But he says they were using Millimeter Wave Scanners, which as far as I can tell, and contrary to his argument, do not use x-rays. That letter refers to another type of machine, x-ray backscatter scanners.
Secondly, it shouldn't be a question of whether the machine is x-ray or millimeter wave. Both of those emit radiation and until there's definitive proof that one or both do not cause damage, they shouldn't be in use.
Because x-rays are used in medical devices that have to be approved by the FDA, we've developed some very good ideas about what sort of doses are harmful and which aren't. The damage done by the x-ray scans used by the TSA do indeed produce damage, measured in Sieverts - a scale used by medical technicians, nuclear power plant operators, NASA, etc. Generally a dose of 1 Sievert all at once is enough to make you sick. Radiation expose is usually measured in milliSieverts and a person who doesn't do anything dangerous will usually receive a couple of milliSieverts a year just from the sun and the radioactive decay of things like the carbon in their body. Going through a TSA x-ray scanner will give you about a microSievert (or 1/1000 of a milliSievert) unless you do something like stop in the middle of the scanner and daydream. Because flying on a plane involves going higher with less atmospher to protect you from radiation from outer space, even short flights tend to cause you to rack up 10 microSieverts and longer flights will give you more. So even if you fly every day the excess dose you're getting from the machines is ignorable, and if you are flying every day its only increasing the amount of radiation you're getting by 10%.
As to millimeter waves, well, I'm not sure quite what mechanism they could possibly use to be dangerous, since they're less energetic than the visible light that we're exposed to every day. If you're inclined to worry about stuff like that, I'd recommend worrying more about fluorescent lights (where all the energy is concentrated in a few frequencies and which we're exposed to for long periods of time) or cell phones and wireless access points (which have about the same energy as the TSA devices, and which we're exposed to for long periods of time).
The fractionation effect only comes into play when you receive such a high radiation does that it can cause large amounts of cell death. Similarly, being burned (with fire) twice at low intensity is better than being burned once at high intensity, since your body can partially recover after the first burn.
Should we ban your light bulbs because they emit radiation that is in every way more dangerous than millimeter waves?
Sorry, but the catch-all "ban all radiation because the word radiation sounds scary" is beyond stupid. I believe there are good reasons not to use this kind of technology (mostly it's about privacy), but luddism like this degrades the legitimate health concerns there are against backscatter x-ray machines.
Millimeter wave and X-ray scanners are not the same thing and should never be confused.
I personally would never go through an X-ray scanner. Are the scanners marked in some way so I know which is which?
By the way, you might be wondering: Can the average traveler standing in a security line tell the difference? Yes, a TSA spokesman says. The X-ray type is blue and has two walls. The millimeter-wave machine is grayish-white and is more cylindrical.
They look like just walking near them will expose you.