HK1079470A - Respirator - Google Patents

Description

Breathing apparatus

Technical Field

The present invention relates to the field of respirators (respirators), and in particular, but not exclusively, to respirators for the protection against toxic chemical and biological agents.

Background

Respirators were first developed in response to the use of chemical warfare agents in world war ii. Almost all respirators share several common features: the seal is adapted to form a seal against the face, thereby providing a cavity into which air is drawn through the filter, which removes toxic substances from the drawn air. The seal prevents ambient, possibly foul, air from entering the cavity and hence the lungs of the wearer. Air is drawn into the cavity by the negative pressure created by the wearer inhaling, or by using positive pressure applied, for example, by a pump. Respirators also typically include some sort of eyepiece.

US 4574799 and GB 1587812 describe a respirator comprising an oronasal mask and an external face sealing mask, wherein in use the oronasal mask forms a seal around the oronasal region of the wearer's face and defines a cavity between itself and the external mask such that there is substantially no pressure differential between the ambient atmosphere and the cavity between the oronasal mask and the external mask which would allow ambient air to enter the cavity formed between the external mask seal and the face, and which also compensates for the pressure drop during inhalation which could result in the ingress of unwanted material through the broken seal.

WO02/11816 discloses a double cavity respirator similar to that described in US 4574799 and GB 1587812. The respirator of WO02/11816 further comprises an eye flap in gaseous communication with the oronasal mask. The eye shield protects the eyes from possible damage caused by foul air entering the cavity between the external mask and the oronasal mask. However, this respirator has several problems. It is difficult to contain the seals of the eye and oronasal masks within a relatively small area defined by the size of the wearer's face, and respirators so constructed are relatively complex and expensive. Moreover, it is difficult to form a seal on the eye mask that is suitable for all users due to the large variation in head and face shape.

The respirator of the present invention seeks to overcome some or all of these problems.

Disclosure of Invention

Accordingly, in a first aspect of the present invention there is provided a respirator comprising: a respirator mask; a first sealing arrangement adapted to form a seal against a user's face so as to define a first cavity between the first sealing arrangement, a respirator mask and a user's face region (including eyes, mouth and nose); a second sealing means adapted to form a seal against the face of the user so as to define a second cavity formed between a portion of the face of the user, the second sealing means, the first sealing means and optionally the respirator mask; a respirator air inlet for introducing inhaled air into the first cavity; a respirator air outlet for directing exhaled air from the first cavity; and air pressure supply means adapted to supply pressurised air to the second cavity such that, in normal operation, air is only inhaled and exhaled through the first cavity, so that there is substantially no air pressure differential between the ambient atmosphere and the second cavity which would allow ambient air to enter the second cavity.

In use, the respirator provides a positive pressure in the cavity between the breathing cavity and the surrounding atmosphere, so that when the second sealing means fails, the positive pressure in the outer cavity will force air out of the point of failure of the seal, thereby reducing the likelihood of contaminants entering the respirator.

The first and second sealing means may comprise discrete components separated from one another. However, it is preferable that they share a common portion.

Accordingly, in a second aspect of the present invention there is provided a seal for a respirator, the seal comprising first and second parts each comprising a substantially compliant material and each having a respective sealing surface adapted to engage with the face of a user, the first and second parts being interconnected by a third part adapted to be mounted on a surface of a respirator, the seal further comprising a gas inlet for allowing pressurised gas to be supplied to the cavity in use, and wherein the first and second parts are shaped such that, in use, the application of positive pressure in the cavity does not disrupt the seal.

The sealing means or seal may be adapted to increase the sealing contact under the influence of the air pressure supply. For example, the first and/or second sealing means or portions may comprise a retro-reflective seal (reverse flex seal). In particular, the first and/or second sealing means or portions may have a J or U-shaped cross-section.

Alternatively or additionally, the first and/or second sealing means or portions may be associated with or include respective air bladders inflatable by air pressure supply, which urge the sealing surfaces into contact with the face. It will be appreciated that the bladder will be located at, adjacent to or integral with the non-contact surface of the sealing means.

In a particularly preferred embodiment, the second sealing means or portion comprises or is associated with a balloon.

