It's not like this week was the first appearance of the full-body X-ray scanners in American airports. Yet, thanks to the looming holiday travel season, leaked X-ray images that were supposed to be kept private, and high-profile rebellion by pilots' organizations and disgruntled passengers, anger is rising against the Transportation Security Administration's new airport rules. Under the policy, those chosen for extra screening face the dilemma of having their naked bodies revealed to TSA scanners or opting out and having agents feel them up in search of explosives. But behind the outrage at being asked to surrender even more of our dignity just to get on a plane, there's another full-body scanning issue simmering: the health dangers of radiation. How much radiation, and where? This was the main concern of the Allied Pilots Association. Pilots are already exposed to higher levels of radiation than nearly all professionals because they spend so much time at altitude and receive radiation from space; asking them to take an X-ray every time they get on a plane (even one that the TSA says is thousands of times less intense than a hospital chest X-ray) was asking too much. Popular Mechanics posted more details on pilot exposure. So what about the rest of us, who fly perhaps only a few times per year? Back in May, professors at the University of California, San Francisco, led by John Sedat sent a letter to the Food and Drug Administration with a litany of red flags about using back-scatter X-ray with such frequency—mostly that the safety has not be independently proven. The FDA finally replied with a lengthy letter citing study after study that show full-body scanning is safe, the agency says. The UCSF profs' main beef is this: We know the risks of medical chest X-rays, for example, which penetrate the skin to make those pictures of our bones. The back-scattering X-rays the TSA uses, however, aren't like that at all—they penetrate just the clothes and the top layers of skin, and the scanner reads what's reflected back. Because the full body scanners don't need to go through your skin, they use less powerful radiation than the X-ray machines in the hospital. That sounds good in theory, but it means the skin absorbs a bigger blast than it would in the hospital, and the professors say we don't know the effects of that skin exposure well enough to say that it's safe.
The low-energy rays do a "Compton scatter" off tissue layers just under the skin, possibly exposing some vital areas and leaving the tissues at risk of mutation. When an X-ray Compton scatters, it doesn't shift an electron to a higher energy level; instead, it hits the electron hard enough to dislodge it from its atom. The authors note that this process is "likely breaking bonds," which could cause mutations in cells and raise the risk of cancer. [Ars Technica]
FDA, in its response letter, said:
