Q: What do we know about EMF from direct current sources?
A: DC lines produce electric and magnetic fields but because the current doesn’t alternate (oscillate) like it does for an AC line, the fields are referred to as static. These fields are similar to other static fields that occur naturally in our environment.
For example, currents running deep in the Earth’s core produce a natural static magnetic field on the surface with a field strength in Alberta of about 580 milligauss (mG). The static magnetic field produced by a typical 500 kV DC transmission line is slightly lower (560 mG) and will either add to or subtract from the Earth’s field depending on which side of the line you stand under. By comparison, the levels of static magnetic fields produced by many battery operated appliances (3,000 to 10,000 mG) and medical devices (15,000,000 to 40,000,000 mG) are much higher.
Static electric fields also occur naturally. Static electricity on a hair brush, “static cling” on clothing, or walking across a carpet can all produce static electric field strengths of 100 to 500 kilovolts per metre (kV/m). The static electric field strength underneath a typical 500 kV HVDC line is about 30 kV/m.
Certain weather conditions can cause an AC or DC line to produce an additional static electric field that temporarily adds to the field strength.
Both electric and magnetic field strengths decrease rapidly with distance from the line. In addition, static electric fields are blocked by trees, shrubs and buildings.
Q: Should I be concerned about EMF from direct current sources?
A: A number of national and international scientific agencies have evaluated the research on health effects associated with exposure to DC static electric and magnetic fields. These organizations concluded that there are no known adverse health effects associated with the low levels of static electric or magnetic fields associated with DC transmission lines.
Q: Are there limits or guidelines for EMF from direct current sources?
A: Yes, but these guidelines are not concerned particularly with the low levels of static electric and magnetic fields associated with DC transmission lines. They target the safe use of devices like medical MRI machines which have static magnetic field levels thousands of times higher than the field under a DC transmission line.
Q: What is ATCO Electric doing about EMF in general?
A: ATCO Electric takes steps to act responsibly. We build and operate our transmission facilities within accepted engineering and safety standards. We try to route new facilities away from built-up areas. We are also committed to monitoring what is being researched, and sharing information with customers, employees, government officials or any other interested people or organizations on matters concerning EMF.
More information on EMF is available by clicking on the following links:
Further information and links can be found on the following websites:
Canadian Electricity Association website: www.emf.electricity.ca.
Health Canada: http://www.hc-sc.gc.ca/
World Health Organization: www.who.int/peh-emf/en
National Institute of Environmental Health Sciences: www.niehs.nih.gov/health/topics/agents/emf/index.cfm
International Commission on Non-Ionizing Radiation Protection: www.icnirp.de
National Radiological Protection Board (NRPB) of the UK (now Health Protection Agency): http://www.hpa.org.uk/
Q: Can you eliminate DC fields by burying the lines?
A: Burying DC lines under ground will block the electric field, but not the magnetic field. Both electric and magnetic fields diminish rapidly as the distance from a transmission line increases.