It will be appreciated that the seal of the second aspect may be used in a respirator of the first aspect of the invention.

Preferably, the respirator further comprises at least one eyepiece and means for directing inhaled air over the at least one eyepiece. The inhaled air helps to demist the eyepiece and/or prevent fogging. The means for directing the inhaled air over the at least one eyepiece may also direct some of the inhaled air directly to the oronasal region of the user. One such device includes a baffle.

The respirator may further comprise an exhaust deflection device capable of preventing exhaled air from contacting the at least one eyepiece. The exhaled air is relatively warm and, if not prevented, will rise to the eyepiece when the user's head is in an upright position. Exhaled air may contain moisture and may mist the eyepiece. Thus, the exhaust deflection means is beneficial to the user.

The exhaust deflection means may comprise a third sealing means which in use engages the face of the user to form an ocular cavity and an oronasal cavity, the third sealing means being provided with means for allowing gas to flow from the oronasal cavity to the ocular cavity. The means for allowing gas to flow from the oronasal cavity to the ocular cavity may take the form of a diffuser, and/or simply a channel in the third sealing means. The third sealing means should be arranged to allow air flow from the ocular cavity to the oronasal cavity.

It will be appreciated that the first and second air inlets may advantageously share a common filter connection and filter.

Accordingly, in a third aspect, the present invention provides a respirator comprising: a first sealing means adapted to form a seal on a user's face to form a first cavity, the first cavity containing an oronasal region of the user; a second sealing means adapted to form a seal on a user's face to form a second cavity; an air pressure supply means in gaseous communication with the first air inlet and capable, in use, of supplying gas to the second cavity so as to form a first gas passageway; a second gas inlet in use in gaseous communication with the first cavity so as to form a second gas pathway, the first and second air inlets being located in a common filter connection, wherein the filter connection is connectable to a suitable filter such that, in use, the first and second gas pathways are isolated from one another such that inhalation by a user does not substantially affect the pressure in the first gas pathway.

This configuration provides clean inhaled air and clean air supplied by the air pressure supply means through a respirator connection means without increasing the work done by the air pressure supply means.

In prior art dual cavity respirators, the first sealing means is used to create a first cavity containing the oronasal region of the user, while the sealing means is used to define a second cavity, which is generally the space between the first sealing means, the second sealing means, the face of the user and the respirator body. An air pressure supply (e.g., a bellows or an electric pump) is used to provide pressurized air to the second cavity. This maintains a positive pressure relative to the surrounding atmosphere and, when the second sealing means fails, air is forced out of the second cavity into the surrounding atmosphere, thereby reducing the possibility of ingress of contaminated surrounding atmosphere. The air pressure supply means is arranged to draw air from the clean air drawn into the first cavity as shown in WO 02/11816.

This simple prior art system has the disadvantage that on inhalation the air pressure in the first cavity decreases. The air pressure supply is a constant volume pump that attempts to maintain a constant air flow through the pump. The pressure drop in the first cavity causes the pump to create an air pressure drop at its air inlet, thereby causing the pump to increase its operating efficiency to maintain a constant air flow into the second cavity. This reduces the service life of the pump's battery. Attempts have been made to solve this problem of prior art respirators. For example, the pump is arranged to be active only when the user exhales. However, this does not provide a satisfactory pressure in the second cavity throughout the user's breathing cycle. In an alternative attempt to solve the problems of the prior art, the inlet of the pump is arranged with a separate air intake and filter, separate from the intake air passage. The pump is provided with its own filter. While satisfactory in some respects, this embodiment requires two separate filters and does not satisfactorily address the problems of the prior art.

In a fourth aspect, the present invention also provides a filter for a respirator, the filter comprising an inlet for inhalation of a gas to be filtered, the inlet being in gaseous communication with a plurality of mutually discrete filter regions, each filter region comprising a filter material capable of removing unwanted substances from the gas to be filtered, wherein each filter region is in gaseous communication with an outlet, each outlet being in gaseous communication with only one filter region, the outlets being located in a common respirator connection means.

