S-2.1, r. 4 - Safety Code for the construction industry

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8.11.2. At the end of all shaft sinking operations and before tunnelling operations, each shaft used for hoisting whose depth is more than 15 m shall be equipped between the bottom of the shaft and the surface with 2 distinct signalling systems which may be electric, pneumatic or mechanical. One of these systems shall be connected to a telephone or to a speaking-tube.
R.R.Q., 1981, c. S-2.1, r. 6, s. 8.11.2.