Many techniques have been used in the respirator art to attach filter elements to respirators.  A common technique has the filter element disposed in a threaded cartridge that is attached to a corresponding threaded fitting on the body of the respirator; see, for example, U.S. Pat.  Nos.  5,222,488, 5,063,926, 5,036,844, 5,022,901, 4,548,626, and 4,422,861.  Known filter cartridges typically possess helical or advancing spiral threads that mate with a tapped collar or socket that receives the threaded portion of the filter cartridge.  Rotating the filter cartridge in an appropriate direction allows the cartridge to be attached to or removed from the respirator.  A resilient, deformable gasket often is used to ensure an airtight fit to the respirator body. 
In lieu of threads, a bayonet type closure has been used to attach a filter cartridge to a respirator; see, for example, U.S. Pat.  Nos.  5,062,421, 4,934,361, and 4,850,346.  The bayonet type closure disclosed in the '421 patent has locking tabs and notches to secure the components together.  The locking tabs project from the filter cartridge and engage the notches in an aperture on the respirator body.  By rotating the filter cartridge in the appropriate direction, the cartridge snaps into engagement.  In the '361 and '346 patents, an audible device is used to indicate that the filter cartridge is properly coupled to the respirator face piece.  A lug on the face piece is provided with a detent ramp or cam having an inclined surface that is positioned to gradually deflect or deform a rib on the cartridge.  As the cartridge and face piece are rotated relative to each other into a locking position, the cam engages the rib and causes the rib and lug to deflect until the rib abruptly drops off the end of the cam.  The abrupt action produces the audible click. 
In another technique disclosed in U.S. Pat.  No.  5,148,803, a bellows is used to fasten a filter to the respirator.  The bellows, together with a rigid band, form a rigid cuff which receives the filter.  The cuff is continued in an elastic sleeve that surrounds the filter in a gas-tight manner.  To change the filter, the sleeve is first folded back to the level of the cuff, the filter element is inserted into the cuff, and the sleeve is then folded back over the filter element. 
U.S. Pat.  Nos.  5,033,465 and 5,078,132 disclose a respirator that uses edge seals to secure a filter element to the respirator's elastomeric face piece.  The filter element includes bonded activated carbon granules, and the edge seals are disposed between the filter element and the elastomeric face piece.  The edge seals are made of a suitable adhesive material such as a hot-melt adhesive, a hot-melt foam adhesive, or a latex adhesive. 
A foam mask shell is disclosed in U.S. Pat.  No.  4,856,508 for receiving a filter cartridge.  The foam mask shell possesses a collar that defines an opening for receiving the filter cartridge.  The filter cartridge has an extension with an outside dimension approximately equal to the inside dimension of the cylindrical passage through the collar.  To mount the filter cartridge, its extension is inserted into the opening where it makes a relatively tight friction fit.  The mask shell is made of a flexible foam material that expands when the extension is inserted in the opening.  To replace a filter element, it is grasped and twisted back and forth while pulling it away from the mask shell. 
In U.S. Pat.  No.  4,790,306, a respirator is described that uses insert molding to permanently secure a bonded absorbent filter element to a respirator face piece. 
A plug-in frame is described in U.S. Pat.  No.  4,771,771 to secure a filter cartridge in a chamber of the respirator.  The filter cartridge is disposed in the chamber by seals that bear tightly against the cartridge to hold it in place.  The filter cartridge can be fitted to the respirator by sliding it through an opening in the plug-in frame. 
In U.S. Pat.  No.  4,630,604, locking tongues are employed on a filter retainer to hold a replaceable filter member in an abutting relationship to the respirator frame.  The filter member can be replaced by snapping off the filter retaining member from the frame. 
A further technique is disclosed in U.S. Pat.  No.  4,562,837 where the respirator is provided with a guide ring for engaging a filter housing.  The guide ring is carried by a sleeve portion that defines an opening through which the gasses pass.  The filter housing slides on the guide ring from a retracted stand-by position to an extended use position.  A bellows, located between the filter housing and respirator, permits movement of the filter housing between its retracted stand-by position and its extended use position. 
Sundstrom Safety AB of Lidingo, Sweden markets a respirator in Europe and Australia under the designation SR-62, which uses an elastomeric rubber filter retainer for accommodating a filter cartridge.  The filter cartridge comprises a gas and vapor or particulate filter in a rigid injection molded plastic cartridge.  To insert the filter cartridge into the retainer, the retainer is stretched over the filter element's periphery.  When two different filters are used in series, they may be snapped together and inserted into the retainer as a single unit.  To separate the filters, a tool is provided on the harness system to pry them apart. 
Although the above-discussed respirators use various techniques for securing a filter and filter cartridges to respirators, these techniques have a number of drawbacks.  For example, the filter cartridges that are threaded to the respirator typically include a housing or canister into which the filter material is retained.  The cartridge's cylindrical geometry typically requires using the filter cartridge as an external appendage that can interfere with a wearer's vision.  Further, the threaded cartridges employ many parts that add to the filter element's total volume and the respirator's overall weight.  In other designs, such as disclosed in U.S. Pat.  Nos.  5,078,132, 5,033,465, and 4,790,306, the filters are not able to be readily replaced, and thus when the filter element's service life has met its limit, the whole respirator is discarded as waste.  In the model SR-62 respirator sold by Sundstrom, the filter cartridge is replaceable; however, the retainer lacks physical strength relative to the filter element, and thus, like placing a rubber tire on a wheel, a number of manipulations are needed to place the filter element in the elastomeric rubber retainer.  In addition, elastomeric materials can be relatively expensive and more difficult to process.  Some of the other respirators discussed above possess the drawback of using gaskets or O-rings to obtain a hermetic seal or use fairly complicated systems for mounting filter elements to respirators.