There is a level of controversy surrounding these ROWs, most notably due to the EMF (Electromagnetic Field) Radiation they create. Let's take a look at some facts:
Transmission Voltages are Extremely High
Due to the great distances the electricity must be transmitted, a ROW will be between 69,000 to 500,000 Volts. At the high end, (250-500 Kilovolts), an audible buzzing and/or crackling sound may be noted. These voltages are obviously extremely dangerous and great care should be taken not to go anywhere near them.
Power Lines Can Move
Power lines may sway as much as 4 meters vertically during windy/bad weather. A fallen transmission can be disastrous, but luckily rarely occurs. If the home buyer is looking at a house directly beside a tower, this is a risk that they should take into consideration before purchasing the home.
No Buildings Permitted Below Them
Homes, Buildings, and even foundations may not be constructed on a ROW, or within 10 meters of one. However, golf courses (such as one in Surrey), sheds, roads, fences, and parking can be constructed with permission from BC Hydro.
Electromagnetic Fields (EMF)
EMF is a physical field that is present around all electronic devices and the equipment powering them. EMF is everywhere electricity flows. However, some groups/individuals believe that EMF causes negative health effects in humans - most notably from Power Lines and "Smart Meters", about which there has been much media coverage. There have been a number of studies performed, particularly one early study that linked childhood leukemia to EMF. Later, the National Cancer Institute (NCI) performed a study that failed to establish a link between elevated EMF levels and leukemia. Only several, long-term studies have been performed, and all have failed to establish a link between EMF and cancer.
Another suggested health effect is Hormonal disruption - there is a anecdotal evidence of Hormone-related problems in people living near power lines, however as of this article's writing we are not aware of any conclusive studies linking the two.
So Are They Dangerous?
The most real, empirical danger involved with overhead power lines is the risk of contact with High-Voltage equipment, either from collapse or from accidental contact with the equipment (kites, ladders, trees, etc.)
EMF Radiation has been proven to drop dramatically over short distances and is already present in areas without overhead power lines (such as near cell towers, microwaves, cell phones, TVs, etc). There is also (so far) no conclusive link between EMF and serious health issues. However, if you feel uncomfortable with power lines nearby you should investigate/research the issue carefully before proceeding.
A Final Note...
A quality home inspection is a thorough visual inspection of the major systems of the home, such as Roof, Exterior, Electrical, Heating, Insulation, and Plumbing. A home inspection will not include evaluation of EMF Radiation, and you should call a specialist if you have any concerns about the property.