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Chance of Dying From Backscatter Radiation Same as Chance of Terrorism (daringfireball.net)
252 points by mcantelon on Nov 18, 2010 | hide | past | web | favorite | 128 comments



Actual web page: http://www.public.asu.edu/~atppr/bodyscan.html

Actual article: https://docs.google.com/viewer?url=http://www.public.asu.edu...

The first thing you'll learn in radiation safety is that the nature of the dose matters a lot. Sometimes you're A-OK if you can survive the initial dose. Other doses are accumulative. It depends on the energy of the radiation, the tissue's scattering cross-section, the time, and the flux, among other things.

This means that the Sievert (a unit of biological impact due to radiation) is only meaningful in the context of the dose geometry. It's great for talking about a chest X-ray, where the dose is spread out over a big volume of tissue. Where it's unclear is in the case of rapidly-thermalizing or compton-scattered particles: like backscatter. Look at the graph in that article. Something like half of the energy is deposited in the first couple centimeters of tissue.

We haven't done this before, and don't have a good model for the long-term effects. My guess? This kind of exposure is a hell of a lot worse for melanomas than a chest X-ray delivering the same energy. Claiming compliance to a metric like the ANSI limits is meaningless.

Edit: Oh, and the concern raised over the beam stopping and delivering a couple Sv to a quarter-sized patch of skin is definitely scary. We did exactly that to several people with medical cyclotrons.

Edit: I should also mention that tissues have varying tolerance to radiation. Rapidly-dividing cells tend to be hit the hardest, which is why your stomach lining, skin, and hair slough off after acute ionizing rad exposure. Your skin, stomach, lungs, breast and thyroid are also the most frequent to undergo cancer in radiation-linked longitudinal studies. See, for example,

http://pats.atsjournals.org/cgi/content/full/5/9/934


And according to David Brenner of Columbia University:

Recent research ... indicates that about 5 percent of the population — one person in 20 — is especially sensitive to radiation. These people have gene mutations that make them less able to repair X-ray damage to their DNA. Two examples are the BRCA-1 and BRCA-2 mutations associated with breast and ovarian cancer, but scientists believe many more such defects are unknown.

http://www.npr.org/templates/story/story.php?storyId=1268330...


Fabulous post.

Even if the thing is absolutely, perfectly safe as designed, if you keep in mind human error, mechanical failure, individual physiology, and variations in flying frequency, it's not to see this as actually significantly more likely to cause death than terrorism.


This is a grossly irresponsible abuse of statistics. What's even stranger is that the author agrees. In his paper (conclusions, page 15):

>The major public health effect of concern at low doses of ionizing radiation is cancer. There is clear evidence of cancer induction at effective dose above about 200 mSv. Below an effective dose of about 100 mSv radiogenic cancer mortality risk estimates for all cancers is highly uncertain. 16 It is not possible to determine reliably whether a radiogenic risk is present in an X-ray screening population because of the high spontaneous incidence of cancer and multifactorial nature of disease causation 17.

>Use of collective dose to estimate public health impacts when large populations are exposed to trivial doses is inappropriate and not reasonable. The assumptions implicit in the collective dose calculation conceal large biological and statistical uncertainties.16 If an individual passenger is not harmed by X-ray screening then the population isn’t either.

"Inappropriate and not reasonable". Yet on his webpage (not submitted to peer review), he does exactly that.


> Use of collective dose to estimate public health impacts when large populations are exposed to trivial doses is inappropriate and not reasonable.

First, let's make sure we are clear about the difference between collective (for a population) and cumulative (adding up repeated doses for an individual).

Second, "inappropriate" and "not reasonable" tend to be weasel words with regard to scientific findings. The real issue is that the effects of small doses haven't been rigorously studied, unlike with high doses.

Rather than actually study them, we see brusque dismissals.


George Bush International doesn't have this yet. I'm going to opt out of scanning for my flight back from Pittsburgh, however.


I'll be opting out as well, karma be damned.


So, the risk from a backscatter radiation machine is roughly equal to the risk from terrorism.

The Federal Government, via the FDA, tells us that the risk of the backscatter machine is "minuscule".

Therefore, in the Federal government's own risk terminology, the risk from terrorism is "miniscule".

Why are we spending all this money on a "miniscule" threat? Why are sexually molesting the population over a "miniscule" threat? (Rhetorical.)

(I say "sexually molesting" on the grounds that if I personally performed those same actions on a stranger, that is what it would be called. It would continue to be called that if I tricked this person into giving "consent" for false reasons. A doctor has a compelling reason. I do not grant that excuse to the TSA. I also do not think I am being unduly inflammatory, I think it's just plain fair.)


Yes, but we'd much rather kill ourselves than give someone else the satisfaction of killing us. My diet and inactivity is likely to take five good years off my lifespan? Meh. There's a tiny chance I might end up in a violent struggle for survival someday and somebody might get the better of me? Jesus, what an awful thought! Pass me the nachos and a Coke while I sit on the couch watching this video on handgun tactics.

As a thought experiment, can you imagine if diabetes was an unstoppable dude who came to your house and beat your ass in front of your wife and kids? I can think of people I know who would suddenly be a lot more afraid of diabetes than they are now.


Yes, but we'd much rather kill ourselves than give someone else the satisfaction of killing us.

Who is the "we" and who is the "someone else"? "We" is a bunch of random people I don't know. And "someone else" is a bunch of random people I don't know.


Terrorism can in both small and very large ways effect entire nations. backscatter radiation? Not so much. It's illogical to compare the two and make judgments on based solely on the death rate. You don't need to kill people (all of them) to influence them.


Erosion of civil liberties can in both very small and very large ways affect entire nations.

I'm actually way more worried about that, and I think that's the rational answer.

(Edit: Implicit in the way I phrased that, BTW, and I'm now making explicit, is that I agree you have a good point and you shouldn't have been downmodded. I believe the secondary effects of civil liberties erosion outweigh the secondary effects of terrorism as the situation now stands, but I agree that your point must absolutely be considered to make a decision based on all the facts.)


