GB2406797A

GB2406797A - High G-force breathing mask

Info

Publication number: GB2406797A
Application number: GB0323686A
Authority: GB
Inventors: Joseph Anthony Griffiths
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-10-09
Filing date: 2003-10-09
Publication date: 2005-04-13
Anticipated expiration: 2023-10-09
Also published as: GB2406797B; GB0323686D0

Abstract

A pilots breathing mask comprising a two-part rigid shell 4, having a main body portion 4A and a peripheral ring portion 4B, and which is attachable to a helmet 2 at a fixed distance therefrom and which houses a flexible oro-nasal mask 3, the periphery of which extends beyond the shell 4, is adapted to make a seal with the pilot's face, and includes extendable means 11 operable to press the periphery 10 of the mask 3 automatically towards the pilot's face to improve the seal therewith when high pressure gas is supplied to the mask and the extendable means reconfigure as a result thereof. The peripheral ring portion 4B is attached to the part of the flexible oro-nasal mask 3 which extends from the shell 4. In another aspect, the flexible oro-nasal mask 3 includes a cushion 35 with a skirt 38.

Description

High G-Force Breathing Mask This invention relates to a breathing mask and

particularly but not exclusively for use by pilots who are subjected to high G forces.

Breathing equipment for aircrew normally comprises a flexible facemask having an inspiratory valve supplied with oxygen or some other breathable gas and an expiratory valve to allow the pilot to expel the air from the mask on exhalation.

The facemask is attached to the pilot's flying helmet by means of a harness lo incorporating a releasable fitting.

in fighter aircraft, it is essential that the facemask makes a seal with the pilot's face at all times. Under normal flying conditions, this is not a problem as the pilot adjusts the harness tension so that the mask makes the necessary seal with Is his face and is also comfortable to wear. The supply of the breathable mixture through the mask is controlled by a breathing gas regulator which is responsive to the G-forces that it is subjected to. In other words, when the G-force increases, the pressure of the gas supply to the interior of the mask is correspondingly 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 means is provided to maintain the seal between the mask and the pilot's face, any substantial increase in pressure within the mask cavity can cause the mask seal to leak so that the pilot will not receive the pressure of breathable gas he requires and he could therefore black out.

C)ne known way of overcoming this problem has been to include an overcentre toggle in the harness assembly which attaches the mask to the pilot's helmet.

This toggle is in a low-tensioned position for normal flight but, when the pilot wants to make a tight turn, he moves the toggle into its high tensioned position before he makes the turn which causes the facemask to be drawn more tightly against his face thereby improving the seal therewith.

After the turn is completed, he then releases the toggle. Indeed, he has to do this because the pressure exerted on his face when the toggle is engaged is so great that the mask is very uncomfortable to wear. 'l'hc main problem with this s arrangement is that the pilot must remember to engage the toggle before he makes a turn (possibly difficult in a combat situation) and release it after the turn has been completed as the pressure on his face is too high to be comfortable for normal flying.

lo In order to overcome these problems, the facemask disclosed in European patent No. ()541549 was developed and a breathing apparatus was provided in which the Oro-nasal mask was mounted in a rigid shell attached to the pilot's helmet at a fixed distance therefrom, the oro- nasal mask including extendable means operable to cause the oro-nasal mask or a portion thereof to move automatically Is relative to the pilot's face to vary the seal therewith dependent on the pressurised breathable gas supplied to the mask.

In one embodiment of the mask in said earlier patent, the extensible means is an inflatable bladder located between the oro-nasal mask and the rigid shell. In so another embodiment, the extensible means is located in the wall of the oro-nasal mask and comprises one or more folds or bellows. In both embodiments, when breathable gas at a pressure above that needed for normal breathing is supplied to the bladder or the interior of the oro-nasal mask, the bladder inflates or the bellows or folds extend to move the mask relative to the rigid shell in which it is Us mounted and thereby automatically vary the pressure of the mask on the pilot's face and its seal therewith dependent on the pressure of the breathable gas supplied to it. The essence of this solution is that the position of the rigid shell in which the oro-nasal mask is mounted is maintained at a fixed distance from the pilot's face and helmet so that the mask can be made to move relative to this do fixed shell and therefore relative to the pilot's face to vary the seal the mask makes therewith dependent on the breathable gas pressure supplied to the mask.

