Those Irradiating Machines at the Airport

Recently by Kathryn Muratore: US Air, Stop the Lies

A brief background

In advance of the publicity of the installation of naked scanners at US airports, some activists and scientists were already making some noise. A group of UCSF scientists – John Sedat, David Agard, Marc Shuman, and Robert Stroud – sent a letter to the President's science advisor, John Holdren, in April 2010 expressing their concern about the scanners. I have written about this elsewhere.

The Republican wing of the mainstream media picked up on a peer-reviewed article published in between the holidays last December that ran some simulations of the x-ray backscatter scanners. Recall that this followed shortly on the heels of the protests of last fall – when the TSA was rolling out more and more scanners, and also stepping up the invasiveness of their so-called pat-downs (known as custody searches by law enforcement). The authors, Leon Kaufmann and Joseph Carlson (again of UCSF) concluded that the reported capabilities of the scanners and the reported safety of the scanners were not consistent with each other. That is, either they don't work as well as advertised, or they are more dangerous than advertised. There are also a number of other results in their paper that should be of interest to travelers, and I summarized them at that time on my blog.

I also wrote up a summary of Dr. Sedat's second letter earlier this summer, this time to the Department of Health and Human Services (HHS). But my purpose here is to discuss a couple of peer-reviewed articles addressing the safety of the backscatter scanners that were published recently.

Why does any of this matter? I am of the opinion that even if the naked scanners are 100% safe and effective, they are still an egregious violation of individual rights. I oppose the use of the scanners on this basis. However, it is instructive of how negligent government is, by its very nature, to look at the case of the lack of scientific evidence showing these scanners to be safe and effective. The use of these scanners has been implemented in an incredibly stealthy manner. If you are a student of economics, history, government, or common sense, then this is not a surprise, but it is easy to ignore. I want to make it harder to ignore how the TSA has acted and harder to excuse those actions.

Brenner's epidemiological estimates

David Brenner is another scientist whose name regularly appears in media coverage of the naked scanners. He is a researcher at Columbia, and has routinely said that exposing the public to radiation is not consistent with accepted standards of protecting the public health. He stands firm that there is no such thing as a safe level of radiation; just safer levels. The reason why can be boiled down to epidemiology. Something with a 1 in 1 million chance of happening is certain to happen if well over 1 million chances are taken.

Brenner published a scientific article outlining his argument in Radiology this past April. His general conclusion is that the backscatter scan is safe for the individual, infrequent traveler. But, there are a lot of caveats to that statement that he carefully clarifies. Now is a good time to note that there are two naked scanners in use: the x-ray backscatter and the millimeter wave. Most questions of safety have focused on the former as it releases ionizing radiation. The last century has seen a vast accumulation of data on ionizing radiation and its effect on health. Comparatively less knowledge about the effects of millimeter wave radiation on health has been gathered, but it is generally viewed a significantly safer than ionizing radiation. In any case, Dr. Brenner's article focuses exclusively on the x-ray scanners.

He begins by defining "safe." The definition that you and I care about is that the individual is unlikely to become ill due to the exposure. Policy makers consider this definition, but also take into account the population risk: how likely is it that someone in the entire population will become ill due to the exposure? Brenner cites international and national policies on radiation exposure that consider population risk to be an important measure of safety even when individual risk is small.

Safe for the individual?

Of course, Brenner must rely on what the TSA and Rapiscan have told us about radiation exposure of the naked scanner, as interpreted by some scientists in a theoretical paper from last fall (whose main conclusion is: "The effective doses for personnel screening systems are unlikely to be in compliance with the American National Standards Institute standard NS 43.17 unless the pixel sizes are >4 mm. Nevertheless, calculated effective doses are well below doses associated with health effects."). Each time someone goes through the scanner, they are irradiated (once from the front and once from behind). This corresponds to a 1 in 10 million risk for fatal cancer (note, that the only measure of safety being used by Brenner is fatal cancer, not other non-fatal health risks). This level of individual risk is deemed okie-dokie by the National Council on Radiation Protection and Measurements (on which Brenner himself sat). If one person were scanned once, it is extremely unlikely that that single person would die of cancer caused by the scan.

