(3)Every shaft in the course of being sunk shall be provided with a permanent lining of metal, concrete or masonry, which Shall at no time, be more than six metres from the bottom of the shaft:Provided that where iron or steel rings with a substantial lagging are used below the permanent lagging and are kept close to the bottom of the shaft, this distance may be increased to not more than 20 metres:Provided further that in the case of a shaft where special conditions exist which make compliance with the provisions of this sub-regulation not necessary, the Regional Inspector may, by an order in writing and subject to such conditions as he may specify therein, grant exemption from the compliance thereof.
