As part of a defensive move in the war on terror, air travelers now have to choose between being scanned by a machine that produces an image of their naked bodies, or submitting to a thoro body search that includes the hands of examiners touching the most intimate parts of their bodies. This move was inspired by the failed Christmas 2009 "underwear bomber" attack [Wikipedia-4]. A previous move was to restrict carry-on liquids in response to a 2006 conspiracy foiled by UK police [TSA]. Prior to that was the requirement that passengers remove their shoes before passing thru the security gate, a response to the bungled 2001 "shoe bomber" attack [Wikipedia-2].
The latest move is worth examining more closely as it involves a number of interesting issues, such as the possible health risks imposed on passengers and others, the issue of human dignity, the matter of efficacy of the process, and the overall question of just how serious is the danger being guarded against.
Two types of body scanners are used in airports. One is the millimeter wave scanner [Wikipedia-3]. Apparently, possible biological effects of exposure to this range of electromagnetic radiation have not been studied to the same extent as the lower frequency radiation associated with cell phones. But there is a credible theory showing how it might damage DNA [KFC].
The other type scanner is the backscatter X-ray machine. Unlike ordinary X-ray machines that generate powerful X-rays that penetrate the body and produce images on film behind it, showing details as shadows, the backscatter system's weaker X-rays penetrate only skin deep and are scattered back to a display screen. Because the energy involved is relatively low, it is claimed that, compared to ordinary X-rays, only a very small amount of energy is absorbed by the body.The TSA (Transportation Security Administration) says that the radiation dose per backscatter X-ray screening is less than that received in 2 minutes when flying at usual airline altitudes [Wikipedia-1]. (Another TSA source gives this number as 3 minutes [AP], and an FDA source states it as 4 minutes [Knox]). In other terms, they say it would take 5000 screenings to equal the exposure corresponding to one chest X-ray. This does not seem to be problematic. But various scientists knowledgeable in the field have expressed concern [Knox][Zeitvogel][Holt].
One point raised by a group at the University of California, San Francisco (UCSF) is that the radiation dose, 0.02 microsieverts (joules/kilogram) given by the manufacturer (Rapiscan) is averaged over the whole body, while, in actuality, the energy is almost all absorbed by the skin. So the relevant number is actually much greater, tho they don't know by how much. This poses increased risks for people particularly vulnerable to skin cancer. Another issue is that people with certain gene mutations, about 5% of the population, are more sensitive to radiation, as are children and pregnant women. The figures given for radiation exposure by the company, and the TSA have not been objectively validated by independent experts. For example, testing by a group from Johns Hopkins University was on units specially prepared by Rapiscan, not on regular production units.
David Brenner, head of Columbia University's Center for Radiological Research, served on a government committee issuing a report approving the scanners several years ago. He feels that the risks posed by the scanners to any individual are very small, but has concerns about those particularly sensitive (see above), and, perhaps more important, about the fact that tens of millions of people may go thru the scanners annually. So, even if only a tiny percentage were adversely affected, it could lead to a significant number of deaths or other harmful affects. He said that he would not have signed the report had he known the scanners would be so widely used.
He suggested that, since it is unlikely that anyone could conceal anything dangerous anywhere above the shoulders, and since the neck and head areas are especially sensitive to radiation, it would be wise to limit the scanning to below the neck. This idea was rejected by the TSA because having to adjust the height of the scanner for each person would slow the process too much.
There are other safety-related concerns. One pertains to maintenance. A hazard associated with any device exposing people to radiation is that some failure might occur that greatly increases the exposure. In the case at hand, a high intensity beam scans the body. Suppose some failure halts the scan so that the beam stays focused on one small area. This could have very serious consequences for the person being scanned. With about a thousand of these machines in use 24/7, a very high quality maintenance program and staff would be needed to rule out disasters. How likely is it that the TSA can achieve this?
Clearly, frequent fliers will undergo numerous scans annually. Pilots are obviously in this category. Treating them as potential terrorists prior to each flight makes little sense. But it took the intervention of the pilot's union to get theTSA to stop requiring them to go thru the scanners. Flight attendants are apparently not as well represented, so they continue to be scanned for each flight.
Presumably there are TSA personnel standing near the scanners, to instruct people, etc. Since there is significant radiation in the vicinity of the devices, those working in such locations might absorb a good deal of radiation. Instead of setting up procedures to monitor such exposure, there are reports that the TSA has explicitly prohibited its staff from wearing radiation badges to record their cumulative exposures [Flatow].
Finally, while Rapiscan assures everybody that their scanners are harmless, they are not taking any chances. They applied for and received protection under the SAFETY act, which limits their liability in the event that their assurances turn out to be unfounded and a lot of damaged people sue them. (The SAFETY act is a federal law to partially shield manufacturers of security related equipment against law suits. E.g., punitive damages are barred [FedReg].)
An obvious question is, "Would the scanners now being deployed have caught the underwear bomber, who inspired their adoption?" The answer is a definite, "maybe" [Hsu][Holt]. One point is that, while the scanners can show dense explosives, such as C4, it may not show more powdery, low density substances such as were used by the underwear and shoe bombers. It might also miss explosives composed of thin sheets, or fabrics.
