WO2009149507A1

WO2009149507A1 - Clean air receiving module and personal respiratory protective systems incorporating the module

Info

Publication number: WO2009149507A1
Application number: PCT/AU2009/000738
Authority: WO
Inventors: Michael James Gill
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-06-13
Filing date: 2009-06-15
Publication date: 2009-12-17
Anticipated expiration: 2010-12-13
Also published as: AU2009257188A1

Abstract

A respirator has a module (10) comprising a mouthpiece, to be inserted into the mouth of a user of the respirator, and a facepiece (20). The mouthpiece has a flange member (11) which, when in the mouth of a user, fits between the user's lips (13) and teeth (12), with the teeth bearing on a bite piece (14) from which, preferably, palate flaps (15) extend, and with the lips bearing on the surface of troughs in a lips receiving member (17). An aperture (16) in the flange member (11) permits the user to inhale air through a breathing passageway (21) in the lips receiving member. The facepiece (20) comprises an inhalation chamber (25) having at least one inhalation inlet (26A) and a first wall (23) which separates the inhalation chamber (25) from the breathing passageway (21). The first wall (23) contains at least one aperture (24) through which air may pass from the inhalation chamber into the breathing passageway. At least one one-way inhalation valve (27) in the facepiece is biased closed to prevent airflow through the inhalation chamber (25), but is opened by the act of inhalation, which reduces the air pressure in the breathing passageway (21). Nostril plugs (19), each containing a one-way valve (34) which prevents inhalation but permits exhalation through the user's nostrils, and means whereby the depletion of a gas filter may be detected, are also described.

Description

"Clean air receiving module and personal respiratory protective systems incorporating the module."

Technical field.

This invention concerns respiratory systems. More particularly, it concerns a breathing module for inclusion in personal respiratory systems (respirators) for use in unsafe ambient atmospheres (for example, in atmospheres containing smoke, dust, or chemical vapours, or - when used with an appropriate filter - in an atmosphere containing a virus or bacteria; this list is not exhaustive). More particularly still, this invention concerns a clean air receiving module for a personal respiratory system, in the form of a "mouth-bit module" to which a source of clean air may be attached. Accessories for use with this invention include (1) nose valve devices which allow a user of the mouth-bit module to smell and taste respired air; (2) means to give a user of the system sensory warning of respirator failure and/or the depletion of filters used in the respiratory system; and (3) the elimination of inward contaminant leakage into the respiratory system.

Preliminary note.

In this specification, including the claims, "directional" terms (such as "top", "bottom", "side", "underside", "upper", "lower", "above", "upwards", "below", "downwardly", "behind", "horizontal", "vertical" and the like) will be used in the sense that these terms would, have with reference to an embodiment of the invention positioned as shown in, inter alia, Figures 1, 5, 10, 15 and 17 of the accompanying drawings. The directional terms "inwards" and "inwardly" mean (unless another meaning in clearly intended) into or in a direction towards the mouth of a user of a respirator; and, similarly, the directional terms "outwards" and "outwardly" mean out of or in a direction away from the mouth of a user of a respirator. Background to the invention.

In the preface to the current Australian standard for respiratory protective devices (Standard No. AS/NZS 1716; 2003), "total inward leakage testing" is identified as one of the sections of the standard that is "very much in need of revision" . New ISO Standards are currently in preparation, but at the tune of writing this specification, there is no projected publication date for a revised Standard. Thus, currently, the situation in Australia, with personal respiratory protection devices is that none of the commercially available protective respiratory devices is fully effective and convenient to use in hazardous atmospheres.

Consequently, people who find themselves in hazardous atmospheres, whether by virtue of their work (for example, firefighters, rescue team members, underground miners, or workers in a chemical plant or other place where there is a sudden, unexpected chemical spill) continue to suffer adversely, and sometimes die, because they are without good respiratory protection.

Relatively recent developments hi respirators are described in the specifications of US patents Nos. 4,365,627 (to Whig; 1982), 5,086,768 (to Niemeyer; 1992), 5,771,885 (to Putrello; 1998), 6,758,212 (to Swann; 2004 and 7,025,060 (to Nicholson; 2006), and in the specifications which are US Patent Office Publications Nos. 2006/0137689 and 2006/0207579 Al (the specifications of US patent applications Nos. 10/533,587 and 11/375,682 by, respectively, Evensson and Wright; both in 2006). None of these specifications describes a respirator which is both fully effective and convenient to use in hazardous atmospheres.

Disclosure of the invention.

It is an object of the present invention to enable the production of effective personal protective respiratory devices (respirators), that (a) supply clean, breathable air to users of the respirators, and (b) are comfortable, safe and easy to use, even if the user of the respirator should be suffering from a head cold.

This objective is achieved by the provision of a module (a "mouth-bit module") which permits inhalation through the mouth only. This module is intended for use with a clean air supply. The clean air supply may be tainted ambient atmosphere air (or tainted compressed air) which has been passed through an appropriate filter, or it may be air from an independent supply of clean air (for example, air from a bottle of clean compressed air, air from a collapsible container of clean air, or air from a hose connected to a remote source of clean air).

Such a module, when included in a personal protective respiratory device, will be used with a device for preventing inhalation through the nares (nostrils) of a user of the personal protective respiratory device, as required by the afore-mentioned Standard No. AS/NZS 1716: 2003.

This module has a mouthpiece which, when in use, is inserted into the mouth of its user. The mouthpiece has a generally vertical, but curved, flange member, preferably made from a flexible but resilient material (for example, a plastics material, or a silicone-based material or latex-based material). The flange member (which is similar to features 74, 32 and 90 in, respectively, the specifications of US patents Nos. 5,771 ,885; 7,025,060; and 5,086,768) has an aperture in its central region, and it has dimensions which enable it to fit between the the lips and the teeth of a user of the respirator. A bite piece extends from one face (the inner face) of this flange member. The purpose of the bite piece is to provide a member on which a user of the respirator may support or rest the user's teeth, and which may be gripped by the teeth of a user of the respirator. The bite piece is constructed and positioned so that, when a user of the respirator inhales air, that inhaled air passes inwardly through the aperture in the flange member and the bite piece does not impede the flow of that inhaled ah" into the lungs of the user. The preferred construction of the bite piece comprises a pair of generally elongate blocks, each extending lengthwise, inwardly from a respective side region of the flange member. The side teeth (the molars) of a user of the respirator can bear against these blocks.

A lips receiving member, having an upper lip receiving portion and lower lip receiving portion, extends from the other (the outer) face of the flange member. When the respirator is in use, the flange member is positioned between the teeth and the lips of the user, with (a) the teeth of the user bearing upon the surface of the bite piece, and (b) the upper and lower lips of the user bearing upon the upper and lower lip receiving portions of the lips receiving member. The lips receiving member may be constructed as two separate lip receiving components (an upper lip receiving member and a lower lip receiving member), one to support the upper lip of the user, the other to receive the lower lip of the user.

The lips receiving member must be able to form a gas-tight seal when the lips of a user of the module are in contact with it. Accordingly, the upper surface of the lips receiving member is shaped to receive the upper lip of the user of the module, and the lower surface of the lips receiving member is shaped to receive the lower lip of the user of the module.

A "breathing passageway" is established between the upper and lower lip receiving surfaces. This breathing passageway provides an air passage between the aperture in the flange member and a facepiece.

The breathing passageway may be created by a material free zone within the material of the lips receiving member, which extends outwardly from the aperture in the flange member towards the facepiece. However, it is preferred that the side (or sides) of the breathing passageway is (or are) defined by a separate, solid (but possibly flexible) tubular member, having any suitable cross-sectional shape. This tubular member - which I have called a "breathing tube" - may have a width dimension which is greater than its length, and it may extend through the aperture in the flange member.

The facepiece comprises a chamber, which I have called an inhalation chamber. This inhalation chamber has

(1) a first wall which (a) is located at the outer end of the breathing passageway and (b) has at least one aperture in it;

(2) at least one clean air inlet (which I have called an "inhalation inlet"), the (or each) inhalation inlet being connected, when the module is in use, to a supply of clean air; and

(3) at least one one-way valve (which I have called an "inhalation valve") positioned in the facepiece to allow clean air to enter the breathing passageway when a user of the module inhales; this (or each such) one-way inhalation valve being biased closed if the air pressure outside the (or each) inhalation inlet is equal to the air pressure in the breathing passageway; this (or each such) one-way inhalation valve being further biased closed when the air pressure in the breathing passageway is greater than the air pressure outside the (or each) inhalation inlet.

The one-way inhalation valve (or valves) may be mounted in the aperture (or in respective apertures) in the first wall of the facepiece, which is located at the outer end of the breathing passageway. If this is the case, it is preferred that the oneway inhalation valve opens into the breathing passageway which, when the module is in use in a respirator, is wholly inside the mouth of the user. Alternatively, if the (or each) inhalation inlet is at the inner end of a tubular structure (which I have called an "inhalation tube"), the one-way inhalation valve (or valves) may be mounted at either end of, or within the inhalation tube (or at either end of, or within a respective inhalation tube) to close the inhalation tube (or tubes), and hence close the inhalation inlet (or inhalation inlets), by virtue of the bias applied to the (or each) one-way inhalation valve, if the air pressure outside the (or each) inhalation inlet is equal to or less than the air pressure inside the inhalation chamber.

Another alternative is for an inhalation inlet to be positioned in an outer wall (that is, a wall of the inhalation chamber that separates the inhalation chamber from the ambient air) and for a one-way valve to be positioned in such an inhalation inlet.

Yet another alternative is for the (or each) one-way inhalation valve to be mounted in an aperture (or in a respective aperture) in an internal wall of the inhalation chamber that divides, in a gas-tight manner, the inhalation chamber into two sub- chambers, the first sub-chamber of which is adjacent to the first wall of the inhalation chamber and the second sub-chamber being adjacent to the inhalation inlet or inlets. In this alternative, the (or each) such one-way inhalation valve is further biased closed when the air pressure inside the first inhalation sub-chamber is greater than the air pressure in the second of the inhalation sub-chambers.

