GB1588442A - Face masks - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO FACE MASKS (71) I, the SECRETARY OF STATE FOR DEFENCE, Whitehall, London, SW1A 2HB, a British Corporation Sole, do hereby declare this invention to be described in the following statement: The present invention relates to respiratory face masks.

Respiratory face masks of various different designs have been proposed heretofore but many of these suffer from disadvantages such as bulkiness, excessive weight, inconvenience in fitting and in operation, all of which serve to reduce the usefulness of the mask. Such disadvantages are at least partially overcdme by the face mask of the present invention which is light in weight and has low breathing resistance and is therefore comfortable to wear, is simple in construction and therefore cheap, and is easily and quickly donned for use. As such the mask is very suitable for use in large numbers as an emergency provision to be carried in the event of a sudden need for protection.

According to the present invention there is provided a respiratory face mask which comprises two substantially identically-dimensioned, substantially symmetrical trapezate areas of charcoal cloth joined together along their respective three shorter edges with their respective longest edges providing face-contacting edges of the mask. The mask preferably also has means, for example, a head strap, which are adapted to keep the two longest edges of the mask in contact with the face when the mask is being worn, one edge bridging the nose, the other going under the chin.

Charcoal cloth is particularly effective at filtering air passing through the mask in order to remove at least a proportion of contaminants which may be present in the surrounding atmosphere. The mask of this invention is especially suitable for use in filtering out gaseous or vaporous contaminants. 1 However the mask may also be adapted to filtering out particulate contaminants for example, by providing it with an additional thin layer of appropriate filter material designed to filter particulate contaminants.

By the term 'charcoal cloth' as used herein is meant a woven or non-woven cloth primarily composed of fibrous or filamental activated carbon. Such cloths are generally prepared by carbonization (charring) of a cloth composed of organic fibres followed by activation, but may in some cases be prepared from pre-carbonized fibres. Preferably the cloth is of the type manufactured to British Patents Nos 1.301.101 and 1,310.011.

In order that the mask should retain its shape better when in use and also generally to increase its strength and resistance to wear. it may be advantageous to provide the charcoal cloth with a backing sheet. which may be applied either to one or to both sides of the charcoal cloth. Suck a backing sheet also helps to protect the charcoal cloth and where this is at all fragile, it is desirable to have a backing sheet on both sides thereof. The material of which the back sheet is made must be pervious to air but may advantageously provide a coarse particulate filtration effect. The backing sheet may be treated to give water and oil repellency.

One or more layers of the charcoal cloth may be used in the mask: the more layers present the greater is the breathing resistance but also the longer is the lifetime of the mask ie the longer the time before it suffers penetration by the contaminant. With charcoal cloth for example it has been found that a second layer increases the lifetime by more than fivefold and this is doubled again by a third layer. Furthermore the layers (including also the back sheet if one is present) may be laminated. With charcoal cloth material. such lamination is conveniently effected by heat-sealing with a polyamide web as this treatment does not degrade the charcoal cloth.

The mask of this invention may conveniently be made by laying down a single sheet of charcoal cloth, optionally placing under and/or on this sheet either one or two backing sheets and folding the sheet or sheets over so that the fold forms one of the three shorter connected edges of the mask. By then cutting the material to shape to give the two short edges it only remains to join the various sheets together along these edges in order to form a completed face mask. Suitable means for joining the edges are such as will provide a reasonably firm connection between the various sheets of material which meet at the edges so that the mask holds together in use. For example, the edges may be stuck together using an adhesive or by heat-sealing or may be stitched together.It is not necessary that the joins between the edges be absolutely leak-tight when charcoal cloth is used since the parallel or near parallel zones of the cloth sheets near to the join proper will act in this case as a parallel flow filter and so effectively filter any air which may be leaking through the joins.

The non face-contacting edges of the mask may if desired be protected from wear by running a strip of a flexible hard-wearing material along these edges, and an adhesive tape is, for example, useful for this purpose.

So that as effective a seal as possible may be obtained between the face and the mask it is preferred to provide a form of sealing along the longest, face-contacting, edges of the mask.

