Fatalities Spur MSHA Safety Alert on Electrical Hazards

Arlington, VA- Prompted by reports of three recent fatalities involving electricity, the Mine Safety and Health Administration has issued a safety alert.

Electricity has killed three people in the mining industry since August 7, 2019.

An electrician contacted an energized component of a 4,160 VAC electrical circuit while adjusting the linkage between the disconnect lever and the internal components of the panel that supplied power to the plant feed belt motors. A contract electrician contacted an energized 120 VAC conductor while working inside a fire suppression system’s electrical
panel. An electrician contacted an exposed energized connector while troubleshooting a 995 VAC flooded bed scrubber motor circuit on-board a continuous mining machine.Electrical Safety Alert

MSHA offers numerous best practices for electrical incident prevention. Among them:

-Perform lockout/tagout procedures on circuits before working on electrical equipment.

-Don’t rush, and never work alone. Talk with co-workers and confirm your plan is safe.

-Identify and control all hazardous energy sources before conducting tasks, and follow safe work procedures.

-Train miners on equipment they may use.

-Always perform troubleshooting without power. If you must troubleshoot an energized circuit, use appropriately rated personal protective equipment to prevent hazards.

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Arc Flash Injures Two Australian Mine Workers

Western Australia – According to WA Department of Mines and Petroleum reports, two workers have been injured in an arc flash and blast incident in a West Australian underground mine. The workers, an electrician and mechanical fitter, were investigating water overflow issues at an unnamed site when the incident occurred.

During their shift, they came across a 90kW submersible pump, supplied from a 415 V motor control centre, that had faulted. The electrician found that a control relay contact had fused in the closed position and a control circuit breaker had tripped, causing the fault. The worker then replaced the control relay for the main contactor and reset the control circuit breaker. However, the electrician failed to properly secure the pump control cubicle door properly after closing it so that when he switched on the main circuit breaker it caused an instant arc flash and blast, blowing the cubicle door open.

The electrician received first degree burns to his neck, face, and ears, while the mechanical fitter also received a minor face injury.

According to a subsequent investigation the main circuit breaker suffered a phase-to-phase arcing fault,  which started within the main circuit breaker terminal on the line side of the blue phase (which was shorted to earth), and then transferred to a three-phase fault. The DMP also found that the circuit was not designed to automatically disconnect the main breaker under an earth leakage or earth fault, and that the protection setting were not co-ordinated correctly, which caused the upstream breaker connected to the 415 V motor control centre to fail to operate.

It also found that the drawings did not match the actual electrical installation, “specifically the trip circuit of the motor overload protection had been bypassed, allowing the pump to operate under overload conditions”.

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