We are exposed to a certain amount of background radiation all the time – it does occur naturally – so of course we would expect to find it on a flight too. In recent years though, there have been a lot of questions about whether radiation levels are significantly higher on a plane than they are on the ground.
In fact the levels of cosmic radiation (ie radiation from away from the Earth, rather than terrestrial radiation) are slightly higher on a plane. This isn’t to do with the plane itself or the fact of air travel, but to the fact that on a flight you are usually somewhere around 1000 metres above the Earth, and at that height the atmosphere doesn’t offer the same protection from radiation as it does on the ground.
Ionising radiation, which is what we are exposed to, is measured in units known as sieverts or Sv. These are divided into units of 1000 called millisieverts, so 1000 mSv is one sievert. The radiation we are normally exposed to varies a lot according to where we live – it is affected by naturally radioactive material which is found in rocks, soil, water and even the air, as well as the kind of buildings in the environment, any nuclear testing facilities nearby and many other factors. Over the whole world, the average yearly dose of radiation for one person is 2.4 mSv. In a few places the dose is much higher; for example, in some parts of India levels of 15 mSv have been recorded. The highest level
The highest permitted level of exposure, for emergency workers after a nuclear accident, for example, is 50 mSv. A similar level was formerly the maximum permitted dose for a year for nuclear plant workers (today in most countries the maximum yearly dose is around 20 mSv). However, occasionally workers are allowed to be exposed to much higher levels even than this, when it is a question of saving lives. At 100 mSv increases in cancer and other radiation related sicknesses are reported. If you get up to 1000 mSv or 1 Sv, it would be expected that about 5% of people exposed to this level would go on to develop cancers, even after short-term exposure.
In contrast to these very high levels, even flight attendants and other airline workers, who of course are exposed to higher radiation a lot of the time, even on routes with a naturally higher radiation level, don’t get anywhere near these rates. For example, the annual radiation dose for airline crew on the Tokyo to New York polar route, which does involve relatively high exposure, is 9 mSv. This is more than three times world average levels, but well below the limit considered safe, and most people working on airlines can expect levels of around 4 mSv, so less than twice the average. No unusual illnesses have been reported in people working in the airline industry so far.
There is some evidence that members of the public who take a lot of journeys on long-haul flights – where, as we saw earlier, radiation protection is less because of the higher altitude – can get increased radiation levels, but the amount is small. Frequent flyers are at much more risk from deep vein thrombosis than any other illness.
In the past there were also scares about the radiation risk from airport scanners. However, it now seems clear that the levels from these are too low to do any harm – about the same as you would get in a minute or so of exposure to the ordinary air.
You can get a good overview of different radiation levels here. A specific article on airline radiation can be found here.