MadSci Network: Engineering

Re: do cords generate EMF when off + does EMF cause cancer?

Date: Mon Sep 4 22:30:05 2000
Posted By: John Moulder, Faculty, Radiation Biology, Medical College of Wisconsin
Area of science: Engineering
ID: 967320397.Eg

Do cords for electrical appliances produce fields that can cause cancer?? There are three separate questions:

  1. "Does a power cord that is turned off generate EMF?"
  2. "Does EMF cause cancer?"
  3. "How far away do you have to be for EMF to be negligible from, say, a blow dryer?"
First, we are talking here about "power-frequency fields", not "EMF". The phrase "EMF" should be avoided since it is an imprecise term that could apply to many very different types of fields, and because the term has a long-standing usage in physics to refer to an entirely different quantity, electromotive force. The term "power frequency" refers to the 50- and 60-Hz alternating current (AC) frequencies used in electric power systems, and term "power frequency field" refers to the electric and magnetic fields produced by 50- and 60-Hz lines and devices.

Question 1: Does a power cord to an appliance that is turned off generate power-frequency fields?

The cord to an appliance that is turned off will generate an electrical field if it is plugged into a live outlet, but it will not produce a magnetic field.

The electric fields associated with the power-frequency sources exist whenever voltage is present, regardless of whether current is flowing. These electric fields have very little ability to penetrate buildings or even skin. The magnetic fields associated with power-frequency sources exist only when current is flowing. These magnetic fields are difficult to shield, and easily penetrate buildings and people. Because power-frequency electric fields do not penetrate the body, it is generally assumed that any biologic effect from residential exposure to power- frequency fields must be due to the magnetic component of the field, or to the electric fields and currents that these magnetic fields induce in the body.

Question 2: Do power-frequency fields cause cancer?

Most of the concern about power lines and cancer stems from studies of people living near power lines and people working in "electrical" occupations. Some of these studies appear to show a weak association between exposure to power-frequency magnetic fields and the incidence of cancer.

However, epidemiological studies done in recent years show little evidence that power lines are associated with an increase in cancer, laboratory studies with animals and cells have shown little evidence of a link between power-frequency fields and cancer, and a connection between power line fields and cancer is physically implausible.

A 1996 review by a prominent group of scientists at the U.S. National Academy of Science concluded that:
"No conclusive and consistent evidence shows that exposures to residential electric and magnetic fields produce cancer, adverse neurobehavioral effects, or reproductive and developmental effects.".

Similarly, a 1999 review by the U.S. National Institutes of Health concluded that:
"The scientific evidence suggesting that [power-frequency electromagnetic field] exposures pose any health risk is weak.".

Overall, most scientists consider the evidence that power line fields cause or contribute to cancer to be weak to non-existent.

Question 3: How far away do you have to be for power-frequency fields to be negligible?

There is no real answer to this.

In short no "safe" distance can be defined.

At the Medical College of Wisconsin we have an entire web site that is devoted to this issue:
Power Lines and Cancer FAQs at:
( John Moulder
Radiation Biologist
Medical College of Wisconsin

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