(It should be pointed out however that as a result of the low breathing resistance of the mask of this invention (about a quarter of that of conventional half-masks) the extent of leakage around the periphery of the mask is anyway much reduced in comparison to that experienced with conventional masks). The sealing provided may conveniently be a flexible rubber seal as used in conventional face masks and may be either stitched or attached by adhesive to the face-contacting edges of the mask, or may be a strip of plastics foam material likewise attached. In the latter case the foam material advantageously incorporates a carbon filter material (carbon granules) which will act as an adsorbent within the plastics foam sealing strip itself and thus provide extra protection against ingress by contaminents around the sides of the charcoal cloth in the mask.In an alternative and preferred embodiment, the sealing means may be provided by a flap of charcoal cloth in the manner described in my co-pending British Patent Application No. 16078/77. (Serial No. 1588441) Preferably the trapezate areas forming the mask of the invention have internal angles of approximately 60 and 1200, but these angles may be varied dependent upon the physiognomy of the wearer or of a class of wearers. The total length of the face-contacting edges of the mask are likewise dependent, so that masks of various sizes are required to provide for all wearers. However a peripheral length of about 20 or 25 cm has been found convenient in use for a mask of average size.

It will be appreciated that as the face-mask of the present invention is of extremely simple construction, it is both very easy and quick to use and cheap to manufacture. Because of this and because of its light weight and small size it may very conveniently be carried on the person by anyone who may be at all likely to come into contact with a contaminated atmosphere, eg chemical or other industrial workers, especially where such contact is likely to be unexpected and sudden. In such circumstances the mask of the invention can be quickly donned and allows the wearer sufficient general protection to enable him to escape from the contaminated-area or to find and fit on more elaborate apparatus such as breathing apparatus.Where a contamination is not so serious eg nuisance vapours which are not toxic, such as paint or malodorous vapours. or is readily dispersed, the mask may provide as much protection as is necessary while the wearer is in contact with the contaminated atmosphere. Another possible longer term use is for protection against low concentrations of anaesthetic vapours in surgical operating theatres. For such cases where a mask is to be worn for a period of time, the mask of the present invention is very well suited since it is light in weight and small and hence not inconvenient or distracting to wear. The mask of the invention is also more comfortable than many conventional masks on account of its low breathing resistance (typically about lOPa at a flow rate of 30 1/min or 27Pa at a flow rate of 85 1/min for a double layer of charcoal cloth).In cases where although the likelihood of exposure of persorknel to dangerous air-borne materials is only remote yet the consequences are grave, the ease of wearing a mask according to this invention may encourage such personnel to wear protection whereas they might not otherwise have troubled to, and in this way serious accidents may be avoided.

A further advantage of the masks according to this invention is that they do not deteriorate significantlv on storage and so have a long shelf life. This is an important economic consideration where, as in for example. a large chemical works, the mask might be issued to a large number of people but only rarely used.

The present invention is now further described by way of example by reference to the accompanying drawings in which: Figure 1 is a general perspective view of an embodiment of the mask of the invention; Figure 2 is a perspective view of the mask of Figure 1 in use with a strap attached; Figure 3 is a sectioned view of part of an embodiment of the mask of the invention which has a plastics foam sealing means, and Figure 4 is a like view to Figure 3 of an alternative embodiment of the mask of the invention, in this case having a fold of charcoal cloth as the sealing means.

In Figure 1, a mask is shown generally at 1 and comprises two symmetrical trapezate pieces of charcoal cloth covered on both sides with co-extensive pieces 2, 3, of a backing material. The pieces are joined together along common edges 4, 5 and 6. At the face contacting edges, 7, 7', the layers of material are folded back as shown at 8 and the fold is stitched down. This prevents the materials from fraying along the face-contacting edges. At the corners of the mask adjacent the face-contacting edges, press studs 9, 9' are provided to which strap means (not shown) to hold the mask on the face may be attached. Adjacent one face-contacting edge 7' and running for short distance on either side of the centre-point of this edge is a deformable strip 10 of soft metal (eg aluminium) held in place by a covering strip 11, eg of adhesive tape.In use, as shown in Figure 2, the face-contacting edges 7, 7' fit respectively across the cheeks and under the chin of the wearer whilst the metal strip is deformed to fit the shape of the wearer's nose as shown in Figure 2 of the drawings. Also in Figure 2 the mask is shown with strap means 12, attached to the press-studs 9, 9'. The strap means may conveniently comprise a single elastic strap which can be stretched to fit round the back of the head, or a pair of short elastic straps having complementary engagement means which can be clipped together at the back of the head. In either case the strap means should be so tensioned as to hold the mask firmly against the face of the wearer.

In Figure 3, there is shown an embodiment of the face mask of the invention in which the charcoal cloth comprises a single sheet 13 folded along edge 14 of the mask and provided on its outer side with a backing material 15, likewise folded. The edge 14 and the other common edge 16 together with face-contacting edges 17, 18 of the mask are all protected by continuous strips of adhesive tape 19 folded over the respective edge. The face-contacting edges also have applied along their whole length, a narrow strip of an active carbon impregnated plastics foam material 20 to act as a sealing means between the mask and the face. Applied to the surface of the mask on one side thereof, adjacent to face-contacting edge 7 is a strip 21 of flexible metal, held in place on said surface by means of a length of, for example, adhesive tape 22 as in Figure 1.

