The site senior executive for an underground mine must ensure—
(a) the mine has a sufficient number of portable gas detectors capable of detecting the presence of methane, carbon monoxide and oxygen in the mine atmosphere; and
(b) each portable gas detector used at the mine is certified as—(i) suitable for use in an underground mine; and(ii) having the following explosion protection category—(A) for parts of the detector other than the gas detector head—Ex ia;(B) for the gas detector head—Ex ia or Ex s; and(iii) capable of detecting the type of gas for which the detector is intended to be used; and(iv) being accurate and reliable.