Any two (or, in principle, more than two) of these alternative ways of mounting the (or each) inhalation valve may be used in a module, thus ensuring that the module contains at least two inhalation valves, in series.

Since the difference between the air pressure outside the inhalation inlet or inlets and the air pressure inside the breathing passageway is established by a user of the respirator module either breathing in or breathing out (or attempting to breath hi or out), it follows that (1) the, or each, one-way inhalation valve (a) is normally biased closed, but (b) is opened when a user of the respirator inhales through the mouthpiece; and

(2) the (or each) one-way inhalation valve closes again if the user of the respirator attempts to exhale through the mouthpiece.

The inhalation chamber contains clean air, either (a) because the - or each - inhalation inlet is connected to a source of clean air, or (b) because the inhalation chamber contains air that has entered the inhalation chamber through a suitable filter. Such a filter a) may be remote from the facepiece, by being included in the connection between a remote source of air and the inhalation chamber, or b) may be attached to the (or each) inhalation inlet or inhalation tube, or c) may be included within the inhalation chamber or within a sub-chamber of the inhalation chamber.

If the bite piece comprises two blocks on which the molar teeth of a user of the respirator make contact, two palate flaps may be included in the mouthpiece. Such palate flaps will extend - one on each side - from the inside edges of the bitepiece. Palate flaps assist in the location of the mouthpiece within the mouth of a user of the module. They also provide mouthpiece stabilisation and improve the comfort of the user when the mouthpiece is in the user's mouth.

The flange member, the bite piece and the lips receiving member (and also the palate flaps, if they are present) may be formed integrally from a flexible and resilient material, preferably from a silicone material. However, since it is desirable, for some applications, for the lips receiving member to be made of a softer resilient material than the flange member and the bite piece, the lips receiving member may be bonded onto the flange member, which may have been formed integrally with the bite piece. If a solid breathing tube surrounds the breathing passageway, it will be attached to the first wall of the facepiece that is located at the outer end of the breathing passageway. The outer end of the breathing tube will surround the (or each) aperture in the first wall of the facepiece, and will form a gas-tight seal between the outer end of the breathing tube and the first wall of the facepiece. The separate breathing tube member may be further held in place by connecting its inner end to the flange member.

It follows, therefore, that in its broadest form, the present invention provides a clean air receiving module for a personal respirator, which comprises a mouthpiece and a facepiece; and is characterised in that: a) the mouthpiece comprises 1) a substantially vertical, but flexible, flange member having a shape and dimensions which enable the flange member to be positioned in the mouth and between the teeth and the lips of a user of said respirator; said flange member having an aperture in the central region thereof; 2) a bite piece extending inwardly from the flange member; and 3) a lips receiving member; said lips receiving member extending outwardly from the flange member and having (i) an upper surface region which has the shape of an elongate, curved, generally horizontal trough, which is transversely substantially arcuate in shape, so that the upper lip of a user of the respiratory system can be positioned in contact with said upper surface of said lips receiving member when the respirator is in use; and (ii) a lower surface region which has the shape of an elongate, curved, generally horizontal, downwardly facing trough, which is transversely substantially arcuate in shape, so that the lower lip of a user of the respiratory system can be positioned in contact with said lower surface when the respirator is in use; b) a breathing passageway extends outwardly from said aperture in said flange member, between said upper and lower surface regions of the lips receiving member; c) said facepiece comprises an inhalation chamber from which clean air is passed into said breathing passageway when a user of the respirator inhales; said inhalation chamber having a first wall member with at least one aperture therein; said first wall member being positioned at the outer end of said breathing passageway with said (or each) aperture in said wall member being surrounded by the outer end of said breathing passageway; a gas-tight seal being established between the outer end of said breathing passageway and said first wall member; d) said inhalation chamber has at least one inhalation inlet that is connectable to a supply of clean air; and e) said facepiece includes at least one one-way inhalation valve; the, or each, one-way inhalation valve being biased closed but opening when the air pressure within said breathing passageway is lower than the air pressure immediately outside said (or each) inhalation inlet, thereby permitting air from said inhalation chamber to enter said breathing passageway and pass through said breathing passageway and through said aperture in said flange plate, to enter the mouth of said user of the respirator; said (or each) one-way inhalation valve being closed when the air pressure within said breathing passageway is equal to or greater than the air pressure immediately outside said (or each) inhalation inlet.

As noted above, the (or each) one-way inhalation valve may be mounted

(1) in the aperture (or in respective apertures) in the first wall of the facepiece, which is located at the outer end of the breathing passageway, which outer end may be within the mouth of a user;

(2) in a wall member (or in a respective wall member) that extends across the inhalation inlet (or inlets);

(3) within, or at the end of, an inhalation tube that extends outwardly from an inhalation inlet; and/or

(4) in an internal wall of said inhalation chamber that divides, in a gas-tight manner, said inhalation chamber into two sub-chambers, one of the sub- chambers being adjacent to the first wall member of the facepiece and the other of the sub-chambers being adjacent to the inhalation Met or inlets.

As also noted above, optionally, (a) the mouthpiece may include a respective palate flap extending inwardly from each side region of the bite piece, (b) the surface of the bite piece may have upper and lower indented regions, to receive the ends of the teeth of a user of the module; and (c) the lips receiving member may be formed as separate upper lip and lower lip receiving members.

In one embodiment of the invention,

(a) the inhalation chamber comprises a box-like construction having at least one inhalation tube extending from a (or a respective) clean air inhalation inlet on a side of the inhalation chamber; and (b) the (or each) inhalation tube is adapted to be connected to a supply of clean air.

Usually, in such an embodiment, two inhalation inlets will be provided, one on each side wall of the inhalation chamber, with a respective inhalation tube extending outwardly from each inhalation inlet.

A filter (or a filter container which, when it contains an appropriate filter material, becomes a filter; or a replaceable filter cartridge) may be connected to the (or each) inhalation Met or Mialation tube.

If the respirator or module is to be used with the air exhaled by the user being exhaled through the mouth of a user of the module, the facepiece will include an exhalation chamber. The exhalation chamber will have an inner wall (which I have called a "second wall member") that (a) is positioned at the outer end of the breathing passageway, and (b) contains at least one second aperture. . The exhalation chamber will also have at least one exhalation outlet. A one-way valve - which I have called an "exhalation valve" - or a respective one-way exhalation valve closes the, or each, second aperture. Alternatively, or additionally, a (or a respective) one-way exhalation valve closes

(a) the (or each) exhalation outlet, or

(b) an internal wall (or a respective internal wall) of the exhalation chamber that divides, in a gas-tight manner, the exhalation chamber into a plurality of exhalation sub-chambers (usually two sub-chambers), the innermost of which includes the second wall member and the outermost of which is adjacent to the exhalation outlet or outlets.

The (or each) one-way exhalation valve is biased closed if the air pressure outside the (or each) exhalation outlet is equal to or greater than the air pressure inside the exhalation chamber, and therefore remains closed when a user of the respirator inhales. However, the (or each) one-way exhalation valve opens when the air pressure outside the (or each) exhalation outlet is less than the air pressure inside the breathing passageway. Thus, when a user of the respirator module exhales through the mouth, exhaled air enters the exhalation chamber, from where it is vented to the ambient atmosphere through the exhalation outlet or outlets.

A particularly convenient facepiece arrangement has the exhalation chamber positioned underneath the inhalation chamber, so that the two chambers share a common wall (namely, the bottom wall of the inhalation chamber and the top. wall of the exhalation chamber). This arrangement allows exhaled air to be vented through exhalation outlets and thence be directed a) to the front of the user's face; b) to each side and to the cheeks of the user's face; and/or c) to exhalation channels which exit to the rear of the user's head.

The preferred exhalation chamber arrangement has

(1) a one-way exhalation valve (or a respective one-way exhalation valve) which closes the (or each) exhalation outlet, and (2) at least one further one-way exhalation valve which closes an (or a respective) inner aperture that is either

(a) the (or each) second aperture, or

(b) an aperture in an internal wall - or a respective internal wall - of the exhalation chamber that divides, in a gas-tight manner, the exhalation chamber into two exhalation sub-chambers, one of which includes the second wall member and the other of which is adjacent to the exhalation outlet or outlets.

In this way, after the user's first exhalation, a buffer zone of exhaled air is established between (a) the one-way exhalation valve or valves in the exhalation outlet or outlets, and (b) the one-way exhalation valve or valves of the second aperture or apertures, or the aperture (or apertures) in the internal wall that separates (or the internal walls that separate) the exhalation outlet (or the exhalation outlets) from the interior of the exhalation chamber. This buffer zone of exhaled air ensures that inward leakage of contaminant(s) through the exhalation valves is avoided and, therefore, there is no possibility that contaminated air can be inhaled, inadvertently, from the exhalation chamber.

The relevant respirator standards currently restrict the use of mouth-bit respirators to emergency-escape-only situations, because mouth breathing respirators impede the ability of the user to smell and taste. To enable respirators having a clean air receiving module of the type described above to be used in a manner which permits a user of the respiratory system to smell and taste the air inhaled, a discreet, separate and novel nose valve may be used with the respirator. This nose valve, when inserted into the nose of a user of the respiratory system, prevents inhalation through the nose, but enables exhalation to occur through the nose. This type of nose valve, conceived by the present inventor, is described later in this specification.

Using such nose valves, the user of the respiratory system should be able to detect all contaminants which are detectable by smell or by taste. Such contaminants may have been breathed in by me user (for example, as a result of incorrect choice of filter type in the respirator, depletion of the filter material, or by respirator malfunction).

In the absence of such nose valves, the user of the respiratory system may still use the equipment with a nose clip only, and with a degree of confidence if, periodically, the user (1) takes a deep breath through the breathing tube, (2) removes the nose clip, then (3) exhales through the nose and, immediately after exhalation, re-applies the nose clip. The user may remove both the mouthpiece and the nose clip and exhale through both the nose and mouth. Using this technique, the user of the respirator will "taste" the exhaled air and discern the presence of any contaminants which have a smell or taste, that may have been inhaled.