When essentially the entire country is united except the political forefront, the effects have reached the entire nation. Once the government gets too distanced from the populace, it loses relevance and becomes the enemy.

How many violations before the populace decides on another Tea Party?


So then perhaps the best way to protect a nation from terrorism is not to be influenced by it.


I hesitate to say "of course", because it sounds trite, and the underlying issue is serious. But this is precisely what we did in the UK during the IRA (Irish terrorist organisation) years. And we were encouraged to do that by the media and government. And as stiff upper lipped Brits, we did so with pride :)

I myself saw the outcomes of three of the bombs personally -- by which I mean still smoking -- and picnicked on the Regent's Park bandstand on the Sunday which was blown up on the Tuesday; the bomb would have been there at the time.

http://en.wikipedia.org/wiki/Hyde_Park_and_Regent%27s_Park_b...

None of this changed my behaviour at the time, nor did it appear to do so for anyone else, other than being vigilant for strange packages.

So yes, the correct response is not to be influenced by it. In other words, do not give up your way of life because of murdering cowards.


I completely agree with this statement.


Overreaction to terrorism is part of what makes a terrorist attack a special threat. Ironically, the wasteful measures we take to prevent damage from possible future attacks are social and economic damage caused by terrorism. Getting rid of these stupid machines and reclaiming some of our civil liberties would reduce the real damage caused by 9/11 -- a real, historical, non-hypothetical terrorist attack.

It would also set a precedent for dealing sanely with terrorism in the future. The more a terrorist attack disrupts our society and undermines our values, the more money and freedom we will part with in response to one, and therefore the more it will disrupt our society and undermine our values. That's a vicious cycle we can avoid by accepting risk and not treating terrorism as a special, incomparable threat.


Isn't this the same utilitarian argument that would restrict all of diets for the sake of healthy, roads for the sake of safety, and civil rights for the sake of efficiency?


I think the point JoseFresco is making, which is a little lost in his reply, is that an event like 9/11 in which 3000 people died had a much bigger impact upon America and the world than the 3000 people who died in on year of a particular form of cancer.

The prevention of terrorism is more than just the prevention of immediate deaths related to the incident itself.

Protecting civil liberties are crucial, and I'm not in anyway agreeing with what the TSA is doing. As a side point, it's worth remembering that terrorism is a world issue and if you look more internationally some Western Countries don't even enjoy the level of civil liberties and freedoms that America does even now.

In the UK you can't even refuse a Back-scatter scan and have a manual pat-down instead (which applies to US citizens returning home from a visit to London too, of course).

http://consumerist.com/2010/11/in-uk-if-you-opt-out-of-body-...


> Terrorism can in both small and very large ways effect entire nations. backscatter radiation? Not so much.

Currently terrorism is effecting an entire nation with backscatter radiation.


Don't know why this was downvoted, other than people just not agreeing with him.


I just voted it down to zero but it might up again soon...

The main thing that justifies the downvotes is that the argument is both wrong and mostly rhetoric rather than argument. As other have said, the installation of vast control mechanism by no means is something with an insignificant effect on the country.

If he had actually made the argument that someone else credits him with, that terrorism's effect is disproportionate to the deaths, then he'd have argument (not sufficient but a real argument). But he didn't make that argument - instead rhetorically (and ultimately dishonestly) dismissed concerns about reaction to terrorists. Down voting seems justified in this case.


I can't speak for everyone, but one reason is that there is also a cumulative effect from these "small things". A progressive eroding of civil rights also affects a nation in "big ways".

Isolating one effect of one loss, and comparing that to the complex effects of terrorism is not a fair comparison.


"Why are we spending all this money on a "miniscule" threat? Why are sexually molesting the population over a "miniscule" threat? (Rhetorical)"

There are companies that are selling these things are and are making fistfuls of money, some of which goes right back into political campaigns etc. In other countries that would be called corruption. In the USA, it's legal.

Think about it - why does the government go on to spend huge amounts of money and piss everyone off? Was there a cause that means we now suddenly need these sensors and groping procedures? Was there a terrorist attack that I missed? Were there politicians campaigning for this who then got elected - I guess I missed that too?!

Kids can certainly forget about putting on sunscreen now, as you're way more likely to get skin cancer from the airport. Either that or they get sexually molested.

The terrorists have very clearly won right now.


Hrm . . . I could turn that logic on its side too: if you say people should not be that worried about terrorism, then why are people so worried about the health effects of backscatter radiation. IMO, a logical person cannot have it both ways.


One is more or less out of our control.

The other is within our control. Why voluntarily subject yourself to more risk?


If the risks are indeed roughly equal, I would like to point out that only one of these two risks costs us money.

Also, being blown up doesn't hurt nearly as much as cancer does.


I'm going to go ahead and take this to mean that the TSA just doubled my chances of death. Seems appropriate in the current climate of hysteria, and makes an excellent sound bite.


I'll take it to mean that (given the 1 in 30 million estimate and that there are well over 250 million outgoing airplane seats filled per year by U.S. airlines), the expected number of scans which will cause cancer is nearly 10. That's 10 people who's lives may be put in very real danger.

It doesn't make a very good soundbite, but it plays well to the climate of hysteria!


According to the Bureau of Transportation Statistics, there were 617,977,711 passengers on domestic flights in 2009 [1].

At the (incredibly optimistic) risk rate of 1 in 30 million, that's about 20 people given cancer, each year, if this policy goes forward and these devices become standard procedure.

[1] http://www.transtats.bts.gov/Data_Elements.aspx?Data=1


The TSA kills 20 people per year. Keep the hysteria simple.

Are you willing to kill 20 people per year to keep safe?


It's the TSA agents standing by the machines all day that are first in the fireing line.

I wonder how long the cancers will take to start showing up.


> Are you willing to kill 20 people per year to keep safe?

Unfortunately, the answer for most is yes. That's more or less the definition of war.

Edit: Yikes! I'm really getting downvoted here, but no one's saying why. I didn't say I agreed with it! I just said that most people would probably say yes.


