Chemical warfare

“The finished masks were then inspected, placed in unit boxes, ten to a box, and returned for the final inspection.

“Final Inspection—Final inspection of the completely assembled masks was as rigid as could be devised, and was closely supervised by army representatives. Only the most painstaking, and careful women were selected for this work and the masks were examined in every detail to discover any defect that might have escaped previous inspection. Finally, each mask was inspected over a bright light in a dark booth for small pinholes which the ordinary visual inspection might not have detected.

“As a check on the quality on the final inspectors’ work a reinspection of 5 per cent of the passed masks was conducted. Where it was found that a particular inspector was making numerous mistakes, her eyes were examined to see whether it was due to faulty eyesight or careless work. Masks containing known defects were purposely sent to these inspectors to determine whether they were capable of continuing the inspection work. In this way the desired standard was maintained.

“A daily report of the final inspection was sent back to each of the assembly departments involved so that defects might be eliminated immediately and the percentage of rejects kept as low as possible.

“After the final inspection the masks were numbered, packed in knapsacks, and the filled knapsacks placed in packing cases, twenty-four to a case.”

Tissot Mask

The French, as has already been pointed out, early recognized that certain classes of fighting men, as the artillerymen, needed the maximum of protection with the minimum decrease in efficiency. The result of this was the Tissot Mask. Before the United States entered the war, the British standard box respirator had reached a greater degree of perfection, with far greater ruggedness and portability. It was therefore adopted as the American standard. At the time of the invention of the British box respirator and practically up to the time the United States entered the war, masks were worn only during the sporadic gas attacks then occurring and only for a brief period at a time. As the war progressed, the men were compelled to wear their masks for much longer periods (eight hours was not uncommon). It was then seen that more comfort was needed, even at the expense of a little safety.

The principle of the Tissot mask was correct so far as comfort was concerned, since it did away with the irritating mouthpiece and noseclip, but the chief danger in the French mask arose from the fact that the facepiece was made of thin, pure gum rubber. The Research Division, together with the Gas Defense Division, developed two distinct types of Tissot masks. The first of these was the Akron Tissot, the second the Kops Tissot. The best features of these have been combined in the 1919 Model.

1919 Model American Mask

Facepiece. This facepiece is made of rubberized stockinet about one-tenth inch in thickness. The stockinet is on the outside only and is for the purpose of strengthening and protecting the rubber which is of very high grade. The facepiece is died out as a single flat piece from the stockinet which is furnished in long rolls. The die is of such shape that when the facepiece is sewed there is but one seam, and that between the angle tube opening and the edge under the chin. This seam is sewed with a zigzag stitch with the stockinet sides flat together. The seam is then stretched over a jig, so as to form a flat butt joint. This seam is then cemented with rubber cement and taped, inside and out, to make it thoroughly gas-proof.

The eyepiece openings are of oval shape with the longer axes horizontal and considerably smaller than the finished eyepieces. The eyepieces being circular, the cloth is stretched to accommodate them, giving the necessary bulge to keep the cloth and metal of the eyepieces away from the face. The harness has three straps on each side. Instead of the single strap over the top of the head, two straps lead from directly over the eyes, both being made of elastic the same as the other straps. All six straps are brought together around a pad of felt and cloth about 2½ × 3½ inches at the back of the head. This pad makes the harness much more comfortable.

The rubberized stockinet is reinforced on the inner or rubber side with thin bits of cloth at all points where the straps are sewed on. The strap across the temples just above the ears is sewed at two points, one about one-half inch from the edge and the other about two inches from the edge. This is for the purpose of helping press the cloth against the temples, thereby adding to the gas-tightness for those heads that have a tendency to be hollow at the temples. The lower strap is just above the chin and is for the purpose of giving gas-tightness in that vicinity. All of the straps except the two over the top of the head are attached to the pad with buckles, and are thus capable of exact adjustment.

The eyepieces are of triplex glass in metal rings with rubber gaskets. In pressing the rings home, the rubberized stockinet is turned and held securely so that there is no possibility of pulling them out. The angle tube containing the outlet valve and the connection to the corrugated tube connecting with the canister is the same as with the latest model R. F. K. mask. The only difference as regards the corrugated tube is that a greater length is needed with the new carrier under the left shoulder. The total length of the tube for this model is about 24 inches. On the inside of the facepiece and connected to the angle tube inlet is a butterfly baffle of rubber, so arranged that the incoming air is thrown upward and over the eyepieces, thus keeping them clear no matter how much the exertion or what the temperature, except in certain rare cases when the temperature is down at zero F. or below.

