27-358. Signaling apparatus
A. Every shaft and each compartment thereof used for hoisting which exceeds fifty feet in depth, and not exempted in writing by the inspector, shall be provided with an efficient means of interchanging distinct and definite signals between the top of the shaft and the lowest level from which hoisting is being done, and the various intermediate levels for the time they are in use.
B. The signaling apparatus shall be either wire or cable actuating a bell, whistle, speaking tube, telephone, electric or electronic system, or two or more of them.
C. Only those employees and supervisors authorized by the operator shall be permitted to ring any shaft or station bells.