Patent Publication Number: US-7213595-B2

Title: Multi-stage respirator filter with TIM filter option

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. patent application Ser. No. 10/257,801, filed Oct. 15, 2002, now U.S. Pat. No. 6,860,267, issued Mar. 1, 2005, which claims priority on International Application No. PCT/US01/12545, filed Apr. 17, 2001, which claims the benefit of U.S. Provisional Application Ser. No. 60/198,012, filed Apr. 18, 2000. 

   BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The invention relates to gas mask filters. In one of its aspects, the invention relates to a gas mask with removable filtration cartridges. In another of its aspects, the invention relates to multi-stage filtration cartridges with an optional TIM filter. In another of its aspects, the invention relates to a gas mask with twist and lock removable filtration cartridges. 
   2. Description of the Related Art 
   It is traditional for combination filters such as those used in industry or by the military to have two filter media in sequence: firstly, a particulate filter to remove solid or liquid aerosols, droplets and particulate matter such as dusts, smokes, bacteria and viruses; and secondly an adsorbent layer, usually an activated charcoal to remove gases and vapors. A wide variety of charcoals with or without impregnants are available for particular filtration applications. The charcoal adsorbent may have more than one type of charcoal in intermixed or filled as separate layers into the filter body. See, for example, U.S. Pat. No. 5,660,173, issued Aug. 26, 1997 to Newton. 
   Military canisters typically have two types of media, particulate and charcoal. The charcoal is impregnated with such metallic salts of Cu, Cr, Ag, Zn, Mo and triethylenediamine in order to broaden the scope of chemical filtration by including both physical adsorption and chemical interaction with the impregnants to remove those chemicals that are poorly adsorbed and retained by physical adsorption alone. See, for example, the Grove et al. U.S. Pat. No. 6,176,239, issued Jan. 23, 2001, which incorporates by reference the U.S. patents to Braun et al. U.S. Pat. Nos. 5,033,465 and 5,078,132. 
   Attempts have heretofore been made to develop a filter medium that has the capability to remove both particulate matter and to adsorb gases. See, for example, British Specification No. 516,268, published Dec. 28, 1939. These filters are often referred to as “intimate mix” filters. One very good example of this type of filter was the “Cheekpad” design of filters used in the U.S. Military M17 Mask. However, it was found that the filtration efficiency of such media was compromised for both chemicals and for particulates. As a result, these types of filters are not in use today. 
   Each filter has a lifespan that relates to the amount and type of filter media. When any of the filter types have been saturated, the filter canister must be replaced. Thus, the life of any canister is only as long as the weakest filter medium. It is possible to construct a filter canister with sufficient amounts of each of the filter media to give a long life for all types of gases. However, the cost, size and weight of the canister must be taken into account in selecting the amounts of filter media that is to be incorporated into each canister. In addition, breathing resistance increases as the amount of the filter material increases. For military purposes, the canisters must be relatively small and light in weight. Yet, the canisters must be able protect the soldier from the exotic as well as the ordinary gases to which the average combatant might reasonably be subjected. Ordinarily, military personnel rarely face industrial gases and the addition of filter material to remove significant amounts of industrial gases is for the most part unnecessary. However, these gases must be filtered when they are encountered in the field, however infrequently. Thus, a balance must be struck between maximum protection against all types of gasses, weight, breathing resistance and bulk. These compromises have been made with smaller canisters that are replaceable when spent. The canister must be easily and quickly replaced so that a spent canister can be discarded and a new one added. 
   U.S. Pat. No. 4,850,346 to Michel et al. discloses a bayonet-type respirator fitting for a respirator port in a gas mask. The inhalation port includes an inhalation valve formed of a resilient membrane or flap, and mounts a chemical cartridge by a bayonet-type mount. The chemical cartridge can further mount a filter retainer housing a mechanical filter such as a felted fibrous disk. 
