That was my concern, too. There's a precedent for a radiation-emitting machine failing in a very bad way: https://en.wikipedia.org/wiki/Therac-25

Of course these new machines cannot fail the exact same way as the Therac 25. But could they fail in a new, unpredicted way? I dunno. I am not familiar enough with how the backscatter machines are implemented to be able to predict how they could fail. But I maintain neither are most of the people who defend these machines as safe.

A well-founded concern. When the CDC inspected luggage scanners in 2003-2004, more than 2% were found in violation of federal radiation standards.

http://usatoday30.usatoday.com/yourlife/health/healthcare/go...

...because then the dose would be equivalent to about a day of natural background radiation.

I think "nobody would notice" is a pretty accurate description of what would happen in that case.

It's very safe to say it's beyond their ability to understand, considering that the TSA operators were never required to take the same health physics courses that literally everyone else whose job involves exposing the public to X-rays must undergo.