GB2394182A

GB2394182A - Respirator with face and nasal masks with first and second sealing means

Info

Publication number: GB2394182A
Application number: GB0302194A
Authority: GB
Inventors: Joseph Anthony Griffiths
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-10-16
Filing date: 2003-01-30
Publication date: 2004-04-21
Anticipated expiration: 2023-01-30
Also published as: GB0302194D0; GB0224099D0; GB2394182B

Abstract

A respirator comprising a face piece (1) with primary sealing means (6) thereon to make a seal with a wearer's face. The face piece (1) has a viewing window (2) therein and an oro-nasal mask (7) mounted in the interior thereof having an inlet (9) for inhalate and an outlet (10) for exhalate both having a one-way valve therein. The oro-nasal mask (7) also has secondary sealing means (8) thereon to make a seal with the wearer's face around the nose and mouth region. The primary sealing means (6) extends around the face piece (1) and makes a seal with the wearer's face around the eyes (3), nose (4) and mouth region (5) but above the wearer's chin. The secondary sealing means (8) also contacts the wearer's face in the chin region but above the location where the primary sealing means (6) is in contact therewith. The face piece (1) is releasably attached to the wearer's helmet (16) by wires (12) which retain the face piece (1) in a fixed position relative to the wearer's face. In use, when pressurised breathable gas is supplied to the interior of the face piece (1) through inlet (11), the primary sealing means (6) expand and contract and move relative to the wearer's face to automatically maintain the seal therewith regardless of the pressure of the breathable gas supplied to the interior of the face piece (1).

Description

- 1 Respirator This invention relates to a respirator for aircrew.

s For such respirators to be acceptable for aircrew (navigators or pilots) , they must not only be capable of fulfilling their function at ground level but they must also enable the pilot to be able to continue to breathe over the full range of cabin pressures which are dependent on the altitudes the aircraft will be flying at. If this is under 40,000 feet, then the pilot will normally be breathing a breathable lo gas mixture supplied at a low pressure of about 1/z"-2" water gauge and no increase in that supply pressure is needed for him to survive a decompression.

However, if the pilot is flying at an altitude over 40,000 feet, then the breathable mixture may have to be supplied at a much greater pressure dependent on the altitude he is at. In some cases this pressure could be as much as 17" water Is gauge. He therefore needs the area outside his eyes to be pressurised at the same pressure as the breathable gas supplied to his lungs otherwise his eyes will become bloodshot. Accordingly, the mask needs to cover his eyes, nose and mouth and it also needs to maintain an airtight seal with the pilot's face.

20 Aircrew breathing equipment normally includes a flexible oro-nasal facemask having an inspiratory valve supplied with oxygen or some other breathable gas and an expiratory valve to allow the wearer to expel the air from the mask on exhalation. The facemask is attached to the wearer's flying helmet by means of a harness incorporating a releasable fitting.

In fighter aircraft, it is essential that the facemask makes a proper seal with the wearer's face at all times. Under normal flying conditions, this is not a problem as the wearer adjusts the harness tension so that the mask makes the necessary seal with his face and is also comfortable to wear. The supply of the breathable 30 mixture through the mask is controlled by a breathing gas regulator which is responsive to the Gforces that it is subjected to. In other words, when the G-

force increases, the pressure of the gas supply to the mask is correspondingly

- 2 increased and vice-versa. Thus, changes in the G-forces applied to the regulator controlling the breathable gas supply result in automatic changes in pressure in the interior of the mask. It will be appreciated that unless some suitable means is provided to maintain the seal between the mask and the wearer's face, any s substantial increase in pressure within the mask cavity can cause the mask seal to leak so that the wearer will not receive the pressure of breathable gas he requires and could black out.

