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

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8.11.8. When tunnels cover a distance of more than 150 m from the base of a shaft, a telephone system shall be installed with extensions:
(a)  at the surface;
(b)  at the base of the shaft; and
(c)  at a maximum distance of 75 m from the face.
Telephone outlets shall be installed at intervals of 150 m along the tunnel.
R.R.Q., 1981, c. S-2.1, r. 6, s. 8.11.8.