   British Specification No. 516,268 discloses a gas mask cartridge in which the air flows through a felted filtering mass comprising homogeneous mixture of a fibrous material adapted for mechanical filtration and substances capable of absorbtive and adsorbtive removal of noxious components in an air stream passing though the cartridge. The cartridge is made of layers of filter material that are axially stacked with radial passages from a central conduit for parallel axial flow through the filter media. 
   SUMMARY OF INVENTION 
   According to the invention, a filter canister assembly for a gas mask comprises a primary filter canister with an inlet opening at a first end and an outlet at a second end. A first filter medium is mounted in the primary filter canister in communication with the primary filter canister inlet opening and is adapted to remove aerosols, particulate materials and droplets from air passing through the first filter canister. A second filter medium that is adapted to remove toxic gases is arranged in serial communication with the first filter medium in the primary filter canister and with the outlet opening in the first filter canister. A supplementary filter canister has an inlet opening at a first end and an outlet opening at a second end and the supplementary filter canister second end is removably mounted to the primary filter canister first end so that the primary filter canister inlet opening is in communication with the supplementary filter canister outlet opening. A third filter media is adapted to filter toxic industrial materials and is mounted in said supplementary filter canister in communication with the inlet and outlet openings in the second filter canister. The first and second filter media are capable of filtering out contaminants in normal hostile environments and the third filter medium is adapted to supplement any ability of the first and second filter media to filter toxic industrial materials from the gasses passing through the first and second filter canisters. 
   The primary canister filters have a broad spectrum capability to remove particulate materials in gases as well as gases that are poorly adsorbed in the physical adsorption process. However, in order to keep the weight and breathing resistance through the filter and mask as low as possible, the mass of charcoal used in the filters is limited and does not give significant protection against some TIMs. On the other hand, it is very effective in dealing with the military chemical warfare gases such as cyanogens chloride and hydrogen chloride. 
   The third filter media is used to boost protection against TIMs. Filter median for TIMs are well known and can include activated charcoal or can be some other alternative adsorbent such as a porous polymer, alumina or molecular sieve material that will remove TIMs. 
   In one embodiment, the first and second filter media are mounted in axially stacked relationship and a barrier is mounted between the first and second filter medium to force air entering the canister through the inlet opening from a central portion of the first filter medium in a radial direction through the first filter medium to an outer portion thereof, then axially to an outer portion of the second filter medium, then radially through the second filter medium to a central portion of the second filter medium to the outlet opening of the housing. 
   Preferably, the third filter medium is a particulate filter and a sorbent filter that is adapted to remove TIMs. In one embodiment, the first filter medium comprises a pleated paper. The second filter medium comprises an adsorbent carbon filter medium, preferably that includes metallic salts that interact with contaminant gases. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     In the drawings: 
       FIG. 1  is an exploded perspective view of a gas mask and filter assembly according to the invention. 
       FIGS. 2–4  are a partial cross-sectional view of the gas mask and filter assembly of  FIG. 1 , with a filter canister mounted to an inlet port assembly on the gas mask, during progressive stages of the inhalation cycle. 
       FIG. 5  is a partial cross-sectional view of the gas mask and filter assembly of  FIGS. 1–4  with the canister of  FIG. 2  removed from the inlet port assembly. 
       FIG. 6  is a cross-sectional view taken through line  6 — 6  of  FIG. 5 . 
       FIG. 7  is exploded cut-away perspective view of the filter assembly used in the gas mask of  FIGS. 1–6 . 
       FIG. 8  is a partial cross-sectional view of a preferred embodiment of an inlet port assembly with a self-sealing valve and a filter canister in spaced relationship from the canister mount. 
       FIG. 9  is a partial cross-sectional view like  FIG. 8  with a filter canister installed. 
       FIG. 10  is a partial cross-sectional view like  FIG. 9  during an inhalation phase of operation of the mask. 
       FIG. 11  is a perspective view of the self-sealing mechanism of  FIGS. 8 and 9  with the self-sealing diaphragm removed for clarity. 
       FIG. 12  is a perspective view of the filtration canister interface of the embodiment shown in  FIGS. 8–10 . 