The respiratory system of the present invention may also be used (with the novel nose valves referred to above, or using the technique described in the last preceding paragraph) when the ambient air contains contamination that is incapable of detection by smell or taste, which may have been inhaled through a filter attached to or included in the facepiece of the respirator. To enable such use of the respirator, a harmless indicator chemical may be included in the filter or filter container. This indicator chemical will be one that (a) is normally absorbed by the filter material, and (b) has a bitter, burning or otherwise irritating nature (that may not be reliant on taste or smell) when inhaled. When it is fully absorbed by the filter material, the user of the respirator will not detect the indicator chemical. With use of the respirator, the filter material is depleted, and is thus less effective in its absorbency of the contaminant (and, therefore, also less effective in its absorbency of the indicator chemical). At a certain point in the depletion of the filter material, some of the indicator chemical passes through the filter and the user of the respirator will detect it.

The indicator chemical may be introduced into the respiratory protective device by sublimation. An indicator chemical that sublimes at normal ambient temperatures and pressures may be stored in a permeable container that may be positioned in the filter material (or at a point where air enters the filter - for example, between the filter's air inlet and the active filter material) so that, when the filter is in use, a small but detectable (that is, able to be sensed) quantity of the sublimed chemical is inhaled with each breath of the user of the respirator. Alternatively, the indicator chemical may be inserted into the filter by a drop- dispersing device, or as an aerosol; or it may be introduced similarly into a filtering layer of a pre-filter, or into ambient air in the vicinity of the air intakes of the respirator. A similar procedure, undertaken inside a test hood, will indicate (a) the presence of damage to the respirator or (b) respirator malfunction.

To demonstrate the range and variety of the respirators that may be constructed using the module of the present invention, embodiments of such modules and respiratory protective systems will now be described, by way of example only. In the following description, reference will be made to the accompanying drawings.

Brief description of the drawings.

Figure 1 is a partly schematic, partly sectional, side view of a respirator module constructed in accordance with the present invention, in the mouth of a user of the respirator. Figure 2 is a partly schematic plan view, from above, of the module illustrated in Figure 1.

Figure 3 is a rear view of the facepiece of the module of Figures 1 and 2.

Figure 4 shows the construction of a nose valve device which prevents inhalation, but permits exhalation, through the nostrils of a user of this device.

Figure 5 is a partly schematic, partly sectional, side view of another respirator module constructed in accordance with the present invention, in the mouth of a. user of the respirator.

Figure 6 is a partly schematic plan view, from above, of the module illustrated in Figure 5.

Figure 7 is a rear view of the facepiece of the module of Figures 5 and 6.

Figure 8 is a partly schematic plan view, from above, of another form of module for a respirator.

Figure 9 is a rear view of the facepiece of the module for a respirator depicted in Figure 8.

Figure 10 is a view, similar to Figures 1 and 5, of another module for a respirator, constructed in accordance with the present invention, in the mouth of a person using the nose valve device illustrated by Figure 4.

Figure 11 is a top view of a module similar to that ilustrated in Figure 10, with a nose clip attached to the facepiece of the module. Figure 12 is a rear elevation of title facepiece of the module shown in Figure 11.

Figure 13 is a rear elevation of a modified form of the module for a respirator shown in Figures 11 and 12.

Figure 14 is a view, from above, of a respirator comprising a module as shown in Figures 11 and 12, fitted with an air filter.

Figure 15 is a side view, partly in section and partly schematic, showing a person using the respirator depicted in Figure 14.

Figure 16 is a front view of a person using the respirator of Figure 14.

Figure 17 is a side view, partly schematic, of another type of respirator that is constructed in accordance with the present invention, in the mouth of a user of the respirator.

Figure 18 is a partly sectional plan view, from above, of the respirator of Figure 17, showing the use of filter cartridges in the respirator.

Figure 19 is a plan view of a person using a respirator that is similar to the respirator shown in Figure 16, but with filtering materials contained in filter cartridges similar to those shown in Figure 18.

Figure 20 depicts a side view of a yoke-like respirator which is constructed in accordance with the present invention.

Figure 21 is a front view of the respirator that is similar to the respirator illustrated in Figure 20, but with exhalation to the cheeks of a user. Figure 22 is a view, from above, of the head of a person using a yoke-like respirator similar to the respirator of Figures 20 and 21.

Figure 23 shows three alternative ways in which a yoke-like respirator may be used with a remote source of air.

Figure 24 illustrates other ways in which a yoke-like respirator may be used.

Figure 25 illustrates persons using other forms of yoke-like respirators.

Figure 26 is a side view of a person wearing a hooded yoke-like respirator.

Figures 27 and 28 are side and front views, respectively, of a person using a hooded respirator having a high capacity filter.

Detailed description of the illustrated embodiments.

Figure 1 shows the head of a user of a respirator with a respirator module 10 in the user's mouth. Figure 2 is a plan view, from above, of the module 10. The module 10 has a flange member 11 which is located between the teeth 12 and the lips 13 of the user. The flange member 11 has an aperture 16 through which air is drawn when the user inhales through the mouth. Inhalation through the mouth is essential in the situation illustrated in Figure 1, for nose or nostril valves 19 (details of which are shown in Figure 4) have been inserted into the nostrils of the user. These nostril valves permit exhalation tiirough die user's nostrils, but prevent inhalation through the user's nose.

Reverting now to the module illustrated in Figures 1 and 2, a bite piece in the form of two blocks (bite piece members) 14, extending inwardly from the flange member 11, is positioned so that the molar teeth of the user bear against the top and bottom surfaces of the bite piece members 14. This is the preferred form of the bite piece, which may have any one of a number of alternative constructions. It may comprise, for example, a short tube, open at each end, which extends inwardly from, and surrounds, the aperture 16 in the flange member. With this alternative construction, the central (incisor) teeth of a user of the respirator will bear against the outer upper and lower surfaces of the bite piece. (The short tube may also extend outwardly from the aperture in the flange member, to form a breathing tube - described below - for the module of the respirator.) In another alternative arrangement, the bite piece may comprise two spaced apart, short, but relatively wide, blocks of material, extending inwardly from, respectively, above and below the aperture 16 in the flange member. The upper of these two blocks provides a surface against which the upper incisor teeth of a user of the respirator may bear; the lower of these two blocks provides a surface against which the lower incisor teeth of a user of the respirator may bear. These alternatives are not exhaustive. Prior art bite pieces include:- features 76, 92 and 43 in, respectively, the specifications of US patents Nos. 5,771,885; 5,086,768 and 7,025,060.

The outer surface of the bite piece, however it is constructed, may have upper and lower indented regions, positioned to receive the ends of the teeth of a user of the respirator.

Palate flaps 15 (the cross-sections of which are shown in Figure 13) extend from the inside edge of the bite piece members 14. As noted above, the palate flaps 15, which are a preferred optional feature of the mouthpiece, assist in the location of the mouthpiece in the mouth of the user. They also assist in the stabilisation of the mouthpiece within the mouth of the user, and they improve the comfort of the mouthpiece within the mouth of the user (by increasing the area of contact of the soft material of the mouthpiece with the skin inside the mouth of the user). A lips receiving member 17 extends from the outer face of the flange member 11, and surrounds the aperture 16. The lips receiving member has upper and lower lip receiving surface regions ("lip receiving surfaces") 18. The lip receiving surfaces 18 are shaped so that the lips of the user of the module can bear against these surfaces and form a comfortable gas-tight seal. Thus the material used for the lips receiving member 17 is preferably a soft silicone material, or other suitable soft material.

In essence, the upper lip receiving surface 18 is the surface of a curved, generally horizontal, upwardly facing trough, adjacent to the outer surface of the flange member 11, with the surface of this trough having an arcuate cross-sectional shape. In a similar manner, the lower lip receiving surface 18 is the surface of a curved, generally horizontal, downwardly facing trough, adjacent to the outer surface of the flange member 11 , with the surface of this trough having an arcuate cross-sectional shape.

The central region 21 of the lips receiving member 17 is devoid of material, so that it forms a passageway - a breathing passageway - between the aperture 16 in the flange member 11 and a facepiece 20. In the illustrated module of Figures 1 and 2, the side or sides of the passageway 21 are defined by a solid (but, optionally flexible) tubular member 22. In the module shown in Figure 1, this tubular member (breathing tube) 22 is flared outwardly, but such flaring of the breathing tube 22 is not essential. An inner surface of the lips receiving member is a tight fit against the outer surface of the breathing tube 22.

If the lips receiving member 17 is constructed as two components, namely (1) an upper lip receiving member, with an upwardly facing trough, against the surface of which the top lip of a user will bear, and (2) a lower lip receiving member, with a downwardly facing trough, against the surface of which the bottom lip of a user will bear, the lower surfaces of the side regions of the upper lip receiving member will be held in gas-tight contact with the correspondingly located upper surfaces of the side regions of the lower lip receiving member. These correspondingly located surfaces may be bonded to each other.

The facepiece 20 is positioned at the outer end of the breathing tube 22 (that is, at the end of the breathing tube 22 that is remote from the flange member 11. The facepiece 20 comprises an inhalation chamber 25 having two inhalation inlets (one in each side wall 25A of the inhalation chamber) to which respective inhalation tubes 26 are connected. Clean air is supplied to the inhalation chamber 25 through the inhalation inlets 26 A, via the inhalation tubes 26. A wall 23 of the inhalation chamber 25, which I have called a "first wall member" or "first wall", abuts the outer end of the breathing tube 22. The first wall 23 has at least one aperture 24 in it. The first wall 23 connects the inhalation chamber 25 to the breathing passageway 21. A one-way valve 27 in the aperture 24 (or a respective one-way valve in each aperture 24) of the first wall 23 is biased to its closed position, in which it provides a gas-tight seal between the breathing passageway 21 and the inhalation chamber 25.