Canister

The canister is radically different from the canisters used in the R. F. K. and earlier types. In the first place, it is longer, the total length finished being 8 inches. It has two inlet valves at the top end protected by a tin cover instead of the single inlet valve at the bottom of the earlier types. The two inlet valves are each ⅝ inch in diameter and are made up of square flat valves on the end of a short rubber tube. The rubber tube is fitted over a short metal tube. Gas-tightness is obtained both by the pressing of the valve against the round edge of the metal tube and by the pressure of the edges against each other. These valves, while delicate, are proving very satisfactory, and being simply check valves to prevent the air going back through the canister, they are not vital. In case of failure, the eyepieces would fog somewhat and the dead air space be increased by that held in the inlet tube.

The canister consists really of two parts—an outer casing that is solid and an inner perforated tin casing. Around the perforated tin is fitted a filter of wool felt ³/₁₆ of an inch in thickness. This wool felt is very securely fastened by turning operations to solid pieces of tin, top and bottom, so that no air can get into the chemicals without passing through the filter. Thus the air coming through the inlet valves at the top circulates around the loosely fitting outside corrugated case to all parts of the filter and after passing through the filter continues through the perforations of the tin into the charcoal and soda-lime granules.

The chemicals are packed around a central wedge-shaped tube extending about two-thirds the length of the can. The wedge is enlarged at the top and made circular where it passes through the top of the can to connect with the corrugated tube. The wedge-shaped inner piece is made of perforated tin and is covered with thin cloth to prevent dust from the chemicals passing into the tube and thus into the lungs. The cans are filled from the bottom and are subjected to two mechanical jarring operations in order to settle the chemicals thoroughly before the spring which holds them in place is added. The outer tin cap protecting the inlet valves has two openings on each side but none at the ends of the canister.

The carrier is a simple canvas case nearly rectangular, about one foot wide and 15 inches in length. The width is just sufficient at the back to hold the canister and the front part to hold the extra length of corrugated tube and the facepiece. There are two straps, one passing over the right shoulder and the other around the body. The one passing over the right shoulder has two “V” shaped seams at the top so as to change the direction of the strap over the shoulder in order that it will pull directly downward instead of against the neck. The flap closing the case opens outward.

It has the usual automobile curtain fasteners. A secondary fastener at the top of the opening is arranged so that when the tube is adjusted to the proper length and the mask is adjusted to the face of the wearer, the flap can be buttoned tightly over the corrugated tube and held tightly. This prevents water from entering the case.

Figures 62 and 63 show the position of the carrier both with the facepiece in the carrier and after adjustment. It will be noted that the carrier does not interfere with the pack nor with anything on the front of the body. The left arm hangs almost entirely natural over the case. It has been thoroughly tried out by the Infantry, Cavalry, Artillery and Special Gas Troops and adopted as eminently satisfactory.

Special Canisters

Navy. The early Navy canister is a drum much like the German canister. The container is a slightly tapered metal cylinder, 9 cm. in diameter at the bottom. The most satisfactory filling for this drum consists of two layers, 98 cc. in each, of a standard mixture of charcoal and soda-lime, separated by cotton wadding pad. The filling is 6-20 mesh, instead of 8-14 mesh. A later type is shown in Figure 41.

Carbon Monoxide. This canister is discussed in Chapter XI.

Ammonia. Ammonia respirators were needed by the Navy and also by the workmen in refrigeration plants. Early protection was obtained by the use of pumice stone impregnated with sulfuric acid. This had many disadvantages, such as the amount of heat evolved, the caustic fumes produced, high resistance and corrosion of the canister. To overcome these, the “Kupramite” canister was developed. The filling consists of pumice stone impregnated with copper sulfate. Pumice stone, 8 to 14 mesh, and technical copper sulfate are placed in an evaporating pan in the ratio of one part by weight CuSO₄·5H₂O to 1.5 parts pumice, and the whole is covered with sufficient water to dissolve the salt at boiling temperature. The mixture is then boiled down with constant stirring until crystallization takes place on the pumice and the crystals are nearly dry. The pumice thus treated is then removed from the dish, spread out and allowed to dry in the air. The fines are then screened out on a 14-mesh sieve. Care must be taken in the evaporating process that the absorbent is still slightly moist when taken from the pan.

In packing the standard Army canister with kupramite a layer of toweling is placed on top of the absorbent to filter out any fine particles which might be drawn up from the absorbent, and the whole is held in place by the usual heavy wire screen and spring. This method of packing is to be used with the present mouthpiece type of army mask. If the new Tissot type mask is used, a modification of the packing is desirable in order to eliminate the trouble due to moisture given off by the absorbent during service condensing on the eyepieces of the mask and thus impairing the vision of the wearer. To remedy this defect a 1-in. layer of kupramite at the top of the canister is replaced by activated charcoal or silica gel, preferably silica gel. This decreases the humidity of the effluent air sufficiently to prevent dimming of the eyepieces. If charcoal is used, a 2-8 cotton pad (Eastern Star Furrier Co., Pawtucket, R. I.) is substituted for the toweling in order to remove charcoal dust. The canister complete weighs about 1.7 lbs.

