Exhaust valves shall be provided, having risers extending to the upper part of chamber, if necessary, and shall be operated at such times as may be required and especially after a blast, and persons shall not be required to resume work after a blast until the gas and smoke have cleared, for at least thirty minutes.
RCW 49.24.110
Severability-1973 1st ex.s. c 154: See note following RCW 2.12.030.