An update on planning and managing trails along power lines.
Trails are often built in utility corridors of all kinds, from underground pipelines to electric power lines overhead. Over the years some articles have raised concerns, apparently unfounded, about electromagnetic fields (EMF) emanating from power lines. But other factors are more important when managing utility line trails.
by Gary Holisko, Senior Environmental Coordinator, BC Hydro Engineering
From an operational perspective, EMF is not much of an issue for trail activities. Use is transient, so exposure is limited. What people react to is what they notice. Working for an electric utility, and being a supporter of public uses on powerline rights of way, I deal with a number of concerns and questions about high voltage lines and people. I see three kinds of concerns expressed about public use of powerline rights of way:
First and foremost, electricity can be hazardous to your health if you come into direct contact with it! Do not go near downed power lines! If you are near lines which have come down, do NOT walk away! Shuffle! 'Step potential' can make you part of the circuit. Because the voltage decreases in an outward direction from where the wire contacts the ground, it means the voltage can be higher at one foot, and lower at your other foot if they are separated (by walking). It is the difference in voltage that creates the 'step potential' and will cause a circuit to be formed using your body which can be fatal. Therefore, either stay put until the power is turned off, or shuffle away. Stay at least 10 metres (33 ft) away from downed lines.
In our part of the world, we have many-fast growing, tall trees that tend to get knocked over during high winds and storms. They also knock down power lines. (So do drunk drivers, but that's another story.) Because transmission lines carry large volumes of power, rights of way are kept clear of tall growing vegetation both to avoid power outages, prevent forest fires and avoid possible electrocutions (sap in trees is an excellent conductor).
Some people who are given better access to transmission towers via trails, etc. have this peculiar idea they should therefore climb them! Although rare (and obviously stupid!), it causes concern to the extent that some authorities require fencing be put around the base of the tower.
Over 25 years of research and hundreds of millions of research dollars have not proven a direct connection between magnetic fields and harmful health effects, but the research continues. There are several government web links which can update you on the current state of knowledge.
BC Hydro and municipal parks people receive more inquiries on this subject than anything else related to public use along our high voltage transmission line rights of way. Touching a grounded metal object (e.g. a sign) can cause a person (who is not grounded, unless they are walking bare foot) to create a small shock like walking across a carpet and touching a door knob. Vehicles parked (the tires insulate the vehicle) on the right of way can also acquire a small electric charge. Longer vehicles (trucks, tractor trailers) will attract a larger charge, and of course a larger shock. This can be an important consideration for horse owners. One suggestion is to create a connection to ground, for example by a chain.
We call these 'nuisance shocks' because while they are below the level to be considered a safety issue, they are none the less annoying.
Of the three, EMF gets the headlines, but it is really the other two which we tend to deal with on an operational basis, in terms of both providing the protection to the public and managing complaints.
A related concern is the impact of powerlines on property values. A recent Wisconsin EIS suggested impacts from zero to 14 percent. Two studies (Ignelzi & Priestley, 1992, California, and Hamilton & Schwann, 1995, British Columbia) found that where the rights of way were used for public uses that property values either were not affected or in fact enhanced by having park or open space adjacent.
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