Airport body scanners that emit low levels of ionizing radiation could pose a long-term threat to public health, an expert on radiation safety has warned, while urging airport security officials to rely on another scanner already in wide use.
Dr. David Brenner, director of the Center for Radiological Research at Columbia University Medical Center, acknowledges that an individual’s risk of dying of cancer from exposure to so-called backscatter X-ray scans is extremely small — about one in 10 million for a trip involving two screening scans. But in an article being published in the journal Radiology, he says public health officials should look at the long-term consequences of a very large number of travelers being exposed to a potential radiation-induced cancer risk.
“If all air travelers are going to be screened this way, then we need to be concerned that some of these billion people may eventually develop cancer as a result of the radiation exposure from the X-ray scanners,” he said. He predicted “100 cancers each year resulting from this activity.”
In testimony before a Congressional panel Wednesday, Brenner questioned why the Transportation Security Administration chooses to use the X-ray scanners when it also has millimeter wave scanners, which do not emit ionizing radiation and pose no known safety risks. “X-rays are a carcinogen,” he told lawmakers.
A TSA official, USA Today reports, said the X-ray technology was safe and had been thoroughly tested by independent experts.
That view gets some support in another article in the April issue of Radiology. David Schauer, executive director of the National Council on Radiation Protection and Measurements, wrote that adding up trivial cancer risks over large populations or time periods produces a distorted image of risk. Schauer favors strict government regulation of backscatter X-ray scanners to ensure that passengers are not exposed to unsafe levels of radiation.
The scanners have raised privacy and health concerns since the TSA began accelerating its deployment of devices to detect explosives. The effort was spurred by a Christmas Day, 2009 incident in which a passenger on a flight from Amsterdam to Detroit tried, but failed, to detonate a bomb hidden in his underwear.
According to USA Today, the TSA has installed almost 500 full-body scanners at airports, and about half use X-rays.
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As has been noted elsewhere, the excess cosmic radiation received by a typical air traveler on a commercial flight at high altitude far exceeds the very small amount of excess X-ray radiation that same traveler receives when passing through the security X-ray scanner. Dr. Brenner’s point of view is not rational in light of the fact that airline passengers choose to accept the extremely small risk of high-altitude radiation–much as we accept the everyday risk of driving a car, crossing the street, or eating food in a restaurant. Why would an airline passenger accept a risk of say, 1-in-a-million chance of getting cancer from high altitude cosmic radiation, but then balk at the smaller 1-in-ten-million chance of passing through the scanner required to board that airline? It would make better sense for Dr. Brenner to testify before Congress that all airline passengers should be informed and warned about the dangers of high altitude travel in general, rather than the specific and much smaller risk of passing through an X-ray scanner. Dr. Brenner’s statistical claims of “100 cancers each year” from such scanners are not supported by scientific data. At exposures below 100 milliSievert there is no evidence of increased cancer risk in humans or other mammals, and extensive animal studies have shown that there is a “threshold effect” –high levels of radiation exposure increase the risk of cancers, but below a certain radiation dose threshold, the cellular mechanisms appear to be able to repair radiation damage to such an extent that there is no statistical evidence of radiation causing increased cancer risk. The airport scanners are set far below this threshold, as you would expect.
@kenricci Just because a passenger accepts one risk (of increased cosmic ray exposure, which is *unavoidably* linked to the convenience of air travel) does not mean that the same passenger would accept another (probably smaller) risk of being deliberately exposed to x-rays in the airport, which is arguably not linked to any benefit to that passenger. (Since that passenger knows that they will not be carrying anything they shouldn’t, that passenger doesn’t benefit from their body being x-rayed.) The benefits to society as a whole of people being x-rayed in airports are open to skepticism at this point as I am not aware of anything important having been detected by the x-ray scanners so far.
Put another way, I accept the risks of me driving a car, but I will not tolerate the smaller risk of you blowing cigarette smoke in my face every time I get into my car. Even if it would be a smaller risk than driving, I still reject that risk, because although this would be a small risk to me each time, it brings me no benefit to accept it.
Some airlines have the policy of immediately removing cabin crew from flying duties when they become pregnant, so the risk of cosmic radiation is not necessarily small enough to ignore. Some passengers already plan their air travel to minimise the unavoidable cosmic radiation exposure (e.g. by avoiding flights across the polar regions and looking at sunspot activity), and to those passengers, adding an additional cancer risk that is completely avoidable seems very unattractive.
I wonder whether the number of cancer deaths caused by the scanners will exceed the number of deaths that the scanners might prevent through preventing some kind of terrorism that would have actually succeeded otherwise. Has there been any documented case of detecting anything? Would the scanners only detect harmless devices that were constructed incompetently by those who did not have the knowledge to hide them in body cavities?
It is also interesting that although quite a lot of people are concerned about the cancer risk caused by airport x-ray body scanners, very few people have commented on the likelihood of inherited deformities and leukaemia which are known to be associated with x-ray exposure.