When the user of the module 10 inhales (the user's inhalation must be through the mouth, because the nostril valves 19 permit only exhalation through the nostrils), the air pressure hi the breathing passageway 21 is reduced, so the (or each) one-way valve 27 in the first wall 23 opens, thus permitting air to be breathed in from the inhalation chamber 25, through the breathing passageway 21 , through the aperture 16 in the flange member 11, and into the mouth and lungs of the user of the module. As soon as the inhalation ceases, the air pressure in the breathing passageway 21 is equal to the air pressure in the inhalation chamber 25, which is the same as the air pressure at the inhalation inlets. Therefore, the (or each) one-way valve 27 mounted on the first wall 23 closes. Any attempt by the user of the module to exhale through the one-way valve 27 reinforces the closure of this valve and its gas-tight seal with the first wall 23.

A single, wide, one-way flap valve 27 is shown in the module illustrated in Figures 1, 2 and 3, so the first wall 23 includes a grill in the form of rigid, thin struts 28, which extend vertically across the aperture 24. These struts 28 prevent the flap of the one-way flap valve 27 from flexing during exhalation by the user of the module. In the absence of the struts 28, flexing of the flap of the one-way valve could result hi the flap entering the inhalation chamber 25 unintentionally.

If , hi the facepiece illustrated in Figures 2 and 3, (a) a plate is included in, and extends across, each of the inhalation tubes 26 - at, for example, the location indicated by the dashed lines 31 in Figures 2 and 3 - and

(b) at least one aperture is included in each of these plates, then at least one inhalation valve may be included in each of the apertures hi these plates (which thus become "valve plates") instead of, or in addition to, the aperture or apertures in the first wall 23 of the facepiece.

The construction of the valved nostril plugs 19, shown inserted into the nares of the user of the module 10 hi Figure 1, is detailed hi Figure 4. Figure 4(a) is a side elevation of a pair of valved nostril plugs 19, separated from each other by, and connected together by, a web 37. Figures 4(b) and 4(c) are perspective views of the connected plugs 19 from, respectively, above and below. Figure 4(d) is a plan view of the connected valved nostril plugs 19.

Each valved nostril plug 19 comprises a rigid tube member 32 having an essentially circular cross-section. The lower end of each plug 19 (that is, the outermost end of the plug when the plug is inserted into a nostril of a user) has an inwardly projecting lip 33. A respective rigid strut 39 extends across the lower end of each tube member 32 from the central region of the straight edge of the lip 33. A segment of an essentially circular flap 34 of a one-way valve is attached (for example, bonded) to the lower face of the lip 33. Thus the lower end of the tube member 32, the lip 33 and the strut 39 constitute a valve plate to which the flap 34 is operatively connected. The tube member 32 is covered with a soft silicone material 35 which is formed into two ridges 36 which (a) form gas-tight seals with the inside skin of the user's nostril, and (b) hold the plug 19 in place within the nostril. Normally, the soft coating of the tubular members 32 will be formed integrally with the web 37.

The valved nostril plugs 19 shown in Figure 4 can be easily inserted into the nares of a user, and they can be easily removed from the nares when the plugs are no longer required. The flap 34 of each one-way valve is biased into its closed position, where it forms a gas-tight seal with the valve plate that includes the lower end of the tube member 32. Any attempt by the user to inhale through the nose will reinforce this seal and will prevent actual inhalation through the nostrils. The rigid struts 39, which extend across the lower end of each tube member 32 from the central region of the straight edge of the lip 33, act to prevent the associated flap 34 from flexing if inhalation through the nostrils is attempted. Flexing of a flap 34 would destroy the gas-tight nature of its seal with the lower end of the tubular member 32. (Note: in practice, the lip 33 may not be a true segment of a circle, and thus the lip need not have an edge that is straight.)

The nostril plugs illustrated in Figure 4 may be modified to prevent both inhalation and exhalation. For example, the tube member 32 may be capped, and the one-way valve incorporating the flap 34 may be omitted, thereby producing nostril plugs that provide complete nose occlusion. Such modified nostril plugs may be used in situations where exhalation through the mouth is essential. If such modified nostril plugs are not available, or are unsuitable, the nostrils of a user of the module 10 must be held closed - preferably by a nose clip - and a respirator must have a different form of module, that permits exhalation through the mouth of the user. One such module is illustrated in Figures 5 and 6. The facepiece for this module is illustrated in Figure 7.

The module shown in Figures 5, 6 and 7 has a similar construction to the module illustrated in Figures 1 and 2. However, the facepiece has a significantly different construction. Accordingly, the features shown in Figures 5, 6 and 7 which correspond to features illustrated in Figures 1, 2 and 3 have been given the same reference numerals in the drawings. (In fact, throughout this description of embodiments of the present invention, similar features in different embodiments, and features performing the same or a similar function in different realisations of the invention, are given the same reference numerals in the drawings.)

The facepiece of the module for a respirator shown in Figures 5, 6 and 7 has an inhalation chamber 25 into which clean air can be inhaled through inhalation tubes 26. A second chamber - an exhalation chamber 45 - is included in the facepiece, directly underneath the inhalation chamber 25. Exhalation tubes 46 extend outwardly from associated exhalation outlets 46A - one on each side - of the exhalation chamber 45. A second wall member (a "second wall") 43 of the facepiece (which, in the embodiment illustrated in Figures 5, 6 and 7, is a continuation of the first wall 23 of the facepiece) has at least one secondary aperture 44 hi it. (A single aperture 44 is shown in these Figures). The (or each) secondary aperture 44 is located in the region of the second wall 43 that is between the breathing passageway 21 and the exhalation chamber 45. The (or each) secondary aperture 44 is closed by a (or by a respective) secondary one-way valve 47. The (or each) secondary one-way valve 47 - normally a flap valve - is biased closed when the air pressure in the breathing passageway 21 is lower than or equal to the air pressure in the exhalation chamber 45 (which is the same as the air pressure at the exhalation outlets 46A). The (or each) secondary valve 47 is opened only when the air pressure in the breathing passageway 21 is greater than the air pressure in the exhalation chamber 45. Since the (or each) one-way flap valve 27 in the first wall 23 of the facepiece is opened only when the air pressure hi the inhalation chamber 25 exceeds the air pressure in the breathing passageway 21 , it follows that the (or each) one-way valve 27 opens only during inhalation by the user of the respirator, and the (or each) secondary one-way valve 47 opens only during exhalation by the user.

The inhalation chamber 25 is directly above the exhalation chamber 45. The wall 30 that extends outwardly from the junction of the first wall 23 and the second wall 43 of the facepiece, is a third wall of the facepiece. The third wall 30 separates, in a gas-tight manner, the inhalation chamber 25 from the exhalation chamber 45 and is, therefore, a common wall of the chambers 25 and 45.

In the embodiment shown hi Figures 5, 6 and 7, there is a single, wide aperture 24 in the first wall 23, and a single, wide secondary aperture 44 hi the second wall 43 of the facepiece. Accordingly, rigid, thin grill struts 28 and 48, extending vertically across, respectively, the aperture 24 and the secondary aperture 44, are included to prevent any deformation of the flaps of the flap valves 27 and 47 that, if it occurred, could destroy the gas-tight seal across the associated aperture when these valves are closed. It will be apparent that the single apertures 24 and 44 could be replaced by two, or more, smaller apertures hi the first and second walls of the facepiece. Such extra apertures could each be closed by an associated oneway flap valve, operating in the same manner as the valves 27 and 47.

If, in the facepiece illustrated in Figures 5, 6 and 7,

(a) a plate is included in, and extends across each exhalation outlet 46A, or across each hollow exhalation tube 46, and (b) at least one aperture is included in each of these plates, then at least one exhalation valve may be included in each of the apertures in these plates (which then become "valve plates") instead of, or in addition to, the aperture or apertures in the second wall 43 of the facepiece.

Reverting now to Figure 5, the lower region 42 of the exhalation chamber 45 forms a saliva trap. Any saliva present in the saliva trap can be drained from it by the temporary removal of a plug 41 from the lowermost part of the saliva trap. Such drainage of saliva should be performed while a user of the respirator holds his or her bream, and replacement of the plug 48 should be effected before the user re-commences inhalation and exhalation. Alternatively, drainage of saliva may be performed outside the contaminated area.

The dashed line A in Figure 6 shows the location of the cheeks and lips of a user of the respirator. A nose clip 29, comprising two nose clip members 49, is mounted on the facepiece of the embodiment shown in Figures 5, 6 and 7. Each nose clip member 49 comprises a nose cup 50 of silicone material, or of a similar material, at or near one end (the upper end when the nose clip is in use) of a nose clip arm 51. The other end of the nose clip arm 51 is mounted on the facepiece using adjusting screws 52 and associated pressure washers 53. The nose clip arm 51 is preferably made of stainless steel, but it may be fabricated from any other suitable material. The nose cups 50 can be moved within locating apertures 51 A in the nose clip arm 51 , to adjust the positions of the nose cups to suit the dimensions of the nose of a user.

When the respirator is to be used, the mouthpiece is inserted into the mouth of the user and lugs 54 on the nose clip arms 51 are used to bring the nose cups 50 into contact with the nose of the user, then to apply sufficient pressure to the sides of the user's nose to close both of the user's nostrils. The adjusting screws 52 may be tightened or loosened to open or close the nose clip arms 51 and the nose cups 50 and to hold them in this position comfortably.

