How the Health are You?
IN-FLIGHT RADIATION AND ITS EFECTS ON CREWMEMBERS
by
David K. McKenas, M.D., M.P.H. Corporate Medical Director
Radiation is not a ‘nice’ topic that we
like to talk about, but I do think that there is critical information regarding
low dose radiation exposure that crewmembers should know.
The FAA considers airline crewmembers as
being “occupationally exposed” workers from low doses of cosmic radiation and
to a lesser degree, from air shipments of radioactive materials. Although
risk from these exposures is extremely low, the FAA recommends that workers
occupationally exposed to radiation and managers of such employees receive
instruction on possible health effects associated with such exposure and on
appropriate actions to take to minimize this radiation.
It is important to note that low-dose
radiation risks are based on mathematical models of the effects of high
radiation doses. There are currently no conclusive studies that show adverse
health outcomes from the kinds of exposures experienced by crewmembers.
Nonetheless, I do feel it is best for the employee to be informed of risks,
so they and their physician can make optimal choices.
The greatest concern for radiation
exposure is for the pregnant crewmember and the effect on the unborn child,
or fetus. AA Medical is pleased to announce a new
Call a Nurse service at 1-800-555-2373 to provide mailed information on
radiation to review with your obstetrician, and assistance in calculating
radiation exposures in flight schedules using the FAA CARI computer
program. Although completely voluntary, we encourage female
crewmembers, at the first indication of pregnancy, to call this number, so
you can get this information to your obstetrician. In addition, AA Medical
departments have pregnancy test kits available at low cost.
Low dose radiation is a highly technical
topic. We have done our best to keep it simple. Please bear with us if the
verbiage gets too technical. The AA Medical Call-a-Nurse can assist you
in understanding concepts as necessary.
IONIZING RADIATION
We cannot escape exposure to ionizing radiation, as it is a naturally
occurring part of our environment. We are exposed to it every day in the form
of cosmic radiation from space and terrestrial radiation from our earth,
which includes such things as radioactive potassium that we normally acquire
in our diet. In addition, we are also exposed to man-made sources of
radiation, such as diagnostic medical and dental X-rays and nuclear power
plants, although the overall contribution of these sources is small.
Both cockpit and cabin crewmembers are
exposed to cosmic radiation levels that are higher than those normally
encountered on the ground. The exposures are very small. At altitudes flown
by airlines, cosmic radiation is present when high-energy subatomic
particles, originating for the most part outside the solar system, collide
with and disrupt atoms of nitrogen, oxygen and other particles that make up
the atmosphere. Additional subatomic particles are produced from these
collisions. The particles from beyond the solar system and particles produced
in the atmosphere are referred to collectively as galactic cosmic radiation.
Another source of in-flight ionizing
radiation is solar cosmic radiation, which comes from several sources, the
most important one from the crewmember’s standpoint being solar flares.
Solar flare particles, coming from the
sun, are usually too low in energy to contribute to the radiation level at
the altitudes commercial airlines fly. However, on infrequent and
unpredictable occasions, the numbers and energies of ejected solar particles
are high enough to substantially increase the dose rates at these altitudes.
This solar flare activity, which occurs in
solar cycles that rise and fall approximately every 11 years, is very
important at this time because during the year 2000, this activity is at its
highest.
Another source of ionizing radiation is
radioactive material that is transported by commercial air carriers.
This material consists mostly of pharmaceuticals used in medical diagnosis
and treatment. Federal regulations established by the Department of
Transportation (DOT) are specific as to packaging and storage of such cargo
in order to limit radiation levels in areas occupied by people or animals.
Again, the hazard of radiation from this source is very low.
VARIABLES AFFECTING THE AMOUNT OF
EXPOSURE
There are a number of factors that affect the amount of radiation exposure
that a crewmember receives during a particular flight. These include:
the flight
altitude
the duration at that altitude
the geographic latitude of the flight
the stage of the solar cycle
Altitude and Duration
In general, the higher the altitude, the greater the increase in the cosmic
radiation levels. For example, in the United States at sea level, the average
dose rate to the average individual is about 0.035 microsieverts per hour,
whereas at 35,000 feet, the dose rate is 4.1 microsieverts per hour over
Oklahoma City and 5.1 microsieverts over Anchorage. The amount of time spent
at altitude will therefore affect the total radiation exposure.
