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FDA Responds to ProPublica Story on X-Ray Body Scanners

Editor’s Note: This week, the Food and Drug Administration sent us a letter, which we have posted below, taking issue with several passages in our story about airport body scanners. The letter generally takes semantic issue with how we presented specific facts. It does not, in our judgment, raise any issues of substance.

Editor’s Note: This week, the Food and Drug Administration sent us a letter, which we have posted below, taking issue with several passages in our story about airport body scanners. The letter generally takes semantic issue with how we presented specific facts. It does not, in our judgment, raise any issues of substance.

For example, a section heading in our story stated that there has been little research on the cancer risks of body scanners. The FDA asserts that studies of radiation risk in general should be accepted as applying to the radiation generated by the scanners.

More broadly, the FDA takes issue with how we conveyed the cancer risk from the scanners. The agency says the amount of radiation the scanners emit is “extremely small.” We call it “extremely low.” The agency says the risk of fatal cancer is 1 in 400 million – an estimate it did not provide to ProPublica before publication – and cites the National Council on Radiation Protection and Measurements (NCRP) to say that estimating cancer cases from low levels of radiation produces “a distorted image of risk.” We cited two peer-reviewed research papers by prominent academics – including one who served on the NCRP panel that examined body scanners – that estimated six or 100 additional cases of cancer over a lifetime could be caused among the 100 million passengers who fly each year. (Those passengers were estimated to take 750 million or one billion flights.) To put this risk in context, we noted that “the same 100 million people would develop 40 million cancers over the course of their lifetimes.”

Separately, the agency asserts that we erred in stating, “The FDA does not review or approve the safety of such products.” But the agency omits our next sentence: “However, manufacturers must provide a brief radiation safety report explaining the dose and notify the agency if any overexposure is discovered.” That sentence is important, because the FDA letter itself states that “a manufacturer of an x-ray security screening product can legally sell a product after they submit the required radiation safety report. Federal law does not include authority for an approval process for the radiation safety of electronic products.”

In another case, the FDA objects to this sentence: “Instead, the FDA decided to go with a voluntary standard set by a trade group largely comprising manufacturers and government agencies that wanted to use the machines.” The agency says that “FDA chose to initiate a balanced consensus standard development process…” But the “consensus standard” is not mandatory. A company could produce a scanner that exceeds it, and the burden would be on the FDA to show the radiation emitted by such a scanner is unreasonable. Also, in explaining the process of how the standards were set, we believe the FDA does not contradict the essence of our reporting: The task of setting the standard was handled by a non-profit group that sets standards for many industries, the American National Standards Institute. ANSI, in turn, relied on what the FDA acknowledges was the “working group which wrote the standard.” As we reported, that working group, which we termed a committee, “was made up of 15 people, including six representatives from manufacturers of X-ray body scanners and five from U.S. Customs and the California prison system. There were few government regulators and no independent scientists.”

ProPublica takes seriously our responsibility to correct mistakes and clarify misstatements. But while the FDA may prefer different terminology, we believe the way we conveyed the facts was accurate.

Paul Steiger, Editor-in-Chief and CEO

The FDA’s Response

FDA spokesperson Erica V. Jefferson emailed ProPublica the following response for publication.

ProPublica article Nov 1, 2011 – clarifications

For further information and references regarding these topics please visit the FDA web page on products for security screening of people - http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm227201.htm

For an overview of FDA’s regulatory authorities over manufactures of electronic products please see the FDA Basics page regarding radiation emitting products: http://www.fda.gov/AboutFDA/Transparency/Basics/ucm193809.htm

  • “Little research on cancer risk of body scanners.”

