GB2564408A

GB2564408A - Anti-pollution mask

Info

Publication number: GB2564408A
Application number: GB1710898.6A
Authority: GB
Inventors: Howard House David
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-07-06
Filing date: 2017-07-06
Publication date: 2019-01-16
Also published as: KR20200054942A; EP3648844A1; AU2018296667A1; GB201710898D0; WO2019008161A1

Abstract

A face mask comprises a face seal 22, wherein the seal comprises 22 an envelope defining a lumen 24 containing an open cell foam core, and wherein the seal comprises one or more valves 26 that control the passage of air to and from the core of the seal. The seal is mounted on a frame 6, housing filter material and at least one exhalation valve. Only the seal is in contact with the face of the user. The exhalation valves have a high flow capacity and provide an effective means for venting exhaled air from the mask. The mask can be used as a better fitting anti-pollution mask

Description

ANTI-POLLUTION FACE MASK

Introduction

The present invention relates to an anti-pollution face mask and to methods of fitting and resetting an anti-pollution mask.

Background to the Invention

Anti-pollution face masks are widely available to the public. The masks act to protect the users from pollutants found in air that may be harmful, particularly in big cities. Generally, the masks are half-masks that provide the user with adequate flexibility and vision to carry out day-to-day activities, e.g. cycling and running, while wearing the mask.

It is common for an anti-pollution mask to comprise a filter and a strap for attaching the filter to the head of the user. More effective masks often also comprise an exhalation valve to allow exhaled air to be channeled out of the mask without passing through the filter. The valve then shuts when the user inhales, in order to ensure inhaled air passes through the filter material and not the exhalation valve.

The global burden of air pollution is ever growing, with economic growth driven through the burning of fossil fuels. In 2013, long-term exposure to air pollution was responsible for approximately 5.5 million deaths worldwide.

Nevertheless, many inhabitants of highly polluted areas worldwide do not wear antipollution face masks at all. The most common type of face mask used in large cities worldwide is the disposable surgical mask. These masks are designed for health professionals to catch the bacteria shed from the user's mouth and nose. They are not designed to protect the user from inhaling airborne bacteria or virus particles, let alone much smaller gaseous air pollutants. Thus, these surgical masks provide almost no protection from air pollution.

Furthermore, anti-pollution face masks known in the art generally have inefficient seals for preventing unfiltered air from entering the mask. Flexible metallic nose bridges are often provided to help adjust the mask to various nose / face types. This can often lead to a disproportionate amount of pressure being placed on the nose of the user and can temporarily reduce the user’s sense of smell. Furthermore, gaps between the mask and the face of the user still exist at various points around the circumference of the mask, meaning that unfiltered air can easily enter the mask and be inhaled by the user.

More effective masks are available and often contain a specific filter for capturing airborne pollutants. Unfortunately, the efficiency of the filter is often adversely affected due to saturation of the filter by the humid air exhaled by the user. As the filter efficiency falls, air is preferentially drawn in under the face seal due to the relatively low resistance. Thus, unfiltered air is inhaled by the user. Exhalation valves are often introduced to attempt to overcome this problem, but are limited by their air flow rate capacity. Furthermore, due to the design of these half-masks, it is common for the filter material to be pressed against the face of the user, meaning the filter is also exposed to heat and sweat therefrom, further decreasing the filter efficiency and decreasing potential air flow through the filter material as one side is blocked by the user’s face.

The present invention aims to provide an alternative and preferably improved antipollution face mask, especially wherein an effective seal is established between the mask and the face of the user, and/or wherein the filter material remains effective over an extended period of use.

Summary of the Invention

Accordingly, the present invention provides a face mask comprising a face seal, wherein the seal comprises an envelope defining a lumen containing an open cell foam core, and wherein the seal comprises one or more valves that control the passage of air to and from the core of the seal.

The seal is typically mounted on a frame, housing filter material and at least one exhalation valve. It is preferred that only the seal is in contact with the face of the user.

The exhalation valve preferably has a high flow capacity and provides an effective means for venting exhaled air from the mask.

The invention also provides a method of fitting a face mask as defined above and below, comprising opening a valve connected to the lumen of the seal, pressing the face mask against the face of a user, in order to deform the seal to match the face of the user and expel air from the seal lumen, and closing the valve.

Preferably, the face mask can be reset by opening a seal valve, allowing the open cell foam core to draw air into the seal lumen by recovering into its partly or fully expanded configuration, and closing the valve.