Uhh, wouldn't these things not have even caught the underwear bomber? Soo.. would you kill 20 people a year for the false sense of security and safety? If so.. well.. you're a douche nozzle, no offense.


I suppose it depends on how many attacks are intercepted by the scanners.


Which also depends on how many attampted attacks there are.

If terrorists never attempt another plane attack they can count every cancer death that results from the scanners as part of their death toll. And they never have to even waste a resource or another moment of planning.

In fact if I were a terrorist I'd be looking at not only the effect of the attack itself, but the downstream residuals. For example, attacking the water supply would have large casualties, but little downstream residual except tightening security around water supplies.

But attacking elementary schools would result in less upfront damage, but if you could force elementary school kids to walk through these types of scanners everyday of their elementary school lives -- well chalk up more deaths for the terrorists.

I really really hope the government knows something we don't, otherwise that tired old saying "then the terrorists have won" is really beginning to apply.


VVVVVV Ahh, ayup, you're correct. Brainfart.


Sorry for being pedantic, but no - these are probabilities not random variates. If the probability of either alone is p then the probability of one or the other or both is:

1 - (1-p)(1-p) = 1 - (1-2p+p^2) = 2p - p^2 ~ 2p

(where the last step is because p^2 << p because p << 1; the basic idea is that it's "certainty minus the probability that neither occur")


Not close to true for two small, independent events.

We can safely assume that the chance of their occurrence together is going to be very small and so the chance of one or the other is approximately the sum of their individual probability.

P(X ∪ Y) = P(X) + P(Y) - P(X ∩ Y) ~ P(X) + P(Y)


I don't think I know anyone who isn't spitting mad about this TSA thing.

Quite an accomplishment, really, for the feds to manage to unite the entire country - left, right, center, and from every strata of society - on a given issue. I didn't think such a thing was possible.


I went and had a long, hard look in the mirror when I found myself in suddenly agreement with Ron Paul, Matt Drudge and, wait for it ... Ann. F'ing. Coulter.


That's what makes it such a fascinating study in how politics works.

Here we have a new issue, which neither party is mad about, and which people of all walks of life are pretty pissed.

Parties keep people consistently voting for them by coming up with some kind of narrative around why their policies are best: "looking out for the little guy" or "getting government off your back"

It looks like this issue could fit into several narratives put forward by the parties over the past decade or two. The killer part is that parties must oppose each other: if party A is for something, party B must find a reason why it's fracked (insert long story about messaging and branding here). So that means that somehow these parties are going to have to choose a side _and_ develop a plausible narrative sometime in the very near future. Right now it's chaos. I can assure you that the spinmasters are currently hard at work.

I'm hearing one narrative already "nobody really cares about this." which sounds a lot like "nothing to see here folks, please move along" Not sure if that one is going to fly, though. I guess we'll find out.


You might not know anybody who is not spitting mad, but I have never seen anyone opt out when I have travelled through equipped airports.

As long as people are going through them like sheep, I am not sure the media storm will change much.


The accomplishment is amazing. I guess our country really still does care about liberty and -- imagine this -- the constitution.

Trouble is, are people going to do anything with their "spitting mad[ness]?" I hope they do.


I think they just have an irrational fear of radiation outside the doctor's office (whether or not that's valid here) - due to it being crammed down their throats for decades - and a massive aversion to being seen naked - also largely due to it being crammed down their throats for decades.

If they like liberty, why did/do they not get as spitting mad about the Patriot Act, the DMCA, and the ACTA? I'm guessing it's because their naked butts aren't staring them in the face after being irradiated.


Absolutely right.

It seems the media for good or ill drives the country and their responses. Hopefully the internet will eventually change that.


Upvoted you, but I would like to add that I'm spitting mad and not afraid of radiation or being naked. I think at least part of it is simply mass hysteria. It's very easy when other people are upset to get swept up into it.


Indeed! My blog post yesterday was "Across The Political Spectrum, A Rare Moment of Agreement — Thanks, TSA!"

http://iwilloptout.org/2010/11/17/across-the-political-spect...


I guess in a weird way the administration, through Janet Napolitano, is uniting the country.


This discussion is properly focused at the core of the matter, the cost benefit analysis.

Some of the costs are easy to see, like the acute embarrassment some experience from an intimate "pat down" if they elect to avoid any risk from x-ray radiation.

Others are much more difficult, such as potential health consequences of the x-ray radiation exposure. Since the TSA has refused to disclose the x-ray flux, it is hard to even get started. The comparisons the TSA makes with other radiation sources are flawed because they assume the dose is uniform throughout your body when it is actually highest at the surface.

But even if an outside evaluator did have good numbers to start with, in the end the best you can expect are extrapolations using data from dramatically different radiation exposure, which is the nature of calculating radiation risks. The only way to have a non-extrapolated number is to expose half of a sample population to the scanner radiation and measure outcomes for 50 years.

Avoided consequences are easier to calculate. Of the 8,000,000,000 or so US domestic air travelers of the past ten years, zero have smuggled a bomb on board, and zero have attempted to. Zero out of billions of passengers.

The worst consequences are the loss of an aircraft. A terrorist cannot take control of an aircraft using a bomb, only destroy it. An X-ray scanner will not stop someone from bringing a knife onboard (even if it could, it is probably not possible to take control of an aircraft with a knife due to cockpit doors, passenger awareness, etc.)

So, cost benefit sum-up: zero attempts to smuggle bomb onto domestic flight over past 10 years, unknown but likely low health risk, consequences limited to loss of one aircraft due to screening failure.


> Of the 100,000,000,000 or so US domestic air travelers of the past ten years, zero have smuggled a bomb on board, and zero have attempted to.

At least two have succeeded in smuggling a bomb on board, but failed to detonate them. Look up the "Christmas bomber" and the "shoe bomber".


Neither of those were "US domestic air travelers"; both boarded U.S.-bound international flights in Europe.


You're right they're not domestic. I've lived in and have family in Europe so I have tendency to not view Canada and Europe as completely foreign. So, anyway, Lockerbie, shoe bomber, Xmas bomber all actually not US departures. Sorry.