Latitude
The earth’s magnetic field acts to deflect many charged particles of solar
and galactic origin that would otherwise enter the atmosphere. This shielding
is most effective at the equator, but it decreases, moving toward the poles,
and then disappearing completely over the magnetic poles of the earth (North
Pole and South Pole). At air carrier cruise altitudes, galactic radiation
doses over the magnetic poles are about twice those over the equator. Since
commercial aircraft usually fly high latitude (polar) routes between the
United States and Europe or Asia, these international operations are more
exposed than domestic operations.
Solar Cycle
Finally, the amount of galactic and solar cosmic radiation particles entering
the earth’s atmosphere varies with the approximate 11-year cycles of rise and
decline in solar activity. Although we can influence the first two variables
through flight bids –altitude/duration of flight and latitude, we have no
control over solar cycles.
HOW MUCH EXPOSURE IS TOO MUCH?
There are a number of national and international organizations that provide
guidelines for ionizing radiation exposure limits. Unfortunately, these
guidelines are not uniform. It is important to note that to the best of
our current medical knowledge, no adverse impacts have been noted for any
exposures less than 100 millisieverts. The guidelines cited below are all in
millisieverts.
National Council on Radiation
Protection and Measurements (NCRP)
50 mSv/yr for
occupationally exposed aviators
5 mSv for
pregnancy, distributed over 9 months with no single month greater than 0.5
mSv
1 mSv/yr for
the general public
Occupational Safety and Health
Administration (OSHA)
50 mSv/yr for
occupationally exposed aviators
European Council
·
6 mSv/yr, begin
monitoring any aircrew at 1 mSv/year
·
Pregnancy: the dose
to unborn will be as low as reasonably achievable (ALARA) and will be
unlikely to exceed 1 mSv during at least the remainder of the pregnancy
·
Nursing women will
not be employed in work involving a significant risk of bodily radioactive
contamination (>1 mSv/yr)
International Commission on
Radiological Protection (ICRP)
- 20 mSv/yr (the
average of 5 years) with no more than 50 mSv in any one year.
- This value includes ones background exposure (which is
around 3-5 mSv/yr)
- 5 mSv/yr for employee involved in non-exposed radiation
occupation
Table 1, at the end of the document,
illustrates the estimated dose to air carrier crewmembers from cosmic
radiation received for each of 32 nonstop flights on a variety of routes.
Depending on the particular flights flown during a work year, the annual
dose, based on flying 700 block hours per year, can range from 0.14 uSv [Houston
to Austin] to 58.2 [Athens to New York]. 700 block hours is a high estimate
of flight time for an average crewmember. Even if a crewmember flew this
much, though, this amounts to 0.7% to 20% of the recommended annual ICRP
limit of 20 mSv/hr for adult occupational exposure.
Looking at the table, you can further
appreciate how the variables of flight altitude, latitude, and duration
affect radiation exposure. For example, flights such as New York to Tokyo,
that are of long duration and flown at higher altitudes and latitudes,
receive higher annual doses than those such as Houston to Austin that are of
shorter duration, lower altitude and lower latitude. For the female
crewmember who may be pregnant, or plans to become pregnant and wants to
decrease risk to her offspring, she might bid for flight assignments to those
of shorter duration, lower altitude and lower latitudes.
It must be pointed out that potentially
large doses of ionizing radiation can be emitted from the sun over short
periods of time [coronal mass ejections and solar flares]. Fortunately, these
so-called solar particle events are rare. Since 1956, there have not been any
events during which the hourly average dose rate exceeded 1 mSv/hour at
40,000 feet. However, they are unpredictable.
If a pregnant crewmember were to receive a
larger than usual radiation dose during such an occurrence, that brought her
total dose closer to the recommended exposure limit, a voluntary change in
flight assignments to those of shorter duration and lower altitude and
latitude could lower her total dose below the recommended limits. Or, her
obstetrician might consider the risk not medically advisable, and recommend
that the crewmember stop flying.
OBTAINING ESTIMATES OF COSMIC RADIATION
There are ways of estimating of the amount of cosmic radiation received by
crewmembers. The FAA has developed a computer software program entitled
CARI-5E, which provides an estimated dose for a particular flight based on
certain parameters of the flight. The program requires the point of origin,
point of arrival, time enroute, and altitude parameters, and then will
calculate an estimated dose received during the flight. CARI-5E also takes
into account the phase of the solar cycle. This number is updated
approximately monthly and can be obtained from the FAA’s Web site
[http://www.cami.jccbi.gov/AAM-600/610/600Radio.html]. Also, a copy of the
CARI 5E can be downloaded from their Web site at no charge.
