In the latest salvo in an exchange that has lasted more than a year, scientists at the University of California, San Francisco (UCSF), and Arizona State University are continuing to press the government to vet the safety of airport security scanners that use x-rays, ProPublica reports:
The TSA says the backscatter technology has been evaluated by the Food and Drug Administration, the National Institute for Standards and Technology and the Johns Hopkins University Applied Physics Laboratory. Survey teams are using radiation-detecting dosimeters to check the machines at airports. The TSA says the results have all confirmed that the scanners don't pose a significant risk to public health.
But the letter to the White House science adviser, signed by five professors at University of California, San Francisco, and one at Arizona State University, points out several flaws in the tests.
John Sedat, a professor emeritus in biochemistry and biophysics at UCSF, is the main author of the 28 April letter to White House Science Advisor John Holdren. Roughly a year ago, Sedat and colleagues wrote a previous letter to Holdren laying out possible health concerns of the technology, which bounces x-rays off passengers' skin. The U.S. Food and Drug Administration (FDA) responded in October with assurances that the dose was far too low to cause cancer. Now, Sedat and colleagues are calling for independent tests of the scanners:
The professors note that the Johns Hopkins lab didn't test an actual airport machine. Instead, the tests were done on a model built by the manufacturer, Rapiscan, and configured to resemble a system previously tested by the TSA.
The researchers' names have been kept secret, and the report on the tests is so "heavily redacted" that "there is no way to repeat any of these measurements," they wrote.
The physics and medical professors also took issue with the device used to measure the radiation. Although the device, known as an ion chamber, is commonly used to test medical equipment, they argue that the detector gets overwhelmed by the amount of radiation the backscatter deposits in a short time and might not provide accurate readings.
The White House Office of Science and Technology Policy, which Holdren heads, say they have once again passed the letter on to FDA and the Transportation Security Administration.