Answer to Question #12724 Submitted to "Ask the Experts"

Category: Security Screening — Airport Screening

The following question was answered by an expert in the appropriate field:

Q

I pushed a stuck bag through a carry-on luggage scanner with my foot/leg. My foot/leg was in the primary beam for 10–20 seconds (four to five seconds at a time for four pushes). The machine has a 140 keV generator. What dose did I most likely receive, is my health at risk?

A

You need not worry about your radiation dose. It was about 0.1 percent of a chest x ray. To go into more details about your extremity dose, I found several items of interest.

From the Centers for Disease Control and Prevention (CDC) Report, Evaluation of Radiation Exposure to TSA Baggage Screeners, page 20, in Table 4, the maximum (worst case) dose (sic exposure) rate is 1,300 µR h-1 (3.3 × 10-7 C kg-1 h-1) or 0.36 µR s-1 (9.3 × 10-11 C kg-1 s-1). Note that the radiation exposure units are given in µR (called traditional units) because that is the unit used by CDC. However, the Health Physics Society has adopted the International System (SI) of units and those are given in parentheses. The exposure that your foot and lower leg received from 20 seconds of exposure may be about 7 µR (1.9 × 10-9 C kg-1). For the purposes of this discussion of screening x rays, we will consider that exposure measured in R (C kg-1) and dose measured in rem (mSv) are essentially the same. 

On Page 14 of the same CDC report, in Table 2, the annual dose limit for a member of the public, as recommended by the National Council on Radiological Protection and Measurements (NCRP) for the extremities (hands up to the elbow and feet up to the knee) is 5,000 mrem (50 mSv), or 5,000,000 µrem (50,000 µSv). So, the radiation dose to your foot and leg was a few millionths of the limit set to assure no adverse health effects. You should also note that you receive about 3 mSv (300 mrem) each year from natural sources of radiation in our everyday environment.

John Hageman, CHP

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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