Answer to Question #5960 Submitted to "Ask the Experts"

I am seeking a clear statement to define a "personal contamination event." This definition is required to be included in our company's radiation protection procedures. I am also seeking considerations that should be reviewed or determined when defining a "personal contamination event."

There is not a formal definition that can be referred to, but the definition is simple: a personal contamination event is any event where radioactivity is detected on the person or on the person's clothing, after any protective clothing that may have been used during the work activities has been removed and discarded and the person has stepped into a clean area. 

There is no lower limit on the activity detected, other than that dictated by the sensitivity of the detector used for frisking. The idea is that anytime radioactive material appears on a person or the person's clothing after exiting a contaminated area (or worse, if the person was never in a contaminated area and some contamination appears on the person), it is taken as an indication of a loss of control of radioactive materials, because radiation safety programs are designed to prevent such occurrences. This is the approach typically used at nuclear power stations and at all materials (nonreactor) facilities that are licensed to use radioactive materials.

Please note that although the US Nuclear Regulatory Commission (NRC) does not regulate contamination as such, NRC does insist that licensees maintain control of licensed material at all times. Accordingly, contamination is, by definition, licensed material that is located where it should not have been, that is, that has escaped control.

Sami Sherbini, PhD
Cynthia Jones, PhD