GB2454491A

GB2454491A - Emergency breathing apparatus

Info

Publication number: GB2454491A
Application number: GB0721917A
Authority: GB
Inventors: Joseph Anthony Griffiths
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-11-08
Filing date: 2007-11-08
Publication date: 2009-05-13
Also published as: GB0721917D0

Abstract

A breathing apparatus 110 comprising a respirator mask 112, a hood 116 secured around the peripheral edge of the mask and a harness 114 for securing the mask and hood to a wearer's head. The mask and hood are such that, in use, the mask 112 defines a first contained volume between the wearer's face and the mask, and the hood 116 defines a second contained volume between the edges of the mask, the wearer's head and the hood. The hood 116 extends from the mask 112 to partially cover the head leaving a portion at the back exposed. The hood includes a lower skirt portion 122 which surrounds the neck. The harness 114 is inflatable comprising of a plurality of expandable resilient tubes 119 in fluid communication, and each contained within a fabric sleeve. When compressed air is supplied to the tubes 119, they inflate enlarging the overall dimensions of the harness, forming a more rigid frame, and thus facilitating the placement of the harness 114 over the head.

Description

Emergency Breathing Apparatus

Description

The present invention relates to an emergency breathing apparatus.

Emergency breathing apparatuses are known in the art for use in situations where there has been a sudden hazardous leak of gas or toxic airborne particles that would injure a person if inhaled. Such breathing apparatuses are known as escape sets', and generally comprise a bag or other container containing a mask and/or hood (generally called a respirator' hereafter) connected via a hose and a valve means to a source of breathable air in a high-pressure compressed air cylinder. In an emergency situation, a user dons the respirator, which, in the case of a mask, makes a seal with his face or, in the case of a hood, seals around his neck enclosing his head, and allows him to hreath from the air supply, isolated from the harmful atmosphere.

The valve means is provided between the cylinder and the respirator to reduce the high pressure from the cylinder to a pressure suitable for the wearer to breathe.

These escape sets are provided in environments where there is a possibility of such a hazardous leak occurring, such as chemical plants or oil platforms, in convenient locations so that if a hazardous leak occurs, the people in the vicinity of the leak can quickly get to an escape set and don the respirator to allow them to leave the hazardous area and get to safety.

The valve means provided in such escape sets generally comprises a reducer' which reduces the pressure in the hose from the high pressure in the cylinder (typically around 200 bar) to a much lower pressure, (around 8 bar), and a demand valve' which supplies air from the reducer and the hose, to the respirator at a pressure

suitable to breathe.

When escape sets are not in use, they are stored in the container in a state of readiness for when an emergency occurs. The situations in which they are required are often ones of extreme danger and the time it takes a user to don the respirator and activate the air-flow is critical. It is therefore imperative that the escape set is designed so that the respirator can be donned as quickly as possible, and that the supply of air from the cylinder is initiated as quickly as possible. To help initiate the air supply quickly, some escape sets have an automatic activation system in which, prior to use, the reducer is closed and seals the compressed air supply from the respirator, but when the respirator is removed from the container, the reducer is opened and the supply of air to the respirator is activated. This can be effected by, for example, a cord secured at one end to the container and at the other end to an activation switch on the respirator.

Demand valves can be of two types -positive pressure' demand valves, and negative pressure' demand valves. Negative pressure demand valves supply air to the respirator when a wearer inhales, which reduces the pressure in the demand valve, thereby opening the valve, allowing the air supply into the respirator. Positive pressure demand valves operate in a different manner, by being biased into the open position and only closing when a predetermined pressure above atmospheric pressure it exerted on the valve to close it. Thus, when the respirator mask is sealingly engaged on a wearer's face and/or a respirator hood is sealingly engaged around his neck, the positive pressure demand valve fills the cavity within the respirator with air until the predetermined pressure is reached, and so maintains the air pressure inside the respirator above atmospheric pressure. Thereby, if there is a break in the respirator's seal with the wearer's face or neck, any leakage of gas will only be one way, i.e. that of air from the respirator cavity to the outside atmosphere, and never of the ambient atmosphere into the respirator. This ensures that, when a wearer is using the respirator in an emergency situation in a harmful atmosphere, the harmful atmosphere will never leak into the respirator cavity.

From the description above, it will be appreciated that if a respirator incorporating a positive pressure demand valve is open to the atmosphere, i.e. not sealed against a wearer's face or around his neck, then it will rapidly gush air out in an uncontrolled manner because there is no sealed respirator cavity for it to fill to the predetermined pressure above atmospheric. This wastes air from the cylinder and thereby reduces the length of time a user can breathe from the respirator. Some respirator demand valves incorporate a first breath' mechanism by which the positive pressure demand valve remains closed until the wearer has fitted the respirator to his face or around his neck and takes his first breath, which then activates the demand valve. However, this has the drawback that when a wearer first dons the respirator in a toxic atmosphere, some of the toxic atmosphere will be trapped inside the respirator cavity, meaning that his first breath will involve inhaling some of the toxic gas.

It is therefore desirable to have a constant but steady and controlled flushing flow of air out of the respirator prior to a user taking his first breath therefrom, so when first donned, the flushing flow purges the respirator cavity of any toxic atmosphere that may have been trapped therein but does not waste the supply of air.

Another aspect of escape sets that causes delay in their operation is the process of donning the respirator and securing it to the wearer's head and making a seal with the wearer's face or neck. Conventional escape sets comprise an arrangement of harness straps and buckles which need to be loosened to allow the wearer to fit the respirator over his head, and then once in place, tightened to secure the respirator in place tight enough against the face, in the case of a respirator mask, and/or around the neck in the case of a respirator hood, to maintain a seal therewith. As mentioned above, escape sets are intended for use in emergency situations which are hazardous and stressful. It is therefore important that the respirator is able to be donned and secured in place as quickly and easily as possible, and that the attachment arrangement is as simple as possible to operate in order to prevent panicked fumbling in trying to don the respirator. Conventional strap and buckle harnesses are problematic in that their fitment is relatively slow and complicated, and so increases the time during which the wearer is at risk from the harmful atmosphere. It is also difficult to tell whether the respirator has been correctly fitted, and so it may leak and waste valuable air from the cylinder, reducing the time available for the wearer to get to safety.

