Where determinations of the firedamp content in any part of a mine which comprises a longwall face are required to be made by virtue of the use of electric power at or within one hundred and fifty feet of that face or the firing of shots in that part of the mine, those determinations shall be made at or as near as is practicable to the point in each airway serving that face thirty feet from the nearest working place at that face. If the air ventilating that long-wall face has ventilated or will ventilate another longwall face determinations shall also be made at such a point in each airway serving each such other face.

An inspector may serve on the manager of the mine a notice requiring determinations to be made also at such additional point at any such longwall face as may be specified in the notice.