Virtual strip search scanners won’t catch key explosives

The TSA is working to put full body visual scanners that see through clothes in the world’s airports. But a British newspaper says what I had thought myself, that they will just see through low-density chemicals such as those used by the Underwear Bomber:

Since the attack was foiled, body-scanners, using "millimetre-wave" technology and revealing a naked image of a passenger, have been touted as a solution to the problem of detecting explosive devices that are not picked up by traditional metal detectors – such as those containing liquids, chemicals or plastic explosive.

But Ben Wallace, the Conservative MP, who was formerly involved in a project by a leading British defence research firm to develop the scanners for airport use, said trials had shown that such low-density materials went undetected.

Tests by scientists in the team at Qinetiq, which Mr Wallace advised before he became an MP in 2005, showed the millimetre-wave scanners picked up shrapnel and heavy wax and metal, but plastic, chemicals and liquids were missed.

If a material is low density, such as powder, liquid or thin plastic – as well as the passenger's clothing – the millimetre waves pass through and the object is not shown on screen. High- density material such as metal knives, guns and dense plastic such as C4 explosive reflect the millimetre waves and leave an image of the object.

About Gene Veith

Professor of Literature at Patrick Henry College, the Director of the Cranach Institute at Concordia Theological Seminary, a columnist for World Magazine and TableTalk, and the author of 18 books on different facets of Christianity & Culture.

  • Pete

    Even though small amounts of chemicals and liquids may be missed by the body scanners, as demonstrated by the shoe and underwear bombers, small amounts of anything are more likely to fail than succeed if you’re trying to blow up an airplane. My recollection is that it took a Ryder truck full of ammonium nitrate for Timothy McVeigh to blow up the building in Oklahoma City. The body scanners, admittedly not perfect, strike me as a useful tool for the good guys. Body scanning would still have to be accompanied by alert observation by trained TSA personnel as well as all the other security measures already in place.

  • Pete

    Even though small amounts of chemicals and liquids may be missed by the body scanners, as demonstrated by the shoe and underwear bombers, small amounts of anything are more likely to fail than succeed if you’re trying to blow up an airplane. My recollection is that it took a Ryder truck full of ammonium nitrate for Timothy McVeigh to blow up the building in Oklahoma City. The body scanners, admittedly not perfect, strike me as a useful tool for the good guys. Body scanning would still have to be accompanied by alert observation by trained TSA personnel as well as all the other security measures already in place.

  • http://wipfandstock.com/store/As_Though_It_Were_Actually_True_A_Christian_Apologetics_Primer Matt C.

    It’s fair enough that security measures need not be infallible — nothing is foolproof and they are merely mean of reducing the number of successful attacks by making it more difficult on terrorists. As Pete points out, stacking different techniques is useful.

    The corollary of this, of course, is that one needs to do a cost-benefit analysis of a new technique rather than a panicked embrace. How useful is the new measure?

    According to the bureau of transportation statistics, there have been about 5 million domestic passengers enplaned by U.S. Air Carriets since Sept, 2001 and about 660,000 international passengers enplaned. This measure would not have protected any of those passengers (since they were fine without it), but it is conceivable that it might protect somebody down the line (the incident that sparked this new security suggestion was closer than we would have liked to come to a disaster). So for the sake of simplicity, let’s say:
    *this scenario will happen again once for the same number of passengers over about the same amount of time on a flight of the same size (290 people).
    *there is a 50% chance the plot will succeed w/o extra intervention.
    *there is a 50% chance the new scanners will catch it.

    Statistically speaking, the new measure would protect 72.5 passengers over about 8 years or .000017 % of passengers. The question that needs to be asked is whether this gain is worth violating the dignity and modesty of 5.66 million (along with any other costs associated with it).

    My opinion: Terrorism of this kind is not a significant threat to me. Would I parade my wife and myself around naked in front of strangers for that extra .000017% of protection? Would I demand that millions of others do the same? No; No I wouldn’t. There’s no such thing as total 100% security and therefore there is a certain point at which one must say “it’s not worth it” when faced with new, invasive security procedures. I think we’re well past that point.

  • http://wipfandstock.com/store/As_Though_It_Were_Actually_True_A_Christian_Apologetics_Primer Matt C.

    It’s fair enough that security measures need not be infallible — nothing is foolproof and they are merely mean of reducing the number of successful attacks by making it more difficult on terrorists. As Pete points out, stacking different techniques is useful.

    The corollary of this, of course, is that one needs to do a cost-benefit analysis of a new technique rather than a panicked embrace. How useful is the new measure?