Preferably, the first filter region is a circular portion and the second filter region is an annular portion, the first filter region fitting snugly with the second filter region.

Preferably, the third and fourth aspects are used in the first and second aspects of the invention.

In any case, the air pressure supply means may be electrically operated. For example, in a preferred embodiment, the filter connection means may comprise a safety interlock device, so that air pressure supply is not possible unless a suitable filter is installed.

Preferably, the safety interlock device comprises an electrical structure. In this way, one or more electrical contacts on the filter connection means may be provided for electrical connection with the air pressure supply means. The filter may also include one or more electrical contacts adapted to electrically connect with contacts of the filter connection means to complete an electrical circuit to enable air pressure supply to the respirator.

When there is no filter, the air pressure supply means maintains the open mode, and therefore, the air pressure supply means cannot be operated. This also prevents the air pressure supply means from operating when an inappropriate filter is fitted to the respirator. The safety interlock may alternatively be mechanical.

The respirator of the present invention may advantageously include an improved valve assembly that provides good protection for the valves of prior art respirators. The improved valve assembly utilizes the teachings of WO02/11816 in that the purge gas flow around the base of the valve assembly reduces the likelihood of ingress of contaminants and/or exhaled air.

Accordingly, in a fifth aspect, the present invention provides a valve assembly comprising: a valve body having a valve assembly outlet and a valve assembly inlet and a valve cavity therebetween; a valve mechanism for allowing gas flow into the valve chamber through the valve assembly inlet and to the valve assembly outlet; a continuous purge outlet means connectable to an air pressure supply means; an air deflecting means spatially arranged in the valve chamber relative to the valve mechanism and the purge outlet means such that, when a suitable air pressure supply means is connected and activated, air is expelled from the purge outlet means and incident on the air deflecting means such that the air curtain can be substantially maintained above the valve mechanism.

The valve assembly in this aspect of the invention embodies the prior art concept by including a purge outlet means connectable to an air pressure supply means and an air deflector means providing a curtain of air over the valve mechanism. The air deflecting means prevents the air from mixing in the vicinity of the valve mechanism and thus causing potentially harmful turbulence.

For the avoidance of doubt, it is specified herein that the air pressure supply means is not part of the valve assembly; the purge outlet can only be connected to the air pressure supply. Also, the term "air curtain" as used herein refers to a substantially unidirectional flow that is generated at any given point in the flow path as long as the air pressure supply means is operating.

Preferably, the purge outlet is located remote from the valve mechanism such that, in use, the pressure experienced in the valve cavity in close proximity to the valve mechanism does not cause the valve mechanism to allow air to flow from the valve cavity through the valve inlet to the interior of the respirator.

Preferably, the interior of the valve body is provided with a cylindrical bore and the valve assembly inlet is located at or near one end of the bore. For the cylindrical bore, the purge outlet means conveniently comprises an annular outlet around the circumference of the bore. If the purge outlet means is annular, it is also preferred that the air deflection means comprises a hollow or solid cylinder.

The purge outlet may be in gaseous communication with the manifold. Preferably, the manifold has a volume large enough to assist in maintaining a curtain of air over the valve mechanism.

The valve assembly may be provided with a plurality of outlet conduits, each outlet conduit providing a tortuous outlet passage to the valve assembly outlet. The cross-section of the gas passage defined by each conduit decreases closer to the valve assembly outlet. This accelerates the gas exiting the outlet. It is also preferred that the valve assembly includes anti-swirl vanes that reduce the cyclonic motion of any air that may enter the valve assembly. The anti-swirl vanes preferably project substantially radially from the air deflection means.

The valve assembly may be used in a respirator according to or incorporating any aspect of the present invention. It will of course be appreciated that it may be used in any respirator, although means for supplying pressurised air must also be provided.

Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows front and rear views of a respirator according to a first aspect of the invention;

FIG. 2 shows a perspective view of a portion of the seal of FIG. 1, showing a second aspect of the invention;

FIG. 3 shows a schematic view of how the seal of the present invention is configured relative to a respirator;

FIG. 4 shows a cross-sectional view of a valve assembly according to a fifth aspect of the invention;

FIG. 5 shows a schematic view of the components of the valve assembly of FIG. 4; and

fig. 6 shows a schematic block diagram of a respirator that represents the first, third and fourth aspects of the present invention.