A further embodiment of the mask of the invention is shown in Figure 4. In this embodiment, as in the embodiment of Figure 1, the charcoal cloth 13 is a single sheet folded at edge 14 and provided with a canvas backing material 15 on each face. In this embodiment the sheet projects beyond the face-contacting edges 17, 18 and is turned back and attached to itself by stitching 23 or by other means thus forming a flexible flap 24 of charcoal cloth.

The backing material 15 is not carried beyond the face-contacting edges 17. 18, leaving the flap of charcoal cloth free. As in Figures 1 to 3 a deformable metal strip 21 is applied to the surface of the canvas backing 15 adjacent the face-contacting edge 17, and is held in place on the surface by a length of adhesive tape 22. The embodiment shown in Figure 4 can conveniently be adapted by providing that the charcoal cloth sheet when folded back on itself should form a second layer in respect of the entire mask.

In use the embodiments of Figures 3 and 4 provide an active filtration seal across any small gaps between the mask and the wearer's face greatly increasing the overall filtration efficiency.

A number of tests have been carried out to demonstrate the effectiveness of masks according to this invention. These tests involved the use of the anaesthetic 2,2-dichloro-1, 1-difluorel-methoxyethane (Penthrane-Trade Mark) as the contaminant and masks comprising four layers of material as follows: an outer layer of an acrylic/glass fibre material (Teklan-Trade Mark) as a protective covering, followed by two layers of charcoal cloth and an inner layer of white cotton mull. At the face-contacting edges the layers were all folded over to give a 2 inch overlap and the overlapping portions stitched together. This prevents fraying of the material which tends to occur if the edges are left free.

As an initial test a double layer of charcoal cloth was checked for penetration of Penthrane (Trade Mark), using a concentration of the latter of 330ssg/l and an air flow rate of 40 1/min over a filtration area of 250 cm2 which is equal to the area of a typical mask. The penetration time under these conditions was found to be 65 min. By exposing subjects wearing masks of the kind described for periods of no more than 60 minutes therefore it was expected that there would be no penetration of the charcoal cloth itself (unless it were punctured or otherwise damaged in any way) and that any contaminant breathed by the subject could thus be attributed to leakage round the mask.

The masks were tested in wearer trials using a total of nineteen different subjects. The subjects were exposed to Penthrane (Trade Mark) at a concentration of about 100 ppm in a chamber for periods of 30 and/or 60 minutes, after which they made a complete exhaustion of the lungs into a glass flask. A sample of this breath was then analysed by chromatography for Penthrane (Trade Mark). This value has to be corrected for each individual to allow for the differing amounts of Penthrane (Trade Mark) absorbed in the lungs, and this was done by exposing the subjects (at least 2 days after the mask trials) to different concentrations of Penthrane (Trade Mark) without mask protection, and again measuring the concentrations of Penthrane (Trade Mark) in the breath after a period of exposure which was the same as for each subject in the mask wearer trial.By extrapolation of these results it is possible to establish the lung absorption rate for each individual.

The results are reported in terms of the percentage efficiency of the mask. This is defined as: (1 - concentration of Penthrane (Trade Mark) in breath at end of trial with mask) percentage efficiency = x 100% concentration of Penthrane (Trade Mark) in breath at end of trial with no facelet The results of the wearer trials are given in the Table below. From the data in the Table it can be seen that with new facemasks the maximum leakage rate (leakage rate = 1-efficiency) was 11% and the minimum 3% with an average value of only 6% and that even with a worn mask, the average leakage rose to only about 13%.These values may be compared for example with the relevant British Standard (BS 2091) for half masks which lays down a maximum mean leakage of 5% (mean of ten measurements with no limitation on the spread of results), using sodium chloride particles as the contaminant which is less penetrating than a vapour such as Penthrane (Trade Mark) TABLE Subject Period of Exposure Subject Period of Exposure No. 30 min* 60 min No. 30 min* 60 min* 1 92) 92) 11 - 96) 2 93) 91) 12 - 93) 3 - ) 93) 13 - 91) 4 - ) 1 93) 1 14 - 89) 5 - ) 94) 15 - 95) 1 ) ) ) 6 97) 94) 16 - 95) 7 97) 96) 17 - 97) ) ) ) 8 96) 86) 18 - 96) 9 87) 2 93) 2 19 - 96) 10 97) 83) * Values are means of two determinations carried out with one flask of breath.

