California Code of Regulations
Title 8 - Industrial Relations
Division 1 - Department of Industrial Relations
Chapter 4 - Division of Industrial Safety
Subchapter 20 - Tunnel Safety Orders
Article 9 - Emergency Plan and Precautions
Section 8427 - Protection Against Water or Gas

(a) When shaft openings, tunnels or tunnel portals are located where a sudden inrush of water might logically be expected, adequate precautions shall be taken to protect against this occurrence.

(b) Whenever any working place in a tunnel is being advanced within 200 feet of areas that contain or are likely to contain dangerous accumulations of water, gas, petroleum products, or mud, representative vertical test holes shall be drilled from the surface where possible to determine if a hazard is present. Where the likelihood of a dangerous accumulation does exist, horizontal test holes of sufficient depth shall be drilled in advance of such workings to insure that at least 20 feet of tested ground remains beyond the face. Test holes 20 feet deep shall also be drilled at angles of 45 degrees into the walls, roof, and floors when necessary.

(c) Employees shall be removed to a safe location at least 2,000 feet from the blasting site before blasting in areas where dangerous accumulations of water, flammable or toxic gas, mud or petroleum products could be encountered. After blasting, the tunnel shall be examined by a competent person and tested by a certified gas tester before other employees reenter the affected area.