World Tour 2011 Day 1: Airplanes and body scanners

Finally made it to Boston; it’s a bit after 6:30 AM local time. I slept for about four hours before the sun woke me up. I spent about 20 hours actually in the air yesterday, and 27 hours total on planes and in airports yesterday.

The flight from Sydney was about as uncomfortable a flight as any I’ve ever been on, even counting other iterations of the same flight I’ve taken in the past. I had the middle seat in one of the back-ish rows in United Economy, with virtually no elbow room and virtually no leg room. The Economy seats never actually go far down enough for me to relieve tension in my body, so I tried to get some rest by keeping my seat all the way forward and bracing my head against the back of the seat in front of me. A piece of added charm was that I had a three-year-old kicking the back of my seat at intervals throughout the flight. (She was otherwise quiet and well-behaved.) I’m pretty convinced I got no rest at all throughout.

After this — US Customs! I missed the opportunity to get my tax refund from Australian Customs for exporting a few pieces of carved wood art for my friends and family, since the items and the receipt were in the bags I checked back in Canberra. After a bit of a wait I was happy to see the bag end up on the carousel, and was able to get it onto my next flight as a carry-on, though of course I had to go back through security in the domestic terminal.

The line for security stretched the entire length of the terminal. I was actually concerned I’d miss my flight for a little while, as were the folks behind me who were flying out half an hour earlier. Despite our worries, though, we were expedited through the system in about half an hour. I elected to give the body scanner a miss and be frisked instead.**

The flight from Boston was much nicer. I had the middle seat once again, not an aisle or a window — but for whatever reason, I got an Economy Plus seat with what I would consider luxurious amounts of leg room. I could easily have climbed over my fellow traveler in the aisle seat without disturbing him in the slightest. I’m told that when I hit Star Alliance Gold status, which should happen after I complete this trip, I’ll get this kind of leg room all the time. In this case the sleeping solution was simple — I just pulled out my tray table and did a face plant on it. I felt remarkably functional, and only slightly delirious, on my arrival into Boston.

** Physics digression: Body scanner technology

Until this time I wasn’t aware that there were millimeter-wave scanners (the kind they had in SFO) as well as the now-infamous backscatter X-ray scanners, which are manufactured by Rapiscan Systems and are currently being deployed by the TSA.

The latter technology uses X-rays, a form of so-called ionizing radiation which can break chemical bonds in the DNA in your cells and therefor produce the increased cancer risk we typically associate with “radiation”. So part of convincing everyone that it’s safe should be some estimate of the dose involved. I was hoping for some numbers on that to be able to decide for myself. If I had to guess based on my physics knowledge, I would assume (and, see below, it looks like I’d be right) that the doses for backscattering would be much less than for the kind of transmission X-ray imaging you get at the hospital. This is because “backscattering” means by definition that the X-rays bounce off you, as some of them always do. Transmission X-ray imaging means you have to send enough X-rays all the way through you that most of them come out the other side. Hard features like bones stand out because they absorb more X-rays than the soft tissues of which the rest of your body is made. Thus for transmission imaging, you have to provide enough X-rays that at least some of them go through you, whereas in backscatter imaging the X-rays which bounce off are the ones that are useful. (On further reflection, this simple fact doesn’t tell you much; the relative doses for each kind of imaging will depend on the cross section for backscattering versus the total scattering cross section, as well as the signal-to-noise needed for your application, neither of which I’ve bothered to work out. Might do it later, I’m kind of curious.)

The numbers available from the Wikipedia page claim the full-body dose for a single backscatter X-ray body scan is less than 0.1 uSv — or less than a percent of the radiation dose from increased flux of cosmic rays, also ionizing radiation, during the flight itself! So, even if the risk of cancer might increase minimally, any effect would be way down in the noise. A mathematically nonzero risk, folks, is by no means necessarily a significant risk! I’m more or less satisfied now, unless the 0.1 uSv figure is for some reason not even close to being accurate.

Millimeter waves, on the other hand, are not nearly energetic enough to cause cancer. For perspective, they’re not too far from the kind of radiation your cell phone produces. Everyone who still thinks that cell phones cause cancer despite presenting no ionization risk, well, I’m afraid I can’t really help you there, although as noted above I disagree.

These considerations are of course separate from whatever arguments you may make against those scanners based on privacy, modesty or dignity, or on civil rights concerns regarding the abuse of such technology. Those are perfectly valid concerns as well. Given the outcry over the use of this technology, I’m not as worried about it as some of my friends seem to be. But it is nice, at least, that if this is a concern for you personally, you can always opt out and request a separate search.

Which I did, this time around — to see what it would be like. The TSA officer who searched me was entirely respectful and forthcoming throughout the process and made it about as pleasant as it could have been. The whole process did take about 15-20 minutes, though, from my requesting that it be done to the completion thereof. If you’re particular about the body scanners, make sure you budget that extra time into your airport arrival estimate.

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About Richard

I'm an American scientist who is building a new life in Australia. This space will contain words about science and math, but also philosophy, policy, literature, my travels, occasional rants, all sorts of things I find strange and awesome. The views expressed in this blog do not necessarily reflect the opinions of my employer at the time (currently University of Sydney), though personally, I think they should.
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2 Responses to World Tour 2011 Day 1: Airplanes and body scanners

  1. Brian says:

    There are a few potential problems with the backscatter machines though, one of which is that it’s not a whole body dose, just a dose to your skin. Smaller dose but much smaller volume. Second is that no data has been released on what that dose really is, the only organization that claims the dose is even safe is the company that makes them. See: http://www.whitehouse.gov/sites/default/files/microsites/ostp/ucsf-jph-letter.pdf

    • Richard says:

      Thanks for the link, Brian; I hadn’t come across it before. They do list a number of concrete good reasons particularly relating to the shallow penetration length and energy scale of the X-rays being used. I’m glad at least that I don’t seem to have propagated patently false information here, although I agree that relying only on the dose averaged over your whole body may be misleading. I really do hope they look into these things before such scanners become mandatory; I appreciated the opportunity for “alternative screening”.

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