conditions.