The invention relates to breathing apparatus and to a breathing bag suitable for use in such apparatus, and especially to 'self-rescue* breathing apparatus (and components for such apparatus) , that is to say, to breathing apparatus that is worn by, for example, a _. miner, as part of his normal equipment but is used only in emergencies to enable the wearer to escape through regions that are flooded or are filled with toxic or suffocating gases. Such breathing apparatus does not need to have a very long operating endurance, but must be sufficiently light and, in its usual inoperative condition, compact, that it does not unduly hinder the wearer's work.

Breathing bags for closed-circuit breathing apparatus have to be airtight and strong, and to give a large change in internal volume over a small range of internal pressures, without havng a disproportionately large actual size. Such breathing bags have in the past been made from heavy, stiff, rubber or plastics materials sewn together from several pieces in elaborate shapes.

The invention provides a breathing bag for closed-circuit breathing apparatus, comprising two sheets of airtight material that are developable and substantially coextensive in an unstressed condition bonded together around edge portions thereof.

Surprisingly, it has been found that such a breathing bag can so be constructed that, for a given surface area and over the usual pressure range, a very large change in volume can be obtained, and the bag has satisfactory mechanical strength.

The two sheets are advantageously bonded together round their entire periphery except for a single portion forming a mouth for the bag. It is then unnecessary for any separate mouth to be formed, and if ^' (as is discussed below) an edge portion around the mouth of the bag is clamped in the breathing apparatus, the conventional manufacturing step of bonding one half of a connector to the material of the breathing bag may - be omitted.

Preferably, the sheets are developable in an unstressed condition into a shape bounded generally by portions of the four sides of a notional rectangle and by oblique lines across the corners of the rectangle. It is then found that when the breathing bag is inflated central portions of the bag remain fairly flat while the edge portions pucker up. The angles of the effectively octagonal shape attract a large proportion of the puckering which is a significant factor in giving a very high inflated volume for the area of the sheets.

The length of the sides of the notional rectangle are advantageously in a ratio of from 1:1.1 to 1:1.5 and preferably about 7:8. Having a rectangle that is

not square enables the bag to be packed more efficiently (as will be discussed below) and in a compact self- rescue apparatus where it is convenient to mount the breathing bag off-centre having an asymmetrical bag can both improve the appearance of the bag and reduce the tendency for it to foul on other parts of the apparatus.

The mouth of the bag is advantageously at or in the vicinity of one of the corners of the notional rectangle, and the bag is then preferably arranged in normal use to hang with the mouth at the top and one diagonal of the notional rectangle substantially vertical.

Two of the edges defined by the said oblique lines may be generally parallel to that diagonal and the perpendicular distance between them is then advantage¬ ously in the range of from 60% to 90%, preferably, about 78%, of the perpendicular distance between notional lines parallel to the said diagonal and passing through the corners of the notional rectangle.

The said oblique line at the corner opposite the mouth may be perpendicular to the said diagonal.

The invention also provides closed-circuit breathing apparatus including a breathing bag according to the invention.

An edge portion around the mouth of the breathing bag may be folded over a ring that is clamped to a connector of the breathing apparatus.

The bag may be folded into a strip with the mouth

at one end, which strip is then folded up and stored within a part of the apparatus which can be opened by removal of a closure member.

The breathing bag, in the usual orientation of the apparatus, is preferably enclosed within a lower end portion of a part of the apparatus closed by a bottom cover member that is removed when the apparatus is brought into operation, and so constructed and arranged as to tend to fall and open out under its own weight to hang from the apparatus when the bottom cover member is removed. With a breathing bag folded according to the invention, that can readily be achieved provided that the breathing bag can fall free, and the opening out of the bag is completed when the user of the apparatus first exhales into the apparatus.

The invention also provides breathing apparatus comprising a unit with top and bottom cover members covering parts of the apparatus that are to be extended when the apparatus is brought into operation to occupy space outside the positions of the cover members, and members in tension extending from one cover member to the other, the cover members being so arranged that they are secured to the apparatus by virtue of being secured to each other by the members in tension, and at least one said member in tension being breakable or otherwise readily removable by a wearer of the apparatus to enable the cover members to be removed speedily.

The said at least one member in tension may be a wire, and at least one other said member in tension is advantageously a mono-filament fibre. The cover members are then preferably so arranged that when the wire is broken the tensile energy in the monofilament will tend to assist in dislodging the cover members from the apparatus. The top cover member may cover a facemask, mouthpiece, or the like and a flexible hose connecting it to the rest of the apparatus, and the bottom cover member may cover the breathing bag.

The invention further provides a breathing bag for closed circuit breathing apparatus, comprising an inner layer of impervious material and an outer layer of liquid-absorbent material.

