Worries about the risks from airport scanners to people have some critics calling for direct action. They're suggesting people opt for a pat-down instead of a scan, which could lead to long lines at the airport.
If you're planning to fly on the day before Thanksgiving, be warned. Going through security may take longer than your time in the air.
It's because of a growing backlash over the new body scanners that the Transportation Security Administration has deployed to 68 airports.
One group that's outraged about what it views as an invasion of privacy -- the new machines see through clothes to detect concealed weapons or bombs -- is calling for a "national opt-out day" on Nov. 24. The group is urging travelers to refuse the body scanning and opt for a pat-down instead.
That would clog security lines at many airports, given the TSA's new especially thorough pat-down procedures.
Meanwhile, your pilot may not get to the plane in time either.
The U.S. Airline Pilots Association and the Allied Pilots Association are urging their members to demand pat-downs too -- in a private area. The pilots are protesting on both privacy and safety grounds.
"Requiring pilots to go through the Advanced Imaging Technology (machines) means additional radiation exposure," Allied Pilots Association President Dave Bates writes to his members. He recommends that pilots avoid the body scanners.
Meanwhile, the government isn't doing very well at persuading critics in the scientific community that X-ray scanners are safe.
A word of clarification here: There are two types of airport body scanners. The controversial one uses very low doses of X-rays to scan travelers front and back and create a "naked" image. A TSA spokesman says there are currently 206 of these machines at 38 airports.
The other type doesn't use X-rays but instead a technology called millimeter-wave scanning. There are 167 of these units at 30 airports.
Earlier this year, four scientists from the University of California, San Francisco, wrote a letter to Presidential Science Adviser John Holdren raising concerns about the cancer risks of exposing hundreds of millions of travelers every year to airport X-ray scans.
Holdren's office asked the TSA and the Food and Drug Administration to respond. Their eight-page letter to Holdren was recently posted on the FDA's website.
After running through all the reviews and advisory committees that have certified the scanners as safe, the letter concludes:
The potential health risks from a full-body screening…are miniscule…We are confident that full-body X-ray security products and practices do not pose a significant risk to the public health.
The response doesn't satisfy John Sedat, a UCSF professor-emeritus of biochemistry and biophysics who was among those who wrote to Holdren last April.
"The response is deeply flawed," Sedat said in an interview. "It's double-talk. It doesn't answer any questions. Sadly, I have to say we still don't have the information we need to decide what are the dangers of this device."
Sedat says the UCSF group will make a formal reply to Holdren.
Dr. David Brenner is equally unpersuaded by the government's response. Brenner is head of the Center for Radiological Research at Columbia University.
Brenner's complaint is that the government experts are entirely focused on the risk of cancer for individuals.
"I don't think anybody would argue the point that the individual risk is small. Whether it's one in 10 million or one in 100 million, it's very small," he said in an interview. "But multiply that times 700 million people – the number of people getting on planes currently – and that's the public health risk."
And Brenner says there's reason to think the radiation dose delivered per scan is about 10 times higher than the government says. It comes from a paper by Arizona State University physics professor Peter Rez that is scheduled to appear in a journal called Radiation Protection and Dosimetry.
Rez says he was skeptical that the X-ray dose the government claims for the machines – about 1/10,000th of a chest X-ray, he says -- could produce a usable image at all. He calculated backward to figure out how big an X-ray dose would be needed to get the kind of images the machines produce.
Rez agrees the individual risk is still negligible. "It's a 1-in-20-million chance of dying from radiation for each scan," he says. "Your chances of being struck by lightning in the US in any year is 1 in 500,00. But the probability of being blown up in an airplane by a terrorist is around 1 in 30 million. So the risk from the scan is about the same as the thing you're trying to prevent."
Brenner says if Rez's dose calculation is right, pilots and very frequent fliers could exceed the recommended annual radiation dose limit of 250 microSieverts. That would require going through the scanner 250 times, by Rez's dose calculations, rather than 2,500 times, by the government's.
The result, he maintains, is "you will end up with some number of cancers coming out of each year's scanning operations." Applying it to the 125,000 commercial airline pilots and perhaps 125,000 other flight personnel, each averaging 250 scans per year, Brenner estimates "there might be five cancers, or two fatal cancers, resulting from a year's worth of X-ray screening" among airline personnel.
This could all be avoided, Brenner says, if the government relied entirely on the millimeter-wave scanners instead of the X-ray scanners.
By the way, you might be wondering: Can the average traveler standing in a security line tell the difference? Yes, a TSA spokesman says. The X-ray type is blue and has two walls. The millimeter-wave machine is grayish-white and is more cylindrical. Copyright 2010 National Public Radio. To see more, visit http://www.npr.org/.