30 CFR 57.5046 - Protection against radon gas.
Where radon daughter concentrations exceed 10 WL, respirator protection against radon gas shall be provided in addition to protection against radon daughters. Protection against radon gas shall be provided by supplied air devices or by face masks containing absorbent material capable of removing both the radon and its daughters.
Title 30 published on 2013-07-01
no entries appear in the Federal Register after this date.