    The risks from the x-ray body scanners are from the dose of x radiation delivered during a scan. The risks from a dose of x radiation (a form of ionizing radiation) has been studied and documented. The effective dose of x radiation delivered to an individual being screened has been verified multiple times by multiple organizations. Thus the incremental increase in cancer risk can be calculated and is extremely small. The dose is so small that it is only a fraction of what is defined as a negligible dose. A strict interpretation of the linear-no-threshold radiation dose to risk relationship indicates for the systems in use by TSA there is an incremental increase in the risk of a fatal cancer of 1 in 400,000,000. The x-ray spectrums emitted by these products are not significantly different from x-ray spectrums used for medical imaging; therefore, studies on x-ray dose from medical imaging are relevant to the dose from a scanner. There have been statements made about very soft x-rays from these products – those statements are not correct, there is at least 1 mm of aluminum equivalent used which eliminates soft x-rays from the spectrum.

    Note: An increase in risk of 1 in 400,000,000 means an individual’s theoretical risk is theoretically raised by this minute amount. It does not mean one screening out of every 400,000,000 screenings will result in a death. The National Council on Radiation Protection and Measurements (NCRP) has said: “The summation of trivial average risks over very large populations or time periods into a single value produces a distorted image of risk, completely out of perspective with risks accepted every day, both voluntarily and involuntarily.” This quote is from NCRP Report No. 121 (1995), Principles and Application of Collective Dose in Radiation Protection.

  • “Although they deliberately expose humans to radiation, the airport X-ray scanners are not medical devices, so they are not subject to the stringent regulations required for diagnostic X-ray machines.”

    FDA has regulatory authority over the manufacturers of electronic products which emit (or could emit) radiation under the Electronic Product Radiation Control (EPRC) provisions of the Federal Food, Drug, and Cosmetic (FFDCA) act. Every x-ray product is an electronic product and some x-ray products are also medical devices. Manufacturers of medical x-ray products are subject to both medical device and EPRC requirements. Manufacturers of medical diagnostic x-ray products are in addition to general requirements required to assure their products meet the requirements of a specific mandatory performance standard under EPRC regulations.

    FDA continues to use the regulatory tools available under the EPRC authorities of the FFDCA to protect the public health and safety from electronic product radiation. Manufacturers of x-ray products are required to provide details of the radiation emission and radiation safety characteristics of their products to FDA prior to selling those products. FDA has authority to inspect electronic product manufacturers for good cause. The EPRC provisions allow FDA to order manufacturers to take a corrective action (repair, repurchase, or replace) if their electronic products are ever discovered to have a radiation safety defect which was caused by the product’s design, manufacturing, or assembly. FDA also has approval authority over a manufacturer’s corrective action plan and can order further action if a manufacturer’s initial corrective action is not adequate. Manufacturers are required to cover all costs associated with corrective actions.

    Note: The law does not include authority for an approval process for the radiation safety of electronic products. Please see our website for legal and regulatory details.

  • “The FDA does not review or approve the safety of such products.”

    FDA does review the radiation safety characteristics of electronic products. FDA can require submission of additional information until we are either satisfied there is not a significant risk to public health and safety or verify there is a problem. However, a manufacturer of an x-ray security screening product can legally sell a product after they submit the required radiation safety report. Federal law does not include authority for an approval process for the radiation safety of electronic products.

  • “Instead, the FDA decided to go with a voluntary standard set by a trade group largely comprising manufacturers and government agencies that wanted to use the machines.”

    FDA chose to initiate a balanced consensus standard development process following the requirements of the appropriate accredited standards committee (ASC). A consensus radiation safety standard provides a reference for the best practices regarding particular products. Additionally, a consensus standard is not limited to product performance requirements (FDA’s mandatory standards are restricted to product performance requirements) – it can include user requirements as well. ANSI manages the accreditation of standards committees to assure the standard approval process is equitable to all parties. ANSI did not write the consensus standard for people screening products. The working group which wrote the standard was chaired or co-chaired by FDA staff. The ASC approved the chair of working group and has to approve a draft standard for the standard to be published. Neither the ASC nor the working group was dominated by manufacturers or users. There were no representatives of people screening product manufacturers on the ASC. In this case the appropriate ASC is designated N43 Equipment for Non-Medical Radiation Applications. The N43 ASC is administered by the Health Physics Society (a professional society for people working in the radiation safety area (health physicists)). The N43 committee determined the standard (both versions) was acceptable and approved it. N43 members are all experienced radiation safety professionals.

