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NPR's Richard Knox assesses the risk.
RICHARD KNOX: At a time when terrorists board airplanes with bombs in their underwear, we're all pretty tolerant of the airport security drill.
U: Sir, do you have anything in your pockets?
U: Please remove your boarding pass and hold that in your hand. Are you wearing a watch?
KNOX: Boston, where I live, has one of the first airports to get the very latest in security technology. At the checkpoint, TSA workers are asking people to take off their shoes and belts and empty their pockets. Nothing new about that. But then passengers are asked to walk between two big blue boxes.
U: You'll be walking through the new body scanners.
KNOX: Most people seem to be taking it in stride, like Jason Snipes, who's on his way to North Carolina.
M: My wife's pregnant. You know, you're not supposed to be around X-rays. But, like, for me, personally, no, I don't have any concerns or anything like that. And if it helps, I'm all for it.
KNOX: Magdi Hannah(ph) is headed home to San Diego. He got X-rayed coming and going.
M: It was a pretty normal thing. I didn't feel like anything made a difference.
KNOX: Most others I saw wore the "whatever" expressions of experienced travelers, and that's striking since we're all indoctrinated with the idea that radiation is a dangerous thing.
KNOX: Many people will approach this as, oh, it must be safe. The government has thought about this, and I'll just submit to it.
KNOX: That's David Agard of the University of California at San Francisco.
KNOX: But there really is no threshold of low dose being OK. Any dose of X-rays produces some potential risk.
KNOX: Agard's a biochemist and a biophysicist. He and several of his colleagues at UCSF recently wrote a letter to President Obama's science advisor, asking for a more thorough look at the risks of exposing all those airline passengers to X-rays.
KNOX: Ionizing radiation such as the X-rays used in not only these scanners, but also in medical X-rays, really have the potential to induce chromosome damage, and that can lead to cancer.
KNOX: The UCSF scientists aren't the only ones with concerns, though. David Brenner heads Columbia University's Center for Radiological Research. He recently briefed congressmen and staffers on the new airport scanners.
KNOX: There really is no other technology around where anyone has been planning to X-ray such an enormously large number of people.
KNOX: Brenner thinks the risk to most individual travelers is miniscule. But he worries about the unknowns of scanning something like 700 million travelers a year. Brenner says recent research indicates that about one person in 20 is especially sensitive to radiation. They have gene mutations that make them less able to repair X-ray damage.
KNOX: I don't know if I'm one of those 5 percent. I don't know if you're one of those 5 percent. And we don't really have a quick and easy test to find those individuals.
KNOX: But TSA officials say that's not practical. Think of the long lines, they say, if the machines had to be readjusted for the height of every passenger. In any case, the TSA's Maurine Fanguy says the health risk is so tiny that it's not necessary to avoid the head or neck or to exempt children.
M: It is optional, and so parents can choose for children not to undergo screening. Personally, as a mother of two young children, I want to ensure that all technology that we use is safe. And we would not deploy technology unless we had done very rigorous and thorough health and safety testing.
KNOX: Over at the FDA, officials are equally confident. Daniel Kassiday is a specialist there in radiation hazards. He says the amount of radiation from an airport scanner is nothing to worry about. It's far below what airline passengers get from cosmic rays at 30,000 feet.
M: At worst case, flying from New York to L.A., assuming a five-hour flight, it would take 75 screenings to equal the dose you get from that one flight. Or, more simply, one screening is equivalent of four minutes in the air.
KNOX: Kassiday also dismisses scientists' concerns that the scanners could malfunction and give passengers too high a dose.
M: Are they going to break? Possibly, you know, eventually. Am I really worried there's going to be a significant dose as a result? Not really.
KNOX: Brenner, the Columbia University radiation expert, says there's an obvious answer to all these questions.
KNOX: Put more interest in the millimeter wave scanners, which, as far as we know, don't have any radiation risks associated with them.
KNOX: Ivor Benton was on his way from Boston to Columbus.
M: I don't think they're safe.
KNOX: What are you worried about?
M: Well, what do you expect them to tell you? Do you expect them to tell you it's unsafe after they've spent millions of dollars for them?
KNOX: Richard Knox, NPR News, Boston.
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