Arg! When did I turn into a shill for the TSA?

[essentialsaltes]

I'm really not thrilled with the new, intrusive TSA rules and procedures, but the danger of the backscatter X-ray scanners continues to be exaggerated, I think. The most recent warning to go viral is this blogpost from My Helical Tryst.

Caveat #1: There is no completely safe dose of radiation. You can't fire a bajillion high energy photons at millions of people and expect no damage to be done.
Caveat #2: I'm not a doctor, radiologist, or epidemiologist, but the relative risks (as far as I can tell) suggest to me that the probability of being significantly harmed by a TSA scan are somewhere between winning the lottery and being struck and killed by a meteorite.

Now to get to the blogpost in particular, it's based primarily on the letter of concern written by researchers at UCSF. Thus, it is relevant to link to the FDA's fairly authoritative response.

Experts can and should continue to discuss, explore, measure, and hammer out all of these issues, but I want to address a few particular points from the blogpost.


#1: The scanners preferentially deposit radiation in the skin, thus 'concentrating' the dose in one particular part of the body.

This is true, but the effect has been taken into account. The National Council on Radiation Protection and Measurements published its most recent report[$35] on "Limitation of Exposure to Ionizing Radiation" in 1993, and this report provides tables that cover exposures to particular organs.
The NCRP has commented on security scans: "NCRP has recommended that the cumulative effective dose to an individual member of the public from such x-ray systems used in security screening of humans should not exceed a control level of 0.25 mSv y–1 at a given venue." [i.e. 0.25 millisieverts per year]
And as the FDA describes in its response, "The recommended limit for annual dose to the skin for the general public is 50,000 µSv. The dose to the skin from one screening would be approximately 0.56 µSv when the effective dose for that same screening would be 0.25 µSv. Therefore the dose to skin for the example screening is at least 89,000 times lower than the annual limit." (my emphasis)
Parenthetically, though I'm not gonna shell out $35 to find out, I'd be interested to know whether the radiation limit for your skin were significantly larger than the limit for your spleen or gall bladder, or whatever. Obviously, the skin is exposed to a great deal of solar radiation, and it grows and falls off. Yeah, you can see how deep my knowledge of biology and medicine is.

#2: The scanners are exposing people to hard [higher energy] x-rays, contradicting the TSA's statement that people are exposed only to 'soft' x-rays. Helical Tryst points out that the x-ray source is a 50 keV X-ray tube, which generates both soft and hard x-rays, and is comparable to a dental x-ray.

Now I haven't exhaustively checked everything the TSA has ever said, but the search TSA button on their website suggests that the phrase 'soft x-ray' appears nowhere on the entire TSA site. There may also be just some confusion about terminology, since backscatter imaging (the technique used by the scanners) to some extent favors lower energy X-rays. As you ramp up the energy, scattering increases, but momentum conservation makes it more likely for the X-ray to be forward scattered.
Anyway, the comparison between dental x-rays and the scanner devices is fair, in terms of the maximum energy of the individual X-ray photons. But the important measure of comparison between these two similar sources is the total dosage. Googling doesn't provide much agreement on the exposure from a dental x-ray, with estimates varying from 1 mrem to 25-35 mrem (though the larger numbers may be for a complete series of x-rays, rather than a single shot). And the exposure from the scanners is limited by the TSA rules to 25 µrem, or 100-1000 times less than the dental x-ray.
So if you're concerned about the TSA pointing an X-ray squirt-gun at you skin, you should be concerned about your dentist pointing an X-ray garden hose at your fucking head. (And you should be. There is no completely safe dose of radiation. There's a reason you can no longer use a fluoroscope to see how well your shoes fit. But the health of your teeth is more important than your shoes.)

#3: "With respect to errors in the safety reports and/or misleading information about them, the statement that one scan is equivalent to 2-3 minutes of your flight is VERY misleading. Most cosmic radiation is composed of high energy particles that passes right through our body, the plane and even most of the earth itself without being absorbed or even detected."

This latter statement is true, but is itself highly misleading. The units we're looking at here are rems (or millirem or microrem), and the rem is itself a peculiar derived unit, the roentgen equivalent man/mammal, which defines the radiation exposure not in terms of the total amount of cosmic whatzits whizzing through you, but in terms of the total energy actually absorbed (rads) by the body, weighted by factors associated with how biologically harmful the particular type of radiation is to mammalian cells. So the fact that cosmic neutrinoes are slicing through you without doing any damage is irrelevant. Measuring the radiation actually absorbed by the body, the scanners are indeed equivalent to a few minutes of air travel.


