POWER LINES AND MAGNETIC FIELDS

The intensity of a magnetic field round a single straight wire is proportional to the current; the voltage is not directly involved. In the neighborhood of a coil, it is also proportional to the number of turns. Near a single wire (with the wire carrying the return current far away), the field is inversely proportional to the distance from it; if the two wires carrying the current to and from the source are very close to each other, a partial cancellation effect sets in and the intensity decreases as the third power of the distance (at double the distance the intensity drops to 1/8^th). Most practical cases lie be-tween these two extremes; they are difficult to calculate and are best measured experimentally. As in the case of ionizing radiation, any possible hazard would be determined by the exposure, which is the product of field intensity and the length of time spent in it, so that the exposure in the (higher) field of an electric shaver will be less than that in the (lower) field of an electric blanket or waterbed heater, because more time is spent near the latter. Some typical and maximum observed values in milligauss (mG) in US homes are (1):

Appliance Typical Maximum

clothes dryer 1-24 93

TV 1-3 100

Refrigerator 1-8 167

Stereo 4-100 500

Kitchen range 1-80 625

Dishwasher 1-15 712

Blow dryer 1-75 2125

Shaver 50-300 6875

And now the punch line: the magnetic field intensity at the edge of the rights of way of electric power transmission typically lie be-tween 3 and 20 mG, repeat: between three and twenty milligauss. I could find no case above 2 mG in the Savitz study.

This would be so for the usual 3.6 kV distribution line. If the line is the dreaded extra-high-voltage line (several hundred kV) with the technophobe's nightmare of high towers, the magnetic field in-tensity is lower: for one thing, the current is lower for the same power (the Savitz study found no correlation between cancers and electric fields), and for another, the conductors are farther away.

So once again I must sing the old refrain: I cannot guarantee that exposure to magnetic fields at 60 Hz is uncorrelated with child leukemia (or, for that matter, with baldness and nostril itch). What I can guarantee absolutely is that if such a correlation exists (and that is still very doubtful), then it is very much stronger in the home than near a power transmission line.

Which leads to the old advice: if Paul Brodeur and the other social engineers grandstanding as safety crusaders are sincere and believe that exposure to magnetic fields is dangerous, they should switch off the power in their own homes; for then they have noth-ing to fear from the lines that carry electric power to the rest of us.