Details of the Invention

The present invention provides a face mask comprising a face seal, wherein the seal comprises an envelope defining a lumen containing an open cell foam core, and wherein the seal comprises one or more valves that control the passage of air to and from the core of the seal.

It is preferred that the face mask is a half-mask and is suitable for a user carrying out everyday activities such as cycling and running. The face mask is suitable for frequent and extended use. In a preferred embodiment, the face mask can be used for over 5 hours a day, more preferably over 10 hours a day. It is also preferred that the face mask can be used for several consecutive days without the need to change any of its components.

The envelope is preferably substantially tubular (defining a lumen therein). Furthermore, the face seal is preferably substantially toroidal and/or annular in shape and effectively circumscribes an area of the user’s face comprising the mouth and nose of the user, while providing a bespoke fit to the contours of the face of the user. The path of the toroid may be adapted or deformed to better surround the area of the user’s face comprising the mouth and nose. Preferably the toroidal shape defines a continuous lumen. In cross-section, the toroidal shape of the seal need not be circular. The toroidal shape is maintained as the seal is in continuous contact with an outer rim of a frame with an annular perimeter.

It is preferred that the toroidal seal is substantially square or rectangular in cross-section. This facilitates forming an effective seal when pressed again the face of the user, since a greater contact surface area is available than when other shaped cross-sections are used. Furthermore, manufacture of the seal is made simpler, since open cell foams are normally manufactured in sheets, which can then simply be cut into pieces with square or rectangular dimensions. This contrasts with the extra cutting steps required to make foam pieces with rounded surfaces, e.g. with a circular cross section. Preferably the open-cell foam is made of a polyether material. It is hence preferred that, in use, the seal has a flat front surface that abuts the face of the user.

It is preferred that the seal passes under the chin of the face of the user. This allows for a greater volume between the face mask and the face of the user, and ensures an effective Flow Zone is formed (see below). Furthermore, this feature provides a greater surface area into which filters can be fitted to the face mask.

It is preferred that the seal extends under the chin when worn by a user of the face mask. This allows the mask to encompass a greater volume between the inner surface of the mask and the face of the user, as well as providing a greater area on which to fit filters to the mask.

It is preferred that the face seal comprises a lumen filled with an open cell foam. In an optional embodiment, the seal is extruded. Preferably, the seal is made of a silicone material. The seal material is preferably no more than 2mm in thickness, more preferably no more than 1mm in thickness.

In preferred embodiments, the face mask comprises a frame. The frame is optionally made of thermoplastic material. Optionally the thermoplastic material is a polyurethane. The frame may optionally be made of a thermoplastic rubber. The frame may optionally comprise polyethylene. It is preferred that the frame has adequate rigidity, in order to maintain its proper form, but also has adequate flexibility to flex out of shape under impact, e.g. if a cyclist has an accident.

The seal is mounted on the frame. Preferably, the seal comprises a U-shaped channel around its circumference that receives the outer rim of the frame. It is preferred that the seal is in continuous contact with the outer rim of the frame. It is also preferred that the seal is mounted on the frame such that it projects away from the frame. These features contribute to ensuring that, in use, only the seal is in contact with the face of the user.

In an optional embodiment, the frame comprises one or more barbs on its outer and/or inner surface. Thus, an interference fit is provided between the frame and the seal. Preferably, two barbs are provided: one on the front surface of the frame and the other on the rear surface of the frame. This configuration simplifies manufacturing of the frame when the frame is formed, as the frame can be partially rotated in order to more easily move the barbed section of the frame and hence ‘jump’ the frame from the forming tool.

The one or more valves on the seal allow the passage of air in and out of the core of the seal. The open cell foam in the lumen ensures that, when the valve is fully open and no pressure is being exerted on the seal, the seal is expanded into a configuration with a relatively large volume of air therein. Provided that the valve remains open, the seal is deformable. When the valve is closed, the deformed state of the seal is set in place. In this way, the lumen is a closed cavity apart from when the one or more valves are open. Thus, the seal has the ability to match the contours of any number of faces.

Many valves types are suitable for use with the seal. Nevertheless, it is preferred that in use the valve is easily opened and closed by the user of the face mask. Thus, it is preferred that the valve is a push valve, as the user is then merely required to push the valve or valve stem to open the valve and then release the valve or valve stem to close the valve. Other preferred valve types include rotary valves.