Detailed Description

Referring now to fig. 1, a respirator according to a first aspect of the invention comprises a face mask 1, eyepieces 2a and 2b, an air outlet 3, an air inlet 4, a first seal 7, a second seal 6, an exhaust deflection means 8, mounting lugs 9, 10, an air guide 11, an air pressure supply means (not shown) and a diffuser 12.

In use, the respirator is placed on the face of a user. The first seal 7 forms a seal on the face around the part of the face that includes the eyes, nose and mouth, so that a first cavity is formed between the first seal 7, the face mask 1 of the respirator and the face of the user. The second seal 6 forms an outer seal around the first seal 7, thereby forming a second cavity defined by the first and second seals and a portion of the user's face. The air pressure supply means supplies pressurized air to the second cavity.

Air is inhaled and exhaled only through the air inlet 3 and the air outlet 4 in the first cavity, so that substantially no air pressure difference is created between the ambient atmosphere and the second cavity, which air pressure difference will cause ambient air to enter the second cavity.

The eyepieces 2a and 2b are made of transparent material and are arranged in suitably sized cavities in the face mask 1 so as to allow the wearer to see outside the respirator when it is in use. The eyepieces may be separate, as shown in fig. 1, or may be formed as a single piece. The eyepieces 2a, 2b are sealed within the mask 1 to prevent ambient gas from entering the interior of the respirator through the junction between the eyepieces 2a, 2b and the mask 1.

The exhaust deflection means 8 reduces the likelihood of warm, moist exhaled air coming into contact with the eyepieces 2a, 2 b. In this embodiment, the exhaust deflection means takes the form of a bar or strip of substantially compliant material that, in use, fits across the bridge of the nose and cheekbones of the user to substantially isolate the oronasal region of the user from the ocular region. The bar or strip is formed on the back of a substantially rigid skirt (not shown) that is attached to the face piece of the respirator. The skirt allows air to pass from the oronasal region to the ocular region through the diffuser 12. The bar or strip does not extend over the entire width between the two sides of the first seal 7. A small gap is formed between the first seal 7 and the skirt to allow air to flow between the eye region and the oronasal region. The exhaust deflection means 8 not only reduces the likelihood of exhaust passing through the eyepieces 2a, 2b, but also helps to control the flow of demisting air through the eyepieces 2a, 2b and into the inlet nose region.

In use, a filter (not shown) is mounted on the air inlet 4 and air is drawn through the filter into the first cavity via the air inlet 4. Those skilled in the art will appreciate that the filter is not an essential element of the present invention. Such filters are well known to those skilled in the art. Air may be drawn into the first cavity using negative or positive pressure. In a negative pressure respirator, the breathing action of the wearer reduces the air pressure in the first cavity relative to the surrounding atmosphere. Air is then drawn into the first cavity from the surrounding atmosphere (preferably through a filter) through the air inlet and then into the lungs of the wearer. In a positive pressure respirator, a pump or fan (not shown) draws air into the first cavity to maintain a positive pressure therein.

The air sucked into the first cavity is guided by the air guide 11. The air guide 11 is a plastic conduit mounted on the mask 1 which directs some of the inhaled air directly to the oronasal region of the user and some of the inhaled air to the void in the exhaust deflection means and to the diffuser 12. The air conductor 11 may be arranged such that all inhaled air is first directed to the diffuser 12 entering the ocular region. The diffuser 12 causes the inhaled air to pass over the eyepieces 2a, 2 b. Thus, the inhaled air helps to keep the eyepiece free of fog or moisture. The air then passes through the gap between the first seal 7 and the exhaust deflection means back into the oronasal region for inhalation by the user.

Exhaled air is expelled into the surrounding atmosphere through the air outlet 3. The air outlet 3 is fitted with a check valve and dead space (not shown) which inhibits ingress of contaminated air from the surrounding atmosphere. Such valves and dead band configurations are well known to those skilled in the art.

