Occupational Radiation Protection: Protecting Workers Against Exposure to Ionizing Radiation: Proceedings of an International Conference on Occupational Radiation Protection - Protecting Workers against Exposure to Ionizing Radiation, Geneva, Switzerland, August 26-30, 2002. Vienna, Austria: International Atomic Energy Agency, Publication 1145, 2003 Jul; :407-408
The average annual effective dose due to occupational cosmic radiation exposure is 3.0 mSv (about 60% neutrons), which is higher than that due to other enhanced natural sources such as coal mining, non-coal mining or mineral processing according to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2000 Report. Individual variability in annual exposures can be up to 25 fold (0.2-5 mSv/a), depending on the routes flown, which are often related to seniority in the profession. The collective dose for aircrew is 320 man Sv/a (UNSCEAR 1993 Report). In the specific case of cosmic radiation exposure of aircrew, the radiation control options include rotation of staff for reduction in individual hours worked, reduction in aircraft altitudes, reduction in flight route latitudes and postponement or rerouting of flights during known solar particle events. In the classic occupational hygiene exposure control paradigm, these measures would be categorized as administrative controls: reducing the time exposed or increasing the distance to source. Clearly, there are no feasible engineering controls or personal protective controls such as aircraft or personal shielding. International Commission on Radiological Protection Publication 60 (1991) provided international recommendations that practices involving radiation exposures be justified by benefit to individuals or society, that protection be optimized by constraining individual doses or risks, and that limits be set for individual doses and risks. Additionally, proposed interventions should do more harm than good and the cost-benefit should be maximized. However, from a regulatory standpoint, differences exist between countries in the approach taken. In the United States of America, aircrew are not yet considered 'radiation workers' and occupational exposures to cosmic radiation are still treated as unregulated natural background radiation. The US Federal Aviation Administration (FAA) provides educational materials to increase awareness among flight crew, supports research and provides a tool (computer model) for estimating doses received on individual flights so that individuals or companies may assess total doses. Additionally, the US FAA has recommended that commercial airline companies provide education and training to aircrew, which some companies already do. Within the European Union, the Council Directive 96/29 Euratom (Articles 10 and 42) specifies that each Member State shall make arrangements for undertakings operating aircraft to take account of exposure to more than 1 mSv/a. The undertakings shall take appropriate measures, in particular: (a) To assess the exposure of the crew concerned, (b) To take into account the assessed exposure when organizing working schedules with a view to reducing the doses of highly exposed aircrew, (c) To inform the workers concerned of the health risks their work involves, (d) To ensure that the dose received by the fetus is kept as low as reasonably achievable and be unlikely to exceed 1 mSv following declaration of pregnancy. Both artificial radiation and naturally occurring occupational radiation exposures and risks require regulatory control, although the mechanisms for routine monitoring to achieve compliance will differ. For aircrew exposures to cosmic radiation, dose estimation rather than measurement is sufficient in most cases owing to the availability of reasonable, accurate models. Although exposure data are available and guidance has been developed for controlling aircrew exposures, there has been slow acceptance of this guidance outside Europe. There will be economic barriers to implementing some methods of exposure control, such as reducing flight altitude or re-routing, which incur fuel cost penalties, or flight postponement during significant solar particle events. In some cases, there may be resistance from affected flight crew, since seniority permits selection of schedules and higher dose schedules are more desirable since they involve fewer trips per month. As with reduction of artificial radiation exposures to as low as possible, optimization of protection against cosmic radiation exposures will require a balancing of societal, industrial and individual good.