To work properly, the outer rigid shell needs to radially restrain the flexible portion of the 'ro-nasal mask that extends towards the pilot's face when the pressure of the gas supplied to the mask is increased. This keeps the oro-nasal mask maintained in its optimum operational configuration for making a seal with the pilot's face, and the peripheral restraint provided by the rigid shell prevents excessive ballooning. However, to allow the flexible oro-nasal mask to move freely in a direction towards and away from the pilot's face, it cannot be bonded to the rigid shell at a point beyond the extensible means.

It is therefore one object of the present invention to provide a mask that can maintain an airtight seal with a pilot's face when subject to forces of up to 9G and radially constrain the moveable portion of the mask that is mounted within the rigid shell.

As mentioned above, it is essential that the portion of the oro-nasal mask that contacts the pilot's face makes an air-tight seal therewith to prevent the pressurised breathable gas escaping, which could result in the pilot blacking out during a turn, or experiencing 'G-loc' (G - loss of consciousness). One way of ensuring this, as described earlier, is for the pilot to tighten the mask against his face ready for high G conditions when the breathable gas will be supplied at elevated pressure.

However, the construction and design of the sealing means itself is critical for the mask to make an air-tight seal against the pilot's face. Many prior art masks feature a rounded rubber cushion as the sealing means. These work adequately under normal flying conditions, but when the pressure in the mask is increased, the curved edge of the sealing means that contacts the pilot's face is inadequate to prevent the pressurised air from escaping from within the oro-nasal mask. Facial geometry varies from pilot to pilot, so it is desirable to design a mask and sealing means which are able to make a perfect air-tight seal under pressure on all pilots' faces, as providing custom made masks to ht the facial contours of each individual pilot would be prohibitively expensive.

It is therefore another object of the present invention to provide a mask that can maintain an airtight seal with a pilot's face when subject to forces of up to 9G, with an improved oro-nasal sealing means that substantially alleviates or overcomes the problems outlined above.

According to a first embodiment of the present invcation, there is provided a s breathing mask comprising a rigid shell attachable to the helmet of aircrew at a fixed distance therefrom, and a flexible oro-nasal mask within said shell, the periphery of the flexible mask extending beyond the shell and being adapted to make a seal with the pilot's face, the oro-nasal mask including extendable means operable to press the periphery of the mask automatically towards the pilot's face lo to improve the seal therewith when gas at a pressure above that required for normal breathing is supplied to the mask and the extendable means reconfigure as a result thereof characterised in that the rigid shell is in two parts and comprises, a main body portion, and a separate peripheral ring portion, the peripheral ring portion being attached to the part of the flexible oro-nasal mask Is which extends from the shell so that when the gas at elevated pressure is supplied to the interior of the mask and causes the extendable means to reconfigure, the periphery of the oro-nasal mask and the peripheral ring attached thereto move together towards the pilot's face and away from the main body portion of the rigid shell.

In a second and alternative embodiment of the present invention however, there is provided breathing mask comprising a rigid shell attachable to the helmet of aircrew at a fixed distance therefrom, and a flexible annular sleeve attached to the periphery of the shell and extending beyond the edge thereof, said sleeve as being adapted to make a seal with the pilot's face, the sleeve including extendable means operable to press the periphery of the sleeve automatically towards the pilot's face to improve the seal therewith when gas at a pressure above that required for normal breathing is supplied to the mask and the extendable means reconfigure as a result thereof characterised in that the rigid shell is in two parts and comprises, a main body portion, and a separate peripheral ring portion, the peripheral ring portion being attached to the part of the flexible sleeve which extends from the shell so that when the gas at elevated pressure is supplied to - 5 the interior of the mask and causes the extendable means to reconfigure, the periphery of the sleeve and the peripheral ring attached thereto move together towards the pilot's face and away from the main body portion of the rigid shell s In a preferred embodiment, the extendable means comprises an annular inwardly directed re-entrant recess formed in the wall of the flexible mask or sleeve adjacent the peripheral seal, the depth of said recess in the bottom half of the mask or sleeve being greater than the depth in the top half thereof. The recess is preferably V-shaped and comprises an inwardly directed flange on the front 0 portion of the flexible mask or sleeve which is attached to a correspondingly dimensioned inwardly directed flange adjacent the peripheral seal on a rear portion of the flexible mask or sleeve.

