§ 7979

In tunnels or underground mines classified extrahazardous, sufficient air shall be supplied to maintain an atmosphere of all of the following conditions:

(a) Not less than 19 percent oxygen.

(b) Not more than 0.5 percent carbon dioxide.

(c) Not more than 5 parts per million nitrogen dioxide.

(d) No petroleum vapors or other toxic gases in concentrations exceeding the threshold limit values established annually by the American Conference of Governmental Industrial Hygienists.

(Added by Stats. 1972, Ch. 1430.)