The other issue besides privacy that has surrounded backscatter X-raying has to do with radiation exposure. Most of us do not get X-rayed on a regular basis; and when we do get X-rayed in a hospital or doctor's office, we've got a lead vest thrown over our vital organs. But at airports, there's no lead vest. So are people who travel a lot going to be subjected to dangerous levels of radiation if they get backscattered too often? Most experts say no. According to the Health Physics Society (HPS), a person undergoing a backscatter scan receives approximately 0.005 millirems (mrem, a unit of absorbed radiation). American Science and Engineering, Inc., actually puts that number slightly higher, in the area of .009 mrem. According to U.S. regulatory agencies, 1 mrem per year is a negligible dose of radiation, and 25 mrem per year from a single source is the upper limit of safe radiation exposure. Using the HPS numbers, it would take 200 backscatter scans in a year to reach a negligible dose -- 1 mrem -- of radiation. You receive 1 mrem from three hours on an airplane, from two days in Denver or from three days in Atlanta. And it would take 5,000 scans in a year to reach the upper limit of safety. A traveler would have to get 100 backscatter scans per week, every week, for a year, in order to be in real danger from the radiation. Few frequent flyers fly that frequently.
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