I have been in the middle of a cross-country move the past few weeks, which has been quite challenging with a baby in tow. According to Google Maps, we moved 1423 miles from our old home to our new home. We also moved 4292 ft higher in elevation (according to Wikipedia). No wonder I am exhausted
For work reasons, we needed to move rather quickly. Normally, we would have driven, which takes about 24 hours. With stops for feeding, changing, and soothing a baby, that would have been at least 3 long days, or 4 or 5 if we took our time and stopped to see things on the way – after all, if you are going to drive more than 1400 miles, you might as well see the sights along the way. Unfortunately, we did not have time for that this trip, and so I flew with my daughter to our new home.
I am a relatively frequent flyer and adept at getting through security quickly and efficiently, though it is definitely more of a challenge now that I have a baby with me. I, like all of you who fly I’m sure, have noticed the increasing number of airport body scanners in the security line over the past couple of years. My first experience with one was returning to the US from an international flight in the spring of 2010. Now they seem to be in all the airports that I frequently fly through.
There are a number of issues surrounding these scanners: privacy, effectiveness, cost, and safety. There are huge numbers of articles around the web on each of these issues. I started to think seriously about the last one – safety – last year when I was pregnant. I went on three plane trips while pregnant and was wondering if the scanners were safe for my unborn baby. I never had to walk through one of these scanners during those trips, and so I did not give it much more thought. Then I started traveling with my daughter and wondered once again whether or not these scanners are safe for her. It is interesting that it never occurred to me to worry about this for my own safety, but I guess we are always more concerned about keeping our children safe.
Ignoring all the other issues (which may also be very important to you), let’s take a look at how these scanners work and whether or not they are safe for us to walk through.
There are two types of scanners that are currently in use in the United States: millimeter wave three dimensional scanners, and x-ray backscatter (two dimensional) scanners. They use different wavelengths of light (both invisible to the eye) and different methods of making an image.
A few weeks ago, I had a blog entry on how CT scans work. These body scanners are very similar in a lot of ways, so let’s review a few of those ideas, starting with wavelength. The electromagnetic spectrum (the different wavelengths and frequencies of light) is shown below:
I did not mention the relationship between wavelength () and frequency (f) in my previous blog entry, but here it is:
where c is the speed of light, 3 x 108 meters/second (or 186 miles/second). This is true for all wavelengths of light traveling through air. Who cares, you say? Well, this means that the millimeter wave beams have a frequency of ~ 300 GHz and below. For reference, your cell phone uses waves that have a frequency of ~ 1 GHz. The x-ray beams have frequencies of greater than a million GHz, or about 10,000 times that of the millimeter beam waves.
Again…this is interesting and all (if you are into numbers), but why should I care? Well, the energy contained in the individual balls of light (photons) in these beams is directly proportional to the frequency of light. That means that the x-ray photons hitting your body have more than 10,000x more energy than the millimeter wave photons. These high energy photons can actually ionize atoms – that means they can remove electrons from the atoms in your body, which can change the ways your atoms chemically bond and form all the organic material your body needs to function correctly.
So that is why x-rays are more dangerous than millimeter waves (which have not been shown to have any lasting harm on your body as far as I know). The question of safety seems to lie in the dosage. The backscatter scanners only send a very small amount of x-rays at your body.
According to the Transportation Security Administration (TSA):
“Advanced imaging technology is safe and meets national health and safety standards. Backscatter technology was evaluated by the Food and Drug Administration’s (FDA) Center for Devices and Radiological Health (CDRH), the National Institute for Standards and Technology (NIST), and the Johns Hopkins University Applied Physics Laboratory (APL). For comparison, a single scan using backscatter technology produces exposure equivalent to two minutes of flying on an airplane, and the energy projected by millimeter wave technology is thousands of times less than a cell phone transmission. Millimeter wave imaging technology meets all known national and international health and safety standards. In fact, the energy emitted by millimeter wave technology is 1000 times less than the international limits and guidelines.”
So this sounds like the scanners are safe, right? But the European Union has banned the x-ray backscatter scanners. From a European Commission Press Release:
“In order not to risk jeopardising citizens’ health and safety, only security scanners which do not use X-ray technology are added to the list of authorised methods for passenger screening at EU airports.”
Why? Well, the backscatter machines concentrate the x-rays on our skin. Unlike for CT scans, the x-rays do not travel through our bodies, but are reflected backwards to a detector to form an image. Some scientists, like the ones from the University of California at San Francisco that wrote a Letter of Concern printed in this news article, are concerned that the scanners have not be accurately tested and evaluated for this use. They believe that until these tests are done, the scanners should not be used in airports.
Okay, so we have heard this all before. They are safe. They are not safe. What does this mean? I feel that there are enough intelligent people (scientists, officials in Europe) who do not feel the machines are safe, especially for children. I will not walk through one of the x-ray backscatter machines with my daughter. (Of course, it is unlikely I will ever have to since I currently have to carry my daughter and that would defeat the purpose of the scanners – I could just hold her in front of my body wherever I was carrying something forbidden on airplanes.)
I do believe that the millimeter scanners are safe and have no problem walking through those. My next question was this: How can I tell which is which? It turns out they look completely different. There are number of pictures online showing what they look like. This article on The Science Behind Airport Body Scanners shows the scanners side by side so you can see what they look like.
Now I can make an educated decision about whether or not to walk through the scanner I see in the airport. I have only seen the millimeter wave machines and am not sure what airports have the x-ray backscatter scanners. If anyone has found a list of what airports carry which scanners, please leave a comment – I would be interested in knowing.
Side note: We are still in the midst of settling in and so the blog entries will likely be shorter and/or later than usual for a few weeks until I can find the time to work on them.