Airport Scanners

One session at the American Association of Physicists in Medicine conference was on the new scanner technology being used in airports. The session had a few speakers, each with their own expertise, covering both backscatter x-ray technology and millimeter wave technology. The focus was on the science, regulation, and policy - not privacy or security efficacy. I'm very glad I went. Here is a summary:

The scanners do not pose a radiation risk, if used properly

For millimeter detectors, this isn't surprising. It is non-ionizing radiation, which means the worst it can do is cause heat. This is the same reason people shouldn't be worried about cell phones. Can heat be bad? Sure, don't put your cat in a microwave. The energy density is what can be used to measure if this type of energy can be bad. The energy density of these is about 5 orders of magnitude below the safety limit for public exposure. For comparison, the loudness of a raindrop (not on a tin roof or anything) is not even 5 orders of magnitude below the safety limit for hearing (for long periods of time).

For the back-scatter technology, part of the concern has been that the dosimetry might not be good. This talk was given to a crowd of people who specialize in dosimetry, and at the end they seemed satisfied. The radiation dose is very small compared to what a person would receive on a flight and two independent measurements have agreed on it.

The big caveat is if used properly. These machines have automatic shut-offs if they are not performing as they should. However, TSA agents apparently have circumvented many of the safety features (interlocks) on the luggage x-ray machines, which exist for the safety of the TSA operators! The TSA agents can only press "scan" on the backscatter machine - they can't control the parameters at all. Could they find a way to circumvent a machine not running do to being out of spec? I don't know.

The communication about these machines is/has been rubbish

The first speaker, a physicist, summarized the safety data very nicely. And stated that MUCH of it had come from private communication with others, not from public data. He said it is not possible to prove these machines are safe from publicly available data. Additionally, the TSA hasn't done a good job reaching out to the non-scientific public. They have compared the energy from the millimeter wave scanners to cell phones. While this is true, the public is now afraid cell phones cause cancer. In the past it has been said (I don't know if this was a "official" TSA statement or not) that the backscatter machines use "special" x-rays that bounce back rather than go through you. Yeah, not quite.

TSA Agents are not going to be trained to administer radiation like clinic workers are

The TSA agents using these machines are not going to have State oversight and aren't going to need any sort of certification. This didn't sit well in an audience who spends a good chunk of their time maintaining their certifications to do similar work.

We were assured that the agents receive training on the machines and how they function. One person in the audience stated that he asked a TSA agent what energy the x-rays were and the agent (and two levels of supervisors) had no idea. The TSA representative who spoke to us didn't see why the agents should be expected to know such things.

It is going to get "worse"

We were shown images and video of a new "standoff" millimeter wave technology that lets someone use a special scope to do this sort of imaging in real time and at a distance. It is planned that there will be TSA agents at the entrance to airports using these devices. This means no opt-out opportunity, and you might not even know you are being scanned since they operate at a distance.

Additionally, the TSA is now deploying technology that allows the computer to automatically detect when someone has a hidden object on them, rather than having a TSA agent in a back room do it. An agent at the scanner is notified as to where on the person's body the object is so a pat-down can be done. The TSA representative claimed this was in response to privacy concerns, but it will also allow the lines at these scanners to move faster.

Some people really suck

While the session reminded me why I occasionally have a disdain for our government, especially the parts associated with "Homeland Security", the worst moment was in the beginning. One of the moderators was doing a short introduction to the topic, which included cargo scans. There are places where trucks are x-rayed to check their contents. There is one type of scan that is low enough dose that the driver can be part of.

There is a second type of scan that is a MeV energies - this is the type of radiation used for treating cancer, not for giving x-rays. For these scans you wouldn't want the driver to be included. The moderator complained that people are concerned over these scans since there may be stow-aways in the back of the truck. He felt that since they were stow-aways (presumably undocumented immigrants) that we shouldn't be concerned with the dose they are receiving. I strongly disagree.