A canister containing 45 cu. in. of this material will protect a man breathing at rest for at least 5 hours against 2 per cent ammonia and for 2½ hours against 5 per cent ammonia. Its advantages are large capacity and activity, negligible heat of absorption, and cheapness.

Physiological Features of the Mask

For some time after the introduction of gas warfare, the gases used were of the so-called non-persistent type. Under these conditions it was necessary to wear the mask for only relatively short periods, after which the cloud dissipated. With the increasing use of gas and the introduction of the more persistent gases, particularly mustard gas, it not only became necessary to wear the mask for long periods of time but also to do relatively heavy physical work, such as serving artillery, when wearing the mask.

Under these conditions, it became evident that the wearing of the mask caused a very great reduction in the military efficiency of the soldier. The reasons for this reduction in efficiency have been made the subject of extensive research by a group of the foremost physiologists and psychologists of the country. As a result of their work, the causes contributing to this reduction in efficiency may be grouped about the following main factors:

(1) The physical discomfort of the mask arising from causes such as pressure on the head and face, due to improperly fitting facepieces and harness, the noseclip, and the mouthpiece.

(2) Abnormal conditions of vision, due to poor optical qualities in eye pieces and restrictions of vision, both as to total field and binocular field.

(3) Abnormal conditions of respiration, among them being (a) the unnatural channels of respiration caused by wearing the box respirator, (b) increase in dead air space in respiratory circuit, and (c) the increase in resistance to both inhalation and exhalation, the last two mentioned being present to a greater or less degree in all types of mask.

Of these general subdivisions the various phases of the first two are so evident that no further discussion will be given. The effects of the changed conditions of respiration are, however, less obvious, and it may be of interest to present in a general way the results of the research along this line, particularly as regards the harmful effects of increasing the resistance and dead air space in the respiratory tract above the normal.

The function of respiration is to supply oxygen to and remove carbon dioxide from the blood as it passes through the lungs. This interchange of gases takes place in the alveoli, a myriad of thin-walled air sacs at the end of the respiratory tract where the air is separated by a very thin membrane through which the gases readily pass. The volume and rate, or in other words, the minute-volume, of respiration is automatically controlled by the nerve centers in such a way that a sufficient amount of air is supplied to the lungs to maintain by means of this interchange a uniform percentage of its various constituents as it leaves the lungs. It will be readily seen therefore, that anything which causes a change in the composition of the air presented to the blood in the alveoli will bring about abnormal conditions of respiration.

Inasmuch as the gaseous interchange between the lungs and the blood takes place only in the terminal air sacs it follows that, at the end of each respiration, the rest of the respiratory tract is filled with air low in oxygen and high in carbon dioxide, which on inspiration is drawn back into the lungs, diluting the fresh air. The volume of these passages holding air which must be re-breathed is known as the anatomical dead air space.

Similarly, when a mask is worn the facepiece chamber and any other parts of the air passage common to inspiration and expiration become additional dead air space contributing a further dilution of oxygen content and contamination by carbon dioxide of the inspired air in addition to that occasioned by the anatomical dead space, which of course, is always present and is taken care of by the functions normally controlling respiration.

Major R. G. Pearce who directed a large amount of the research along this line, sums up the harmful effects of thus increasing the dead air space as follows:

1. Interpretation from the physiological standpoint:

(a) A larger minute-volume of air is required when breathing through dead air space. This, interpreted on physiological grounds, means that the carbon dioxide content of the arterial blood is higher than normal. The level to which the content of carbon dioxide in the arterial blood may rise is limited. Anything which wastefully increases the carbon dioxide level of the blood decreases the reserve so necessary to a soldier when he is asked to respond to the demand for exercise which is a part of his daily life.

(b) A larger minute-volume of air must be pulled through the canister, which offers resistance proportional to the volume of air passing through it. If resistance is a factor of harm, dead air space increases that harm, since dead air space increases the volume of air passing through the canister.

(c) As will be noted below, the effect of resistance is a tendency to decrease the minute-volume of air breathed. Dead air space increases the minute-volume. Accordingly, if breathing is accomplished against resistance and through a large volume of dead air space, the volume of air breathed is reduced more in proportion to the actual needs of the body than when breathing against resistance without the additional factor of dead space; this, again, causes the level of carbon dioxide in the blood and tissues to be raised to a higher level than normal, and thus again there is some reserve power wasted.

2. Interpretation from the standpoint of the canister.

The life of the canister depends on the volume of the gas-laden air passed through it. The dead space increases the minute-volume of air passed through the canister and, therefore, shortens its life.

Physiologically, the reason for the harmful effects of breathing resistance is more involved: