United States Nuclear Regulatory Commission - Protecting People and the Environment

U.S. Nuclear Regulatory Commission

Question 27: Do licensees have to post controlled areas

(outside the restricted area) as airborne radioactivity

areas if derived air concentrations (DAC) are exceeded?

Answer: Yes, if the airborne radioactivity is indoors.

If the airborne radioactivity is outdoors, the answer

depends on the particular situation. In certain situations

the licensee may need to identify and delineate an outdoor

airborne radioactivity area. For example posting would be

required in a small area, accessible to workers, in the

immediate vicinity of a vent on the outside of a building,

exhausting air containing concentrations of radioactive

materials in excess of the DACs specified in Appendix B to

10 CFR Part 20. (References: 10 CFR 20.1003, 10 CFR


Page Last Reviewed/Updated Thursday, March 29, 2012