HARNESS FOR BREATHING APPARATUS

The present invention relates to a harness for use with breathing apparatus, and more particularly, but not exclusively to a pneumatically operated harness for use with breathing apparatus such as masks or other headgear.

BACKGROUND OF THE INVENTION

Expanding harnesses for use in face masks are already known.

GB1175080 describes one such expanding harness which consists of flexible extensible tubes of an elastomeric material inside a loose fabric sheath. In order to don the mask, the user can pressurise (typically from 50 to 100psi) the extensible tube by means provided on the equipment. This is then allowed to stretch until the fabric sheath is taut, allowing the wearer to put the harness over their head. The user can then vent the harness using means provided on the equipment, allowing the extensible tube to collapse and hold the mask onto the face. The extensible tube serves as both an expandable member and as a tension member, the fabric sheath providing no tension.

Extensible tubes can also be made relatively thin, since expansion due to pressure of the gas is limited by the fabric sheath, (rather like an inner tube inside a tyre).

One of the advantages of the expanding harness is the ability to don the mask very quickly, even one handed, since the pressurising and venting means can be made by a one handed operation of the valve. Accordingly, the expanding harness has applications to any equipment where rapid donning of a mask or goggles or similar equipment is an advantage. One application is in escape equipment, to protect against gas or other

irrespirable atmospheres, where a mask with a cylinder is stored in places where there is risk of harmful or irrespirable atmospheres. When an alarm sounds indicating the presence of the harmful or irrespirable atmosphere, the user would want to don the mask as quickly as possible. Another application, to which GB 1175080 is directed, is to pilots' oxygen breathing apparatus to protect against the effects of decompression when flying at high altitudes.

Despite the advantages of the known expandable harness there are limitations with regard to the comfort of such harnesses, particularly in situations where the same size harness has to fit the largest and smallest heads. There is a limitation both to how thin the extensible tubes can be made, and how much they can expand. For example, the maximum extension available for silicone rubber is about 300% in one direction. With the type of harness used in the prior art described above, when the harness is inflated, there is both radial and axial extension, so the axial expansion (which is necessary to go over a head) available is limited to about 120%. This arises as the radial expansion uses some of the extension capability of the material, so only some of it is left for axial expansion.

Further disadvantages arise due to practical limits as to the minimum thickness of the extensible tube that can be made, while still maintaining adequate control of tolerances, typically of about 0.7mm wall thickness. The need to make secure end connections also limits the ability of the tube to be made thinner. A thinner tube may also be too weak.

The ratio of wall thickness to internal diameter of such tubes that allow them to expand at the minimum pressure means that the ratio of wall thickness to internal diameter has to be about 8:1 with conventionally used materials such as silicone rubber. The lower this ratio, the less the tube is

able to expand at the same pressure. A larger internal diameter, whilst keeping the same wall thickness, would allow the tube to expand more easily, but at the same time would proportionally increase the effective spring rate or spring constant of the un-pressurised tube, increasing the spring rate or spring constant of the harness and increasing the load applied to the head, particularly in the case of an oversize head. When designing a harness, the harness needs to apply adequate force to hold the breathing apparatus onto the smallest head for which it is designed to provide an adequate seal. For example, about 2ON in the case of a full face mask would be the typical minimum force. The spring rate of the harness determines the increase of this force when used on larger heads, therefore the smaller the spring rate of the harness the more desirable the harness is for the purpose of comfort to a user.

The variation in head sizes also means that a harness that is adequately tight on the smallest heads can be very uncomfortable on the largest heads. This is particularly a problem where the harness has to apply a high load to the face, for example a mask with a high positive pressure as might be used in a pilot's breathing apparatus.

Numerous patents have been filed in an attempt to address this problem e.g. FR2784900, WO9920349, EP-628325, WO8907961 , EP-288391 , for example by maintaining a residual pressure in the harness to limit the contraction. However, all are related to dealing with the limitations of the harness, rather than dealing with the harness itself.