Alternatively, the extendable means comprises a plurality of annular inwardly Is directed recesses formed in the mask or sleeve wall to provide a bellows therein.

In a further alternative embodiment, the wall of the mask or sleeve includes a convoluted rolling section, the thickness of the mask or sleeve wall in the region of the convoluted rolling section being less than the remainder of the mask or sleeve thereby allowing the mask to be rolled back on itself into an S-shaped con Egu ration.

According to a third embodiment of the invention there is provided a breathing mask comprising a rigid shell with a flexible oro-nasal mask attached to the periphery of the shell and extending beyond the edge thereof, said flexible oro s nasal mask being adapted to make a seal with the pilot's face, the periphery of the flexible oro-nasal mask including a cushion having a skirt projecting therefrom in a direction away from the pilot's face so that, in use, the skirt lies flush against the pilot's face to make an air-tight seal therewith.

However, a yet further fourth embodiment according to the present invention provides a breathing mask comprising a rigid shell with a flexible annular sleeve attached to the periphery of the shell and extending beyond the edge thereof, () said flexible sleeve being adapted to make a seal with the pilot's face, the periphery of the sleeve including a cushion having a skirt projecting therefrom in a direction away from the pilot's face so that, in use, the skirt lies flush against the pilot's face to make an air-tight seal therewith s Preferably, the cushion is hollow and toroidal in shape and includes an air hole therein to allow gas pressure to balance between the interior and the exterior of the cushion. Alternatively the cushion is C-shapcd in cross-section and forms an envelope.

In a preferred embodiment, the hollow interior of the cushion is partially filled with open cell foam. However, the hollow interior of the cushion may be completely filled with open cell foam.

(conveniently, the first embodiment described above with preferred variations is provided in combination with the third embodiment described above together with the preferred features of said third embodiment.

Alternatively, the second embodiment described above with preferred variations is provided in combination with the fourth embodiment descriLcd above together with the preferred features of said fourth embodiment Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which: Figure I is a side view of a facemask of a first embodiment of the invcotion in use with an airctcw helmet and breathable gas supply; Figure 2 is an enlarged view of the facemask shown in Figure 1; Figure 3A is a schematic cross-section of the facemask of Figure 2; Figure 3B is a schematic cross-section of the facemask of Figure 2 when air under high pressure has been applied thereto; Figure 4 is a side view of a facemask of a second embodiment of the invention; Figure 5 is a cross-section view of the mask of Figure 4 along line X - X; - 7 - Figure 6A is a schematic cross-section of a prior art facemask on a pilot's face when breathable gas under high pressure has been applied thereto; Figure GIN is a schematic cross-section of the facemask of Figures 4 and 5 on a pilot's face when breathable gas under high pressure has been applied thereto; s Figure 7 is a side view of a mask having a combination of features of the first and second embodiments of the invention shown in Figures 1 - 3 and 4 - 6 respectively; Figure 8 is a cross-section view of the mask in Figure 7 along line Y - Y. Referring now to the drawings, Figure 1 shows a pilot 1 wearing a rigid protective helmet 2. A flexible oro-nasal mask 3, usually made of a natural or synthetic rubber material, surrounds the pilot's nose and mouth and is mounted in a rigid shell 4 attached to the helmet 2 by means of harness arrangement 5 which includes adjustable means (not shown) so that its length can be readily Is altered to ensure that the oro-nasal mask 3 rests comfortably on the pilot's face with its peripheral edge 10 making a proper seal with the area of the pilot's face surrounding the nose and mouth. It should be noted that the harness 5 is made of an inextensible material such as webbing or a metal wire secured at mounting point P to the rigid shell 4 and at its opposite end in mounting 7. Thus, when the shell 4 and mask 3 are in position on the pilot's face, the position of the rigid shell 4 relative to the helmet 2 cannot change and it remains at a fixed distance therefrom.

A breathable gas such as oxygen is supplied to the interior of the mask 3 from an oxygen regulator 9 through hose 8.

Inspiratory and expiratory valves (not shown) are provided in the mask 3 in known manner.