1 in 30M? so, with over 600M passengers per year, that's roughly 20 people a year who would get cancer (and die?) because of those machines. I'm not sure how credible are those stats, but I wouldn't want to be making decisions at the TSA right now...


>I'm not sure how credible are those stats,

The author himself doesn't believe them. Here's what he (Peter Rez) says in the paper this is based on:

>The major public health effect of concern at low doses of ionizing radiation is cancer. There is clear evidence of cancer induction at effective dose above about 200 mSv. Below an effective dose of about 100 mSv radiogenic cancer mortality risk estimates for all cancers is highly uncertain. 16 It is not possible to determine reliably whether a radiogenic risk is present in an X-ray screening population because of the high spontaneous incidence of cancer and multifactorial nature of disease causation 17.

>Use of collective dose to estimate public health impacts when large populations are exposed to trivial doses is inappropriate and not reasonable. The assumptions implicit in the collective dose calculation conceal large biological and statistical uncertainties.16 If an individual passenger is not harmed by X-ray screening then the population isn’t either.

https://docs.google.com/viewer?url=http://www.public.asu.edu... (page 15)

linked from

http://www.public.asu.edu/~atppr/bodyscan.html


Not everyone gets screened. So only a fraction of those 600M passengers are getting a dose.


at the moment... not long ago not everyone went through the metal detectors...


seriously? when was that? was it not so long ago we had armed plane hijackings almost every month?



thanks for that, excellent read. many forget that guns were allowed on flights until relatively recently, not everyone was xrayed and hijacking was common.

also like the point raised in the comments that the main thing that killed off the IRA as a major terrorist movement in Europe, was when their American supporters finally remembered what terrorism was in 2001.


The plan is that all 2200 checkpoints in the USA will have backscatter or millimeter wave scanners within 2 years.


More tellingly, on an average two-hour flight, you'd receive about 100 times the radiation from a single scan.

But, by using the transitive property, you're more likely to die from radiation at flying altitudes than from a terrorist attack on said airplane.

EDIT: Sorry, I forgot to include the link:

http://en.wikipedia.org/wiki/Backscatter_X-ray#Health_effect...

Which comes from:

http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/radexp.htm...

Which explicitly states its references.


This comparison is meaningless.

The risk of cancer is caused by DNA errors. Your cells are constantly checking and repairing your DNA for mutations and damage. They can usually repair or detect a low error rate, like the kind you get from living at high altitude, in a house with a minor radon source, or flying on a plane. What they can't deal with as well is a sudden burst of many errors. Backscatter X-ray scanners deliver their entire dose to a tissue region in a few microseconds. That's the kind of exposure we're talking about, and it has an entirely different biological impact.


>What they can't deal with as well is a sudden burst of many errors.

Actually that is false, as far as low doses:

>When you are asked whether there is a critical time period over which 1 rem of dose may have a greater biological impact than it might otherwise have, the answer is "No." One rem of dose is sufficiently low that whether it was delivered within one second or spread over a year or more, we would not expect any difference in biological effects.

https://hps.org/publicinformation/ate/q8325.html

(For comparison, 1 uSv = 0.1 mrem).

>The risk of cancer is caused by DNA errors. Your cells are constantly checking and repairing your DNA for mutations and damage. They can usually repair or detect a low error rate

But in this dose regime, ionization events are so rare, that they are so far apart that no cell experiences more than one. There is no variation in error rate.


Good point uvdiv: if the ionization events are sufficiently rare in both cases we ought to be able to treat them as cumulatively equivalent. I guess it would depend on the error correction time and the size of the affected nucleotide sequence, especially in a double-break error. The dose delivered by these scanners is probably well-below that threshold.

My remaining concern would be that the biological effects of this particular energy regime are as-of-yet uncharacterized.


Let me quote from your own source:

"There have been numerous biological experiments conducted, with nonhuman organisms, that demonstrate that the rate at which radiation dose is delivered can affect the extent of biological response. Thus a sufficiently high dose delivered over a period of a few minutes may be expected to have a greater biological impact than the same dose spread over a year."

The only question is what constitutes a "sufficiently high" dose, due to extrapolation. See 5).

THEIR OWN POSITION PAPER on backscatter scanners recommends per-screening and per-year (time limit!) maximums FAR below the threshold that they claimed wasn't a problem in the first place -- see 8).

4) Further, the terse "no" answer looked disingenuous. The cited position paper link was broken but I tracked it down.

It appears to be "Radiation Risk in Perspective", PS010-2 (which I assume is the updated version of PS010-1).

It has nothing to say about doses over short time periods.

http://www.hps.org/hpspublications/positionstatements.html

5) The issue seems to be that there is very little data about low-dose exposures, so regulations are based on extrapolation from high-dose exposures.

See http://www.ncrponline.org/PDFs/TST_NRC%20_04-08-08.pdf (third slide)

6) What it does say is this:

"the Health Physics Society recommends against quantitative estimation of health risks below an individual dose of 5 rem in one year or a lifetime dose of 10 rem above that received from natural sources."

7) The whole point of their objection was that we lack the empirical evidence to extrapolate from high doses to low doses. Then the article you cite does exactly that. They go from saying, "we lack proof that the answer is X" to saying, "the answer is ~X".

8) The recommended standard "limits the reference effective dose delivered to the subject to 0.25 microsieverts (25 microrem) per screening. Additionally, a screening facility should not expose any individual to more than 250 microsieverts (25 millirem) reference effective dose in a year."

"Use of Ionizing Radiation for Security Screening Individuals" PS017-1

http://www.hps.org/hpspublications/positionstatements.html

How they can go from saying in the first paper, "However, below 5–10 rem (which includes occupational and environmental exposures), risks of health effects are either too small to be observed or are nonexistent" to supporting a maximum of 0.025 rem per year is entirely unclear.

Except that the Health Physics Society seems to have turned into a pro-industry spokesgroup.

The current president works for Dade Moeller, who are embroiled in a number of controversies, to put it lightly.

