There is one thing no-one seems to want to talk about concerning full body scanning of air travellers following the attempted crotch bombing of a Delta flight arriving in Detroit by a now seriously burned Nigerian terrorist.

That is the health consequences for frequent fliers of being repeatedly digitally stripped and intimately imaged at airports by devices that can see through clothes and at least part of the way into places where the sun don’t shine.

Sure, the expert advice if you search for it is that there is no health risk. Just as there was no risk from exposure to asbestos fibres (1960s) or smoking (1950s-1980s).

Older, if not ancient readers might recall that in the early 50s parents buying shoes would examine the bright green X-ray images of their children’s feet in special fitting boxes in the footwear departments of stores, and the use of glowing radium laced paint to illuminate the hands of clocks and watches was nearly universal. And perfectly safe, no, really!

But what is missing in relation to the machines now being pressed into everyday use at London and Amsterdam and possibly soon in Australia is a cast iron guarantee, that can be framed and hung on the wall, that says that repeated exposure to these techniques will not increase the risk of cancer.

Given that authorities are often quoted as saying that the chances of being killed by a terrorist attack on a plane are around one in ten million or arguably ten times less likely than choking to death from an allergic reaction to a peanut contaminated in-flight snack, ANY increased risk of death from cancer from such scans implies that the costs as well as risks of these additional measures are logically insupportable.

The Australian government hasn’t said it will introduce body scanners, so the guarantee question isn’t yet applicable here except that many of us will fly itineraries that may take us through such scanners twice daily at times, or many times in the course of the journey.

In fact the government supported a remarkably thorough trial of both X-ray backscatter devices and those using the millimetre wavelength part of the radio spectrum in the Adelaide, Melbourne and Sydney airports late in 2008, and will have the benefit of a detailed review of the copious amounts of data collected in those voluntary trials in the near future.

These trials seemed to lack the knee-jerk urgency with which such techniques have been endorsed abroad, in the US, UK and Europe.

That’s the good news bit. The differences in techniques are important. X-ray backscatter imaging uses X-rays and X-rays have carcinogenic potential, and because it works on the differential rate at which high energy photons are absorbed by organic rather than metallic or synthetic materials it can show up suspicious concentrations of stuff in places not even a pat down search might discover.

The backscatter technique can also be deployed passively over a significant area of the terminal, and zero in to and track persons if considered necessary. The millimetre wavelength techniques can achieve a similar result, but in general, involve standing in an open side kiosk, roughly the size of Dr Who’s Tardis, while rotating radio beams create a 3D in-depth nude image.

Note that the radio spectrum exploited by this technique is also used by the wi-fi networks you find in places like airports. It is very good over short distances, but doesn’t interfere with more widely used parts of the radio spectrum over larger distances.

Which brings us to privacy. The claims that the devices will distort a person’s face or other features to protect privacy are nonsensical. They are supposed to find bombs stuck up backsides! The logical response to the facial distortion claim would be to encourage nasal canal bombs. And the devices are supposed not to record any data. So much for evidence gathering, but then again, some nerd in one of the lounges has probably already captured the data using his wi-fi capable PC, filed it to a Fickr album, and told the Twitterverse of is whereabouts!

And, the news gets worse. None of the techniques coming into use abroad can detect explosives inserted way, way, up a rectum, in say a reinforced condom like device that could be passed and then detonated.

The whole ‘threat’ seems capable of lurching toward invasive physical examinations, ending in the collapse of air travel, if we follow the absurd logic that pervades a security scare industry that constantly seeks to create and then offer to solve new risks.

Is there any hope? A glimmer of hope comes from the caution with which the Obama review of security procedures is being conducted. Some of the more excessive responses to the Detroit incident has been dropped, notably through the limiting of special additional security procedures to passengers arriving in the US to only 14 countries. Security arrangements between Australia and the US remain very strict, but not as strict as they are for passengers who have started their journeys from or recently been in Afghanistan, Algeria, Iraq, Lebanon, Libya, Nigeria, Pakistan, Saudi Arabia, Somalia and Yemen, and the four countries the US State Department lists as sponsoring terrorism, Cuba, Iran, Sudan and Syria.