Frequent flyers on transatlantic flights are exposed to the equivalent of 170 chest X-rays a year, putting them at increased risk of cancer, according to the US Federal Aviation Administration.

The law ensures that people who work in hospital X-ray units and nuclear plants are get as much protection as possible from exposure to radiation, but there are no similar laws applying to the risk from air travel.

The European Commission is currently examining the issue, and from May 2000 airlines will have to measure radiation levels on flights.

Tackling the issue

Specialists from government bodies, the health service and industry will discuss the problems at a one-day seminar on cosmic radiation organised by the Aviation Health Institute.

The National Radiological Protection Board (NRPB) says that aircrews are exposed to 4.6 millisieverts (mSv) each year, compared to nuclear workers who are exposed to 3.6mSv.

Cosmic radiation from the sun gets stronger at higher altitudes because the atmosphere thins out and is less able to offer protection from the rays.

Different types of plane fly at different altitudes - 737 jumbo jets, for example, cruise at 37,000 feet while Concorde goes to 60,000.

Although the danger posed on a single flight is insignificant, repeated exposure does appear to increase the risk of cancer.

Nine studies in North America and Europe have shown increased rates of cancer among those who work in aeroplanes.

Pilots are more likely to get colon, rectal, prostate and brain cancers, while flight attendants are twice as likely to suffer breast cancer.

Aircrew members who are pregnant could also be putting their unborn children at risk of diseases such as Down's syndrome and leukaemia.

Low risk for casual flyer

The general public is at little risk because they are unlikely to make enough journeys at a high enough altitude to suffer high exposure over time.

One study showed double the risk of breast cancer among flight attendants

However, there is some concern over the effect on couriers or businessmen who may fly regularly.

Executives are also likely to fly regularly in private jets, which fly at around 43,000 feet.

There is currently no legislation addressing exposure to radiation through air travel, although a European Commission directive could change that.

The Euratom directive will require European airlines to measure levels of radiation on flights.

The information will be used to assess the risk of cancer and birth defects, and will include about 80,000 people. The earlier studies involved about 5,000 to 10,000.

'Companies should be aware'

Farrol Khan, director of the Aviation Health Institute, said companies who sent employees on regular trips by plane should be aware of the risks and inform their staff accordingly.

"Otherwise, this could become litigation in the future if you knew there is a problem and you didn't tell your employees about it," he said.

"Then six years later they end up with cancers, and they say 'ah, but you knew there was a risk six years ago, why didn't you tell us? We're going to sue you'."

Patrick Slomski, an aviation lawyer who will address the seminar, said better information was better for all parties.

"This may help forestall litigation that is clearly undesirable for the airline or its customers."

Dr Michael Clark of the NRPB said it may be possible that certain cancers were more likely among aircrews, but on the whole their health was good.

He said: "As far as I understand it, aircrews are actually healthier than the general public, because to be selected as a pilot or a flight attendant you have to go through a health check.

"After that you have regular check-ups, so you may get the healthy worker effect."