GB2046102A - Improvements in and relating to respirators - Google Patents

Abstract

A respirator, and particularly to the type of respirator called a filtering face piece is made from a flat pocket of filtering material of generally frustoconical shape having an open edge 4 at the larger end of the frusto-cone and a closed end at the smaller end of the frusto-cone, and the closed end of the pocket is formed with fold lines 8, 11, 12 defining a generally quadrilateral surface composed of two identical triangular surfaces 7 which have a common base 8 which in use extends generally in a plane including the mid line of the wearer's face. The pocket may be provided with additional fold lines 9, 15 defining an inverted V-shaped channel 16 for receiving the wearer's nose and a fold line 10 underlying the chin of the wearer, the fold lines 9, 10 being colinear with line 8. The or some of the fold lines may be longitudinally rigidified e.g. welding the filtering material, if weldable. <IMAGE>

Description

SP ECIFICATION Improvements in and relating to respirators The present invention relates to improvements in respirators and particularly to filtering face pieces.

Filtering face pieces have been known for many years, originally in the form of simple surgical masks giving a degree of protection to a patient from germs contained in a doctor's or nurse's breath. Such masks are normally of simple, usually pleated, construction and are held on the face covering the nose and mouth by tapes or rubber bands. These masks give a degree of filtration and protection to no specified level. In recent years filtering face pieces have been introduced into industry, and these industrial face pieces offer a degree of protection to the wearer hitherto not obtainable. This has been made possible by the appearance on the market of new filtration materials, together with improved methods of manufacture which in many cases are automated resulting in high volume production at low cost.

Such filtering face pieces are generally of one of two types, being either a moulded cup or a pleated sheet material mask. In the moulded cup, either the filtration material is sandwiched between two low resistance fibrous moulded cups forming an inner and an outer layer which are joined together at the open mouth of the cup normally by welding or adhesive, or the filtration material is moulded to form the cup. One or two light rubber bands are attached to the edge of the open mouth of the cup and usually a small deformable metal nose piece is provided to give better sealing around the nose.

The second type of filtering face piece is made from a flat sheet of filtering material which is folded in the shape of a flat pocket with an open edge and provided with a number of transverse pleats, one or two head bands being attached to the open edge of the pocket. The purpose of the pleats is to increase the filtration area and thus decrease face velocity through the material and hence reduce the inhalation and exhalation resistance and improve the efficiency of the filtration material.

There are now appearing on the market improved filtration materials of increased performance giving higher efficiencies, i.e. lower penetrations, combined with reduced pressure drop thus making it unnecessary to increase the filtration area by providing pleats. This means that a lighter, less cumbersome face piece can be provided having in some cases greater flexibility.

Whereas the previous filtration materials worked generally on the interception principle, being composed of fibres, typically cellulose fibres, with added short glass fibres, or of glass fibres made up into paper, or felt-iike materials of varying degrees of efficiency, the new generation materials comprise micro-fibres having both an electrostatic and mechanical efficiency. These micro-fibres are normally contained within two sheets, known as scrim sheets, which are of very low resistance and normally play no part in the filtration action; they are there merely to protect and hold the micro fibres together. The micro-fibres are composed typically of p.v.c. or polycarbonate. There is also on the marker an electret type of material of.

similar action.

The design of a face piece to take advantage of the increased efficiency of these new materials thus poses new problems. Since the filtration material is relatively expensive, economy of material is a prime factor. Fortunately, the compensating advantage is that less material is needed and it is therefore an object to use as little material as possible consistent with strength and wearability. The very simplest face pieces, consisting of little more than a flat pocl < et of material which pocket is opened out to fit over the face of the wearer, suffers from several disadvantages not least of which is a tendency to collapse onto the face of the wearer, during inhalation, which can be uncomfortable when the respirator is worn for a considerable length of time and which makes speech difficult.Also such simple face pieces tend to suffer from face seal leakage, i.e. leakage around the mouth of the respirator pocket between the edge of the mouth and the face. It will be appreciated that high face seal leakage reduces the efficacy of the face piece.

According to the present invention there is provided a filtering face piece made from flexible filtering sheet material in the form of a flat pocket of generally frusto-conical shape having opposed side walls, an open edge at the larger end of said frusto-cone and a closed end at the smaller end of said frusto-cone, wherein said closed end of said pocket is provided with first fold lines defining a generally quadrilateral surface composed of two triangular surfaces, said triangles of which have a common base, the apices of said triangles opposite said common base lying at the corners of said closed end of the pocket, and said common base extending in a direction perpendicular to the line joining said corners, said triangular surfaces facing each other and being, in use, relatively inclined to each other.