This article by two-time Pulitzer Prize winner Andrew Schneider affirms that there is “No Proof TSA Scanners Are Safe”—->

http://www.aolnews.com/2010/12/20/aol-investigation-no-proof-tsa-scanners-are-safe/

All of the numbers that I see about exposure treats the passengers disconnected.  But they aren’t.  Do the calculations account for roundtrips? Commuting?  What accumulation factors do the calculations account for when saying “extremely low”?

Medical personnel that work every day with radiology machines have explicit protocols in place to protect themselves because exposure accumulates.  Patients are warned not to have too many xrays in a given year.  How many flights is too much?

Am I really supposed to trust the company selling the machines to the TSA?  A medical device company that knowing exposes employees to 3 lifetimes worth of radiation in 2 years is still in business today.  Companies don’t care about anyone but themselves.

You should not use collective dose (a summation of many small stochastic risks when considering effective whole body dose), over a large population or occurrences (e.g. number of passengers being scanned) to come up with ‘no. of cancer per X or Y’. It is not how collective dose at these levels was supposed to be used. If you really must do that, and you should not, then you cannot ignore the cosmic radiation component of all those that then go on and fly – it makes the scanner doses for those persons totally negligible. If you, in addition, then suspect that LNT DOES have a threshold (currently this is not assumed to be the case), then there are no additional cancer cases in the population full stop.

I agree with Mark, but also want to emphasize the importance of putting risk into perspective. The decision to fly in an airplane includes the assumption of a certain amount of risk, even without body scanners. There is a probability that the airplane will fall out of the sky, a probability of catching a contagious disease from other passengers, a probability of eating tainted food, a probability of drinking tainted water, and a probability of being on a plane that is highjacked and flown purposely into vulnerable targets.

There is also, inherently, an acceptance of an increased dose of naturally occurring cosmic radiation that happens simply by increasing your altitude. The higher you go and the longer you are in the air, the higher the dose rate and the higher the dose that accumulates.

The additional radiation doses imposed by the use of X-ray body scanners are trivial compared to the additional radiation doses voluntarily accepted as a result of choosing to fly. I have not run the numbers, but I would bet that they fall into a range similar to adding a few minutes to the length of a flight - something that happens with great regularity as a result of prevailing winds, bad weather, or airport congestion.

My personal choice is to fly if that is the most convenient way to get from point A to point B. If scanners reduce the amount of time required to safely get on a plane, I am willing to accept the radiation dose as being less risky than the diesel smoke I will breathe as I walk through the parking garage into the airport.

People who want to spend their life worrying have plenty of other more important things to worry about other than the radiation dose they receive from passing through airport x-ray scanners designed to reduce the risk of flying with armed people bent on imposing ill upon their fellow passengers and people on the ground.

Good one Rod.
Using UK data – dose rate at 37,000 (typical latitude above Manchester) is about 5 micro Sv/h of high energy cosmic radiation. For a trip from London to NY, going ‘over the top’ it is going to be similar for the entire routine (once at cruising altitude).
The dose per scan from the screening device is often miss-quoted. For comparison purposes it needs to be expressed as a whole body dose (effective dose). Note that effective dose is a derived quantity representing ‘risk’ – there is no actual physical ‘whole body exposure’ in the screening units since the x-rays are not penetrating enough. If one considers that a typical screening might be 0.06 micro Sv (a lot less has been reported), then this represents about 43 seconds of flight given the flight data I have quoted.

The comments miss the point here - the dose is extremely low, and ProPublica states that.  A side note: the skin likely receives a larger dose than is accounted for except by the scientists criticizing the scanners.  While we risk cosmic radiation every time we fly, and some people live in areas of higher background radiation, why expose yourself to any addition extra radiation when it is unnecessary?  That is the real point here:  while the dose is low, the scanners have NOT proven to be very effective at detecting threats.  They have caught guns (which metal detectors do cheaper & w/o ionizing radiation) and have caught drugs (not a threat to airplane safety and many consider an overstepping of TSAs duty).  The underwear bomber could still get through a scanner as long as he hid the material on his body in a contoured way.  The GAO said these things are questionable when it comes to effectiveness.

