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Subchapter 20. Tunnel Safety Orders
Article 2. Definitions

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§8405. Definitions.

The following definitions shall apply in the application of these orders.

Acceptable. Acceptable to the Division.

Access Shaft. A shaft used as a regular means of worker access to or from underground operations.

Air Supply Lines. Pipe, hose, or combination of pipe and hose, that supplies compressed air to equipment.

Approved. Those products, devices, systems, or installations meeting the requirements of Section 3206 of the General Industry Safety Orders.

Automatic Coupler. A connecting device between rail equipment that automatically engages when one car strikes another.

Back. The roof, ceiling or arch of a tunnel.

Barricade. To obstruct by use of planking, sawhorses, etc., placed around an excavation, sump, shaft or drop off to prevent entry of persons, vehicles or flying materials.

Barrier. A fence, wall or other structure built to bar passage with openings no greater than 2 inches.

Barricade Natural. Natural features of the terrain such as hills.

Block System. A switching system which prevents trains from entering specific sections of track occupied by another train.

Brakeman. An employee who performs switching, loading, or other train operations and assists the motorman.

Bulkhead. A tight partition, brattice or stopping in a tunnel, raise, or shaft.

California Switch. A movable switching track resting on top of the regular track upon which trains can be diverted for passing.

Car Passer. A device by which rail equipment can be moved to one side of the regular tunnel track to permit passage of the train or for other purposes.

Chamber. An opening, room, or vault excavated completely or partially underground which may be open to the surface at the top or connected to the surface by a tunnel or shaft.

Cherry Picker. A lifting device used to pick up muck cars or other equipment, from the track so as to set it to one side or raise it high enough for passage on the track of trains or equipment.

Combustible. Capable of being ignited and consumed by fire. Wherever combustible substances or materials are mentioned in these Orders, flammable and extremely flammable substances and materials are included.

Certified Person. A person certified by the Division.

Competent Person. One who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them.

Conveyance. A cage, cab, enclosure, bucket conveyor or similar device used to lift, hoist or otherwise carry employees and/or materials.

Crown. Highest point of a tunnel cross-section.

Crown Bars. Timber or steel beams that extend ahead of the jumbo, the last set of timber or rib steel supports for temporary tunnel support and protection of workers near the face.

Cut and Cover. A work method which places a temporary roof over open excavation while doing further excavation or other work beneath the cover.

Division. The Division of Occupational Safety and Health (DOSH).

Exhaust Purifying Device (scrubber). Any of a number of devices, such as water bath scrubbers or catalytic scrubbers that reduce contaminants from internal combustion engine exhausts to an acceptable level.

Explosion Relief Mechanism. Explosion-doors, weak-wall, panel or other equivalent devices so located to relieve the pressure that would be created by an explosion underground and reduce possible damage to a ventilation system.

Extremely Flammable. Having a flash point of 20 degrees Fahrenheit or less, when tested by the Tagliabue open-cup method.

Face-Underground. That part of any adit, tunnel, or raise where excavating is progressing, or was last done.

Fan-Auxiliary. A fan used to provide ventilation or circulate air to areas off the main fresh air course.

Fan-Booster. A fan installed in the ventilation system to increase the ventilation flow rates of the system.

Fan-Main. A fan or system of fans that are located at the surface which controls the primary ventilation of a tunnel or underground chamber.

Fire Resistant. Protected against fire by a covering equivalent to a one-hour fire resistant covering applied in a manner acceptable to the Division.

Fire Resistant Hydraulic Fluids. An approved fluid of such chemical composition and physical characteristics that it will resist the propagation of flame, or meet the requirements of 30 CFR Part 35.

Flammable. Capable of being easily ignited or burning rapidly.

Flammable Gas. A mixture which when once ignited will allow flame to be self-propagated throughout the mixture, independent of and away from the source of ignition.

Flash Point. The temperature at which a material gives off flammable vapor in sufficient quantity to burn instantaneously at the approach of a flame or spark.

Ground Support System. Wood, steel, concrete, rock bolts, or other materials used for bracing or supporting the ground.

Highway. Any street, alley, or road, publicly or privately maintained and open to use for the public for purposes of vehicular travel.

Hoist-Material. A hoist for lifting, lowering, or pulling materials. It includes tugger-type and slusher.

Hoist, Personnel. A hoist equipped with the necessary safeguards to raise or lower personnel as required by Section 8495(b).

