Multipurpose Breathing Apparatus

Abstract

A versatile closed-circuit breathing apparatus has a rectangular canister which is partitioned to provide for two separated volumes of CO.sub.2 absorbent. A mouthpiece, tubing and nonreturn valves, including a demand valve on the inhalation side, define a breath flow circuit in which exhalation passes through one volume of CO.sub.2 absorbent then through an expansible breathing bag and which is also a moisture trap and then back to the mouthpiece through the other volume of absorbent. Loss of effectiveness from moisture channelization is initially confined largely to one-half of the total volume of absorbent thereby providing for more uniform effectiveness over a long period of use. The construction is readily adaptable to a variety of uses including protection from contaminated atmospheres of various kinds, diving, resuscitation, decompression and medical uses.

Description

Background of the Invention

This invention relates to devices which facilitate breathing under adverse conditions and more particularly to a breathing apparatus of the class capable of carrying a carbon dioxide absorbent material whereby the user's exhalations may be recirculated and rebreathed.

Breathing apparatus of the kind used under water or in the presence of smoke or other atmospheric contaminations and for other purposes to be hereinafter discussed may have an open circuit or a closed-circuit breath flow path. In open circuit apparatus, typified by certain underwater breathing devices which are extensively used by skin divers, the user inhales breathable gas from a bottled supply and exhales through a nonreturn valve to the ambient environment. These open circuit devices are bulky and inefficient in a sense in that the user often absorbs only about 5 percent of the oxygen in each breath. Thus about 95 percent of the oxygen which the user must carry in his bottle is ultimately expelled and wasted.

To provide for more compact bottles and/or longer use times, a variety of closed-circuit systems have been used. In this second class of breathing apparatus, the user exhales into a closed container and then rebreathes essentially the same gas. This is made possible in a closed-circuit device in that the gas flow between the user's lungs and the breathing bag is passed through a canister containing a carbon dioxide absorbent material and in that a small amount of oxygen from a bottle is introduced into the system to replace the oxygen which is actually absorbed in the user's lungs.

While prior closed-circuit breathing devices provide for relatively long use periods in terms of the amount of oxygen which the user carries with him, there have still been very serious problems which limit the period of use and which tend to vary the effectiveness of the device in the course of a period of use. A prominent problem in this respect results from the effects of moisture on the CO.sub.2 absorbents normally employed in these devices. Moisture is exhaled from the user's lungs and the reaction by which CO.sub.2 is absorbed is itself a water-producing one in addition to being exothermic. As a practical matter, the CO.sub.2 absorbent becomes progressively wetter in use and a phenomenon known as channelization occurs. Specifically, the granules of absorbent tend to fuse thereby shrinking the total absorbent volume and opening up channels through which exhalation may pass without making adequate contact with the absorbent. Thus the ability of the canister to remove the exhaled carbon dioxide is progressively reduced. This is undesirable in that continued breathing of an atmosphere containing a greater than normal amount of carbon dioxide has adverse physiological effects. Further, prior closed circuit devices provide replacement oxygen only to the extent that CO.sub.2 is absorbed and any decrease in CO.sub.2 absorption results in a corresponding decrease in oxygen content.

Moreover, closed-circuit breathing devices as heretofore constructed have been subject to certain further problems including undesirably high breathing resistance, structural complication, costly construction and a lack of adaptability to uses other than the specific one for which the device was designed.

With respect to the latter factor, it should be noted that breathing apparatus of one kind or another may be employed in a variety of different situations in which environmental conditions are radically different. Such devices for example, are used by divers in underwater operations and may also be used by firemen or other personnel who must enter smoke-filled buildings. In still other instances, a breathing apparatus may be used to carry out decompression procedures by personnel working in a caisson or other high-pressure environment. In still other instances, some form of breathing apparatus may be required to protect personnel exposed to toxic sprays or to a radioactively contaminated atmosphere. Still other forms of breathing apparatus may be utilized as resuscitator for victims of heart attacks, electrical shock or other medical emergencies which affect breathing. In general, these different use conditions have heretofore involved distinctively different breathing devices. Apparatus designed primarily for one of these uses has not tended to be readily adaptable to others thereof.