The real reason we have these scanners & they didn’t go through any regulatory hoops (safety, public comment periods, effectiveness, etc) is clear from the money trail.

The skin dose is important, but not an issue if the dose per screening is given as effective dose - if so, the skin dose is accounted for.

The issue regarding its use as an effective ( or not) security device is valid.

Mark

@SL - I am perfectly willing to agree that the cost of the devices and the additional burden on travel may not be worth the investment in the security theater.

What I am not willing to do is to stoke silly fears about minor quantities of radiation that are roughly equivalent to adding just a few minutes (or seconds as Mark has calculated) to a flight. The radiation of the devices is NOT the issue and should not be a source of concern.

If you want to fight what appears to have been a corrupt decision to buy useless devices and put a lot of money into the pocket of selected contractors, I’ll fight alongside you. I will not, however, ever agree that there is any need to work hard to avoid the tiniest doses of radiation.

Some comments. If the medical risk is so negligible, why did the airline pilot’s union win the right to avoid the strip search scanners? Four flights a week is 8 potential scans over, what, a 40 week work week? 160 scans would be 320 minutes or 5 hours a year which is negligible given the 1 in 400 million statistic thrown about.

Also, in tests the TSA has gotten guns past through scanners, so they decrease the effective legal security in place that has worked for decades.

However, the real problem with the scanners is the destruction of the 4th amendment. The purposeful strip search, no matter how convenient, completely wipes out the 4th amendment and establishes a precedence for further erosion. Even if the strip search scanners replace unwanted nude pictures of us and our children, they still perform a warrantless inch-by-inch search of our bodies.

If I ignore the fact that the 4th amendment doesn’t include “because of fear or gutlessness then this right may be ignored”, and accept “reasonable” as taking the vague “government deciding the ‘public good’ “, the strip search scanners still fail. There have been 0 fatalities out of 48 years of suicidal airline passengers causing fatalities through working non-metallic bombs - the whole purpose of the scanners. That is much less than 1 in 400 million odds of passengers causing problems of any import.

Contrast this with citizens being killed every week in major cities. It is much more security for the US if all citizens in public places can be strip searched and sexually assaulted (as in unwanted touching of genitals and female breasts) at will by police as this would undoubtedly contribute to a more secure society.

Fortunately, the courts are barely protecting us from this complete destruction of the 4th amendment….

Cannot comment on all the US legal stuff.

The fact that pilots do not like them says everything about what they do not know about cosmic radiation!

Mark

@Jeff - once again, if your argument is against the principle of being scanned and the illogic of enriching the suppliers of ineffective monitoring equipment, I am with you.

However, I remain adamantly unwilling to accept health based arguments because of the tiny quantities of additional radiation emitted by the machines. I will concede that the machine operators, who have to be next to the devices for as much as 40 hours per week, should wear monitoring badges. There is a level of radiation dose that can be harmful and there is a remote possibility that the machines can be defective and emit that level of radiation.

However, for pilots and passengers who just have to pass through the devices, there is no danger at all.

They are an intrusion, the rush to purchase them can be legitimately questioned, and their effectiveness is certainly an issue worth investigating, but worry about the health effects is completely baseless. All it does it propagate the irrational fear of radiation that is hampering society’s access to an incredible source of wealth and power for all of us who do not work for oil and gas companies.

aligatorhardt

Nov. 15, 2011, 6:36 a.m.