Horsepower-Brake (BHP). The power of an engine or other motor as calculated from the force exerted on a friction brake or absorption dynamometer applied to the flywheel or the shaft.

Incline. Shaft greater than 20 degrees from the horizontal but less than 70 degrees.

Intrinsically Safe. A device or system which is incapable of releasing enough electrical or thermal energy under normal or abnormal conditions to cause ignition of a mixture of flammable gas and air in its most ignitable composition.

Invert. The floor of a tunnel.

Jumbo. A mobile platform or series of platforms, usually on wheels, to provide work areas for employees and the machines, tools, or materials being used.

Lanyard. A flexible line to secure a wearer of a safety belt or harness to a drop line, lifeline, or fixed anchorage.

Laser. Light Amplification by Stimulated Emission of Radiation and is used as a coherent beam of light for alignment.

LEL. Lower explosive limit of a flammable gas or vapor.

L.P.G. Liquified Petroleum Gas.

Magazine. A building, other than the explosives manufacturing building, or other structures especially designed for the storage of explosives, or any cave or other structure adapted to the storage of explosives.

Mechanical Tunneling Equipment. Equipment such as mechanical excavators, tunnel boring machines, shields, roadheaders, and raise boring machines.

Motorman. The operator of a locomotive or other similar rail mounted equipment.

MSHA. The United States Department of Labor Mine Safety and Health Administration.

Muck. Excavated rock, earth or other materials.

Permissible. A machine, material, apparatus, or device which has been investigated, tested, and approved by the Mine Safety and Health Administration, and is maintained in accordance with the requirements of the approving agency.

Personnel or Person. Those persons affected by the referenced standard, including those other than employees of the employer.

Pneumatic Loader. A device for injecting an explosive or blasting agent into a bore hole or other cavity, using compressed air as the propulsive force. There are two basic types of air loaders; the pressure vessel system that forces the explosive or blasting agent through a loading hose, and the ejector system which operates on the venturi principle, in that the explosive or blasting agent is sucked out of an open container and carried into the bore hole by the air stream.

Qualified Person, Attendant or Operator. A person designated by the employer, who by reasons of their training and experience has demonstrated their ability to safely perform their duties and, where required, is properly licensed and/or certificated in accordance with federal, state or local laws and regulations.

Railroad. Any railroad or tramway which carries passengers for hire on the particular line or branch in the vicinity where explosives are stored, or where explosives-manufacturing buildings are situated.

Raise. A vertical or inclined underground excavation driven from bottom to top.

Raise Climber. A mechanical powered work platform used to provide access to the raise face.

Ramp. A sloping passageway connecting two different levels.

Return Air. The portion of the ventilation system between the point where fresh air is introduced into the underground environment and its point of release into the outside atmosphere.

Safety Factor. The ratio of the ultimate strength of the material to the actual working stress or safe load when in use.

Scrubber. A device used on internal combustion engines to reduce discharge of harmful exhaust gases. See “exhaust purifying device”.

Shaft. Any excavation where its depth is at least twice its greatest cross section dimension. The sides are nearly parallel or cylindrical. A shaft is considered to be vertical if its alignment is within 20 degrees of vertical. For the purpose of these safety orders, shaft shall include incline and raise (also see Incline and Raise).

Shall. Mandatory.

Skip. A shaft conveyance, generally for hoisting muck and materials.

Spoil. See “Muck.”

Switch. A device for enabling rail-mounted equipment to pass from one track to another.

Tunnel. An underground passageway, 30 inches in diameter or greater, excavated by employees working below the earth's surface, that provides a subterranean route along which employees, equipment or substances can move; other than passageways excavated by mine or quarry operators in connection with such operations. For the purpose of these safety orders, “tunnels” include shafts, raises, underground chambers and premises appurtenant thereto.

Two-Block. A condition in hoisting where the load, or termination assembly is hoisted to the point of making contact with an obstruction normally present in the hoisting system which can result in parting of the hoisting cable and damage to the hoisting system. Generally, a condition resulting from the load or termination assembly being hoisted under power into a headframe assembly or crane boom-tip.


Authority cited: Sections 142.3 and 7997, Labor Code. Reference: Sections 142.3 and 7997, Labor Code.


1. Amendment of section and new Note filed 3-5-96; operative 4-4-96 (Register 96, No. 10).

2. Amendment filed 7-11-2003; operative 8-10-2003 (Register 2003, No. 28).

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