But this is the statistic for an average person. Children are rapidly growing, and, therefore, they are more susceptible to DNA damage. Embryos and fetuses are in a similar situation. Brenner estimates that for children, the risk may be 1 in 1 million. Considering how careful many mothers are about protecting their children – born and unborn – from hazards like second-hand smoke, caffeine, alcohol, and heavy metals (mercury and lead come to mind), it is within reason for them to be concerned about an avoidable radiation exposure. Frequent flyers, including airline personnel, are exposed to many more than one scan a year, which means their individual risk increases; Brenner estimates this risk at 1 in 100,000 – still small, but much larger than acceptable standards. (And, don't forget the ill. Cancer patients undergoing radiation treatment are already receiving a lot of radiation and no doctor would advise them to receive extra just for fun. And some people, for reasons we don't always know, are more likely to be afflicted with fatal cancer than others and may be more susceptible to the ill effects of radiation.)

Safe for the population?

Brenner is unequivocal here: No, the scanners – used as primary screening at all airports – are not safe for the population. There are approximately 750 million passenger boardings per year. If the TSA meets its goal of nearly 100% scanning, and half of all scanners are the x-ray type, there will be about 375 million x-ray scans per year. So, by all of the evidence, 37 people per year will get a fatal cancer due to the scans. (Again, this assumes that all travelers are infrequent travelers and healthy adults.)

So Brenner falls back on the "As low as reasonably achievable," or ALARA, principle. Are the x-ray scans avoidable? Do they present a non-zero risk to the population? Then there is no justification for using them!

Brenner does also give attention to a point brought up in the Sedat letters: the reliability of the mechanics of these heavily used machines is a serious issue that has not been adequately addressed. If the beam pauses for too long in one spot, then the assumptions being made her are best-case scenarios.

Smith-Bindman's callous disregard

The other article that has come out, by Mehta and Smith-Bindman in June, takes the opposite stance. (Interestingly, Smith-Bindman is also at UCSF.) They take the individual radiation exposure (using a lower number reported by TSA, not the higher Rez, et al value cited by Brenner) and compare it to other radiation exposures that a person experiences. This is the favorite argument of the TSA: "An airline passenger that has been screened receives an equivalent dose of radiation from less than two minutes of flight at altitude."

To get to individual risk, they claim that the exposure will be concentrated in the skin (a half-truth, according to Kaufmann and Carlson's earlier paper), but acknowledge that breast tissue will get a good dose, so they use a breast cancer model to get from exposure to individual risk. This model is also useful because they can consider the effects on children (5-year old girls) as well as separate out casual versus frequent flyers.

Here's what they find for infrequent flyers: 6 cancers per year, but "[t]hese 6 cancers need to be considered in the context of the 40 million cancers that would develop in these individuals…" ALARA, anyone? Glad to know there is a doctor who is so flippant about a handful of deaths here and there.

For frequent flyers, they find there will be 4 additional cancers per year, but "[t]hese 4 excess cancers need to be considered in the context of the 600 cancers that could occur from the radiation received from flying at high elevations." This is not the way it normally works for dangerous jobs. As someone who has formerly worked with radioactive materials, I can tell you that if I was close to reaching my maximum allowable dose for the quarter, my boss wouldn't assign all remaining radioactive experiments to me since I was already at such great risk! Of course, my boss would cut back on my radioactive work to keep me from being overexposed.

For girls, they find a single extra cancer per year. And (you guessed it): "This increase of 1 cancer per 2 million young girls needs to be put in the context of the 250,000 breast cancers that will occur in these girls over the course of their lifetimes…" I'm not sure that the extra flight to grandma's is worth my daughter having a bout of breast cancer. I think grandma might agree with me here! I know this may be seen as an "emotional plea" that has no place in science, but I disagree. Life is supposed to be highly valued by scientists, and, particularly, by doctors. I understand that I can't protect my daughter from everything (indeed, I don't want to). But neither should public policy be based on this principle. We are guaranteeing that more people will get cancer, just so we can maybe, possibly, kinda, sorta prevent a terrorist attack.