As can be seen more clearly from Figure 3, the wall of the flexible mask 3 housed within the rigid shell 4 includes extendable means 11 therein. The extendable means is shown as an inwardly directed V-shaped bellows. The rigid

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shell 4 comprises two separate portions, a main body portion 4A and a separate ring portion 4B. The portion of the flexible mask 3 on the side of the extendable means 11 distal from the pilot's face is housed within the main rigid body portion 4A. The portion of the flexible mask 3 on the side of the extendablc s means 11 proximate to the pilot's face is outside the main rigid body portion 4A, but is constrained within the rigid ring portion 4B. The purpose of the extendablc means 11 is to enable the peripUcral edge 10 of the flexible mask 3 to move in a direction (shown by arrow A) generally parallel to the wall of the rigid shell 4 when the prcssurised breathable gas supplied to the interior of the flexible lo mask 3 is increased as a result of the regulator 9 being activated when the aircraft makes a turn. When the pressure supplied to the interior of the flexible mask 3 increases, its wall tries to radially extend to cope with the increased pressure.

However, as the flexible wall cannot move radially outwardly because it is contained within the rigid shell 4A, it is forced to move in a direction generally Is towards the pilot's face in the direction of the arrows A (see Figures 1 and 3) and thereby improve its seal therewith. The portion of the flexible mask 3 extending beyond the main body 4A is also radially constrained by the ring portion 4B of the rigid shell 4 attached thereto, so said ring portion 4B also moves relative to the main body portion 4A together with the portion of the mask 3 to which it is attached. As the portion of the oro-nasal mask 3 extending beyond the main body 4A of the rigid shell cannot expand radially, the force exerted by the pressure within the mask is therefore transformed into a force exerted on the pilots face in the direction of arrows A, and so maximises the increase in mask pressure on the pilot's face to achieve the optimum air-tight seal therewith.

Figure 3A shows the flexible mask 3 of Figures 1 and 2 in schematic form prior to the breathable gas being supplied to the interior of the mask 3 and with the extendable means 11 un-extended. Figure 3B shows the flexible mask 3 of Figure 3A after the pressuriscd breathable gas has been supplied to the interior do thereof, the rigid ring portion 4B exerting an inward radial constraining force in the direction of arrows B to compensate for the pressure acting on the inside of the flexible oro- nasal mask 3. It can be seen that the extendable section 11 has extended and reconfigured to the illustrated shape so the edge 10 of the mask is moved in the direction of the arrows A (see Iigurc 3B) to press more tightly against the pilot's face and thereby improve the seal therewith.

s Although the extcodable means shown in the drawings is a V-shaped bellows, it will be appreciated by one skilled in the art that alternative extendable means could be used, such as an S-shaped convoluted rolling section, or a concertina bellows section, as known from the prior art, for example UI: Patent Application no. GB 0221687.7.

Figures 4 and 5 show a second embodiment of the present invention which comprises a rigid shell 14 with a flexible annular sleeve 13 made from a natural or synthetic rubber to surround a pilot's nose and mouth and which is bonded at 13A to the inner peripheral edge surface of the shell 14. The flexible sleeve 13 and rigid shell 14 arc adapted to be fitted to a helmet of the pilot as hercinbefore described with reference to the first embodiment of the invention. The peripheral edge 20 of the flexible sleeve 13 that contacts and makes a seal with the pilot's face comprises a cushion 15 having a hollow core which is partially hlled with an open cell foam 1G, leaving the remaining space as an air gap 17. A vent hole 19 is provided in the cushion 15 which is in fluid communication with the air-gap 17 inside the cushion.

A skirt 18 extends inwardly substantially tangentially from the edge of the cushion around its entire perimeter. The skirt 18 has an inocr surface 18A and an outer surface 1 8B.

In use, the mask is attached to the pilot's helmet in the same manner as shown in Figure 1. The peripheral edge 20 of the cushion 15 contacts the pilot's face and surrounds his nose and mouth. In use the outer surface 1 8B of the skirt 18 presses against the pilots face and makes a seal therewith.

