(a) As used in these Orders, “breathing apparatus” means a device which supplies the wearer with oxygen or air under low pressure for breathing purposes. By use of this device, the wearer carries his air with him and is independent of the atmosphere around him.

“Gas mask” is a device which is equipped with a canister containing chemicals. The wearer draws his air through the chemicals, which remove small amounts of poisonous gases by filtering or chemical action. As the gas mask does not provide oxygen for the wearer, it cannot be worn safely in an atmosphere containing a high concentration of gases or so low in oxygen that a flame safety lamp will not burn.

There are many types of gas mask canisters which are permissible for use as protection against certain gases or combinations of gases. However, there is only one type of canister that affords protection against carbon monoxide, the poisonous gas which is always present during mine fires and after mine explosions. This is the Type N canister, which is easily recognizable because of its red color.

No gas mask shall be used in a mine unless such gas mask is of a type designated as “permissible” by the U. S. Bureau of Mines and used only with a permissible Type N canister.

(e) Each apparatus shall be carefully inspected and tested before it is worn in irrespirable air.

The test shall be sufficient in scope to assure that the apparatus is air tight, and that its various parts are in good condition, functioning properly, and in safe condition to wear.

(i) Care shall be used that the rescue crew does not proceed farther from its fresh air base than it can return safely to such base.

It is recommended that, except in extreme emergency, the rescue crew does not travel farther than 1,000 feet from its fresh air base over a level, unobstructed traveling way where visibility is good. Where necessary to climb ladders or other obstructions, or travel in dense smoke, the distance traveled should be shortened accordingly.

(j) Breathing apparatus should not be used to explore inactive mines or parts of mines because of the many dangers in addition to irrespirable air. Instead, it is recommended that a temporary ventilation system be installed and the exploration be made in fresh air.

If such exploration is undertaken, it shall be done only with a full rescue crew of not less than five men, with a second full rescue crew acting as a reserve in fresh air. Such crews shall be equipped with permissible breathing apparatus. Gas masks shall not be used for such exploration.