       FIG. 13  is a partial cross-sectional view of a further embodiment of an inlet port assembly with a self-sealing valve and a filter canister in spaced relationship from the canister mount. 
       FIG. 14  is a partial cross-sectional view like  FIG. 8  with a filter canister installed. 
       FIG. 15  is a partial cross-sectional view taken through line  15 — 15  of  FIG. 14 . 
       FIG. 16  is a partial cross-sectional view taken through line  16 — 16  of  FIG. 13 . 
       FIG. 17  is a partial cross-sectional view of a visor hinge formed by complete encapsulation. 
       FIG. 18  is a partial cross-sectional view of a visor hinge formed by lamination. 
   

   DETAILED DESCRIPTION 
   A gas mask and filter assembly  10  according to the invention is shown in the drawings, beginning with  FIG. 1 . The assembly  10  comprises a mask housing  12  that fits onto the users face and defines an interior chamber, and a primary filter canister  14  and a supplemental filter canister  20 . The housing  12  comprises a pair of circular or elliptical canister mounts  13  including an inlet port assembly and self-sealing mechanism  16  and twist-and-lock connector  18  (shown without detail) for affixing circular or elliptical filter canisters  14  to mask housing  12 . 
   Housing  12  further comprises a facepiece  330  and a visor  332 . In a preferred embodiment, facepiece  330  is constructed in multiple sizes of a butyl-rich polymer or other polymer or polymer blend such as butyl/silicone material that will provide the desired level of resistance to penetration of toxic chemicals and will be readily de-contaminated. 
   The facepiece  330  further includes a face seal (not shown) that is also injection molded in a separate co-molding process using a silicone-rich polymer or other polymer or polymer blend that is comfortable for the user and forms an effective seal on the face. In this concept, the outer materials would be selected for chemical agent resistance, decontamination, low set, low flammability, mechanical strength and long-term durability. The seal material would be selected for high level of comfort, low skin toxicity, high flexibility at low temperature and the ability to conform closely to facial features. The materials would have to have acceptable bond strength. In concept, it would be possible to bond polymer-to-polymer, polymer to blend, or blend to blend as necessary. 
   In an alternative embodiment, the facepiece and seal can be constructed of from the same polymer or polymer blend in a single injection molding operation. The face seal is an in-turned periphery  334  of facepiece  330  and including a built-in chin cup (not shown) for correct location on the user&#39;s face. In another embodiment, face piece  330  is constructed solely of one type of elastomeric material, such as butyl rubber or a blend of silicone and butyl rubber. 
   Visor  332  comprises a panel  336 , constructed for example of polyurethane and configured to give maximum visibility and flexibility to the user, and providing close eye relief. In the depicted embodiment, the visor  332  further includes an elastomeric central hinge  338 , although the visor  332  can be formed without a central hinge. The visor  332  should provide ballistic protection and be configured to receive outserts (not shown) to provide sunlight and laser protection. The visor  332  can further include an anti-scratch surface. 
   The panel  336  must be acceptable for light transmission, haze and reflectivity and must be resistant to the effects of exposure to chemical contaminants and decontaminants. The panel  336  must also have acceptable performance against impact, and be resistant to other challenges such as scratches or abrasions. In general, optical quality materials such as cast or injection-molded polyurethane or polycarbonate are suitable for the visor panel  336 . 
   The hinge  338  should have adequate tensile strength and should be sufficiently flexible to withstand repeated flexing even at low temperatures (−32 C). Hinge  338  materials must bond to the panel  336  materials, must not take a set during storage, and should preferably be transparent. Polyurethane, styrene butadiene styrene, styrene ethylene butadiene styrene and some vulcanized or thermoplastic materials are suitable hinge materials. 