The frame comprises one or more windows to accommodate filter material. In a preferred embodiment, the frame comprises four windows. In a further preferred embodiment, the frame comprises two windows. At least one removable filter is provided on the face mask. Preferably, two or more sequential filters are provided. Most preferably, three sequential filters are provided. The one or more windows in the frame ensure air can easily pass through the filter material without being blocked by the frame. Optionally, the filters are housed in one or more cassettes.

In a preferred embodiment, three filters are provided, wherein the first removable filter captures airborne material above 100 microns in diameter, the second removable filter captures airborne material above 10 microns in diameter, and the third removable filter captures airborne material above 2.5 microns in diameter. In an optional embodiment, a fine filter is included additionally or in place of one of the other filters; the fine filer captures airborne material above 0.3 microns in diameter. The sequential filters of the invention ensure that a wide range of pollutants are captured and thus prevented from being inhaled by the user of the mask.

Many filter materials are suitable for use in the face mask. Filter types usable in the invention include, for example, screen or depth filters. Suitable filters include, for example, HEPA (high efficiency particulate air), ULPA (ultra-low penetration air) and electrostatic filters. Nevertheless, it should be understood that the specific combination of filters chosen by the user of the face mask will be with the aim of producing a sufficient quantity of clean respirable air for the user’s needs in a variety of polluted environments.

The filters lie substantially flat across the frame of the face mask, and are thus easily replaceable by the user. The filters may optionally be placed in cassettes that are mounted in on the frame by way of a snap fitting and are held in place due to an interference fit. Optionally, a portion of filter material is located in the mask so that it is not involved in filtering air when the mask is in use. By comparing the colour of the section of unused filter with the colour of a portion of filter material involved in air filtration, the user is able to determine whether the filter is saturated with pollutants and needs to be changed.

The frame optionally further comprises one or more windows to accommodate one or more exhalation valves. Preferably, two exhalation valves are provided. These exhalation valves are one-way valves that allow air to be expelled from the mask when the user exhales, but close when the user inhales to ensure inhaled air passes through the filter material.

It is preferred that the one or more exhalation valves are high-flow exhalation valves. Preferably, the exhalation valves have a peak air flow rate capacity of approximately five litres per second under typical pressures exerted thereon by exhaled air from the user of the face mask. In a particular embodiment, this is achieved by providing the exhalation valve with a relatively wide outlet compared with the inlet from which exhaled air is received. This reduces resistance against the flow of air thus allowing more air to pass through the exhalation valve in a shorter space of time.

The exhalation valves preferably comprise a diaphragm. This diaphragm is preferably lightweight, reducing any resistance to exhaled air passing through the exhalation valve. Furthermore, it is preferred that the diaphragm’s resting position is closed, i.e. falls under gravity into the closed position. This helps to reduce the volume of unfiltered air passing through the exhalation valve when the user inhales. Nevertheless, it should be understood that inhalation of air through the exhalation valve further forces the diaphragm into its closed position.

The diaphragm preferably comprises a slender neck that is considerably narrower than the part of the diaphragm that touches the valve seat. This assists in reducing any resistance against exhaled air passing the diaphragm. This shaped neck and its position in the valve ensures that this part of the diaphragm is out of the path of the airflow when the diaphragm is in its open position.

The valve seat, on which the diaphragm rests when in its closed position, is preferably tapered. This further reduces the force required to open the exhalation valve, i.e. the cracking pressure of the valve.

The face mask typically comprises a supporting means for securing the face mask to the head of the user. In a preferred embodiment, a supporting strap is provided that lies over part of the frame and is secured, e.g. by Velcro®, at the rear of the head of the user.

The frame, filters, exhalation valves and supporting means are preferably secured together in a way that allows each feature to be easily removed and replaced by the user. It is preferred that one or more valve caps are used to fulfill this function. Preferably, the valve caps are removably attached to the exhalation valves and act to fix the face mask components in place. This fixing is optionally achieved by a flange on the valve cap. In another optional embodiment, the valve cap comprises a mesh-covered window to prevent insects and debris entering the mask through the exhalation valve.

As described above and below, it is preferred that only the seal is in contact with the face of the user. This means that a cavity exists between the filter material and the face of the user, said cavity being referred to as the Flow Zone. The Flow Zone minimizes the filter(s) from becoming damp with sweat and humid exhaled air, meaning that the filter(s) remain effective over longer time periods.