During operation of the respirator, the air pressure supply means supplies air to the second cavity (the cavity between the first and second seals) to maintain a positive pressure relative to the surrounding atmosphere and thereby reduce the likelihood of contaminated air entering the second cavity.

The sealed space 5 is shown in more detail in fig. 2 and comprises a first seal 7, which first seal 7 is connected to a second seal 6 and to mounting lugs 9, 10. The seal 5 comprises first and second portions 7, 6, each portion 7, 6 comprising a substantially compliant material and each having a respective sealing surface adapted to engage the face of a user to define a substantially sealed cavity between the seal and the face of the user, the first and second portions 7, 6 being connected by a third portion 13 adapted to be mounted on a surface of the respirator, the seal further comprising a gas inlet for allowing pressurised gas to be supplied to the cavity in use, wherein the first and second portions are shaped such that, in use, positive pressure applied in the cavity does not break the seal. The first seal 7 and the second seal 6 are connected by a connecting portion, the surface 13 of which may be mounted on the respirator body. Straps (not shown) may be mounted on the mounting lugs 9, 10 to enable the respirator to be fitted tightly to the head of the user.

FIG. 3 shows how the seal of the present invention is incorporated into a respirator. Fig. 3a shows that the second and first seals 6, 7 may be incorporated in a single piece component. Figure 3b shows that the seals 6, 7 can be mounted separately on the respirator body. The one-piece component 5 is advantageous, however, because it allows the first and second seals to be incorporated in a relatively small space, reduces manufacturing costs and complexity, and allows the relative positions of the first and second seals to be simple. Of course, the one-piece sealing member 5 is made in one piece. Fig. 3c and 3d show a further alternative embodiment of the structure of the sealing elements 6, 7.

The first seal 7 is a retro-reflective seal and the second seal 6 is a standard reflective seal. When a positive pressure is applied in the cavity between the seals 6, 7, the second seal 6 is urged into greater engagement with the user's face.

Referring now to fig. 4, the valve assembly 20 includes: a valve body 25 having a valve assembly outlet and a valve assembly inlet and a valve chamber 30 therebetween; a one-way valve mechanism 24 for allowing gas flow into valve chamber 30 through the valve assembly inlet and to the valve assembly outlet; a continuous purge outlet 27 connectable to an air pressure supply; an air deflector 28, spatially disposed in the valve chamber 30 relative to the one-way valve mechanism 24 and the purge outlet 27, is incident on the air deflector 28 such that the air curtain 22 is maintained substantially above the one-way valve mechanism 24.

A cylindrical bore is formed in the valve body 25 to create a valve chamber 30. The valve assembly 20 is shown located within the respirator air outlet 3 in the respirator mask 1. In use, exhaled air 21 is driven through a one-way valve mechanism 24 located in a valve seat 23. The one-way valve mechanism 24 is typically a diaphragm. The one-way valve mechanism 24 inhibits the flow of exhaled and ambient air into the respirator through the valve assembly 20. A pressurized air source, such as an air pump or blower (not shown), is connected to a purge air inlet 31, which purge air inlet 31 is in fluid communication with manifold 26. The manifold 26 is annular and is in fluid communication with a purge outlet 27.

In use, the source of pressurized air provides pressurized air to the manifold 26. The charge air then passes through a purge outlet 27 (in this case, the purge outlet 27 is annular). The outlet 27 is continuous around the circumference of the inner surface of the valve body 25. Air is forced out of the purge outlet 27 in the form of a curtain of air 22 over the one-way valve mechanism 24. This arrangement inhibits the accumulation of exhaled air 21 or ambient air in the area of the one-way valve mechanism 24 and forces potentially stale air away from the user, thus reducing the likelihood of any harmful gases entering the respirator. The purge outlet 27 should not be located too close to the one-way valve mechanism 24 because the moving air creates a low pressure region in its vicinity. If this low pressure region is too close to the one-way valve mechanism 24, the diaphragm of the mechanism rises, thereby enabling the user to breathe air in the vicinity of the valve mechanism 24. The shape and size of the purge outlet 27 defines the angle at which air is discharged from the purge outlet 27. The air deflector 28 causes the air curtain 22 to form above the one-way valve mechanism 24. After passing through the purge outlet 27, the air is directed to an air deflector 28. The position, shape and size of the air deflector 28 is selected such that there is no or little turbulent air flow in the air discharged through the purge outlet 27 in the region above the one-way valve mechanism 27. The air curtain 22 is deflected by the air deflector 28 to the conduit 41 a. In this example, the air deflector 28 is cylindrical in shape.