There are in fact so many different situations in which a breathing device can be useful, or absolutely necessary that it would be highly desirable for such devices to be widely available in homes, offices, vehicles, first aid stations and many other locations. This has not heretofore been practical because of the cost, bulk and functional specialization of prior devices.

SUMMARY OF THE INVENTION

This invention provides a compact efficient and versatile breathing apparatus for closed-circuit usage and is adaptable in addition to a variety of semiclosed circuit breathing applications.

As a closed-circuit device, the invention provides for longer use periods and a more uniform effectiveness during such use periods in part by dividing the CO.sub.2 absorbent into two separate volumes along the breath flow circuit. In a preferred form, exhalation passes through a first absorbent volume and into a breathing bag and then back through the other absorbent volume to the mouthpiece or mask. As a consequence of the divided absorbent volume arranged in a series relationship, moisture accumulation and the loss of effectiveness which results therefrom is largely confined to only a portion of the total absorbent during the initial portion of a period of use. The second volume of absorbent remains near maximum effectiveness until such time as the first volume has been fully utilized and then takes over the load with respect to removing the CO.sub.2 from the exhaled breath. The breathing bag may advantageously be utilized as a water-trapping means in the flow path between the two absorbent volumes for maximum protection of the second volume without excess bulk or structural complication.

In another aspect, the invention provides a flow circuit whereby the breathing device may readily be interconnected with another such device or whereby a plurality of such devices may draw upon a common oxygen supply without interfering with the operation of each other.

The invention further provides a partitioned canister and breathing bag construction in which breathing resistance is desirably low and which results in a very compact and economically manufactured apparatus.

Accordingly it is an object of this invention to provide a breathing apparatus which remains highly effective over long periods of use in closed-circuit applications and which is readily adaptable to variety of semiclosed circuit breathing functions.

It is a further object of the invention to provide a very compact, simple, reliable and economical breathing apparatus construction capable of usage under many different conditions and for a diversity of purposes.

The invention, together with further objects and advantages thereof will best be understood by reference to the following description of preferred embodiments taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

In the accompanying drawings:

FIG. 1 is a frontal view of a closed-circuit breathing apparatus embodying the invention;

FIG. 2 is a cutaway exploded perspective view of the canister portion of the apparatus of FIG. 1 further illustrating the detailed construction thereof;

FIG. 3 illustrates one method of carrying the apparatus of FIGS. 1 and 2 on a user and further illustrates a highly advantageous technique for coupling the breathing apparatus of two users in emergency situations;

FIG. 4 illustrates the adaptation of the apparatus of FIGS. 1 to 3 as an emergency resuscitator; and

FIG. 5 is a perspective view of a decompression chamber embodying the invention whereby the hazardous accumulation of oxygen therein a heretofore encountered in such operations is prevented.

Description of Preferred Embodiments

Referring now to FIGS. 1 and 2 of the drawings in conjunction, there is shown a closed-circuit breathing apparatus 11 having a canister 12 to which a majority of the other components of the apparatus are attached. Canister 12 has a rectangular configuration in this example and in accordance with an important aspect of the invention, is partitioned into two chambers 13 and 14 to maintain a carbon dioxide absorbent material in two separate distinct volumes 16 and 17.

To define the two chambers 13 and 14, the canister has a central vertical partition 18. To provide for the input and removal of absorbent material, a rectangular opening 19 is situated at the top of the canister and spans the top edge of the central partition 18 with the top of the partition being situated slightly below the top of the canister. Canister 12 is normally closed by a conforming rectangular cover 21 which fits over opening 19, the cover having apertures 22 which receive upwardly extending threaded canister studs 23 with wing nuts 24 being engaged on the studs to hold the cover in place.