One known way of overcoming this problem has been to include an overcentre lo toggle in the harness assembly attaching the mask to the pilot's helmet. This toggle is in a low-tensioned position for normal flight but, when the wearer knows in advance that he will require pressurised breathing, for instance, when pulling G or in emergency conditions, he moves the toggle into its high tensioned position which draws the facemask more tightly against his face Is thereby hopefully improving its seal therewith., Once this need has passed, he then releases the toggle. Indeed, he wants to do this as soon as possible because the pressure exerted by the mask on his face when the toggle is engaged is so great that it makes the mask very uncomfortable to wear over long periods of time. The problem is overcome in European patent No. 0541549 which discloses a breathing apparatus in which the flexible oro- nasal mask is mounted in a rigid shell attached to the wearer's helmet at a fixed distance therefrom, the oro-nasal mask including extendable means operable to cause the oro-nasal mask or a as portion thereof to move automatically relative to the wearer's face to vary the seal therewith dependent on the breathable gas pressure supplied to the mask.

In a first embodiment of this prior art mask, the extensible means is an inflatable

bladder located between the oro-nasal mask and the rigid shell. In a second do embodiment, the extensible means is located in the wall of the oro-nasal mask and comprises a series of folds or bellows. In both embodiments however, when breathable gas at a pressure above that needed for normal breathing is supplied

( - 3 to the bladder or the interior of the oro-nasal mask, the bladder inflates or the bellows or folds extend to move the mask and/or seal thereon relative to the rigid shell in which it is mounted and thereby automatically vary the pressure of the mask on the wearer's face and its seal therewith dependent on the pressure of s the breathable gas supplied to it. The essence of this solution is that the position of the rigid shell in which the dynamically movable oro-nasal mask is mounted is held and maintained at a fixed distance from the wearer's face and helmet so that the mask and seal can be made to move relative to this fixed shell and therefore relative to the wearer's face.

This solution provided a substantial improvement over the prior art systems

because it automatically positioned and sealed the oro-nasal facemask onto the wearer's face as the G-forces generated during a turn increased, the pressure on the wearer's face reducing automatically as the turn was completed and the G 15 forces reduced.

Modern fighter aircraft can now generate up to 9G in a turn so the pressure of breathable gas supplied to the interior of the mask has to be substantially increased if he is to be able to breath satisfactorily and not lose consciousness 20 and black out during the turn due to a lack of oxygen supplied to the brain.

Thus, any breathing system that he uses must ensure that the periphery of the oro-nasal mask makes and maintains a seal with his face at all times otherwise the breathable gas at high pressure supplied to the interior of the mask will leak out at its edge seal and he will not receive the required amount of high pressure 25 gas needed to keep him conscious.

It has been found therefore that the commonly used reflex seal of the prior art

systems referred to above tend to leak when they are subjected to high Gforces for a variety of reasons. For instance, each wearer has a different facial 30 configuration particularly in the nose and cheek area on either side of the nose which is the area so it is difficult to achieve the seal necessary. It has been found

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that whilst prior art reflex seals work satisfactorily at low G-forces, they can leak

at higher G-forces which could have fatal consequences.

These high G-force sealing problems have been solved in the oro-nasal mask s disclosed in my UK patent application No. 0218705.2 which includes a body shaped to fit around and enclose a wearer's nose and mouth, the mask having sealing means around the periphery thereof to make a seal with the wearer's face when fitted thereto, the sealing means comprising a resilient member provided around the periphery of the body which, in use, locates the mask on the wearer's face so lo that the mask makes a seal therewith and a flexible sealing membrane overlying said resilient member and operable independently thereof to reinforce said seal when pressurised breathable gas is supplied to the interior of the mask.

The preferred embodiment has a body moulded with an annular inwardly 5 directed web around the periphery thereof which forms the resilient member which is pressed against the wearer's face around the wearer's nose and chin when the mask is fitted thereto, the flexible membrane being attached to the resilient member at a location axially spaced away from the part of the resilient member which is pressed against the wearer's face and the resilient member 20 being curved in cross section with a rolled tapered peripheral edge, the flexible membrane being secured to the resilient member.

