It will be readily understood from the above figures why the Coal Mines Act, 1911, requires that at least 19 per cent. of oxygen shall be present in the atmosphere of all roads and workings that are in use.

Exemption is made where ventilation is accidentally inter­rupted, but no person is to work in less than 19 per cent. of oxygen unless engaged in restoring the ventilation. Another exemption is granted in the case of mines liable to spontaneous combustion, but only by order of and subject to conditions laid down by the Mines Department.

The gases most commonly found in mines are oxygen, nitrogen, carbon dioxide, and methane. In connection with gob fires, blasting operations, and explosions, carbon monoxide is very common, while in these and cases hydrogen sulphide, hydrogen, ethylene, nitrous oxide, etc., sometimes occur.

The chief noxious gases are the very poisonous carbon monoxide and carbon dioxide. Hydrogen sulphide is extremely poisonous, but rarely occurs in dangerous quantity. These gases are also said to be deleterious, as they arc more or loss destructive of life.

The Chief Inflammable Gas is methane, which constitutes 97 to 100 % of the inflammable constituent of firedamp.

The Damps

The word " Damp " originally meant " Mist " or " Vapour," but is now used as meaning " Gas," and prefixes are attached to indicate the various gases according to their peculiarities

Fire-damp is inflammable and consists chiefly of methane (marsh gas).

Black-damp extinguishes flame and causes death by suffocation It is composed of carbon dioxide and nitrogen. It is also known as stythe or choke-damp.

White-damp is a subtle and extremely poisonous gas, also known as carbon monoxide.

After-damp is the gas resulting from an explosion; it nearly always contains dangerous amounts of carbon monoxide.

Stink-damp, or sulphuretted hydrogen, is hydrogen sulphide and is a very poisonous gas with a pungent smell of rotten eggs, but it is seldom found in dangerous quantities.