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Comment by stcredzero | Hacker News Reader

One thing that came out in this blog post -- it seems there may be a policy that the TSA employees are specifically forbidden to wear radiation dosimetry badges.

What!? How in the world is this a sane policy? Who is this policy meant to protect?

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If a lot of TSA employees wore dosimeters, chances are there would be at least one false positive and the media would latch onto it.

I work at a nuclear reactor, and for the type of dosimeters we wear on the job (thermoluminescent dosimeters), there's no chance of a false-positive, as far as I'm aware. The only thing that can cause the crystal to lose electrons is ionizing radiation in a certain energy range. As long as there were procedures to ensure that the badges are only worn on the job, false positives shouldn't be an issue.

As long as there were procedures to ensure that the badges are only worn on the job, false positives shouldn't be an issue.

And that's how your false positives happen. How many people would have to wear dosimetres? Would they be mandatory? How many people per year will leave them at home and borrow their workmate's dosimeter so the boss doesn't give out? How many will drive home in their uniforms? Go to the shops in their uniforms? There are loads of ways for errors to happen.

Nuclear reactors are (I'm guessing) very strict on their policys, it's foolish to extrapolate that to airport workers.

After all this, you don't think the TSA is strict on their policies?

It's not very hard to solve this problem. At work, we just have a bunch of small cubbies where everyone keeps their dosimeters. When you come in, you take it out and put it on; when you leave, you take it off and put it in. Occasionally people forget to take their dosimetry off, but it's not a big deal–it's extremely unlikely you're going to receive a significant dose outside of the facility (although you are constantly receiving a low-level radiation dose from cosmic rays, and, if you're below ground, from radon gas). I should mention that I work at a test reactor where the typical dosage is so low that the Federal Government doesn't even require us to track employee dose. I get more dose from flying cross-country several times a year[1] than I do working at the reactor. So, I don't know how dosimetry policy differs at power reactors.

Regardless, I think it would be particularly illuminating if there <i>were</i> false positives. Why not have employees who are concerned wear dosimeters constantly, and at the same time stick reference dosimeters near where they usually stand while a scanner is in operation. If their dose is roughly the same as that of the reference dosimetry, there's not much room to complain about the scanners.

The fact is we are being constantly bombarded by low-level radiation from cosmic rays and radon gas simply by virtue of standing on the surface of the earth. The level of radiation these scanners output is much smaller than that. Wikipedia[2] cites an article in the European Journal of Radiology that gives a dose range for backscatter machines of between 0.07 and 6 micro-Sieverts. For reference, the National Council on Radiation Protection and Measurements reports that the annual radiation dose from naturally occurring radiation is on the order of several hundred micro-Sieverts [3].

TSA employees have a right to be concerned, because they are involuntarily being exposed to it as a course of their job, without this being made clear to them when they were hired. If you're a traveler, you should be much more concerned about the radiation dose you receive on the plane than the one you receive from the scanner.

[1] Health Physics Society page on radiation exposure on commercial airflights: http://hps.org/publicinformation/ate/faqs/commercialflights..... [2] https://secure.wikimedia.org/wikipedia/en/wiki/Backscatter_X... [3] http://hps.org/documents/environmental_radiation_fact_sheet....

If you're a traveler, you should be much more concerned about the radiation dose you receive on the plane than the one you receive from the scanner.

I dislike "spherical cow" assumptions when they are applied to my health. If you are a government agency, then applying "spherical cow" assumptions by imposition to large numbers of people is inexcusable.

http://compilerbitch.livejournal.com/218216.html

Backscatter X-rays are completely unlike the radiation you receive on a cross country flight. Natural high energy tends to deposit energy evenly throughout your body. The energies in backscatter are manipulated so that the majority of the energy is deposited near the surface of your body.

We don't have that much data on the effects of low energy X-rays, because we didn't have many applications for them until recently. We do not understand in complete detail the mechanisms by which radiation causes cancer. We have equations for predicting cancer rates for radiation doses, but these are entirely adhoc and empirical! We don't have a first-principles understanding of this stuff yet. We don't know enough to say for sure that this application of X-rays is safe. I'd only feel safe if there were experiments on a bunch of lab animals.

Yes, with standardized work-issued dosimeters, training, and strict obedience to policies, you will reduce false positives. They'll still happen, though. Some types of dosimeters will read positive if exposed to heat or sunlight. Some are sensitive to oils or dirt. One nuclear waste disposal facility had false positive rates around 5% per quarter (http://www.osti.gov/bridge/product.biblio.jsp?osti_id=515496). They eventually found the lights in their building to be a major cause.

Now take that information and extrapolate it to using dosimeters in every airport in the nation. Even if the TSA deployed dosimeters as competently as a nuclear waste disposal facility, they would still get so many false positives that the dosimeters would be useless.

You'll get false positives if anyone goes for a cardiac stress test...

That's why you only wear your dosimetry when you're at work.

Wouldn't matter. Cardiac stress tests usually use technetium or some other radioactive tracer which remains in the body for a day or two after the test. That means that, for the next day or so, you are a "radiation hazard" (not really, but the dosimeters don't know the difference, or at least that's what I was told by the radiation control officer).

From all this uproar lately, sounds like work is a cardiac stress test for the TSA.

Not nearly as much as it is for the passengers.

For all the uproar, as of the last time I went through TSA security (about a week before the new "sexual assault" procedures started), the screeners seemed to be perfectly happy in their roles.

Of course, the chance of there being a true positive is nill. Government equipment never malfunctions. So it's better to ban dosimeters and eliminate the possibility of a media problem.

I did not say anything like what you are suggesting. Those are all things to be concerned about, but dosimeters aren't an effective way to measure or prevent them. If the backscatter machines are completely safe, dosimeters for such a large group will still cause a panic because there will be false positives. There are other devices that can measure radiation more accurately and reliably.

I feel contempt for the TSA as much as everyone else around here, but one has to be aware of the halo/horn effect. I don't know if banning dosimeters is the best decision, but I can see why they did it, and it seems rather unobjectionable compared to most of the TSA's actions and policies.

I was under the impression that all of the "x-ray" scanners aren't x-rays. Instead they are high frequency (100GHz+) back scattering machines.

The ones in the MKE air port are L3 ProVisions which fit the description I was aware of (http://www.sds.l-3com.com/products/mmwave.htm). No ionizing radiation means no "x-rays" etc.

I haven't been subjected to them yet, but before I walked into the airport I made my decision if I was going to be scanned or not.

There are 2 classes: millimeter wavelength machines and x-ray backscatter machines. These are definitely backscatter x-ray machines.

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