Are Airport Scanners Safe?
IRA FLATOW, host:
This is SCIENCE FRIDAY. I'm Ira Flatow.
Lots of talk this week about public resistance to the new full-body scanning machines at the airports. The full-body scan, which penetrates your clothes, showing great detail, is done using one of two different machines. There's one machine that uses millimeter waves that's - millimeter wave machine, and there's another one that uses X-rays. And it's the latter that have radiation experts buzzing because they subject passengers to what the TSA and the FDA say is a miniscule amount of ionizing radiation.
But just because it's a small amount, does that mean it's safe? And how do scientists know what a safe dose of radiation is? In addition, some TSA workers are exposed to small amounts of radiation that may leak or escape the baggage X-ray machines. How much of a risk do they face from accumulated radiation exposure?
Joining me to talk about it is my guest. David J. Brenner is the Higgins Professor of Radiation Biophysics at Columbia University. He's also director of the Center for Radiological Research there, and that's the oldest and largest radiological research center in the country. It was founded by a student of Marie Curie.
Welcome to SCIENCE FRIDAY, Dr. Brenner.
Dr. DAVID J. BRENNER (Higgins Professor of Radiation Biophysics, Columbia University): A pleasure to be here, Ira.
FLATOW: Yeah. Thank you. Let's talk about the machines that scan the people -there are two basic types, right?
Dr. BRENNER: Yes, there are. One is usually called millimeter wave scan machine and the other is called X-ray backscatter machine. In fact, they both work on the same basic principle of firing a beam of radiation at the individual and looking at what it's reflected back, quite similar to radar or sonar, but in one case using millimeter waves which are not so different from microwaves, in fact, and the other uses X-rays.
FLATOW: Mm-hmm. And it's the backscatter X-ray machines that give you a dose of X-ray radiation?
Dr. BRENNER: That's correct. As far as we know - one can never say something is safe - but as far as we know, there is no health hazard associated with the millimeter wave scanners. So the concern is more about the X-ray scanners.
FLATOW: Mm-hmmm. And what is that concern?
Dr. BRENNER: Well, we know that X-rays can damage DNA in cells, and we know that X-rays can ultimately produce cancer. So the concern is about the possibility of inducing X-ray-induced cancer in one of the individuals who's scanned.
FLATOW: Mm-hmm. On their website, the FDA says that these X-ray machines, quote, "deliver an extremely low dose of radiation to the person being screened. The radiation is so low that there's no need to limit the number of individuals screened or in most cases the number of screening an individual can have in a year."
Dr. BRENNER: Well, I certainly agree with the first part of that statement. The radiation doses we're talking about here are exceedingly low. I think there's some evidence they're a little bit higher than the TSA are stating, but even then the dose is still very low. And what that means is that the risk is extremely low for any individual going once through one of the scanners.
Dr. BRENNER: The concerns we have are actually twofold. One is that there are actually a lot of people who go through airport security many times. One group, of course, is airline pilots, another group is frequent fliers. A typical commercial airline pilot in this country goes through security anywhere from 200 to 400 times a year. So that means that the very small risk from an individual scan is multiplied by that number 200 or 300 times for a pilot, or for a frequent flier, in fact. There's certainly frequent fliers who go through the security that many times in a year.
FLATOW: Or a flight attendant.
Dr. BRENNER: Or flight attendants, indeed.
FLATOW: I was talking to one on the plane the other day about this and I asked her if she was fearful. And she said, you know, I've been a flight attendant for 40 years. And she said just being up here at 35,000 feet for six hours at a time, I get plenty of radiation alone from just being that far above the Earth and the pilots do also. And, you know, I'm the last person who wants to walk through one of these machines.
Dr. BRENNER: Well, I would agree with that. And you could argue that the radiation that pilots and the rest of the air personnel get from natural sources is inevitable. There's nothing you can do about that. But the radiation from the scans, certainly, one could avoid if one used, for example, a millimeter wave scanners, which don't involve X-rays at all.
FLATOW: Well, why don't we just use those then? Why not use the - do away with the X-ray scanners and just use the millimeter ones and everybody might feel better?
Dr. BRENNER: I certainly would. It's hard to know what the logic is. I mean, I think the logic must be that the TSA believes both of them are safe and so they're using both of these devices. But there is certainly not conclusive evidence but convincing evidence that there will be some cancers induced some time in the future by these X-ray devices.
Dr. BRENNER: The issue, Ira, is even though the individual risk is very small, we also think, when we think about risk, in terms of the population risk -that's the risk - we've factored in the number of people exposed to that risk. And what's happened in this field is until 2010, these machines were used actually quite rarely. They were not first-line screening devices. They were used for random checks and for people with - who have some special interest in.
But after the Christmas Day bombing of last year, the so-called underwear bomber, the TSA changed their policy and decided to use these devices as a frontline screening device, essentially, ideally for everybody.
