Cosmic Radiations

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FLIGHT SAFETY F O U N D AT I O N HUMAN FACTORS & AVIATION MEDICINE Vol. 43 No. 2 For Everyone Concerned with the Safety of Flight March–April 1996 Flight Crews and Cabin Crews Encouraged to Increase Awareness of In-flight Ionizing Radiation Crew members who regularly fly at high cruise altitudes receive higher levels of ionizing radiation than the general population. The increased risk appears to be slight, but greater attention is being focused on monitoring of, and education about, ionizin
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  Vol. 43 No. 2 For Everyone Concerned with the Safety of Flight  March–April 1996 FLIGHT SAFETY FOUNDATION HUMAN FACTORS &AVIATION MEDICINE and even a sheet of paper will obstruct them. X-rays and gammarays pass through the body, but can be stopped by a thick shield-ing of lead, concrete or water. Neutrons (which are byproductsof nuclear power plants) also require barriers of water orconcrete. 1 For most people on the earth’s surface, the atmosphere of-fers considerable insulation against cosmic rays. For example,at Oklahoma City, Oklahoma, U.S. (about 1,200 feet [360meters] above sea level), galactic radiation is approximately0.5 percent of the galactic radiation at 39,000 feet (11,895meters). 2 The U.S. Federal Aviation Administration (FAA) in 1994 is-sued an advisory circular 3 that recommends subjects that aircarriers should cover in programs to inform crew membersabout the known health risks of exposure to ionizing radia-tion, so that they can make informed decisions about their work in commercial aviation. The recommended subjects includeinformation about:ãTypes and amounts of radiation received during air travel,compared with other sources of exposure such as radonin the home and medical X-rays;ãVariables that affect the amount of radiation exposurein flight; Flight Crews and Cabin Crews Encouraged toIncrease Awareness of In-flight Ionizing Radiation Crew members who regularly fly at high cruise altitudes receive higher levels of ionizing radiation than the general population. The increased risk appears to be slight, but greater attention is being focused on monitoring of, and education about, ionizing radiation. All life is continually exposed to ionizing radiation. Ionizingradiation comes from several sources — from the earth ( ter-restrial radiation), from space ( cosmic radiation, which pro-duces ionizing radiation after colliding with nitrogen, oxygenand other atoms in the atmosphere), from a combination of cosmic radiation and secondary radiation ( galactic radiation)and even from radioactive atoms in the human body.Air carrier crew members are exposed to more cosmic radia-tion — high-energy subatomic particles and photons (energy)that srcinate primarily outside the solar system — than mostof the general population. The less-dense, high-altitude atmo-sphere offers less protection against ionizing radiation, whichproduces electrically charged atoms known as ions. An ioncan react with surrounding matter, including body tissues, andlead to unwanted biological effects, such as cancer, geneticdefects and fetal damage; some of ionizing radiation’s effectson tissues are cumulative.Ionizing radiation is also produced — but carefully controlledfor useful benefits — by medical X-ray examinations, indus-trial products and pharmaceuticals for medical treatments anddiagnostics.Natural and manmade barriers provide considerable protec-tion against some forms of ionizing radiation. Alpha particleshave little penetrating power beyond the first layer of skin, Stanley R. Mohler, M.D.Wright State University School of Medicine Dayton, Ohio, U.S.  2FLIGHT SAFETY FOUNDATION ã HUMAN FACTORS & AVIATION MEDICINE ã MARCH–APRIL 1996 exposure time. 1 [The sievert has replaced the rem as the inter-national unit of measurement; one sievert is equal to 100 rem.]The basic EPA ionizing radiation guideline is a maximum of five mSv (500 millirem) per year. For adult male and nonpreg-nant female flight crew and cabin crew, the FAA recommendedmaximum exposure is a maximum 20 mSv per year, averagedover five years. For pregnant females, recommended maximumexposure is a more conservative two mSv until the end of preg-nancy, with a maximum exposure of 0.5 mSv per month.A typical chest X-ray exposes the subject to 0.02–0.05 mSv.Ground-level ionizing radiation across the contiguous UnitedStates averages about 0.06 µ Sv per hour. 5 At 35,000 feet(10,675 meters), the dose-equivalent rate from cosmic radia-tion is about four µ Sv per hour. At 41,000 feet (12,505 