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.
Most of the concerns in the letter are addressed. It's easy to spread FUD, but these devices are likely safe. Other organizations and governments have evaluated their safety independently.
There is some evidence that extremely low radiation do not increase your cancer risk. However, if you realize that a pilot already receives increased radiation by flying several hours a day and could average 2+ of these scanning’s a day for 30+ years you are probably adding a significant risk (compared to getting a pat down).
As to passenger safety the annual dosage delivered in a short period of time is not safe. So take someone with say, a bad sun burn or a recent CAT scan and walking though those things is probably a bad idea.
Also due to poor training / incompetence some people are going to be sent through these things several times and or be required to stand there while someone get's distracted.
PS: The corresponding annual effective dose... and 500 mrem for the more exposed routes. (Bottollier-Depois JF et al. Assessing exposure to cosmic radiation during long-haul flights. Radiat Res 153(5 Pt. 1):526-32; 2000.)
>It's easy to spread FUD, but these devices are likely safe.
We have two facts here:
* These machines should not be in use as they do nothing to help security and they are ripe for abuse (and have already been abused in their short time of being used)
* The public is not ever going to be bothered enough by privacy concerns to actually do something about it. They would, however, do a great deal if they felt their lives depended on it.
Taking these two facts into account, if a leading scientist says these things may be dangerous I would tend to take his word for it without digging into it. That sounds bad but how else can one deal with people who value convenience over what is right?
I accidentally upvoted you. There is the truth and there is falsity. None of our principles, including the one that says minimum wage security workers shouldn't be looking at us naked, mean anything if we can't look each other in the eyes and articulate them truthfully.
It is falsity that is allowing people to convince airport authorities that these machines make sense. If you want to get into the bullshitting arms race, know a priori that you will lose; those people are much better at it than you are, and they have more to gain or lose.
I'm not saying to lie. I'm saying if someone with credentials comes out and says there may be health issues with these things we don't need to look any further. They shouldn't be in the airport whether they present a safety risk or not. Instead of wasting energy chasing something that doesn't change the over all outcome (finding out they're safe still doesn't mean they should be used), use that energy to research things that do matter. It's just about being efficient. :)
It's a tiny line between FUD and alertness. I prefer people bring this stuff up every now and then to remind all of us to never stop questioning things.
It's so easy to get caught up in the halo/horn effect and try to make every fact about backscatter machines bad. But the truth is complicated. It requires weighing all evidence, not just looking at evidence that agrees with your current views.
89,000 times lower than the annual limit.
I'm not a fan of the TSA or backscatter machines, but facts are not up for debate. If backscatter machines cause cancer, it would be very surprising and it would tell us something new about physics and/or biology.
Also, if you worried about every risk that was as low as backscatter machines, you simply wouldn't be able to function in society. 5 minutes in a car is a 1 in 5 million chance of death.
I think most would rather the use of these devices be banned on principles of their invasiveness rather than on safety concerns. Otherwise, you just get a "safer" version of the same thing in a few years.
That's a different discussion. I'm just talking about safety. The scientists in the letter are just talking about safety. The FDA is just talking about safety.
"Should we put these things in airports?" brings a lot more baggage with it than "Are these things safe?" I wish our opinions about backscatter devices could stay out of this discussion about their safety.
I'm going to mention my opinion anyway, because otherwise people will suspect me of being on The Other Side. I think these devices are a waste of money and I don't want to be subject to them. They raise a ton of privacy concerns and make me wonder, "What's next?" But they're almost certainly safe.
Thanks for pointing to this very thorough response which addresses the concerns of the letter. I don't think the authors of the letter are spreading FUD, however: they're asking for more information about the means by which the dose is being calculated and pointing out potential health consequences of the lower-energy beam in skin absorption:
<em>if the key data (flux-integrated photons per unit values) were available, it would be straightforward to accurately model the dose being deposited in the skin and adjacent tissues using available computer codes.</em>
There is a big difference between a little fud and being willing to say anything. These machines have been called, by a reputable scientist, as potentially very dangerous. I see no problem making sure everybody knows that they are dangerous, nor do I particular care to present both sides of the argument.
These machines have been called, by a reputable scientist, as potentially very dangerous.
