Section 7139 - Hoist Signal System(a) (19-90) Every shaft shall be provided with an efficient means of interchanging distinct and definite signals between the top of the shaft and the lowest level and all other levels from which hoisting is done.(b) (19-92) Every shaft in which hoisting is done shall be provided with an emergency signal system that can be operated from the shaft conveyance at any point in the shaft.(c) Special care shall be taken to keep all signaling apparatus in good order, and necessary precautions shall be taken to prevent electric signal and telephone wires from coming into contact with other electric conductors, whether insulated or not.Cal. Code Regs. Tit. 8, § 7139