Cataract, cosmic rays and air travel
The annual radiation doses received by pilots and cabin crew are two to three times that of normal background radiation
VULNERABLE WORKFORCE: Research shows that exposure to cosmic radiation increases the risk of `nuclear cataract’ in airline pilots and other frequent flyers. — Photo: K. Pichumani
COSMIC RADIATION increases the risk of nuclear cataract in airline pilots, according to a study by Dr. Rafnsson and his colleagues in the August 2005 issue of the Archives of Ophthalmology. Cosmic rays are highly energy particles and radiation, which bombard the earth from outer space.
Nuclear cataract, the most common form occurs at the centre of the lens. The researchers examined 445 men (71 commercial pilots and rest were control group), aged 50 years or older. 71 had nuclear cataract; only 15 were pilots.
The authors found that pilots with long years of flying experience had about three times risk from nuclear cataract compared to others, even after accounting for other risks factors.
They estimated the radiation dose to pilots based on employment time, annual number of hours flown on each type of aircraft, timetables and flight profiles. Pilots who worked for more time had more exposure to cosmic radiation; they had greater chance of developing nuclear cataract.
Dr Michael Clark from the UK Health Protection Agency thinks that cosmic radiation was unlikely to be the cause of the pilot’s cataract.
BBC quotes him as saying that the annual radiation doses received by the pilots and aircrew are two to three times that of normal background radiation. “This is well within the range of variations in background doses at ground level, so we would not expect to see any health effects,” Dr Clark clarified. The report on cataract of pilots remains controversial.
In 1990, the International Commission on Radiological Protection (ICRP) proposed that employers should consider pilots and cabin crew as occupationally exposed and that they must monitor their exposure levels.
European Union directed that for the crew who are liable to be exposed to more than one millisievert (mSv) annually, the employers must assess their exposures. (millisievert is a unit of radiation dose; one mSv per year is the ICRP dose limit for general public and 20 mSv per year averaged over five years is the dose limit for radiation workers including pilots).
The employers should consider the assessed exposures when organising work schedules. Control of dose to aircrew is feasible.
Doses to aircrew
FAA’s Civil Aero-medical Institute, USA, estimated the radiation doses to aircrew in 32 one-way flights (including some long haul) to different destinations. It varied between 0.023 to 0.80 mSv in a 100 hr block.
The largest annual dose received by a crew member who works for 1000 block hours a year is much less than the dose limit of 20 mSv recommended by the ICRP.
The European Directive stipulates that the radiation exposure to pregnant crew should be as low as reasonably achievable. ICRP considers the foetus as a member of public; the dose limit to foetus is one mSv starting from the declaration of the pregnancy. In addition, the Federal Aviation Administration (FAA), USA prescribes a monthly limit of 0.5mSv.
Pregnant crew can minimise dose by working on short, low altitude, low latitude flights. At the lower exposure level, radiation dose to foetus would not exceed the limit, regardless of the number of months flown.
Dose to some frequent business travellers may exceed the annual limit of one mSv. For them, we may justifiably apply the annual occupational limit of 20 mSv. ICRP supports this view. The radiation dose to an occasional airline passenger will be negligible. Both groups need not worry over radiation risks.
(The author is Raja Ramanna Fellow with the Department of Atomic Energy