Although CARI-5E takes into account the
phase of the solar cycle in estimating cosmic radiation exposure, it does not
account for solar cosmic radiation as might occur during a rare, but large
solar particle event.
THE PREGNANT CREWMEMBER
Radiation exposure poses the greatest threat to the pregnant crewmember. For
that reason, we urge crewmembers to notify their supervisors or American’s
Corporate Medical Department at 1-800-555-2373 once they become aware of the
pregnancy. AA Medical occupational-certified registered nurses will provide
additional radiation documents and information, and assist the crewmember
with dosage calculation procedures. This information can be shared with the
obstetrician so that the crewmember and obstetrician can make optimal
choices.
The incidence of one or more serious
congenital abnormalities in the general population is about 2.5 %, or about 1
in 40. Radiation exposure can theoretically add to these risks, although this
has never been confirmed by scientific population studies. These risks would
fall into two general categories: genetic risk and in utero risk. Genetic
risk is risk of damage to the genes of a child and subsequent generations due
to one or both parents being exposed to radiation prior to the child’s
conception. In utero risk is the risk of birth defects in a child due to
direct exposure of the fetus to radiation between conception and birth.
Genetic Risk
The NCRP estimates that the genetic defect risk increases by about 8 in one
million live births in all generations for each mSv of radiation exposure to
the parent. For example, suppose that before conceiving a child, a female
crewmember works on flights between Minneapolis and New York (See TABLE 1)
for five years and averages 700 block hours per year. The resulting added
genetic risk to all her subsequent generations would be 1 per 10,000 live
births. Thus any risk of genetic defects to a child due to a parent’s
exposure to cosmic radiation is an extremely small addition.
In Utero Risk
For a child exposed to radiation in utero, the risk of harm depends on the
stage of development at the time of exposure as well as the amount of
radiation received. Here the math is a little tedious, because several
factors have to be accounted for: the estimated amount of radiation on each
flight flown, the number of flights flown during each phase of pregnancy and
the individual coefficients for each potential health defect. The
calculations are not shown, but if we assume the mother worked 800 block
hours during the entire pregnancy (all nine months, which is highly unlikely)
on the Minneapolis-New York route described previously, the added risk to the
unborn child due to cosmic radiation exposure is still very small – about one
in every 1,800 births.
During pregnancy, one recommended
radiation exposure limit is 2 mSv total, starting when the worker informs her
employer of her pregnancy. This notification is encouraged but is
strictly voluntary. In addition, the NCRP recommends that the exposure of the
unborn child not exceed 0.5 mSv in any month (excluding medical exposure)
once a pregnancy becomes known. For radiation protection purposes, it is
assumed the unborn child receives the same dose as the mother. These
recommended exposure limits have been established based on an attempt to keep
the risk of adverse effects at a minimum.
SHOULD YOU FLY IF PREGNANT?
The timing of when a pregnant crewmember should stop flying -- or if flying
internationally, transfer to domestic flying -- should be determined by the
crewmember and her obstetrician. We hope the information you receive from
1-800-555-2373 through AA Medical Call-a-Nurse and the help with the
radiation program calculations, can assist you and your obstetrician with
this determination.
SUMMARY
This guide is meant to provide you with a basic familiarity with the added
risks of exposure to cosmic radiation because of their career choice.
However, it is important to keep the radiation risks associated with
aviation-related work in perspective with other health risks.
Chronic diseases (heart disease, cancer
and cerebrovascular disease) are the major causes of death, serious illness
and disability in the United States today. Behind most of these chronic
diseases, disabilities and premature deaths are diverse environmental and
behavioral factors that can possibly be changed for prevention’s sake. In-flight
cosmic radiation exposure is only one such environmental risk, and a very,
very small one. On the other hand, there are a few individual and societal
lifestyle patterns that constitute far greater risk to developing chronic
disease and disability than many of the environmental factors. Other major
health risks can be reduced if the health-conscious crew member:
Stops cigarette
smoking
Limits alcohol intake
Practices good nutrition
Participates in regular aerobic exercise
Please feel free to contact me at DAVID.MCKENAS@AA.COM or other AA
Medical Department staff, whenever we can be of assistance to you.
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