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Friday, 10 December, 1999, 02:05 GMT
Flying boosts radiation dose

High altitudes increase radiation exposure

Increased air travel is responsible for a jump in the amount of natural radiation to which Britons are exposed.

The official figures, from the National Radiological Protection Board (NRPB), come as separate research shows that airline pilots have more chance of developing one form of leukaemia.

It's surprising how few members of the public are aware of this cosmic radiation
Dr Michael Clark, NRPB
This is blamed on "cosmic radiation" from the sun, which is more intense at the altitudes reached by modern aircraft.

However, the increased risk of acute myeloid leukaemia was noticed only in pilots who had clocked up more than 5,000 flying hours in their careers.

Experts have stressed that even frequent flyers will not accumulate a high dose.

The NRPB's 1999 radiation dose review reveals that nuclear power workers, on average, now receive a lower annual average dose of radiation than aircrew.

Radiation doses (milli Seiverts)
UK yearly dose 2.6
Chest x-ray .02
Fortnight in Cornwall 0.2
Bag of Brazil nuts a week 0.2
Jar of Mussels a week 0.25
Frequent flyer 0.4
Overall, the average exposure of the UK population to radiation has stayed the same, due partly to decreasing exposure to "man-made" radiation.

The average UK dose is 2.6 milli Seiverts (mSv), but the highest average was in Cornwall, where naturally-occurring radioactive radon gas raises this to 7.8 mSv.

A frequent flyer aloft for around 100 hours a year would receive an additional annual dose of approximately 0.4 mSv.

Medical procedures increase radiation doses
Dr Michael Clark, a scientific spokesman for the NRPB, said: "It's surprising how few members of the public are aware of this cosmic radiation.

"But even frequent flyers get doses that are within the acceptable normal ranges."

The study, published in the Lancet, examined Danish male jet cockpit crew flying more than 5,000 hours.

The researchers estimated that such crew members receive up to nine mSv a year.

Out of 3,877 crew, 169 developed cancer, compared to 153 in a similar-sized sample of non-pilots.

The pilots suffered more cases of skin cancer, but this was explained by the theory that many spent more time than non-pilots in sunny climes.

The increase in leukaemia cases was described as "significant" - and the researchers suggested that as airline pilots may be naturally more healthy than the average person, the risk may even have been underestimated.

However, they said the increase did not represent a "major effect".

Other studies

Four other studies have shown increased cancer mortality in pilots, and one found a higher incidence of breast and bone cancer in female cabin crew who had been flying for more than 15 years.

One, involving Air Canada pilots, showed an increase in acute myeloid leukaemia.

However, a study carried out by British Airways showed that its pilots and flight engineers had a reduced risk of dying from cancer.

The airline has installed cosmic radiation monitors in its flagship aircraft Concorde, which flies at much higher altitude than conventional aircraft.

Because the flight is far quicker, passengers and crew under normal circumstances would receive a lower dose than on a normal flight, but in times of abnormally high radiation levels, such as during a period of solar flares, the pilot may be warned to reduce height.

As much as 85% of the average annual radiation dose comes from natural sources.

Half the "natural" exposure comes from exposure to radioactive radon gas, with the rest from internally produced radiation, small levels of uranium and other radioactive substances in soil and rocks, and cosmic radiation.

"Man-made" sources are mostly medical x-rays and CT scans, with less than one per cent coming from nuclear discharges, fallout from nuclear testing in the 1960s and radioactive paint used on "glow-in-the-dark" watches.

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