If a person has a large amount of facial hair, such as a large beard, this can prevent mask-style respirators from being able to effect a seal against his face. For such users, the hood-style respirators are much more suitable because the hood completely encloses the wearer's head and makes a seal with the smooth skin of the wearer's neck below the facial hair-line. However, known respirator hoods which completely enclose a wearer's head and seal around the neck also suffer their own drawbacks, the primary one being achieving a satisfactory seal around the wearer's neck. Conventionally, this is achieved by using a rubber neck seal in the form of a disc-shaped sheet with a central hole which stretches over a wearer's head when donning the respirator hood, the outer edge of the disc being sealed to the respirator hood. In such devices, the neck seal must be made such that one-size-fits -all' and to achieve this, a relatively thin rubber seal must be used. It has been found that materials other than natural rubber do not stretch enough and recover back to their original shape to effect a satisfactory seal around a wearer's neck. However, temperature and UV can adversely affect the thin rubber material during storage and may cause it to perish, resulting in it tearing when being fitted over a wearer's head, which, in an emergency situation, could have serious consequences.

The applicant's earlier published UK patent application no. GB 2430159 discloses an emergency breathing apparatus comprising a face mask and hood which provides a solution to the above-described problems of other known breathing apparatuses.

This breathing apparatus comprising a respirator mask securable around a user's face and an inflatable harness to secure the mask onto the wearers face. The application also discloses the mask having a hood portion which is attached around the edge of the mask and completely encloses the wearer's head, and a portion of the inflatable harness being positioned to surround the wearer's neck to make a seal therewith.

The feature of the hood cavity providing a secondary substantially sealed chamber which encloses the wearer's head, which extends around the first sealed chamber -i.e. the area between the wearer's face and the mask itself, results in the breathing apparatus achieving operating performance which far exceeds that which can be attained by other known devices, even when a wearer has facial hair which can compromise the seal between the wearer's face and the mask. For instance, when a user breathes in, there may be an instant just before the demand valve allows air from the breathable gas supply into the mask, where air is drawn past the face/mask seal. This would be especially likely if the wearer has a large amount of facial hair since the hair compromises the face/mask seal. However, in such cases, air is only drawn from the hood volume which is filled with breathable gas leaked from the mask itself, and so any minute leakage into the mask is only pure breathable gas, and not harmful ambient gas from the surrounding environment.

Indeed, in use, it is known that the seal between the wearer's face and the mask may leak slightly, and it is also known that the hood seal around the wearer's neck is not 100% efficient and may also leak slightly. Therefore, the neck seal acts as more of a restriction to the flow of gas rather than a total barrier to the flow of gas. However, due to the flow of breathable gas from the gas supply being provided to the mask, and leaking into the secondary chamber of the hood, even with such leaks in the mask/face and hood/neck interfaces, the performance of the apparatus in test conditions is exceptional.

Standards for UK Fire brigades' breathing equipment specify that it must achieve a sealing factor of 1:2000 -that is, it must not let in more than one part of ambient atmosphere in 2000 to the mask and therefore, to the user to inhale. As such, UK fire-fighters are prohibited from having facial hair so that when using standard breathing equipment (not like the Applicant's mask/hood device), the face/mask seal isn't compromised. For comparison, the standard set for military air crew respirators to achieve is a sealing factor of 1:1 o, although some known air crew respirators only achieve 1:1 o in practice.

Oil refineries in certain eastern countries, in particular, Kazakhstan, are known to have gas leak problems in certain areas, and gas masks only achieving a sealing factor of 1:2000 in such environments are insufficient to avoid workers being asphyxiated, such is the toxicity of the gas in these environments. However, local cultural traditions mean the workers often have large beards, meaning standard breathing masks are incapable of providing adequate protection for the workers.

Aside from full beards, facial stubble has been proven to cause mask face seals to fail, 3-day stubble, on average, being the worst. This is due to the upstanding rigidity of the hairs in stubble compared to the relative softness of full beard hair which tends to lie flat when a mask is put on over a beard.

However, in trials, the Applicant's breathing apparatus incorporating the hood disclosed in 0611646.1, achieved a sealing factor of 1:106, despite the test subjects having 3-day facial stubble. Self Contained Breathing Apparatus test standards require a delivery test volume rate of 40 litres/minute. However, the above exceptional sealing factor was still achieved with test subjects drawing an average of litres/minute, with a maximum volume rate of one test subject reaching 90 litres/minute.

Although the sealing factors achieved with the Applicant's mask and hood apparatus was highly satisfactory, there remained one problem, that being that in high breathing volume rates -induced by the test subjects exercising during the test, the mask and hood combination resulted in the test subjects' heads becoming uncomfortably hot.

It is therefore an object of the present invention to provide a respirator which substantially alleviates or overcomes the problems mentioned above.

According to the present invention, therefore, there is provided a breathing apparatus comprising a respirator mask, a hood secured around the peripheral edge of the mask and a harness for securing the mask and hood to a wearer's head, the mask and hood being configured such that when the breathing apparatus is worn by a wearer, the mask defines a first contained volume between the wearer's face and the mask, and the hood defines a second contained volume between the edges of the mask, the wearer's head and the hood, wherein the hood extends from the mask to partially cover the wearer's head such that a portion of the rear of the wearer's head remains exposed.

Preferably, the hood has a peripheral edge remote from that mask and said peripheral edge includes a constricting means to seat the peripheral edge of the hood against the wearer's head to close the second volume.

The hood preferably comprises a lower skirt portion that, when the breathing apparatus is worn, surrounds the wearer's neck, and the lower skirt portion preferably includes a constricting means to hold the lower skirt portion against the wearers' neck when the breathing apparatus is worn.

In a preferred embodiment, the hood comprises a cut-away portion that extends from above the lower skirt constricting means to the top of the hood to expose substantially the rear half of the wearer's head when the breathing apparatus is worn.

Conveniently, the harness is inflatable, and preferably comprises an expandable resilient tube. Preferably, the inflatable harness comprises a plurality of expandable resilient tubes in fluid communication. In a preferred embodiment, the constricting means around the peripheral edge of the hood comprises an inflatable expandable resilient tube, which may be in fluid communication with the harness and/or the neck tube.

Preferably, the lower skirt constricting means comprises an inflatable expandable resilient tube secured therearound, so that, when inflated, it holds the hood opening apart to allow it to be placed over the wearer's head and, when deflated, it extends contracts against the wearer's neck.

Conveniently, the hood is secured to a portion of the inflatable harness.