Preferably the fold line defining the common base is longitudinally rigidified to act as a strengthening rib. The rest of the first fold lines may also be longitudinally rigidified.

Preferably the flexible filtering sheet material is weldable, the first fold lines being defined by welds made in the material which have the effect of longitudinally rigidifying the fold lines. The initial flat pocket may be made from a single blank having the shape of two frusto-cones arranged end to end with common shorter ends, the two frusto cones being superimposed and connected together along the lateral edges of the pocket, e.g.

by welding.

The open edge of the pocket may be provided -with an inwardly directed sealing strip as described in copending patent application no.

7911595.

According to another aspect of the present invention there is provided a filtering face piece made from flexible filtering sheet material in the form of a flat pocket of generally frustoconical shape having opposed side walls, an open edge at the larger end of the frusto-cone and a closed end at the smaller end of the frusto-cone, and a framework defining a generally quadrilateral surface at the closed end of the pocket and composed of two triangular surfaces, said triangles of which have a common base, the apices of said triangles opposite said common base lying substantially at the corners of said closed end of said pocket, and said common base extending in a direction perpendicular to the line joining said corners, said triangular surfaces facing each other and being, in use, relatively inclined to each other.

The present invention will be more fully understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings.

In the drawings: Figure lisa plan view of a sheet of filtering material showing the manner in which the blanks for an embodiment of a filtering face piece according to the present invention can be cut therefrom; Figure 2 is a perspective view of the cut blanks of Figure 1 at the end of the cutting operation; Figure 3 is a plan view of a blank for an embodiment of a filtering face piece according to the present invention; Figures 4 (a) and (b) are diagrammatic sectional views showing welds which can be used in the manufacture of the filtering face piece; Figures 5 to 9 show stages in the production of a filtering face piece from the blank of Figure 3; Figures 10 to 12 show additional stages in the production of a filtering face piece; Figure 13 is a side view of the filtering face piece in an open condition;; Figure 14 is a front view of the filtering face piece of Figure 13 again in an open condition; Figure 1 5 is a perspective view of the filtering face piece of Figures 13 and 14 in use; Figure 1 6 is a diagrammatic view showing the operation of the filtering face piece of Figures 13 to 15; Figures 1 7 (a) to (e) show various stages in the production of a modification of the face piece of Figures 13 to 15; Figure 1 8 is a side view of another embodiment of a filtering face piece according to the present invention in open condition; Figure 1 9 is a view of the filtering face piece of Figure 18, again in an open condition, and viewed from the open edge thereof; Figure 20 is a view similar to that of Figure 1 9 but during opening of the face piece;; Figure 21 shows a stage in the production of the face piece of Figure 18; and Figures 22 and 23 are plan views of the filtering face piece of Figure 1 8 when folded flat.

The face piece shown in Figure 13 to 1 5 is made from flexible filtering sheet material for example as described above which is initially in the form of a flat pocket 1, as shown in Figure 5, of generally frusto-conical shape having a closed end 2 along the smaller end of the frusto-cone, closed lateral edges 3 and an open edge 4 at the larger end of the frusto-cone. For convenience hereafter, the pocket 1 will be described as having an upper wail 5 which in use overlies the nose of the wearer and a lower wall 6 which in use underlies the chin of the wearer.

This flat pocket 1 is folded as will be described hereafter to create at the closed end of the pocket a quadrilateral surface composed of two substanially identical triangular surfaces 7, the triangles of which have a common base 8 and apices e, opposite the base 8 which lie at the corners or ends of the closed end 2 of the flat pocket. The common base 8 lies on a line perpendicular to the line joining apices e, f and the triangular surfaces 7 face each other and are, in use, inclined to each other.

Advantageously the fold line defining the common base 8 of the triangular surfaces 7 is extended at 9 and 10 on each wall of the pocket to the open edge 4 of the pocket.

In addition to the above fold lines, the face piece advantageously has fold lines 1 5 extending from the apices e, fon the upper wall 5 of the pocket to points on the edge 4 intermediate the fold line 9 and the lateral edges 3. These fold lines 1 5 together with fold line 9 define in the upper wall 5 an inverted V-shaped channel 16 which seats on the nose of the wearer and thus positively adapts the upper wall 5 of the pocket to the shape of the wearer's face so as to decrease edge seal leakage around the nose and in the area between the nose and the cheeks.

