Washington (CNN) -- Studies by the U.S. government and professional organizations conclude the level of radiation emitted by full-body airport scanners is safe for passengers, according to a Department of Homeland Security Inspector General report, but the findings likely will not end the dispute over backscatter X-ray machines.
The Transportation Security Administration started deploying the devices two years ago. The TSA says there are 247 Advanced Imaging Technology units in operation at 39 commercial airports around the country. They are used to detect a range of metallic and nonmetallic threats, including weapons and explosives.
The backscatter machine "delivers an extremely low dose of ionizing radiation" with levels "below the acceptable limits," the report stated.
The report issued by Carlton Mann, assistant inspector general for inspections, said independent radiation studies concluded radiation levels did not pose a danger.
"Specifically, to reach annual radiation dose limits, a passenger would have to receive more than approximately 17,000 screenings in a 12-month period, which is equivalent to approximately 47 screenings per day, 365 days per year," the inspector general's office concluded in an executive summary.
Nevertheless, federal investigators issued a half dozen recommendations, including making sure backscatter calibrations are "consistently conducted and documented, ensure Transportation Security Officers complete annual radiation safety training... and develop procedures to ensure appropriate notifications of unintended radiation emissions or overdoses."
Sen. Susan Collins, R-Maine, has reiterated her call for an independent study of the health effects of the airport scanners, saying an alternative screening technology is available.
Last November, TSA Administrator John Pistole said he would initiate an independent study but then later said the inspector general report would eliminate the need for a new study. At the time, Collins said the report needed to do more than "just a study on whether TSA is doing an adequate job of inspecting, maintaining and operating AIT machines."
"This report is not the report I requested," Collins said in a statement. "An independent study is needed to protect the public and determine what technology is worthy of taxpayer dollars." She said passengers should be informed about screening options and signs should be posted so they can decide whether they want to go through the machines or request alternative screening.
The American Federation of Government Employees, a labor union representing 625,000 federal employees including 40,000 transportation security officers, would like to see a more comprehensive, independent study focused on TSA employee exposure.
The inspector general study "allays concerns for the flying public but not for the people working the equipment," said Milly Rodriguez, a health and safety specialist at AFGE. "We don't know their exposure," she said. The inspector general report "essentially has no new information as far as we are concerned."
The use of AIT scanners has increased since the Christmas Day 2009 attempt by Umar Farouk AbdulMutallab to blow up a plane over Detroit by detonating plastic explosives hidden in his underwear.
In addition to the backscatter machines, the TSA has also deployed about 260 millimeter-wave machines which use radio waves and do not emit X-rays.