Dr. BRENNER: So what that meant is that the number of people being scanned has gone up or is going to go up quite dramatically. You know, the number of people going through airports at the moment is something like 750 million per year in the U.S. That's a big number.
So imagine all of those people getting scanned. So we have a small risk, but we have an awful lot of people exposed to that small risk. And that gives you a public health concern as well as a concern for the individuals.
FLATOW: Have independent labs verified that these scanning machines are giving the low-level radiation that the TSA says they are?
Dr. BRENNER: Well, the answer is no. It would be good - and I think this really should happen - that these machines become available for the general scientific community to actually assess what the radiation doses actually are. At the moment, people are having to do it in a rather indirect way. You look at the images, the pictures that you've probably seen on the Internet from these devices, and you can work backwards from the quality of the image to how much radiation dose was actually produced...
Dr. BRENNER: ...needed to generate that image.
Dr. BRENNER: And it's actually rather larger than the TSA's numbers. But what we really need is some independent measurements.
FLATOW: So you suspect that those numbers may be higher because the picture is so good?
Dr. BRENNER: Well, because the picture is moderately good, I would say.
Dr. BRENNER: And even if they're higher, the doses are still very low - that, I think, one must say. But they're probably somewhat higher than the TSA's estimates at this point.
FLATOW: Let's talk a bit - only a couple of minutes we have left - about the baggage handlers, because they stay by those baggage machines. And there was a study that came out in 2008 that sort of flew under radar screen, I think, of anybody's attention. It was a study by NIOSH, the National Institute for Occupational Safety and Health, at the request of the TSA, to determine the level of radiation emissions from these systems that scan the baggage. And they had some very disquieting conclusions about what they found.
Dr. BRENNER: Yeah, indeed. They found that the handlers were actually getting radiation exposure that we didn't expect, in part, because they were reaching into the machines. And, yeah, that that really shouldn't have happened. And it indicates some failure in terms of the quality control of the whole system.
FLATOW: Well shouldn't the TSA workers being wearing badges? Everywhere you go that people are around radiation in hospitals, in clinics or dentists, wears a badge to see what their cumulative exposure is.
Mr. BRENNER: Absolutely I work at Columbia Presbyterian Hospital here and everybody associated with radiation work wears a film badge and it's easy and it's inexpensive and so every month there is a reading of how much radiation exposure anyone wearing the film badge gets. It would sound an alarm if there are any possible over-exposures. So it's a no-brainer in many ways for the folks associated with these devices to wear film badges.
FLATOW: Yet they tell us from personal communications that they're afraid or discouraged from wearing them. It's not against the rules but they're told, you know, it has to be out of sight, some people have said.
Mr. BRENNER: Yeah, that's a little surprising. I mean, and the film badges have to be organized by the employers because the film badges then have to be sent off to be read and analyzed so it's not something you can really do on an individual personal basis. It's something that the employers have to organize.
FLATOW: And so we don't know even after this report came out, we don't know if any practices have changed.
Mr. BRENNER: I certainly haven't seen film badges on personnel in airports. I don't know if you have.
FLATOW: No, well as I say when I don't see them I ask them and I ask why and some people know about it. Some people don't know about it. And you get some of the answers from when I go through there and I say, are you fearful of the machine? Are you getting any exposure? And many of them tell you, oh, I'm getting a little bit but it's not harmful.
Mr. BRENNER: Well, small amounts, very low doses of radiation on an individual basis probably are not so harmful but radiation is cumulative. It builds up over time. And if a large population of people are being exposed to radiation that's also a problem.
FLATOW: Mm-hmm. And so as far as the personal scanning and the choice between these two machines, one ,if we did away with the X-rays people might not worry about any X-ray radiation because there is a technology to use the millimeter.
Mr. BRENNER: I think that's true.
FLATOW: Is there any sound, sonic kind of ultrasound scanner that they might develop?
Mr. BRENNER: Ultrasound has not proved very successful. It has been tried in fact and it doesn't seem to have worked very well. The two devices that seem to give the best images are the X-ray and the millimeter wave scanners, although it must be said there are lots of people working on different and newer technologies right now.
FLATOW: Well, thank you Dr. Brenner for taking time to be with us.
Mr. BRENNER: A pleasure.
FLATOW: I should point out to you and our listeners that we did invite the TSA to come on and talk about it but they have declined to take us up on our invitation. David J. Brenner is the Higgins professor of radiation, biophysics at Columbia and he is also director of the Center for Radiological Research there and that's interesting to note that. As I said the oldest radiology center in the country founded by a student of Marie Curie.
We're going to take a break and come back and change gears and talk about music, how every time you listen to music or play an instrument you're doing a little physics experiment. Why does a note make a certain sound and a hammer hitting a nail make a different one? There's physics behind all of this and how you listen to music so stay with us. We'll be right back after this break.
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