Additionally, the high-flow exhalation valves described above provide an effective means for expelling humid exhaled air from the Flow Zone. This further ensures that the filter(s) remain effective over longer time periods.

In an alternative embodiment of the invention, the face mask can be adapted to work with an external filter system. It is preferred that the frame of the face mask is connected to an external housing via one or more air hoses. Preferably, these air hoses are 22mm in diameter.

The external housing of the external filter system preferably comprises one or more filters as defined above and below. Air drawn through the external filter system is filtered before passing through the hoses and into the Flow Zone of the face mask. As filtering is achieved externally to the mask, the windows in the mask otherwise used to mount filter material are blocked off. Preferably, the air hoses connect to the frame of the face mask via one or more of these blocked off windows. More preferably, the air hoses are secured to one or both of the lower blocked off windows. Exhaled air passes through the exhalation valves on the face mask, as described above and below.

The external filtering system is particularly useful for long-term use and when the user performs aerobic exercise. This is because the filters have a larger surface area and volume, meaning they can absorb more pollutants before they become saturated. It is therefore preferred that the external housing can be worn as a backpack while the user is on the move. Optionally, a fan can be built into the external housing to assist the passage of air through the hoses and into the Flow Zone of the face mask. This helps the user of the face mask inhale with less effort. Nevertheless, when required, the user is still able to pull additional air through the external filter system in volumes greater than that supplied by the flow of the fan.

In another aspect of the invention, there is provided a method of fitting a face mask as defined above and below, comprising opening the seal valve, pressing the face mask against the face of the user, in order to deform the seal to match the face of the user, and closing the valve.

In a further aspect of the invention, there is provided a method of resetting a face mask as defined above and below, comprising opening the seal valve, allowing the open cell foam core to recover into its expanded configuration, and closing the valve.

Examples

The invention is now illustrated in a specific example, with reference to the accompanying drawings, in which:

Fig. 1 shows a cross-section of a transverse plane of a face mask on the face of a user;

Fig. 2 shows a front view of a face mask on the face of a user;

Fig. 3 shows a cross-section of a high-flow exhalation valve;

Fig. 4 shows a cross-section of a seal connected to a frame via an extruded U- channel, wherein the valve inlet/outlet channel traverses both seal and frame;

Fig. 5 shows an external filter housing in isometric and cross-section views;

Fig. 6 shows a cross-section of a transverse plane of a further face mask on the face of a user;

Fig. 7 shows a cross-section of a high-flow exhalation valve and a further view of its two-piece configuration; and

Fig. 8 shows a cross-section of a seal connected to a frame via an extruded U-channel, wherein the valve inlet/outlet channel traverses both seal and frame.

Example 1

Referring to the figures, a face mask is provided, wherein the mask is a half-mask and is in contact with the face of the user 1 via a deformable hollow toroidal seal 4 made of silicone. As is discussed below, the seal 4 also comprises air valves and a core of open cell foam; the seal 4 is thus deformable in such a way that allows its shape to be manipulated to match the contours of the face of the user 1. The seal 4 is also attached to and sealed to a frame 6 around its circumference, the frame 6 being composed of polyethylene to provide a strong, resilient and flexible supporting structure for the mask. The frame 6 is spaced away from the face of the user 1 by the seal 4, meaning that a cavity (known as the Flow Zone) 3 is formed between the face of the user 1 and the frame 6.

The frame 6 supports three sequential filters 8 with different pore sizes for capturing different types of airborne matter; these filters 8 are visible through four windows in the frame 6 (see Fig. 2) and thus air passes easily from the external environment into the Flow Zone 3 when the user inhales. The air is filtered as it passes through the sequential filters 8. Therefore, the user breathes in only filtered air from the Flow Zone 3.

The frame 6 also comprises two further windows that each support a high-flow exhalation valve 10 (see Fig. 3). These valves are formed of a housing 20 that extends through the mask, meaning that corresponding windows must be cut out of the frame 6, the filters 8 and the supporting strap 14. The various components of the mask are then secured in place via the valve cap 12 which has a flange that comes into contact with the supporting strap 14. The valve cap 12 is secured to the housing 20 via a corresponding screw-threaded connection 15 on the housing 20 and the valve cap 12. The effect of the valve cap 12 being screwed onto the housing 20 is that the flange 17 of the valve cap 12 applies a force to the sandwich of materials of the mask, comprising the strap 14 and filters 8, that is borne by a flange surrounding the base of the filter housing, such that the materials of the mask are pressed between and secured by the flanges 17 of the valve cap 12 and the housing 20. The valve cap 12 also comprises a mesh covered window 13 to prevent the passage of insects and the like.