1. Values obtained with new facemasks.

2. Values obtained with masks which had been worn intermittently for a week beforehand.

WHAT I CLAIM IS: 1. A respiratory face mask comprising two substantially identically dimensioned, substantially symmetrical trapezate areas of charcoal cloth joined together along their respective three shorter edges with their respective longest edges providing face-contacting edges of the mask.

2. A face mask according to claim 1 wherein said areas of charcoal cloth are backed by a backing material on either or both sides thereof.

3. A face mask according to claim 1 or claim 2, wherein said trapezate areas are formed from a single sheet of charcoal cloth such that the joining at one of the respective shorter edges comprises a fold in said sheet.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. of the lungs into a glass flask. A sample of this breath was then analysed by chromatography for Penthrane (Trade Mark). This value has to be corrected for each individual to allow for the differing amounts of Penthrane (Trade Mark) absorbed in the lungs, and this was done by exposing the subjects (at least 2 days after the mask trials) to different concentrations of Penthrane (Trade Mark) without mask protection, and again measuring the concentrations of Penthrane (Trade Mark) in the breath after a period of exposure which was the same as for each subject in the mask wearer trial. By extrapolation of these results it is possible to establish the lung absorption rate for each individual. The results are reported in terms of the percentage efficiency of the mask. This is defined as: (1 - concentration of Penthrane (Trade Mark) in breath at end of trial with mask) percentage efficiency = x 100% concentration of Penthrane (Trade Mark) in breath at end of trial with no facelet The results of the wearer trials are given in the Table below. From the data in the Table it can be seen that with new facemasks the maximum leakage rate (leakage rate = 1-efficiency) was 11% and the minimum 3% with an average value of only 6% and that even with a worn mask, the average leakage rose to only about 13%.These values may be compared for example with the relevant British Standard (BS 2091) for half masks which lays down a maximum mean leakage of 5% (mean of ten measurements with no limitation on the spread of results), using sodium chloride particles as the contaminant which is less penetrating than a vapour such as Penthrane (Trade Mark) TABLE Subject Period of Exposure Subject Period of Exposure No. 30 min* 60 min No. 30 min* 60 min* 1 92) 92) 11 - 96) 2 93) 91) 12 - 93) 3 - ) 93) 13 - 91) 4 - ) 1 93) 1 14 - 89) 5 - ) 94) 15 - 95) 1 ) ) ) 6 97) 94) 16 - 95) 7 97) 96) 17 - 97) ) ) ) 8 96) 86) 18 - 96) 9 87) 2 93) 2 19 - 96) 10 97) 83) * Values are means of two determinations carried out with one flask of breath.

1. Values obtained with new facemasks.

2. Values obtained with masks which had been worn intermittently for a week beforehand.

WHAT I CLAIM IS: 1. A respiratory face mask comprising two substantially identically dimensioned, substantially symmetrical trapezate areas of charcoal cloth joined together along their respective three shorter edges with their respective longest edges providing face-contacting edges of the mask.

2. A face mask according to claim 1 wherein said areas of charcoal cloth are backed by a backing material on either or both sides thereof.

3. A face mask according to claim 1 or claim 2, wherein said trapezate areas are formed from a single sheet of charcoal cloth such that the joining at one of the respective shorter edges comprises a fold in said sheet.

4. A face mask according to any one of claims 1 to 3, wherein the areas are joined along

at least two of their respective shorter edges by stitching them together.

5. A face mask according to any of claims 1 to 3, wherein the areas are joined along at least two of their respective shorter edges by heat sealing or by use of an adhesive.

6. A face mask according to any of claims 1 to 5, having two layers of charcoal cloth.

7. A face mask according to claim 6, wherein said layers, and said backing material if present, are laminated together.

8. A face mask according to claim 7 wherein said lamination is effected by interpolation of a polyamide web between the layers to be laminated and heat-sealing the layers to the web.

9. A face mask according to any of claims 1 to 8 wherein the face-contacting edges of the mask are provided with sealing means.

10. A face mask according to claim 9, wherein said sealing means comprise a flexible rubber seal or a plastics foam material seal.

11. A face mask according to claim 10, wherein said plastics foam material is a charcoal impregnated foam material.

12. A face mask according to claim 9, wherein the sealing means comprises a flap of charcoal cloth.

13. A face mask according to any of the preceding claims wherein the trapezate areas have internal angles of substantially 60 and 1200.

14. A face mask according to any of the preceding claims wherein the total length of the free-contacting edges of the mask if from 20 to 25 cm.

15. A face mask according to any of the preceding claims, and further including means adapted to keep the two longest edges of the mask in contact with the face when the mask is being worn.

16. A face mask according to claim 15, wherein said means comprises a strap which passes round the head of the wearer.

17. A respiratory face mask substantially as herein described and with particular reference to the accompanying drawings.