The NRC is modernizing nrc.gov with an updated design and improved navigation to enhance usability. We are committed to a smooth transition and will work to minimize any disruption. The site may be briefly unavailable at times during launch. Thank you for your patience.
Derived Air Concentration-Hour (DAC-hour)
The product of the concentration of radioactive material in air (expressed as a fraction or multiple of the derived air concentration for each radionuclide) and the time of exposure to that radionuclide, in hours. A licensee may take 2,000 DAC-hours to represent one annual limit on intake (ALI), equivalent to a committed effective dose equivalent of 5 rems (0.05 Sv).
Page Last Reviewed/Updated Thursday, August 27, 2026
Page Last Reviewed/Updated Thursday, August 27, 2026