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Mobile plant contacting energised overhead powerlines

Truck Connecting with Powerlines
Truck Connecting with Powerlines

The Queensland Government has released a mining safety report detailing requirements for the prevention of mobile plant and equipment from entering exclusion zones of energised overhead powerlines. The report follows a number of incidents in the industry where mining equipment has contacted overhead powerlines.

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What happened?

Six recently reported incidents at mines and quarries have involved mobile plant contacting energised overhead powerlines:

  • After a truck and dog trailer dumped material, the dog trailer was driven off with the tray fully raised. The raised tray became entangled with a 110,000 Volt (V) transmission line. The driver lowered the tray, got out of the truck and then returned to turn the engine off. Several tyres exploded.
  • A non slewing crane was carrying an item of fixed plant. After reversing across the quarry access road, the crane contacted an overhead 12,700 V Single Wire Earth Return (SWER) powerline. The Safety Observer (spotter) had gone to control the traffic on the access road, prior to the contact.
  • A 40 tonne excavator walking along a damn access road contacted and pulled down 11,000 V power lines. The grounded powerlines started a bush fire.
  • A drill rig slewed with the boom raised, near 11,000 V powerlines. The operator saw the electricity arc from the powerline to the drill rig mast.
  • A drill rig boom was raised into energised 11,000 V powerlines. A worker saw the boom contact the lines.
  • A 22 tonne excavator was walking along a mine road while carrying an electric motor. The boom contacted and brought to ground a low voltage overhead powerline.

The electrical protection operated in all cases resulting in the mine and/or other consumers losing power. No injuries were sustained in these incidents.

How did it happen?

Some contributing factors to the above mobile plant contacting powerline incidents include:

  • Inadequate mine design or layout, with mine infrastructure such as haul roads, dam walls, stockpiles, wash down bays, workshops and storage areas located beneath or too close to overhead powerlines.
  • The mines adding material to the natural ground level under the powerline, lowering the clearance to the powerline.
  • Failure of the mines to implement reasonably achievable engineering controls.
  • An over reliance on administrative controls.
  • Workers (including contractors) not inducted or trained in:
    • the hazards of operating mobile plant near overhead powerlines, and
    • the location of the overhead powerlines at the mine.
  • Failing to lower components of mobile plant when in the vicinity of overhead powerlines.
  • Powerlines not sign posted, or not adequately sign posted and/or delineated.
  • Spotters not used or were given multiple tasks.

Comments

Contact with powerlines is one of the leading causes of electrocution. Each specific situation must have effective controls so that the risk of contacting overhead powerlines is as low as reasonably achievable. It is not sufficient to rely on generic risk assessments or administrative controls.

Recommendations

Before any risk assessment is carried out at least the following information about the powerline should be known:

  • The owner and their contact details, often this can be an electricity entity (Energex/Ergon).
  • The location of powerlines in relation to infrastructure such as stockpiles, roads and fixed plant.
    • (Also refer to the link to “Look up and live map” in the References).
  • The voltage.
  • The NO GO Zone, exclusion zone and safety observer zone.
  • The maximum height above ground of all the mobile plant, including its load, any plant attachment extended to its full height, aerials or persons on the equipment.
  • The minimum clearance which is the difference between the lowest height of the overhead powerline and the maximum height as stated in the previous dot point.
  • Does the powerline have an automatic recloser (re-energisation) system? Mine controlled powerlines must not automatically reclose after a fault.
  • The location and conditions of the powerline easement.

The risk assessment team should:

  • Include documented safety advice from the owner of the powerline.
  • Study the appropriate reference material listed at the end of this Safety Bulletin.
  • Determine whether the mobile plant is working in the vicinity or travelling under the powerline.
  • As far as reasonably practicable, apply the hazard controls (Hierarchy of Controls) listed in the Mining and Quarrying Safety and Health Regulation 2017 section 8 or Coal Mining Safety and Health Regulation 2017 section 10(3)(b) and –
    • Determine those which will most effectively reduce the risk to as low as reasonably achievable.

Whenever mobile plant is going to work in the vicinity of a powerline, a risk assessment must be carried out and should at least consider the following:

  • If the mobile plant used has the potential to breach the NO GO Zone or exclusion zone, the powerline must be removed or isolated or other engineering controls implemented
  • A spotter is required if the mobile plant could breach the required clearances outside the NO GO Zone and the stated clearances in AS/NZS 3007.
  • Designated spotters should have accredited safety observer training.
  • Designated spotters must not be assigned any other task.

Wherever mobile plant is travelling under a powerline, a risk assessment must be carried out and should at least consider the following:

  • Eliminating the need to travel routes under the powerline.
  • Determine if any mobile plant on site or brought to site (newly purchased, contractor’s, etc) is capable of breaching the minimum clearances required below the powerline as stated in AS/NZS 3007.
  • Nominating designated travel routes and implementing effective controls to prevent any contact with powerlines.

A risk management process must be carried out for foreseeable emergencies that might result from mobile plant contacting overhead powerlines. The risk assessment should at least consider the following:

  • What the operator should do if contact is made with a powerline.
  • What action to take if the powerline is in contact with the mobile plant.
  • How to confirm that the powerline is energised or not.
  • What to do if there is a fire on mobile plant.
  • What action to take to avoid the consequences of a tyre explosion due to pyrolysis.

From this risk assessment for foreseeable emergencies, develop an emergency response plan that will reduce the risk of harm to the mobile plant operator and any worker involved in responding to the emergency.

The outcomes of all risk assessments must be incorporated into the Safety and Health Management System sections such as induction, operator mobile plant training, traffic management plan and emergency response plan. Practice drills should be carried out at appropriate intervals to maintain awareness of how to respond.

To view the full  report click here

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