Who watches the watchers?

This came out just before the holidays, but there's actually some good investigative reporting that happened, so it's worth looking over if you haven't already. The TSA lied (shocking, I know) by stating that there were several agencies checking into the safety of the scanners. Well, reporters have contacted all of the named agencies and found that they are not ensuring the safety of the scanners.

"The safety of our scanning systems are routinely and thoroughly tested by the manufacturer, FDA, the U.S. Army, the Health Physics Society, Johns Hopkins Applied Physics Laboratory and others," the [TSA] spokesman said.

... FDA says it doesn't do routine inspections of any nonmedical X-ray unit...

...Two-person teams from the Army unit this year performed surveys of scanners at only three airports — in Boston, Los Angeles and Cincinnati, [an Army Health Command physicist] said...

"[Johns Hopkins Applied Physics Laboratory's] role was to measure radiation coming off the body scanners to verify that it fell within [accepted] standards. We were testing equipment and in no way determined its safety to humans," said Helen Worth, the lab's head of public affairs. "Many news articles have said we declared the equipment to be safe, but that was not what we were tasked to do."

...[The nonprofit Health Physics Society] says it did not and does not monitor the safety of TSA devices — only that, if the devices operate as promised, safety should not be an issue, said Howard Dickson, the society's immediate past president.

Not only that, but - as I stated previously - TSA is not providing access to the scanners to researchers nor releasing its own data:

...[Johns Hopkins Applied Physics Laboratory] scientists were unable to test a ready-for-TSA scanner because the manufacturer would not supply one. Instead, tests were performed on a scanner cobbled together from spare parts in manufacturer Rapiscan Systems' California warehouse.

...TSA has refused the [Health Physics Society's] requests for data that the agency collects on radiation exposure in and around its scanners.

and,

"We found that essentially none of this information was known or made public, and more interestingly, it looked like this technology had not been independently vetted by the scientific community, published, peer-reviewed or even discussed openly," [UCSF researcher John Sedat] said. "Essentially, all the information was coming from companies that were making the devices, and it looked like it was being parroted by the FDA and the TSA, which didn't seem reasonable."

They may be safe, but what evidence do you have for believing this to be so?