In a preferred embodiment, the expandable resilient tube(s) of the inflatable harness is/are surrounded by a sleeve of inextensible material to limit the maximum expansion of the expandable resilient tubes. Preferably, the sleeves are made of a flexible corrugated material which can be extended to a straight, un-corrugated configuration on expansion of the resilient tubes, but which are inextensible once extended to said straight configuration.

The breathing apparatus preferably includes a control valve to control a flow of air from a supply to them mask, the control valve preferably being configured to allow air to flow to the inflatable harness.

A preferred embodiment is configured so that the harness automatically inflates and expands prior to the respirator being secured to the wearer's head, and automatically deflates and contracts once the respirator is sealed on the wearer's head.

The control valve is preferably configured so that, in a first position, a restricted flushing flow of compressed air from the supply is allowed to flow to the mask and a flow of compressed air is allowed to flow to the inflatable harness to inflate and cause the harness to expand to facilitate the placement of the harness over the head of the wearer and, in a second position, an unrestricted flow of compressed air is allowed to flow to the mask and the flow of compressed air to the inflatable harness is prevented so that the harness deflates and contracts to secure the breathing apparatus to the wearer's head.

The constricting means around the peripheral edge of the hood may comprise an elastic member.

An inhalation demand valve is preferably disposed between the control valve and the respirator, and the demand valve is preferably a positive pressure demand valve configured to maintain the air pressure within the respirator at a pre-determined value above atmospheric pressure.

The breathing apparatus preferably includes a cylinder for compressed breathable air connected to the control valve via a supply hose, and a supply valve disposed between the cylinder and the control valve, wherein the supply valve includes a coupling for connection to an auxiliary air supply, and a switching means to selectively switch between the cylinder and the coupling for the supply of air to the control valve.

The switching means preferably includes a spool valve slidably mounted within the supply valve and moveable from an open position to allow the flow of air from the cylinder to the control valve and, a closed position in which the cylinder is sealed from the control valve.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to Figures 3 -8B of the accompanying drawings, in which: Figure 1 is a perspective view of a known breathing apparatus; Figure 2 is a cross-sectional view of the breathing apparatus of Figure 1 in place on a wearer's head; Figure 3 is a perspective view of a breathing apparatus of the present invention; Figure 4 is a cross-sectional view of the breathing apparatus of Figure 3 in place on a wearer's head; Figure 5 is a schematic cross-sectional view of a control valve of the breathing apparatus of Figure 3, in a first position; Figure 6 is a view of the control valve of Figure 5 in a second position; Figure 7 is a cross-sectional view of the positive pressure demand valve used in the breathing apparatus of Figures 3 and 4; Figure 8A is a sectional view of a portion of the inflatable harness of the breathing apparatus in a deflated state; Figure 8B is a sectional view of a portion of the inflatable harness of Figure 8A in an inflated state; Referring now to Figures 1 and 2, a known emergency breathing apparatus 10 is shown, comprising a respirator mask 12 and an inflatable harness 14 to secure the mask 12 to a wearer's head. The mask 12 has a seal 13 around its peripheral edge that, when worn, makes a substantially air-tight seal around the wearer's face. The mask 12 and harness 14 are fluidly connected to a source of compressed air (not shown) by a supply hose 15 via a control valve 20 on the front of the respirator 12.

The mask 12 also includes a positive pressure exhalation valve (not shown) to allow air exhaled by a wearer to be expelled from the mask 12, and an inhalation valve 50 -10 -to allow air into the mask 12. The whole breathing apparatus 10, including the compressed air supply, is contained within a bag 17 made of suitably tough material, such as PVC coated weatherproof material, or an anti-static material if the apparatus is to be used in potentially explosive environments.

The breathing apparatus also includes a hood 16 secured around the edge of the mask 12 to completely enclose a wearer's head. As can be seen from Figure 2, the hood 16 is secured to the mask 12 adjacent the edge seal 13. The inflatable harness 14 extends over the outside surface of the hood 16 and is secured thereto by a plurality of retaining loops 18.

A neck seal 19 is provided encircling a lower portion of the hood 16 and is connected in fluid communication with the harness 14 via a connecting hose 19A.

The neck seal 19 is made of the same construction as the harness 14 and is also secured to the hood 16 by a plurality of retaining loops 18.

As described above, this known prior art breathing apparatus suffers a drawback that the mask 12 and hood 16 combination means that the wearer's head can become uncomfortably hot and sweaty, especially if the breathing apparatus is to be used during exertion or in hot and/or stressful situations.

Therefore, the present invention provides an improved breathing apparatus that ensures a high level of breathing performance and sealing factor from ambient atmosphere, but additionally addresses the over-heating problems with the prior art.

A breathing apparatus 110 of the present invention is shown in Figures 3 and 4, and comprises a respirator mask 112 and an inflatable harness 114 to secure the mask 112 to a wearer's head. The mask 112 has a seal 113 around its peripheral edge that, when worn, makes a substantially air-tight seal against the wearer's face. The mask 112 and harness 114 are fluidly connected to a source of compressed air (not shown) by a supply hose 115 via a control valve 20 on the front of the mask 112.

The mask 112 also includes a positive pressure exhalation valve (not shown) to allow air exhaled by a wearer to be expelled from the mask 112, and an inhalation -11 -valve 50 (described in detail hereafter) to allow air into the mask 112. The whole breathing apparatus 110, including the compressed air supply, is contained within a bag 117 made of suitably tough material, such as PVC coated weatherproof material, or an anti-static material if the apparatus is to be used in potentially explosive environments.

The breathing apparatus also includes a hood 116 secured around the peripheral edge of the mask 112 and adjacent the mask edge seal 113. The inflatable harness 114 extends over the outside surface of the hood 116 and is secured thereto by a plurality of retaining loops 118. The hood 116 includes a lower skirt portion that, when worn, surrounds the wearer's neck. A neck tube 119 is provided encircling the lower skirt portion of the hood 116 and is connected in fluid communication with the harness 114 via a connecting hose 11 9A. The neck tube 119 is made of the same construction as the harness 114 and is also secured to the hood 116 by a plurality of retaining loops 118.

It can be seen from Figures 3 and 4 that the hood 116 does not entirely enclose the wearer's head. Instead the hood 116 extends from the peripheral edge seal 113 of the mask 112 but stops at a hood peripheral edge 120 which extends from one side of the neck tube 119 across the top of the wearer's head, to a corresponding point on the opposite side of the neck tube 119. This leaves the rear portion of the wearer's head exposed, but the front portion surrounding the mask 112 enclosed within the hood 116.

