Respirators are only to be regarded in the light of secondary aids and for occasional use.
During temporary exposure to an atmosphere charged with poisonous dust the wearing of an efficient apparatus—preferably one protecting the head—is very desirable.
Fig. 36.—Smoke Helmet, Flexible Tubing, and Foot Bellows (Siebe, Gorman & Co.)
Respirators afford no protection, or a very imperfect one, against dangerous gases or fumes. If soaked with an absorbing or neutralising fluid they can scarcely be worn for any length of time.
In an atmosphere charged with poisonous gas recourse should be had either to a smoke helmet with flexible tubing and bellows or to an oxygen breathing apparatus so constructed that the workman carries the necessary supply of oxygen with him in a knapsack on his back. In the latter case oxygen from a compressed cylinder of the gas is conveyed to the breathing mask, so that respiration is independent of the surrounding atmosphere.
Fig. 37.—Diagram of Draeger 1910-11, Pattern H (R. Jacobson)