When the user's nostrils have been closed by the nose clip 29, the user cannot inhale or exhale through the nose. Inhalation is effected by the user reducing the air pressure in his or her mouth (by the act of attempting to breathe in), which causes the one-way flap valve 27 to open and permit clean air from the inhalation chamber 25 to enter the breathing passageway 21 and pass through the aperture 16 in the flange member 11, into the mouth of the user and then into the lungs of the user. Exhalation increases the air pressure inside the user's mouth, and also in the breathing passageway 21, causing the flap of valve 27 to close. The same increase in air pressure in the breathing passageway 21 causes the secondary flap valve 47 to open, thus permitting air in the user's mouth to be passed through the aperture 16, the breathing passageway 21 and the secondary aperture 44 (in the second wall 43), to enter the exhalation chamber 45, from where it is vented through the exhalation outlets 46 A and the exhalation tubes 46.

Figures 8 and 9 depict, respectively, a modified form of the mouthpiece and facepiece of the module illustrated in Figures 6 and 7. The main modification is the absence of exhalation tubes from the exhalation chamber 45, and the presence of two (one on each side) exhalation outlets 46A in the side walls of the exhalation chamber. These outlets 46 A are covered by respective grills 38. With this arrangement, exhaled air is vented from the exhalation chamber 45 through the grills 38 and is directed onto the cheeks of the user of the respirator. Each exhalation outlet 46 A may be fitted with a secondary one-way exhalation valve, and each grill 38 may be covered with a protective and directive cap 57 (for example, in the manner shown in Figure 10). Figure 10 illustrates another module for a respirator. This module - shown with the plug 41 temporarily removed from the bottom of the exhalation chamber to drain saliva from that chamber - has a single exhalation outlet 46A in its facepiece. This exhalation outlet 46 A comprises a vent in the front wall 55 of the facepiece. This vent in the wall 55 is closed by the secondary one-way flap valve 47A of the exhalation chamber 45. A protective cap 57 fits over the vent. The cap 57 has a solid top member 58 so that exhaled air is vented only to the side of and below the facepiece of the module.

Since there is no nose clip attached to the facepiece of the module, the user has a valved nostril plug 19, of the type illustrated by Figure 4 and described above, in each nostril, as a precaution against accidental inhalation of contaminated air. If valved nostril plugs similar to those shown in Figure 4 are not available, a) an independent nose clip may be used, or b) nose clip members 49 can be attached to the facepiece of the module of Figure 10, as shown in Figures 11 and 12; or c) occlusive nostril plugs may be used.

(The dashed line A in Figure 11 shows the line of the lips and cheeks of the user of the respirator.)

Figure 13 is the rear view of another module for a personal respirator. This module provides a different view of the preferred arrangement of bite piece members 14 and their associated palate flaps 15. The module of Figure 13 has a single piece nose clip 59, which uses the spring force created by appropriate bending of a length of thin steel rod to press its nose cups 50 against the outside of the user's nose and close the nostrils of the user. To ensure that the nose clip remains always with the module of Figure 13, a coiled lanyard 56 connects the nose clip

59 to the facepiece 20. The clean air entering the inhalation inlets of the modules illustrated in Figures 1 to 3, Figures 5 to 7, and Figures 8 to 13, may come from any one of a number of sources. Obvious clean air supplies, connected by a suitable hose or line to filter cases 80 which are attached to the inhalation tubes 26, are (1) air that is drawn in by the user's natural breathing or is pumped from a remote source of clean air;

(2) clean compressed air from a storage cannister or compressor; and

(3) potentially clean compressed air, taken from a storage cannister or compressor and passed through an appropriate filter to remove any suspected possible contaminant particles, mists, gas or gases.

(This list is not exhaustive.) Such sources of clean air are not always available, or are not suitable for use in situations in which a respirator may be used. It is useful (and is often necessary), therefore, to include a filter attached to the (or each) inhalation inlet, so that ambient air (with its contaminant, if present, removed by the filter material) can be safely inhaled by a user of the respirator. Such filters may also be used to purify contaminated compressed air within the respirator,

A respirator with a replaceable filter connected to its inhalation inlets is shown in Figures 14, 15 and 16. The module of this respirator is similar to the module shown in Figures 8 and 9, with exhaled air directed across the cheeks of a user of the respirator. The filter attached to the inhalation inlets comprises a filter chamber 60 having inner and outer walls which consist of at least one layer of a material 62 (a cloth or paper material) which filters particulate contaminants. The (or each) layer of material 62 is supported by perforated, rigid, internal fins 61, which are rigidly attached to and extend from a rigid cage 61 A located in the filter chamber 60. The cage 61A is detachably connected, in a gas-tight manner, to an inhalation inlet (or an inhalation tube) of the module. The fins 61 are shaped so that the chamber 60 extends, generally arcuately and substantially symmetrically, sideways from the facepiece around part of the head of the user of the respirator, covering, but not touching, the cheeks or face of the user. Air can enter the filter chamber 60 freely by passing through the layer (or layers) of the particulate filter material 62 and the perforations in the fins 61. The filter chamber 60 may also be filled with a gas-absorbing filter material (for example, activated carbon).

To allow the respirator of Figures 14, 15 and 16 to hang conveniently around the user's neck when it is not in use, a tether comprising two strips 63 is attached to the fabric cover 62. Each strip 63, which, conveniently, may be a soft, elasticised material, has one end attached to the fabric cover 62, adjacent to a rearmost end of the filter chamber 60. The other end of each strip 63 is free. Each strip 63 has a length such mat it can be passed to behind the head of a user of the respirator and, when so positioned, its free end can overlap the free end of the other strip 63, and the two free ends can be fastened together. Press studs, or buttons and button holes, may be used for this purpose. However, the preferred fastening arrangmeent - which is illustrated in Figure 14 - uses patches 64 of "Velcro" material ("Velcro" is a trade mark), which hold to each other when pressed together. The tether 63 is worn loosely and does not support or hold the respirator in position in any way when the respirator is in use. The tether is constructed as two strips so that the respirator may be removed without the tether being passed over the head or over any other safety equipment (for example, goggles, ear muffs, helmet, etc.) being worn.

As shown in Figures 15 and 16, a nose shield 65 may be included above the filter container 60. Figure 16 also shows - in dashed outline - the locations of rigid, perforated fins 61 of a filter cage designed by the present inventor.

The filter material contained within the chamber 60 will depend upon the nature of the contaminant to be removed from the ambient air. If the contaminant is gaseous, activated charcoal is the likely filter material. Other filter materials may also be included. Those other filter materials include - but are not limited to - particulate materials (such as paper, wool and synthetic materials) which are effective to remove particulate contaminants.

Figures 17 and 18 depict a compact respirator which has a different type of filter chamber associated with its inhalation inlets. It also has an exhalation chamber 45 with two secondary one-way valves 47 and 47 A, in series, to create a buffer zone of exhaled air in the exhalation chamber 45. One of these secondary one-way flap valves 47 is located in the second wall 43 of the facepiece. The other secondary one-way flap valve 47A is located at the exhalation outlet of the facepiece, which is covered by the cap 57. With this arrangement, after the first breath taken by a user of the respirator, the exhalation chamber is always filled with exhaled air; and no contaminated ambient air can enter the exhalation chamber and be inadvertently inhaled because a fully gas-tight seal is established by the secondary valve 47 in the second wall 43 of the facepiece. This secondary valve 47 never comes into direct contact with contaminated air; it is only in contact with exhaled air.

The rigid filter case or chamber 60 shown in Figure 18 has a removeable end cover 76 that comprises a grill. The end cover 76 is removed to allow a cartridge 75 containing filter material (typically, an arrangement of layers of material to filter particulate material - three layers are shown in the lower part of this drawing - followed by a mass of activated carbon) to be inserted into the filter case 60. The cover 76 is preferably a snap-on cover, as illustrated. The filter cartridge 75 has a soft, thin, impermeable jacket 79 and is a sliding fit into the filter case 60. Normally, the filter cartridge 75 will be provided with a grill 73 which allows air to enter the cartridge. A rubber seal 77 around the perimeter of the grill 73 forms a gas-tight seal between the filter case 60 and the cover 76. Air that has been inhaled through the cartridge enters the inhalation chamber 25 of the respirator via a porous section 78 of the filter jacket 79.

It should be apparent that the filter cartridge 75 is designed to be replaced, quickly, from a supply of unused filter cartridges when the air passing through the cartridge ceases to be adequately filtered (or when the cartridge has been in use for a predetermined safe period of time). The respirator of Figures 17 and 18 may be fitted with a nose shield (similar to the nose shield 65 of the respirator illustrated in Figures 15 and 16).

The compact respirator illustrated in Figures 17 and 18 may be stowed, with or without replacement cartridges, in a small bag or case.

Part of each edge region of the filter case or chamber of the respirator of Figure 18 extends behind the plane of the first wall 23 of the facepiece of the respirator, towards the cheeks of a user of the respirator. In the respirator shown in Figure 19, two filter cartridges 75 are connected directly to respective inhalation tubes of the module of the respirator. These filter cartridges 75 each have a shape such that they extend, generally arcuately and substantially symmetrically, sideways from the facepiece to cover - but not to touch - the cheeks of a user of the respirator. The end of each cartridge 75 that is remote from the facepiece has an air inlet that is closed by a grill (over which a removeable cover may be fitted) and each cartridge is shown to contain - moving inwardly from the air inlet grill - three layers 71 of different particulate filtering material, then a mass of a gas absorbing filter material 70.

The filter cartridges 75 of the Figure 19 embodiment are provided with tethers 63, which are similar to, and are provided for the same purpose as, the tethers 63 of the respirator embodiment illustrated in Figure 14. Figures 20, 21 and 22 depict a person using a "yoke-like" respirator. The yoke- like configuration is the result of attaching two rigid, elongate, curved filter cases 80 to a respirator module having two inhalation inlets. Each filter case 80 is attached to a respective inhalation tube by a concertina hose 81. If the module of the respirator is similar to that shown in Figures 5, 6 and 7, each filter case 80 and its associated concertina hose is constructed with two channels - an upper channel and a lower channel. The upper channel is connected to an inhalation tube 26 of the respirator; the lower channel is connected to an exhalation tube 46. This arrangement is illlustrated in Figure 20, in which the internal wall dividing the upper (inhalation) channel from the lower (exhalation) channel in the filter case is indicated by the dashed line 82.