The flexible membrane is shaped so that when a pressurised breathable gas is supplied to the interior of the mask when it is fitted to a wearer's face, it is 25 inflated and pressed into sealing engagement with the wearer's face to improve and reinforce the seal therewith as the pressure of the breathable gas increases.

A major advantage of this mask is that, in use, it is capable of receiving a high pressure breathable gas (up to 60mm of mercury) while still maintaining an 30 effective seal with the wearer's face and being comfortable to wear.

( - 5 Another type of aircrew mask is what is known as a 1/z mask which extends around the wearer's eyes, nose, mouth and, most importantly, under the wearer's chin, the mask front piece or exo and the oro-nasal mask mounted therein being attached to the wearer's flying helmet. The reason for the under chin s feature is that it was believed that it was necessary to keep the helmet and mask on the pilot in an ejection situation and stop the helmet being inflated by the windblast and torn off the pilot's head. It is important to retain the helmet and mask in position on the pilot's face "post ejection" so that the pilot breath using the seat mounted emergency oxygen supply systemduring descent, especially if 10 this is from high altitudes. al Another reason why aircrew 1/2 masks to date have tended to use "under chin" seals is that there is a belief that the jaw can "pop-out" of the mask due to jaw movement. If the respirator is to protect the pilot against nuclear, biological or chemical agents (NBC) Turning now to respirators worn by aircrew, once the aircrew wearing the respirator has reached the aircraft and connected the respirator to the pressurised breathable gas supply in the aircraft, the respirator needs to have 20 some form of sealing means on it which will ensure that the seal with the wearer's face is maintained at all times during flight even when the aircraft generates high G-forces (up to 9G) in tight turns.

It is an object of the invention therefore to provide a respirator which avoids the 25 need to have an under-the-chin seal and which can maintain its seal with the pilot's face at G-forces up to 9G.

According to the invention, there is provided a a respirator for aircrew comprising a face piece with primary sealing means thereon to make a seal with so a wearer's face, the face piece having a viewing window therein and an oro-nasal mask mounted on the interior thereof having an inlet for inhalate and an outlet for exhalate, said inlet and outlet having a oneway valve therein, the oro-nasal

mask having secondary sealing means thereon to make a seal with the wearer's face around the nose and mouth region, the primary sealing means extending around the face piece and making a seal with the wearer's face around the eyes, nose and mouth region but above the wearer's chin, the secondary sealing means s contacting the wearer's face in the chin-region above the location where the primary sealing means contacts said chin region, the face piece being attachable to the wearer's helmet by unextendable attachment means which retain the face piece in a fixed position relative to the wearer's face, the arrangement being such that when pressurised breathable gas is supplied to the interior of the face piece, lo the primary sealing means move relative to the wearer's face to automatically maintain the seal therewith regardless of the pressure of the breathable gas supplied to the interior of the face piece, the arrangement being such that when pressurised breathable gas is supplied to the interior of the face piece, the primary sealing means move relative to the wearer's face to automatically Is maintain the seal therewith regardless of the pressure of the breathable gas supplied to the interior of the face piece.

Preferably the primary sealing means comprises a resilient member provided around the periphery of the face piece which, in use, locates the face piece on ho the wearer's face to make a seal therewith and a flexible sealing membrane overlying said resilient member and operable independently thereof to reinforce said seal when pressurised breathable gas is supplied to the interior of the face piece. as In the preferred embodiment, the flexible membrane includes a skirt which contacts the wearer's face and the resilient member is moulded with an annular inwardly directed web around the periphery thereof which, in use, is pressed against the wearer's face around the wearer's forehead, temples, nose and chin.

do The flexible membrane is preferably attached to the resilient member at a location axially spaced away from the part of the resilient member which is

- 7 pressed against the wearer's face and the resilient member is curved in cross section with a rolled tapered peripheral edge.