The difference between this arrangement and prior art facemask seals can be seen in Figures GA and GB. The seal in Figure GA is rounded and presents a curved edge 21 leading to a contact point 22 on the pilot's face. 1 his arrangement is such that when breathable gas at high pressure is supplied to the interior of the mask, it tends to - 10 push the edge 21 away from the pilot's face and escapes outside the mask as shown by the arrows. As mentioned above, this loss of breathable gas pressure can tJC very dangerous during high-{ manocuvrcs and can lead to 'G-loc'. In contrast, the mask of this second embodiment of the invention is shown in ligure 6B, and it can be s seen that the skirt 18 extcods inwardly from the cushion 15 and the outer surface 18B of said skirt 18 lies against the pilot's face. Unlike the seal of the prior art masks described above, this configuration does not present a curved edge leading to the point of contact on the pilot's face. 'Ihus, when high pressure breathable gas is supplied to the interior of the mask, the gas pressure exerts a force on the inner surface 18A of the skirt 18, as illustrated by the arrows 'F' in I;igure 6B and pushes the skirt 18 into tighter contact with the pilot's face, to strengthen the air-tight seal therewith. It will be appreciated therefore that increasing the pressure of gas supplied to the interior of the mask increases the integrity of the seal, rather than

weakening it as in the prior art.

The function of the vent hole 19 is to allow the pressure of the gas in the air gap 17 to equalise with the ambient pressure in the cockpit as the plane changes altitude, to prevent damage occurring to the cushion 15.

Referring now to Figures 7 and 8, a faccmask 30 is shown comprising a combination of features of the first and second embodiments of the present invention. The facemask comprises an outer rigid shell 34 and an inner flexible annular sleeve 33, the outer rigid shell 34 being formed in two portions, namely a main body portion 34A and an outer ring portion 34B. lthe flexible sleeve is housed within the rigid shell 34 and is bonded at 33A and 33P, respectively to the inner peripheral edge surfaces of the two rigid shell portions 34A, 34B. The flexible sleeve 33 has extendable means 41 as previously described with reference to the cxtendable means 11 of the first embodiment of the invention. The two portions 34A, 34B of the rigid shell 34 are as previously described with reference to the first embodiment. A cushion 35 is formed around the perimeter of the oro- nasal mask 33 and has a skirt 38 extending inwardly therefrom as previously described with reference to the second embodiment of the present invention. The cushion 35 is hollow and is partially filled with an open-cell foam 36 leaving the remaining space as an air-gap 37. The skirt 38 has an inner and an outer surface 38A, 38B, and a vent hole 39 in fluid communication with the air gap 37.

It will be appreciated by those skilled in the art that a pilot's breathing mask with is the combination of features of the extendable means 41 as previously described with reference to the first emboditnent of the invention, and the skirted cushion 35 on the peripheral edge of the oro-nasal mask 33 as previously described with reference to the second embodiment of the invention, will provide the user with all of the air-tight sealing benefits around the mouth and nose offered by each embodiment, as described separately above.

For the avoidance of doubt, the flexible breathing masks can comprise either a flexible oro-nasal mask 3 in the form of shell contained within a rigid shell 4 as illustrated in Figures 3A and 3B, or alternatively, it may comprise a flexible annular sleeve 13/33 bonded to the inner peripheral edge surface of the rigid shell 14/34 as illustrated in Figures 5, 6A, 6B and 8. Both embodiments of the invention are intended to fall within the scope of the claims. - 12

Claims

Claims 1. A breathing mask comprising a rigid shell attachable to the

helmet of aircrew at a fixed distance therefrom, and a flexible oro-nasal mask within said shell, the periphery of the flexible mask extending beyond the shell and being adapted to maLc a seal with the pilot's face, the flexible oro-nasal mask including extendable means operable to press the periphery of the mask automatically towards the pilot's face to improve the seal therewith when gas at a pressure above that required for normal breathing is supplied to the mask and the lo extendable means reconfigure as a result thereof characterised in that the rigid shell is in two parts and comprises, a main body portion, and a separate peripheral ring portion, the peripheral ring portion being attached to the part of the flexible oro-nasal mask which extends from the shell so that when the gas at elevated pressure is supplied to the interior of the mask and causes the Is extendable means to reconfigure, the periphery of the oro-nasal mask and the peripheral ring attached thereto move together towards the pilot's face and away from the main body portion of the rigid shell.

2. A mask as claimed in claim 1 wherein the extcodable means comprises an annular inwardly directed re-entrant recess formed in the wall of the flexible mask adjaccut the peripheral seal, the depth of said recess in the bottom half of the mask being greater than the depth in the top half thereof.

3. A mask as claimed in claim 2 wherein the recess is V-shaped and comprises an inwardly directed flange on the front portion of the flexible mask which is attached to a correspondingly dimensioned inwardly directed flange adjacent the peripheral seal on a rear portion of the flexible mask.

