On full-body scans and air-travel safety

To go along with opt out day last week — a loosely organized day in which air travelers were encouraged to resist the new body-scanner machines, and in which some travellers did some special things to protest the feel your genitals ‘pat down’ that has been set up as an apparently punitive alternative — the New York Times published one of their Room for Debate columns on the topic.^[1]

I agree particularly with what Bruce Schneier and Rafi Sela have to say about it. That won’t surprise many, and it’s also not surprising that I have comments about the segments by Arnold Barnett and David Ropeik. Both present the standard false dichotomy, asking whether you’d rather be scanned and be safe, or opt out and let a bomber onto your plane.

Professor Barnett:

But then I remember a basic question. What if the 9/11 terrorists had been thwarted at the security checkpoint? We would have been spared not only the worst terrorist attack in American history, but probably two wars that have gone on for nearly a decade.

Mr Ropeik:

Flying any time soon? Would you rather the T.S.A. folks kept their hands off your body, or terrorist bombs off your plane? Seems like a simple choice, but as National Opt-Out Day looms, it’s worth considering why what seems like a simple question isn’t.

They both give us the same, basic argument: the scanners will thwart the terrorists. The arguments start with the presumption that they make us safer. The trouble is that there’s no clear evidence that they do. It’s not a choice between scanning and terrorist bombs. There are other inspection and investigation techniques, there are other ways to block the terrorists, and it’s easily arguable that these scanners are neither sufficiently effective to make us willing to submit to them, nor sufficiently cost effective for the expenditure to be worthwhile.

Mr Ropeik goes on to say this:

Compare those concerns against the reduced fear of being bombed on a plane. The emotional sharpness of September 11, 2001, and our fears, have faded. The threat hasn’t. We’ve had a shoe bomber, an underwear bomber, liquid bombers. But since our fear has ebbed, feeling coerced into taking a radiation risk or having our privacy invaded carries more weight.

He mentions three bombing plots. He doesn’t mention how many were successful: none. The shoe guy and the underwear guy were prevented, by older inspections that didn’t involve x-ray scanners, from bringing effective bombs aboard. What they did manage to get on board didn’t work, and they were apprehended in the process of trying to make them do something, anything. These weren’t screening failures, but screening successes. If we stop someone from bringing a sword into the plane and he has to try to make do with a plastic knife from the cafeteria, we don’t call that a failure, and suggest cavity searches to find plastic cafeteria-knives.

The liquid bombers, whether or not their plot would have worked, were stopped by investigation before the fact. They never made it to the security checkpoints at all, so screening was irrelevant to that case. Our security money should be going to more of these sorts of investigations, so we’re aware of the terrorist plots before they reach the airports, the train stations, the shopping malls, or the sports arenas.

Professor Barnett dismisses criticism without really addressing it:

The critics instead make two other arguments. The first is that the backscatter machines are ineffective because they cannot detect explosives in body cavities. The second is that recent security measures are very literally reactive: after the Shoe’s Bomber’s effort, the liquid-explosives plot, and the Underwear Bomber’s attempt, procedures were adopted to respond to these specific menaces. Indeed, the Yemeni bombs have led to a ban on printer cartridges in carry-on luggage.

All he has to say about either argument is, The more options we take ‘off the table’ from the terrorists, the more they are driven to more desperate plots that are less likely to succeed. But the point isn’t that we shouldn’t be taking terrorist options off the table. The point is that we have limited resources to throw at the problem, and we should be using them wisely.

A security mechanism that’s expensive and intrusive, that violates some of the basic rights we hold dear, that causes delays in travel and anger among the travellers, and that has an enormous potential for abuse by the authorities who administer it... had better be sufficiently effective to be worth all the expense, intrusion, violation, delay, anger, and abuse.

These machines don’t appear to meet that requirement.

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^[1] I have not yet experienced either the machines or the enhanced pat downs. I’ll report in these pages if and when I do.