The face piece is held on the face by one, or as shown two head bands 13, 14 attached to the pocket adjacent the edge 4. The head bands may be attached at points Al, A2 and B1, B2 or both may be attached at C1, C2 at the ends of the lateral edges 3, or a single band may be attached at points C1, C2.

The production of a face piece as described above will now be described initially in connection with filtering sheet material which is weldable, e.g.

by high-frequency welding, ultrasonic welding or heat welding. The face piece is made from a blank 20 as shown in Figure 3 which is composed of two frusto-conical parts arranged with the smaller ends together. This blank shape has advantages from the point of view of economy of manufacture from a sheet 21, Figure 1, of the material which is substantially wider than the blank, e.g. 3 m wide by approximately 100 m long. It will be seen from Figure 1 that a plurality of blanks can be cut out of the sheet 21 on a continuous basis, the blanks being arranged in longitudinal rows, with the blanks on one row being off-set longitudinally by a half blank length relative to the blanks in an adjacent row. The only wastage of sheet material then occurs at the two edges of the sheet. The blank may, for example, be 21 cm wide at the wider end of each frusto-cone, 9.5 cm wide at the smaller end of each frusto-cone and approximately 19 cm long so that the angle of the cone is approx 59ops A sheet 21 of filtration materials is passed through a high speed cutting machine on a continuous basis, the machine making continuous longitudinal zig-zag cuts 22 defining the lateral edges of the blanks and possibly also making transverse cuts 23 defining the ends of the blanks.

These cuts 23 do not extend the full width of each row of blanks to ensure that the rows of blanks remain connected together for convenience of subsequent processing. At the end of the cutting machine the row of blanks are folded in zig-zag fashion as shown in Figure 2.

The next operation, which may be combined with the cutting operation, or only with the production of the cuts 23, is to impress upon each blank a pattern of welds as shown in Figure 3.

These weíds comprise sealing welds 24 along the end edges of the blank to prevent fraying of the material along these edges, a central longitudinal weld 25 which defines the fold lines 8, 9 and 10 and four welds 26, 27 which define the fold lines 11,12.

The whole weld pattern may be impressed in a single operation or may be built up from a number of straight line welds.

The effect of these welds is as shown in Figure 4 (a) to compress and flatten the material in the region of the weld, and it is found that this does provide a degree of longitudinal rigidity to the welded line. It is possible, by use of suitably shaped electrodes or by a subsequent heating operation, to profile such a weld, e.g. as shown in Figure 4 (b), so as to increase the longitudinal rigidity of the weld. This profiling may be effected in relation to the part of the weld 25 defining the common base 8 of the triangular surfaces 7, at least.

After this operation, the blank is folded in half as shown in Figure 5 to superimpose the two frusto-conical parts which eventually form the upper and lower walls 5, 6 of the face piece pocket, and to form the closed end edge 2. When in this folded condition, the lateral edges 3 of the walls 5, 6 are welded together to create the flat pocket, of which the open edge 4 is formed by the welded edges 24. In the next operation, shown in Figure 6, the pocket is opened by pulling on the ends n, m of the central weld 25, and at the same time the centre point of weld 25 is depressed to fold the blank along the welds 25, 26 and 27 and create the triangular surfaces 7, as shown in Figure 7. Further separation of the points n and m brings the triangular surfaces 7 together, as shown in Figure 8.This produces triangular wings 30 which are then folded towards the point n to lie flat against the remainder of the pocket, as shown in Figure 9. This operation creates the fold lines 1 5 extending from the apices e, fto the open edge 4 of the pocket. These fold lines 5 may however have been predefined by making appropriate welds in the originai blank, simultaneously with the production of welds 24 to 27.

The face piece as shown in Figure 9 is completely formed except for the attachment of head bands to points previously described.

A further folding operation may be performed, as shown in Figures 10 to 12. As shown the triangular surfaces 7 are separated and folded downwardly in opposite directions about fold line 8 until they lie against the rest of the pocket, as shown in Figure 1 This creates a generally rectangular flat pack which can easily be slipped into the pocket of the wearer, possibly inside an envelope. The head bands can be wound round the pack, as shown in Figure 1 2.

A small deformable metal strip 31 (Figure 14) may be attached to the upper wall 5 of the face piece so as to extend over the apex of channel 1 6 adjacent edge 4 for improving sealing across the bridge of the nose.