In the embodiment shown and described, the hood peripheral edge 120 is provided with an elastic tensioning member 121 such that when the breathing apparatus is worn, with the neck tube 119 in place around the wearer's neck, the elastic member 121 tensions the hood peripheral edge 120 and holds it tights against the wearer's head.

The fully fitted arrangement of the breathing apparatus results in a first closed volume, designated 124, defined within the mask 112 between the mask 112 inner surface and the wearer's face. There is also defined a second closed volume, -12 -designated 126, adjacent and surrounding the first sealed volume 124, defined between the outer surface of the mask 112 and its edge seal 113, the hood 116 and the wearer's head. As defined above, the fitted breathing apparatus 110 leaves the rear of the wearer's head exposed so that (s)he can lose heat efficiently therefrom whilst still breathing from the breathing apparatus 110.

The control valve 20 is shown in detail in Figures 5 -6, and comprises a housing 21 having a first chamber 22 and a second chamber 23, fluidly connected by a connecting passage 24. The housing 21 has an inlet port 25 leading to the first chamber 22 for the supply of compressed air thereto, and a first outlet 26 extends from the first chamber 22 through the valve housing 21 for the supply of compressed air to the inside of the respirator mask 12. A second outlet 27 extends from the first chamber 22 through the wall of the housing 21 and is open to atmosphere providing a first vent 27 for reasons which will be explained hereafter.

A third outlet 28 extends from the second chamber 23 through the housing 21 to supply pressurised air to the inflatable harness 14, and a fourth outlet 29 extends from the second chamber 23 through the housing 21 and is open to atmosphere to provide a second vent 29 to enable air in the second chamber 23 to vent to atmosphere.

A piston 31 is slidably disposed in the first chamber 22, and comprises a head 32 and an elongate shaft 33. A rubber seal 34 extends around the head 32 and makes an air-tight seal against the inside wall of the first chamber 22. The shaft 33 extends from the centre of the head 32 perpendicularly therefrom, away from the inlet port 25, and extends through the connecting passage 24. A passage seal 35 is provided to make an air-tight seal between the shaft 33 and the inside wall of the connecting passage 24 to ensure that air is not able to pass therebetween. The piston 31 is thereby able to slide axially within the first chamber 22 and the connecting passage 24 from a first position shown in Figure 5, to a second position shown in Figure 6.

The first vent 27 allows air trapped in the first chamber between the piston head 32 and a wall 21a adjoining the second chamber 23, to escape to atmosphere, to prevent the pressure of air trapped therein increasing through compression, which -13 -would increasingly restrict the movement of the piston 31. The piston 31 has a hollow bore 36 extending axially through the head 32 and though the shaft 33 which allows the flow of air though the piston 31 from the inlet port 25 into the second chamber 23.

A first valve seat 37 is located where the inlet port 25 opens into the first chamber 22 and is positioned such that the head 32 of the piston 31 abuts the first valve seat 37 when in the first position, shown in Figure 5, and makes a seal therewith. In this position, the hollow bore 36 is in fluid communication with the inlet port 25. A piston spring 38 is provided around the piston shaft 33 between the piston head 32 and the adjoining wall 21a of the first and second chambers 22, 23 to bias the piston 31 into the first position.

A small bypass orifice 39 extends from the inlet port 25 though to the first outlet 26 and is dimensioned so as to only allow a restricted flow of air therethrough when the piston 31 is in the first position sealingly engaged with the first valve seat 37.

A poppet 41 is slidably disposed in the second chamber 23 and comprises a head 42 and a shaft 43 extending perpendicularly therefrom. The poppet 41 is similar in configuration to a small piston, except that the head 42 of the poppet does not make a seal against the inside surface of the second chamber 23, as a piston' would, but instead is spaced therefrom. The second chamber 23 has a narrow section 23a and a wide section 23b and a second valve seat 47 is disposed at the transition between the narrow 23a and wide 23b sections. The third outlet 28 extends from the narrow section 23a and the fourth outlet (or second vent') 29 extends from the wide section 23b. The poppet 41 is slidable from a first position (shown in Figure 2) to a second position (shown in Figure 3). In the first position, the head 42 of the poppet 41 abuts the second valve seat 47 and seahngly engages therewith so that the third and fourth outlet outlets 28, 29 are sealed from each other. A poppet spring 48 is provided in the wide section 23b of the second chamber 23, between the poppet head 42 and an adjacent wall 21b of the valve housing 21, to bias the poppet 41 into the first position. When the poppet 41 is in the second position, the head 42 is spaced from the second valve seat 47 and so the narrow and wide sections 23a, 23b -14-of the second chamber 23 are in fluid communication, and so the third and fourth outlets 27, 28 are also in communication with each other.

The inflatable harness 114 comprises a plurality of expandable resilient tubes I 14A in fluid communication with each other, each contained within a fabric sleeve I 14B (see Figures 8A and 8B). The sleeves I 14B are made from an inextensible, flexible corrugated material and loosely cover the tubes 114A when the tubes 114A are in their relaxed deflated state (see Figure 8A). However, when compressed air is supplied to the tubes I 14A, the tubes I 14A inflate and expand within the sleeves 114B, enlarging the overall dimensions of the harness 114, and also forming a more rigid frame shape (as shown in Figure 3). The degree to which the tubes I 14A are able to expand is limited by the sleeves 114B surrounding the tubes 114A. As the tubes I 14A expand, the corrugations of the sleeves I 14B are straightened out until the material of the sleeves I 14B is pulled taut. At this point, the sleeves I 14B are unable to extend any further and they thereby limit the maximum size which the harness 114 can expand to.

The breathing apparatus 110 comprises a reducer valve (not shown) disposed between the compressed air supply and the control valve 20. This serves to reduce the pressure from the compressed air supply (typically around 200 bar) to a less elevated pressure above atmosphere (around 8 bar). As mentioned above, the reducer may include an automatic activation switch which is shut to isolate the compressed air supply from the mask 112 when the breathing apparatus 110 is not in use, but is automatically activated upon removal of the breathing apparatus 110 from the bag 117 when it is to be used. This can be any suitable mechanism, such as a release cord secured to the bag and to the reducer valve, which, for example, pulls a switch or releases a pin to open the reducer valve when the breathing apparatus is removed from the bag I 17 and the cord is thereby pulled.