   The hinge  338  and panel  336  may be joined together by chemical bonding in a two-part process, or may be adhesively bonded as a post-process operation. The hinge  338  may also be formed as a mechanical hinge, a molded joint, a living hinge or by reduction in the cross-sectional area of the material. The hinge  338  may be formed by complete encapsulation (see  FIG. 17 ) or lamination (see  FIG. 18 ) or the joint between the materials may be made by a form of welding technology using laser, ultrasonic, infra-red or radio frequency (RF) induction. 
   Housing  12  further comprises a primary speech module  342  that combines the functions of speech, drinking system, and outlet valve assembly. The shape of the primary speech module is acoustically formed to eliminate the need for a speech diaphragm. The inlet and outlet valves are interchangeable, reducing the number of unique spare parts required. Housing  12  is held to a user&#39;s face by a plurality of low-profile harness straps  344  defining a flat brow-seal that eliminates hot spots and fits comfortably with a helmet. Harness straps  344  fold over exterior of housing  12  to aid user in rapidly donning mask  10 . The interior chamber of housing  12  further comprises a nose cup (not shown) that is formed of a suitable material such as silicone or polyisoprene and is provided in multiple sizes for comfort and fit on different users. The nose cup also acts as an air guide to eliminate misting of the visor  332 . 
   Referring to  FIGS. 2–6 , inlet port assembly and self-sealing inhalation mechanism  16  comprises a raised perimeter wall  60 , a central cavity  62  having a wall comprising a frusto-conical seating  66 , a plug  64  having a central depending post  76  and a chamfered face  65 , and a spring  28 . Central cavity  62  terminates at a lower portion in a central hub  70  and a plurality of radial spokes  72 . The hub  70  is connected to the wall of the cavity  62  by the spokes  72 , and further includes a central recess  74  for receiving depending post  76  of valve plug  64 . Post  76  is further received within spring  28 , the spring  28  being interposed between the hub  70  and plug  64  to bias plug  64  away from the hub  70  and against the seating  66 . Hub  70  further comprises a depending stud  82  for receiving a resilient inhalation valve  68 . Valve  68  is generally umbrella-shaped and includes an annular dome-shaped portion  80  and a perimeter edge  84 . 
   The inlet port assembly  16  is received in an opening formed in the mask housing  12  and includes a circumferential channel  17  for sealingly receiving the edge of the mask housing  12  circumscribing the opening. 
   Referring now to  FIG. 7 , the filter canister  14  comprises a stacked radial-flow configuration. The canister  14  comprises a hollow divided disk having opposing inlet and outlet faces  30 ,  32  joined by an annular outside wall  34 . The opposing faces  30 ,  32  each have one of a central inlet and outlet opening  36 ,  38 . The canister  14  further comprises a dividing wall  40  parallel to the opposing faces  30 ,  32 , fluidly isolating the inlet and outlet openings  36 ,  38  except for an annular passage  42  formed adjacent to the interior of the annular outside wall  34  because the dividing wall  40  is smaller in diameter than the annular outside wall  34 . An inlet cavity  23  is formed between the dividing wall  40  and the inlet opening  36 . The inlet cavity  23  is surrounded by an annular array of a particulate filtration medium, such as a W-pleated fiberglass paper  44 , completely filling the space between the inlet face  30  of the cartridge  14  and the dividing wall  40 , except for the annular passage  42 . An outlet cavity  24  is formed between the dividing wall  40  and the outlet opening  38 , and is surrounded by an annular carbon filter  46 , likewise completely filling the space between the outlet face  32  and the dividing wall  40 , except for the annular passage  42 . A projection  22  extends perpendicularly from the dividing wall  40  into the center of the outlet cavity  24 , approaching the level of the outlet face  32 . The fiberglass paper  44  is a high efficiency filtration medium to remove aerosols, particulate materials and droplets from contaminated air, and is herein disclosed as a W-pleated paper, but other particulate filtration media are contemplated, including electrostatically-charged fibers in pleated, rosette or pad configurations. The carbon filter  46  is disclosed as a “cookie cutter” surface configuration, and is depicted as an immobilized adsorption bed, but use of a granular adsorbent, in more cylindrical configurations and single or multiple layers of adsorbent, is also contemplated. The carbon filter  46  is further contemplated as a charcoal adsorbent bed impregnated with metallic salts for chemical interaction with those gases, such as cyanogen chloride and hydrogen cyanide, which are poorly adsorbed by physical adsorption processes. 
