Sizes of Faces For Masks
When adopting the British respirator in August, 1917, it was decided that the American face as well as the American stature was probably larger than the English. Accordingly inquiry was made in regard to the sizes of masks issued to the Canadians as it was thought probable they required a greater proportion of the larger size masks than did the English. When prescribing the relative quantities of each size of mask to be furnished Americans, the Canadian requirements were taken as a base but with the larger sizes increased slightly over the Canadian requirements. As a matter of fact even these increases proved considerably too small, so that the numbers in the two sizes above normal had to be finally more than doubled.
Objections to German Type Mask
The American Gas Service felt from the beginning that a design which attached the box of chemicals to the facepiece was unsound in principle (this design was used in the German mask and in the French A. R. S. masks), since it did not allow proper flexibility for increasing the size of the box to care for new gases. Furthermore, the weight of the box during movement caused the facepiece to swing slightly from side to side. This interfered with vision and tended to lift the facepiece away from the face and allow gas to enter. That the objections of the American Gas Service to this type were correct was proved by the difficulty encountered toward the end of the war by both the French and the Germans in trying to provide a suitable filter for protection against particulate clouds and the smokes, such as stannic chloride and diphenylchloroarsine.
Struggle Between Mask and Gas
As between the mask and poisonous gases, we have the old struggle of the battleship armor against the armor-piercing projectile. While the armor-piercing projectile has always had a little the better of the game, it is just the reverse with gases. The gas mask has always been just a little better than the gases, so that very few casualties have occurred through failure of the mask itself. This margin of safety has never been any too great, and that we have had a margin at all is due to the energy, skill and enthusiasm of those developing and manufacturing masks in England, France, and particularly in the United States.
However, the mask at the best is uncomfortable, causes some loss of vigor, and even with the very best American masks there is some loss in vision. The wearing effect on troops results mostly from the increased resistance to breathing. Accordingly a tremendous amount of study and effort was made to decrease this breathing resistance. In the English type masks this resistance was equal to the vacuum required to raise a column of water about four and one-half inches. Adding the sulfite paper to protect against diphenylchloroarsine increased this resistance by about one inch. This put a heavy burden on the wearer of the mask whenever it was necessary for him to do any manual labor while wearing it. In addition earlier masks left a good deal to be desired in the way of reducing resistance by proper sized tubes, angles and valves through which the air was drawn. This was much more easily overcome than reducing the resistance through the chemicals and charcoal and the materials for protection against diphenylchloroarsine. In the latest type canister, devised after long trials for the American forces, this resistance was brought down to about two inches of water. What this reduction in resistance means no one knows except one who has worn the old mask with its mouthpiece and four to six inches’ resistance and has then replaced that mask for one through which he breathes naturally with only two inches’ resistance.
Design of New American Mask
The American Gas Service felt from the beginning that the mouthpiece and noseclip must be abandoned and bent every effort toward getting a mask perfected for that purpose. The English opposed this view fiercely for nearly a year. This position on the part of the English was more or less natural. They developed their mask in the beginning for protection against cloud gas. In those days the opposing trenches were close together. Moreover, front line trenches were quite strongly manned. The result was that a large number of men were exposed to a very high concentration of gas, but—and highly important—for a short period only. Inasmuch as the German feared this cloud gas even more than the English there was no danger of his attacking in it. The English rules of conduct during a gas attack called for all movement to stop and for every man to stand ready until the cloud passed. Accordingly, the man was breathing the easiest possible and hence did not suffer particularly from the resistance.
With the advent of mustard gas, however, the whole general scheme of protection changed. Mustard gas, as is well known, is effective in extremely low concentrations and has very great persistency. In dry warm weather mustard gas, scattered on the ground and shrubbery, will not be fully evaporated for two to three days and accordingly will give off vapors that not only burn the lungs and eyes but the soft, moist parts of the skin as well. In cool, damp weather the gas remains in dangerous quantity for a week and occasionally longer. Since this gas, in liquid form, evaporates too slowly for use in gas clouds, it is used altogether in bombs and shells. Accordingly it could be expected to be and actually is fired at all ranges from the front line to nearly eight miles back of that line. Hence, with the coming of mustard gas, the need for protection changed from high protection for a short period to moderate protection for very long periods. Indeed, mustard gas makes it necessary for men to wear masks just as long as they remain in an area infected with it. There is still occasional need for high protection for short periods, but with the increase in the efficiency of charcoal alone, it is found that the amount of charcoal and chemicals in the canister can be very greatly reduced and still maintain sufficient protection for the high concentrations encountered in cloud gas and projector attacks.