The first outlet 26 from the valve housing 21 communicates with an inlet valve of the mask 112 which comprises a positive pressure demand valve 50. This demand valve 50 is shown in more detail in Figure 7, and is designed to allow a flow of breathable air from the compressed air supply and the control valve 20 to the -15 -interior of the mask 112. Before the mask 112 is sealed against a wearer's face, it is open to atmosphere, and so the demand valve 50 allows a constant flow of air through it. However, once the mask 112 is sealed against a wearer's face and the first closed volume 124 is created between the wearer's face and the mask 112, the demand valve 50 is configured to allow a supply of air into the mask 112 until the pressure within the first closed volume 124 reaches a predetermined value, after which the demand valve 50 stops the supply of air to the mask 112, and thereafter maintains the pressure within the first closed volume 124 at the predetermined pressure. The way the demand valve 50 is configured to achieve this function will be explained in detail hereafter with reference to Figure 7.

The positive pressure demand valve 50 (hereafter referred to simply as demand valve') comprises a housing 51 including an inlet jet 52 in communication with the first outlet 26 of the control valve 20, and an outlet 53 in communication with the inlet jet 52 and with the interior of the mask 112. A seal 54 is mounted on a sliding seal carrier 55 and is positioned adjacent to the inlet jet 52. A diaphragm 56 is pivotally mounted to the housing 51 at a pivot point 57 and comprises a solid rigid disc 56a with a flexible outer skirt 56b which connects the periphery of the rigid disc 56a to the housing 51 and closes the housing such that the only inlet and outlet to the housing are the inlet jet 52 and the outlet 53. The pivot point 57 is positioned proximate an edge of the rigid disc 56a off-centre thereof. A portion of the rigid disc 56a between the pivot point 57 and the closest edge thereto, is disposed adjacent the end of the seal carrier 55 remote from the seal 54, such that pivoting the diaphragm 56 about the pivot point 57 causes the rigid disc 56a to contact the seal carrier 55 and push the seal carrier 55 so that the seal 54 seals against the open end of the inlet jet 52 to prevent air from flowing therethrough. A protective cover 58 encloses the front of the demand valve 50 to hide the diaphragm 56, and includes an aperture 59 therethrough to ensure the space between the diaphragm 56 and the cover 58 is maintained at ambient atmospheric pressure.

The operation of the positive pressure demand valve 50 will now be described with reference to Figure 7. Air above atmospheric pressure is supplied from the control valve 20 (as will be explained later) to the inlet jet 52. The pressurised jet of air -16 -impinges on the seal 54 which pushes the seal carrier 55 away from the inlet jet 52 and so tilts the diaphragm 56 about the pivot 57, and allows air to flow through the demand valve 50 and out of the outlet 53 into the mask 112.

If the mask 112 is not in place on a wearer's face with the edge seal 13 sealing thereagainst, no first closed volume 124 is formed between the mask 112 and the wearer's face, and so no air pressure is able to build up inside the mask 112. In this case, the air simply continues to flow through the mask 112 to atmosphere providing a flushing flow of air into the mask 112 so that when a user dons the mask 112, fresh breathable air fills the first closed volume 124 to displace a large proportion of the harmful atmosphere to avoid it being trapped in the resulting first closed volume 124. However, once the wearer dons the mask 112 and creates the first closed volume 124, the air flowing into the mask 112 though the demand valve collects inside the mask 112 and so the air pressure in the mask 112 increases.

The pressure F,, inside the mask 112 acts over the main area 56c of the diaphragm 56 on the side of the pivot 57 remote from the sliding seal carrier 55. This moment is counteracted by the force F, of the air flow from the inlet jet 52 impinging on the seal 54 and being exerted, via the seal carrier 55, on the other side 56d of the diaphragm 56, on the other side of the pivot 57 from the main area 56c. So long as the moment about the pivot 57 caused by the inlet airflow force F, acting on said other side 56d of the diaphragm 56 is greater than the moment caused by the respirator cavity pressure F,, active over the main area 56c of the diaphragm, the seal 54 is held away from the inlet jet 52 and so air continues to flow into the first closed volume. Other additional forces also affect this balance of the diaphragm 56 about its pivot 57, although these forces are small compared to those major moments of force described above. Such additional forces include the pressure F also acting over said other side 56d of the diaphragm 56 against the pivoting moment of force created by the pressure F,, acting over the main area 56c of the diaphragm 56. Also, the flexible outer skirt 56b connected between the demand valve housing 51 and the rigid disc 56a of the diaphragm 56 will exert a small resistance to pivotal movement of the diaphragm 56 about its pivot 57.

-17 -So long as the seal 54 on the seal carrier 55 is held away from the inlet jet 52, the respirator cavity pressure F increases until it reaches the pre-determined value, at which point, the demand valve 50 is configured such that the moment about the pivot 57 caused by the respirator cavity pressure F acting over the main area 56c of the diaphragm 56 is greater than the inlet airflow force F, acting on said other side 56d of the diaphragm 56, taking into consideration the additional moments of force mentioned above, and so the diaphragm 56 tilts about the pivot 57, pushing the seal carrier 55 towards the inlet jet 52 and engaging and holding the seal 54 against the inlet jet 52, preventing further airflow into the first closed volume, and thereby maIntaining the pressure F therein at the pre-determined value. In practice, the pressure F maintained in the respirator cavity is around 3OmmH2O, although the geometry of the demand valve 50 (e.g. position of pivot 57, surface area of diaphragm 56) can be adjusted to maintain other pressures as required.

It will be appreciated that as a user inhales air from the mask 112, the pressure F will drop, and so the diaphragm 56 will pivot to allow more air into the first closed volume 124, until the pre-determined pressure is reached again, when the diaphragm 56 will pivot back to seal the inlet jet 52 once more. As mentioned above, the outlet valve (not shown) provided in the mask 112 is a positive pressure valve which means that it is biased to remain closed up until the predetermined pressure is reached within the mask 112, so that such pressure may build up in the first closed volume and so that the pressurised air supplied to the mask 112 does not simply flood straight out of the outlet valve.

For the breathing apparatus 110 to function correctly, it is important that the demand valve 50 is in its open position prior to, and at the moment of, the supply of air being activated. This is because any momentary build up of pressure caused by the demand valve 50 being closed when the air supply is activated, may cause the control valve 20 to operate prematurely, as will be better understood from the description hereafter. To avoid this, the diaphragm 56 may be configured to normally rest in the open position, or separate biasing means may be provided to ensure that the diaphragm 56 is biased away from the inlet jet 52. Such biasing means could include a spring located adjacent the seal carrier 55 to push the other -18 -side 56d of the diaphragm 56 away from the inlet jet 52. Alternatively, a spring could be provided between the rigid plastic disc 56a part of the diaphragm 56 on the main side 56c thereof, and the outer protective cover 58 to push the main side 56c away from the protective cover 58 and thereby bias the other side 56d of the diaphragm 56 away from the inlet jet 52.