I find piles of red flags here. The FDA accepts information supplied by manufacturers, it does not test the scanners, that is a problem. Back scatter machines claim that X-rays are reflected, that is a physical impossibility. X-rays cannot be reflected, they are absorbed and re-emitted if the energy is sufficient. In medical equipment exposures of radiation below 50KV are prevented by filtering, because skin absorption is increased at lower energy levels. The scanners claim to be filtered by 1mm aluminum equivalent, but the energy level is not disclosed, so we have no determination of the energy level of the x-ray beam that strikes the body. The claim that a person is being exposed by cosmic radiation, so more exposure should be ignored is ridiculous. One could say that being shot by a single bullet is usually not fatal, so why be concerned if shot twice or three times? That would make as much sense, as saying additional risks should be ignored. The average cancer risks quoted ignores the fact that people have very different sensitivities to damage from radiation. The risk for a mature adult is completely different than the risk to reproductive tissues in a child. the risk to superficial tissues like the thyroid gland, is very different than the risk to the liver. These comparisons of exposures between adults and children, between medical procedures and cosmic ray exposure, or background radiation are all invalid. While many in the radiation delivery business like to claim that radiation can be good for you, this has no basis in fact, and no evidence to support the idea that low levels of radiation can be anything other than harmful. 

The FDA has a long tract record of capture by the very industries it is designed to regulate. The FDA has no credibility as a public oversight organization, but continues to rubber stamp anything that makes money for it’s sponsors, regardless of public harm. The fact that employees of the airlines are forbidden to wear radiation monitors shows that exposure is known to be excessive. The only reason why so many efforts are made to avoid documentation, or allow independent testing is to hide the fact that these scanners are not safe or advisable.

Do not have time tonight to go into all of this….

We are talking about Compton scatter.

The point of using effective dose is that it is not a real dose, its a risk factor. As long as effective dose is considered then comp with cosmic radiation is valid.

I have personally monitored the radiation dose from these units.

More later as I have time to comment in detail.

mark

Rod, Mark, Jeff and others who believe radiation levels are too low to cause medical harm… Perhaps, you could be correct IF, and ONLY IF, the amount of radiation being emitted is truly at the low levels specified by the manufacturer…HOWEVER, the actual levels are NOT being checked, nor regulated, by ANY reliable source (I do not regard the manufacturer self-regulation as reliable) in regular, timely manner.  This is just one of the issues that has scientists, the medical community, and concerned citizens worried regarding the safety of the body scanners.  Please do some research on CT scanners…turns out many people were exposed to extremely excessive levels of radiation from poorly calibrated CT scanners.  And, since they are a machine used for medical purposes, they were suppose to undergo more stringent regulation and monitoring than the body scanners are required to undergo.

@Elaina - Once again, I will accept the common ground argument that there should be some requirements in place to monitor the radiation levels that are emitted from the devices. As you pointed out, there is a demonstrated history where devices that were designed to expose people to low doses were improperly operated or had technical failures that resulted in actual doses that were harmful.

My assertions about the safety of the radiation levels involved in the body scanners is based on knowledge of the effects at the levels that are claimed. The risk of harm to people at the claimed levels is no greater than the risk of harm to people from exactly the same dose given by natural sources like cosmic radiation or emissions from naturally occurring radioactive materials like radium, potassium-40 or radon. As Mark pointed out, passing through the scanners gives people a calculated dose that is roughly equivalent to the cosmic radiation dose received in about a minute of flying at normal cruising altitudes.

Radiation that is received at high dose rates can overwhelm the human body’s natural defense and repair mechanisms. It is always a good practice to measure radiation and understand how the measured dose rate relates to the danger levels; I will not argue about the need to require measuring and reporting.

That, however, is a completely different aspect of the discussion. Measuring radiation is rather simple and requiring those measurements would not add a significant burden to the machine operators.

There is no need, however, to try to make people worry about being exposed to low dose rate radiation for a short period of time while passing through a scanner. It is not dangerous and does not pose any health risk.

(As I noted up thread, I will also argue on the side of those who believe that the scanners are an unnecessary expense because they are not actually very effective at finding hazardous materials and because the actual risk of an attack on an aircraft is so tiny as to be below concern.)

Radiation is only intended for medical reasons. That is actually stated in the FDAs regulations. This also, is taken directly fro the FDA website:

“Radiation dose per person from medical X-rays has increased almost 500 percent since 1982.”