But what about the terrorists?

Dr. Brenner suggests that the sensible thing to do (from a health perspective) is to use millimeter wave scanners. Neocons like the so-called "Israeli model" (uhh… no thank you). Tea partiers like dogs. I say, let the market decide. The airlines have a heck of a lot to lose if they are hijacked and know that there is no federal safety net. Not only is their property in danger, and they fail to please their customer, but they may also be on the hook for a lot of damages due to negligence if they can't show that they have reasonable policies in place to prevent such a tragedy. It is the airlines who have a profit-loss incentive to protect their passengers' (and crews') safety. (I'm certain that causing multiple excess cancers per year would lead to the airlines being successfully sued.)

Is Smith-Bindman on solid ground?

Fortunately for the reputation of all scientists, the editor of Archives for Internal Medicine solicited the commentary of Peter Rez on the Mehta and Smith-Bindman paper. (Rez is not from UCSF – he is a physicist from Arizona State. And we all know that physicists are smarter than doctors, and pretty much everyone else!) He questions the breast cancer model, but, in a reply from Smith-Bindman, it seems that this may not suffer from the shortcoming that Rez suggests. More importantly, Rez points out that the exposure calculation is uncertain – primarily because the TSA has not actually allowed an independent scientist to have access to the machines, a point that Smith-Bindman concedes in her reply. So, he thinks that all of the numbers presented are on the low end.

More state-sponsored approval

However, just a couple of weeks ago, the Army presented research in which they used an actual Rapiscan machine and measured the radiation dose. The results are very similar to the values that have been reported by the TSA's NIST and Hopkins Applied Physics Lab reports. This is currently available as a Powerpoint presentation only – it has not been peer-reviewed and, furthermore:

To reassure travelers, the TSA asked the Army Public Health Command to conduct radiation surveys at airports around the country. The new study, paid for by the TSA and done at a TSA lab, was part of that work.

Dr. Rez is quoted in the article, pointing out that this is not really the independent review that scientists have been clamoring for (although, I can only imagine that federal funds will still be used in those studies, at least the scientists are not nominally federal employees). At least three important questions are not addressed by the Army presentation:

  1. Why does the Johns Hopkins APL report (earlier solicited by the TSA) indicate such high radiation exposure in the area surrounding the scanner? This high reading in the surroundings is inconsistent with the low readings reported by the Army.
  2. What happens if the beam gets stuck in one spot?
  3. What is the resolution of the images produced at these exposure levels? The papers from last fall indicate that the machines would be ineffective at such low radiation levels. Either our understanding of the theory of backscattering is deficient, or these machines are useless (when they're not dangerous).


So, let's summarize what this tells us about the TSA's behavior. First, the TSA rolled out the scanners on the sly. The majority of the flying and non-flying public, including airline employees, had no clue what was going on. Many passengers went through the scanners without knowing what they were. Scientists at government-run (NIST) or government-contracted (JHU-APL) labs were given limited access to the technology and were also given a limited scope of research. This research did not include an assessment of safety. Nonetheless, the TSA repeatedly claimed these scientists had shown the scanners were safe, and, in the past year-and-a-half, they have not made the machines available to independent scientists or addressed the major concerns that have been brought up by "independent" (or at least, critical) scientists. The only additional data to come out has not been peer-reviewed and still does not address the primary questions that are necessary to assess the safety of these machines.

I have no reason to expect the collectivist mentality that leads to concerns about public security would even remotely consider individual rights. But, if the naked scanners are being used in the name of "public security," then why is the matter of "public safety" being treated so cavalierly? The answer is that these machines are not in place to protect you or me, or even all Americans. They are in place to protect the state and its bureaucrats.

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