California Code of Regulations
Title 8 - Industrial Relations
Division 1 - Department of Industrial Relations
Chapter 4 - Division of Industrial Safety
Subchapter 17 - Mine Safety Orders
Article 31 - Air Quality, Radiation, and Ventilation
Underground Mine Ventilation
Section 7098 - Ventilation

(a) The operator of every mine shall cause a good and sufficient current of fresh air to be circulated through every working place in the mine.

(b) The quantity of fresh air circulated through each working place shall be at least 200 cubic feet per minute for each person.

(c) Where workings are of such size or shape that air does not circulate satisfactorily in the vicinity of the workers, auxiliary ventilation shall be used.

(d) If the quantity of fresh air required by subsection (b) of this section is not sufficient to prevent harmful accumulations of dust, fumes, vapors, or gases, enough additional fresh air shall be provided to remove and prevent such accumulations.

(e) Men shall not be permitted, except in extreme emergencies, to work in a place where the oxygen content of the air is less than 19 1/2 percent by volume (dry basis).

(f) No man, unless he is wearing permissible, self-contained breathing apparatus, shall be permitted to work in a place where a flame safety lamp will not burn.

(g) (5-28) Unventilated areas shall be sealed or barricaded and posted against entry.