    According to the bureau of transportation statistics, there have been about 5 million domestic passengers enplaned by U.S. Air Carriets since Sept, 2001 and about 660,000 international passengers enplaned. This measure would not have protected any of those passengers (since they were fine without it), but it is conceivable that it might protect somebody down the line (the incident that sparked this new security suggestion was closer than we would have liked to come to a disaster). So for the sake of simplicity, let’s say:
    *this scenario will happen again once for the same number of passengers over about the same amount of time on a flight of the same size (290 people).
    *there is a 50% chance the plot will succeed w/o extra intervention.
    *there is a 50% chance the new scanners will catch it.

    Statistically speaking, the new measure would protect 72.5 passengers over about 8 years or .000017 % of passengers. The question that needs to be asked is whether this gain is worth violating the dignity and modesty of 5.66 million (along with any other costs associated with it).

    My opinion: Terrorism of this kind is not a significant threat to me. Would I parade my wife and myself around naked in front of strangers for that extra .000017% of protection? Would I demand that millions of others do the same? No; No I wouldn’t. There’s no such thing as total 100% security and therefore there is a certain point at which one must say “it’s not worth it” when faced with new, invasive security procedures. I think we’re well past that point.

  • Bryan Lindemood

    Invasion of privacy a little bit? If virtual or real strip searches become the standard procedure at airports for me and my grandma, I will not fly. This would be ineffective security at too great a cost to the liberty, not to mention the fear and intimidation that comes from making people “undress” before perfect strangers. Anyone remember the Fall and the whole clothing thing? Remember whose idea the clothes were? There can be reasonable security without laying bare the nations before the TSA lady and those disturbed looking guys behind the shielded glass.

  • Bryan Lindemood

    Invasion of privacy a little bit? If virtual or real strip searches become the standard procedure at airports for me and my grandma, I will not fly. This would be ineffective security at too great a cost to the liberty, not to mention the fear and intimidation that comes from making people “undress” before perfect strangers. Anyone remember the Fall and the whole clothing thing? Remember whose idea the clothes were? There can be reasonable security without laying bare the nations before the TSA lady and those disturbed looking guys behind the shielded glass.

  • http://www.toddstadler.com/ tODD

    Pete (@1), you do realize that not all explosives are the same, right? The ammonium nitrate you refer to has a relative effectiveness (RE) factor of 0.42. The pentaerythritol tetranitrate (PETN) the Christmas-day bomber had in his underwear has an RE factor of 1.66. That’s quite a difference. Besides, he wasn’t trying to blow up an entire building, just damage or take down an airplane. And, from what I’ve heard, he had enough to do just that.

  • http://www.toddstadler.com/ tODD

    Pete (@1), you do realize that not all explosives are the same, right? The ammonium nitrate you refer to has a relative effectiveness (RE) factor of 0.42. The pentaerythritol tetranitrate (PETN) the Christmas-day bomber had in his underwear has an RE factor of 1.66. That’s quite a difference. Besides, he wasn’t trying to blow up an entire building, just damage or take down an airplane. And, from what I’ve heard, he had enough to do just that.

  • http://mesamike.org Mike Westfall

    I tried to post this before and it disappeared, so I hope this isn’t a duplicate:

    Here’s something we’ve been working on where I work that shows some promise for distinguishing harmless liquids from suspicious ones. It was tested at the Albuquerque airport about a year ago with good results. Not sure if they’re working on a full-body scanner version of it though, which is what is going to be needed to detect stuff hidden in people’s underwear.
    “http://www.youtube.com/watch?v=xT2zncrtU-s

  • http://mesamike.org Mike Westfall

    I tried to post this before and it disappeared, so I hope this isn’t a duplicate:

    Here’s something we’ve been working on where I work that shows some promise for distinguishing harmless liquids from suspicious ones. It was tested at the Albuquerque airport about a year ago with good results. Not sure if they’re working on a full-body scanner version of it though, which is what is going to be needed to detect stuff hidden in people’s underwear.
    “http://www.youtube.com/watch?v=xT2zncrtU-s

  • DonS

    In addition to the serious privacy concerns and expense, I read that security experts “hope” that they can scan passengers in 12-15 seconds. Which means, with all of the other attendant delays while passengers disgorge their pocket change, keys, computers, handbags, etc. onto the X-ray conveyor belt, they are hoping to screen 3-4 passengers per minute. That would never cut it at busy airports if the intention is to screen everyone. This technology should never be more than a secondary screening tool and Grandma should never have to walk through it.

  • DonS

    In addition to the serious privacy concerns and expense, I read that security experts “hope” that they can scan passengers in 12-15 seconds. Which means, with all of the other attendant delays while passengers disgorge their pocket change, keys, computers, handbags, etc. onto the X-ray conveyor belt, they are hoping to screen 3-4 passengers per minute. That would never cut it at busy airports if the intention is to screen everyone. This technology should never be more than a secondary screening tool and Grandma should never have to walk through it.

