After the “underwear bomber” incident on Christmas Day, President Obama accelerated the deployment of new airport scanners that look beneath travelers’ clothes to spot any weapons or explosives.
Fifty-two of these state-of-the-art machines are already scanning passengers at 23 U.S. airports. By the end of 2011, there will be 1,000 machines and two out of every three passengers will be asked to step into one of the new machines for a six-second head-to-toe scan before boarding.
About half of these machines will be so-called X-ray back-scatter scanners. They use low-energy X-rays to peer beneath passengers’ clothing. That has some scientists worried.
“Many people will approach this as, ‘Oh, it must be safe, the government has thought about this and I’ll just submit to it,'” says David Agard, a biochemist and biophysicist at the University of California, San Francisco. “But there really is no threshold of low dose being OK. Any dose of X-rays produces some potential risk.”
Agard and several of his UCSF colleagues recently wrote a letter to John Holdren the president’s science adviser, asking for a more thorough look at the risks of exposing all those airline passengers to X-rays. The other signers are John Sedat, a molecular biologist and the group’s leader; Marc Shuman, a cancer specialist; and Robert Stroud, a biochemist and biophysicist.
“Ionizing radiation such as the X-rays used in these scanners have the potential to induce chromosome damage, and that can lead to cancer,” Agard says.
The San Francisco group thinks both the machine’s manufacturer, Rapiscan, and government officials have miscalculated the dose that the X-ray scanners deliver to the skin — where nearly all the radiation is concentrated.
The stated dose — about .02 microsieverts, a medical unit of radiation — is averaged over the whole body, members of the UCSF group said in interviews. But they maintain that if the dose is calculated as what gets deposited in the skin, the number would be higher, though how much higher is unclear.