To use the face piece it is restored to the condition shown in Figure 9 and is then opened by pulling apart the ends of the lateral edges 3 which results in the face piece having the form in Figures 13 and 14.

It will be appreciated that the shape of the above described face piece is inherently advantageous in two important respects.

The shaping of the upper wall 5 of the face piece with the channel 1 6 predisposes the face piece to nestle into the difficult-to-seal areas to either side of the nose. Additionally, the strip 31 is predeformed into a U-shape, by the folding up of the face piece, and is thus ready for clipping over the nose of the wearer when the wearer places the face piece on his face. No conscious action is required on the part of the wearer to deform the strip, although conscious action may be required to relieve the shape of the strip until it fits comfortably onto the nose.

While the face piece described above is described as being made from weldable material so that the fold lines, 8, 9, 10, 11 and 12 can be defined by welds, it will be appreciated that, whether or not the material is weldable, these fold lines may be defined by other means or may simply be defined by preformed crease lines.

Some or all ofthese fold lines may be reinforced, the reinforcement being created by applying strengthening elements along the fold lines, for example by applying strips of plastics, e.g. by injection moulding or otherwise, along the fold lines, the strips of plastics being profiled or not as required and/or holding the material in a folded condition.

Other filtering materials which could be used for the face piece include, for example, charcoal cloth arranged between two scrim sheets, forming a respirator having gas and vapour filtering capabilities. The charcoal cloth is activated charcoal in the form of a cloth made initially of a woven synthetic fibre; e.g. rayon. Charcoal impregnated filtering materials may also be used.

Alternatively the charcoal cloth or charcoal impregnated filtering material may be combined with one or more layers of particulate filtering material to provide a respirator having particulate as well as gas and vapour filtering capabilities.

The overall shape of the finished face piece, and consequently the degree of fit, is dictated by the dimensions of the original blank shown in Figure 3 and by the dimensions of the quadrilateral area composed of the triangles 7. If this quadrilateral area is a square, the resulting face piece is symmetrical about a centre line extending parallel to the line X in Figure 12. By making the lengths of the fold lines 11 and 12 unequal some variation in the shape of the face piece is possible. For example the quadrilateral area can be a rhomboid.

Alternatively lines 11 can be made longer than lines 12, i.e. the line joining apices e, f (Figure 3) is made shorter than the line joining apices g, h and these lines do not cross at their centre points. The resulting shape may be described as an upsidedown kite and this leads to the face piece having a side view as shown in Figure 1 2 in which the fold line 12 is parallel to the centre line X and the fold line 9 is at an angle of approximateiy 250 to the centre line X. This is a close approximation to the classic orinasal cup shape.

In one embodiment, the length of the line joining the apices e, fis 8 cm, the length of the line joining the apices g, h is 10 cm and the lines intersect at a point which is 4 cm from apex h and 6 cm from apex g so that the angle between welds 25 and 26 is 450 and that between weld 25 and 27 is 33.70.

For convenience of manufacture however, the quadrilateral area may be made square with the lines joining apices g, h and e, fboth having a length of 9.5 cm, and intersecting gt their mid points.

Referring to Figure 1 6 it can be seen that the completed face piece can be regarded as comprising a frame defined by the fold lines 8, 9, 10, 11 and 12 between which the filtration material extends. The folds 8, 9, 10, 11 and 12 can be likened to struts in compression which are pin jointed at their ends. The welds along the lateral edges 3 are under tension during exhalation and may be under compression during inhalation and therefore rigidity in compression is desirable.

The-strut formed by fold line 8 is particularly important since this lends stiffness to the face piece in a vertical position. The effective pin joints at the apices e, fcan thus radius around the strut 8 giving a degree of flexibility and mobility to the face piece, which can thus easily adapt to flat or thin faces. When the jaw of the wearer is moving, as for example in speaking, the apices e, fmove in space thus relieving the load which would otherwise occur on the bridge of the nose causing the face piece to fall off. Furthermore, the reinforcing of the face piece provided by the fold lines 8 to 12 effectively prevents the face piece collapsing on the face of the wearer even when becoming clogged and therefore inefficient.

The above described face piece may be modified to provide it with inwardly extending sealing strips for example as described in copending patent application no. 7911 595. For this purpose, a reversely frusto-conical portion 35 may be added to each end of the blank as shown in Figure 1 7(a) and the end edges inwardly curved to a greater or lesser extent. After creation of the fold lines 8 to 12, the blank is folded in half and welded along its lateral edges 3, as shown in Figure 1 7(b).The flat pocket so formed is then turned inside out as shown in Figure 17(c) and the additional frusto-conical portions are folded inwards to create the inwardly directed sealing strip 36 which may extend the full way round the open mouth of the pocket or to a lesser extent, for example only in the regions of the ends of edges 3, or in the regions of the ends of edges 3 and over the nose but not under the chin, as described in the above referred to copending patent application.

It will be appreciated that the pocket has to be turned inside out between the stages shown in Figure 1 7 (b) and (c) to ensure that the sealing strip presents only a smooth surface to the face.

A further modification of the filtering face piece shown in Figures 1 3 to 1 5 is shown in Figures 1 8 and 19.

As shown, the face piece corresponds exactly with the face piece shown in Figures 1 3 and 14 (and the same reference numerals have been used for like parts) except for the additional feature that, in the lower wall 6 of the face piece, fold lines 40 are formed defining a triangular area 41 centred on fold line 10. A base of this triangular area extends along the open edge of the pocket, intermediate the lateral edges 3, and the apex opposite this base is positioned at or in the region of the apex g of the triangular areas 7.

As shown in Figures 21 and 22, the triangular area 41 is defined, and the fold lines 40 are created, at the same time as the wings 30 are folded flat. The fold lines 40 are created by pushing point m inwardly and folding the adjacent parts of the wall 7 together. This creates two half triangular areas which are folded flat against one another and have a common base along the fold line 12.

The face piece is opened in exactly the same way as the face piece described above except that when the ends of the lateral edges 3 have been pulled apart the triangular area 41 extends across the pocket opening, as shown in Figure 20. It is then merely necessary to pull the end of fold line 12 outwardly to flatten the triangular area 41. This area 41, when the face piece is placed on the face, underlies the chin with the'fold lines 40 running generally along the edge of the lower jaw. The lower wall 7 of the face piece is thus conveniently adapted to the shape of the chin and adjacent parts of the cheeks of the wearer.

An additional advantage arising from the folding in of the triangular portion 41 is that the face piece in its flat folded condition, as shown in Figures 22 and 23, has a generally rectangular shape which will conveniently fit in a pocket without the need for the additional folding operations described with reference to Figures 10 to 12. It is pointed out that Figures 22 and 23 show the same face piece in a flat folded condition but in Figure 23 the face piece is orientated for insertion in, for example, a breast pocket.

The above described face pieces may be further strengthened by the addition of further weld lines or plastics strips to the triangular surfaces 7, the further weld lines or plastics strips extending parallel to the fold line 8, or at an angle thereto, e.g. parallel to the fold lines 11 and 12.

It will be appreciated that the term 'filtering material' used hereinbefore and hereafter is used to denote a material which removes one or more unwanted components from a gas or vapour; the component may be in the form of particles and/or molecules and may be removed mechanically and/or electrostatically and/or may be absorbed and/or adsorbed by the filtering material.

Claims (29)

1. A filtering face piece made from flexible filtering sheet material in the form of a flat pocket of generally frusto-conical shape having opposed side walls, an open edge at the larger end of said frusto-cone and a closed end at the smaller end of said frusto-cone, wherein said closed end of said pocket is provided with first fold lines defining a generally quadrilateral surface composed of two triangular surfaces, said triangles of which have a common base, the apices of said triangles opposite said common base lying at the corners of said closed end of the pocket, and said common base extending in a direction perpendicular to the line joining said comers, said triangular surfaces facing each other and being, in use, relatively inclined to each other.

2. A face piece as claimed in claim 1, wherein said fold line defining said common base is longitudinally rigidified.

3. A face piece as claimed in claim 1, wherein said first fold lines defining said quadrilateral surface are longitudinally rigidified.

4. A face piece as claimed in either claim 2 or claim 3, wherein said sheet material is weldable and the or each said longitudinally rigidified fold line is defined by a weld in said sheet material.

5. A face piece as claimed in either claim 2 or claim 3, wherein the or each said longitudinally rigidified fold line is defined by a rigidifying member affixed to the sheet material.