“X-ray Risks

The risks of medical X-rays include

  * a small increase in the chance of developing cancer later in life
  * developing cataracts and skin burns following exposure to very high levels of radiation

The small risk of cancer depends on several factors:

  * The lifetime risk of cancer increases as a person undergoes more X-ray exams and the accumulated radiation dose gets higher.
  * The lifetime risk is higher for a person who received X-rays at a younger age than for someone who receives them at an older age.
  * Women are at a somewhat higher lifetime risk than men for developing cancer from radiation after receiving the same exposures at the same ages.”

http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm095505.htm

@RealAmerican

Without numbers, your comments are not terribly useful. What is the number associated with “high levels” that are dangerous and how does that compare to the doses given by the airport scanners? How do airport scanner doses compare to the radiation dose per person for medical x-rays? How does it compare to the dose they will get after they sit down on the airplane and fly to their destination?

The FDA may have some written regulations that say that radiation is only for medical purposes, but that is a limited federal agency that apparently has no knowledge of or no responsibility for the thousands of other useful ways that radiation is used in useful activities. It is an integral part of many industrial processes including producing aluminum foil, making shrink wrap, drilling for oil, sterilizing medical devices, measuring material thickness, and defeating insects without pesticides.

Eric Frederick

Nov. 17, 2011, 9:03 a.m.

There is a medical and health physics principle known as As Low As Reasonably Achievable (ALARA). The essence of this principle is that we need to keep the dose ALARA. If safe alternatives exist, those alternatives should be used over all others. Safe alternatives such as submillimeter scanners expose people to no ionizing radiation and therefore, there is zero dose. You can’t get any lower than that.

The ALARA principle is universal and any organization (FDA, NCRP, etc.) regulating devices that emit ionizing radiation should be aware of it. I am disheartened by this response from the FDA

In this country, we used to live by certain principles, but it appears that living a principled life has become pass’e…at least in Washington.

The principle of “As Low As Reasonably Achievable” (ALARA) is based on the Linear, No-Threshold (LNT) dose response assumption. There are many scientific studies that refute that assumption, but the people who make their money as radiation protection specialists tend to discount any science that might make their profession less important.

In addition, the fossil fuel industry has a serious monetary interest in stoking as much fear of radiation as possible - did you notice how many advertisements for “clean natural gas” were played during all of the breathless reporting about the events taking place at Fukushima? Did you know that the market price of LNG has increased by about 40% in the seven months since that event due to the irrational actions in Germany and Japan to shut down unaffected nuclear plants and burn natural gas instead?

Here is a link to a radiation protection researcher who has a different idea of how radiation protection standards should be set.

http://www.youtube.com/watch?v=Uj8Pl1AiOuA&feature=youtu.be

Rod

Careful, not all Radiation Protection Advisers like me are in it for the money?! You know my views despite the fact that I have to deal with the law. That said, I also have to deal with plants and work which can potentially deliver 10,000 Gy/h and therefore LNT is not the only thing that drives work :)

Anyway, I can assure you that there is no ban on X-ray scanners for security in the EC. They are just not on the approved list ... Yet.

Mark

@Mark - I apologize. I did not mean to direct my fire at all radiation protection specialists, just at the ones who establish the rules. The LNT dose assumption is silly, but even when you apply it to this case, the risk is so small that it disappears into the risk of all other accepted hazards. As you calculated above, the dose from passing through the scanner is equivalent to about 45 seconds worth of cosmic radiation from flying. Anyone who is so worried about radiation health effects that they will not pass through a scanner should not get on an airplane.

The bottom in is until the TSA allows these radiation scanners to undergo independent testing, their claims are not based in fact, nor are the FDA’s.

Plus, no one has yet to address the issue of a mechanical malfunction.  These MECHANICAL devices are running for months straight, with who knows what (if any) kind of regulation.  How are they assuring us a malfunction isn’t going to deliver a sudden concentrated dose?

And finally, as Dr. David Brenner of Columbia pointed out, the type of cancer most likely to develop from these scanners is basal cell carcinoma, which often occurs on the head and neck.  This just goes to show the kind of thought that went into hastily installing these things.  A bomb on a passengers face? 