To provide a fluidtight seal at the top of the canister and to maintain a small pressure on the granules of absorbent, a rectangular block of sponge rubber or other suitable resilient material 26 fits into opening 19 below cover 21 and is compressed by a conforming rectangular boss 27 on the underside of the cover. Seal 26 contacts the top surface of both absorbent volumes 16 and 17 and for this purpose is provided with a transverse groove 28 on the underside to receive the upper edge of central canister partition 18. Most CO.sub.2 absorbent materials shrink during a period of use and this construction of the resilient seal 26 provides for expansion of the seal as absorbent shrinkage occurs to prevent the development of excess void space in the absorbent volumes.

To provide for the recirculation of the user's exhalation as will hereinafter be described in more detail, the canister 12 is further provided with a pair of rectangular openings 29 and 31 in the base thereof in chambers 13 and 14, respectively, adjacent the lower end of center partition 18.

While the canister 12 may be formed of a variety of materials, high-strength plastics, such as fibre glass for example, are particularly desirable from the standpoint of low manufacturing cost. However most CO.sub.2 absorbent materials are arranged to change color as their absorbent ability is used up to provide a visible warning to the user. Accordingly, if an opaque material is used for the canister 12, transparent windows should be provided in the forward face or else the entire forward face should be formed of a transparent material such as Lucite as in the present example.

Referring now to FIG. 1 in particular, further components of the breathing apparatus 11 include a mouth piece 32 or a mask which may be of any of the various known constructions, the mouthpiece of the present embodiment being of the type adapted to be held by the teeth of the user. This form of mouthpiece has a transverse flow tube 33 which transmits exhalations and inhalations. A flexible exhalation side hose 34 connects one end of tube 33 with a nonreturn valve 35 which is secured to an elbow fitting 36 at the upper portion of the outer sidewall of canister 12 adjacent the previously described chamber 13 thereof. Nonreturn valve 35 is a check valve of standard construction arranged to limit gas flow between the mouthpiece 32 and canister 12 to a direction towards the canister. Thus the user may exhale into the upper lateral region of canister chamber 13 through valve 35 but a gas flow in a reverse direction cannot occur.

To provide for the rebreathing of gas which has been reconstituted in the canister 12, the opposite end of mouth piece tube 33 is coupled to an elbow fitting 37 at the center of the outer sidewall of canister chamber 14 through a section of flexible hose 38 and an additional nonreturn valve 39. Nonreturn valve 39 is in part a check valve arranged to limit gas flow between canister chamber 14 and valve mouthpiece 32 to a direction towards the mouthpiece and to block flow in an opposite direction. Valve 39 is also a demand regulator of the type which blocks gas flow toward the mouthpiece except at such times as inhalation by the user generates a pressure decrease at the outlet side of the valve indicating that a gas flow is needed for the purpose of breathing. The valve 39 is further of the type provided with a bypass button 41 which may be depressed by the user's thumb to override the normal valving action and provide for a two-way flow passage between mouthpiece 32 and canister 12 irrespective of pressure conditions. Suitable constructions for a nonreturn demand regulator with manual bypass are known to the art and accordingly the detailed structure of valve 39 is not shown in FIG. 1.

The above-described mouthpiece, valve and connecting hose structure thus provides for the passage of the user's exhalations in canister chamber 13 and through the CO.sub.2 absorbent 16 therein and out through opening 29 at the base of such chamber and further provides a different inhalation flow passage wherein the gas to be inhaled is drawn through opening 31 at the base of the canister into chamber 14 thereof and passes through the other CO.sub.2 absorbent volume 17 to return the mouthpiece through fitting 37, valve 39 and hose 38. To provide for functioning of the system as a closed-circuit device wherein the exhalation is purified of carbon dioxide and rebreathed, a collapsible and expansible breathing bag 42 is utilized to receive the exhaled gas from canister opening 29 and to maintain such gas available for inhalation through canister opening 31.