   The central outlet opening  38  of the outlet face  32  is bordered by a perimetric rim  39  having an internal diameter closely approximating the external diameter of the perimeter wall  60  of the inlet port assembly  16 . Filter canister  14  and inlet port assembly  16  are configured to interlock in a twist-and-lock connection, as is well known to ordinary workers in the gas mask industry. 
   As further illustrated in  FIG. 7 , the assembly  10  includes add-on filter  20  that can be use to filter out toxic industrial materials (TIM). Filter  20 , as a supplemental filter, is selectable depending on contaminant conditions, and filter  14  is effective, without supplement, in many hostile environments. Filter  20  is disclosed as an axial-flow filter, but a radial-flow filter is also contemplated. Filter  20  includes an outer case  47  enclosing a first, particulate layer  48  and a second, adsorbent layer  50  separated by a permeable membrane  49 . Filter  20  further includes an inlet face  51  having a central inlet opening  52 , and an outlet face  53  having a central outlet opening  54 . The inlet and outlet openings  52 ,  54  are fluidly connected through the first and second layers  48 ,  50  and membrane  49 . A second twist-and-lock connector (not shown), is used to releasably mount filter  20  to filter  14  and to form a fluid-tight seal between the outlet opening  54  of filter  20  and the inlet opening  36  of filter canister  14 . 
   As the filter canister  14  is drawn toward the mask housing  12  by the twist-and-lock connector, the projection  22  bears against the plug  64 , overcoming the bias of the spring  28  and opening the seal between plug  64  and the seating  66 .  FIGS. 2–4  illustrate the self-sealing mechanism  16  in the open position, wherein the canister  14  has been mounted on the inlet port assembly  16  and the projection  22  has depressed the plug  64  against the bias of spring  28 . In  FIG. 2 , the user is exhaling, as evidenced by the valve  68  being in a flush seating against rear face  78 . The flow of air A in  FIG. 3  shows a low-level air flow, from the cavity  24  through the inlet port assembly  16 , and then by a partially open inhalation valve  68 , wherein the perimetric edge  84  is separated from rear face  78  to permit air flow, but valve  68  still retains its general umbrella shape with respect to mechanism  16 .  FIG. 4  illustrates a further state of valve  68 , wherein an increased opening pressure developed by the user has inverted valve  68 , further separating edge  84  from rear face  78  to provide a larger channel for air flow. The unique cross section of valve  68  allows it to invert under expected opening pressures to provide a greater air channel, while retaining internal biasing forces that return valve  68  to its original umbrella-like shape to form a seal against rear face  78  upon reduction of the inhalation air flow of the user. 
     FIG. 5  illustrates the mechanism  16  with canister  14  removed. Spring  28  biases plug  64  away from hub  70  and into sealing engagement with seating  66 . Spring  28  is selected to afford ready mounting of the canister  14 , but of sufficient strength to maintain plug  64  in sealing engagement with seating  66  against any opening pressure developed by the user with canister  14  removed, thereby preventing inadvertent inhalation of unfiltered air. 
   The assembly  10  can function with the canister  14  alone mounted to canister mount  13 , thereby opening self-sealing mechanism  16 , but in those field situations where threat conditions warrant, the canister  14  is supplemented by filter  20 . The flow of air A through the combined filter assembly canister  14  and filter  20  is shown in  FIG. 7 , wherein contaminated air enters filter  20  through inlet opening  52 , passes axially through the layers  48 ,  50  and membrane  49 , and exits through outlet opening  54  to enter the corresponding central inlet opening  36  of the canister  14 . The air in the inlet opening  36  then flows radially outwardly through the fiberglass paper  44  to the annular passage  42 , downwardly in the annular passage  42  to the outside of the carbon filter  46 , radially inwardly through the carbon filter  46  to the cavity  24 , to exit the filter  14  through the central outlet opening  38 . 
