Travel tradition dictates that this is the week when business travelers cede control of the nation's airports to hordes of holidaymakers who no longer get to grandmother's house by going over the river and through the woods. And just like the big bad wolf, the Transportation Security Administration has a nasty surprise for all those innocent holiday flyers.

On Monday, the agency announced that 16 more airports will get the full-body scanners that first caused an uproar last holiday season. Coupled with last month's deployment of "nude-o-scope" scanners in nearly a dozen other cities, there are now more than 500 of what the agency calls "advanced imaging technology" (AIT) units in operation at more than 100 airports.

But I do bring you limited, government-approved, and totally conditional tidings of comfort and joy: The new scanners are of the "millimeter wave" variety, a much less controversial system than the so-called "backscatter" X-ray machines that dominated the initial TSA deployment of full-body imagers.

Why does that gobbledygook terminology matter? Because in the nearly two years since Umar Farouk Abdulmutallab unsuccessfully stuffed his shorts with explosives and the TSA moved AIT devices to the front lines of airport security, the debate over the full-body scanners has shifted dramatically.

In the months immediately after the Underwear Bomber tried to strike on Christmas Day 2009, the argument centered on the ability of the new scanners to better detect terrorists. By Thanksgiving Day 2010, the argument was over privacy: Were the "nude-o-scope" images too revealing? Was the TSA inappropriately "groping" passengers who invoked their rights to decline to pass through the scanners?

But now that the government has switched to a less-invasive type of imaging software and courts have ruled that scanners are legal, lots of folks are questioning the safety of the backscatter X-ray units.

Do they subject flyers to too much radiation each time they pass through the device? Are they dangerous when the cumulative effect after many security scans are considered? Has the TSA known all along that the backscatter scanners were unsafe? Why won't the agency allow an independent study of the devices? Are the devices calibrated properly? Does anyone even know how much radiation the backscatter units actually emit during each scan?

I can tell you with confidence that I have no idea what the truth really is. I'm no doctor, and I don't play one in this column. I'm not a scientist, either. And there is so much conflicting evidence that it is impossible for even a well-informed business traveler to get a handle on the controversy. Besides, I'm not even a well-informed business traveler in this particular matter. Everything I "learned" about radiation came from a scary episode of the Outer Limits. I saw it when I was 10 years old, and the mere mention of radiation reminds me of Warren Oates' spooky, bug-eyed, cue-ball-bald mutant.

I can relate to the prevailing narrative, though. A lot of business travelers think backscatter scanners are bad for their health, and they can cite a plethora of scientific and anecdotal evidence to support their suspicion. (Just Google "backscatter x-ray" and start reading.) And they'd rather submit to the full-metal-grope from a TSA screener than voluntarily walk through a backscatter X-ray imager.

"My doctor told me they're dangerous, and that's enough for me," says Sylvia Religter, who flies about 75,000 miles a year. "[My doctor] says that she won't go through them when she goes to the airport, so why should I?"

The no-backscatter brigade can also point to last month's decision by the European Commission to ban backscatter scanners at airport checkpoints in the 27 European Union countries. The machines were barred "in order not to risk jeopardizing citizens' health and safety."

If you're unaware of the backscatter backstory, you can get a surprisingly cogent and dispassionate overview at Wikipedia. I don't usually take Wikipedia at its word, of course, but when we're talking about things like ionizing radiation, where else are we going to turn for a plain-English explanation? After all, this stuff is the airport equivalent of rocket science, and most of us will never get the finer points. However, if you want the oversimplified Seat 2B summary, try this: The X-rays that the backscatter imagers emit have enough energy to cause a DNA mutation, and that could lead to cancer. As I said, real Outer Limits stuff.