Safety for Security Screening Using Devices That Expose Individuals to Ionizing Radiation
What are these devices? Does this include the general walk-through magnetic screeners?
What this FAQ refers to are the devices often seen in airports or courthouses that expose people to ionizing radiation (x rays) when a person walks through them. These x-ray-emitting devices are more commonly called "backscatter screeners," although they have been called "people scanners" and "security screeners."
We won't be talking about the magnetic screening units or another type of device called a millimeter wave unit—those use nonionizing forms of radiation.
To how much radiation am I being exposed? Is this something I need to be concerned about as a frequent flier (I fly twice a month)?
There is an American National Standards Institute/Health Physics Society (ANSI/HPS) consensus standard (listed in the reference information at the end of this document) stating that people-scanning devices should expose an individual to no more than 0.25 microsievert per screening (one screening procedure generally consists of two scans). The two primary companies that sell people screeners say that their devices expose people to half that amount of radiation.
For perspective, 0.25 microsievert is also received by flying about a minute and a half (cosmic radiation during commercial flight exposes fliers to about 10 microsievert per hour). It is also received by living for 40 minutes (natural background radiation exposes people to about 0.35 microsievert per hour).
Frequent fliers will be exposed to more radiation because they will go through the people scanners more often, plus they will be receiving more cosmic radiation while they are flying. The consensus standard took into account extra scans for frequent fliers and put a recommended limitation on the total radiation dose from this activity. That limit is 250 microsieverts per year, which would be 1,000 scans per year if the scanner is operating at the per scan limit.
Is it safe to take my children through this device? What if I am pregnant?
The American National Standards Institute/Health Physics Society (ANSI/HPS) consensus standard took into account the varying sensitivity of different groups of people who might be scanned. The authors first looked at a number of reports and published studies on the health effects of radiation. They then chose the 0.25 microsievert dose level to ensure that children and pregnant individuals can be safely scanned with these devices. The x-ray scanner uses a very low-energy and low-intensity radiation, so that an embryo/fetus is not exposed to any radiation that could possibly increase the developmental risks of radiation to the embryo.
Who decided that it is okay to use radiation on so many people?
The final decision was made by the Department of Homeland Security (DHS). This was made, however, only after experts gave their input on the safety of the devices. DHS needed to weigh the potential risk of exposing people to ionizing radiation versus the overall societal benefit of detecting terrorist threats. Because the amount of radiation someone receives from being screened is so low, the benefit was determined to far outweigh the risk (if any).
What about concerns that people have raised regarding the skin dose from these devices? Some have said that the skin dose must be high if most of the x rays only come in contact with the skin.
The American National Standards Institute/Health Physics Society (ANSI/HPS) consensus standard addresses this issue. The 0.25 microsievert limit is an overall whole-body effective dose. To calculate that dose, measurements of the entrance exposure at the skin were taken first. The standard indicates that the associated skin absorbed dose is even less than the overall whole-body effective dose.
What about concerns people have raised about the possible radiation dose to organs that sit just under the skin—like the thyroid? Or what about the eyes?
Some organs do get a radiation dose—a higher dose if they are close to the skin and a lower dose if they are deeper inside the body. They won't, however, get a dose higher than the skin dose because the x rays all come in contact with the skin, while only a few penetrate deeper into the body. As a result of that, even the organs that are close to the skin surface receive less than 0.087 microgray. This is a dose that is considered to have negligible risk for harmful effects.
Aren't all radiation doses cumulative—doesn't all this radiation add up?
It isn't as simple as saying we can add up all of the radiation to which we've been exposed in our lifetime to determine what the effect might be. When radiation interacts with a cell in the body, several things can occur:
- The cell might have some minor damage that is repaired.
- The cell might have some minor damage that remains inactive until another agent interacts with the cell again.
- The cell might have damage that causes it to become cancerous.
- The cell may simply stop functioning.
- The cell may die.
So, radiation doses aren't necessarily cumulative.
Who measured these doses, anyway? How do they really know that is the dose to a person?
The radiation measurements from these devices were performed by some independent researchers along with the manufacturers. The American National Standards Institute/Health Physics Society (ANSI/HPS) standard indicates how these measurements are to be performed, with what types of measuring instruments, and from the resulting data, how the dose is to be determined.
References and additional information:
The consensus standard referenced in this document: ANSI/HPS N43.17-2009 Radiation Safety for Personnel Security Screening Systems Using X-Ray or Gamma Radiation
The Food and Drug Administration website on this topic: http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/SecuritySystems/ucm227201.htm
The Health Physics Society position statement on this topic: Use of Ionizing Radiation for Security Screening Individuals (2009)
A reference standard created by an interagency committee to assist federal agencies in setting guidance on these devices: Guidance for Security Screening of Humans Utilizing Ionizing Radiation (GSSHUIR)
A couple of items from the National Council on Radiation Protection and Measurements:
Some TSA reports on the scanners: http://www.tsa.gov/traveler-information/advanced-imaging-technology-ait
A Health Physics Society slide presentation: "X-Ray Security Screening of People"
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