Leading scientists say backscatter X-ray may be far more dangerous than thought
npr.org
npr.org
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.
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.)
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?
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.
... are "likely" safe.
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.
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.
"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.
In a few years, we will call them cancer machines again and see if we can win then.
If you have a way to win on privacy issues the more power to you, but I doubt it can be done.
<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>
This looks like science to me, not FUD.
A little fud now and then is a good thing.
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?
And it was a leading scientist.
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).
This, my friend, is the problem with politics and science today.(And probably all of human history, but I was going for affect.)
But until then, I have to work with what we have.
"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."
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?
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!)
He didn't give me numbers, though. It would be nice if a radiotherapist (or another expert) could chime in on this topic.
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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.
[1] http://www.sciencedirect.com/science?_ob=ArticleURL&_udi...
>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).
[1] http://www.fda.gov/Radiation-EmittingProducts/RadiationEmitt...
[2] http://www.npr.org/templates/story/story.php?storyId=1268330...
/hides
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.
Cancer machines are bad for you, say no to cancer machines.
(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.)
Not saying you're not being frivolous, but it's annoying how often people take the easy route.
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 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.
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.