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Airport Screening
From Health Physics Society May 2011
Introduction
With air travel regaining popularity and increased security measures, airport security screening has become an area of interest for many people. Travelers are required to go through metal detectors and/or x-ray systems and their personal belongings are x-rayed. Even with all of the screening, radiation exposure, both to the traveler and the screener, is minimal and far below any level that would be of concern. This document will introduce and explain airport screening equipment and its potential for exposing travelers to radiation. As with any use of radiation, the overarching concept is one of risk versus benefit. In the case of air travel, the tiny incremental amount of risk posed by radiation exposure is far out weighed by society's need for safe air travel.
Metal Detectors
Metal detectors use low-intensity magnetic fields to detect metallic objects. When metal passes through these fields, sensors detect a change in the fields and an alarm goes off. Even though magnetic fields are a form of radiation, the radiation the machine emits is nonionizing. Essentially, this means that exposure to these low-intensity magnetic fields does not cause biological damage. Therefore, even repeated exposure to metal detectors has no associated radiation risk.
Luggage Screening
Self-contained machines are used to screen baggage (both checked and carry on) by using x-rays to analyze the contents. The amount of radiation used is higher than in other screening technologies (like backscatter x-ray systems described below), but this is contained within the x-ray machine. Passengers and workers are exposed to very little radiation. These x-ray machines are designed with built-in shielding to help prevent radiation from exiting the device. However, a small amount of radiation may come out of this shielding. This is termed leakage radiation. There are federal limits placed by the U.S. Food and Drug Administration on acceptable leakage rates for all types of x-ray producing equipment. These limits are established to keep people safe. Any item that goes through an x-ray screening machine will receive ionizing radiation exposure; however, it is too low to damage your personal belongings and they cannot become radioactive from this procedure. However, some photographic film may need to be hand-screened because the x-rays can damage the film (just like a plain film x-ray at the doctor's office).
Backscatter/Soft X-Ray Systems
Some of the newest traveler screening systems use x-rays for full-body scanning of travelers. In these systems, low-energy x-rays bounce off of the skin and back to detectors to show an image. That image will show hard objects (such as weapons) as well as soft objects (like a packet of gel or powder, which would not be caught by metal detectors). Unlike metal detectors, these systems use ionizing radiation. Ionizing radiation, like x-rays, has the potential for damaging human DNA. Because the public is being exposed to this radiation, exposure must be limited to a safe level. An American National Standards Institute/Health Physics Society industry standard states that the maximum allowable effective radiation dose for an individual from one screening (which generally consists of two scans) is limited to 0.025 mrem (ANSI 2009). Actual doses are on the order of 0.001 to 0.005 mrem per scan. This amount of exposure is well below any level of concern and, in fact, is less than 1 percent of the radiation you receive from natural sources in a single day or less than two minutes of airplane flight. This means the risk from the exposure is very small (TSA 2010). One alternative to backscatter x-ray systems, millimeter wave scanners, can also be found in use at security check points. These systems do not emit ionizing radiation.
Conclusion
Air travel is a part of modern living and the need for safe travel continues, especially given the ongoing threat of terrorism. The technology used in screening people and their belongings exposes the travelers to minimal amounts of radiation.