A harness according to the prior art has a very non-linear expansion, where, once expanded, a very significant drop in pressure is required before the harness will contract, meaning that any means that relies on controlling the pressure in the harness has to work on a very steep part of

the pressure v contraction curve, which will be discussed in more detail later.

There is in addition the problem of stowage of such harnesses, when fully collapsed, as they are difficult to pack away, since significant length is left.

The present invention strives to overcome or diminish the disadvantages associated with the known harnesses.

SUMMARY OF THE INVENTION

According to the present invention there is provided a harness comprising an extensible tension member and a separately functioning expandable member whereby pressure applied to the inside of the expandable member selectively controls the size of the harness.

In one aspect of the invention, there is provided a head harness comprising an extensible tension member, for providing an adequate tension across a plurality of head sizes, and an expandable member, for extending the tension member.

Preferably the expandable member provides a smaller tension relative to the tension in the tension member, when distended on the largest head size, whilst allowing pressure to expand both the expandable member and the tension member.

In a preferred embodiment the expandable member is manufactured from a flexible material, which is selectively inflatable and deflatable. The flexible material may typically comprise an elastomeric material, for example a flexible plastic like polypropylene, neoprene, thermoplastic elastomers or silicone rubber. The expandable member may be in the form of a bag or

bladder. In one embodiment the expandable member has a bellow-like or corrugated tubular design. In another embodiment the expandable member is convoluted, the convolutions being plain or spirally formed.

The tension member is enclosed anywhere within the expandable member, for example in the centre of the expandable member.

In one embodiment a sheath, for example made from fabric, is provided over the outside of the expandable member.

In various embodiments the tension member may be a tension spring, an elastic band or other means of creating tension when stretched. For example, in one embodiment the tension member may comprise multiple fibres placed anywhere in the structure of the harness.

If the expandable member is spirally convoluted in form it is advantageous for the tension member, if for example, it is a spring, to be wound in the opposite direction to those convolutions to prevent the expandable member being caught up in the spring during expansion and contraction.

In yet a further embodiment the tension member is located between the expandable member and the sleeve.

In a further embodiment the tension member is located outside the sleeve, or woven to be part of the sleeve, while still maintaining the limit to expansion function.

The sheath, when provided over the outside of the expandable member and tension member, protects the tension member and the expandable member from over-expansion.

Preferably the sheath is designed and adapted to become taut in both the axial and radial directions before either the tension or expandable members become over extended axially, or the expandable member becomes too large by radial expansion.

The fabric sheath may be corrugated, woven or braided to allow the desired level of expansion before the fibres become taut. The sheath may be spiral in form. If the sheath is wound spirally it is advantageous to wind the sheath in a counter-rotational direction to a spirally wound expandable member to prevent the sheath being trapped in the windings of the expandable member's spiral convolutions.

The subject of the present invention provides an improved harness that separates the functions of expansion and tension, allowing greater comfort, while still providing the expansion due to pressure essential for function.

By separating the two functions or expansion and tension, it is possible to optimise each function substantially separately, thus achieving a much better solution for a wider range of applications as one can design the harness to function at lower pressures.

In addition to the potential of working at lower pressures, there are also advantages of improved stowage, as the resulting harness made to the present invention can be made to contract to a shorter length. There is improved compatibility with any of the pressure retention means of improving comfort as the harness has a more linear pressure vs. expansion characteristic.

The invention will be described further by way of examples, and with reference to the drawings, in which:

Figure 1 shows part of a harness, according to one embodiment of the invention, in an un-expanded state,

Figure 2 shows the harness of Figure 1 in an expanded state,

Figure 3 shows a further embodiment of a harness with convoluted design in the semi-expanded state,

Figure 4a is a graph illustrating a harness extension against pressure, with pressure rising and falling,

Figure 4b is a graph of force applied by the harness against extension and

Figures 5a, 5b, 5c show examples of heads wearing a mask attached by a harness.

Referring to Figures 1 and 2 there is shown a short length of harness, enough to explain the principles of operation, and the length of which can be made to suit a required application. A typical application is a head harness for use with inflatable respiratory apparatus, the apparatus including a mask (see Figure 5) presenting a fitting surface adapted to fit against the face of a user.