6. Aface piece as claimed in claim 5, wherein said rigidifying member is made of plastics material.

7. A filtering face piece made from flexible filtering sheet material in the form of a flat pocket of generally frusto-conical shape having opposed side walls, an open edge at the large end of the frusto-cone and a closed end at the smaller end of the frusto-cone, and a framework defining a generally quadrilateral surface at the closed end of the pocket and composed of two triangular surfaces, said triangles of which have a common base, the apices of said triangles opposite said common base lying substantially at the corners of said closed end of said pocket, and said common base extending in a direction perpendicular to the line joining said corners, said triangular surfaces facing each other and being, in use, relatively inclined to each other.

8. A Face piece as claimed in claim 7,w'h'eiein said framework defines first fold lines in said pocket.

9. A face piece as claimed in either claim 7 or claim 8, wherein said framework defines longitudinally rigidified fold lines.

10. A face piece as claimed in any one of the preceding claims, wherein said generally quadrilateral surface is a square.

11. A face piece as claimed in any one of claims 1 to 6, wherein said generally quadrilateral surface is a rhomboid.

12. A face piece as claimed in anyone of claims 1 to 6 adapted for use with said common base extending in a generally vertical plane, with one side wall of said pocket extending over the nose of the wearer and with said other side wall extending under the chin of the wearer, wherein said, line joining said corners of said closed end'of said pocket intersects said common base above the mid point of said common base.

13. A face piece as claimed in any one of the preceding claims, wherein the cone of said frusto cone of said pocket subtends an angle of 600.

14. A face piece as claimed in any one of the preceding claims adapted for use with said common base extending in a generally vertical plane, with one of said side walls of said pocket extending over the nose of the wearer and with the other of said side walls extending under the chin of the wearer, wherein a second fold line is provided in said one side wall extending from the corresponding end of said fold line defining said common base to the open edge of said pocket, which second fold line, in use, lies along the nose of the wearer.

1 5. A face piece as claimed in claim 14, wherein a third fold line is provided extending in said other side wall from the other end of said fold line defining said common base to the open edge of said pocket, which third fold line, in use, extends under the chin of the wearer.

1 6. A face piece as claimed in either claim 14 or claim 1 5, wherein said second fold line or each of said second and third fold lines is colinear with said fold line defining said common base.

1 7. A face piece as claimed in any one of claims 14 to 16, wherein fourth fold lines are provided in said one wall extending from said one end of said fold line defining said common base to said open edge of said pocket on either side of said second fold line to define therewith a generally V-shaped channel for receiving the nose of the wearer.

1 8. A face piece as claimed in any one of claims 14 to 17, wherein a deformable element is provided in the region of the open edge of said pocket and extending across said second fold line for engagement round the nose of said wearer, said deformable element being bent along said second fold line to a generally Ushape.

19. A face piece as claimed in claim 17 or claim 18, wherein said face piece is initially folded flat, with said side walls folded about said second and third fold lines to superimpose the parts thereof, and said one side wall is folded about said fourth fold lines to superimpose parts thereof.

20. A face piece as claimed in any one of the preceding claims, wherein said side walls are connected together along lines extending from said apices of said triangular areas to said open edge of said pocket.

21. A face piece as claimed in claim 20, wherein said connections of said side walls are longitudinally rigidified.

22. A face piece as claimed in any one of the preceding claims, including an inwardly directed sealing strip extending along at least part of said open edge of the pocket so as, in use, to bear against the face of the wearer.

23. A face piece as claimed in claim 22, wherein said sealing strip is formed integrally with said pocket and has a generally frusto-conical shape, the apex of the cone thereof being directed inwardly of said pocket.

24. A face piece as claimed in any one of claims 1 to 22, wherein an edge portion of the side wall of the pocket which in use underlies the chin of the wearer is folded inwardly to create an inwardly extending flange which, in use, bears against the chin of the wearer.

25. A face piece as claimed in any one of the preceding claims made from a blank of flexible filtering sheet material having the shape of two identical frusto-cones connected integrally by the smaller ends of the frusto-cone, which blank is folded to superimpose the two frusto-conical parts which are connected together along the mutually inclined edges of said frusto-cones, said fold lines being defined in the initial blank.

26. A face piece as claimed in any one of the preceding claims made from filtering sheet material including microfibres having electrostatic and mechanical efficiency.

27. A face piece as claimed in any one of the preceding claims made from filtering sheet material including activated charcoal.

28. A face piece substantially as herein described with reference to Figures 1-17 of the accompanying drawings.

29. A face piece substantially as herein described with reference to Figures 18-23 of the accompanying drawings.