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20-Mar-1981
Dear Cecil:
Dentists, physicians, and certain industrial workers are considered "occupationally
exposed" to radiation. Given the fact that an average cross-country flight in an
airplane is bombarded with the same amount of radiation one might receive from an average
series of dental X-rays, are airline pilots considered "occupationally exposed"
too? The airlines seem to be keeping this a secret. --Michael K., Baltimore
Dear Michael:
During the 1960s and 70s the Federal Aviation Administration and the National Aeronautics
and Space Administration conducted studies of the radiation hazard you describe, but to
date airline workers have not been classified as occupationally exposed, and probably
won't be in the near future. The radiation hazard arises from cosmic rays, chiefly
high-speed protons and helium ions, as well as from solar radiation, which can get intense
during solar flares. In 1968 an English researcher estimated that a pilot flying a very
heavy schedule (160 trips) might absorb 1,300 millirems per year, well above the maximum
permissible dose of 500 millirems for the general public, but below the 5,000 millirem
limit for radiation workers. Most subsequent studies, though, have found much lower
average annual doses. A 1978 survey estimated the annual dose for flight crews to be
around 160 millirems per year, which was not considered excessive.
Cosmic rays get more intense at higher altitudes as well as at higher latitudes, due to
the shape of the earth's magnetic field. For that reason it was conjectured that
supersonic transport flights over the polar regions (such as on the Paris-Washington
route) might get a little hairy. The British-French SST, the Concorde, was equipped with
radiation detectors that signaled the pilots when the 10-millirem-per-hour level was
reached (during a solar flare, for instance). At 50 millirems per hour, the pilots were
required to descend to a safer altitude. A report issued by the British government after a
year of Concorde operation indicated that none of the alarms had ever gone off. Concorde
pilots are limited to 500 hours flying time per year (as opposed to 1,000 hours for crews
on conventional aircraft), so that, given an average dose of 0.9 millirems per hour while
flying at SST altitudes, their average annual exposure remains within recommended limits.
On the other hand, it should be noted, flying time for cabin crews (stewards and
stewardesses) is not so strictly governed, so their potential exposure may be greater.
THE TEEMING MILLIONS BEG TO DIFFER
Dear Cecil:
You missed the boat entirely in your discussion of the occupational radiation exposure of
airline flight crews. You note the results of a 1978 study which estimated the annual
radiation dose to be around 160 millirems per year. You then conclude that this level of
exposure is "not excessive."
You have evidently swallowed hook, line, and sinker the myth that there is some
"safe" level of radiation exposure below which one will not experience any ill
effects. The nuclear industry and the federal government have been hard at work
brainwashing us to this effect for several decades. You need only read the 1980
Encyclopedia Britannica article "Hazards of Low Level Radiation" to learn that
all exposure to ionizing radiation is harmful, that there is no dose so low that it may be
considered safe, and that low doses may be even more harmful, per unit of exposure, than
higher doses. It is well documented that radiation causes cancer, genetic diseases, and
birth defects. Radiation also has been linked to an increased infant mortality rate,
increased aging, and stroke.
The point is not that we should have an unreasoning fear of radiation. We've always lived
with--and suffered from--a certain amount of "natural" radiation. Rather, we
should try to minimize our radiation exposure from "unnatural
sources"--radiation exposure which is the result of our human activities, and about
which we can do something. Radiation is obviously of great benefit in many situations:
medical X-rays, for example. But we should always be sure that the benefits of an
increased radiation exposure outweigh the risks.
With regard to the increased radiation exposure incurred by airline flight crews, you'd
have done better to inquire if there isn't some simple way of reducing this radiation
exposure, e.g., by providing a thin layer of lead shielding in the upper part of the
aircraft fuselage. Here there is an obvious, major benefit, fast air travel, and the risks
may not be all that great. The risk should be minimized, but it cannot be done away with
without eliminating jet planes.
With regard to the increased exposure we all get from nuclear power plants, the situation
is different. Here the benefit is electricity, but there are several alternative ways of
obtaining electricity which are much safer, more economical, and which expose us either to
no radiation--e.g., conservation, wind power, and solar power--or to greatly reduced
radiation--e.g., drastically cleaned-up coal plants. There is no need to incur the risks
posed by the radiation exposure resulting from radioactive releases from nuclear power
plants. --Edward G., Evanston, Illinois
Cecil replies:
I am going to be patient with you, Ed, because you seem reasonably intelligent, and thus
may profit from instruction. Listen up. (1) When we are talking about the price of mangoes
in Sumatra, I am not interested in having you drag in your opinions on the temperature of
spit in Wichita. We were talking about the effect of cosmic rays on airline pilots, not
nuclear power plants. (2) Make no blithe assumptions about what "boats" I may or
may not have "missed," since they will usually be erroneous. I am well aware
that there is no known dose threshold beneath which ionizing radiation can be said to be
"safe." The mechanism of carcinogenesis is not well understood, but some believe
that a single high-speed particle striking a cell nucleus in the right way can produce the
biological event necessary to trigger cancer. (3) Do not lecture me on the obvious.
Risk-benefit analysis has been a fundamental tool of both pro- and anti-nuke scientists
since the dawn of the atomic age. It is a cold-blooded business. When I say that a certain
radiation level is "not excessive," I do not mean that it is harmless; I mean
that it will kill or maim a relatively small number of people. In the 1978 study, it was
estimated that the biological effects of air travel on the U.S. population would be so
small as not to be directly observable, but that purely from a statistical point of view
it was likely that there would be 3 to 75 cases of disability due to genetic defects and 9
to 47 early cancer deaths over a period of years. Out of a population of 225 million, this
was not thought to be significant. Some years ago, the possibility of outfitting jetliners
with lead shielding was considered but rejected after it was calculated that carrying
capacity would be substantially reduced in doing so.
Whether a risk is justifiable has more to do with ethics and politics than it does with
biology. For the present a radiation dose limit of 500 millirems per year has been
somewhat arbitrarily set for the general public. At this level, it is believed, only a few
people will die before their time. Others are paid to subject themselves to higher risks.
Radiation workers in the U.S., who presumably know what they're getting into, can be
subjected to up to 5,000 millirems per year by their employers. One hopes that every
conceivable precaution is taken, but nonetheless it is certain that a substantially higher
percentage of these people will die as a result of their jobs than is true of the general
public. In Europe there is an intermediate category of 1,500 millirems per year for
workers who are incidentally exposed to radiation in the course of their jobs but who
derive no direct economic benefit therefrom. This would include airline pilots, who could
do their jobs just as well without cosmic rays, but excludes workers in nuclear power
plants, who would be out of a job if there were no such thing as uranium-235. Readers may
find discussions of this sort heartless, but essentially the same sort of calculation goes
into estimates of death from coal dust.
--CECIL ADAMS
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