And 1 out of 5 dentists recommend sugar gum. There are enough scientists in the world that you can always find one who shares your belief. Scientific consensus is a much more reliable indicator of correct beliefs.
...nor do I particular care to present both sides of the argument.
I can think of half a dozen pieces of evidence that would change my belief about whether or not backscatter devices are safe. What evidence would you need to convince you that they are safe?
This isn't about whether they are safe or not (a subject I don't give much of anything about), but about getting them banned. If we can't get them banned for privacy issues (as they should be) but we can get them banned for something else, then I will take that.
Maybe they shouldn't, but when you're going up against the kind of ruthlessness that will stop at nothing to invade your privacy by any means, limiting your angles of attack for ethical concerns might not be palatable for everyone. I'd like these machines to be banned for privacy concerns as well, but if they're banned for safety concerns that I made up, that's still better than them being put in every airport.
That's a dangerous path to go down; if we abandon factual standards or arguing issues on the legal merits, then what's left is basically just marketing. And there will always be someone who can afford better marketing.
It's like torture; one can't torture on behalf of the 'good guys' and say it's for a higher purpose, because acceptance of torture as a legitimate means of inquiry is exactly the sort of thing that divides good government from bad (this, of course, assumes one is opposed to the practice in the first place).
I think the point is that we're already at that place. These machines are only there because of what you call marketing. You may think a knife is an elegant weapon for a more civilized age, but you're still screwed if you bring one to a gunfight. It's a difficult choice.
When the machines become sentient, you may have a point.
In addition, the machines are bad on privacy terms, but since the debate has been frame such that those who advocate privacy are considered suspect, we have to work with what we have and make the best of it.
I found the most interesting part of this to be the end when they list one of the concerns as Software. For those who want a point of reference of what could go wrong check out the Therac-25 story http://en.wikipedia.org/wiki/Therac-25
"Because this device can scan a human in a few seconds, the X-ray beam is very intense. Any glitch in power at any point in the hardware (or more importantly in software) that stops the device could cause an intense radiation dose to a single spot on the skin."
The document was linked here before but is very detailed and interesting, even naming specific issues:
A) The large population of older travelers, >65 years of age, is particularly at
risk from the mutagenic effects of the X-rays based on the known biology of
melanocyte aging.
B) A fraction of the female population is especially sensitive to mutagenesis provoking
radiation leading to breast cancer. Notably, because these women,
who have defects in DNA repair mechanisms, are particularly prone to cancer,
X-ray mammograms are not performed on them. The dose to breast tissue
beneath the skin represents a similar risk.
C) Blood (white blood cells) perfusing the skin is also at risk.
D) The population of immunocompromised individuals--HIV and cancer
patients (see above) is likely to be at risk for cancer induction by the high skin
dose.
E) The risk of radiation emission to children and adolescents does not appear to
have been fully evaluated.
F) The policy towards pregnant women needs to be defined once the theoretical
risks to the fetus are determined.
G) Because of the proximity of the testicles to skin, this tissue is at risk for
sperm mutagenesis.
H) Have the effects of the radiation on the cornea and thymus been determined?
That's fine though. Society has already determined that 3000 people dying in a terrorist attack is much scarier than 500,000 people that die every year from heart disease. Otherwise we'd be spending money on encouraging a heart-healthy lifestyle rather than preventing someone from bringing a toothpaste-bomb onto a plane.
It's clear that if we can save 200 business travelers and vacationers from incineration, it's worth killing off a few senior citizens. Won't someone please think of the children?
(Hey, this isn't my policy. If someone asked me, "is it worth hurting someone to possibly save someone else", I would have said no. But nobody ever asks me about these things!)
I've been told by an engineer friend of mine that the radiation dose these scanners deliver was dwarfed by the in-flight cosmic irradiation.
He didn't give me numbers, though. It would be nice if a radiotherapist (or another expert) could chime in on this topic.
----------------------------
edit: answering my own question: he's wrong.
from [1] :
>The estimated occupational effective dose for the aircraft crew (A 320) working 500 h per year was 1.64 mSv.
> Other experiments, or dose rate measurements with the neutron dosimeter, consisting of LR-115 track detector and boron foil BN-1 or 10B converter, were performed on five intercontinental flights.
