Agreed, I opt-out every time I can. This gives me a chance to talk to the TSA agent. This puts human faces on the, typically, blurry screen of human mass.
When they ask why I opt-out, I explain about the numerous times I have filled out the comment cards mentioning the real danger of cataracts because you don't tell people to close their eyes. Explain that my engineering background fully understands both the x-ray and mm-wave technology. I explain that even the weak, yet not disclosed, powers of mm-wave back scatter can, over time, cause damage to your eyes.
This gives them something to think about, that isn't the typical "freedom" complaint they hear. I hope, one day, to overhear a TSA agent tell people to close their eyes.
First, the threat to your eyes is real. But, my underline reason is by making people close their eyes it will give a sense of vulnerability that the current systems don't have. I am hoping, one day, that this is the tipping point needed for more people to opt-out.
Can you elaborate on the risk to eyes? I've not heard about this, and Wikipedia doesn't mention it, either for mm-wave or backscatter (I hadn't even realised there were two different technologies in use until now). What kind of risk level are we talking about? Do your eyelids offer any real protection against it?
As far as I can tell, the x-ray works similar to the dentist office. While, the basic idea behind the active backscatter mm-wave is similar to radar. It is my understanding that the majority of the TSA owned mm-wave machines are active. You have a number of antennas that pulse and listen. I would need to look up the specs, but I suspect they are in the 75 GHz range which is above the oxygen absorption (60 GHz) but below more expensive technologies in the 100+ GHz range. There are a number of "cheap" technologies that have emerged for radar in this range on the market at the 75 GHz frequency, and I think it is being driven by this technology.
All in all, the mm-wave at the powers they use are harmless. The depth of penetration to the skin is sub millimeter and your body dissipates any heat that would be generated. It is most likely a pulsed system and your overall exposure time is small. But, the most fragile part of your body is your eyes. The capillary blood vessels are much smaller and wouldn't dissipate the heat as readily as the body. And it is my professional opinion, that overtime, it could do damage to your lenses and cause cataracts. I would love to get a grant to study these effects.
As far as I have seen, there are no IEEE specs on specific absorption rates (how much heat energy is created by being irradiated with a source), they are typically categorized as "body", "head", and "appendages". If anyone has information on specific body parts (I personally need it for teeth and fingernail work I do) I would be very interested in the FDA specific absorption rates.
When you close your eyes your eyelids will dissipate any heat generated and the mm-wave will not penetrate through the skin. One interesting test would be if anyone could get what the images look like, and see if you can tell where the eyes are. If there there is a difference in the backscatter, that would mean that the mm-wave is being absorbed differently in the soft tissue of the eye.
In my professional opinion, just close your eyes. If you fly once a year, it probably isn't a big deal. If you fly all the time, I would close my eyes.
