A CONTRACT electrician recommissioning high-voltage electrical equipment in a mine site switchroom has been severely burnt by an 11kV arc flash explosion inside the cubical containing the main incoming circuit breaker.
To test the switch gear, the electrician withdrew, or ‘racked out’, the Yorkshire YSF6 Indoor metal-clad circuit breaker, according to the Queensland Mine Inspectorate.
This disconnected it from the high-voltage supply bus behind, and safety shutters sprang closed automatically to protect the electrician from the exposed high-voltage bus conductors.
These shutters can then be manually locked closed.
The electrician placed the locking device for the top set of shutters in the locked position and was about to secure it with a safety lock when the explosion occurred behind the shutters.
The arc flash explosion set the electrician's clothes alight and he ran out of the switchroom.
Co-workers doused him with water before he was moved to a first-aid facility.
He received severe burns to his hands, arms and legs (requiring several skin graft operations), as well as burns to his face and chest.
“The investigation into the incident has so far failed to find evidence of mechanical failure, electrical supply abnormalities, vermin, moisture, foreign objects or excessive dust that may have caused the fault,” Queensland Chief Inspector of Mines Roger Billingham said.
“However, it has highlighted the need to ensure risk assessments, procedures and switching sheets for all high-voltage work are completed and available; and that workers have been trained and assessed as competent.
“Safe work procedures for the task must be available on site and followed.
“Suitable clearances in switchrooms must be maintained so that equipment can be easily accessed and safely operated,” Billingham said.
“Electrical workers must conduct tests to ensure there is no electrical energy present prior to working on equipment, and should not make assumptions about which cables are the incoming feed to the switch gear.”