First, let me remind you this is the same government that assured our soldiers that Agent Orange was "safe", and that the air quality at ground zero was "safe". We are now spending billions for medical treatment for those poor souls who believed the government's assurances of safety. That said...
NO amount of radiation is safe. Radiation accumulates in the body. That, alone, is cause for serious concern.
These scanners scan the entire body - a very large area. Per square inch the amount of radiation may be small, but collectively, not so much. Consider...
You dentist uses radiation to x-ray an area the size of a silver dollar. Just enough to penetrate cheek and gums. But have you noticed that it is SO safe that even with such a small amount, you must wear a lead flack jacket, and the dentist must, by law, LEAVE THE ROOM!
That's how "safe" it is.
But here is the REAL safety hazard - by using scanners and pat-downs - neither of which provides very much security - we give up our RIGHTS, our FREEDOM and our DIGNITY. And once you give up all those things that America stands for, and is built upon, the terrorists have already won. And that is the ultimate in being UN-safe - giving up who we are.