In the preferred embodiment, the flexible membrane is secured to the resilient s member which is moulded from a natural or synthetic rubber material. The flexible membrane is preferably moulded from a natural or synthetic rubber material and shaped so that when pressurised breathable gas is supplied to the interior of the face piece fitted to a wearer's face, the membrane can only be positioned in sealing engagement with the wearer's face to improve and reinforce lo the seal therewith as the pressure of the breathable gas increases.

In use, the portion of the flexible membrane extending over the portion of the resilient member which is pressed against the wearer's face and the peripheral I edge region of the flexible membrane are both pressed into contact with the Is wearer's face when pressurised gas is supplied to the interior of the face piece.

The secondary sealing means can also comprise a resilient member provided around the periphery of the oro-nasal mask which, in use, locates the mask on the wearer's face so that the mask makes a seal therewith and a flexible sealing 20 membrane overlying said resilient member and operable independently thereof to reinforce said seal when pressurised breathable gas is supplied to the interior of the mask.

The flexible membrane preferably includes a skirt which contacts the wearer's 25 face and the oro-nasal mask is moulded with an annular inwardly directed web around the periphery thereof which, in use, is pressed against the wearer's face around the wearer's nose and chin.

Preferably, the flexible membrane is attached to the resilient member at a 30 location axially spaced away from the part of the resilient member which is pressed against the wearer's face and the resilient membrane is curved in cross section with a rolled tapered peripheral edge.

( - 8 In the preferred embodiment, the flexible membrane is secured to the resilient member and the oro-nasal mask is moulded from a natural or synthetic rubber material. Preferably, the flexible membrane is shaped so that when a pressurised breathable gas is supplied to the interior of the mask when said mask is fitted to a wearer's face, the membrane can only be positioned into sealing engagement with the wearer's face to improve and reinforce the seal therewith as the pressure lo of the breathable gas increases, the portion of the resilient member which is pressed against the wearer's face being located behind the flexible membrane.

In the preferred embodiment, in use, the portion of the flexible membrane extending over the portion of the resilient member which is pressed against the Is wearer's face and the peripheral edge region of the flexible membrane are both pressed into contact with the wearer's face when a pressurised gas is supplied to the interior of the mask.

The oro-nasal mask can be a discrete member to which the secondary sealing ho means are attached or the sealing means can be an integral part thereof.

The respirator can include means for pivotally mounting the window on the face piece so that said window can be moved relative thereto.

as A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a front view of a respirator of the invention; Figure 2 is a schematic side view partly in cross section of the respirator shown Jo in Figure 1; Figure 3 is a schematic plan view of the respirator shown in Figures 1 and 2; and

( 9 Figure 4 is a front view of the respirator shown in Figures 1-3 but with an NBC hood or cowl attached thereto.

Referring to the drawings, there is shown a respirator comprising a rigid face 5 piece or exo 1 preferably made of a rigid plastics material with a clear viewing window 2 therein. The face piece 1 is sized so that it contacts the wearer's forehead, temples and chin region to enclose the wearer's eyes 3, nose 4 and mouth 5. Primary sealing means 6, to be described in more detail hereafter, ensures that the face piece 1 makes an airtight seal with the wearer's face at all lo times.

The face piece 1 has an oro-nasal mask 7 of known type attached to its internal surface to surround and enclose the wearer's nose and mouth. The oro-nasal mask 7 has an annular re-entrant reflex edge seal 8 (see Figure 2) and one or Is more one-way inhalatory valves 9 and a one-way exhalate valve 10 therein whose function and operation will be described shortly.

Breathable gas is supplied to the interior of the respirator outside the oro-nasal mask 7 via an inlet hose 11. The breathable gas is connected in known manner 20 to a regulator (not shown) including a G valve which automatically supplies the breathable gas at the pressure required for breathing dependent on the G force to which the plane and pilot are being subjected during flight.