I don’t see how anyone can defend any aspect these body scanners in good conscience.  Keep up the good work ProPublica.

@Sarah - I am not defending the scanners. I am resisting the fear, uncertainty and doubt (FUD) that is being spread about radiation. Go ahead and require testing. Ensure that the devices are carefully maintained. Require operators to monitor radiation doses. Heck, take them out for all I care; I refuse to live in a state of fear about terrorism anyways and pine for the days when I could comfortably arrive at an airport just 30 minutes before my scheduled flight and walk down to the gate. I pine for the days when families could see each other off right at the gate and wait together when flights were delayed.

What I get angry about is when people try to fight the devices on stoking baseless fears about brief doses of low level radiation where the total computed dose is roughly equivalent to the amount of radiation one receives by staying aloft an additional 45 seconds. That is not a health risk and anyone who is actually worried about it should never, ever fly in the first place.

Ditto ... and to add..

I too have no big deal with the scanners with respect to their useful purpose. If they are no good at security enhancement – then why use them, I agree. Furthermore, I can accept that the way the TSA in the US has handled the situation is compromised. What I can say is that the Health Protection Agency (HPA) in the UK has looked at these devices and provided a statement to the effect that the devices have negligible risk (with respect to ionising radiation exposure).

I have also looked at the devices, monitored them with bloody great ion chambers with massive volume over 100’s of measurements. This is required because the dose delivered per scan is so low it is hard to measure. Stand inside the device and have a scan with a conventional cheap monitor (GM Tube based as being sold all over Japan at the moment) and it will not flinch. This is partly because the instrument response is to slow to react to the peak dose rate which passes by.

As far as skin doses are concerned - many people are missing the point. What is not being made clear is that the quoted dose per pass (which I gave above) is in the units of Effective Dose. This unit is a derived risk unit and is not obtained by standing next to the monitor and taking direct measurements which I described above. It is obtained by taking raw data and then converting with filtration (Al equivalents etc) and photon flux / energy conversions (etc) to come up with an Effective Dose. This then accounts for skin dose, but puts it in the form of whole body effective dose. The reason for doing this is that you then CAN then compare a scan with cosmic radiation exposure (for example) – as long as they comparator exposure is also in the units of effective dose.

As far as independent tests are concerned – all I can say is that this has taken place (in the UK and US). It is true that I do not believe the test results have been made public, but as I have said the HPA in the UK issue a statement.

I am not sure what the problem is with a mechanical device – I prefer them to the blue screen of death?! Seriously, we rely on mechanical devices in our car to make a sudden stop when emergency breaking – it is designed not to fail in all reasonably foreseeable events.

@ Rod Adams:  You say you aren’t defending the scanners?  I just read you and your buddy Mark’s posts going back and forth about how the radiation from the scanners is negligible, etc. etc.  Could you please point out in which peer-reviewed article and in which scholarly journal I can find the following statement:  “Total computed dose is roughly equivalent to the amount of radiation one receives by staying aloft an additional 45 seconds.”  You can’t because it doesn’t exist.

Your defending of these body scanners on any level, even considering your personal non-fear of their radiation, is sad in a free country.

I am an expert, simples.

In a free country we can all say what we like. We can agree or disagree.

The calc I gave, to which you refer, could be worked out by a first grade student of Health Physics. It may not be specifically in an article because it’s frankly beneath the readership of said publication.
Mark

How many of those commenting have actually been directed into these machines?  Do you have that personal experience? 

This clean-cut, law-abiding, tax-paying, plump, middle-aged, Caucasian grandmother, who hasn’t had so much as a parking ticket in well over a quarter of a century, was herded into one of those machines by a yelling male TSA agent in the midwest some months ago.  Holding a criminal stance—legs far apart, arms up in the air—and listening to that machine rumble for those ten very long seconds was humiliating and frustrating.  And as I stood there, I decided it wasn’t going to happen to me again.

But that was easier thought than done.