The canister arrangement of the present invention provides for a very simple and low-cost construction in what the breathing bag 42 may be a plastic sack of polyethylene film or other suitable flexible fluidtight material having an open upper end which is simply fitted onto the lower end of the canister 12. The bag 42 may be retained thereon in a very simple manner by one or more elastic rings 43 which may, pg,11 for example, conveniently be rubber 0 rings. Other forms of clamping means may be substituted for the elastic rings 43 if desired. Referring now again to FIG. 2 in conjunction with FIG. 1, the canister 12 is preferably provided with grooves 44 around the lower portion thereof in which the elastic rings 43 may seat to forestall any movement of the rings on the canister.

Accordingly, the user's exhalation passes into canister chamber 13, through the first absorbent volume 16 therein and then into the breathing bag 42 which expands in response to the pressure. During the subsequent inhalation, the gas trapped in bag 42 passes through the second canister chamber 14 and the additional separate absorbent volume 17 therein and back to the mouthpiece 32 through valve 39. Thus with the simple breathing bag 42 in place, the breathing apparatus is a closed-circuit system in which the user rebreathes his own exhalation after the carbon dioxide content thereof has been removed by the absorbent 16 and 17.

As the use metabolizes a small portion of the oxygen in each breath in a closed system of the present kind, it is usually necessary to provide a source of replacement oxygen or oxygen-containing gas mixture. For this purpose, a conventional gas bottle 52 is provided and is coupled to a fitting 53 at the forward face of canister 12 through a flexible hose 54. Bottle 52 is provided with a manually adjustable metering valve 56 and preferably with a gas pressure gauge 57 which provides an indication of the amount of gas remaining in the bottle at any time.

Unlike prior closed-circuit breathing devices, the gas bottle 52 itself need not be provided with a demand valve as this function is performed by valve 39 which has been relocated as described above. In contrast to prior closed-circuit breathing devices, replacement oxygen is continually metered into the canister 12 through hose 54 at a rate determined by the setting of valve 56. The disposition of a demand valve in the inhalation passage from the breathing bag to the mouthpiece in conjunction with a continuous flow of replacement oxygen provides for advantageous interconnections of the breathing apparatus with other such devices as will hereinafter be discussed in more detail. For such purposes, the bottle 52 is further provided with an additional normally closed fitting 58.

The breathing apparatus 11 has some usages which do not require a gas bottle 52. Since the user metabolizes only a small portion of the oxygen in each breath, it is possible to breathe for a few minutes with the bottle 52 absent and fitting 53 capped. This provides an adequate period for certain uses of the apparatus. Use for emergency escape from a caisson or underwater craft is one such instance, If desired, a small oxygen-containing capsule may be disposed in the breathing bag 42 in a position where it can be broken by the user's hands in an emergency.

Since a user may not be able to adjust the oxygen-metering valve 56 to maintain a flow precisely similar to his rate of oxygen absorption, causing a pressure buildup in the flow circuit, a pressure relief valve 46 of standard construction is situated at the forward face of canister 12. Relief valve 46 is normally closed and opens in response to a predetermined pressure differential between the canister and the external environment to release gas from the canister to restore an approximate equilibrium.

Canister 12 is further provided with pair of rings 59 along each side at the back surface. Rings 59 engage with suitable harness means 61 as shown in FIG. 3 for carrying the apparatus on a user's body, in front of the user's chest in the present example. Preferably, the gas bottle 52 is carried on the body by a separate harness strap 62. In the present example, the bottle 52 is shown carried on one hip of the user, which is a convenient position where the user must walk about such as in use by a fireman entering a smoke-filled building. It will be appreciated that other dispositions of the bottle 52 may be preferable in other circumstances. In underwater usage, for example, the bottle 52 is more advantageously carried on the user's back.

