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 41 - Telephones
Underground
Section 7165 - Emergency Telephone

At every mine with an escape exit required by these Orders, telephone communication for emergency purposes shall be provided between the underground telephone stations and the principal surface telephone station, by way of the escape exit, provided, however, that other equally rapid means of communication may be used between surface stations.

Such emergency system shall be in addition to the telephone system required by Section 7164.