There is provided a pressuring gas connection (1 ), to which is attached, by any conventional means, such as a hook or adhesive, a tension member (2), which may be a tension spring, an elastic band or other means of creating tension when stretched. The tension member on its own would be capable of providing substantially adequate tension for the harness application from the smallest to the largest head.

Over the tension member (2) is provided an expansion member in the form of a bag or bladder, of a flexible material, such as an elastomeric material, or a flexible plastic like polypropylene. The tension member (2) may also be pre-tensioned, such as a pre-tensioned spring. In the embodiment illustrated the expandable member takes the form of a corrugated tube (3) or bellows. This is designed to have adequate effective surface area perpendicular to the axial direction such that, at the lowest operating pressure, for example 10 psi , the force generated by the multiplication of the pressure times the effective area is capable of expanding the tension member (2). The corrugated construction of the expandable member (3) can expand by a high percentage under the effect of pressure, but still not apply significant tension when fitted over the largest head.

A fabric sheath (4) is provided over the outside of the expandable member (3), and protects the tension member (2) and the expandable member (3) from over-expansion. The sheath (4) is designed to become taut (as shown in Figure 2) in both the axial and radial directions before either the tension or expandable members (2, 3) become over extended axially, or the expandable member becomes too large radially.

The expandable member (3) can be pressurised and depressurised as required and in Figure 1 is shown in its depressurized condition. In this condition it is suitable for stowage as it takes up little volume with the ridges 7 and grooves 8, which define the corrugation configuration, collapsed into close juxtaposition. As can be seen in this un-extended state the unsupported parts opposite the grooves of the flexible sheath can fold into those grooves so enhancing the compact nature of the harness when stowed.

Although the ridges 7 are shown as spikes, other designs of corrugations can be adopted, for example, each of the ridges can have a general

curvature and their apices can be curved or flat top instead of the sharp points shown in Figure 1 and 2.

When pressurizing, the elongate member (3) expands as shown in Figure 2 such that the apices of the ridges push against the underside of the sheath 4, eventually forcing the sheath 4 into a taut condition which limits the extent to which the expandable member 3 can be expanded. Likewise the sheath 4 also acts, when in its taut condition, as a constraint on the extent to which the tension member 2 can extend, as the tension member extension no longer continues when the expandable member 3 stops expanding.

The fabric sheath (4) may be corrugated, woven or braided to allow the desired level of expansion before the fibres become taut. However, the sheath (4) may be omitted if the expandable member (3) on its own is capable of withstanding the maximum pressure it is likely to encounter. If the expandable member (3) is manufactured from elastomeric material, fabric reinforcement may be built into the structure to give it strength. There may be special braiding used in the sheath to prevent excessive radial expansion, whilst allowing axial expansion.

The end opposite to the gas connection (1 ) may have another gas inlet or outlet, or a blank end (6) as shown in Figures 1 and 2. Conventional binding (5) means such as hose ferrules or cord can be used to hold the ends onto the fittings. The ends (1 ) and (6) also provide attachment means to the mask or other device to be fitted to the face, which are known technology so are not shown.

It is not essential that the tension member (2) is in the centre of the expandable means, and in one embodiment the tension member (2) may comprise multiple fibres placed anywhere in the structure. The tension

member (2) may be between the expandable member and the fabric sleeve (4), outside the fabric sleeve, or woven to be part of the fabric sleeve, while still maintaining the limit to expansion function.

The tension member (2) can be made at a much lower rate than the existing art, so can be shorter at the un-extended length (Figure 4b) Because of this, the tension on a large head and on small head can be more consistent, so, when adequate tension is applied to a smallest head, the level of comfort on the largest head can be made better. Tension springs with some pre-tension can be used instead of extensible tube, further reducing the rate and thus improving the comfort on the largest head, while still maintaining adequate tension on the smallest head.

Since the tension member (2) can be shorter, and the expandable member (3) is corrugated, when not pressurised, the harness will collapse to a shorter length than the prior art, aiding easier stowage.