In use, face piece 1 is held in position against the wearer's face by attachment as means in the form of a pair of inextendable wires or straps 12. One end 13 of each wire 12 is connected to the front of the face piece 1 whilst the other end is received in known coupling 15 mounted on rigid helmet 16 worn by the pilot. It will be appreciated therefore that the face piece 1 is maintained at a fixed distance from the helmet 16 at all times. The length of the wires 12 can be finely 30 adjusted using known adjustors 12A.

- 10 The primary sealing means 6 to be described more fully hereafter ensures that the face piece 1 makes an airtight seal against the wearer's face 1A. In use, breathable gas is supplied to the interior of the face piece 1 through the inlet 11 at a pressure governed by the regulator (not shown). Having inhaled the 5 pressurised gas in the oro-nasal mask 7, the pilot then exhales into the interior of the oro-nasal mask which shuts the or each inhalate valve 9 and opens the exhalate valve 10 allowing harmful CO: to be exhaled to the exterior of the face piece 1. The operation of the respirator just described is well known to those skilled in the art so no further description thereof will be given here.

In the event of a nuclear, biological or chemical attack, ground staff and particularly aircrew must be protected against NBC agents. In particular, pilots must be able to reach their aircraft breathing clean filtered air. Once inside the aircraft, they can then either connect their breathing mask to the on-board Is oxygen supply or they can continue to use their portable blower assisted system.

Accordingly, if the respirator is to provide NBC protection, a rubber or butyl hood or cowl 17 having a neck piece 18 attached to the outer periphery 19 of the face piece 1 in any suitable way, e.g. by gluing or using Velcro strip 19 (see 20 Figure 4).

In known respirators, the seal around the periphery of the face piece 1 is normally a re-entrant flange known as a reflex seal. The problem with seals of this type is that they do not necessarily adapt to the contours of the wearer's 25 face. In the case of the respirator illustrated in the drawings in which the breathable gas can be supplied to the interior of the respirator at very high pressure (up to 75mm of Hg), if the primary sealing means was a known reflex seal, it would tend to leak which could prove fatal to the wearer in a combat situation. The preferred primary seal is therefore of the type used on the oro 30 nasal mask described in my pending UK patent application No. 0218705.2 the disclosure of which is incorporated herein by reference.

( - 11

Referring now to Figure 3, this shows in more detail the primary edge seal 6 on the facemask 1. An annular flexible sealing section 20 made of natural or synthetic rubber having a re-entrant portion 21 is attached at 22 to the peripheral edge of the face piece 1. The sealing section 20 includes a rolled portion 23 s shaped and adapted to fit against the wearer's forehead, temples, cheeks and chin area. A thin membrane 24 is attached to the section 20 closely adjacent the re-

entrant portion 21 and extends over the rolled portion 23 but is unattached thereto. The free end of the flexible membrane extends beyond the end of the rolled portion 23 and provides an annular inwardly directed web 26 which lo contacts the wearer's face 1A.

The way in which the dynamic peripheral edge seal 6 works is as follows: First of all, the wearer fits the face piece 1 onto his face and attaches it to helmet Is 16 using the wires 12. He then finely adjusts the length of the wires 12 using known adjustors 12A so that the face piece 1 is a comfortable fit on his face and makes a general seal therewith. In this position, the rolled edge 23 of the sealing portion 20 which is located underneath the flexible membrane 24 pushes it into engagement with his face and a seal is achieved therewith. As the rolled edge 23 20 is annular, the seal formed will extend around his forehead, temples, cheeks and below his mouth but above his chin, the inwardly directed web 26 resting against the wearer's face in these regions. Because the flexible membrane 26 extends generally inwardly from the edge of the rolled edge 23 generally normal thereto, when the mask is fitted to the wearer's face, it lies closely against the wearer's 25 face and adapts to the contours thereof. When breathable gas under pressure is supplied to the interior of the face piece 1, the gas will apply pressure to the annular membrane 26 lying against the wearer's face in the direction of the arrows so it operates independently of the seal already created by the rolled edge 23 and presses the membrane 26 into better engagement with the pilot's face 30 thereby improving and reinforcing the seal therewith. It should be noted that there is a space between the sealing section 20 and the membrane 24 in this region as the membrane 24 is not attached to it over its whole width. As a result,