Referring again to FIGS. 1 and 2 in conjunction, the invention provides a disposition of the absorbent volume 16 and 17 within canister 12 which has distinct advantages. In particular, within canister chamber 13 the absorbent material 16 is retained between a pair spaced-apart rectangular screens 63 and 64 which slant with respect to the central partition 18. The innermost screen 64 has an upper edge adjacent the center partition 18 near the top of the chamber 13 and extends downwardly and slightly outwardly to engage the base of the canister along the outer edge of the opening 29 thereof. The other screen 63 has a lower edge engaged with the base of the canister along the outside corner thereof and slants upwardly to the outer side of opening 19. The screens 63 and 64 should be formed by corrosion-resistant material and may advantageously be thin stainless steel plates each having a multiplicity of small gas-pervious apertures 66. The absorbent material 16 contained between the screens 63 and 64 may be of any of the known types such as sodalime or barylime. The absorbent 17 within the inhalation side chamber 14 of the canister may be a similar material and is retained in an essentially similar manner by two additional spaced screens 67 and 68 which have an opposite inclination. This configuration for the two volumes of absorbent 16 and 17 and the associated screens 63, 64, 67 and 68 thus defines a pair of oppositely tapered plenum regions in each of the canister chambers 13 and 14 at each side of the corresponding absorbent volumes.

One result of the above-described canister and absorbent configuration is relatively low breathing resistance throughout a long period of use. Considering now still another advantageous feature, the two screens 63 and 64 of chamber 13 are made slightly nonparallel and thus diverge slightly in the upward direction. The two screens 67 and 68 in chamber 14 are similarly divergent. In general, the gas flow through the absorbent volumes will tend to concentrate in a particular region of lowest resistance until the absorbent in that region becomes wet whereupon the principal portion of the flow will shift to a dryer adjacent region. The varying thickness of the two absorbent volumes 16 and 17 takes advantage of this effect in that the gas flow initially tends to pass through the narrow lower portion of the absorbent volumes and shifts progressively upward as the breathing apparatus is used.

In use, the user's exhalation passes through the absorbent 16 of canister chamber 13 into the breathing bag 42 and is subsequently returned to the mouthpiece 32 through the absorbent volume 17 of the canister chamber 14 as described above. Due to the above-described construction of the canister and breathing bag, the system remains effective for a very long period of use relative to prior closed-circuit devices. An important reason for this is the separation of the total volume of absorbent which is provided for by the described construction. In particular, a major cause of loss of effectiveness in carbon dioxide absorbents is the progressive wetting of the absorbent material which occurs in part because the absorbing reaction is itself a water-producing one and is in part due to the moisture in the user's exhalation. The present construction takes advantage of a further phenomenon in carbon dioxide absorbing systems specifically the tendency for absorption to be concentrated in the first region of effective absorbent which the gas flow encounters. Thus, in the present system, virtually the whole burden of absorbing carbon dioxide is performed by the initial absorbent volume 16 during the first portion of the period of use and the damaging effects of moisture accumulation are largely confined thereto. pg,16 During this initial period, the second absorbent volume 17 is largely inactive and retains maximum effectiveness until such time as appreciable quantities of carbon dioxide begin to pass through the first absorbent volume 16. At this point, the second absorbent volume 17 picks up the burden of absorbing carbon dioxide to a progressively increasing extent. The net effect of this is that the total effectiveness of the system for absorbing CO.sub.2 is extended and remains more uniform throughout the extended period of use.

Considering now a further very advantageous feature of the invention, a moisture-trapping element is situated in the flow path between the two absorbent volumes 16 and 17 whereby moisture from the first absorbent volume 16 is blocked to a considerable extent from reaching the second absorbent volume 17. This moisture trap is preferably defined by the breathing bag 42 as in this example.