If the module of the respirator of Figures 20, 21 and 22 has exhalation tubes 26 arranged in a similar manner to the exhalation tubes of the module shown in Figure 9 or Figure 12, the filter cases 80 and their associated concertina hoses 81 have a single channel construction. Figure 21 shows a respirator with a module having exhalation outlets 46A of the type shown in Figure 9, with exhaled air directed to the cheeks of the user of the respirator, and with a single air intake channel defined by each filter case 80 and its associated concertina hose 81.

In the respirator shown in Figure 20, the upper (the air intake) channel of the filter case has an air intake grill 83 at the end of the filter case which is most remote from the inhalation inlet of the respirator module. Filter material, appropriate to remove the expected contaminant, is contained in a replaceable filter cartridge within this upper (air intake) channel. The lower channel of the filter case has vents 84 through which exhaled air is vented to the ambient atmosphere. The vents 84 are absent from the filter case of the embodiment illustrated in Figure 21 , as air is exhaled to the user's cheeks. Preferably, the dimensions of the filter cases 80 are such that the filter cases 80 touch each other behind the neck of a user of the respirator. At their contact point or zone, the filter cases 80 are held, detachably, in contact with each other, preferably by using pads 8OA of "Velcro" (trade mark) material which are attached to the rearmost region of each of the filter cases 80. This arrangement allows the respirator to be donned and removed conveniently, without the need to remove or adjust any other safety gear that the user may be wearing.

The filter cases 80 fit snugly around the neck of a user of the respirator, without touching the user's neck, cheeks, face or chin, irrespective of the size or capacity of the filter cases. They are supported comfortably on two small contact zones 82 A only. These zones 82 A are on the trapezius muscles to either side of the user's neck. Because the filter cases slide smoothly on the small support zones 82A, they allow the user full head movement.

Figure 22 is a plan view, from above, of a yoke-like respirator, with filter cases 80, in use. The positions that would be occupied by a higher capacity filter case, and by a very high capacity filter case, are shown by dashed lines 8OA and 8OB, respectively. The respirator illustrated in Figure 22 differs in some ways from the respirator illustrated by Figures 20 and 21, in that each filter case 80 has an ambient air intake 92, covered by a grill. The grill may be closed, to prevent ambient air entering the air intake 92, by a seal 92 A, when the respirator is to be used with air from a remote source, supplied to the filter case 80 via an air line or hose.

Figure 23 illustrates three ways in which a yoke-like respirator may be used with a remote air supply.

Figure 23 (a) depicts a back view of a user of a yoke-type respirator which is similar to the respirator of Figure 20, having vents 84 for exhaled air. However, in the embodiment shown in Figure 23 (a)

(a) there may be, or there may not be, a filter cartridge in the filter case 80, and

(b) each of the two outlets of the bifurcated upper end of an air supply hose 86 is connected directly to, respectively, one of the two filter cases 80

(there being no ambient air intake grill 83).

Thus each filter case 80 is supplied with remote air via the air supply hose 86. The other end (the lower end) of the air supply hose 86 is connected to a U-tube connector 91 , in which an emergency back-up filter 87 is located. The back-up filter 87 is normally sealed by an external, removeable, air-tight seal (similar to the seal 92 A of the respirator shown in Figure 22). Conveniently, as also shown in Figures 23(b) and 23(c), the U-tube connector 91 can be attached to the waist belt 90 of a user of the respirator.

The input to the U-tube connector 91 is an air supply hose 85 that is connected, via a further hose 85 A, to a remote source of clean air. Clean, remote air may be supplied to the respirator via the hoses 85 A and 85, the U-tube 91 and the bifurcated hose 86, a) at ambient atmospheric pressure, by being drawn into the respirator by the user's natural breathing; or b) under pressure (that is, at a pressure greater than ambient atmospheric pressure) by being pumped, if the air supply hose 85A is too long to allow the user to breathe naturally.

The emergency back-up filter 87 is included to enable me user of the respirator to "self-rescue" should the supply of clean air through the hose 85 A fail or become contaminated by accident. In this event, the user disconnects the hose 85A from the hose 85 and seals hose 85 with the cap 89) to prevent the ingress into the respirator of contaminated ambient air from the immediate workplace environment of the user. The user quickly removes the air-tight seal which normally closes the emergency back-up filter's air intake grill 92 and escapes the contaminated area, breathing ambient air through the newly-exposed air intake grill 92 of the back-up filter 87, which contains filtering materials that are appropriate for the known contaminants present.

Figure 23 (b) depicts a user of a yoke-like respirator of the type shown in Figure 22, with a supplied air arrangement similar to that illustrated in Figure 23 (a). The Figure 23 (b) realisation has the emergency back-up filter present in the filter cartridges in the filter cases 80, and not attached to the U-tube 91 (which has become simply a connection between the air supply hoses 85 and 86). Each filter case 80 is divided longitudinally into two channels which are separated by a gas-tight wall. The upper channel contains a filter cartridge having an ambient air intake grill 92 that, in normal use, is sealed by a removeable seal (similar to the seal 92A of the respirator shown in Figure 22). The lower channel is an unemcumbered passageway that, in normal use, conducts the air supplied by the air supply hose 86 to the mouthpiece module of the respirator. If the remote air supply to the respirator should fail, or should become accidentally contaminated, the user of the respirator will follow the self-rescue procedure described above with reference to Figure 23(a).

Other ways in which a respirator having a yoke-like filter may be used are shown in Figure 24. In Figure 24(a), the yoke-like filter cases 80 have two channels in them, with one channel containing filter material, and the other channel containing exhaled air which is vented to the ambient atmosphere through exhaled air vents

84. Air is supplied by a source of compressed air (not shown in the drawings), through an air supply line 93, a regulator 94 and an air supply hose 86 (which is bifurcated a short distance below the inputs to the filter cases 80). Each branch of the bifurcated portion of the air supply hose 86 is connected to a respective input to a filter case 80. The filter material in the filter cases 80 (a) ensures that the air from the compressed air source is actively purified and screened of contaminants, and (b) acts as an emergency back-up filter if the compressed air source ceases to supply air to the regulator 94. In normal operation, the air intake grills 92 of the filter cases 80 are sealed by air-tight seals 92A which the user of the respirator quickly removes should an emergency self-resue become necessary.

A modified form of the respirator shown in Figure 24(a) is illustrated in Figure 24(b). A belt-mounted filter 97 ensures that air from a compressed air source connected to a regulator 94 is cleaned of contamination before being supplied through a bifurcated air supply hose 86 to the air inlets of the filter cases 80 of a yoke-like respirator. Each filter case 80

(1) contains filter material in a filter cartridge in a filter channel mat (a) is connected to the inhalation chamber of the respirator, and (b) has air intakes 92 covered by a grill that, in normal use, is sealed by an air-tight seal; and

(2) has an exhaled air channel which terminates in the exhaled air vents 84. When air from the source of compressed air fails (by accident), the seals covering the grills are removed so that ambient air may be inhaled through the air intakes 92 at the ends of the filter channels.

Belt mounted filters of this type can be ergonomically shaped and positioned on the waste belt 90 to provide comfortable lumbar support to a user of the respirator who needs to sit at work for extended periods of time.

Illustrated in Figure 24(c) is a very high capacity respirator which may be used (a) as a negative pressure device, operated by the user's natural breathing at ambient atmospheric pressure, or (b) as a supplied air device when a compressed air line 93 is attached to an air inlet 98 via a regulator 94. In the "supplied air" operating mode, an ambient air intake 96 of a belt filter 97 is normally sealed by an air-tight seal which is removed by the user if the air supply should fail and self-rescue becomes necessary. The respirator shown in Figure 24(c) has a gas filter cartridge in the air input channel of each filter case 80, and an exhaled air channel which terminates in exhaled air vents 84. The air input to the filter cases 80 is exclusively through the bifurcated air supply hose 86. The lower end of this air supply hose 86 is connected to the outlet of a particulate filter 97, worn on the belt 90 of the user of the respirator. When used as a negative pressure device, air is inhaled through a grill 96 on the base of the filter 97.

Protective fabric hoods may be worn with yoke-like respirators similar to those shown in Figures 20, 21 and 22. The material of which the hood is constructed will vary according to the nature of the contaminant present - or potentially present - in the ambient atmosphere.

In Figure 22, the attachment of a fabric hood 100 to the filter cases 80 is indicated. Such a hood will envelop the head of the user of the respirator and the respirator itself. When the respirator is the respirator illustrated in Figure 22, the air intakes 92 are positioned outside the fabric of the hood 100. The hood fabric may be attached to each filter case 80 in a gas-tight manner, around the periphery of the air intake, with a fold IOOA at the point where the two filter cases 80 are connected to each other by the pads 8OA of Velcro material. The fold IOOA allows the filter cases to be separated for donning and doffing the hooded respirator. Ambient air enters the filter cases through the air intakes 92. Exhaled air, instead of being vented past the cheeks of the user, is vented either

(1) to the front of the mouthpiece of the module of the respirator, through an exhalation outlet (a) that is positioned outside the hood, but (b) to the periphery of which the hood is attached in a gas-tight manner; or (2) to the rear of the user's head via exhalation channels in the filter cases 80. With each of these arrangements, exhaled air is not vented into the interior of the hood. To maintain this situation, the user's nostrils must be occluded. (Figure 22 shows a user with a nose clip 49 closing the nares of the user, and preventing both inhalation and exhalation through the user's nostrils.)

In general, hooded respirators may be used with a reasonable degree of comfort for a relatively short time, especially in warm conditions. Embodiments of the respirators of the present invention have hoods which are pressurised by supplied air and thus provide more comfortable protection during extended periods of routine work. Such respirators are illustrated in Figures 25 and 26.

Figure 25 comprises back views of three persons using supplied air respirators having a pressurised protective hood attached to the respirator in a gas_τtight manner. To understand the way in which these hoods operate, it will be helpful to consider, first, the hooded respirator shown Figure 26.