meters)at polar latitudes, the dose-equivalent rate is about eight µ Svper hour. 6 The biological effects of low levels of radiation exposure areso small they are difficult to determine with certainty, particu-larly since some effects may not be apparent for many years.However, radiation protection standards assume that there is adirect relationship between dose (level of exposure) and ef-fect, even at small doses, and that effects are cumulative.Table 1 (page 3) shows estimates of the ionizing radiation dosesreceived by aircraft occupants during flights within the UnitedStates and also during transoceanic flights.The flight crews and cabin crews of flights that reach the higheraltitudes and the higher latitudes receive the highest doses of ionizing radiation. The accumulated dose is proportionate tothe total hours of exposure at these altitudes and latitudes, butit is also influenced by solar activity. 7 The flights shown in Table 1 range from a potential exposureof 0.0001 mSv to 0.0644 mSv. At the exposure rate of 0.0644mSv per flight, it would take approximately 78 flights to reachthe EPA-recommended yearly maximum exposure level of fivemSv — about 6.5 flights per month.Studies have estimated that for the adult U.S. population, therisk of dying of cancer from all causes is approximately 220in 1,000. 4,8 ( For every 1,000 persons, 220 would be expectedto die of cancer.) Radiation exposure caused by 20 years of high-altitude flight may increase this risk to as much as 225cancer deaths in 1,000 people. 4 These figures suggest that flight crew and cabin crew face asmall increase in the likelihood of incurring a radiation-in-duced ailment under such circumstances. An assessment of in-flight ionizing radiation risks must also take into accountthe age and sex of the person exposed. If, for example, the risk of developing a certain type of leukemia occurs 25 years afterexposure to specified levels of high-altitude ionizing radia-tion, the impact of the risk will be greater for youngerãGuidelines for exposure to ionizing radiation, includingrecommended limits for workers and the generalpublic;ãThe risks — including cancer and genetic defects — tocrew members and fetuses associated with exposure tocosmic radiation;ãSpecial considerations relating to pregnancy;ãManagement of exposure to radiation risks, includingfrequency of flights or types of flight assignments, andthe use of monitoring devices or a computer program;ãRadioactive material shipments as a source of radiationexposure; and,ãAny other subjects that the air carrier believes would beuseful in connection with the subject.In-flight ionizing radiation exposure of flight crew and cabincrew for flights at specific altitudes and routes at specifieddates has been studied and measured. Most exposure to ion-izing radiation by crew members occurs during flight at thehigher altitudes and higher latitudes (away from the equatorand toward the polar regions). The intensity of the ionizingradiation also increases during periods of increased solar ac-tivity that occur approximately every 11 years. 2 (The most re-cent solar maximum occurred in 1989.)In addition to the 11-year solar cycle, solar flares — powerfulmagnetic disturbances on the sun — emit various kinds of ionizing radiation. There is a small risk that crews could beexposed to even greater levels of ionizing radiation during in-tense solar flares, such as those that occurred on Feb. 23, 1957,and on Sept. 29, 1989.The human body can tolerate some low-level ionizing radia-tion effects, but further exposure increases health risks includ-ing the risk of developing cancer; the risk of genetic mutationsin egg cells and sperm cells; and the risk of damage to a devel-oping embryo or fetus.Groups of experts have established safe exposure levels forspecific periods of time (e.g., one year) and also for a lifetimecumulative dose. Ionizing radiation limits are recommendedby the International Commission on Radiological Protection,the U.S. National Council on Radiation Protection and Mea-surements, the U.S. Environmental Protection Agency (EPA),the FAA and other organizations.One international unit of measure for ionizing radiation is thesievert (Sv). Smaller quantities are measured in millisieverts(mSv — one-thousandth of a sievert) and microsieverts ( µ Sv— one-thousandth of a millisievert). An Sv is not an absoluteamount of radiation, but rather a measure of the biologicaleffect of the ionizing radiation. This allows comparison of dif-ferent radiation types that produce different effects for the same  FLIGHT SAFETY FOUNDATION ã HUMAN FACTORS & AVIATION MEDICINE