14.—(1) Determinations of the firedamp content shall be made at every point required by or under the last preceding regulation once in every week at the time when the firedamp content is likely to be greatest:
(a)if any determination at any such point shows a firedamp content exceeding 0.8 per cent. by volume determinations shall be made at that point at intervals not exceeding twenty-four hours so long as the content is shown to exceed or to have exceeded that percentage and for the seven next following working days;
(b)if every determination made during a period of thirty days at any such point showed a firedamp content not exceeding—
(i)in the case of a point in a length of road not ventilated by air which has ventilated a working face, 0.2 per cent. by volume;
(ii)in the case of a point in any other length of road, 0.6 per cent. by volume;
it shall be sufficient to make determinations at that point at intervals not exceeding thirty days for so long as the firedamp content shown thereby does not exceed that percentage.
(2) Notwithstanding anything in the last preceding paragraph, whenever any alteration is made in the arrangements for ventilating a mine which affects or may affect substantially any length of road in which determinations of the firedamp content are required by or under this Part of these regulations to be made, a determination of the firedamp content at each point in that length shall be made as soon as any substantial effect of the alteration would be apparent.
(3) Where a determination of the firedamp content made for the purposes of these regulations is made by means of a sample of air, it shall be deemed to be made at the time and place at which the sample is taken.