The outer layer may be of fibrous material, and is advantageously of a mixture of cotton and polyester fibres. Such a fibrous outer layer provides resistance to tearing and abrasion of the breathing bag caused by contact with external objects, and reduces the risk that the impervious inner layer will be ruptured in use.

The invention also provides breathing apparatus that includes such a breathing bag.

Advantageously, the breathing apparatus is for emergency use, the outer layer of the breathing bag is soaked with liquid, and the breathing bag is stored in a sealed compartment of the apparatus, and is arranged to be exposed to the exterior- when the apparatus is

brought into operation. The liquid will then tend to evaporate, cooling the breathing bag and thus the gas in the breathing circuit within it. Such evaporative cooling will last only for a short period, until the liquid is completely evaporated, unless the cooling liquid is replenished, but the cooling pattern can be made to correspond to the typical operating cycle of a self-rescue breathing apparatus. The said liquid is preferably aqueous, because the high specific latent heat of evaporation of water makes it possible to obtain a large total cooling action from a necessarily limited volume of liquid. The liquid may include an additive, or a combination of additives, that is a bacteriostatic agent, and/or is a wetting agent, and/or reduces the freezing point of the liquid, and/or reduces the boiling point of the liquid. It has been found that a single additive will produce all four of those effects, at the expense of some loss of latent heat capacity.

One form of breathing bag constructed in accordance with the invention and a breathing apparatus including it, will now be described by way of example only with reference to the accompanying drawings, in which:

Fig. 1 is a front elevation view of the breathing bag;

Fig. 2 is a fragmentary cross-section through a connection between the breathing bag and other parts of the apparatus; and

Fig. 3 is a diagrammatic front elevation view of the apparatus.

Referring to the accompanying drawings, one form of breathing bag indicated generally by the reference numeral 1 comprises two developable sheets of material (that is to say, sheets that can be spread out flat in an unstressed condition) .

Each sheet is of a laminated material with the inside consisting of one or more layers of nylon or polythylene sheet to give a material that is substantially airtight and the outside consisting of polycotton, that is to say, of a mixture of polyester and cotton fibres. The plastics layers are welded together around edge portions of the sheets in a strip (not shown) that is continuous except for a single gap to form an inlet and outlet 2 for the bag. The polycotton may be either welded to the rest of the bag or adhesively united therewith. If adhesive is used, it may be coated onto a release-paper or similar carrier, the adhesive on the carrier applied to the outer face of the plastics material, the carrier stripped off leaving the adhesive on the plastics material, and the polycotton material applied to the adhesive. The resulting laminate is resistant to tearing and abrasion in use because the plastics material, which must remain

airtight, is protected on the outside by the fibrous polycotton material.

As may be seen from Fig. 1, the bag is in the shape of an octagon, or of a notional rectangle with the corners cut off. If it is regarded as a rectangle with the inlet 2 occupying one of the cut-off corners, then the edge of the breathing bag 1 across the inlet is approximately perpendicular to that diagonal of the rectangle that runs towards the inlet. In use, the breathing .bag 1 will usually be disposed with the inlet at the top and the said diagonal substantially vertical. The breathing bag will hereinafter be described with reference to that orientation. The edges 3 to 5 defining the other three cut-off corners are all substantially parallel or perpendicular to that diagonal. The two vertical cut-off edges 3 and 4 at the sides are separated by a perpendicular distance that is about 22% less than the width of the notional rectangle between vertical lines through its corners. The inlet 2 and the bottom cut-off edge 5 cut off triangles of similar size to those at the sides. The lengths of the sides of the notional rectangle are in a ratio of about 7:8.

Referring now to Fig. 2, the breathing bag 1 may be connected to a breathing apparatus by turning an edge portion 6 at the inlet 2 back over a rigid ring 7. The ring 7 is then seated against a shoulder of a connector portion 8 of the apparatus and secured in

place by a resilient O-ring 9. The ring 7 may be seated on either a male or a female surface of the connector 8. Because it is not necessary to have a connector part welded to the breathing bag, manufacture of the bag is greatly simplified.

In order to pack it compactly when the breathing apparatus in not in use, the breathing bag 1 may be folded along lines parallel to the vertical diagonal, for example, it may be folded along the lines 10 to 15 shown in Fig. 1 to form a strip approximately one-seventh as wide as the flattened bag. Preferably, the right-hand side of the bag (as seen in Fig. 1) is folded forward at the line 12. Then the left-hand side is folded forward at the line 13, and at the line 11 which is then co-incident with the line 13. The right-hand side is then folded forward at the co-incident lines 10 and 14, and the left-hand side is finally folded forward at the line 15. The bag 1 then has creases that (as seen in Fig. 1) form grooves along the lines 10, 12, 13, and 15 and ridges along the lines 11 and 14. The lines 10 to 15 may be printed onto the polycotton layer on one side of the bag, or they may until the bag is folded be only notional. Instead of the sequence of folding just desribed, the strips may be folded in a different order, and/or to different sides, and there may be a different number of strips.