The CO.sub.2 absorbing reaction in the first absorbent volume 16 is exothermic in addition to being a water-producing one. It is inherent in the system that the gas expands and is cooled as it reaches the breathing bag 42 from chamber 13. Further, under many operating conditions, the surfaces of the bag 42 are inherently cooler than the absorbent volume 16. Still further, the configuration of the canister and breathing bag structure discourages any direct flow of condensed moisture between absorbent volumes 16 and 17. Because of these and other effects, the breathing bag constitutes a fairly efficient water trap to forestall and reduce moisture damage to the inhalation side absorbent volume 17.

In addition to providing for long use periods with excellent effectiveness, the above-described construction has further unique advantages. It is an important object of the invention to provide a practical breathing apparatus which is not specialized to any specific type of usage but which is adaptable to a wide variety of purposes. The invention has been described primarily with reference to use as a closed-circuit breathing device. As such, it is usable as described for virtually any situation in which the ambient environment around the user cannot be breathed either because of the lack of oxygen in usable form or because of the presence of substances which would have toxic effects if inhaled. This includes use in diving, use in the presence of atmospheres contaminated by smoke, toxic gases or sprays or airborne radiation of a harmful character and use at high altitudes.

Further the breathing apparatus 11 is readily converted to a variety of open circuit or semiclosed circuit functions. With the breathing bag 42 removed and the oxygen supply turned off or disconnected at fitting 53, the apparatus may be utilized where there is adequate oxygen in the external environment but where some environmental component must be blocked from the user's lungs as in gas mask applications. It will be apparent that the absorbent volumes 16 and 17 or only the absorbent volume 17 on the inhalation side may be replaced with an air-purifying material suitable for the particular purpose. The plenum regions at each side of chamber 14 may also be packed with an appropriate filter material. This may, for example, be a carbon monoxide absorbent or in the case of severe asthmatics a polon-filtering material may be disposed therein. In the latter cases, the filtering charge may be treated with various medicinal substances known to be helpful if inhaled.

FIG. 4 illustrates still another essentially medical usage of the breathing apparatus 11, specifically use as a resuscitator for individuals whose natural breathing functions have been stopped or impaired from some cause such as a heart attack, electrical shock or the like. For this usage it is desirable, although not essential, that the breathing apparatus 11 be equipped with a mask 69 rather than the previously described mouthpiece and ideally a pressure gauge 71 is coupled thereto to monitor the pressure in the victim's lungs. With the mask 69 in place, an operator need only rhythmically depress the breathing bag 42 with one had while simultaneously depressing the bypass button 41 of inhalation side nonreturn demand valve 39.

Referring now again to FIG. 3, still another advantageous property of the breathing apparatus 11 is illustrated. In particular, it is a simple matter to interconnect two of the breathing devices 11 so that one user may draw upon the oxygen supply of the other in emergency situations where his own supply is exhausted or has failed for some reason or another. This has not been practical in prior systems wherein a demand type of valve is situated at the gas bottle rather than between the canister and mouthpiece as in the present invention as pressure conditions in one such breathing apparatus may interfere with operation of the other. As a consequence, difficult expedients have been resorted to in emergency conditions such as passing the mouthpiece of one breathing apparatus back and forth between two submerged divers.

To make the necessary interconnection a suitable length of flexible tube 72 may be utilized with opposite ends being coupled to the previously described fittings 58 at the gas bottles 52 of the two separate breathing devices 11.

FIG. 5 illustrates a related and highly useful application of the invention to decompression procedures for personnel who work in a caisson or other high-pressure environment. As is well known, an individual who has been subjected to high atmospheric pressure for any length of time absorbs an excess of nitrogen in his blood stream and will suffer from the bends, with possibly fatal consequence, if suddenly returned to a normal atmospheric environment. To forestall this result, such personnel customarily spend a period of time in a decompression chamber 73 where they breath oxygen or a nitrogen-free mixture of oxygen and some other gas to clear the dissolved nitrogen from the blood stream. There has been a serious risk associated with these operations as heretofore conducted in that the worker inhales oxygen from a source within the decompression chamber and then exhales a large portion of the oxygen into the interior region of the chamber 73. One principal risk in this procedure is the danger of a flash fire or explosion in the oxygen- enriched atmosphere. This can easily occur from electrical sparks or other causes. FIG. 5 illustrates an adaptation of the invention wherein decompression is carried out with no release of excess oxygen into the interior of the decompression chamber.

