Section 6(3)(b) in The Prohibition of Employment as Manual Scavengers and their Rehabilitation Rules, 2013
(b)The atmosphere within the confined space shall be tested for oxygen deficiency and toxic and combustible gases including but not limited to poisonous gases like Hydrogen Sulphide, Carbon Monoxide, Methane, and gasoline vapours, through detection tests including the following :-(i)lowering a detector lamp into the manhole,(ii)inserting wet lead acetate paper which changes colour in the presence of hazardous gases,(iii)detection of gases through gas detector masks.