A lot of extremely damaging information is cited in the original link below.

""Hirsch then zeroed in on Dade Moeller’s radiation plan and on the controversial company itself, whose namesake testified back in the 1990s that money spent on cleaning up Cold War-era nuclear facilities was being wasted since there would be a cure for cancer."

Original comment:

http://news.ycombinator.com/item?id=1889673


>THEIR OWN POSITION PAPER on backscatter scanners recommends per-screening and per-year (time limit!) maximums FAR below the threshold that they claimed wasn't a problem in the first place -- see 8).

>...How they can go from saying in the first paper, "However, below 5–10 rem (which includes occupational and environmental exposures), risks of health effects are either too small to be observed or are nonexistent" to supporting a maximum of 0.025 rem per year is entirely unclear.

Where they support that 0.025 rem/year recommendation, they explain that the point is to keep "individual doses as low as reasonably achievable (ALARA) while achieving the desired objective." (Same source, PS017-1).

And you mischarcterize their claims. HPS does not claim <5 rem doses are "not a problem" -- they said the effects are such are "either too small to be observed or nonexistent". (It does not follow that a health effect too small to be epidemologically noticable is "not a problem"). "Too small to be observed" is NOT a quantifier of significance; it is an explanation for the lack of empirical observations. That position statement (PS010-2) is a recommendation against quantiative estimation of the effects of <5 rem radiation doses, not an assertion of their absolute safety.

>It appears to be "Radiation Risk in Perspective", PS010-2 (which I assume is the updated version of PS010-1). It has nothing to say about doses over short time periods.

It does not appear to have been referenced for that purpose.


> It does not appear to have been referenced for that purpose.

Your comment referenced it for that purpose.

Your comment about dose per unit time not mattering referenced an article which referenced their position paper which didn't support what the article said. Hence the article was simply the opinion of the author.

> (And you mischarcterize their claims. HPS does not claim <5 rem doses are "not a problem" -- they said the effects are such are "either too small to be observed or nonexistent". (It does not follow that a health effect too small to be epidemologically noticable is "not a problem").

"Nonexistent" sounds like "not a problem" to me.

"Too small to be observed" is the same. How is a problem that causes no observable effects a problem? That's the practical definition of "not a problem".

And if dose per unit time doesn't matter, then their per-screening and annual limits for these small doses wouldn't matter. They are contradicting themselves.

Further, as mentioned, they are not an independent safety group. They are an industry group for the pro-nuclear lobby. This is like relying on the Business Software Alliance (BSA, a front group for Microsoft and other large software corporations) for opinions on the harmful nature of DRM, copyright laws, etc.


Where 'an entirely different biological impact' may just as well mean 'no impact at all': it may even turn out to prevent melanomas.

While everyone is busy losing themselves in radiation hysteria, where facts are only guessed at, the government is laughing their ass off, because everyone lost sight of the actual problem: that these machines are assumed to improve safety in the first place. The radiation scare is an enormous red herring that mainly harms the public perception of 'radiation', that wasn't too good to begin with, for all the wrong reasons.


We know that short-term small doses of X rays results in increased probability of developing skin cancer. We know that prolonged exposure to low-level radiation sources increases your probability of developing skin cancer. We know that acute high doses of ionizing radiation leads to your skin falling off. Skin cancers are abnormally elevated in radiologists, survivors of Hiroshima who experienced even relatively low doses, radioisotope miners, and people who are treated with X rays for skin conditions.

I'll hazard a guess here and say there's close to zero probability that backscatter machines are lowering your risk of cancer.

Don't get me wrong: I love radiation. I think Cherenkov glow is the coolest thing about working in a reactor. I've handled more sources than I probably should have by this point in my life. At the same time, we should be honest that there is probably a small risk, and it is probably higher than currently stated.


  We know that short-term small doses of X rays results in
  increased probability of developing skin cancer.
An increase that is so minute that we don't mind the dentist or doctor X-raying us. An increase that is so minute that we would accept it, if it actually reduced our chances of dying due to a terrorist attack. The radiation is not the problem: it is the intended goal that we have no reason to believe in.

  We know that prolonged exposure to low-level radiation
  sources increases your probability of developing skin
  cancer
Do we? Not WiFi or the low-energy spectrum of the sun. What energy is 'low' in this respect?. And how long is 'prolonged exposure'? These claims are undoubtedly true for some values of the aforementioned quoted terms, but are they relevant here? Do most of the people repeating this stuff even wonder about that? Again, the problem is a slightly increased risk. But why is that increased risk a problem in the first place?

  I'll hazard a guess here and say there's close to zero
  probability that backscatter machines are lowering your
  risk of cancer.
And I agree. But the "we don't know for sure" argument is pretty shallow, when we accept certain risks on a daily basis and when we all know certainty doesn't exist and we all take aspirin to prevent a second heart-attack, even though a thousand doctors will argue with another thousand doctors about whether that actually works, all citing studies supporting their side, and the net effect is quite small even according to the side affirming it works.


Preface: I totally agree with your argument that risks must be weighed against outcomes. I also believe that even if the scanning technology were totally safe, it would be objectionable on privacy grounds. I think we're going about the whole problem of security backwards. :)

An increase that is so minute that we don't mind the dentist or doctor X-raying us.

Actually, we do. There are good reasons we impose strict limits on your medical X-ray exposure annually, and why you wear a lead vest or use collars to protect other tissue. There's also a good reason the radiologist stands outside the other room to press the button. Two x-rays a year is not significantly mutagenic. Fifty? Then you start getting nervous.

Not WiFi or the low-energy spectrum of the sun. What energy is 'low' in this respect?. And how long is 'prolonged exposure'

UV exposure from solar radiation is one of the biggest melanoma risks. A few orders of magnitude up the frequency scale, X rays for far shorter durations also have mutagenic effects on skin tissue. It's possible that low-energy X rays, falling in the middle of that energy range, also cause cancer. We don't know for sure yet because we don't regularly expose people to them.

