TPM Reader TT chimes in on the safety issue. Before getting to TT’s comments, let me say that despite the fact that there are no levels of radiation with zero potential health consequences it’s also true that there are various sorts of x-rays we’ve decided as a society are acceptable levels of risk versus what’s gained — dental x-rays, medical x-rays, going high in the atmosphere, etc. What I would say, based on reading several articles about this, is that while the total amounts of radiation are less than what people get from other kinds of exposure we believe are innocuous, there are knowledgeable people saying that the comparisons the TSA is making involve apples to oranges comparisons between how different sources of radiation are absorbed by the body.
I just wanted to weigh in on several points on the new TSA scanners and procedures as a scientist and as someone that frequently works on homeland security topics. First, as any scientist can attest, that one of the major training messages in radiation safety courses is to always minimize the dose of ionizing radiation. There is NO safe level of ionizing radiation (there are three major types of ionizing radiation: alpha particles [helium nucleus], beta particles [electrons], and gamma rays [short wave, high energy electromagnetic waves]). Nada. Zip. None. Argonne National Lab did studies in the 1950s-1960s on many generations of beagle dogs to determine if there was a safe, minimum exposure level. The theory was that radiation exposure was like chemical exposure in that at some point the dose is so low that no damage occurs. The evidence proved otherwise. Also, the damage from ionizing radiation is cumulative, so frequent or repeated exposures have much longer lasting effects. The US and other governments have set some standards to limit radiation exposure for workplace and health safety, but there is no lower threshold dose that does no damage.
The TSA pulls a couple intellectual “sleights of hand” in its discussion of these machines. First, the TSA website compares the dose of radiation received from the machines to the radiation from cell phones (I will note this comparison is for the millimeter wave machines, not the back scatter variety). This is not a good comparison and may lead to confusion about the two different types of machines being used. Cell phones emit radio waves. Radio waves, while electromagnetic waves like gamma radiation, are much longer and of significantly lower energy, and, thus are not ionizing radiation. That is, they do not have the ability to damage DNA and to cause cancer. I can put a flask of cells next to a radio wave emitter and the cells will grow just fine and not accumulate any additional mutations from that exposure. Second, the TSA often compares the radiation from the back scatter machines to chest X-rays or cosmic radiation. These are much higher energy and typically pass through the body, so the dose is more diffuse and over a much larger part of your body. The back scatter radiation from the scanners is lower energy, but still ionizing, so the exposure is concentrated within a small amount of your body (the top layers of skin). This could potentially increase the effective exposure by 10-100-fold over what the TSA is saying. This second point is the one that the UCSF letter discusses in much greater detail.
The TSA also admits that the ionizing radiation penetrates through 1/10 of an inch of the skin. While that might not sound like much to many lay folks, that is actually quite significant. There is A LOT going on in your skin at 1/10 of an inch. To expose that layer of skin to increased ionizing radiation will lead to increased damage and the potential for mutations and ultimately cancer. It would take years to figure this out and maybe that is what the TSA/DHS is hoping for…the fog of epidemiology to hide the true health impacts. Look how long it took for the risks of smoking cigarettes, with a clear danger, to become well accepted with tons of independent data confirming the point.
The FDA response to the UCSF letter basically says, “the machines are below the threshold of an arbitrary dose limit we developed with the help of the manufacturers of these machines.” Some scientists don’t think that that is good enough. So, what to do? DHS cannot now do as the scientists from UCSF recommended and empanel a group of independent researchers to examine these machines and the ionizing radiation doses. If this panel did find that these machines were emitting dangerous amounts of radiation that causes cumulative damage, the authority and credibility of the US government would be irrevocably and permanently damaged. And not to mention the class action lawsuits that would follow. How could the US ever again say something was safe? Would anyone believe or trust the US government again on a wide range of health topics (the anti-vaxers would go nuts with this)? No, the US government will not allow a public, independent panel to evaluate these machines. They may do it internally and then graciously and secretly decide that the “benefits” (catching the one in a hundred million passengers that are terrorists) more than outweigh the “risks” (needlessly giving 1 in a million passengers skin cancer).
Why not put some dosimeters on TSA agents that work the machines? It would be interesting to follow over time to see if there are increased risks. Other folks that work around radiation are required to wear such devices to monitor potential exposures. According to the TSA website, there is exposure beyond the machine itself as evidenced by this statement:
“All results confirmed that the radiation doses for the individuals being screened, operators, and bystanders were well below the dose limits specified by the American National Standards Institute (ANSI).”
Notice that they included operators and bystanders in that evaluation. They are receiving doses as well and it is below the arbitrarily set limit. The TSA folks should be demanding dosimeters to evaluate that claim. Too bad they don’t have a union to represent them in this.
For me, I will do as instructed in every radiation safety class I have ever received: limit exposure whenever possible. I cannot do anything about cosmic radiation, but i can do something about walking through a back scatter machine. I will opt out.