- 12 the membrane 24 in this region will inflate slightly due to the gas pressure which further improves the seal with the wearer's face in the region of the annular rolled edge 23.

s It will be appreciated that when breathable gas is supplied to the interior of the face piece 1 through the inlet hose 11, the sealing portion 20 of the primary sealing means will expand and contract. However, it cannot move forwardly away from the wearer's face because it is constrained within the rigid face piece 1 which itself cannot move because it is constrained by the wires 12. The sealing lo portion 20 can therefore only move towards or away from the wearer's face thereby varying the pressure of the seal therewith. As the gas pressure supplied to the interior of the face piece 1 increases or decreases, so the re- entrant section 21 can extend or contract thereby allowing the sealing portion 20 to move towards or away from the wearer's face automatically in response to the gas Is pressure and automatically vary the seal therewith.

Modern fighter pilots now have avionics on their helmets which project images on to their visor which need to be in the direct line of sight of the pilot. It is an essential requirement of such systems that the visor remains in a fixed position 20 relative to the pilot's eyes for the images to be properly in focus. Accordingly, the visor 2 of the respirator of the invention can be mounted on a pivotal axis 30 at the base thereof, the edges of the visor being attached to the face piece 1 by a membrane to allow it to be pivoted relative thereto while still maintaining an airtight seal therewith. The pivot 30 can include a known ratchet type of 25 adjustment so that the visor 2 can be clicked from one position to another and retained therein. This adjustment on the visor allows the pilot to set the visor in the correct position for his eyes after donning the respirator which makes it more versatile in that one respirator size can be used to fit numerous different facial contours or head sizes.

Another advantage of respirator of the invention is that the exterior of the wearer's eyes can be pressurised by the breathable gas to be at the same pressure

- 13 as his nose and mouth so the internal head pressure (i.e. behind his eyes) will be the same as the external pressure applied thereto so they do not go blood red when subjected to the pressurised breathable gas as in prior art masks.

Claims

- 14 Claims

1. A respirator comprising a face piece with primary sealing means thereon to make a seal with a wearer's face, the face piece having a viewing window s therein and an oro-nasal mask mounted in the interior thereof having an inlet for inhalate and an outlet for exhalate, said inlet and outlet having a one-way valve therein, the oro-nasal mask having secondary sealing means thereon to make a seal with the wearer's face around the nose and mouth region, the primary sealing means extending around the face piece and making a seal with the lo wearer's face around the eyes, nose and mouth region but above the wearer's chin, the secondary sealing means contacting the wearer's face in the chin region above the location where the primary sealing means contacts said chin region, the face piece being attachable to the wearer's helmet by unextendable attachment means which retain the face piece in a fixed position relative to the Is wearer's face, the arrangement being such that when pressurised breathable gas is supplied to the interior of the face piece, the primary sealing means move relative to the wearer's face to automatically maintain the seal therewith regardless of the pressure of the breathable gas supplied to the interior of the face piece.

2. A respirator as claimed in claim 1 wherein the primary sealing means comprises a resilient member provided around the periphery of the face piece which, in use, locates the face piece on the wearer's face to make a seal therewith and a flexible sealing membrane overlying said resilient member and operable Us independently thereof to reinforce said seal when pressurised breathable gas is supplied to the interior of the face piece.

3. A respirator as claimed in claim 2 wherein the flexible membrane includes a skirt which contacts the wearer's face.

4. A respirator as claimed in claim 2 or claim 3 wherein the resilient member is moulded with an annular inwardly directed web around the periphery thereof

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which, in use, is pressed against the wearer's face around the wearer's forehead, temples, nose and chin.