The particular arrangement of the diaphragm 56 contacting a sliding seal carrier 55 to push the seal 54 into engagement with the inlet jet 52, is particularly advantageous over, for example, a portion of the tilting diaphragm 56 directly contacting the inlet jet 52 to seal it, because in the illustrated embodiment, the seal 54 approaches and engages the inlet jet 52 completely square-on -that is to say, the whole of the seal 54 comes into contact with the inlet jet 52 at one instance. If the tilting diaphragm 56 directly sealed the inlet jet 52, the pivoting configuration of the diaphragm means it would approach the inlet jet 52 at an angle from one side, which would adversely affect the ability to effectively seal the inlet jet 52.

The general operation of the breathing apparatus 110 of the invention will now be described. When a user wishes to use the breathing apparatus 110 of the invention, (s)he opens the bag 117 and pulls out the breathing apparatus 110 and compressed air supply, and the automatic activation system opens the reducer valve to allow compressed air at around 8 bar to flow into the control valve 20. The air enters the inlet port 25 and flows through the hollow bore 36 of the piston 31, into the narrow section 23a of the second chamber 23, and out of the third outlet 28 into the harness 14. This inflates the harness 114 and the resilient flexible tubes 114A expand within the corrugated fabric sleeves 11 4B until they reach their maximum permitted expansion.

The edge of the hood 116 around the open end of the lower skirt portion is provided with a stiffening band 122 to give the edge a degree of support and keep it in an open state and prevent it from crumpling closed. However, the band 122 is resilient and can be deformed into a compressed state, but when released, will return to its expanded form. This stiffening band is a preferred feature only and -19 -invention is not limited thereto, as the hood 116 may equally not include such a feature.

As the neck tube 119 is in fluid communication with the harness 114 through the connecting hose 119A, the neck tube 119 also expands. Since the harness 114 and the neck tube 119 are secured to the hood 116 by the retaining ioops 118, they pull the hood 116 outwards as they expand causing the opening around the lower skirt portion of the hood 116 to enlarge and the space within the hood 116 to expand. In addition, the resilient band 122 around the lower skirt portion opening of the hood 116 springs outwards to keep the hood opening as wide open as possible. Once the harness 114 and neck tube 119 are in the expanded, semi-rigid state, it is easy for the user to don the breathing apparatus 110 by placing the hood 116 over their head and the mask 112 against their face.

The elastic member 121 around the hood peripheral edge 120 functions as a constriction means to secure the hood peripheral edge 120 against the top and sides of the wearer's head, although at this stage, the neck tube 119 is still expanded and so the lower portions of the elastic member 121 are still held away from the wearer's neck/head.

Simultaneously, the air flows from the inlet port 25, through the bypass orifice 39 and out of the first outlet 26 to the demand valve 50. As described above, because the user has not put the mask 112 against his face to create the first closed volume 124, no pressure can build up within the mask 112 and so the demand valve 50 remains in its open state and allows a flushing flow of air though the mask 112 to atmosphere. In this condition, the piston 31 is biased into the first position against the first valve seat 37. Any air pressure exerted on the area A1 of the head 32 of the piston 31 though the inlet port 25 is not sufficient to overcome the biasing force of the piston spring 38, and so the piston 31 remains in the first position. Because any air around the first outlet 26 can flow freely through the demand valve 50 and out through the mask 112, no air pressure above atmospheric pressure acts over the larger surface area A2 of the head 32 of the piston 31.

-20 -When the wearer dons the breathing apparatus 110 and the edge seal 113 seals against his face, the first closed volume 124 is formed and so the air flowing into the mask 112 builds up pressure therein. Once the pressure reaches the pre-determined value, the demand valve 50 automatically pushes the seal 54 against the inlet jet 52 to prevent any further inflow of air into the mask 112. This back-pressure that has then built up in the inlet port 25, in the first outlet 26 and in the first chamber 22 on the inlet port 25 side of the piston 31, is able to act over the larger surface area A2 of the head 32 of the piston 31. The resulting force is sufficient to overcome the biasing force of the piston spring 38, and so the piston 31 moves to the second position. In doing so, the end of the shaft portion 33 of the piston 31 abuts the end of the shaft 43 of the poppet 41. Firstly, this blocks the hollow bore 36 through the piston 31 and so prevents any more air from flowing into the second chamber 23. Secondly, the force exerted by the air pressure acting over the larger surface area A2 of the piston 31 is sufficient to overcome the biasing force of the poppet spring 48 as well as that of the piston spring 38, and so the piston 31 pushes the poppet 41 into the second position, as shown in Figure 3. As the piston 31 moves to the second position, air between the piston head 32 and the wall 21a adjoining the second chamber 23 is expelled though the first vent 27, preventing the build up of pressure which would further restrict movement of the piston 31. Therefore, the only force resisting movement of the piston 31 is that of the piston spring 38. Thirdly, the head 32 of the piston 31 moves away from the first valve seat 37 and so allows a full, unrestricted flow of air from the inlet port 25 through the first chamber 22 and out of the first outlet 26 to the demand valve 50 and mask 112. This full flow is then sufficient to provide the wearer with enough air to breath comfortably and maintain the elevated pressure within the mask 112.

When the poppet 41 is in the second position, the head 42 is spaced from the second valve seat 47, which allows air to flow between the narrow and wide portions 23a, 23b of the second chamber 23, and thereby allows the inflatable harness 114 to deflate via the third outlet 28 to outside of the valve housing 21 though fourth outlet, or second vent, 29. As the resilient tubes 11 4A of the harness 114 deflate, they contract around the wearer's head, and hold the mask 112 into sealing engagement with his face, maintaining the first closed volume 124. In -21 -addition, being in fluid communication with the harness 114, the resihent neck tube 119 also deflates and contracts around the wearer's neck, thereby pushing the material of the hood 116 against the wearer's neck. This brings the lower ends of the elastic member 121 around the hood peripheral edge 120 into contact with the wearer's head, so that the entire hood peripheral edge 120 is held against the wearer's head, creating the second closed volume 126.

