CHAPTER 2. Gassy and Extrahazardous Tunnels [7965. - 7985.]

Cal. Labor Code - LAB 2.

in effect

Cal. Labor Code - LAB § 7965. Section 7965.

Any tunnel or underground mine classified by the division as gassy shall operate under special procedures adopted by the board, as well as rules, regulations, special orders, or general orders for nongassy underground mines and tunnels.

Cal. Labor Code - LAB § 7966. Section 7966.

In any tunnel classified as gassy by the division, there shall be tests for gas or vapors taken prior to each shift and at least hourly during actual operation. If a mechanical excavator is used, gas tests shall be made prior to removal of muck or material and before any cutting or drilling in tunnels or underground mines where explosives are used. A log shall be maintained for inspection by the division showing results of each test. Whenever a tunnel excavation or underground mine operation approaches a geologic formation in which there is a likelihood of encountering gas or water, a probe hole at least 20 feet ahead of the tunnel face or area where material is being mined shall be maintained.

Cal. Labor Code - LAB § 7967. Section 7967.

Whenever gas levels in excess of 10 percent of the lower explosive limit are encountered initially in a tunnel or underground mine classified as gassy, the division shall be notified immediately by telephone or telegraph. The chief of the division or his authorized representative may waive subsequent notification for gas readings less than 20 percent of the lower explosive limits upon a finding that adequate ventilation and other safety measures are provided to assure employee safety.

Cal. Labor Code - LAB § 7968. Section 7968.

In any gassy tunnel or underground mine, the division may order work halted until adequate testing can be completed to determine the level of hazard from gases or vapors. A notice of such shutdown shall be filed by the division inspector with his superiors as soon as practicable. Any overruling of such order must be made by the chief or his designated representative and must be in writing. An onsite inspection must be made by the person overruling an inspector’s order prior to resumption of work.

Cal. Labor Code - LAB § 7969. Section 7969.

In any gassy tunnel or underground mine the division shall review plans for electrical lighting and power for equipment. When it is necessary for safety, the inspector may require changes in the amount and type of lighting, and may require permissive-type wiring, switches, tools, and equipment.

Cal. Labor Code - LAB § 7970. Section 7970.

In any tunnel or underground mine classified gassy, smoking shall be prohibited and the employer shall be responsible for collecting all personal sources of ignition such as lighters and matches from employees entering the tunnel.

Cal. Labor Code - LAB § 7971. Section 7971.

Whenever there is any ignition of gas or vapor in a tunnel or underground mine, all work shall cease, employees shall be removed, and reentry except for rescue purposes shall be prohibited until the division has conducted an inspection and authorized reentry for maintenance or production in writing.

Cal. Labor Code - LAB § 7972. Section 7972.

If the level of gas in any tunnel or underground mine reaches 20 percent of its lower explosive limit at any time all men shall be removed, the division notified immediately by telephone or telegram, and no one shall reenter the tunnel or underground mine until approval is given by the division.

Cal. Labor Code - LAB § 7973. Section 7973.

In any tunnel or underground mine classified as gassy, all employees shall be informed of any special orders made by the division following an inspection. Such notice shall be given before entering the tunnel or underground mine. A copy of any orders subsequently written by the division shall be posted and all employees shall be notified at a safety meeting called by the safety representative before they are permitted to start work.

Cal. Labor Code - LAB § 7974. Section 7974.

In any tunnel classified as gassy by the division, ventilation shall include continuous exhausting of fumes and air, unless an alternative ventilation plan which is as effective or better is approved by the division. Fans for this purpose shall be located at the surface, and shall be reversible from a single switch at the portal or shaft. These requirements shall not preclude the use of auxiliary fans to supply more air or greater exhaust to a tunnel or underground mine.

Cal. Labor Code - LAB § 7975. Section 7975.

A “kill” button capable of cutting off all electrical equipment shall be maintained in any gassy tunnel or underground mine. The safety representative or his designated representative shall cut off power at any time gas or vapor levels reach 20 percent of the lower explosive limit or more. Before work is restarted every employee underground shall be informed of the level of gas or vapor recorded, and a permanent record shall be called to the surface and retained in a special log.

Cal. Labor Code - LAB § 7976. Section 7976.

In any tunnel or underground mine classified as gassy, the division shall determine the number of fire extinguishers necessary and their locations.

Cal. Labor Code - LAB § 7977. Section 7977.

Any tunnel or underground mine classified as extrahazardous by the division shall comply with the provisions for gassy tunnels in this chapter, as well as regulations, rules, special orders, and general orders of the division or board.

Cal. Labor Code - LAB § 7978. Section 7978.

In any extrahazardous tunnel or underground mine smoking by employees or open flame shall be prohibited. Welding or cutting with arc or flame underground in other than fresh air shall be done under the direct supervision of qualified persons who shall test for gas and vapors before welding or cutting starts and continuously during such an operation. No cutting or welding shall be permitted in atmospheres where any concentration of gas or vapor reaches 20 percent of the lower explosive limit or more while a probe hole is being drilled or when the tunnel face or material from a mine is being excavated.

Cal. Labor Code - LAB § 7979. Section 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.

Cal. Labor Code - LAB § 7980. Section 7980.

All electrical equipment and machines, including diesel engines, used in tunnels or underground mines classified extrahazardous shall be permissible equipment. The division may, however, permit the use of nonpermissive equipment in a tunnel or underground mine in areas where it finds there is no longer danger from gas or other hazards.

Cal. Labor Code - LAB § 7981. Section 7981.

An escape chamber or alternate escape route shall be maintained within 5,000 feet of the tunnel face or areas being used to excavate material in an underground mine classified as gassy or extrahazardous. Workers shall be provided with emergency rescue equipment and trained in its use.

Cal. Labor Code - LAB § 7982. Section 7982.

Records of air flow and air sample tests to assure compliance with required standards shall be maintained by the employer at the site of any tunnel or underground mine classified extrahazardous. Such records shall be made available to any division representative upon request.

Cal. Labor Code - LAB § 7983. Section 7983.

The main fan line used for ventilation in any tunnel or underground mine classified extrahazardous shall contain a cutoff switch capable of halting all machinery underground automatically should the fan fail or its performance fall below minimum power needed to maintain a safe atmosphere.

Cal. Labor Code - LAB § 7984. Section 7984.

In any tunnel or underground mine classified extrahazardous a device or devices which automatically and continuously test the atmosphere for gases or vapors shall be maintained. Such device or devices shall be placed as near the face or area of operation as practical, but never more than 50 feet from such point. The division shall determine if additional monitors are necessary and where they should be located. This requirement shall apply only to tunnels or underground mines where excavation of material is by mechanical means.

Cal. Labor Code - LAB § 7985. Section 7985.

All such testing device or devices shall be U.S. Bureau of Mines approved or acceptable to other authorities recognized by the division and shall automatically sound an alarm and activate flashing red signals visible to employees underground whenever the concentration of gases or vapors reaches or exceeds permissible levels. Permissible levels may be established lower than the limits set in division rules, regulations, or general orders whenever a division inspector considers such action necessary to make the operation safe for employees.

Source: CA Legislative Counsel Bulk DataURL: https://downloads.leginfo.legislature.ca.gov/pubinfo_2025.zipFetched: 6/27/2026