body_scanners_web.jpgCHICAGO (AP) — They look a little like giant refrigerators and pack a radiation dose big enough to peer through clothing for bombs or weapons, yet too minuscule to be harmful, federal officials insist.

As the government rolls out hundreds more full-body scanners at airports just in time for crowds of holiday travelers, it is working to reassure the public that the machines are safe.

An independent group of experts agrees, as long as radiation doses are kept within the low limits set for the scanners. Still, a few scientists worry that machines might malfunction, raising the risk of cancer.

The Transportation Security Administration says radiation from one scan is about the same as a person would get from flying for about three minutes in an airplane at 30,000 feet, where atmospheric radiation levels are higher than on the ground. That amount is vastly lower than a single dental X-ray.

You would have to go through scanners more than 1,000 times in one year to even meet the maximum recommended level – and even pilots don't do that.

“We are confident that full-body X-ray security products and practices do not pose a significant risk to the public health,” officials from the Food and Drug Administration and the TSA wrote in a letter last month to White House science adviser John Holdren.

Yet ripples of concern have surfaced among some passengers fearful about excess radiation, among some flight crews already overexposed to radiation in the air and even among a few scientists.

“The thing that worries me the most is what happens if the thing fails in some way” and emits too much radiation, said Arizona State University physics professor Peter Rez.

The risk for failure is higher than in a medical setting because the machines are operated much more often, by TSA workers without medical training, Rez said.

American Airlines pilot Sam Mayer said pilots he knows are opting out of
being scanned.

“All they're telling the public is that it's fine. We're looking for some science” to back that up, Mayer said. The FDA says the science does establish the machines' safety.

Airline pilots and other flight crew members face a slightly increased lifetime risk of developing cancer, about one percent higher than the general population, according to the Health Physics Society, a nonprofit group of scientists and other professionals involved in radiation safety.

“Radiation has always been a concern of pilots because of what we do,” Mayer said.

“This is just one more exposure on top of what we're getting.”

Mayer said that pilots are equally upset with the TSA's option for people who don't want full-body scans: body pat-downs that critics say are akin to groping.

“We want the TSA to stop the bad guys, and that's not us,” Mayer said.

About 385 scanners, each costing up to $170,000, are already in place at more than 60 airports. The TSA is adding more and expects to have a total of 500 in place by year's end.

About half are what are known as millimeter-wave units, made by L-3 Communications, which are not the focus of safety concerns because they emit a less potent kind of radiation.

The remaining machines are Rapiscan System's “backscatter” scanners which emit X-ray-like ionizing radiation. This kind of radiation in larger doses can cause cell changes leading to cancer.

The FDA has estimated that the risk of fatal cancer from the maximum allowable dose would be one in 80 million per backscatter screening.

By comparison, the chance of dying in a car driven for 40 miles are one in one million.