The conduit 41a is one of six conduits provided by a dead band protection component 45 (shown in detail in fig. 5). The air deflector 28 shown in fig. 5 is merely representative of the spatial relationship between the air deflector 28 and the dead-zone protection component 45. The air deflector 28 is not part of the dead band protection component 45. Six ducts are provided by a series of 6 guide walls. For clarity and ease of reference, only one conduit 41a and two guide walls 42a, 42b are labeled. The exhaled air and the purging air curtain pass through the inlet 46a of the conduit 41 a. The walls 42a, 42b diverge in a spiral fashion from the central cavity of the valve assembly toward the valve outlet 40 a. The helical nature of the conduit 41a increases the length of the gas path between the ambient atmosphere and the one-way valve mechanism 24, thereby reducing the likelihood of an undesirable increase in ambient gas. The closer the duct is to the surrounding atmosphere, the smaller the cross-section of the duct 41 a. This accelerates exhaled air and purge air outwardly, thus reducing the possibility of harmful ambient air ingress. Exhaled and purified air exits each conduit through a smaller outlet 40 a. The conduit 41a is shaped to divert any exhaled air and purge air and, more importantly, to cause any incoming air to exit the spiral plane. This effectively diverts air through mutually perpendicular directions. This slows down any incoming air. The guide walls 42a, 42b are provided with radial projections 43a, 43b respectively, the projections 43a, 43b decelerating any incoming air as it is driven into the valve outlet and helping to prevent the air from creating a cyclonic motion in the valve assembly. The use of multiple smaller valve outlets (rather than one larger vent) will reduce the risk of ambient air being blown in by the wind.

The air curtain 22 may be provided continuously, or during a suction process where contaminant ingress may occur.

Air deflector 28 may be provided with radially projecting vanes 47. These vanes further help prevent cyclonic motion from being created by the valve assembly 20.

One configuration of a respirator of the first embodiment of the present invention is shown in FIG. 6. In use, the respirator air inlet 55 is in air communication with the first cavity 52 to form a first air passageway, the second air inlet 54 is in air communication with an air pressure supply 53, the air pressure supply 53 being capable of supplying air to the second cavity 51 to form a second air passageway in use, wherein the respirator air inlet and the second air inlet are located in a common filter connection 57, and the filter connection 57 is connectable to a suitable filter 60, such that in use the first and second air passageways are isolated from one another, such that inhalation by a user does not substantially affect the pressure in the second air passageway. Referring to fig. 1, a first cavity 52 is formed between the first seal 7, the mask 1 and the face of the user. A second cavity 51 is formed between the second seal 6, the first seal 7 and a portion of the user's face. A valve 56 is located in the first gas passageway to prevent contaminated air from reaching the first cavity 52. The filter 60 is adapted to mate with the respirator of the present invention. Filter 60 includes first and second filter air inlets 62, 63, filter material 61, first and second filter air outlets 64, 65, and respirator connection means 66. The first and second filter air outlets 64, 65 are located in a common respirator connection 66. In use, air is drawn through the first filter air inlet 62 and through the filter material to the first filter air outlet 64. Air enters the respirator through the second air inlet 54 into the second cavity 51. Similarly, air is drawn through the second filter air inlet 63 and through the filter material to the second filter air outlet 65. Inhaled air is drawn from the second filter air outlet 65 into the respirator air inlet 55 into the first cavity 52 and then into the user's lungs. The air passageway through the first filter air inlet to the first filter air outlet is isolated from the air passageway through the second filter air inlet to the second filter air outlet.

Thus, inhalation by the user does not affect the pressure in the second gas pathway and, therefore, the air pressure supply means 53 does not experience a pressure drop and, therefore, does not have to increase its energy consumption to maintain the required pressure in the second cavity 51.