Another problem is a human one. The people operating the scanners are sitting in a booth staring at a screen showing an endless sequence of human bodies that they must inspect to look for anomalous features. This might be an exciting job at first, but surely would become exceedingly tedious when performed day after day. It is not the sort of thing that people do well. One commentator, who spent some time in such a booth, referred to his eyes glazing over after 15 minutes [Leocha][Goldberg].
The scanners are intended to detect attempts to carry explosives or weapons onto airliners. How serious is this problem? First note that, if the blundering underwear bomber had succeeded in detonating the 80 grams of explosive material he had smuggled onto the plane, he would have been killed, and very possibly the person sitting next to him would also have died. A number of other passengers might have suffered ruptured eardrums. But that's about it. There probably would have been no significant damage to the airplane, according to the results of a BBC study based on an experiment [Bland]. The results would probably have been similar if the shoe bomber had managed to set off his explosives, as he carried a similar amount of the same material.
Almost every week, several attempts are made by diabolically clever terrorists to down another US airliner, and about half of these attempts are succeeding, killing about a thousand Americans monthly. Of course, this statement is nonsense. There have been no successful terrorist attacks on US aircraft since 9/11. Over the past decade, since 9/11, I believe the only attempts made to attack American airliners were the three botched efforts mentioned above. (Were there others that I overlooked?). It is noteworthy that these were not 9/11-style hijack attempts designed to use the planes as missiles to destroy other targets. Rather they were efforts to bring down a single airplane.
But our government is behaving as tho the nightmare scenario sketched above corresponded to reality and justifies extreme measures. Does it make sense to grossly violate the dignity and privacy of millions of Americans on a regular basis, exposing them to possibly life-threatening radiation, and to spend billions of dollars annually, in order to defend against a threat that is largely fictitious?
I am not claiming that there is no threat at all, or that we should not do anything to ward off attacks on airliners. Reasonable measures include screening passengers and their carry-ons via metal detectors to check for firearms or other serious weapons (not including pen knives with two-inch blades), arming the pilots, and keeping the door to the flight deck locked. Explosive-detecting dogs (currently used in some places) might be deployed more widely in airports [Clayton]. Perhaps the TSA could learn something from the Israelis, who rely heavily on questioning passengers [NextBig].
Making passengers take off their shoes is absurd, and only slows down the process, wasting everybody's time. No matter what we do, we won't be able to guarantee that no attack could succeed. That simply reflects the nature of the real world. With roughly 30,000 commercial fights daily in the US, the possibility of one being sabotaged every year or so should not lead to panic any more than the occasional airliner crash due to technical failure.
A more fundamental way to combat terrorism would be to stop doing what motivates people to sacrifice their lives in attempts to harm us. Every assault by US forces in Iraq or Afghanistan or Pakistan or Yemen or Somalia that kills or injures Muslim civilians outrages other Muslims, some of whom join or support groups hostile to us, and a few of whom seek revenge directly. The War on Terror is, paradoxically, a great machine for producing anti-American terrorists [Unger].
AP, "Gov't: Airport body scanners' radiation not a health threat", USA Today, 11/18/2010
Eric Bland, "'Underwear Bomber' Could Not Have Blown Up Plane", Discovery News, Mar 10, 2010
Mark Clayton, "Should TSA let airport passenger screening go to the dogs?", The Christian Science Monitor, November 30, 2010
FedReg, "DHS Safety Act", Federal Register / Vol. 71, No. 110, June 8, 2006
Ira Flatow, "Airport Screeners: Denied radiation badges?", Science Friday, September 13, 2010
Jeffrey Goldberg, "The Things He Carried", Atlantic Magazine , November 2008
Rush Holt, "Holt Continues to Question Science, Effectiveness of TSA Full Body Scanners"Holt Website, November 22, 2010
Spencer S. Hsu, "GAO says airport body scanners may not have thwarted Christmas Day bombing", Washington Post, March 18, 2010
KFC, "How Terahertz Waves Tear Apart DNA", Technology Review, 10/30/2009
Richard Knox, "Scientists Question Safety Of New Airport Scanners", NPR, May 17, 2010
Charlie Leocha, "Would full-body scanners have stopped the Christmas bomber? Probably not", Consumer Traveler, January 5, 2010
NextBig, "Israeli Airport Security", nextbigfuture.com, December 30, 2009
TSA, "UK 2006 Liquid Explosives Plot Trial Overview", TSA News Ticker, September 7, 2009
Stephen H. Unger, "The War On Terror: An Exercise in Hypocrisy", Ends and Means, March 19, 2009
Wikipedia-1, "Backscatter X-ray", Wikipedia
Wikipedia-2, "Richard Reid (shoe bomber)", Wikipedia
Wikipedia-3, "Millimeter wave scanner", Wikipedia
Wikipedia-4, "Northwest Airlines Flight 253", Wikipedia
Karin Zeitvogel, "'Naked' scanners at US airports may be dangerous: scientists", AFP, Nov 12, 2010
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