Figure 26 is a side view of a person wearing a protective hood 100 that is being held away from the head and face of the person by a positive air pressure (that is, an air pressure that is greater than the air pressure outside the hood). This positive pressure differential is maintained for the entire time that a supplied air source is connected to, and passes air through, an air supply hose or line 86 (Figure 26 shows a bifurcated air supply hose 86). The bifurcated upper ends of the hose 86 enter the hood by passing beneath the lower edge of the the hood's cowl, between the wearer's back and neck. These ends are connected, respectively,, to the underside of each filter case 80 of the yoke-like respirator via a supplied air inlet 98 A.

Each filter case 80 is divided longitudinally by an air-tight wall 82 which separates the two channels thus formed into

(a) a filter housing channel 82B (the upper channel), and (b) a perforated supplied air distribution channel 82C (the lower channel). A cartridge containing the appropriate emergency back-up filter material is included in the upper channel 82B, which has ambient air inlets, that are covered by a grill 92, at its end that is remote from the mouthpiece of the respirator. In normal use, each grill 92 is sealed so that ambient air cannot enter the channel 82B. The outer wall only of the lower channel 82C is perforated, and the perforations are such that they direct supplied air into the hood 100, but away from the wearer's head, face, throat and neck. The channel 82C terminates at its junction with the respirator's concertina hose 81 so that supplied air does not enter the mouthpiece of the respirator module.

This arrangement, in normal use, holds the hood away from the wearer's head without allowing jets of air to play directly onto the wearer's skin. Thus the hooded respirator shown in Figure 26 will touch the wearer at two small zones 82 A only, on the wearer's trapezius muscles.

Exhaled (and, therefore, warm) air is carried along with excess pressurised air and is vented continuously to the exterior of the hood 100 through an array of one-way exhaust valves 106 that are mounted in a capped exhalation port 105 positioned above the visor 103 of the hood. Another valve-containing, capped, exhalation outlet 108 is positioned directly in front of the wearer's mouth.

The region of the fabric of the hood 100 that is in front of the user's nose and eyes is replaced by a transparent visor 103 which, preferably, is made as two transparent layers in the manner of "double glazing" . This construction assists in keeping the visor mist free, even after conventional anti-fogging liquids - if applied to the visor - have ceased to be effective. The double glazing construction may be effected by fusing the two transparent layers together at their peripheries, thus trapping dry air, or another gas, between these layers. A gap of from 10mm to

12mm, between the two transparent layers, will ensure that the visor region of the hood is also a heat-insulated region.

The fabric of the hood may be a very light, fine, single layer of gauze-like material, or it may comprise multiple layers of a heavy, coated fabric. The choice of hood fabric will depend on the nature of the contaminant that is likely to be present in the environment in which the hood will be used.

Reverting now to Figure 25, Figure 25 (a) depicts a respirator to which, in normal use, clean, purified air is supplied by a bifurcated air supply line 86 from a source of previously filtered compressed air, through a regulator 94 that is carried on the waist belt 90 of the user of the respirator. The two branches of the air supply line 86 are connected to respective air inputs of the two filter cases 80 of the yoke-like respirator.

The yoke-like respirator of Figure 25(b) is similar to the respirator shown in Figure 25(a), but a filter 97 is also mounted on the waist belt 90 of the user of the respirator. Air from the regulator 94 is supplied to the filter 97 through a connector 98. This air supply arrangement ensures that any contamination in the air from the compressed air source is removed before the air enters the air supply line 86, the upper bifurcated lines of which are connected to respective filter cases 80. The operation of this respirator embodiment is similar to that described above, including the self-rescue procedure.

The air supply to the respirator shown, in use, in Figure 25(c) is ambient air that is sucked through the air input grill 96 at the base of a belt-mounted filter 97. A motor-driven fan in a housing 95 sucks in the ambient air and blows it through the filter 97 and into the bifurcated air supply hose 86. The air supply hose 86 feeds the air from the filter 97 into the filter cases 80 of a yoke-like respirator. The operation of this respirator embodiment is also similar to that described above, including the self-rescue procedure.

The respirator and hood combination of Figures 27 and 28 is designed for escaping from a location where the ambient atmosphere has become contaminated (for example, the inside of a burning building, a disaster site, or the site of a chemical spill). The respirator in Figures 27 and 28 is the respirator illustrated in Figure 22, with very high capacity filter cases 80. The edges of the filter cases 8OB which are adjacent to the air intakes 92 may be attached to the outer layer of the hood in a gas-tight manner. The inside of the hood may be dried to minimise misting of the visor. In the illustrated embodiment, the drying is effected by a dessicant - for example, silica gel - which is held hi a permeable sleeve 103 A which is detachably mounted aound the edge of the visor 103, which may be double glazed. To seal the hood around the neck of its wearer, a draw string 107, which is covered by a soft, sponge-like draw string sleeve 110, is tightened around the user's neck to exclude contaminants in the ambient air.

An exhalation port 111 may be gripped easily to effect rapid removal of the respirator's mouth-bit module from the user's mouth, to allow the user to speak. The coiled lanyard 112 of the nose clip 113 allows the mouthpiece to be removed without dislodging the nose clip. An occlusive nostril plug, of the type described earlier in this specification, may be attached to a similar coiled lanyard and be used instead of a nose clip.

The hood 100 has an outer protective layer 101, appropriate for the expected hazard (for example, a fire or "smoke" hood may have a heat-reflecting, fire-resistant foil outer layer 101), and an inner lining layer 109 of a soft fabric. If necessary, heat insulation may be provided by including a layer of an insulating material 108 between the hood's outer protective layer 101 and the soft fabric liner 109. A soft sponge pad 102 at the top-most region of the hood prevents the hood lining layer from touching the head of a user of the respirator.

The various illustrated embodiments of the present invention provide a high standard of respiratory protection, wearer comfort and convenience, thereby avoiding all aspects of known user-resistance to respirators. The fit of the respirators and their efficacy are unaffected by facial hair. By selecting from the optional features described above, a respirator constructed in accordance with the present invention 1) can be used with nasal breathing (a) restricted - with novel nostril plugs - to exhalation only, or (b) totally restricted by the use of a nose clip; 2) can be made with no "bad" or "dead" air space due to exhaled air being retained in the respirator in a region from where it could be inhaled;

3) can allow a user to detect depletion of a gas filter material;

4) will present little, or no, impediment to a user's vision;

5) can be used without touching the user's chin, cheeks, head, neck or throat; 6) has the option of use with disposable, replaceable or re-fillable filters; and

7) requires no supporting strap, buckle or head harness.

This list of benefits is not exhaustive.

Engineers and other persons skilled in this field will appreciate that variations to and modifications of the modules and personal respiratory protective systems illustrated in the accompanying drawings and described above may be made without departing from the present inventive concept. Examples of a number of such variations and modifications are included in the specification of my Australian provisional patent application No. 2008902988, and are incorporated into this specification by this reference thereto.

Claims

Claims:

1. A clean air receiving module for a personal respirator, said module comprising a mouthpiece and a facepiece; characterised in that: a) the mouthpiece comprises 1) a substantially vertical, but flexible, flange member having a shape and dimensions which enable the flange member to be positioned in the mouth and between the teeth and the lips of a user of said respirator; said flange member having an aperture in the central region thereof; 2) a bite piece extending inwardly from the flange member; and

3) a lips receiving member; said lips receiving member extending outwardly from the flange member and having (i) an upper surface region which has the shape of an elongate, curved, generally horizontal trough, which is transversely substantially arcuate in shape, so that the upper lip of a user of the respiratory system can be positioned in contact with said upper surface of said lips receiving member when the respirator is in use; and (ii) a lower surface region which has the shape of an elongate, curved, generally horizontal, downwardly facing trough, which is transversely substantially arcuate in shape, so that the lower lip of a user of the respiratory system can be positioned in contact with said lower surface when the respirator is in use; b) a breathing passageway extends outwardly from said aperture in said flange member, between said upper and lower surface regions of said lips receiving member; c) said facepiece comprises an inhalation chamber from which clean air is passed into said breathing passageway when a user of the respirator inhales; said inhalation chamber having a first wall member with at least one aperture therein; said first wall member being positioned at the outer end of said breathing passageway with said, or each, aperture in said wall member being surrounded by the outer end of said breathing passageway; a gas-tight seal being established between the outer end of said breathing passageway and said first wall member; d) said inhalation chamber has at least one inhalation inlet that is connectable to a supply of clean air; and e) said facepiece includes at least one one-way inhalation valve; said, or each, one-way inhalation valve being biased closed but opening when the air pressure within said breathing passageway is lower than the air pressure immediately outside said, or each, inhalation inlet, thereby permitting air from said inhalation chamber to enter said breathing passageway and pass through said breathing passageway and through said aperture in said flange plate, to enter the mouth of said user of the respirator; said, or each, one-way inhalation valve being closed when the air pressure within said breathing passageway is equal to or greater than the air pressure immediately outside said, or each, inhalation inlet.

2. A clean air receiving module for a personal respiratory system as defined in claim 1 , in which there is one aperture in said first wall member and said inhalation chamber has a single inhalation valve; said inhalation valve being positioned within said aperture in said first wall member; whereby, when said inhalation valve is closed, air in said breathing passageway is isolated from air in said inhalation chamber.

3. A clean air receiving module for a personal respiratory system as defined in claim 1, in which there are a plurality of apertures in said first wall member and said inhalation chamber has an equal plurality of inhalation valves; said plurality of inhalation valves being positioned within respective apertures in said first wall member; whereby, when said inhalation valves are closed, air in said breathing passageway is isolated from air in said inhalation chamber.

4. A module as defined in claim 1, in which

1) an inhalation tube extends outwardly from said, or each, inhalation inlet;

2) an inhalation valve plate is located within, or at either end of, said, or each, inhalation valve tube; 3) said, or each, inhalation valve plate extends across its associated inhalation tube;

4) said, or each, inhalation valve plate has at least one aperture therein; and

5) said, or each, aperture in said, or each, inhalation valve plate is closed by (a) said inhalation valve or by a respective one of said inhalation valves; or (b) a respective additional one-way inhalation valve.

