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Subchapter 7. General Industry Safety Orders
Group 18. Explosives and Pyrotechnics
Article 116. Handling and Use of Explosives--Blasting Operations

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§5300. Firing Switches.
(a) The firing switch shall conform to the following minimum standards:

(1) It shall be an externally operable switch, enclosed in a tight case provided with a lock.

(2) It shall be a double pole, double throw switch with the handle arranged to be locked in the “off” position only.

(3) It shall be provided with a bar for short-circuiting, but not grounding the leading wires when the switch is in the “off” position.

(4) Switches shall have adequate rating for the maximum voltage and current to be used.

(5) The service entrance switch fuse or circuit breaker rating shall be fused not exceeding 33 percent of the maximum calculated current requirement and will blow at 15 times the rated capacity in 1/20 of a second.

(6) The switch shall be mounted so that the handle is down when the switch is in the “off” position. The leading wires shall be attached to the blade terminals and the power line wires to the up-throw terminals.

(b) When firing by means of a light or power circuit, the circuit shall be open at all times in at least one place by an air gap of at least 5 feet underground and 15 feet on the surface, between the firing and the auxiliary switches at all times, except during the actual firing operation. The air gap shall be established by means of a cable and 2-pole plug and receptacle of adequate capacity. The plug shall be provided with a device, preferably of automatic type, to short-circuit the wires when the plug is removed from the receptacle.

(c) The shot firing switch shall be no less than 1,000 feet from the face of a tunnel if the tunnel length exceeds 1,000 feet.

(d) For tunnels less than 1,000 feet in length, the shot switch shall be outside the portal.


Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code.


1. New subsections (c)-(d) and new Note filed 7-11-2003; operative 8-10-2003 (Register 2003, No. 28).

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