   The stacked, radial-flow filter provides a greater surface area through which intake air can flow compared to the overall size of the filter. The consequence of increasing the surface area of the particulate and charcoal elements is to increase protection while reducing resistance to airflow in as small a space envelope as possible. This concept compares favorably with the current design of military axial flow filters. The stacked radial-flow filter has the additional advantage of having a central cavity that can contain the projection of the canister mount and inlet port assembly according to the invention, further maintaining a reduced spatial envelope for the mask and filter assembly. The concept is not, however, to be construed as only compatible with a radial-flow filter, as it is adaptable for use with other filter canister types, including axial-flow filters, and other connection types including bayonet and screw-thread mountings, and such use is contemplated. 
   Referring now to  FIGS. 8–12 , a second embodiment of the self sealing valve  100  comprises a valve body  110 , a resilient self sealing diaphragm  150 , and a resilient inhalation diaphragm  170 . Although only a half of the self sealing valve  100  is shown in  FIGS. 8 and 9 , the other side is a mirror image of the half shown in these drawings. Self sealing valve  100  has an outer face  102  and an inner face  104 , the inner face  104  adapted to face the interior chamber of the gas mask  12 . 
   The self-sealing diaphragm  150  is arranged on an outer face of the valve body  110 , mounted on a stud  112 . The inhalation diaphragm  170  is arranged on an interior face of valve body  110 , mounted on a stud  114 . 
   Valve body  110  includes an annular channel  116  having a bottom surface  118 , an outer wall  120 , and an inner wall  122 . Valve body  110  further includes an annulus  124  projecting outwardly from an upper end of channel outer wall  120 . The upper end of channel outer wall  120  includes an annular chamfer  126  at an upper end  138 . Valve body  110  further defines at an interior portion thereof a hub  128  comprising a planar portion  130 , the studs  112 ,  114 , and an upstanding annular rib  132  between the hub  128  and the inner wall  122 . The rib  132  includes an upper annular surface  134 . Planar portion  130  further comprises a number of pressure relief holes  136  passing therethrough. The rib  132  is connected to an upper end  138  of inner wall  122  of channel  116  by a plurality of spokes  140 , defining a number of open passages  142  therebetween. Inner wall  122  further comprises a sealing surface  144  at upper end  138 . 
   The self-sealing diaphragm  150  includes a substantially cylindrical central portion  152  and an umbrella-like outer portion  156  integrally formed with the central portion  152 . Central portion  152  includes a cavity  154  for receiving stud  112  and attaching diaphragm  150  to hub  128 . Outer portion  156  includes a convex hinge portion  158  positioned between the central portion  152  and radially inwardly of rib  132 . Outer portion  156  includes an annular skirt  160  having an outer edge  162  for forming a seal in cooperation with sealing surface  144 . Skirt  160  is further arranged to contact or be in close proximity to the upper annular surface  134  of rib  132 . 
   Diaphragm  150  and hub  128  define therebetween a cavity  164  fluidly connected with relief holes  136 . 
   Inhalation diaphragm  170  includes a substantially cylindrical central portion  172  and an outer portion  176 . Central portion  172  includes a cavity  174  for receiving stud  114  to connect inhalation diaphragm  170  to hub  128 . Outer portion  176  includes a convex hinge  178  and a skirt  180 . Skirt  180  includes an outer portion  182  arranged to form a seal with upper end  138  of inner wall  122 . 
   A filtration canister  200  comprises an annular lower face  202  which includes an interface  210  for fluidly and sealingly connecting the filter element of the filtration canister  200  to the self sealing valve  100 . The interface  210  comprises a first depending annular rib  220  and a central hub  240 . Lower face  202  includes an annular chamfer portion  204  connecting outer surface  222  of the rib  220  with lower face  202 . 