5. A module as defined in claim 1 , in which said inhalation chamber is divided into two inhalation sub-chambers by an internal wall, said internal wall having at least one aperture therein; said, or each, aperture in said internal wall being closed by said inhalation valve or by a respective one of said inhalation valves.

6. A module as defined in claim 2, claim 3 or claim 4, in which said inhalation chamber is divided into two inhalation sub-chambers by an internal wall, said internal wall having at least one aperture therein; said, or each, aperture in said internal wall being closed by a respective further inhalation valve.

7. A module as defined in claim 1, claim 2, claim 3 or claim 5, in which a filter container is attached to said or each inhalation inlet.

8. A module as defined in claim 7, in which said filter container extends, generally arcuately and substantially symmetrically, from in front of said facepiece past the cheeks of a user of said module.

9. A module as defined in claim 4 or claim 6, in which a filter container is attached to said or each inhalation tube.

10. A module as defined in claim 7, claim 8 or claim 9, including filter material within said or each filter container.

11. A module as defined in claim 7, claim 8 or claim 9, including a filter cartridge, or a respective filter cartridge, within said or each filter container, said or each filter cartridge containing filter material.

12. A module as defined in claim 10 or claim 11, in which said filter material is selected from the group consisting of: a) at least one particulate filtering material; b) a gas-absorbing filter material; and c) at least one particulate filtering material and a gas-absorbing filter material.

13. A module as defined in claim 10, claim 11 or claim 12, in which said filter material has absorbed a quantity of an indicator chemical that (a) sublimes at ambient temperature and air pressure; and (b) has a bitter, burning or irritating nature when inhaled.

14. A module as defined in any preceding claim, in which

(a) said, or each, inhalation valve is a flap valve, and

(b) said or each aperture that is closed by said, or by a respective, inhalation valve has at least one associated strut that extends across that aperture, to prevent flexing of the flap of the associated flap valve when said, or said respective, inhalation valve is closed.

15. A module as defined in any preceding claim, in which said bite piece comprises first and second bite piece members; each bite piece member extends inwardly from a respective edge region of said flange member; and respective palate flaps extend from the edge regions of each bite piece member which are remote from said flange member.

16. A module as defined in claim 15, in which said flange member, said bite piece members and said palate flaps are formed integrally.

17. A module as defined in any preceding claim, in which said breathing passageway is defined by a tubular member positioned within said lips receiving member.

18. A respirator comprising a module as defined in any preceding claim and two nostril plugs; characterised in that a) each nostril plug comprises a rigid cylinder, open at each end, having a wall of essentially circular cross-section; said wall of said cylinder being covered with a soft, deformable but resilient material; at least one radially extending ridge being formed in said resilient material; said cylinder having a diameter such that said cylinder with its resilient material cover is insertable into a nostril of a person, but such insertion deforms said at least one ridge, whereby said at least one ridge forms a gas-tight seal with the skin of the inside of said nostril; and b) one end of said cylinder is closed by a one-way nostril flap valve that is biased closed, but when the air pressure inside said cylinder exceeds the ambient air pressure, said one-way nostril flap valve opens.

19. A respirator comprising a module as defined by any one of claims 1 to 17, in which said facepiece includes an exhalation chamber; characterised in that

(1) said exhalation chamber has a second wall member that (a) is positioned at the outer end of the breathing passageway, and (b) contains at least one second aperture therein;

(2) said exhalation chamber has at least one exhalation outlet;

(3) said exhalation chamber has at least one one-way exhalation valve; said or each exhalation valve being biased closed when the air pressure outside the, or each, exhalation outlet is equal to or greater than the air pressure inside the exhalation chamber, but the, or each, one-way exhalation valve opens when the air pressure inside said breathing passageway exceeds the air pressure outside said, or each, exhalation outlet.

20. A respirator as defined in claim 19, hi which there is one aperture in said second wall member and said exhalation chamber has a single exhalation valve; said exhalation valve being positioned within said aperture in said second wall member; whereby, when said exhalation valve is closed, air in said breathing passageway is isolated from air in said exhalation chamber.

21. A respirator as defined in claim 20, in which there are a plurality of apertures in said second wall member and said exhalation chamber has an equal plurality of exhalation valves; said plurality of exhalation valves being positioned within respective apertures in said second wall member; whereby, when said exhalation valves are closed, air in said breathing passageway is isolated from air in said exhalation chamber.

22. A respirator as defined in claim 19, in which 1) an exhalation tube extends outwardly from said, or each, exhalation outlet;

2) an exhalation valve plate is located within, or at either end of, said, or each, exhalation valve tube;

3) said, or each, exhalation valve plate extends across its associated exhalation tube;

4) said, or each, exhalation valve plate has at least one aperture therein; and

5) said, or each, aperture in said, or each, exhalation valve plate is closed by (a) said exhalation valve or by a respective one of said exhalation valves; or (b) a respective additional one-way exhalation valve.

23. A respirator as defined in claim 19, in which said exhalation chamber is divided into two exhalation sub-chambers by an exhalation internal wall, said exhalation internal wall having at least one aperture therein; said, or each, aperture in said exhalation internal wall being closed by said exhalation valve or by a respective one of said exhalation valves.

24. A respirator as defined in claim 20, claim 21 or claim 22, in which said exhalation chamber is divided into two exhalation sub-chambers by an exhalation internal wall, said exhalation internal wall having at least one aperture therein; said, or each, aperture in said exhalation internal wall being closed by said exhalation valve or by a respective further exhalation valve.

25. A respirator as defined in any one of claims 19 to 24, in which said exhalation chamber has two exhalation outlets positioned to direct exhaled air to wards the cheeks of a user of said respirator.

26. A respirator as defined in any one of claims 19 to 25, in which said exhalation chamber has an exhalation outlet which, (a) when said respirator is in use, is positioned substantially in front of the mouth of a user of the respirator; and (b) is covered by an external cap that directs exhaled air to the side of and below said external cap.

27. A respirator as defined in any one of claims 19 to 26, in which said inhalation chamber is positioned directly above said exhalation chamber, and a third wall of said facepiece comprises the lower wall of said inhalation chamber and the upper wall of said exhalation chamber.

28. A respirator as defined in any one of claims 19 to 27 when appended directly or indirectly to claim 9, in which said inhalation chamber has two inhalation tubes positioned one on each side of said inhalation chamber, further characterised in that: a) a respective filter container is attached to each inhalation tube; and b) each filter container comprises an arcuate box-like filter case which extends from its associated inhalation inlet past a respective cheek of a user of said respirator.

29. A respirator as defined in claim 28, in which each filter case contains filter material and apertures in each filter case provide air inlets through which air enters when a user of said respirator inhales.

30. A respirator as defined by claim 28, in which a) each filter case is connected to its associated inhalation tube by a concertina hose; and b) each filter case comprises an air intake channel with at least one air inlet aperture at the end of said channel that is remote from said facepiece.

31. A respirator as defined by claim 30, in which each filter case includes an exhaled air outlet channel that is connected to a respective exhalation outlet of said respirator, each exhaled air outlet channel having at least one vent at the end thereof that is remote from said facepiece.

32. A respirator as defined by claim 30 or claim 31, including an air supply line or hose connectable to a remote source of air; said air supply line or hose being bifurcated to provide a respective air inlet to each of said air intake channels independently of said air inlet apertures.

33. A respirator as defined in claim 32, in which said remote source of air supplies air to an air filter to which said air supply line or hose is connected, prior to its bifurcation.

34. A respirator as defined in claim 33, in which said air filter to which said air supply line or hose is connected, prior to its bifurcation, is an air filter adapted to be supported on a belt around the waist of a user of said respirator.

35. A respirator as defined by claim 33 or claim 34, in which each filter case includes filter material through which air, inhaled through said at least one air inlet aperture at the end of said air intake channel that is remote from said facepiece, passes.

36. A respirator as defined by any one of claims 28 to 35, including means to connect together the ends of said filter cases that are remote from said facepiece.

37. A respirator as defined by any one of claims 28 to 36, including a hood to cover the head of a user of said respirator and said respirator.

38. A respirator as defined by claim 37, in which said hood has an outer layer which covers the head and at least part of the shoulders of a user of said respirator, an inner soft fabric layer, and a transparent visor set into said inner and outer layers.

39. A respirator as defined in claim 38, in which said hood includes insulating material between said inner and outer layers; said visor is constructed as two transparent layers; and a drawstring is attached to a neck-encircling portion of said hood.

40. A respirator as defined by claim 37, in which said hood has a) an outer layer which covers the head and at least part of the shoulders of a user of said respirator, b) an inner soft fabric layer, c) a transparent visor set into said inner and outer layers, and d) at least one air vent in said hood, above said visor.

41. A respirator as defined in any one of claims 18 to 40, including a nose clip attached to said facepiece.

42. A respirator as defined in claim 41, in which said nose clip is attached to said facepiece by a coiled lanyard.

43. A module for a personal respiratory system as defined in claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

44. A respirator as defined in claim 18, substantially as hereinbefore described with reference to the accompanying drawings.

45. A nostril plug comprising a rigid cylinder, open at each end, having a wall of essentially circular cross-section; said wall being covered with a soft, deformable but resilient material; at least one radially extending ridge being formed in said resilient material; said cylinder having a diameter such that said cylinder with its resilient material cover is insertable into a nostril of a person, but such insertion deforms said at least one ridge, whereby said at least one ridge forms a gas-tight seal with the skin of the inside of said nostril; one end of said cylinder being closed by a one-way nostril flap valve that is biased closed, but when the air pressure inside said cylinder exceeds the ambient air pressure, said one-way nostril flap valve opens.

46. A nostril plug as defined hi claim 45, substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.