Air-crew radiation doses climbing.

Because studies conducted through the early 1970s indicated that the average cosmic-radiation dose to commercial flight crews was only about 90 percent of the recommended annual public-exposure limit, the Federal Aviation Administration (FAA) decided against developing radiation safety regulations. But for a variety of reasons, those earlier dose estimates are no longer valid, according to Edward T. Bramlitt, a health physicist working for the Defense Nuclear Agency in Albuquerque, N.M. Calculations he reports in the November HEALTH PHYSICS suggest that many occupation air-crew exposures are "comparable in magnitude to doses received by groundbased radiation workers." Yet, he notes, unlike those "radiation workers," air crews are neither routinely monitored for radiation nor informed of their exposures and the risks they may pose.

Bramlitt sees several implications of this finding. First, female flight attendants, who can now work into their seventh month of pregnancy, may receive radiation doses to the fetus that exceed the annual 500 millirem (mr) limit recommended by the National Council on Radiation Protection (NCRP). Second, Bramlitt suspects that within 15 or 20 years, crew veterans will begin questioning--in court--whether any cancer they have is radiation-induced.

Last year Bramlitt petitioned FAA to implement rules that could head off these problems. They would require: that airlines begin monitoring doses to crews; that FAA set standards for allowable radiation exposures to crews; and that crews be informed of their exposures and the risks these might pose. They would not affect passengers, Bramlitt notes, because their cumulative radiation increases -- except, perhaps, for some very frequent fliers--would still be negligible. An FAA spokeperson says the agency is formally considering Bramlitt's petition.

Natural cosmic radiation, which bathes the solar system, is largely shielded from earth's surface by the atmosphere. According to the Air Transport Association, today's planes try to fly as high as possible to maximize fuel efficiency. And an increase in cruising altitude from 36,000 feet (the peak altitude for many older jets) to 45,000 feet (the peak allowed many newer jets) can double exposures, Bramlitt says.

Those earlier analyses studied by the FAA considered only domestic routes at midlatitudes, he says. Since cosmic rays tend to flow along magnetic field lines, the earth is not shielded as well from them at high latitudes--especially the poles--as it is at the equator. Moreover, he says, dosimeters used in early tests were not designed to measure the high-energy neutrons spawned by cosmic rays' interactions with the atmosphere. According to NCRP, those particles are 10 to 20 times more hazardous than the gamma rays measured.

The FAA also assumed flight crews worked an average of 60 hours per month. Today, work hours are higher Bramlitt notes that one U.S. carrier requires attendants on international routes to work at least 95 hours per month.

Finally, Bramlitt says FAA ignored solar flares when estimating crew exposures, even though flares can substantially boost exposures. Herbert Sauer at the National Oceanic and Atmospheric Administration's Solar Environment Laboratory in Boulder, Colo., told SCIENCE NEWS THAT AT 40,000 FEET, flares can increase cosmic radiation for several hours from about 0.7 mr/hr to 200 mr/hr; very rare events could spike it to 2,000 mr/hr or higher.