Radiation in the Skies
In Depth: The Solar System: The Sun
Join a Discussion on Health in the News
The Frequent Flier and Radiation Risk
By MATTHEW L. WALD
Radiation in the Skies
WASHINGTON, June 11 In Greek myth, Icarus flew too close to the sun and
crashed when its heat melted the wax that held his wings together. That idea
seems quaint, but now some scientists think the Greeks may have been right
to fear flying too close to the sun.
The problem is not the sun's heat, but the ionizing radiation it emits. For
the last few months the sun has been at or near the peak of its "storm"
season, when the solar wind, a thin but steady stream of protons that flows
by at a gentle million miles an hour or so, is supplemented by bursts of
protons moving at nearly the speed of light.
These proton bursts, called solar flares or coronal mass ejections, comprise
billions of tons of particles. Unlike the solar wind, the flares are
strongly directional; when the sun's magnetic field directs them to earth,
they can expose people flying at high altitude, above much of earth's
protective atmosphere, to ionizing radiation.
There is no evidence so far that this exposure is dangerous. In fact, the
flares' disruption of radio communication is probably a bigger threat to
Still, Northwest and Continental Airlines sometimes reroute polar flights,
both to avoid solar storms and to avoid seasonal headwinds at lower
latitudes. It is possible, experts agree, that a pregnant woman could be
exposed to enough radiation on a single flight to exceed government health
But experts disagree over how big the overall threat is.
Crew members who fly polar routes for years can accumulate doses that are
large relative to those received by nuclear power plant workers and others
who are conventionally thought of as "radiation workers."
"People may be hurt," said Dr. Robert J. Barish, a medical radiation
specialist in New York who published a book on in- flight radiation in 1996,
"The Invisible Passenger: Radiation Risks for People Who Fly."
The effect, if any, that small radiation doses have on the body is unknown,
Dr. Barish said, but the current regulatory system ignores doses aloft that
people on earth take precautions to avoid.
Christopher J. Witkowski, the director of air safety and health for the
Association of Flight Attendants, said the airlines should have radiation
monitors on board so that they could change altitude or routes to avoid
radiation during solar storms. But the union, more concerned with immediate
issues like pay, has never raised the issue in contract negotiations.
Pregnant flight attendants should be given other work at equal pay, Mr.
Witkowski said, but it would be "impractical" to expect them to ground
themselves if they had to sacrifice income, he added.
An expert in monitoring the sun, Dr. Joseph M. Kunches, the acting chief of
the operations group at the National Oceanographic and Atmospheric
Administration's Space Weather Operations branch in Boulder, Colo., played
down the threat. Dr. Kunches said airline passengers were at higher risk
from germs carried by other passengers than from radiation. And other
experts said there would be too many false alarms to make evasive action in
the air practical.
For people on land, the planet's magnetic field deflects many of the
incoming protons, and the atmosphere filters out most of the rest.
But the atmosphere's shielding drops by about half with every 6,500 feet in
altitude. So health experts have long wondered whether flight crews suffer
from their long hours at high altitude. So far, studies are inconclusive.
Over all, flight crews have higher rates of a variety of diseases, but they
may be related to other factors of the job, like years of disruption of
biorhythms from time-zone changes, not radiation exposure.
Dr. Duane E. Woerth, president of the Air Line Pilots Association, said he
was concerned with the incidence of the skin cancer melanoma, which is
higher among pilots than in the general population. "We've got this spike
that needs to be explained," Dr. Woerth said.
But a Federal Aviation Administration radiation specialist, Dr. Wallace
Friedberg, the supervisor of the radiobiology section of the Civil
Aeromedical Institute in Oklahoma City, said the reason might be that pilots
could fly free to sunny beaches.
The radiation question has become more important as more people fly; also,
aviation has changed since the last solar peak, in 1989. Today, more people
are flying at higher altitudes, and in long-haul flights that travel over
the poles, where the magnetic field concentrates charged particles and
exposure is therefore more pronounced. At airliner altitudes, the radiation
dose over the pole is about twice as high as the dose over the equator.
The streams of protons can hit human flesh hard enough to shake an electron
off an atom in body tissue, creating a charged particle, or ion. That is the
same mechanism by which gamma rays or alpha or beta particles from
radioactive materials on earth deliver ionizing radiation. The effect,
whatever the source, is the same; these particles can disrupt cells. At some
dose as yet unknown they may increase the risk of cancer.
Most of the protons do not make it down to airliner altitude because, as
charged particles, they interact magnetically with molecules in the
atmosphere. But if they hit an atom in the air, or in the structure of a
plane, they shake loose neutrons that hit people.
Neutron radiation is unusual on earth; it is generally a hazard only near
the core of a nuclear reactor, or in a direct line to a nuclear explosion.
In recent years, scientists have raised their estimate of the amount of
biological damage caused by neutrons.
Scientists and regulators disagree about the extent of the risk to human
health. European authorities have gone so far as to classify flight crews as
radiation workers. As a result, their employers must educate them about
radiation risks, and track how much they are exposed to. In this country,
the F.A.A. also considers flight crews as radiation workers, but it simply
advises airlines to educate their crews; a few have made written materials
available to employees.