ã MARCH–APRIL 19963 Table 1Ionizing Radiation Exposures on Specific Aircraft Flights a Nonstop One-way FlightsAltitude C Calculated DoseBlockAir TimeHighest AltitudeMean AltitudeOrigin and DestinationHours b Hours(feet in thousands)(feet in thousands) µ SvmSvMilliremMinneapolis MN – New York NY2.11.837317.70.00770.77London, England – Dallas/Fort Worth TX10.19.7393236.10.03613.61Los Angeles CA – London, England10.29.7373444.30.04434.43London, England – New York NY7.36.8373432.50.03253.25Seattle WA – Washington DC4.44.1373419.70.01971.97San Francisco CA – Chicago IL4.13.8413519.00.0191.90New York NY – Seattle WA5.34.9393424.50.02452.45Tokyo, Japan – New York NY12.612.6413559.70.05975.97Chicago IL – London, England7.77.3373536.90.03693.69New York NY – Tokyo, Japan13.413.0433664.40.06446.44London, England – Chicago IL8.37.8393541.50.04154.15Athens, Greece – New York NY9.79.4413956.10.05615.61Seattle WA – Portland OR0.60.421120.10.00010.01Houston TX – Austin TX0.60.520120.10.00010.01Tampa FL – St. Louis MO2.22.031254.00.0040.4Denver CO – Minneapolis MN1.51.233273.30.00330.33Los Angeles CA – Honolulu HI5.65.2353312.00.0121.20Honolulu HI – Los Angeles CA5.65.1403413.90.01391.39Chicago IL – New York NY2.01.637295.90.00590.59Los Angeles CA – Tokyo, Japan12.011.7403435.20.03523.52Tokyo, Japan – Los Angeles CA9.28.8373427.70.02772.77Washington DC – Los Angeles CA5.04.7353216.50.01651.65New York NY – Chicago IL2.31.639318.30.00830.83 a Based on a heliocentric potential of 457 millivolts (mV) — the extrapolated 1,000-year average. b The block hours of a flight begin when the aircraft leaves the gate (blocks) before takeoff and end when it reaches the gate after landing. c Including initial climb and final descent.1 sievert (Sv) = 100 rem1 millisievert (mSv) = 100 millirem (mrem)1 microsievert ( µ Sv) = 0.1 millirem (mrem)Source: Dr. Wallace Friedberg, U.S. Federal Aviation Administration (FAA), Civil Aeromedical Institute exposed crew members than older ones, because the forecastonset of the leukemia would more closely coincide with theforecast life expectancy for the older person. 9 Likewise, a post-menopausal female crew member would not face the risk of transmitting possible unwanted genetic changes to future gen-erations, as would males and premenopausal females.An FAA report notes: “The likelihood of developing fatal can-cer because of occupational exposure to galactic radiation is asmall addition to the general population risk. ... Any risk to achild of a serious handicap of genetic srcin because of aparent’s occupational exposure to galactic radiation would bea very small addition to health risks experienced by allchildren.” 2 Real-time monitoring of exposure to ionizing radiation byflight crews and cabin crews is made possible by a com-plex dosimeter, which is standard equipment on high-altitude supersonic transport flights. The instrument alsocalculates the total dose of ionizing radiation accumulatedduring the flight.The dosimeter display has color-coded sectors — green for“safe” ionizing radiation levels, yellow for “building” ioniz-ing radiation levels and red for “unsafe” ionizing radiationlevels. Thus, a pilot who knows that unsafe radiation levelshave been reached during flight can descend to a lower alti-tude, where the ionizing radiation level is diminished by theshielding effects of the denser air.A computer software program, CARI-3, which calculates theionizing radiation dose that can be expected for a specific flight,was developed by Dr. Wallace Friedberg and other scientistsat the FAA Civil Aeromedical Institute (CAMI). The com-puter program calculates the dose based on flight date, flightdistance, estimated times at en route altitudes, and heliocen-tric potential, which is the degree of solar activity. Data re-garding heliocentric potential are available via modem fromCAMI. The DOS (disk operating system)-based program isreported to be user-friendly. 10 Although it makes sense for flight crews to minimize to theextent practical the risks associated with ionizing cosmic  4FLIGHT SAFETY FOUNDATION ã HUMAN FACTORS & AVIATION MEDICINE ã MARCH–APRIL 1996 We Encourage Reprints Articles in this publication may be reprinted in the interest of contributing to aviation safety, in whole or in part, in all media but may not be offered forsale or used commercially without the express written permission of Flight Safety Foundation’s director of publications. All reprints must credit FlightSafety Foundation,  Human Factors& Aviation Medicine, the specific article(s) and the author(s). Please send two copies of the reprinted material tothe director