With respect to the larger issues of safety vs. freedom, I think in the end we should be willing to live with a certain amount of risk. When you get on a plane, you know there's a non-zero chance that the engines will fall off or some other accident will occur that will kill you. (And, of course, every time you get in your car, you're accepting an even greater risk of death.) Terrorism is not so different a risk, and I think we should be willing to live with a certain amount of risk, even if that means that government officials don't get to grope 8-year-olds or probe your cavities. And if groping and/or cavity searches are the only way to really have an effective backscatter x-ray system in place, then we can do without having a backscatter x-ray system in place.
If the terrorists happen to succeed in dropping planes like flies, then maybe we would reconsider the proper balance between safety and freedom.

Comments

[(Anonymous)]

A lot of people are going for the security vs. freedom approach on this matter, but I prefer to resort to pure math. About 1.5 million people travel by air each day in the United States. Let's say that going through security -- whether it involves scanners, pat-downs, or neither -- takes a mere five minutes. That's a total of 7.5 million minutes lost every day, which equals 14.25 total years lost every day. Multiply that out for every day of the year and you get over 5,200 years lost every year. Given that the average lifespan in the U.S. is 78 years, that means that security checks are killing the equivalent of 67 people each year. If we didn't have them, it could be convincingly argued that we'd lose a lot more lives. On a cost-benefit basis, these measures seem worthwhile -- which actually came as a surprise to me. (Of course, my numbers could be all wrong, but you get the idea.)

Donovan

[essentialsaltes.livejournal.com]

Interesting numbers, but I'm not sure you can really compare delaying a million people for a millionth of a lifetime with killing somebody -- of course, if anything that would make the security measures more worthwhile.
This would also provide an interesting way to set highway speed limits... lifetimes 'saved' by getting to one's destination faster vs. lives lost in accidents.

But I would argue that this analysis is not simply 'resorting to pure math' as though time wasted were the only and obvious objective measure of whether these security measures are justified.

[(Anonymous)]

Well, that's how the CDC and actuarial firms like insurance companies do it, so who am I to argue with them? And, sure, it's not literally "pure math", but now you're picking nits.

Donovan

[essentialsaltes.livejournal.com]

Well, that's how the CDC and actuarial firms like insurance companies do it, so who am I to argue with them?

I doubt that calculations about how long it takes to buckle a seatbelt, or receive a vaccine entered into the decision to promote these practices.

And, sure, it's not literally "pure math", but now you're picking nits.

I think I have a deeper point here that is not nitpicking. Although you may be uninterested in considerations of safety and freedom, I think these are, so to speak, relevant variables. Presenting the issue in terms of the single variable of total time wastage is an oversimplification of the issue.
It's as if I were to say, "A lot of people are going for the divine contemplation vs. divine communication approach on the matter of prayer, but I prefer to resort to pure math. Since intercessory prayer has no statistically significant effect on patient outcome, it's a big waste of time and people should just stop praying. After all, that's what the CDC and the actuarial firms would dictate."

[(Anonymous)]

Actually, the amount of time involved in these practices does factor into the decision to promote them, along with other obvious factors such as cost. For example, if it took two hours to vaccinate each person in the U.S. against some disease but saved only two lives, then it clearly wouldn't be worth it, even if the vaccine was free.

Also, I didn't say that I'm "uninterested in considerations of safety and freedom". Instead, I implied that measuring the risk of such measures through actuarial techniques might demonstrate that it didn't result in greater safety. As a result, there would be no reason to adopt it and abridge anyone's freedoms.

[essentialsaltes.livejournal.com]

Actually, the amount of time involved in these practices does factor into the decision to promote them, along with other obvious factors such as cost. For example, if it took two hours to vaccinate each person in the U.S. against some disease but saved only two lives

Yes, well my argument only applied to the real world, where seatbelt fastenings and vaccinations take a few seconds.
I agree that when time is a relevant variable, it is relevant. And when it isn't, it isn't. The question is whether the time is a relevant variable (indeed, the relevant variable) in the case of the new transportation guidelines compared to the previous transportation guidelines.