   Rib  220  includes an outer surface  222 , an inner surface  224  and an end  226 . An annular resilient seal  228  encapsulates end  226  of rib  220 . Resilient seal  228  is, for example, made of elastomeric material, and includes a tongue  230  projecting radially outwardly from seal  228 . 
   Hub  240  is connected to chamfer portion  204  by a plurality of spokes  206  and centered within the annular rib  220 . An air passage  208  is defined between spokes  206  and between an outer edge  242  of hub  240  and chamfer portion  204 . The air passage communicates with the filter medium in the filtration canister  200 . 
   Hub  240  is substantially in the form of the disk  244  having a depending annular lip  246  at outer edge  242 . Hub  240  further comprises a depending annular rib  248  having a tip  250 . Annular rib  248  defines a cavity  252  fluidly connected through a relief passage  254  to the interior of filtration canister  200 . A shallow cavity  260  is defined between lip  246  and rib  248  and is fluidly connected through relief holes  262  to the interior of filtration canister  200 . 
   In the arrangement shown in  FIG. 8 , wherein filtration canister  200  is removed from self sealing valve assembly  100 , any attempt to pass a gas in either direction through the self sealing valve assembly  100  will be stopped by the self sealing diaphragm  150  or the inhalation diaphragm  170 . When installed on the gas mask  12 , inhalation by the wearer of the gas mask  12  might dislodge the inhalation diaphragm  170 , but will only draw the self sealing diaphragm  150  into closer contact with the valve body  110  preventing the inhalation of outside air. Exhalation by the wearer of the gas mask  12  will likewise press of the inhalation diaphragm  170  into closer contact with the valve body  110  to prevent passage of air. 
   Referring to  FIG. 9 , the filtration canister  200  is connected to the self sealing valve assembly  100 , such that the interface  210  is inserted in the valve body  110  and opens the self sealing valve by displacing the self sealing diaphragm  150  from the sealing surface  144 . 
   As the filtration canister interface  210  is placed over the self sealing valve assembly  100 , the first portion of the interface  210  to contact the valve assembly  100  is the tongue  230  of the seal  228 . As tongue  230  contacts outer wall  120  of channel  116 , an effective seal is formed between interface  210  and valve body  110  such that the self-sealing diaphragm  150  is now fluidly isolated from the outside atmosphere. This fluid isolation is perfected as resilient seal  228  seats against the bottom surface  118  of channel  116 . 
   Filtration canister  200  is lowered over self-sealing valve assembly  100  until chamfer portion  204  of filtration canister  200  abuts chamfer  126  of valve body  110 . During this descent, tip  250  of rib  248  of filter interface  210  contacts convex hinge  158  of self-sealing diaphragm  150 . Further descent of the filtration canister  200  causes of the rib  248  to depress convex hinge  158  of diaphragm  150 , causing skirt portion  160  of diaphragm  150  to pivot about upper tip  134  of the rib  132 , thereby lifting outer edge  162  away from sealing surface  144 . 
   As shown in  FIG. 9 , with filter canister interface  210  fully inserted into self sealing valve assembly  100  outer edge  162  of self sealing diaphragm  150  is removed from sealing surface  144  and has been lifted into cavity  260  behind lip  246 . Convex hinge  158  of self sealing diaphragm  150  is depressed into the cavity  164 . During this process, any air trapped in cavity  164  has been released through relief holes  136 , air trapped in cavity  260  has been released through relief holes  262  and air trapped in cavity  252  has escaped through relief passage  254 . 
   With outer edge  162  of self sealing diaphragm  150  removed from sealing surface  144  and residing behind lip  246 , air passages  208 ,  142  are fluidly connected and unobstructed.  FIG. 9  shows the valve assembly  100  and a time when a wearer of the mask is not inhaling, specifically, there is no air flowing through the filtration canister  200  and through the self-sealing valve assembly  100 . 