4. A mask as claimed in claim 1 wherein the extendable means comprises a so plurality of annular inwardly directed recesses formed in the mask wall to provide a bellows therein. - 13

5. A mask as claimed in claim 1 wherein the wall of the mask includes a convoluted rolling section, the thickness of the mask wall in the region of the convoluted rolling section being less than the remainder of the mask thereby allowing the mask to be rolled back on itself into an Sshaped configuration. s

6. A breathing mask comprising a rigid shell attachable to the helmet of aircrew at a fixed distance therefrom, and a flexible annular sleeve attached to the periphery of the shell and extending beyond the edge thereof, said sleeve being adapted to make a seal with the pilot's face, the sleeve including exteodable lo means operable to press the periphery of the sleeve automatically towards the pilot's face to improve the seal therewith when gas at a pressure above that required for normal breathing is supplied to the mask and the extendable means reconfigure as a result thereof characterised in that the rigid shell is in two parts and comprises, a main body portion, and a separate peripheral ring portion, the Is peripheral ring portion being attached to the part of the flexible sleeve which extends from the shell so that when the gas at elevated pressure is supplied to the interior of the mask and causes the extendable means to reconfigure, the periphery of the sleeve and the peripheral ring attached thereto move together towards the pilot's face and away from the main body portion of the rigid shell.

7. A mask as claimed in claim 6 wherein the extendable means comprises an annular inwardly directed re-entrant recess formed in the wall of the flexible mask adjacent the peripheral seal, the depth of said recess in the bottom half of the mask being greater than the depth in the top half thereof.

8. A mask as claimed in claim 7 wherein the recess is V-shaped and comprises an inwardly directed flange on the front portion of the flexible mask which is attached to a correspondingly dimensioned inwardly directed flange adjacent the peripheral seal on a rear portion of the flexible mask. - 14

9. A mask as claimed in claim 6 wherein the extendable means comprises a plurality of annular inwardly directed recesses formed in the mask wall to provide a bellows therein.

s 10. A mask as claimed in claim 6 wherein the wall of the mask includes a convoluted rolling section, the thickness of the mask wall in the region of the convoluted rolling section being less than the remainder of the mask thereby allowing the mask to be rolled back on itself into an Sshaped configuration.

11. A breathing mask comprising a rigid shell with a flexible oro-nasal mask attached to the periphery of the shell and extending beyond the edge thereof, said flexible oro-nasal mask being adapted to make a seal with the pilot's face, the periphery of the flexible oro-nasal mask including a cushion having a skirt projecting therefrom in a direction away from the pilot's face so that, in use, the skirt lies flush against the pilot's face to make an air-tight seal therewith.

12. A mask according to claim 11 wherein the cushion is hollow and toroidal in shape and includes an air hole therein to allow gas pressure to balance between the interior and the exterior of the cushion.

13. A mask according to claim 11 wherein the cushion is C-shaped in cross section and forms an envelope.

14. A mask according to claim 12 or claim 13 wherein the hollow interior of the cushion is partially hlled with open cell foam.

15. A mask according to claim 12 or claim 13 wherein the hollow interior of the cushion is completely filled with open cell foam.

1G. A breathing mask comprising a rigid shell with a flexible annular sleeve attached to the periphery of the shell and extending beyond the edge thereof, said flexible sleeve being adapted to make a seal with the pilot's face, the lo ' periphery of the sleeve including a cushion having a skirt projecting therefrom in a direction away from the pilot's face so that, in use, the skirt lies flush against the pilot's face to make an air-tight seal thctcwith.

s 17. A mask according to claim 1G wherein the cushion is hollow and toroidal in shape and includes an air hole therein to allow gas pressure to balance bctwccn the interior and the exterior of the cushion.

18. A mask according to claim 16 whctcin the cushion is (-shaped in crosssection and forms an envelope.

19. A mask according to claim 17 or claim 18 wherein the hollow interior of the cushion is partially filecd with open cell foam.

20. A mask according to claim 17 or claim 18 wherein the hollow interior of the cushion is completely filled with open cell foam.

21. A mask as claimed in any of claims 11-15 when dependent on any of claims 1 -5.

22. A mask as claimed in any of claims 16 - 20 when dependent on any of claims 6 - 10.