In the name of anti-terrorism, governments worldwide are turning to new machines. There is a new type of airport security scanner, which has already been accused of causing cancer and invading your privacy. Thankfully, it doesn’t require us to sit in a grey tub on a conveyor belt.
I took four round-trip flights last year: if you do the same next year, what effects might the radiation from scanners and flying have on your health?
A new type of scanner shines X-rays on to you, and measures what bounces off. It’s flash photography with an invisible flash. The machines use this back-scattered radiation to reveal guns, liquids, and knives, and also an intimate outline of your beautiful body. It’s in use in the United States, and is less widespread in the UK, and we’re mostly allowed to opt out of it in favour of a pat-down.
Radiation from airport scanners sounds dangerous, but is it? To answer this, we need to understand how some types of radiation can cause cancer – and then whether the new scanners pose a threat to air passengers’ health. ‘How dangerous’ is something that can be quantified, as a probability: which is more likely: developing cancer after 4 round trips, or dying in a plane crash in one of them? The main difference between catastrophe and cancer is that people almost always die quickly from a plane crash, but radiation exposure might kill them with cancer twenty years later.
Radiation exposure does not have a straightforward relationship with risk of cancer. Overexposure to radiation is like sunburn, except the burn is more than skin deep. Gentle sunshine does little harm, but half an hour at midday at the equator would burn my light skin. The intensity makes a difference to the health effects because of the way your body deals with the damage.
When a particle of radiation damages the DNA in a cell of your body, exquisite protein machines repair it in a few minutes. In some circumstances, the cell can spiral out of control and begin dividing into rogue cells, ultimately becoming cancer. This often happens when the DNA which codes for the repair mechanism itself is damaged – rather as Douglas Adams described the amusing fate of a spaceship hit by an asteroid: unfortunately the asteroid destroyed the ship’s asteroid impact detection and repair module.
There is a soft light of radiation around us all the time. This comes mostly from rocks beneath us, and the sky above, but if you concentrate a year’s worth of background radiation into a few seconds, it is more harmful, because it is more likely that vital parts of the DNA are broken.
Radiation from flying
Astronauts are exposed to high levels of radiation when in space. When we fly, typically at about 30,000 feet (~9,000m) this puts us above most of the dense protective part of the lower atmosphere. But we get a lot less radiation than astronauts, because there is still some thin upper atmosphere above us.
It is impossible to say that an individual will get cancer because of a particular flight, or even from frequent flying over a lifetime. Cancer gets nearly half of us in the end, and we are surrounded by causes of cancer, not least second-hand cigarette smoke, half of our food, (the other half cures cancer, according to some magazines), alcohol, pollution, and so on. Despite this, all these radiation sources are low intensity: for the 100 million people who make at least one flight per year, the radiation exposure at high altitude will account for only 600 cancer deaths over a lifetime (0.0006%).
Now consider the four round-trip flights: this means a risk of death of 1 in 110,000. Although this may seem large, imagine being in a crowd of 110,000 people, for example, in a completely full sports stadium, standing room only; of those people, 44,000 would die of cancer, but in only one unidentifiable person would it be due to flying.
How do the new scanners compare?
If 100 million fliers in the world were scanned before every flight they made during one year, an extra six cancer deaths would be caused over their lifetime. Remember that 40 million out of the 100 million would have got cancer anyway; in contrast, the risk of a scanner eventually causing my death from cancer for my four round trips is 1 in 16 million.
Here is a comparison of the risks of death for eight medium length flights:
cancer from x-ray back-scatter: 1 in 16,000,000 (death after many years)
air terrorism: 1 in 11,500,000 (immediate death)
air crash: 1 in 1,070,000 (immediate death)
cancer from flying at altitude: 1 in 110,000 (death after many years)
The radiation dose from an airport scanner is low, and we can see that scanners are a tiny contribution to the total risk of using air transport.
Going out with a scan or with a bang: is the scanner radiation worth the risk?
The risks of cancer from the scanner and the risks from terrorism for my four round trips are both very small compared to the others. The difference is that the scanner cancer death is decades away, but a terrorist takes away more of my potential life. Governments need to weigh the privacy invasion of the new scanners against their terrorism-reducing benefit. As far as my life and country are concerned, I should accept a scan; but as a private individual, I’d opt for the pat-down.