It will be seen that the folded strip has a thickness that increases towards the centre of the

strip, and that cutting off the side corners at the edges 3 and 4 has reduced the thickness of the thickest part of the strip by one layer. Because the notional rectangle is not square, the stips outside the lines 10 and 15 overlap over less than half of their lengths, and the thickness of the folded strip is considerably more evenly distributed over its length than would be the case with a comparable folding of a square bag.

The folded strip may then be folded along lines perpendicular to the lines 10 to 15 to form a cuboidal wad. It is preferred to have about five folds, alternating to form a zig-zig pattern, except that the last two folds at the bottom end are preferably to the same side of the strip so that the bottom end portion of the bag is tucked between the next two.

If the breathing bag 1 is folded up while it is attached to the breathing apparatus, then the top end portion of the bag will not, of course, fold up neatly, but the rest of the bag may be folded up substantially as described and located close to, or even within, the connector 8.

Referring now to Fig. 3, one form of breathing apparatus is a breathing apparatus for emergency use that consists, in a stored condition, of two cylindrical units 16 and 17 side by side and of substantially equal length. One unit 16 may contain an oxygen cylinder and the other unit 17 a carbon-dioxide absorbing purifier. The apparatus is arranged in use to

be worn on the chest of the user with the cylindrial units vertical. The second unit 17 has a top end cap 18 within which are stored a mouthpiece and its connecting hose (not shown) and a lower end cap 19 (shown dashed) that covers the connector 8 and within which is stored the breathing bag 1. The top and bottom end caps are held together by two ties one of which is elastic (for example, a nylon monofilament strand) and is in tension and the other of which is arranged to be broken, detached from one of the end-caps or otherwise disengaged fairly easily. The arrangement of the end caps 18 and 19 and the ties is such that in order to bring the apparatus into operation the said other tie is disengaged, and the end caps can then be removed, assisted by the tension in the elastic tie. When the bottom end cap 19 is removed, the breathing bag 1 falls out and at least partly unfolds under its own weight, and opens out completely, as shown in Fig. 3, when the user of the breathing apparatus first exhales into it.

Preferably, the breathing bag is so attached to the connector 8, as shown in Fig. 3, that a long side of the notional rectangle is towards the first cylindrical unit 16 and the bag, when empty, tends to lie flat against the weaver's body. Not only is there then less risk of the first cylindrical unit 16 fouling the bag 1, because the long sides of the notional rectangle are nearer to vertical than the short sides, but the result is considered to be more aesthetically

pleasing too. In that case, the cut-off portion on the side away from the first unit 16 may be larger than that on the side towards the first unit to distribute the width of the bag more evenly with respect to the width of the apparatus, reducing the risk that the projecting corner will be caught on obstacles.

The polycotton material on the outside of the breathing bag 1 is soaked in an aqueous liquid before the breathing bag is stowed inside the bottom end cap 19, which forms with the bottom end portion of the second cylindrical unit 17 a substantially liquid-tight and vapour-tight seal, at least as regards the liquid with which the polycotton is soaked and the vapour of that liquid. The liquid may be introduced by pouring a measured quantity of liquid into the bottom end-cap 19 immediately before the end-cap is sealed to the puri¬ fier housing. The polycotton material will then act as a wick to distribute the liquid all over the breathing bag. The liquid is thus sealed in between the end cap 19 and the impermeable inner lamina of the breathing bag 1.

The purpose of the liquid is to cool the breathing bag 1, and thus the breathing gas inside it, by evaporation when the breathing apparatus is in use. For that purpose water, which has a comparatively high latent heat of evaporation, is suitable, and if desired additives, such as an additive to lower its freezing point and additive to raise or lower its boiling point.

a wetting agent, or a bacteriostat, may be included. It is possible to achieve all four of those effects with a single additive, although some reduction in latent heat may result as a side-effect.

If the polycotton material is soaked in liquid, then the adhesive bonding the polycotton to the plastics must be one that will remain effective in spite of being permanently exposed to the liquid while the apparatus is in its normal ready-for-use condition.

When the user first inhales into the apparatus and the breathing bag expands, the material of the bbag folds to allow it to do so. In general, the central portions of the two sheets making up the bag remain fairly smooth, while more peripheral portions are increasingly puckered. It has been found that with the octagonal shape shown in Fig. 1 the puckering is concentrated efficiently in the corners of the octagon and an extremely high ratio of inflated volume to area of surface is achieved.