I haven’t been directed into another body scanner until this past week, this time by a barking female TSA agent on the east coast.  I refused.  The agent would not accept my denial and quickly became threatening, yelling at me, and then rabidly screaming out some code over the sound system which seemed to draw everyone’s attention to the situation.  I was horrified at how quickly an innocent person could be treated like a criminal, just because I said I wasn’t going into that machine. 

In the end, another TSA female agent performed a public violation of my modest person, an invasive and intrusive pat-down, in full view of the entire screening area, even going so far as to look down my underclothing, front and back.  And that was after I was forced to stand and wait next to the whole body scanner while they ran another two or three people through it and subjecting me to the machine’s back scatter by only a couple of feet.  From what I’ve since read, my experience of being forced to stand and wait within several inches of the machine after refusing to go into it, is not uncommon.

Now if these machines are so safe, if this whole issue is about making us all safer, why isn’t everyone sent through the body scanners?

And if they’re to make me feel safer, to make us all safer, why wasn’t a metal detector also used on me?  And along that line, why weren’t my carry-on items searched?  Potentially adding injury to insult was the fact that my valuable carry-on items were sent unattended and unprotected down a distant conveyor belt and were vulnerable to being snatched, while I was subjected to those ten minutes of a public and demoralizing groping, which I felt to be an unwarranted invasion of my person.

Well there it is.  One personal experience.  But I’m probably just spitting into the wind.

@Missus

I have been through the scanners. Security theater at airports has converted me from a 10-20 times per year flying traveler to one who has only been on a plane 3 times in past two years. I agree with your sense of outrage at the nature of the searches and the waste of time. As a taxpayer, I am outraged at the incredible waste of resources. I would prefer living in a country that is willing to accept a little risk in return for enhanced freedom. I never asked the government to attempt to enforce perfect security or to protect me from boogymen.

All that said, my point on this thread has been, and remain, a desire to reduce irrational fear of low level radiation exposure that can be directly compared to the radiation exposure passengers get from flying in the first place. A trip through the scanner gives you about the same total dose as remaining at altitude for about 45 seconds to a minute. The “backscatter” that you mention is at a far lower level than inside the scanners where images can be created from the return.

I would support requirements to measure the radiation, requirements to badge the operators, and even an effort to remove the machines because they are not effective and violate personal freedoms. However, I will never support any effort to spread fear, uncertainty and doubt about the beneficial use of radiation - this might just be one case where the particular implementation is not particularly useful, but it is not dangerous unless there is a serious malfunction in the machinery.

Measure the doses, sure. But stop worrying about something that will not hurt you and will not cause any long term risks.

The most damning, and telling, piece of evidence (or lack thereof, haha) against the backscatter scanners is that neither the manufacturer nor the TSA nor the FDA are have yet published the only number that matters: the dose, in Sieverts or centigray, that the average passenger will receive per security scan from this device. Without that number being made public, no one is free to make a properly informed choice about these scanners and whether they constitute a danger or an acceptable risk. Anyone with sufficient interest in the matter can find out, for example, how much dose comes from a CT scan or a chest x-ray. this information is widely published. So why not backscatter scanners? the skeptical would opine that there is only one reason to keep this number under wraps - and that is that the number must be unusually high.

Glad i don’t have to fly to the US in near future…flying out of Europe and having to walk through a millimeter wave machine was alarming enough.

They have. But I conceed it has not be communciated that well. Neither have the units of dose been clearly explained.

The value is Effective Dose (Whole Body Dose) - which is not a real dose at all (its a risk factor). The value per screening is less than 0.05 micro Sv (effective dose).

Mark

I should have added a reference here:

See PDF Data Sheet on this page:

http://www.rapiscansystems.com/en/products/item/productsrapiscan_secure_1000_dual_pose

It is written as “Less than 10 microRem” per scan. S

In SI units that is < 100 nSv (0.1 micro Sv).

The publication should state the unit is Effective Whole Body dose as I have explained higher up the page. The actual doses I have seen from these units are much less than 100nSv, but that is in the noise because its all low.

Mark

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