31 May Incident : Excavator Damages Buried 11,000V Cable

Excavator damages buried 11,000V cable

Mines safety alert no. 103 | 30 July 2003 | Version 1

Incident

The bucket of an excavator made contact with a buried 11kV cable at a quarry as work was being performed to remove oil soaked ground in the laboratory area. Approximately 300mm of soil cover had been removed. The excavator operator was chasing some damp soil and excavated down to the level of the cable – approximately 600mm. A loud bang and a puff of smoke was witnessed by the operator who then backed the machine away and alighted the machine. The electrical supervisor was called, and upon arrival at the site cordoned off the area and called the supply authority to isolate the high voltage circuit.

Equipment

35t excavator, Buried 11kV electrical distribution cable.

Hazard

Machinery contact with electrical cables and other equipment can cause fires, tyre explosions and can result in severe electric shocks, burns or death for machine operators and bystanders. Depending upon the situation, large amounts of energy can be released from electrical systems when insulation failure occurs. Fault current will flow in the system until circuit protective devices operate. Until the supply is interrupted or isolated, personnel may be at risk of directly touching live conductors or indirectly coming into contact with the fault current flowing through exposed metal parts or through the ground around the fault.

Cause

There were no standard procedures for excavation of ground where buried services might be installed. No pre-work risk assessment to identify local hazards and controls required, was performed.

Comments and recommendations

All buried cables at the quarry were marked on a plan however the operator did not know about the cable.

Two out of three 65A pole top, drop out fuses adjacent to the site of work ruptured to clear the fault. The third phase remained live until isolated by a supply authority line crew about 45 minutes later.

• Develop and implement standard procedures for excavation of ground where buried services are installed or where there could be a service buried. Ensure all personnel are aware of these procedures and use them.
• Conduct a pre-work risk assessment to identify job hazards and appropriate control measures in all cases.
• Develop standard protocols, train personnel and practice emergency response to ensure the hazards associated with this type of incident are controlled and that the damage is minimised.
• Mark the location and depth of all buried services on plans. Ensure that depth of cover is maintained and that the plans are kept up to date and are accessible by all persons who might need to use them.

Authorised by Peter Garland – Regional Inspector of Mines, Southern 
Contact: minesafetyandhealth@dnrm.qld.gov.au

Issued by the Queensland Department of Natural Resources and Mines

REFERENCE : https://www.dnrme.qld.gov.au/business/mining/safety-and-health/alerts-and-bulletins/mines-safety/excavator-damages-buried-11000v-cable