Worker suffers electric shock forming concrete slab

WorkSafe Queensland (WSQ) has reported that a worker received an electric shock while he was preparing to form up a concrete slab next to an existing structure. The incident occurred in May this year.

Initial enquiries indicate he was using a sledgehammer to drive a star picket into the ground to support the wooden framework. As he hammered the star picket into the ground it contacted an energised electric cable which gave him an electric shock.

Investigations are continuing but WSQ offers the following information on safety when working near underground electrical lines, including control measures to prevent similar incidents:

Safety issues

Contact with underground electric lines can have deadly consequences. The most common electrical risks and causes of injury associated with working near underground electric lines are:

• electric shock
• arcing, explosion or fire (arcing or explosion can occur when high fault currents are present)
• electric shock from ‘step-and-touch’ potentials.
   

Examples of work that involves risk of contact with energised underground electric lines can include:

• excavating a trench
• digging fencing holes
• driving posts or pegs (such as star pickets/stakes) into the ground.

Possible control measures to prevent similar incidents

Before carrying out ground-disturbing work, consider whether underground essential services (including electric lines) could be present in the area. If they could, you should identify the risks and implement effective control measures associated with the work. This includes complying with any requirements under relevant work health and safety and electrical safety legislation in relation to the work (eg, WHS Regulation — Excavation work — Underground essential services).

The best way of eliminating these hazards is to prevent people, plant, equipment and materials from coming close enough to contact electric lines. Even if a line is de-energised, direct contact with it can still be dangerous if nearby energised high-voltage services are inducing a voltage onto it. Methods to eliminate potential contact with an electrical line may include:

• relocating the digging work away from underground services, if possible;
• de-energising and isolating the electric line for the duration of work. In some situations, earthing the line would also be necessary, especially if near high-voltage services;
• re-routing the electric line away from the work area.
   

Develop a safe system of work for ground-disturbing work. This could include, but is not limited to the following examples:

• If it is not known whether cables, conduits, apparatus or situations form an electrical safety risk, you should either assume that the risk exists, or have a qualified person investigate and report.
• Obtain current information about underground essential services such as electricity, gas and telecommunications. Dial Before You Dig is a free enquiry service for information on underground assets anywhere in Australia. Dial Before You Dig will advise if electrical cables owned by one or more of its contributory members are located in the vicinity of your worksite.
• Consult maps or talk to the property owner and electricity entities.
• Conduct a site-specific risk assessment: think about where underground electric line pits are, inspection covers and building entry markers for underground services; what lies in a path between them; in what directions do cables or conduits leave these pits and therefore where are services most likely to be located.
• Verify locations of underground services via non-ground-disturbing methods. For example, ground penetrating radar or electromagnetic location. (Note: electromagnetic location will not find de-energised cables and ground-penetrating radar cannot distinguish between service types).
• Pothole to confirm locations or service types definitively. Potholing involves digging with hand tools to a predetermined depth to verify if assets exist in the immediate location. Insulated hand-digging tools suitable for the voltage concerned may be used. Vacuum extraction of potholes may also be used to locate underground cables.
   

Develop safe work practices and procedures and ensure they are followed; safe work method statements (SWMS) are developed where required; and appropriately trained and qualified people are authorised to carry out the work.

Develop control measures in consultation with workers performing specific tasks and consider training they require or already have. Formal or on-the-job training may be appropriate depending on the circumstances. Examples include:

• Induction training — to ensure new starters or workers new to a job are trained on safe systems of work and other relevant health and safety matters.
• Supervisor and management training — to ensure that safety issues are appropriately managed at the workplace.
• Work-specific training — to ensure that workers carrying out particular work are trained on any electrical and other risks specific to the work, as appropriate.
• Emergency procedure training — to ensure workers know what to do in the event of an emergency, for example, procedures to follow if a person receives an electric shock.
• First aid training — to ensure appropriate procedures are followed for administering first aid, for example proper treatment for electric shock.
   

Any remaining risk of live contact must be minimised with suitable personal protective equipment. For example:

• Electrical insulating gloves which have been electrically tested in accordance with Australian Standards
• Rubber soled boots
• Safety helmets
• Standing on a rubber insulating mat
• Standing on an equipotential conductive mat
• Dry clothes, especially in wet or humid conditions.
   

Adopting and implementing higher order controls, before considering administrative or PPE controls, will significantly reduce the likelihood of a similar incident occurring. The control measures you put in place should be reviewed regularly to make sure they work as planned.

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