> Comparison of the dose rates of the non-neutron component (low LET) and the neutron one (high LET) of the radiation field at the aircraft flight level showed that the neutron component carried about 50% of the total dose.
> The dose rate measurements on the flights from the Middle Europe to the South and Middle America, then to Korea and Japan, showed that the flights over or near the equator region carried less dose rate; this was in accordance with the known geomagnetic latitude effect.
The PR video/slideshow at the last checkpoint I went through said that the dose was safe because it was equivalent to being in the airplane for 3 hours. This presumably was meant to be comforting, but in my mind I was computing a 3hours:3sec ratio and trying to remember if time-dose averaging was appropriate (I work in MR, and it's been a while since my ionizing radiation course). I was not asked to go through the machine, but I would have refused simply because of the flippant tone of the 3hrs in the air claim.
No, actually your data validates him. Maybe you are confusing 'm' with 'μ', that is, milli- (10^-3) with micro- (10^-6)?
>The estimated occupational effective dose for the aircraft crew (A 320) working 500 h per year was 1.64 mSv.
1.64 mSv (milliSieverts) / 500 hours = 3.28 μSv/hour. A 3-hour flight is 10 μSv.
For comparison, the FDA letter [1] linked in another comment here cites the effective dose of the backscatter x-rays as 0.25 μSv.
The cosmic ray dose from a 3 hour flight is 40 times that of the backscatter x-ray. Pretty much "dwarfs it".
(Note that while the FDA letter says the effective dose is 0.25 μSv, the footnote there (11) says that RapiScan is <=0.05 μSv. Not sure how to parse this -- maybe the 0.25 μSv is a regulatory definition, not the real dose. An NPR article [2] I cited earlier claimed 0.02 μSv, consistent with that <=0.05 μSv figure.
While I'm in these parentheses, NOAA has a table [3] of cosmic ray doses as a function of altitude. Pretty much consistent with your source -- 3 μSv/hr at 30,000 ft, 6 μSv/hr at 40,000 ft).
The health risks can't just be quantified by the overall radiation dose. It depends on how that dose is deposited in the subject. The letter raises the concern that the since almost all the radiation is absorbed by the skin, the dose to your first centimeter or two of epidermal tissue may be fairly high. If the calculations that concluded the devices were safe assumed that the radiation was evenly distributed throughout the body, then the safety of the devices could be suspect.
I could not find the energy of the X-Rays used for these scans, but they would likely be low-energy (high energy rays don't scatter much), hence absorbed mostly superficially, as you said.
The airplane itself is much less superfluous, but irradiates you far more than the backscatter machines. Are you sure you're not just putting a sort of halo of evilness around the backscatter machines because you dislike them for other reasons?
(Full disclosure: I'm not particularly bothered by backscatter machines as such, but I vehemently object to the paranoid, theatrical, and statistically silly approach to security that has provided the impetus for their installation.)
Seriously? We could implement pipelined multi-stage inspections, like a security line to get into another security line, and hire more TSA people to make sure everyone is spread out. And have bomb-sniffing dogs everywhere. This would be silly, but I wouldn't put it past the TSA to actually do it.
I believe what's happening is the use of the radiation concerns is a proxy for the underlying problem: regularly taking naked pictures of the population in the name of security.
I don't think anybody can effectively argue that the whole enterprise is in dire need of grownups -- too easy to get screwed the next time there is an attack. But you could argue that radiation is a key factor, or just wave your arms around and yell a lot. With enough arm-waving, smoke, and mirrors you can make the case that the population is deeply concerned about radiation effects -- regardless of the science -- so "something must be done". "Something must be done" is what got us here in the first place, perhaps "something must be done" is what can get us out.
More to the point, it's the government engaging in pornography, illegal search, and sexual assault combined with radiation overdoses in the name of FALSE security.
We already know that they don't work, and they don't even pretend to address any of the real security vulnerabilities. They'll only deter idiot terrorists, not real ones.
The problem, of course, is that you are not solving the underlying problem... you are, at best, potentially treating one isolated symptom, and you are doing so by deflecting the conversation from the real problem as well as potentially compromising some scientific integrity along the way.
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.
Most of the concerns in the letter are addressed. It's easy to spread FUD, but these devices are likely safe. Other organizations and governments have evaluated their safety independently.