Four overhead powerline incidents involving plant and machinery

Use the hierarchy of controls to help decide how to eliminate and reduce risks in your place of work. The hierarchy of controls ranks types of control methods from the highest level of protection and reliability to the lowest. It’s a step-by-step approach to eliminating or reducing risks. You must work through the hierarchy of controls when managing risks, with the aim of eliminating the hazard, which is the most effective control.

Possible control measures to prevent similar incidents

Effective control measures for working near overhead electric lines are often made up of a combination of controls. This includes eliminating the risk of electric shock by turning off the power. The PCBU, principal contractor, or operating plant owner should discuss options for de-energising or re-routing the electricity supply with the relevant electricity entity.

De-energising or re-routing powerlines should be arranged with the electricity entity as quickly as possible as this can take some time to arrange. Where overhead powerlines have been de-energised, written confirmation should be sought from the person in control of the powerline before undertaking any work.

If eliminating the risk of contacting overhead powerlines by de-energising or re-routing powerlines is not reasonably practicable, you must consider using a combination of control measures, to minimise the risk.

If you must work near powerlines, you should follow these steps:

• Develop a safe system of work that ensures a safe distance from powerlines can be maintained at all times (stay outside the exclusion zone).
• Identify overhead powerlines by consulting maps and/or talking to the property owner and electrical entity. For Ergon Energy and Energex, visit lookupandlive.com.au for your free powerline safety plan.
• Consultation regarding the work and the related risks should occur between the PCBU and the plant operator before setting up in the vicinity of overhead powerlines.
• Conduct a site-specific risk assessment and consider:
  • Identifying the minimum clearance distance from the closest part of the mobile plant, (e.g.,) for a crane, the suspended load to the powerline).
  • Material that would normally be non-conductive, may become conductive when in contact with high voltage. All materials should be assumed to be conductive unless a competent person can confirm otherwise. Crane operators will need to take into account the nature of their load to be moved, (e.g., dimensions and whether the load is conductive).
  • For cranes, whether the load is being carried above the electric lines and may accidentally fall onto the live lines – lifting over power lines should be avoided.
  • Unexpected movement of the terrain, ground or surface upon which the mobile plant is located, possibly resulting in a corresponding surge or sudden movement towards live electric lines.
  • Prevailing or unexpected wind strength and direction and other weather conditions.
  • The possibility of sway and sag of the overhead powerlines (sway of overhead powerlines is usually caused by wind, while sag may vary as temperatures vary).
  • In the case of a crane, the size and shape of the load, particularly the surface area facing the wind.
  • Functional behaviour of the crane, load, or other mobile plant that could result in inadvertent contact with electric lines.
  • Possibility of crane or other mobile plant becoming live through voltage-induced by adjacent electric lines, (especially high voltage lines).
  • How the load being carried by a crane is secured and whether any part of the load may inadvertently move during the operation and encroach on the exclusion zone.

Avoid going into exclusion zones

An exclusion zone is a safety envelope around an overhead electric line. No part of a worker, operating plant or vehicle, should enter an exclusion zone while the overhead electric line is energised (live). Different exclusion zones apply depending on the level of competence, training and skills of workers, and whether the worker has been authorised by the owner or person in control of the electric line to work within a closer distance. Examples include:

• Using alternative plant which cannot physically enter the exclusion zone.
• For mobile cranes, using programmable zone limiting or warning devices to prevent the crane boom or load from entering the exclusion zone, or to warn the crane operator before the boom enters the exclusion zone. If a limiting device is used, the system must be designed to ‘fail-safe’, or should generally meet a reliability level of Category 4 under AS 4024: Safety of machinery or a ‘Safety integrity level’ (SIL) of 3 under AS 61508: Functional safety of electrical/electronic/programmable electronic safety-related systems.
• Make powerlines and poles more visible. Ask your electrical entity for permission to paint power poles and/or have them install markers or flags on the powerlines to act as a visual aid to highlight the presence of overhead powerlines.
• Where possible, use insulated or non-conductive tools and equipment.
• GPS geofencing solutions may help keep machinery away from overhead powerline exclusion zones. Electrical detection and alarm systems may also help.
• Using ultrasonic measuring devices instead of the mechanical types for measuring heights of overhead lines.
• Where the crane or other mobile plant could enter the exclusion zone, use a safety observer to make sure you stay well clear of exclusion zones. The PCBU is responsible for appointing a safety observer. The safety observer should:
  • Not carry out any other work or function that compromises their role as a safety observer such as dogging duties.
  • Not be required to observe more than one crane or operating plant at a time.
  • Be able to communicate effectively with the operator of the crane or operating plant at all times and should warn the operator about the approach to the exclusion zone.
  • Be trained to perform the role.
  • Have the authority to stop the operation of the crane or operating plant.
• Follow the safety advice you obtain from your electrical entity.
• Although the following are the minimum safe distances, the best way to stay electrically safe is to maintain the greatest possible distance from powerlines.

Keep your workers and contractors informed about electrical safety:

• Induct and train your workers and contractors in safe work procedures, emergency procedures, and exclusion zones (Figure 1).
  
  

Figure 1: Powerline exclusion zones

• Carefully plan the tasks to be completed near powerlines and work away from them whenever possible, not underneath them. Also avoid storing equipment under powerlines.
• Show your workers the safe distance from a powerline by marking it on the ground.
• Ensure people are aware that powerlines can sag or sway in hot or windy weather (Figure 2).
  
  

Figure 2: Powerlines sag or sway in hot or windy weather

• Harvesters, elevating work platforms, cranes, tippers and excavators, have the potential to enter exclusion zones. Ensure operators know the maximum height and reach of their mobile plant or machinery to be used, and where applicable the nature of the load to be moved.

The controls that are put in place to ensure electrical safety must be reviewed regularly to make sure they are working effectively.