of publications. These reprint restrictions also apply to all prior and current articles and information in all Flight Safety Foundationpublications. What’s Your Input? In keeping with FSF’s independent and nonpartisan mission to disseminate objective safety information, Foundation publications solicit crediblecontributions that foster thought-provoking discussion of aviation safety issues. If you have an article proposal, a completed manuscript or a technicalpaper that may be appropriate for  Human Factors& Aviation Medicine, please contact the director of publications. Reasonable care will be taken inhandling a manuscript, but Flight Safety Foundation assumes no responsibility for material submitted. The publications staff reserves the right to editall published submissions. The Foundation buys all rights to manuscripts and payment is made to authors upon publication. Contact the PublicationsDepartment for more information. HUMAN FACTORS & AVIATION MEDICINECopyright © 1996 FLIGHT SAFETY FOUNDATION INC. ISSN 1057-5545 Suggestions and opinions expressed in FSF publications belong to the author(s) and are not necessarily endorsed by Flight SafetyFoundation. Content is not intended to take the place of information in company policy handbooks and equipment manuals, or tosupersede government regulations. Staff: Roger Rozelle, director of publications; Girard Steichen, assistant director of publications; Rick Darby, senior editor;Karen K. Ehrlich, production coordinator; and Kathryn L. Ramage, librarian, Jerry Lederer Aviation Safety Library.Subscriptions: US$60 (U.S.-Canada-Mexico), US$65 Air Mail (all other countries), six issues yearly. ã Include old and new addresseswhen requesting address change. ã Flight Safety Foundation, 601 Madison Street, Suite 300, Alexandria, VA 22314 U.S. ã Telephone: (703) 739-6700ã Fax: (703) 739-6708 radiation, those risks must be kept in perspective. The FAAreports that “radiation is not likely to be a factor that [should]limit flying for a nonpregnant crew member.” But it also notesthat “on some flights the galactic radiation received by an un-born child may exceed the recommended limits, dependingon the [crew member] woman’s work schedule.” 2 Pregnantcrew members should pay particular attention to monitoringor calculating their exposure. o References 1.University of Michigan, Student Chapter, HealthPhysics Society, World Wide Web home page (http://www-personal.umich.edu/%7Ebbusby), March 13, 1996.2.FAA Civil Aeromedical Institute.  Radiation Exposure of  Air Carrier Crewmembers II  . Authors: Friedberg, W.;Snyder, L. et al. Washington, D.C., U.S.: FAA Office of Aviation Medicine. Report no. DOT/FAA/AM-92-2.January 1992.3.FAA. Advisory Circular 120–61, Crewmember Trainingon In-flight Radiation Exposure . May 19, 1994.4.Friedberg, W., Faulkner, M., Snyder, L., Darden, E. andO’Brien, K. “Galactic Cosmic Radiation Exposure andAssociated Health Risks for Air Carrier Crewmembers.”  Aviation, Space and Environmental Medicine Volume 60(1989): 1104–1108.5.U.S. National Council on Radiation Protection andMeasurement (NCRP).  Exposure of the Population in theU.S. and Canada from Natural Background Radiation .Bethesda, Maryland, U.S. NCRP Report no. 94. 1987.6.O’Brien, K.  LUIN, a Code for the Calculation of Cosmic Ray Propagation in the Atmosphere . New York:Environmental Measurements Laboratory, Department of Energy. Report No. EML–338 (update of HASL-275).7.For a more detailed discussion of ionizing radiation onair carrier flights, see Cabin Crew Safety , July/August1993.8.Seidman, H., Mushinski, M., Gelb, S., Silverberg, E.“Probabilities of Eventually Developing or Dying of Cancer – U.S. 1985.” Ca — A Cancer Journal for Clinicians Volume 35 (1985): 36–56.9.Mohler, S. “Ionizing Radiation and the SST.”  Astronauticsand Aeronautics (September 1964): 60–68.10.Information about obtaining the program is availablefrom Dr. Wallace Friedberg, U.S. Federal AviationAdministration (FAA), Civil Aeromedical Institute, P.O.Box 25082, Oklahoma City, OK 73125 U.S. Telephone:(405) 954-6276; Fax: (405) 954-1010.  About the Author Stanley R. Mohler, M.D., is a professor and vice chairman at Wright State University School of Medicine in Dayton, Ohio,U.S. He is director of aerospace medicine at the university. Mohler, an airline transport pilot and certified flight instruc-tor, was director of the U.S. Federal Aviation Agency’s Civil Aviation Medicine Research Institute (now the Civil Aeromedi-cal Institute) for five years and chief of the Aeromedical Ap- plications Division for 13 years.
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