Airline body scanners


A ground swell seems to be building against the introduction of full body scanners at airports around the world.  The SMH reports today that Dubai has banned the scanners for privacy reasons.  On top of privacy concerns there are concerns about the radiation from the machines calling cancer.

One of my sisters is a radiologist.  She is a leader in her field of breast cancer screening and has published over 20 papers on the subject.  I asked her about the danger of extra radiation the other day.  She said that more radiation means more deaths, as simple as that.  If full body scanning becomes ubiquitous then tens of billions of scans at 0.1micro sieverts per scan will cause either hundreds or possibly thousands of extra deaths.

A full chest x-ray is apparently 100 micro sieverts; a lot more than a body scan.  The radiation is not intended to penetrate the body, but instead ‘back scatter’ from the skin to give an image of anything under clothing.  Moreover, airline travel involves a lot of radiation anyway.  A body scans equates to a few minutes of flying at altitude (I spend nearly 200 hours per year up in the air), and you inhale some nasty compounds when flying; who knows what they do to you.  But there is a problem will calibration.  A properly operated machine will give 0.1 micro sieverts but some machines will give much more, even ignoring the temptation for operaters to turn them up.

The cancer risk is low.  Probably a few hundred people will die young per decade if full body scanning is implemented world-wide.  The problem is that the terrorism risk is low too.  How many extra people do you expect to die on aircraft from terrorism over the next decade if the scanners are not installed —  a few hundred maybe, or fewer?  It is hard to compare improbable events.  We don’t know whether the cancer risk is higher or whether the terrorist attack risk (attacks that would not otherwise be prevented) is higher.

What weighs against the scanners is the right to privacy.  Going into public spaces involves giving up the right to some privacy.  The police have a reasonable right to insist the drivers submit to breath tests, for instance.  Saliva tests are on the edge of what is reasonable and they do not have the right to test your blood.  Police, in Australia, do not have the right to stop and search citizens without due cause (they soon will in WA).

I think I know how this will pan out politically.  The fear of terrorism will trump privacy and radiation issues if terrorism is front of mind.  Opposition to the scanners was building slowly until the planned attacks at Christmas time were narrowly thwarted.  Then, terrorism was back to front of mind.

It seems that the public has hyperbolic discounting of data when it comes to forming subjective probabilities.  Recent events are exponentially more important than more distant events.  This was true after Sept 2001.  It is also true in the global warming debate, where the public’s demand for action on global warming has collapsed since the end of the drought in Eastern Australia.

For me, the scanners are too much and the issue is privacy.  We should be able to go through public spaces without having our naked bodies exposed.  The invasion of privacy does not match the terrorist threat, net of the deaths from extra radiation.

3 Responses to "Airline body scanners"
  1. I wouldn’t be too worried about the radiation dose. According to Wikipedia the expected number of deaths is one per 200 million scans. If those numbers extrapolate with dose, that means about one death per million short-haul flights! Anyway, it depends on the technology – millimetre wave scanners are harmless.

  2. Average background radiation worldwide is about 2.4 millisieverts, about the same as 24,000 airport scans. So the passenger isn’t really at risk in this regard. For radiation workers a maximum exposure of another 20 millisieverts is considered “safe”. For the general public 1 millisievert is considered concerning – but that by itself is 10,000 scans.
    The radiation concern is a red herring where it comes to passengers, of more concern are the operators of the scanners and other airport employees, where continuous regular daily exposure could significantly build up.

  3. Plus there is the simple resource cost of scanning everyone – how many million dollars in capital costs, labour costs and extended checkin times will this cost per net life saved?

    I’d suggest that even within air safety there are an awful lot of things you could put the money into that would give a far bigger payoff.  Computer-assisted ground control systems, for a start.  But of course there’s another cognitive bias operating here – body scanners are salient to the public, ground control isn’t.

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