Section 835.209 - Concentrations of radioactive material in air(a) The derived air concentration (DAC) values given in appendices A and C of this part shall be used in the control of occupational exposures to airborne radioactive material.(b) The estimation of internal dose shall be based on bioassay data rather than air concentration values unless bioassay data are:(3) Internal dose estimates based on air concentration values are demonstrated to be as or more accurate.58 FR 65485, Dec. 14, 1993, as amended at 63 FR 59682, Nov. 4, 1998