30 CFR § 77.1904 Communications between slope and shaft bottoms and hoist operators.
(a) Two independent means of signaling shall be provided between the
hoistman and all points in a slope or shaft where men are required to work.
At least one of these means shall be audible to the hoistman. Signal codes
used in any communication system shall be posted conspicuously at each slope
(b) Signaling systems used for communication between slopes and
shafts and the hoistman shall be tested daily.