If you've been following the story, you'll know that Johns Hopkins played a role in evaluating these scanners, but the institution has been vociferous in its insistence that the study did not evaluate the safety of the scanners. Not to be dissuaded, HHS has continued to imply that the Johns Hopkins analysis supports their claim that scanners are safe to use on all people as primary screening at airports. Sedat starts by saying:
There is Still No Rigorous Hard Data For The Safety of X-Ray Airport Passenger Scanners.
...The [Johns Hopkins] document is heavily redacted ... In every case the electric current used which correlates one to one with X-ray dose has been specifically redacted. Thus there is no way to repeat any of these measurements. While the report purports to present the results of objective testing, in fact the JHU APL personnel, who are unnamed anywhere in the document either as experimenters or as authors, were not provided with a machine by Rapiscan. ... There are also [technical] issues ... The data given in the Johns Hopkins report indicate that there must be something wrong.I've deleted much of the technical points (which are important for context) to make one of Sedat's points clear: This does not in any way, shape, or form follow acceptable standards for scientific research. If the TSA just wanted to bake a birthday cake, it wouldn't be such a big deal. But they are currently shooting ionizing radiation at the general population in airports across the nation without so much as a single peer-reviewed study on the safety of the machines being published. The letter continues:
The whole issue of software was not addressed....
In summary, the independent testing of the safety of these specific scanners has not been rigorous nor has it been held to the standards usually associated with new devices before approval for utilization in the public sector. Usually the exact technology, as installed, is sent to a university, national laboratory or other outside facility that has the expertise to test, for an extended period of time to enable an indepth study--usually by several independent groups. Different test equipment, optimal for this configuration, can be used at a site that specializes in the potential problems of this technology. The hardware and software is tested in all aspects, finally arriving at a place where the true capabilities of this system are totally known, similar to testing of new aircraft, spacecraft and other technology that impacts on a national level.In between, they bring up the questions from the first letter of concern that have still not been addressed (read: ignored or dismissed by HHS) and elaborate on their importance.
They then go on to explain what type of tests could be done to directly assess safety, using published scientific techniques to look for DNA damage, mutations, and cancer when human cells or live animals are exposed. However, since the actual machine and the precise settings on the scanner have not been made available to scientists, these tests can not be done. It also calls into question the way that doses are being reported (coincidentally, under HHS's own safe-exposure threshold) since they don't take into account the response of different organs and tissues, and different categories of people (old, young, pregnant, sick, etc...) in response to radiation. For example, we have eye cells that don't regenerate, but are getting a direct X-ray beam shot at them by these machines, and may lead to eye diseases. Children are (obviously) smaller, which means that their most sensitive organs are getting more exposure than an adult's would.
Finally, the letter addresses the abysmal maintenance schedule and emergency responses planned for the scanners:
Hospitals usually check for problems on X-ray machines daily, but we understand that TSA will only check once a year, at best, in spite of the fact that these machines are being used 24 hours a day, 7 days a week.
The manufacturers are required to notify the FDA immediately upon discovery of an accidental radiation exposure. What is the trigger for discovery? What actions will the TSA personnel operating the system take in the event of a suspected malfunction? Will they notify the individual of exposure to a radiation level of 0.25 mSv, or a level considerably higher if the fail-safe mechanisms also malfunctioned? Who will be directly responsible for the medical care of passengers who are overexposed? How probable are these events? Have exhaustive tests of mean time between failures for these systems been done in realistic operational settings? How often will the machines be calibrated?I'd like to say Bravo! to Dr. Sedat and his colleagues for taking the time to seriously address this issue and speak out on something that most of the population is ill-equipped to evaluate.