(I should mention that just because the X rays are low energy does not mean their effects scale linearly. Medical X rays are well above the Compton shoulder. IIRC (not enough time to check now) they're thermalizing slowly in heavy tissues as opposed to bouncing inelastically off the surface layers. Depending on the scattering cross-section for those energies, the backscattered X rays could be more ionizing. Total conjecture... I haven't done this for a while.)

Again, the problem is a slightly increased risk. But why is that increased risk a problem in the first place?

You're absolutely right. We have no good characterization of the risk. Radiation biometrics is fucking hard. I only want to argue that our current risk statement is inaccurate and poorly understood (for instance, we don't even know the angular flux of these machines), and offer some potential reasons why the risk might be higher than currently stated.


You are understating the risk from backscatter radiation. Because the radiation is sent in a burst, and targets skin tissue, the DNA damage may be far greater than a similar dose of cosmic radiation.

You are also assuming that the backscatter machines are functioning properly and aren't overdosing people.


  Because the radiation is sent in a burst, [..] the DNA
  damage may be far greater than a similar dose of cosmic
  radiation.
People keep repeating that, but it is not simply true. DNA can get damaged when a single photon excites an electron and consequently influences the molecular structure. The chances of multiple photons operating on the same electron at the same time, even in cases of a radiation burst, are negligible. The person is affected by the same number of photons, which results in the same number of chances of electrons being excited. The number of excited electrons will be equal and the resulting damage will be equal.

Now it may matter that the damage is more localized in both space and time, but no one has shown this. Firstly space: spreading the radiation over only the surface, for instance 1/10th of the body (remember that surface times a small depth is always a relatively large part of a volume), means 10 times as much damage. But if the average amount of damage in the skin was one broken bond per 1000 cells, it will now be one broken bond per 100 cells. As the repair takes place per cell, that doesn't change anything for the total chances to get cancer. Only if the amount of damage in a single cell, and close enough to each other to be relevant, changes, then this type of operation may pose a problem.

Secondly for time: everything depends on the amount of time it takes a cell to repair DNA damage. If the average time of repair takes 3 seconds, then during a flight, some damage will be repaired before other damage takes place. The backscatter machine delivers its dose faster and damage may accumulate. However, if repair takes 30 minutes on average, the difference is again neglible.

The point is not that I know the numbers: the point is that people making claims don't know them. They are just claiming things that seem to make sense to them, when they draw an analogy with a car crash or something. They don't understand what is actually involved.


A single backscatter X-ray scan gives a radiation dose of 0.009 mrems, about the same as eating a banana.

http://en.wikipedia.org/wiki/Banana_equivalent_dose

Don't get me wrong, I'm opposed to the scanners as much as anyone for privacy reasons and general pointlessness. But I'm seeing a lot of bad science thrown around here.


You're not comparing bananas to bananas.

As I understand, the limited information that has been publicly released about the backscatter machines is a useless measurement when you take into account how they actually work. You can't apply a standard measurement from a medical x-ray machine that targets a small part of your body using one technique to a different machine that targets your entire body using a different technique.

So the two problems are:

1. You don't have good numbers to even evaluate how dangerous they are, many evaluations, including possibly the article above, are useless because they don't have the real data to compare to.

2. The radiation exposure from a banana also effects your body differently than a medical x-ray machine which is in turn different from a backscatter machine targeting your entire body.

I'm not saying people aren't trying to evaluate the actual risk in good faith. I'm saying they're skipping the step where we get useful numbers from the manufacturer of the machine to even apply good science to.

Edit: by "whole body" I mean "whole surface of your body" since it's concentrated on your skin


While I might agree that the worried about an X-ray scan are overblown (I assume that is your position), that number is looking at a whole body number. Part of the argument is that the amount may be significantly higher because the dose is concentrated near the surface of the skin, rather than across the whole body like cosmic ray and chest X-ray exposure.


So instead of being equivalent to eating a banana, it's probably equivalent to mashing one up and using it as skin cream.

In other news, millions of small children who enjoy playing with food exposed to RADIATION! Are bananas safe for your children?


Oh, well if they're equal, then that means this is a perfectly proportional and appropriate response.


That only holds if being sexually molested and having naked pictures of yourself taken is weighted at zero.

Furthermore, this statistic in no way indicates that these screenings reduce the risk of dying in a terrorist attack. 1 plus 1 does not equal 0. You've allegedly doubled your risk of dying, not reduced it.


The second paragraph is almost verbatim to the statement I was about to say in response to the OP.

Blacklists do not work. Antivirus software checks for a hundred thousand individual known problems, yet viruses and malware continue to evolve and bypass the blacklist. So do explosives hiding in containers that the TSA doesn't expect to find explosives in.


Well, you're right to question what the reduction in risk these scanners produce, but your first point is way off. The cost of terrorist attacks is hardly limited to death. Those planes and buildings aren't free. Not that cancer treatments are, either, but if you weigh in the psychological damage to the public (you know, why they call it "terrorism"), terrorist attacks are far more costly.


The real cost of terrorism is having to deal with all the people talking about "the real cost of terrorism", and instituting retarded policies like these scanners/molestation sessions.

Planes and buildings are cheap as shit in comparison.


1 unsuccessful underwear bomber => $500 million in contracts for scanners.

There's your cost of terrorism right there.


A "terrorist" would just find another way to terrorize.. duh. Real terrorism is a drama, as orchestrated by our overlords, to polarize the public in attempt to deprive them of their liberty. That is all.


Judging by the other replies, I guess you should put explicit sarcasm tags around your comment.


Yes. And then it still won't be very funny. It's too similar to something an actual TSA flack would say.


If it weren't similar at all it wouldn't be funny either. It's a hard balance to set.


I don't even know the name of that fallacy, but it ought to have one.

(Yes I know parent is sarcastic.)


Something like `false proportionality'?


Only if:

• the scan completely offsets the risk of terror death. I suspect not; someday someone will tell the TSA and/or terrorists about drug mules.

• the economic cost of the scanning infrastructure/training/delays etc. is equal or less than the economic cost of the terror deaths offset.


as if they are delivering total immunity from terrorist attacks in exchange.


