With the recent round of terrorist attacks we can guess that airport security will be upgraded; that security will almost inevitably include additional x-ray screening – screening of luggage, of carry-on items, and possibly even of people. Given that there are always concerns about radiation exposure, it seems a good time to write about where we can find radiation at the airport and how this might affect the health of not only travelers, but also of those who operate the machines and work near them. So let’s take the sources of radiation one at a time and see what we can learn. But first, we need to know what radiation can do to us, so first let’s have a quick reminder of the health effects of radiation exposure in the short term and over a lifetime.
Radiation health effects
First, the units of radiation exposure are not well-known. Most of the world uses units of Sieverts (and all of the multiples of those) to measure radiation exposure. On average, people around the world receive about 2-3 mSv of radiation exposure from nature from cosmic radiation, radioactivity in the rocks and soils, radon, and radioactivity that occurs naturally in the human body. Around the world the levels can change considerably, from about half to over 10 times this average. It’s important to note that this variability in natural radiation exposure does not seem to have any negative impact on the health of people living in these areas – this suggests to me (and others) that our bodies might be able to tolerate this level of variability in radiation exposure without posing us harm.
In the short term, the lowest dose that has any noticeable health impact is about 0.25 Sv – equal to about 10,000 years of exposure to natural radiation and what one would receive from, say, 10-20 whole-body CT scans. At this level of exposure the person receiving the radiation will not feel any physical symptoms at all, but a doctor would notice that their blood cell counts drop steadily for a few weeks or so, then would creep back up over the next few months. At about 1 Sv of exposure a person will develop mild radiation sickness that could last for a few weeks, after which they’ll recover. A dose of 4-5 Sv gives a person severe radiation sickness and a 50% chance of death in the absence of medical treatment (with the best medical treatment it takes about 7-8 Sv to be 50% fatal), and a 10 Sv dose is invariably fatal. Now – having said all this, the x-ray machines at airports are not nearly powerful enough to cause even the least of these effects – I’ll get to this shortly.
Over the long term we worry about developing cancer as from radiation exposure. But at a dose of 1 Sv (100 rem) the risk of dying of cancer is only about 5%; the risk is about 1% at a dose of 200 mSv (about a century’s worth of natural radiation). At the much lower levels that radiation workers and the public are exposed to the risks of developing a fatal cancer are far, far lower. For example, in most of the world the annual dose limit for a radiation work is about 20 mSv annually – a decade’s worth of receiving this level of radiation would give one only a 1% chance of contracting a fatal cancer. And in reality the risk is likely smaller still, according to a number of epidemiological studies.
X-ray machines are used to scan luggage, carry-on items, and (sometimes) to scan people. Let’s take the last one first.
X-rays can be used to scan people by either passing through a or by looking at how they’re reflected off of a person (and whatever they might be hiding inside or beneath their clothing); what’s called backscatter x-rays. I’ve measured radiation exposure from both of these methods and both expose a person to measurable – but low – levels of radiation. Specifically, a backscatter x-ray machine exposes the person being surveyed to a fraction of a microSv of radiation each time and I’ve measured comparable doses from the x-ray machines that send the radiation through a person to look for, say, something harmful that might have been swallowed or implanted. At this level of exposure, it would take over 200,000 such scans to give a person a 1% chance of developing a fatal cancer.
For people standing outside the x-ray scanners the risks are also low. By law in the developed world (and in most of the rest of the world as well) radiation exposure leaking from the machines is limited so that the operators cannot be exposed to dangerous levels of radiation. After a working lifetime (50 years) of exposure to these machines a person would have about 50 mSv of radiation exposure, posing a much lower risk to their health than their daily drive to and from work. And if you make a mistake and pass your pet through the carry-on luggage scanner (believe it or not this happens – one guard told me he’s even seen children in car seats pass through the devices) – you don’t need to worry about their health. This, again, is based on measurements I’ve made myself.
Cosmic radiation during the flight
We are continually bombarded with radiation from the cosmos, some of it from the Sun, but most (at least at sea level) from beyond the Solar System. Normally this gives us about 0.25 mSv every year. Although air is not a very effective radiation shield there’s about 1 kg of air in the atmosphere above every single square centimeter of the Earth’s surface at sea level, and 1 kg of air will reduce radiation dose rates by a factor of tens of millions. Without air, the Earth’s surface would be blasted by cosmic radiation; with air we can live here quite comfortably.
During flight, we’re above a good fraction of the Earth’s atmosphere and we lose that amount of radiation shielding, so radiation dose rates are higher at higher elevations. Flight crews, who spend a great deal of time aloft, receive up to 10-15 mSv annually and business travelers, unless they really on the miles, receive less. During my years as a consultant I was flying from 100,000 – 150,000 km annually, picking up about 1-2 mSv as measured on my dosimeter. This is certainly a measureable exposure, but if I were to receive this dose every year for 50 years my cumulative exposure would be about 100 mSv, giving me about one half of one percent (0.5%) risk of developing a fatal cancer. As far as the pilots and flight attendants, according to the scientific studies that have been performed, flight crews don’t have any higher risk of cancer than do the public at large. What does this mean for you? Worry about deep vein thrombosis, sharing air with possibly sick strangers, and bad food, but don’t sweat the radiation.
We can’t get away from radiation – from nature or when we fly. And radiation can cause health risks – there’s no doubt of that. But the amount of radiation that it takes to cause health effects is so much greater than the amount of radiation we encounter at the airport or in the air that it’s safe to say it simply does not put us at risk. This is not only my opinion – it’s also based on measurements I’ve made with my own instruments and it’s corroborated by epidemiological studies performed on flight crews.