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Powerline Contacts - Know Your Limits

Overhead powerlines or conductors have been a part of the Ontario skyline for more than a century now. They carry thousands of volts of electricity to our homes and businesses and at first glance look harmless. That is a dangerous assumption. Coming into contact with, or even in proximity to, live electrical plant can be fatal.

In 2008, the Electrical Safety Authority compiled a report outlining Ontario powerline incidents. The report states that between 2001 and the first half of 2007 more than 50 per cent of the total reported electrical occurrences in the province were powerline contacts. These resulted in 34 fatalities and 1,431 powerline incidents.

Some of the most hazardous activities that caused these incidents included overhead contacts:

  • during the loading and unloading of dump trucks
  • cement trucks and garbage trucks
  • roofing and other exterior building work
  • cranes, boom trucks
  • tree trimming.

In recent years, several Ontario utilities have hosted seminars and meetings with contractors, boom truck drivers, and other high risk goups that may come in proximity to overhead powerlines, in order to share their knowledge of electrical safety. Utilities and utility contractors not only have the knowledge and experience in dealing with high voltage electrical plant, they are also more than aware of the safe limits of approach.

What can a contact do to you?

An electric shock can do damage to the body in a number of ways:

  • An electric current will force your muscles to contract very quickly, thereby creating an involuntary movement than can cause you to fall, jump back, or otherwise injure yourself.
  • Muscle contractions may be so severe that you are unable to pull free of the energized circuit. Burns and blisters (resulting from heat generated by the current flow) will develop very quickly.
  • Vital body organs such as your brain, heart, and lungs may also sustain damage, the extent of which is determined by the amount of current flowing and the duration of the contact.
  • Electrical arcs release incredible amounts of energy almost instantly. They can cause thermal burns to the body strictly from the intense ultraviolet light they radiate, even without making any electrical contact.

What are the limits of approach?

The safe limits of approach are defined in the Construction Regulation, the regulation called Industrial Establishments and also in the Electrical Utility Safety Rules published by the Infrastructure Health & Safety Association.

There are three classifications of limits of approach and these are dependent upon the worker's training and qualifications. The first (Figure 3) or the "General" limits of approach are for personnel who have not had training on the safe limits of approach. Between 750 and 150,000 volts, unqualified personnel may work no closer than 3 m (10 ft.) from live equipment. At 150,000 to 250,000 volts the limit of approach is 4.5 m (15 ft.), and over 250,000 volts unqualified personnel must remain at least 6 m (20 ft.) away from live equipment.

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