5. A respirator as claimed in any of claims 2-4 wherein the flexible s membrane is attached to the resilient member at a location axially spaced away from the part of the resilient member which is pressed against the wearer's face.

6. A respirator as claimed in any of claim 2-5 wherein the resilient member is curved in cross section with a rolled tapered peripheral edge.

7. A respirator as claimed in any of claims 2-6 wherein the flexible membrane is secured to the resilient member.

8. A respirator as claimed in any of claims 2-7 wherein the resilient member Is is moulded from a natural or synthetic rubber material.

9. A respirator as claimed in any of claims 2-8 wherein the flexible membrane is moulded from a natural or synthetic rubber material.

20 10. A respirator as claimed in any of claims 2-9 wherein the flexible membrane is shaped so that when pressurised breathable gas is supplied to the interior of the face piece fitted to a wearer's face, the membrane can only be positioned in sealing engagement with the wearer's face to improve and reinforce the seal therewith as the pressure of the breathable gas increases.

11. A respirator as claimed in claim 10 wherein the portion of the resilient member which is pressed against the wearer's face is located behind the flexible membrane. 30 12. A respirator as claimed in claim 10 wherein the portion of the flexible membrane extending over the portion of the resilient member which is pressed against the wearer's face and the peripheral edge region of the flexible membrane

- 16 are both pressed into contact with the wearer's face when pressurised gas is supplied to the interior of the face piece.

13. A respirator as claimed in any preceding claim wherein the secondary s sealing means comprises a resilient member provided around the periphery of the oro-nasal mask which, in use, locates the mask on the wearer's face so that the mask makes a seal therewith and a flexible sealing membrane overlying said resilient member and operable independently thereof to reinforce said seal when pressurised breathable gas is supplied to the interior of the mask.

14. A respirator as claimed in claim 13 wherein the flexible membrane includes a skirt which contacts the wearer's face.

15. A respirator as claimed in claim 13 or claim 14 wherein the oro-nasal Is mask is moulded with an annular inwardly directed web around the periphery thereof which, in use, is pressed against the wearer's face around the wearer's nose and chin.

16. A respirator as claimed in any of claims 13-15 wherein the flexible 20 membrane is attached to the resilient member at a location axially spaced away from the part of the resilient member which is pressed against the wearer's face.

17. A respirator as claimed in any of claims 13-16 wherein the resilient member is curved in cross section with a rolled tapered peripheral edge.

18. A respirator as claimed in any of claims 13-17 wherein the flexible membrane is secured to the resilient member.

19. A respirator as claimed in any of claims 13-18 wherein the oro-nasal mask 30 is moulded from a natural or synthetic rubber material.

- 17 20. A respirator as claimed in any of claims 13-19 wherein the flexible membrane is moulded from a natural or synthetic rubber material.

21. A respirator as claimed in any of claims 13-20 wherein the flexible s membrane is shaped so that when a pressurised breathable gas is supplied to the interior of the mask when said mask is fitted to a wearer's face, the membrane can only be positioned into sealing engagement with the wearer's face to improve and reinforce the seal therewith as the pressure of the breathable gas increases.

lo 22. A respirator as claimed in claim 21 wherein the portion of the resilient member which is pressed against the wearer's face is located behind the flexible membrane. 23. A respirator as claimed in claim 21 wherein the portion of the flexible I5 membrane extending over the portion of the resilient member which is pressed against the wearer's face and the peripheral edge region of the flexible membrane are both pressed into contact with the wearer's face when a pressurised gas is supplied to the interior of the mask.

20 24. A respirator as claimed in any of claims 13-23 wherein the oronasal mask is made from a resilient material.

25. A respirator as claimed in claim 24 wherein the oro-nasal mask and the resilient member are moulded from the same material.

26. A respirator as claimed in claim 13 wherein the oro-nasal mask is a discrete member to which the secondary sealing means are attached.

27. A respirator as claimed in any preceding claim including means for 30 pivotally mounting the window on the face piece so that said window can be moved relative thereto.