During normal operational use, the piston 31 and poppet 41 of the control valve 20 remain in their respective second positions so that a full flow of air is provided to the demand valve 50 for the wearer to breathe, and the inflatable harness 114 and neck tube 119 remain deflated and contracted around the wearers head and the elastic member 121 remains constricted against the wearer's head. The wearer can thereby safely breathe from the compressed air supply despite being surrounded by a harmful atmosphere, and get to safety. The compressed air supply is typically designed to provide 10 -15 minutes breathing time, although more or less breathing time could be provided by altering the size of a compressed air supply cylinder provided with the breathing apparatus 110.

If the seal of the edge 113 of the mask 112 against the wearer's face is compromised, the air will only escape into the second closed volume 126 defined between the mask 112, the wearer's head and the hood, and the elastic member of the constricting means 121 around the peripheral edge 120 of the hood 116.

Therefore, the breathing apparatus 110 is still able to maintain an elevated pressure within the first closed volume 124 and the second closed volume 126 to enable the control valve 20 and demand valve 50 to continue to work properly and for the wearer to continue using the breathing apparatus 110. This capability is particularly important when the apparatus is being used by someone with a large amount of facial hair, such as a large beard, and operation of the apparatus in such circumstances is described in more detail below.

When worn by a user with a significant amount of facial hair, a portion of the seal 113 of the mask 112 will contact the wearer's beard and so will not be in contact with the smooth skin of the face. At this portion, the mask edge seal 113 may not -22 -be able to affect an air-tight seal with the wearer's face, and so, because the interior volume of the mask 112 is maintained at a positive pressure, somewhere in the region of 50 millibars or 2 inches of water, some of the breathable air supplied to the mask 112 may escape into the hood 116. However, since the resilient tube 119 around the neck portion and the elastic member 121 of the constricting means around the peripheral edge 120 of the hood 116 create the second closed volume 126, which resists the flow of gas out of the second closed volume 126, any air that escapes from the mask 112 past the edge seal 113 is held in the second closed volume 126 of the hood 116. Furthermore, since the mask pressure is elevated relative to the ambient atmosphere, the pressure within the second closed volume 126 of the hood 116 is also elevated. This has the dual benefits of, firstly, if the neck tube 119 of the hood 116 or the elastic member 121 around the peripheral edge 120 of the hood 116 against the user's head, is compromised in any way, the leakage of gas would only be of air from the second closed hood volume 126 to atmosphere, and not the other way round, thereby ensuring that any toxic gases in the ambient surroundings do not enter the second closed volume 126; secondly, if the user starts breathing very heavily, and so begins to consume air faster than the breathable gas supply system can deliver it to the mask 112, the pressure within the mask 112 may drop. If this happens, and since the wearer's beard may affect the seal 113, any leakage of gas into the mask 112 at the beard portion of the seal 113 would be from the second closed hood volume 126, which would comprise only breathable air that had previously escaped from the mask 112, and not any toxic gases from the ambient atmosphere.

In addition, in such circumstances, where the wearer is exerting him/herself and/or is in a hot and/or stressful environment, as emergency escapes from burning/malfunctioning industrial plants are, the exposed rear portion of the wearer's head through the hood 116 allows him/her to cool down, improving body temperature and reducing stress and their air consumption.

When the supply of compressed air runs out, the breathing apparatus 110 is designed to automatically release the harness 114 from the wearer's head to prevent him from suffocating. As the pressure from the air supply drops, the force exerted -23 -over the area A2 of the piston 31 reduces, until it is less than the combined biasing force of the piston and poppet springs 38, 48, and then less than the biasing force of the piston spring 38. This results in the piston 31 and poppet 41 moving back to their respective first positions, and so the head 42 of the poppet 41 seals against the second valve seat 47 sealing the inflatable harness 114 from the fourth outlet 29. As the piston 31 moves away from the poppet 41, the hollow bore 36 of the piston 31 is open again, and so the remaining air pressure from the supply is able to flow though the piston 31 to the second chamber 23 and into the inflatable harness 114.

The resilience of the tubes 11 4A of the harness 114 is designed such the tubes 11 4A are able to inflate even with the reduced air pressure available as the air supply runs low. Therefore, the inflatable harness 114 expands, loosening from around the wearer's head, allowing the wearer to easily remove the breathing apparatus 110 from his head and face.

The breathing apparatus 110 described above all include a supply of breathable air provided with the kit which would generally be in the form of a pressurised air cylinder (not shown), as is known in the state of the art. However, to make the escape sets' of a convenient size, the air cylinder must be small enough to fit into the bag 117, and light enough for a user to easily carry around with them as they make their evacuation from the hazardous environment. This means that a compromise must be made between size and weight of the air cylinder, and the amount of pressurised breathable air available with each escape set cylinder.

Generally, a cylinder which provides between 20 -30 minutes of breathing time is suitable. Therefore, it is important to be able to conserve the air in the cylinder as much as possible to maximise the available breathing, and therefore escape, time.

However, if the escape sets are to be used in large premises, such as big industrial plants or chemical factories, an evacuation procedure may well involve hundreds of people, and would very often be organised in a regimented and well-practiced operation. In such procedures, groups of people are often trained to congregate at designated areas or muster stations' and once it is ascertained that everyone on a register has been accounted for, the group then evacuates together. This can result in people waiting around the muster station for S -10 minutes, maybe even longer, and so if they have been wearing their respirator all of that time, the valuable supply -24 -of pressurised breathable air would be severely depleted, possibly meaning that not enough air would be left for the time taken to complete the evacuation from the large building/plant. Therefore, it is possible that the designated muster stations could be provided with a plurality of air hoses connected to a pressurised breathable air supply system. Such a system could comprise a network of pipes running throughout the building/plant and could be fed by an external air pump and filter device so that pressurised breathable air is always available though any air hose at any of the designated muster stations. To be useable in such cases, the breathing apparatus of the invention may include a special external supply valve disposed either on the cylinder itself, or between the cylinder and the reducer valve. Such a supply valve is disclosed in the Applicant's earlier published patent application no. GB 2430159 and so a detailed description thereof will not be provided here.

Although a specific embodiment of the invention has been described in detail above, it will be apparent to those skilled in the art that modifications may be made to the above embodiments within the scope of the invention, which is defined in the claims hereafter.

