So long as, in a mine of coal, stratified ironstone, shale or fireclay, more than one shaft or outlet is available to any persons employed below ground in the mine for affording to them means of ingress and egress, there shall be provided and maintained between—
each entrance to each shaft or outlet that is available to those persons for that purpose, being an entrance whereby those persons gain access to the shaft or outlet from the workings ; and
some point or points on another shaft or outlet so available ;
a communication following a reasonably short and reasonably convenient route.
The height of every communication provided in pursuance of the foregoing subsection shall be maintained throughout at not less than five feet and the width of every such communication shall be maintained throughout at not less than four feet:
Provided that—
if the Minister is satisfied that, owing to special circumstances affecting mines of coal, stratified ironstone, shale or fireclay of any class, it is inadvisable for reasons of safety or unnecessary, in the case of the communications provided as aforesaid therein or any class of those communications, for the minimum height or width, or height and width, thereof to be as great as provided by the foregoing provisions of this subsection, regulations may provide that those provisions shall have effect, in their application to those communications or that class thereof, with the substitution, for the minimum specified in the said provisions in relation to height, that so specified in relation to width or both of those minima, as the case may be, of such less minimum or minima as may be prescribed; and
if an inspector is satisfied that, owing to special circumstances affecting a particular mine of coal, stratified ironstone, shale or fireclay, it is inadvisable for reasons of safety or unnecessary, in the case of all or any of the communications provided as aforesaid therein, for the minimum height or width, or height and width, thereof to be as great as provided by the foregoing provisions of this subsection, he may, by notice served on the manager of the mine, direct that those provisions shall have effect in their application to those communications or to such of them as may be specified in the notice, with the substitution, for the minimum specified in the said provisions in relation to height, that so specified in relation to width or both of those minima, as the case may be, of such less minimum or minima as may be specified in the notice.