> Peter Rez ... calculated the risk of getting cancer from a single scan at about 1 in 30 million

His odds were for a single flight, but I wonder if the scanner radiation has a cumulative effect?

Surviving a plane flight has no impact on the likelihood of the next one, so taking a lot of flights would edge the odds in favour of dying from the scanner cancer.

But then there`s the wide difference in the type of death.


> But then there’s the wide difference in the type of death.

Good point, I would rather die in a terrorist attack than after months of chemo and hospital food… that said, one is a lot more premature! (Edit: Actually, if you got cancer from the scanner, it would probably kill you within a few years.)


Airport in Orlando opts out of using TSA to screen their passengers:

http://www.examiner.com/libertarian-in-national/florida-airp...


This is the best news I've heard on this topic. If enough airports were to do this, things would change at the TSA.


America is a nation of goose-stepping cowards willing to give up their most fundamental freedoms based on an incredibly unlikely event. They'll shove cheeseburgers down their gaping maws and virtually guarantee they get diabetes and heart disease, which is vastly more likely to kill them, while cowering and whimpering about terrorism.

I live in Newark. I'd be about 100 times more likely to get killed walking to the bus to get to the airport than I would be in the plane, even if we had no security at all.

Anyone willing to tolerate this shit is a drooling fascist who also doesn't understand security if they think this bullshit will stop even one determined and competent terrorist.

We should do security like El-Al, modifying it of course for the practical differences between the threats we face, and for our own constitutional protections. People say that would be "expensive" but then, these are the same morons who think we should piss away fundamental rights millions of Americans have fought and died for for hundreds of years. And these morons want to talk of "expensive?" Please.


With all due respect to Dr. Reiz, and the Dept. of Physics at ASU, I think I'll be taking my advice from the group of doctors from UCSF (a school well known and respected for its medical research) who wrote a formal letter to the president's science advisor. The letter is worth reading.

"Agard and several of his UCSF colleagues recently wrote a letter to John Holdren the president's science adviser, asking for a more thorough look at the risks of exposing all those airline passengers to X-rays. The other signers are John Sedat, a molecular biologist and the group's leader; Marc Shuman, a cancer specialist; and Robert Stroud, a biochemist and biophysicist."

Story here: http://www.npr.org/templates/story/story.php?storyId=1268330...

Letter here: http://www.npr.org/assets/news/2010/05/17/concern.pdf


I'll go with the physics prof. He did some calculations, admittedly imperfect, based on generally known principles of dosimetry, and got what seems like a reasonable order of magnitude result.

All the MD's at UCSF said was "oh noes, the possibility of radiation danger isn't ruled out precisely by a previously done study, it might be dangerous." I'd be very curious to know whether they would use this same logic on a less politically charged topic.


Even on non-politically-charged topics, that is pretty much the standard operating practice, at least in the more science-oriented parts of medicine. If you want to know, "is this practice safe?", you run a study to find out, rather than speculating from first principles (though you can use speculation from first principles to come up with reasonable hypotheses and narrow down how to best design a study).


Reasonable doesn't necessarily mean correct. In the face of specific questions raised by doctors with expertise in this specific field, is reasonable is good enough?

From the NPR article:

"The stated dose — about .02 microsieverts, a medical unit of radiation — is averaged over the whole body, members of the UCSF group said in interviews. But they maintain that if the dose is calculated as what gets deposited in the skin, the number would be higher, though how much higher is unclear."

The observation about how high a dose gets deposited is a very specific observation made by people who actively apply radiation to people on a daily basis.


In the face of specific questions raised by doctors with expertise in this specific field, is reasonable is good enough?

You are trying to appeal to authority. That's a logical fallacy.

Radiation transport, ionization mechanisms, and dosimetry are all fairly well understood topics. Not perfectly, but well enough that one can make reasonably good ab-initio predictions. The physicist is doing exactly that.

Now, ab-initio dosimetry calculations are sometimes off by largish factors, (e.g., 500%) due to reactions of certain tissues. But they are rarely off by orders of magnitude, which they would need to be in this case for us to actually care.

The doctors at UCSF are just scaremongering, regardless of their credentials.


Radiation transport, ionization mechanisms, and dosimetry are all fairly well understood topics. Not perfectly, but well enough that one can make reasonably good ab-initio predictions.

There are a lot of people that would disagree with this statement as it applies to the human body. I think its fair to say that there is no such thing as ab-initio studies when it comes to human reaction to radiation (at least none that are worth a lick).


"The doctors at UCSF are just scaremongering, regardless of their credentials."

Thats a very blithe statement to make about a group of professionals.

Here's the thing -- I know several people who have been treated for cancer at UCSF, and my understanding is that you couldn't ask for a better group of doctors/scientists. Their expertise is very well-regarded. So if taking the advice of a doctor who has made this his/her life's work is appealing to authority, then guilty as charged. If I'm going to try and make the best decision I can without understanding the topic as well as you seem to, I'm certainly not going to chose the people who generally work in the field over the the people with real medical experience. My plumber is a very smart guy who knows a lot about electrical, but I'm not going to hire him to re-wire my house. The devils is in the details, and I'm going with the guy who has a very good grip on the details.


can somebody please down vote him? (i'll pay back with interest when i get my downvoting ability :)


This part of their letter doesn't make sense:

Unlike other scanners, these new devices operate at relatively low beam energies (28keV). The majority of their energy is delivered to the skin and the underlying tissue. Thus, while the dose would be safe if it were distributed throughout the volume of the entire body, the dose to the skin may be dangerously high.

The main issue is that the limit for a smaller volume of the body is actually greater than the body as a whole. Radiation dose is somewhat similar to a density, in that it's measured in energy deposited per mass. Your body is better at dealing with a high dose in a small volume, than it is with a low dose in a large volume.

...these new airport scanners are largely depositing their energy into the skin and immediately adjacent tissue, and since this is such a small fraction of body weight/vol, possibly by one to two orders of magnitude, the real dose to the skin is now high.

