A body scanning machine previously used in U.S. airports to check passengers for explosives and other potential threats meets federal standards for radiation exposure, a report released Tuesday concludes.
The backscatter advanced imaging technology was removed from all U.S. airports in 2013 because of privacy concerns. However, safety experts also cited worries about whether passengers would be exposed to high and unnecessary levels of potentially harmful radiation.
The 148-page report comes as the Transportation Security Administration is considering a second-generation model that will be equipped with updated privacy software.
The technology creates detailed images of those being scanned using X-rays, a type of ionizing radiation that in high doses can result in cellular mutations that eventually lead to cancer.
A 14-member multidisciplinary National Academies of Sciences, Engineering and Medicine committee evaluated whether the scanners comply with health and safety standards for public and occupational ionizing radiation exposure, and whether the system design, operating and maintenance procedures were appropriate to prevent overexposing travelers to the rays.
The committee found the backscatters were in compliance with the 250 nanosieverts per-scan maximum whole body dose a passenger should receive. No person, regardless of age and weight, would exceed the effective dose limit per scan under routine operations, the report found.
For perspective, the authors noted that any dose below 100,000 nSv is “considered negligible,” that a 100,000,000 nSv dose might result in excess risk of cancer, and that a 6,000,000,000 nSv dose could result in death soon after exposure.
Still, the group acknowledged concerns that “any dose, no matter how small, is assumed to be linked to an increase in the risk of contracting cancer” and pointed out limitations to conducting the research.
The machines are not currently in use, so could not be tested in real-world settings. The committee's access to the decommissioned machines was restricted and their time with the machines was limited. They also could not perform “destructive testing,” a way of evaluating the machine in a damaged or suboptimal state to document whether use could be safely terminated.
The TSA began using X-ray backscatter technology as a secondary passenger screening in U.S. airports in 2008. The tool became the primary method in December 2009, when a Northwest Airlines passenger failed in his attempt to set off plastic explosives that he had hidden in his underpants.
The Department of Homeland Security requested that the National Research Council provide the independent study of the radiation exposures resulting from the X-ray backscatter imaging systems.
The National Academies committee also recommended future areas of research, including studies on X-ray radiation exposure to people who are outside the inspection area, and safeguards that ensure no person is scanned for longer than the recommended time. They also encourage future destructive testing that includes daily verification of safety parameters are being followed.