One embodiment of the present invention not described above, but intended to fall within the scope of the invention, is that the constricting means around the hood peripheral edge 120, described above as an elastic member 121, could alternatively comprise an inflatable tube, as per the inflatable harness 114 and neck tube 119. In such an embodiment, the constricting means of the inflatable tube could be in fluid communication with the rest of the inflatable harness 114 and neck tube 119, such that during donning of the breathing apparatus 110, the hood 116 and its peripheral edge 120 is held wide apart to allow the user to easily place their head into the apparatus, and when the harness 114 vents and contracts as described above, the tube around the hood peripheral edge 120 would also contract, thereby constricting the hood 116 to the wearer's head and forming the second closed hood volume 126.

The invention is shown and described with the improved hood 116 in combination with the inflatable harness 114. However, the invention is not limited thereto, and -25 -the breathing apparatus of the mask and hood as shown could equally be employed with a non-inflatable harness such as elastic members or adjustable straps.

In additional, the material of the hood 116 can be specifically designed to withstand certain environments to make it adaptable for various situations. For example, the material of the hood may be heat resistant for use in escape and rescues from fires, either industrial or domestic.

The bag 17 that is used to contain the emergency breathing apparatus of the invention is intended to be of a high visibility colour, such as bright orange, so that in emergency situations, users can quickly find an available emergency set, even if there is some smoke or gas in the atmosphere that may limit visibility. The bag 17 may also incorporate one or more optional features, such as being water-tight for increased protection of the breathing apparatus when not in use, or have tamper-evident tags to show if the breathing apparatus has been interfered with and so might not be safe to use in an emergency. The breathing apparatus could also include a waist-belt or shoulder strap to carry the bag or air supply when in use.

The respirator can be made from any suitable material such as moulded rubber or silicone, with the front visor portion made of a suitable transparent plastic or toughened glass. The breathing apparatus can be in the form of a full-face respirator or may alternatively comprise a full head-covering hood, as show in the drawings, or may only comprise an oro-nasal mask to surround a wearer's nose and mouth, yet still including the inflatable harness 14 and control valve 20.

Claims

-26 -Claims 1. A breathing apparatus comprising a respirator mask, a hood secured around the peripheral edge of the mask and a harness for securing the mask and hood to a wearer's head, the mask and hood being configured such that when the breathing apparatus is worn by a wearer, the mask defines a first contained volume between the wearer's face and the mask, and the hood defines a second contained volume between the edges of the mask, the wearer's head and the hood, wherein the hood extends from the mask to partially cover the wearer's head such that a portion of the rear of the wearer's head remains exposed.
2. A breathing apparatus according to claim 1 wherein the hood has a peripheral edge remote from that mask and said peripheral edge includes a constricting means to seat the peripheral edge of the hood against the wearer's head to close the second volume.
3. A breathing apparatus according to claim 1 or claim 2 wherein the hood comprises a lower skirt portion that, when the breathing apparatus is worn, surrounds the wearer's neck.
4. A breathing apparatus according to claim 3 wherein the lower skirt portion includes a constricting means to hold the lower skirt portion against the wearers' neck when the breathing apparatus is worn.
5. A breathing apparatus according to claim 4 wherein the hood comprises a cut-away portion that extends from above the lower skirt constricting means to the top of the hood to expose substantially the rear half of the wearer's head when the breathing apparatus is worn.
6. A breathing apparatus according to any preceding claim wherein the harness

is inflatable.

-27 -
7. A breathing apparatus according to claim 6 wherein the inflatable harness comprises an expandable resilient tube.
8. A breathing apparatus according to claim 7 wherein the inflatable harness comprises a plurality of expandable resilient tubes in fluid communication
9. A breathing apparatus according to any of claims 6 -8 when dependent on claim 2, wherein the constricting means around the peripheral edge of the hood comprises an inflatable expandable resilient tube.
10. A breathing apparatus according to any of claims 6 -9 when dependent on claim 4, wherein the lower skirt constricting means comprises an inflatable expandable resilient tube secured therearound, so that, when inflated, it holds the hood opening apart to allow it to be placed over the wearer's head and, when deflated, it extends contracts against the wearer's neck.
11. A breathing apparatus according to any of claims 6 -10 wherein the hood is secured to a portion of the inflatable harness..
12. A breathing apparatus according to any of claims 6 to 11, wherein the expandable resilient tube(s) of the inflatable harness is/are surrounded by a sleeve of inextensible material to limit the maximum expansion of the expandable resilient tubes.
13. A breathing apparatus according to claim 12 wherein the sleeves are made of a flexible corrugated material which can be extended to a straight, un-corrugated configuration on expansion of the resilient tubes, but which are inextensible once extended to said straight configuration.
14. A breathing apparatus according to any of claims 6 -13 comprising a control valve to control a flow of air from a supply to them mask.

-28 -
15. A breathing apparatus according to claim 14 wherein the control valve is configured to allow air to flow to the inflatable harness.
16. A breathing apparatus according to claim 15 configured so that the harness automatically inflates and expands prior to the respirator being secured to the wearer's head, and automatically deflates and contracts once the respirator is sealed on the wearer's head.
17. A breathing apparatus according to claim 16 wherein the control valve is configured so that, in a first position, a restricted flushing flow of compressed air from the supply is allowed to flow to the mask and a flow of compressed air is allowed to flow to the inflatable harness to inflate and cause the harness to expand to facilitate the placement of the harness over the head of the wearer and, in a second position, an unrestricted flow of compressed air is allowed to flow to the mask and the flow of compressed air to the inflatable harness is prevented so that the harness deflates and contracts to secure the breathing apparatus to the wearer's head.
18. A breathing apparatus according to claim 2 wherein the constricting means around the peripheral edge of the hood comprises an elastic member.
19. A breathing apparatus according to any preceding claim when dependent on claim 14, wherein an inhalation demand valve is disposed between the control valve and the respirator.
20. A breathing apparatus according to claim 19, wherein the demand valve is a positive pressure demand valve configured to maintain the air pressure within the respirator at a pre-determmed value above atmospheric pressure.
21. A breathing apparatus according to any preceding claim including a cylinder for compressed breathable air connected to the control valve via a supply hose, and a supply valve disposed between the cylinder and the control valve, wherein the supply valve includes a coupling for connection to an auxiliary air supply, and a -29 -switching means to selectively switch between the cylinder and the coupling for the supply of air to the control valve.
22. A breathing apparatus according to claim 21 wherein the switching means includes a spool valve slidably mounted within the supply valve and moveable from an open position to allow the flow of air from the cylinder to the control valve and, a closed position in which the cylinder is sealed from the control valve.
23. A breathing apparatus substantially as hereinbefore described with reference to the accompanying drawings.