  • http://www.toddstadler.com/ tODD

    Matt (@2), I have to seriously question your analysis. For one thing, you said, “According to the bureau of transportation statistics, there have been about 5 million domestic passengers enplaned by U.S. Air Carriets since Sept, 2001.” I don’t know what you’re reading, but according to this page on the BTS site, there were 651,669,046 domestic passengers and 157,873,308 international passengers in 2008 alone. I think the figures you were reading were in thousands.

    Also, reducing this to a mere probability really misses the point, to say nothing of the fact that you don’t calculate the probability of a future event by looking at past performance. Consider how many flights there were before 9/11/2001 that didn’t involve hijackers flying planes into buildings. Why, the “odds” one could calculate from that mean that it’ll practically never happen again, so why bother trying to do anything about it? As you said, “terrorism of this kind is not a significant threat to me.” Except when it happens. Or when its effects reverberate significantly through the lives of you and your countrymen.

  • http://www.toddstadler.com/ tODD

    Matt (@2), I have to seriously question your analysis. For one thing, you said, “According to the bureau of transportation statistics, there have been about 5 million domestic passengers enplaned by U.S. Air Carriets since Sept, 2001.” I don’t know what you’re reading, but according to this page on the BTS site, there were 651,669,046 domestic passengers and 157,873,308 international passengers in 2008 alone. I think the figures you were reading were in thousands.

    Also, reducing this to a mere probability really misses the point, to say nothing of the fact that you don’t calculate the probability of a future event by looking at past performance. Consider how many flights there were before 9/11/2001 that didn’t involve hijackers flying planes into buildings. Why, the “odds” one could calculate from that mean that it’ll practically never happen again, so why bother trying to do anything about it? As you said, “terrorism of this kind is not a significant threat to me.” Except when it happens. Or when its effects reverberate significantly through the lives of you and your countrymen.

  • Jonathan

    @6, unless, grandma hails from a terrorist sponsoring nation, perhaps?

  • Jonathan

    @6, unless, grandma hails from a terrorist sponsoring nation, perhaps?

  • DonS

    Jonathan @ 8: LOL. Yeah, I guess so. :-)

  • DonS

    Jonathan @ 8: LOL. Yeah, I guess so. :-)

  • Bryan Lindemood

    Here in SLC, it sure seems that somebody’s got a contract to install about a hundred new security cameras every day. Boy am I thankful that I can be so secure. This may be unrelated to today’s post, but it sure seems that if they can’t strip search you at the airport you can be sure they have their eye on you! I really wonder who exactly the government’s more afraid of? I also wonder what such surveillance does to the souls of men? Both those being watched and the watchers too.

  • Bryan Lindemood

    Here in SLC, it sure seems that somebody’s got a contract to install about a hundred new security cameras every day. Boy am I thankful that I can be so secure. This may be unrelated to today’s post, but it sure seems that if they can’t strip search you at the airport you can be sure they have their eye on you! I really wonder who exactly the government’s more afraid of? I also wonder what such surveillance does to the souls of men? Both those being watched and the watchers too.

  • http://wipfandstock.com/store/As_Though_It_Were_Actually_True_A_Christian_Apologetics_Primer Matt C.

    tODD @ 7, you’re right that I was reading it in thousands. Thanks for catching my sloppiness. Adding a bunch of zeroes strengthens my point, though (if one accepts the approach, anyways).

    you also wrote:
    “Also, reducing this to a mere probability really misses the point, to say nothing of the fact that you don’t calculate the probability of a future event by looking at past performance. Consider how many flights there were before 9/11/2001 that didn’t involve hijackers flying planes into buildings. Why, the “odds” one could calculate from that mean that it’ll practically never happen again, so why bother trying to do anything about it?”
    For the record, I never intended that post to be a comprehensive approach to the issue but rather a suggestion of what is missing. Predicting an event is, of course, more in the realm of intelligence than statistics. And if anyone has intelligence that shows terrorists are planning a bunch of similar operations, then please let us know. However, as far as I’ve seen, the conversation on this topic to date has not been “implement these measures because we know people are planning this kind of attack as we speak and we need to put countermeasures in place at these specific at-risk airports until the threat has passed” but rather “this event has uncovered a vulnerability in our flight security system that must be corrected everywhere the system reaches.” This is not a specific threat but a generic threat. This puts the solution in the realm of engineering which does involve probabilities based on acquired data. As you note, this can never predict big changes like 9/11, but unless you have evidence pointing to big changes on the horizon, that observation doesn’t make the approach useless.