In particular, each worker is provided with a closed-circuit breathing apparatus 11 in accordance with the invention. While the worker may decompress while breathing from an oxygen bottle as hereinbefore described provided the gas mixture in the bottle is relatively nitrogen-free, it is advantageous to remove the oxygen bottles from each breathing apparatus and to couple the gas input hose 54 thereof to a common manifold conduit 74 within the chamber through which oxygen or a suitable mixed gas is supplied. A metering valve 76 is provided at each outlet along the manifold so that the worker may adjust his oxygen intake to the breathing apparatus. This arrangement is made practical in that each breathing apparatus 11 contains its own demand valve as heretofore described.

It will be apparent from the foregoing that the present invention differs from the various highly specialized breathing devices which it replaces by being a highly adaptable multipurpose instrument which may be kept available in many different places such as first aid stations, in vehicles, in the home, or on boats to serve a variety of very different emergency situations which are related only in that the normal breathing of individuals is affected in some way. It should further be noted that this is made practical for the first time by the construction of the invention as described above wherein all principal elements which are contacted by the user's breath may be of a very simple and low-cost construction. This includes the canister 12, breathing bag 42, nonreturn valves 34 and 39, mouthpiece 32 and the interconnecting tubing 38 and fittings 36 and 37. Each of these components are in face of sufficiently low cost that aside from the gas bottle 52 and appertenances, it is practical to treat the apparatus as a disposable item.

While the invention has been disclosed with respect to certain exemplary embodiments, it will be apparent that many modifications are possible and it is not intended to limit the invention except as defined in the following claims.

Claims

I claim:

1. A breathing apparatus comprising:

an element engageable with a user's mouth;

a partitioned canister having first and second chambers therein and having a pair of openings each communicating with a separate one of said chambers;

means for retaining a separate charge of carbon dioxide absorbent material in each of said chambers;

an exhalation nonreturn valve providing a one-way gas flow passage from said mouth-engaging element to said first chamber of said canister;

an inhalation nonreturn valve normally defining a one-way gas flow passage from the second chamber of said canister to said mouth-engaging element; and

an expansible breathing bag fitted onto the region of said canister having said pair of openings to form a gas flow passage from said first chamber of said canister to said second chamber thereof,

a disengageable cover for said canister providing for access to said charges of absorbent material, and

a layer of resilient material situated between said cover and said absorbent material of both of said chambers and compressed by engagement of said cover on said canister to maintain said absorbent material in a packed condition as shrinkage occurs.

2. A breathing apparatus comprising:

an element engageable with a user's mouth;

a partitioned canister having first and second chambers therein, wherein said canister is of a substantially rectangular configuration and has a central partition parallel to the two sidewalls thereof to define said two chambers therein;

means for retaining a separate charge of carbon dioxide absorbent material in each of said chambers; wherein said means for retaining said charges of absorbent material in said chambers comprise a pair of spaced-apart gas-pervious screens extending between opposite ends of the associated chamber in an oblique relationship to said center partition whereby tapered plenum regions are defined at opposite sides of each of said charges of material in each of said chambers,

an exhalation nonreturn valve providing a one-way gas flow passage from said mouth-engaging element to said first chamber of said canister;

an inhalation nonreturn valve normally defining a one-way gas flow passage from the second chamber of said canister to said mouth engaging element; and

an expansible breathing bag coupled to said canister and defining at least a portion of a gas flow passage from said first chamber of said canister to said second chamber thereof.

3. A breathing apparatus as defined in claim 2 wherein said pair of screens in each off said chambers are divergent in one direction whereby said charge of absorbent material therebetween is of a nonuniform thickness along said screens.