Is exposure to cosmic rays during cross-country flight dangerous?

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.

Cecil replies:

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.

Send questions to Cecil via cecil@straightdope.com.

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