    You also wrote:
    “As you said, “terrorism of this kind is not a significant threat to me.” Except when it happens. Or when its effects reverberate significantly through the lives of you and your countrymen.”

    Sure. Winning the lotto is also not a significant possibility for me to consider except when it happens. Moral issues aside, though, I’m still not going to play because the stats make it a waste of money. Unless you put this issue in the category of “this must be prevented at all costs” your point is not really relevant. If plane-based terrorism should only be stopped at reasonable costs, then one must look at the level of the generic threat in relation to the options for prevention in a level-headed manner. If it must be stopped at all costs, the only realistic option is to ground all planes. That’s fine for a specific threat, but not a generic one. Tragedies happen this side of heaven. That doesn’t make them any less tragedies, but that does mean we shouldn’t lose our perspective over them.

  • http://wipfandstock.com/store/As_Though_It_Were_Actually_True_A_Christian_Apologetics_Primer Matt C.

    tODD @ 7, you’re right that I was reading it in thousands. Thanks for catching my sloppiness. Adding a bunch of zeroes strengthens my point, though (if one accepts the approach, anyways).

    you also wrote:
    “Also, reducing this to a mere probability really misses the point, to say nothing of the fact that you don’t calculate the probability of a future event by looking at past performance. Consider how many flights there were before 9/11/2001 that didn’t involve hijackers flying planes into buildings. Why, the “odds” one could calculate from that mean that it’ll practically never happen again, so why bother trying to do anything about it?”
    For the record, I never intended that post to be a comprehensive approach to the issue but rather a suggestion of what is missing. Predicting an event is, of course, more in the realm of intelligence than statistics. And if anyone has intelligence that shows terrorists are planning a bunch of similar operations, then please let us know. However, as far as I’ve seen, the conversation on this topic to date has not been “implement these measures because we know people are planning this kind of attack as we speak and we need to put countermeasures in place at these specific at-risk airports until the threat has passed” but rather “this event has uncovered a vulnerability in our flight security system that must be corrected everywhere the system reaches.” This is not a specific threat but a generic threat. This puts the solution in the realm of engineering which does involve probabilities based on acquired data. As you note, this can never predict big changes like 9/11, but unless you have evidence pointing to big changes on the horizon, that observation doesn’t make the approach useless.

    You also wrote:
    “As you said, “terrorism of this kind is not a significant threat to me.” Except when it happens. Or when its effects reverberate significantly through the lives of you and your countrymen.”

    Sure. Winning the lotto is also not a significant possibility for me to consider except when it happens. Moral issues aside, though, I’m still not going to play because the stats make it a waste of money. Unless you put this issue in the category of “this must be prevented at all costs” your point is not really relevant. If plane-based terrorism should only be stopped at reasonable costs, then one must look at the level of the generic threat in relation to the options for prevention in a level-headed manner. If it must be stopped at all costs, the only realistic option is to ground all planes. That’s fine for a specific threat, but not a generic one. Tragedies happen this side of heaven. That doesn’t make them any less tragedies, but that does mean we shouldn’t lose our perspective over them.

  • http://www.bikebubba.blogspot.com Bike Bubba

    My take is simply that technology won’t protect us when we’re not even bothering to heavily scrutinize guys coming through without a passport and with multiple suspicions about their motives in travel. Ain’t no invention that can conquer stupid.

  • http://www.bikebubba.blogspot.com Bike Bubba

    My take is simply that technology won’t protect us when we’re not even bothering to heavily scrutinize guys coming through without a passport and with multiple suspicions about their motives in travel. Ain’t no invention that can conquer stupid.

  • http://www.toddstadler.com/ tODD

    Bubba (@12), he had a Nigerian passport. People continue to spread this story, without having read any articles since the confusion of the first day or two.

  • http://www.toddstadler.com/ tODD

    Bubba (@12), he had a Nigerian passport. People continue to spread this story, without having read any articles since the confusion of the first day or two.

  • http://www.bikebubba.blogspot.com Bike Bubba

    OK, he had one where people had recommended his visa be revoked. Paid cash. Checked no baggage. Multiple comments on his radicalism.

    And nobody evidently lifted a finger at the State Department, DHS, or TSA. I would suggest that “you can’t design out stupidity” remains a valid working hypothesis here.

  • http://www.bikebubba.blogspot.com Bike Bubba

    OK, he had one where people had recommended his visa be revoked. Paid cash. Checked no baggage. Multiple comments on his radicalism.

    And nobody evidently lifted a finger at the State Department, DHS, or TSA. I would suggest that “you can’t design out stupidity” remains a valid working hypothesis here.

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