The respirator connection means includes means for engaging a safety interlock of the mounted respirator (not shown) so that the air pressure supply means of the mounted respirator can be actuated when the filter is properly mounted on the respirator. The filter to be fitted to the respirator may include suitable electrical contacts which cooperate with the contacts of the respirator to complete an electrical circuit to enable the air pressure supply means and thus the respirator to function. When the filter is not present, the air pressure supply means is maintained in an open circuit mode, thereby rendering the air pressure supply means inoperable.

Claims (13)

1. A respirator that comprises: a respirator mask; a first sealing arrangement adapted to form a seal against a user's face so as to define a first cavity between the first sealing arrangement, a respirator mask and a region of the user's face including the eyes, mouth and nose; a second sealing means adapted to form a seal against the face of the user so as to define a second cavity formed between the second sealing means, the first sealing means, a portion of the face of the user and the optional respirator mask; a respirator air inlet for introducing inhaled air into the first cavity; a respirator air outlet for directing exhaled air from the first cavity; and air pressure supply means adapted to supply pressurised air to the second cavity such that, in normal operation, air is only inhaled and exhaled through the first cavity, so that there is substantially no air pressure differential between the ambient atmosphere and the second cavity which would cause ambient air to enter the second cavity.

2. The respirator of claim 1, further comprising: at least one eyepiece and means for directing intake air across the at least one eyepiece.

3. The respirator of claim 2, wherein: the means for directing the inhaled air over the at least one eyepiece is capable of directing some of the inhaled air directly towards the oronasal region of the user.

4. A respirator according to claim 2 or claim 3 further comprising an exhaust deflection means capable of preventing exhaled air from contacting the at least one eyepiece.

5. The respirator of claim 4, wherein: the exhaust deflection means comprises a third sealing means which in use engages the face of the user to form an ocular cavity and an oronasal cavity, the third sealing means being provided with means for allowing gas to flow from the oronasal cavity to the ocular cavity.

6. The respirator of any of the preceding claims, further comprising a valve assembly comprising: a valve body having a valve assembly outlet and a valve assembly inlet and a valve cavity therebetween; a valve mechanism for allowing gas to flow into the valve chamber through the valve assembly inlet and to the valve assembly outlet; a continuous purge outlet means connectable to an air pressure supply means; an air deflecting means spatially arranged in the valve chamber relative to the valve mechanism and the purge outlet means such that, when a suitable air pressure supply means is connected and activated, air is expelled from the purge outlet means and incident on the air deflecting means such that the air curtain can be substantially maintained above the valve mechanism.

7. The respirator of any of the preceding claims, wherein: the respirator air inlet is in use in gaseous communication with the first cavity to form a first air passageway and the second air inlet is in gaseous communication with an air pressure supply means which in use is capable of supplying air to the second cavity to form a second air passageway, wherein the first and second air inlets are located in a common filter connection means and the filter connection means is connectable to a suitable filter such that in use the first and second air passageways are isolated from one another such that inhalation by a user does not substantially affect the pressure in the second air passageway.

8. A seal for a respirator, the seal comprising first and second parts each comprising a substantially compliant material and each having a respective sealing surface adapted to engage with the face of a user so as to define a substantially sealed cavity between the seal and the face of the user, the first and second parts being interconnected by a third part adapted to be mounted on a surface of a respirator, the seal further comprising a gas inlet for allowing pressurised gas to be supplied to the cavity in use, and wherein the first and second parts are shaped such that, in use, application of positive pressure in the cavity does not disrupt the seal.

9. The seal of claim 8, wherein: in use, application of positive pressure in the cavity will cause at least one of the first and second sealing surfaces to more positively engage the face of the user.

10. A seal according to claim 8 or 9, wherein: the first and second portions have a partial J or U-shaped cross-section.

11. The seal of any one of claims 8 to 10, wherein: at least one of the first and second portions includes a retroreflective seal.

12. A respirator comprising a seal as claimed in any one of claims 8 to 10.

13. A respirator substantially as hereinbefore described with reference to figures 1 to 3 and 6 of the accompanying drawings.