This statement doesn't make sense either. Dose is J/kg, so the fact that the volume (read mass) is small is taken into account.

This part sounds the most interesting:

In addition, it appears that real independent safety data do not exist. A search, ultimately finding top FDA radiation physics staff, suggests that the relevant radiation quantity, the Flux [photons per unit area and time (because this is a scanning device)] has not been characterized. Instead an indirect test (Air Kerma) was made that emphasized the whole body exposure value, and thus it appears that the danger is low when compared to cosmic rays during airplane travel and a chest X-ray dose.

The problem with this statement is that Air Kerma is the quantity that you'd use to calculate the dose. It is only measured indirectly in the sense that you can set the detector to have the conversion coefficients built in (you actually measure the quantity Exposure).

It seems that the letter was probably written by people with concern, but not expertise. I just know enough to see some problems.


This article from NPR a few days ago has a lot more details, and gives context for the estimates: http://www.npr.org/blogs/health/2010/11/12/131275949/protest...


If the argument that the risk of backscatter radiation damage is acceptable, and it is the same risk as the chance of terrorism, then by extension the risk of terrorism is acceptable as well. So basically this isn't about terrorism, it is about taking away our liberty.


Sigh.

While interesting, arguing about the methods used to violate your basic civil rights only distracts from the real discussion about YOUR CIVIL RIGHTS ARE BEING VIOLATED BY THE VERY GOVERNMENT FORMED TO PROTECT THEM.

Keep your eye on the ball people.



Do you know who else was told that the product they were dealing with was completely safe?

http://en.wikipedia.org/wiki/Radium_Girls

The group who would come to be known as the Radium Girls. They were told that Radium was safe if ingested, and many of them would lick the tips of their paint brushes, or paint their teeth and nails with the substance. Soon after they began suffering radiation poisoning, but were discredited of their claims by the company publicly defaming them as contracting syphilis.


I'm just thankful that the TSA makes people mail home their keychain Swiss Army knives with 1-inch, non-locking blades. Goodness knows what sort of carnage someone could inflict with that. Almost as much as with a ballpoint pen, which I notice they are still allowing. For shame.

I will not feel truly safe until each of us is forced to change into a hospital gown, be cavity-searched, and be duct-taped inside of a cargo container for the duration of the flight.


My takeaway: -I don't like the privacy ramifications of these scans. -I don't like being bombarded with additional radiation for no good reason, regardless of whether people think it will harm you.

Just as I will get an x-ray for a good reason, but decline getting one for a silly reason, I would decline this if able. Maybe taking an aspirin a day is bad for you, maybe it's not, but I'm not going to start doing it for no reason.

So one more reason I don't like the scan.


Yes, but the peace of mind one experiences while being groped or ionized makes it all worth while.

Regarding how much radiation you receive on the plane itself, I always try to sit away from the window and on the north side of the plane if possible.


My impression was that the increased radiation experienced on a flight was due to cosmic radiation, not radiation from the sun. So it shouldn't matter where you sit on the plane, right?


After reading about the backscatter, i'm wondering why i was so much against the gropping. Nobody got cancer from being gropped, and after 10th or 20th time i may even start to enjoy it. Some hands would become familiar... :)


I can't believe that even on HN there are so many posts about something so dumb. Our country is up in arms about some new X-ray machines that a corrupt defense contractor sold to an overzealous department of homeland security in a panic after 9/11, and yet we are hardly this angry about the 2 wars we are fighting or the fact that the New Start treaty is about to be ran over with a bulldozer.

Please, let's get over the stupid X-rays machines. Let Fox News and CNN cover this one.


I can believe it, and you know why? Because our country still cares about personal American liberty.

Viva la libertad!


Sometimes I get hyperbolic. What I mean to say is that these machines are a symptom of a larger problem. The time that we spend trying to get rid of these machines is time that we don't spend on solving the real problems.

I love freedom, too.


Maybe I suck at basic prob/stats but if you remove the scanners, I bet the chance of a plane getting blown up by a terrorist is significantly increased. ;)


Two things have made the US safer

1- Pilots with guns & keeping the doors closed for the full flight

2- Passengers not willing to allow others on the plane do harm to the plane. If passengers see things happen now, they will stand up and makes attempts to stop them. We won't have a 9/11 style hijacking. Even if someone gets a box cutter in, people will take them down before they'll let them take the plane.

I can't imagine how these body scanners would make us significantly safer.


What we are trying to stop has shifted from someone hijacking the plane to someone trying to blow it up. However, this is not a new threat at all, and there are always more ways of getting a bomb on the plane as well as more targets.


Perhaps, but why do we still focus then so much on 'hijacking' items, like knitting needles that would do little good in making bombs? We haven't reverted to pre 9/11 search coverage of hijack items. Actually, we haven't backed down at all on anything.

It seems that once something is identified a threat, it will always now be seen as a threat.


won't work. Flight 93 was taken back by the passengers and Bush ordered it to be shot down anyway.

http://www.youtube.com/watch?v=3V9MD15qs5s http://www.abovetopsecret.com/forum/thread624915/pg1


I don't think we'll ever have a good idea about what happened with flight 93. If the plane was 100% under control and in communication with other planes/ground control, it wouldn't have been shot down.

But the real point is that now no one would allow a few guys with boxcutters to take over the plane in the first place. They aren't getting in the cockpit, because that isn't going to open in almost any circumstance.

I know if I see some guy stand up and start threatening the plane, I will do whatever it takes to disarm and disable them with what I have available on me- even if I am outmatched physically by size or weaponry. I'd feel certain that if other passengers think that someone is going to take over the plane, they will help out.


I would take that bet. I also have an inside track on a great bridge for sale, and some choice coastal real estate, if you're interested.


The effect of you dying from terrorism is not the same as the effect of you dying from backscatter radiation.

From a utilitarian standpoint, the chance of dying from something is not the most important factor in deciding where to put resources.

I'd also say, the neither of these numbers can be known in any accuracy right now, and there would be fast disagreement on any guess at what they might be.


So my chances of dying have been doubled?




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