Well, another day, another fiasco from our friends at the Transportation Security Agency. Remember those perfectly safe backscatter x-ray machines? Here's what they said a year ago:
Advanced Imaging Technology: "Radiation Risk Tiny"
.
But today, guess what (per USA Today):
The Transportation Security Administration announced Friday that it would retest every full-body X-ray scanner that emits ionizing radiation — 247 machines at 38 airports — after maintenance records on some of the devices showed radiation levels 10 times higher than expected.
Pursuant to a Freedom of Information Act request, today (3/11/11), TSA released ten page letter with attachments written on 12/15/10 to someone at the Transportation Security Agency, and what it says is interesting indeed.
This letter came from Rapiscan Systems, the client of former People's Commissar of Homeland Security, Michael Chertoff, and it refers to review of the radiation testing reports prepared by the firm's "Field Service Engineers".
… the (Radiation Safety Office) also noted that the relevant report form and work instructions can be confusing to Rapiscan Field Service Engineers. This confusion results in inconsistent reporting of radiation survey findings on the forms. …
By design the Secure 1000 prevents significant changes in scan energy, even those still well within the applicable ANSI standard, as even a modest increase in scan energy, while still well within the applicable ANSI standard, would overload the system's detectors and dramatically degrade its imaging ability in a way that would be obvious to the operator. This design has been independently verified to an extremely high standard.
It appears then, that the sole protection against overdoses of radiation is the operator noting a "degraded image". Of course, these same operators have to be alert enough to notice this, and since they have already let a gun go through in somebody's underwear, one can doubt their attentiveness.
But the money quote is still to come:
… during our review we have found that ambiguites in the formatting of the (radiation inspection form) have been inducing data recordation errors by Field Service Engineers. For example, because of the extremely low amount of X-ray produced by the Secure 1000 Single Pose, the radiation survey procedure calls upon the (Field Service Engineer) to take a cumulative meter reading for 10 scans, and to divide that value by 10 to obtain an average meter reading. Oftentimes the (Field Service Engineer) will bypass the step of dividing by 10. While the resulting entry, at a pragmatic level, is understandable on its face and usable for monitoring purposes, the value, if read literally by persons unfamiliar with our system and the survey process, would imply energy outputs that are unachievable by the Secure 1000 Single Pose.
Got that? If the radiation on the report says that it is 10 times higher than expected, that's because of error in the way the inspectors are filling out the report. There is however no evidence that anyone actually checked with the machine operators to see if there had been any observations of degraded images that would have, or so it is said, indicated the machine was generating excessive radiation. There is simply an assumption that no such event ever occurred.
But wait, there's more. Other sources of error include "failure to measure background radiation" and "other documentation errors", which are unspecified. Background radiation it is presumed would have to be deducted from the measured radiation produced by the machine. Obviously this is necessary to reduce the overall level of reported radiation exposure.
There is no description of "other documentation errors" but the company has produced a new report form, which includes the following option:
Considerable document errors and/or discrepancies as noted in the comments below. Corrective action required.
Conclusion:
At the time that TSA was assuring us that these machines were perfectly safe, there existed no reliable and consistent means of measuring the radiation produced by the machines.