"We think we've done fairly well approaching this from an educational point
of view," said Dr. John L. Jordan, the top F.A.A. medical official. But Dr.
Jordan said he did not know how many airlines provided printed information
or training to their employees.
The United Nations Scientific Committee on the Effects of Atomic Radiation
estimated last year that air crew members, who made up about a
quarter-million of the nearly four million people worldwide who are
occupationally exposed to radiation, received about 24 percent of all the
radiation to which humans were exposed because of the nature of their work.
Thirty percent goes to the 450,000 people involved in the uranium fuel
cycle, including mining and running nuclear reactors. The average flight
crew member has an exposure 70 percent larger than the average person
exposed in the fuel cycle, according to the United Nations estimate.
"It's very clear to me that the radiation protection establishment is
unequivocal about the need to do something, but not the aviation
establishment," said Robert Alvarez, a radiation expert and former senior
adviser to the secretary of energy.
And the United Nations analysis does not count as "occupationally exposed"
people who fly very frequently as passengers, Mr. Alvarez pointed out.
By some estimates, thousands of couriers and other frequent fliers can
accumulate more radiation than the limits recommended for the general
In contrast, the European Commission decided in 1996 to require monitoring
for high-altitude doses. Airlines are supposed to reassign personnel to keep
individual doses low.
Some airlines, including British Airways, responded by reassigning female
crew members to ground duties as soon as they said they were pregnant.
(Complicating the problem is that the human fetus is believed to be most
vulnerable to radiation exposure in the first few weeks after conception,
possibly before the pregnancy is known.)
Dr. Jordan of the F.A.A. said the agency was not able to advise pregnant
women about flight risks. "The agency was created for purposes of safety in
flight, to keep airplanes from crashing into the ground or into each other,"
he said. The agency's Civil Aeromedical Institute concerns itself mostly
with tasks like assuring that pilots are healthy enough to fly.
With the exception of the Concorde which does not fly at high latitudes
and lately has not flown at all airliners do not carry radiation monitors
that give instant exposure readings.
Dr. Wallace Friedberg, the supervisor of the radiobiology section at the
Civil Aeromedical Institute, wrote a program, available on the World Wide
Web, for calculating the dose from cosmic radiation the steady rain from
the stars, and not the solar dose, which is much more variable and hard to
predict on a flight between two cities. The program is on the Web at
But at the moment, estimating doses on a specific flight is largely
guesswork. Dr. Friedberg's office recently issued a contract to a physicist
to translate readings from the weather satellites in geosynchronous orbit
into specific doses at various altitudes and latitudes.
Dr. Barish has urged the F.A.A. and the airlines to issue alerts when solar
activity is high, and to advise passengers, especially pregnant women, to
consider delaying their trips. Dr. Barish tried to turn that into a
business, offering people a number to call for his reports on solar
conditions, but gave up because of lack of public interest. But he is still
pushing the federal government to act.
Dr. Friedberg is largely unmoved. "The problem is, you can't predict these
things reliably," he said. "If you took every possible thing, you'd ground
the planes too often."
A colleague, Kyle Copeland, a health physicist at the F.A.A., said, "For
every actual event, there'd be tons and tons of false alarms."
Some carriers have provided training or literature to flight crews, but they
have not approached the European standard of keeping records or grounding
pregnant crew members. And they have not installed monitoring devices in
But to varying extents, some have begun rerouting flights in periods of high
solar activity, both to reduce potential radiation exposure and to ensure
good radio communications.
"There's no hard science for it," said Mitch Dubner, a spokesman for
Continental. Nevertheless, he said, "We feel we have an obligation to our
flight crews and passengers; we protect them and eat the cost."
On flights from New York to Hong Kong, Continental has been routing many of
its Boeing 777's to an area between 60 and 67 degrees north, over Canada,
Anchorage and down the Russian Far East, rather than between 80 and 85
degrees north, nearly over the pole.
Northwest Airlines planned to fly its Detroit-to-Beijing flights over the
pole but did so only once in April because of solar activity, said Jay
Byornstad, the chief flight dispatcher for international flights. In May,
the airline said, solar activity was normal and was not a factor in choice
of routes. But route choice is also driven by a more conventional factor,
seasonal headwinds, and the airline uses the polar route less often from May
to October for that reason.
On April 15, the rerouting meant sending a Boeing 747-400 on a route that
took an extra three hours, Mr. Byornstad said. Sometimes the flights have to
stop en route for fuel because of more severe headwinds on the southerly
route. (Winds are lower at the pole, dispatchers say.) Rerouting costs
thousands of dollars in fuel per flight.
Scientists differ about the importance of radiation dose picked up in
flight, partly because there is no scientific agreement about the importance
of any small dose of radiation; most of the predicted effects are derived
from extrapolation from higher doses, not from observation.
"When you put it in the big picture, there's probably some detrimental
biological effect from being in the wrong place at the wrong time when the
sun produces a large proton event," said Mr. Kunches, of the Boulder
laboratory. But with the uncertainty about the effect of small doses, "I
don't view this as a show stopper," he said. "It's a subject of scientific