How Airport Full-Body Scanners Work - and the huge national debate around the TSA right now

by | Nov 17, 2010 08:10 AM ET

There is a huge uproar right now about the new full body scanners being deployed in airports around the United States. There are people loudly claiming that the TSA is handcuffing them to chairs for refusing to be scanned...

TSA agents yelled at her, handcuffed her to a chair, ripped up her ticket...

...and TSA responses:

Response to "Female radio host cuffed to chair, ticket ripped up..."

There are reports of toddlers screaming during pat downs:

TSA pats down a screaming toddler

There are calls for congressional oversight, passenger boycotts, acts of private protest, TSA abolishment...

It's a big debate.

There are many reasons why people tend not to like these machines, but the two primary complaints are health concerns (from x-ray radiation) and privacy concerns (both from being groped during pat downs and from the possibility of scanned photos being distributed).

Whether you love or hate the Transportation Safety Administration and its mission, the mission is clear. The TSA's goal is to keep passengers from carrying weapons and explosives onto airplanes. We can generally agree as a society that this is a worthwhile goal. No one wants to see a terrorist wearing a suicide bomb blow up an airplane and kill 300 people in the air. One obvious way to carry the weapons on is in luggage and handbags. The other is to attach them to your body.

The x-ray machines used to scan luggage are generally considered to be safe and effective. See this page for a concise description of the technology.

But when it comes to searching the bodies of passengers, the use of metal detectors and pat-downs appears to have problems. First, metal detectors cannot detect some explosives, which often do not contain much metal. And a normal pat-down may not be very effective. Passengers wiggle and complain. Passengers are naturally reluctant to have their personal areas explored by a stranger's hands. Therefore, the person doing the pat-down may not be very thorough. And if certain parts of the body (e.g. genitals) or certain types of people (e.g. toddlers) are deemed inappropriate for patting, then those become obvious places to hide weapons.

What is an alternative to full-body scanners? One alternative would be to have each passenger enter a private booth in which he or she would remove all clothing and hand it to an agent. Then the clothing and the passenger's naked body (or photographs thereof) would be examined. Then the passenger would re-dress and exit the screening area.

This would be effective, but it has two problems: 1) many (perhaps most) passengers would openly rebel, and 2) it could really slow down the screening process, making it more expensive. There might also be problems with pornography and child pornography laws.

Instead of making everyone get naked, the TSA has deployed two types of screening machines that let passengers skip the undressing part. A machine "undresses" you by using either x-rays or millimeter radio waves. The backscatter x-ray technique is the one getting the most publicity at the moment. In this machine, visualize a beam of low-power x-rays, similar to a laser beam in dimensions, scanning across your body, left to right, top to bottom. The machine uses detectors to see how many of the x-rays scatter off each point of your body. Certain materials (like clothing) don't cause much scatter at all. Skin has a certain characteristic scattering effect, as do different metals and certain explosives. The machine paints an image of the backscattered results point by point, and an agent looking at the image can see things like metals, ceramics and explosives attached to a passenger's body. See this page for a concise description of the technology.

The image that comes back is basically an image of a naked human body – it is a strip search without the stripping. It is fast and efficient.

So what is the problem? There are three actually. First, many people don't like the idea of having photos of their naked bodies taken by any means. In addition, there are a number of stories of abuse (e.g. about attractive women being more likely to be scanned) and leaked images (e.g. supposedly impossible but obviously not), which doesn't help in that regard. Second, because x-rays involve ionizing radiation, many (perhaps most) people have health concerns. All you have to do is look at public reaction to new nuclear power plants and the public acceptance of sunscreens to understand these concerns, even if experts and the TSA say the machines are safe (see this letter from UCSF faculty for the counterpoint).

The third problem is the perception that it is much ado about nothing – that the TSA represents "security theater" rather than actual security. This idea first took root because the TSA has not traditionally been very proactive. A terrorist had to bring explosives in the soles of his shoes before the TSA scanned shoes. A terrorist had to bring in innocent-looking liquids to mix a bomb in the air before liquids were prohibited. Printer cartridges were not banned until explosives showed up in printer cartridges.

In the case of backscatter scanners, the TSA actually is being proactive. It is plugging a security hole before anyone exploits it. In doing this the TSA has met significant resistance:

Amid airport anger, GOP takes aim at screening

In addition to being large, impersonal, and top-heavy, what really worries critics is that the TSA has become dangerously ineffective. Its specialty is what those critics call "security theater" -- that is, a show of what appear to be stringent security measures designed to make passengers feel more secure without providing real security. "That's exactly what it is," says Mica. "It's a big Kabuki dance."
Now, the dance has gotten completely out of hand. And like lots of fliers -- I spoke to him as he waited for a flight at the Orlando airport -- Mica sees TSA's new "naked scanner" machines and groping, grossly invasive passenger pat-downs as just part of a larger problem. TSA, he says, is relying more on passenger humiliation than on practices that are proven staples of airport security.
For example, many security experts have urged TSA to adopt techniques, used with great success by the Israeli airline El Al, in which passengers are observed, profiled, and most importantly, questioned before boarding planes. So TSA created a program known as SPOT -- Screening of Passengers by Observation Techniques. It began hiring what it called behavior detection officers, who would be trained to notice passengers who acted suspiciously. TSA now employs about 3,000 behavior detection officers, stationed at about 160 airports across the country.

More on the techniques used in Israeli airports can be found in this article:

The 'Israelification' of airports: High security, little bother

Another problem is that a passenger who is strip-searched still has a currently-undetectable way to bring in explosives. The passenger could swallow plastic explosives wrapped in rubber or plastic along with a detonator. The human stomach can hold a couple liters of food and is fairly resilient (one person was known to swallow 78 forks and spoons). There is no easy way right now to detect this approach short of medical x-rays or ultrasound.

Which leaves us with our current spectrum of choices:

  • At one end of the spectrum, we could let passengers walk onto airplanes like we let them walk onto subway trains - zero security of any kind.
  • At the other end we could give naked passengers full body CAT scans before every flight.

Somewhere in the middle is a level of security that the majority of passengers will willingly accept. Apparently full-body x-ray scanners may be a little beyond that limit at this moment in history.

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