3.21.2.In confined spaces, the employer must take the contaminant concentration readings mentioned in subparagraph e of the first paragraph of section 3.21.1 and make sure that no worker, even when wearing protective breathing equipment, enters a confined space containing or which may contain:
(a) oxygen in a proportion lower than 19.5% or higher than 23%;
(b) flammable gas or vapour with a concentration higher than 25% of the lower explosion limit;
(c) contaminants in the air with a concentration higher than the threshold limit values mentioned in Schedule I to the Regulation respecting occupational health and safety (chapter S-2.1, r. 13);
(d) any other contaminant in a concentration which could be hazardous to a workman’s health.