[(Anonymous)]

And even a few seconds, multiplied by millions of people, adds up. Time is always a relevant variable because it's the one resource that's non-renewable and non-fungible. It's more valuable than cash, oil, diamonds, or corn. Really, all we have is time.

Donovan

[stevenkaye.livejournal.com]

If we didn't have them, it could be convincingly argued that we'd lose a lot more lives.

I call rhetorical shenanigans - the choice isn't between ineffective but annoying security or no security.

[(Anonymous)]

And I never stated that was our only choice. I only stated that, given the choice between no security and what you termed "ineffective but annoying security" (and no one's yet demonstrated whether it's ineffective, though I'll agree it's annoying), that the latter may be preferable. Whether it is nor not comes down to how many lives we believe these methods will save, and none of us have satisfactorily addressed this issue. Ultimately, I would prefer effective (financially and temporally) and non-annoying security, but no one's concluded just what that is.

Donovan

[neverjaunty.livejournal.com]

But nobody is offering (or asking for) "no security" as a choice, so yes, it's rhetorical shenanigans. As is "it could be argued". Argued by whom? Are you making the argument?

[arcane-nitehawk.livejournal.com]

Also saying that anything is comparable to a "dental x-ray" is BS. There was a article in the NYT saying that there is absolutely no standard in dental x-rays with doses in a single exposure varying by two orders of magnitude.

[essentialsaltes.livejournal.com]

Yeah, I was surprised by the lack of unanimity when I looked into that. I expect part of the discrepancy is that newer digital radiography systems require less radiation, compared to traditional film x-rays.
Regardless, airport scanners are still more than an order of magnitude smaller than the smallest dental x-ray dose I saw.

[freudinshade.livejournal.com]

Wanna go into business with me on a backscatter resistant body spray? We could make it in traveller friendly scents and basically all we'd need is a sunscreen base...

[neverjaunty.livejournal.com]

Measuring the radiation actually absorbed by the body, the scanners are indeed equivalent to a few minutes of air travel.

Assuming they are properly calibrated, and assuming that they affect the body the same way that cosmic radiation from flying does - things we don't know because the TSA has fucked off on the required studies it was supposed to do before putting these things into use. Also, as has been pointed out, forget flyers - what's the risk to TSA workers from being in proximity to these things all day, especially as they're (again) not subject to rules about calibration and testing?

You don't need a tinfoil hat to be aware that the TSA has lied over and over about the scanners - first saying it was impossible to capture images, then that the images were fuzzy, then that they could be captured and were very revealing but were immediately deleted, then admitting they weren't deleted but claiming they were only stored for 'training purposes'. So why should anyone now believe that the scanners are safe as advertised?

[aaronjv.livejournal.com]

1. Personally, I only want to make sure I'm priapic before being backscattered.

2. I think the machines, though relatively harmless (compared to, say, teabaggers), are a waste of resources...yet if people can get a job building/servicing/running the Electric Eye, yay for them.
2a. I think a wiser form of security would be more education and pay for our armed forces and intelligence agencies, especially in foreign (mainly Arabic) languages.

3. I think the terrorists won. They fundamentally changed America. Will we ever be able to walk through airport security with out shoes on again?
3a. Many would-be terrorists were thwarted on the planes, in fact the fourth 9/11 plane was also stopped by the passengers and crew. Has a terrorist infiltrated a ground crew (the ones loading your luggage into the belly of the plane)? Or why not attack the security check point, before the screening? Or hit a subway, like in Spain.
3b. I'm really surprised Al-Qaeda doesn't simply get a dozen or so shooters (they don't really have to be good) picking people off with NRA-endorsed assault rifles in a mall on Black Friday. They'd be taken out by SWAT teams, go to heaven, and if only two different malls have fatalities, you could wrap up American retail in a box and seal it for ten years before anyone would set foot in a brick and mortar again.

Life has risks. In fact, I can guarantee that each and every human being will, at some point, lose to one of those risks and die. No, we don't want to be blasé, but it's unconscionable that the military-industrial complex is fomenting and then profiting off fear. Rather than create a world where terrorists do not exist, we found a way to make a buck off of them.

"Quite an experience to live in fear, isn't it? That's what it is to be a slave."
--Roy Batty

[neverjaunty.livejournal.com]

Or, as has been pointed out many a time, simply having the suicide bomber set off the explosives AT THE GATE during the security check. Lots of densely-grouped people, serious disruption of travel, not much that can be done to prevent it.