California Code, Labor Code - LAB § 7951

(a) Tunnel shall include excavation, construction, alteration, repairing, renovating, or demolishing of any tunnel except tunnel work covered under the compressed air safety orders adopted by theOccupational Safety and Health Standards Board and manhole construction.

(b) “Tunnel” means an underground passageway, excavated by men and equipment working below the earth's surface, that provides a subterranean route along which men, equipment, or substances can move.

(c) “Mine” means any excavation or opening above or below ground used for removal of ore, minerals, gravel, sand, rock, or other materials intended for manufacturing or sale. It shall include quarries and open pit operations, other than a gravel pit or other pit where material is removed by a contractor or other person for his own use and not for sale to others. The term “mine” shall not include a mine that is operated exclusively by persons having a proprietary interest in such mine or by persons who are paid only a share of the profits from the mine, nor shall it include during any calendar year, any mine that produced less than five thousand dollars ($5,000) in ore, minerals, sand, rock, or other material during the preceding calendar year.

(d) “Access shaft” means a vertical shaft used as a regular means of worker access to underground mines and tunnels under construction, renovation, or demolition.

(e) “Lower explosive limit” means the lowest concentration at which a gas or vapor can be ignited or will explode.

(f) “Face” means the head of the tunnel where soil is being removed, or that area in a mine where digging is underway.

(g) “Muck” means excavated dirt, rock, or other material.

(h) “Permissible equipment” means equipment tested and approved by the U.S. Bureau of Mines or acceptable to other authorities recognized by the division, and acceptable by the division, which is safe for use in gassy or extrahazardous tunnels or underground mines.

(i) “Division” means the Division ofOccupational Safety and Health.

(j) “Board” means theOccupational Safety and Health Standards Board.

(k) “Underground mine” means a mine that consists of a subterranean excavation.