Since the expandable member (3) can be adjusted to suit the working pressure, the diameter can be adjusted to match the working pressure, so, for example a larger diameter can be used to lower the pressure for which full expansion without increasing the tension on the head. Thus the design can be used at a lower pressure.

Figure 3 illustrates a different embodiment of the harness, only a small section of which is shown, in which a convoluted tension member 9, for example a pre-tensioned tension spring, is located between two hose ferrules 10. The tension member 9 is located along the central axis of a barrel-shaped expandable member 11 , which is also convoluted in construction with its windings wound in counter-rotation to the convolutions of the tension member 9 thereby preventing the inner portions of the expandable member 11 becoming snagged within the convolutions of the

tension member 9. A sheath 12 is provided over the expandable member 11 and can also be constructed with a convoluted design, its winding being counter-rotational to the windings of the expandable member 11 to prevent snagging between the sheath and the expandable member 11.

Graph 4a shows the extension in mm of a harness against pressure in psi. The solid line A is representative of the extension under various pressures of a typical prior art harness, whereas dotted line B is representative of the extension under various pressures of a harness like that shown in the embodiments of Figures 1 to 3 of the present invention. The dotted curve B will be substantially the same both during the inflating and deflating of the harness, making control of comfort by retention of pressure in the harness much easier. This is in contrast to solid line A in which it can be seen that the hysteresis is large, the pressure having to be reduced considerably before the extension of the harness drops back to a lower length. The contrast in the shape of curve A and curve B reflects the degree to which the compatibility of the harness embodiments according to the present invention with comfort features that retain some pressure in the harness to maintain comfort is better than for harnesses made according to prior art. This is particularly useful for applications where the breathing apparatus is designed for pressure breathing, as with pilots. In such applications, the apparatus requires a tight harness, and, because they are one size fits all, even people with small heads can find masks uncomfortable. As they are worn in situations where there is an increased risk, but no decompression e.g. when the co-pilot leaves the cockpit to attend to other matters, the tight harness is not needed until there is a decompression. Some of the comfort patents retain a pressure in the harness which is released when there is a decompression.

Graph 4b shows typical harness length (mm) vs. harness tension (N), illustrating the advantage of a lower spring rate harness that can be

provided using the present invention. In graph 4b, dF A is the difference in force exerted by a harness like one made to the prior art between a small head and a large head, whereas dF B, which is much smaller than dF A, is for a lower rate harness as can be made using the present invention. It will be self evident that because of the lower load differential, the harness on a larger head will be much more comfortable with the new harness in accordance with the invention.

It will be evident to those skilled in the art that the above information can be used to tune a harness to a particular application and range of head sizes. It will further be appreciated that other features, for example a net, can be incorporated into the harness to aid the disposition and secure retention of the mask in a desired position on the head of a person. A plurality of elements of a harness as shown in Figures 1 and 2, or in Figure 3, may be combined in various ways to make a harness, such as that shown in Figures 5a, 5b and 5c.

In Figure 5a a mask 14 covers much of the face of a person's head 13, two harnesses 15, 15a having been expanded by means of pressurised gas from a gas regulator device 16 so that the harnesses 15, 15a can be fitted comfortably over the head 13. The harness 15 is coupled to the left (as seen from the wearer) of the pressure regulator device 16 and loops around the head 13 to the top right of the mask 14, whilst the harness 15a is coupled to the regulator device 16 on the right and loops around the head 13 to the top left side of the mask 14. There is conveniently provided a buckle where they cross over at the back of the head (not shown) to keep the harnesses 15, 15a in position.

Figure 5b illustrates a smaller mask 18, covering only the nose and mouth. The harness 15 is like that in Figure 5a but is shown with a head strap 19 adjustably connected to the harness 15.

Figure 5c illustrates a mask like that in Figure 5b with an arrangement in which two harnesses 15, 15a are connected to the pressure regulator device 16, the harnesses 15, 15a being secured together by a spacer 20 to keep the harnesses apart and in position above and below the ear.