   Referring to  FIG. 10 , inhalation diaphragm  170  is being subjected to a negative pressure differential in the interior chamber of the mask  12 , such as during inhalation by a wearer of the mask, flexing the inhalation diaphragm  170  about hinge  178  and separating the sealing relationship with upper end  138 . Thus, a fluid passage is opened from the filtration canister  200  through air passages  208 ,  142  to the interior chamber of the mask as shown by the arrows. 
   The lip  246  performs a shielding function for the upper end  138  of the self-sealing diaphragm to divert the air passing through the passage  208 . Thus, the air flows around the lip  246  and does not catch the upper end  138  of the self-sealing diaphragm and thereby tend to close the valve. The upper end  138  is thus positioned out of the flow path of the air that passes through the passage  208 . 
   As illustrated in  FIGS. 11 and 12 , the filter canister  14  is elliptical in shape and has several lugs  264  with inwardly directed overhanging flanges  266  radially spaced about the relief passage  254 . The valve body  110  has a circular shape with indentations  268  spaced about the outer periphery. The valve body  110  has ramps  270  adjacent each of the indentations  268 . The outer periphery of the valve body is shaped to fit within the outer wall  276  of the filter canister  14 . The indentations  268  are received within the lugs  264  and the projecting flanges  266  are adapted to slide beneath the ramps  270  as the canister is rotated counter-clockwise with respect to the facemask to tightly draw the canister against the facemask canister mount  13 . Clips  280  are resiliently mounted to the canister  14  through integral flanges  278  to provide a grip for the user to rotate the canister onto and off of the facemask canister mount. An indentation  272  is further provided on the outer periphery of the valve body  110  for a slide lock (not shown) that seats in a radial slot  274 . 
   A third embodiment of a self-sealing mechanism  400  according to the invention is shown is  FIGS. 13–16 . Mechanism  400  comprises a raised perimeter wall  420  having an inwardly projecting lip  416  and defining a central cavity  402  that terminates at a lower portion in a central hub  404  parallel to lip  416 . Hub  404  and annular pivot ring  418  are centered in cavity  402  by a plurality of radial spokes  424  connecting hub  404  and pivot ring  418  to lip  416 , spokes  424  further defining a plurality of radial openings  426  therebetween. Annular pivot ring  418  comprises an annular upstanding pivot rim  419  perpendicular to the pivot ring  418 . Hub  404  further comprises opposing studs  406 ,  408 , perpendicular to the plane defined as the bottom of cavity  402 , for receiving conical seal  410  and resilient inhalation valve  428  respectively. Valve  428  is substantially as described above as valve  68  in  FIGS. 2–6 . 
   Seal  410  includes a central portion  411 , an annular concave hinge portion  412 , and a conical skirt portion  414  having a perimetric edge  415 . The diameter of the hinge portion  412  is smaller than the diameter of pivot ring  418 , so that with the seal  410  received on stud  406 , centered in cavity  402 , hinge portion  412  lies within pivot ring  418 , and skirt portion  414  overlies pivot ring  418 . Edge  415  is further configured to abut lip  416  in a sealing engagement, held in place by the material resilience of seal  410 . 
   Self-sealing mechanism  400 , as described, comprises a sealed opening, in that a user attempting to exhale through mechanism  400  is prevented from so doing by valve  428 . Mechanism  400  is sealed against the user attempting to inhale, as any suction drawn within the mask draws skirt  414  inwardly, thereby increasing the seal between edge  415  and lip  416 . 
   Mechanism  400  is used in conjunction with a filter having a complementary configuration comprising a projecting annular rim  422  having a diameter substantially conforming to the diameter of hinge portion  412 . Rim  422  is configured to descend in alignment with hinge portion  412  as the filter is seated about mechanism  400 . As rim  422  descends, it depresses hinge portion  412 , forcing conical skirt portion  414  against upstanding annular pivot rim  419 . Conical skirt portion  414  pivots about rim  419 , lifting perimetric edge  415  upwardly and out of contact with lip  416 , thereby exposing radial apertures  426 . The user can then inhale by overcoming the opening pressure of valve  428 . 
   While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the foregoing description and drawings without departing from the spirit of the invention.