Correspondence

Frasch G, Kammerer L, Karofsky R, Schlosser A, Stegemann R. Radiation exposure of German aircraft crews under the impact of solar cycle 23 and airline business factors. Health Phys 107: 542–553; 2014. DOI:10.1097/HP.0000000000000150. NOAA. Halloween space weather storms of 2003. NOAA technical memorandum OAR SEC‐88; Boulder, CO: Space Environment Center; 2004. NOAA. Solar proton events affecting the earth’s environment. Boulder, CO: Space Weather Prediction Center; 2013. Available at http://swpc.noaa.gov/ftpdir/indices/SPE.txt. Accessed 17 December 2013. Tierney D, Briggs MS, Fitzpatrick G, Chaplin VL, Foley S, McBreen S, Connaughton V, Xiong S, Byrne D, Carr M, Bhat PN, Fishman GJ, Greiner J, Kippen RM, Meegan CA, Paciesas WS, Preece RD, von Kienlin A, Wilson-Hodge C. Fluence distribution of terrestrial gamma-ray flashes observed by the Fermi gamma-ray burst monitor. Geophys Res Space Phys 118:6644–6650; 2013. DOI:10.1002/jgra.50580. Tsuchiya H, Hibino K, Kawata K, Hotta N, Tateyama N, Ohnishi M, Takita M, Chen D, Huang J, Miyasaka M, Kondo I, Takahashi E, Shimoda S, Yamada Y, Lu H, Zhang JL, Yu XX, Tan YH, Nie SM, Munakata K, Enoto T, Makishima K. Observation of thundercloud-related gamma rays and neutrons in Tibet. Menlo Park, CA: SLAC National Accelerator Laboratory; arXiv 1204.2578, KIPAC, SLAC PUB‐153; 2012.

RESPONSE TO BRAMLITT AND SHONKA Dear Editors: BRAMLITT AND Shonka responded to our paper “Radiation Exposure of German Aircraft Crews under the Impact of Solar Cycle 23 and Airline Business,” recommending that aircraft crewmember (ACM) doses should be measured. We appreciate their critical acclaim and comments. We would like to clarify some criticized aspects and shed light on the practical problems of implementing official dose measurement of aircrews. Route doses that aircraft crews receive are composed of a systematic dose component that occurs inevitably on every flight from high altitude radiation and of components that contribute only stochastically to route doses; e.g., solar particle events in solar storms or terrestrial gamma flashes in tropical thunderstorms. The systematic component is the major contributor to the accumulated annual dose of ACM and can be calculated with sufficient accuracy for the purpose of official occupational dose monitoring. Exposures from the stochastic components require elaborate inflight measurements. Because of their small probability of occurrence and the route mix of the aircrew personnel, they contribute far less to the annual occupational dose compared to the systematic component. We concede that, in rare cases of solar storms, significant additional doses cannot be excluded. However, constant in-flight measurements in two Airbus 340s from 2008–2011 did not give any hint of enhanced route doses caused by solar particle events or terrestrial gamma flashes. The official German dose monitoring of occupational exposure from cosmic radiation is based on German

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law and transposes the European Council Directive 96/29 EURATOM. It has to focus explicitly on the systematic component of cosmic radiation as the dominant contributor to the annual dose of aircrew personnel. It also has to exclude, per definition, potential exposures from any other civilian or natural radiation sources such as medical x ray, radioactive cargo or terrestrial gamma flashes. Bramlitt and Shonka quoted a possible dose of 3 mSv during a single major solar particle event. This refers to a supersonic flight via pole route (Beck et. al. 2009). As German airlines do not operate supersonic aircraft, this scenario is irrelevant for Germany. We agree that dose measurements can provide for more confidence in occupational dose monitoring than dose calculations under the precondition that adequate measurement and dosimetry are performed. From the perspective of official radiation protection, we support the idea of a graded approach by measuring route doses, but only in long-range aircrafts. One reason is to register stochastically-occurring doses from solar particle events or terrestrial gamma flashes, not so much because we expect substantial dose contributions but to preserve evidence. The other and, from our perspective, stronger reason lies in the application of the optimization principle in radiation protection: Measured ambient equivalent dose rates can give immediate feedback to pilots and could allow them to optimize a route dose during the flight (e.g., by abstaining from the last step climb, etc.). However, this requires the use of radiation detection systems on board that cover the energy spectra of all relevant particles, calculate valid dose rates and route doses from the measurements, and provide the results instantly visible within the set of instruments enabling the pilots to act. To call for in-flight dose measurements is one thing; to put this into the praxis of official dose monitoring is another (not trivial) task. Any attempts to convince airlines to implement cost-intensive dose rate instruments in their aircraft on a voluntary basis and to develop flight operational procedures for pilots in order to react on measured dose rates will be in vain as they increase costs. The airline business is under strong pressure financially from international competition. It was very difficult to implement official aircrew monitoring on the basis of route dose calculation programs in European Union Member States. Meanwhile, some European countries monitor aircraft crews fairly well for 10 to 15 y, while other highly industrialized nations have not even begun. Thus, official in-flight dose measuring can only be implemented on a legal basis with international consensus, and it will be a stony way. On the other hand, the history of radiation protection teaches us that all occupational dose monitoring started small and emerged more or less rapidly. This applies for the dosimetry technique as well as for the monitored groups

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of workers. During recent years, exposure to cosmic rays came increasingly into the focus of public and international radiation protection organizations. It was discussed at the recent IAEA Occupational Radiation Protection Conference in December 2014 (IAEA 2014a). One of the action items resulting from this conference calls for a graded approach for the protection of flight crews (IAEA 2014b). We would not be surprised if, in the near future, international radiation protection organizations recommend inflight dose measurements and the inclusion of frequent flyer groups (e.g., air couriers and sky marshals) in occupational dose monitoring. The authors declare no conflicts of interest. GERHARD FRASCH, LOTHAR KAMMERER, RALF KAROFSKY, AND ANDREA SCHLOSSER

May 2015, Volume 108, Number 5

RALF STEGEMANN Division Federal Supervision for Radiation Protection Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety Robert-Schumann-Platz 3, D-53175 Bonn, Germany

REFERENCES Beck P, Dyer C, Fuller N, Hands A, Latocha M, Rollet S, Spurny F. Overview of onboard measurements during solar storm periods. Radiat Protect Dosim 136:297–303; 2009. IAEA. 2014a. Available at http://www-pub.iaea.org/iaeameetings/ 46139/International-Conference-on-Occupational-RadiationProtection-Enhancing-the-Protection-of-Workers-GapsChallenges-and-Developments. Accessed 17 December 2014. IAEA. 2014b. Available at www.iaea.org/newscenter/news/ next-frontier-worker-radiation-protection. Accessed 17 December 2014.

Occupational Radiation Protection & Radiation Protection Register Federal Office for Radiation Protection D-85762 Oberschleissheim, Germany

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Response to Bramlitt and Shonka.

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