TSA accepting comments on their cancer scanners

[asterroc]

Finally, the TSA is accepting comments on their "AIT" x-ray and microwave scanners of passengers. Here's the comment I submitted. Feel free to model after mine.

I do not feel that there is sufficient necessity for x-ray and microwave machines to justify the additional exposure. I have not seen sufficient evidence from independent third-party evaluators that the dosage of x-ray and microwave radiation used by AIT machines is safe, and I have not seen any evidence that exposing me to these types of radiation is either in my best interest, or in the public good. I understand that I am already exposed to these types of radiation on a daily basis due to other devices (such as medical x-rays and cellphones), but in those cases I feel that the need to use such devices justifies the exposure. Neither x-ray nor microwave radiation are inherently harmless, and even types of radiation which are harmless at typical dosages can cause harm at high dosage - for example, visible light is harmless at the dosage in flashlights, but can cause blindness at the dosage in laser pointers. In the absence of evidence of sufficient need for the increased risk to my health, it is my wish that I not be exposed to potentially harmful x-ray and microwave radiation.

I always opt out of the AIT machines when traveling by air, however I do not feel this option is sufficient to maintain my safety because I am usually told to stand next to the AIT machines while waiting for the pat-down, resulting in exposure to x-ray and microwave radiation despite my decision to opt out. I feel that the only resolution which would maintain my safety by reducing my exposure to unnecessary and potentially harmful x-ray and microwave radiation is to remove AIT machines from airports entirely.

Tracking # 1jx-84jq-nset

Originally posted on Dreamwidth. comments there. Comment here or there.

Comments

[sildra.livejournal.com]

In what way is microwave radiation harmful?

[zandperl.livejournal.com]

At an extreme, microwaving food. Other than that, my understanding is that the majority of the medical/scientific community says that a typical low dosage of microwaves are not harmful to adults in good health, but not as large a majority as that supporting anthropogenic climate change. My understanding is that there have been some studies showing that cellphone use and power lines can cause cancer clusters, and that these have only appeared in studies not funded by cellphone or power companies. I do not know however whether the dosage of microwaves from these machines is more like that of cellphones, or more like that of microwave ovens. I am obviously not an expert, so in the end my preference is to limit my exposure to radiation that I feel is questionable, especially since I have yet to see any evidence that the microwave scanning machines actually improve anything.

I already have one chronic/acute skin condition with significant negative effects on my quality of life. I know that the chance of microwave radiation causing other skin diseases such as cancer is extremely small, however neither I nor anyone else should be forced to endure even the slightest increase in risk factors for skin disease as a condition for travel.

In the end the issue is risk/cost vs. necessity. The TSA could just have everyone take off all their clothes and be photographed while their clothes are scanned. This has zero physical risk/cost, and yet we don't do it. Why? Because we feel that there isn't a necessity for it. Even if you disagree with me and feel that there is zero risk/cost to being microwave scanned, do you feel there is a necessity for it? I feel there is both a non-zero risk to being microwave scanned, and zero necessity, therefore it should not be done.

[sildra.livejournal.com]

If you stuck your hand in a microwave oven it would result in surface burns. Microwaving food works by vibrating the surface layer of the food, generating heat, and then the heat conducts within the food--this is why if you put, say, a big piece of lasagna in the microwave without cutting it up first you can end up with the cheese on the outside nice and melted and the inside still cold. You'd feel your skin heating up and then burning before any actual damage was done.

Looking up some numbers online right now, the attentuation of the light used in the mm scanners due to water is about 10^6 higher than the attentuation of visible light due to water. So, in water, the skin depth of the microwaves used in those microwave scanners is only about 100 microns, which is less than the thickness of your epidermis, and only about 4 times the average thickness of the dead part of the epidermis. (In contrast, a microwave oven uses a 100 times longer wavelength and the attentuation is only about 10^3 higher than that of visible light, and cell phones use a wavelength that's 3 times longer still and another order of magnitude closer to transparency.)

My understanding is that some studies show weak correlations between cellphone use or power lines and cancer, some studies show no correlation, and there are enough of both--and the ones that show correlation are all weak enough--that oncologists (at least the ones I've talked to) tend to be agnostic. Or if they aren't agnostic it's because of much older studies relating to soldiers working at early radar stations. But in any case there is no known mechanism by which microwaves should be able to cause cancer.

The possible mechanisms for damage vary considerably based on wavelength/frequency. Cell phones are at a frequency where, although the center-of-mass motion of molecules are effected, it's slow enough that not much heating goes on (at room temperature) unless you pour tons of amplitude in. Microwave ovens are at a good frequency to affect the center-of-mass motion of molecules, and so tend to heat things up pretty efficiently. The mm wave scanners are at a frequency where they are just barely slow enough to affect the center-of-mass motion of molecules, although I think they are already almost an order of magnitude too slow to effect any vibrational modes of molecules. Meanwhile, infrared light (which, as a category, spans more than 2 orders of magnitude in frequency) affects vibrational modes of molecules (which also span about 2 orders of magnitude in frequency, depending on the molecule). Near-infrared and visible light are at too high a frequency to affect vibrational modes, but at about the right frequency for electronic excitations, but a photon of visible light doesn't have quite enough energy to break a molecular bond. And then in the blue/ultraviolet, we finally get to a point where a photon has enough energy to break a weak molecular bond, which is the known mechanism for cancer.

So even ignoring the issue of lack of mechanism for cancer, it isn't really fair to compare "dosage" of mm wave scanners to cell phones to microwave ovens, because the frequencies of all three are so different that they don't all fall in the same regime. (But if you're concerned about dosage you could probably look that up. I didn't pay any attention because I was more interested in the obviously harmful x-ray machines. At the time, I did an order of magnitude calculation for risk of cancer (which I was only able to do because a lot of information specifically relating to the cancer risks of the airport x-ray machines had been made publicly available by the TSA--I don't know nearly enough to do a calculation like that from first principles), and looked up how often planes get hijacked by terrorists, and found that the probability of getting cancer from the x-ray machines at airports was about the same order of magnitude as the probability of being hijacked by terrorists. Although both probabilities are really vanishingly low (not taking into account that the cancer calculation is a little bit cumulative, nor that for the elderly the risk goes up considerably), cancer is a much worse death than being blown up, so I'd really rather take my chances with the terrorists.)