The high-flow exhalation valve 10 further comprises a lightweight 0.8mm thick silicone diaphragm 16 that falls under gravity into its closed position wherein it is in contact with a valve seat 18 situated on the valve housing 20. The valve seat 18 is tapered to further reduce the cracking pressure required to move the diaphragm 16 into its open position (as illustrated in Fig. 3). The diaphragm 16 is suspended by a shaped neck.

The valve is open when the user exhales and closed when the user inhales. Thus, inhaled air is forced to pass through the filter material 8. The air inlet of the exhalation valve 10 is smaller in diameter than the air outlet; this results in reduced resistance as air is exhaled through the valve 10. The low cracking pressure of the diaphragm 16, coupled with the low resistance arrangement of the exhalation valve 10, results in a high flow capacity of approximately 5 litres per second.

The high flow capacity of the exhalation valves 10 ensures that the filters 8 do not become damp with humid exhaled air, as the air is efficiently expelled. The Flow Zone cavity 3 also helps to ensure that the filters remain dry and effective, since in use the face of the user is not in contact with the filters 8.

The frame 6 also supports a supporting strap 14. The filters 8 are therefore sandwiched between the frame 6 and the supporting strap 14. As is the case with the frame 6, the supporting strap 14 comprises four windows that align with the four filter windows on the frame 6, providing a direct passageway for air to pass from the external environment into the Flow Zone 3 via the filters 8. The supporting strap 14 functions to secure the mask to the head of the user. Velcro® is provided on the free ends of the supporting strap 14 and the free ends are secured to each other toward the rear of the head of the user. This ensures the mask remains on the face of the user when in use.

The toroidal seal 4 of the face mask is prepared using a silicone extrusion method. As illustrated in Fig. 4, this method produces a tubular silicone toroid of 1mm thickness 22, comprising a lumen 24 filled with open cell foam. The seal 4 is then fitted with a push button valve 26 for controlling the volume of air held in the lumen 24 at any given time. The open cell foam is resilient and is naturally biased to an expanded state whereby it occupies the maximum volume possible. Thus, the open cell foam in the lumen 24 expands to ensure that the largest volume of air possible is maintained in the lumen 24 when the valve 26 is in its open position. When fitting the face mask, the seal 4 is pressed against the face of the user, causing the seal 4 to deform and mould to the contours of the face of the user, while air is expelled from the seal 4 through the valve 26.

In order to achieve the bespoke shape of the seal 4 required for a given user’s face, the user opens the valve 26 by pressing on the valve stem 30. This moves a spring 32 that is otherwise biased to keep the valve 26 in its closed position. The user then presses the face mask against his/her face causing the seal 4 to deform and air to be expelled through the valve 26. Once the seal 4 is properly moulded to the face of the user, the user can release the valve stem 30 to close the valve 26, causing the seal 4 to be set in its deformed state.

In order to reset the seal 4 from its deformed state, the user must remove pressure from the seal 4 (e.g. by removing the mask or changing its position of their face) and then open the valve 26 by pressing the valve stem 30 to allow the foam to expand. The user can then release the valve stem 30 to close the valve 26.

The seal 4 is attached to the frame 6 by way of a U-channel 34 in the silicone extrusion. The U-channel 34 envelopes the outer rim of the frame 6 ensuring that the seal 4 is securely attached to the frame 6 along the entire circumference on its toroid. Additionally, two barbs (not shown) are provided on the frame 6; one on the front of the frame 6 near the outer rim and the other on the rear of the frame near the outer rim. These barbs help secure the frame 6 within the U-channel 34 of the silicone seal extrusion by providing an interference fit of the frame 6 to the seal 4.

In use, the face mask provides a means of protecting the user from air pollution, wherein a number of air pollutants are captured by the filters 8 and are thus prevented from being inhaled by the user. The user is able to assess whether the filter(s) need changing by removing the mask and observing a portion of the filters on the rear side of the mask that are not involved in filtering air when the mask is in use. By comparing the unused filter colour with the colour of the portion of filter(s) involved in air filtration, the user is able to determine whether the filter(s) are saturated with pollutants and need to be changed.

The face mask can also be adapted for more efficient use during aerobic exercise, e.g. when cycling.

As illustrated in Fig. 5, an external filter housing 36 encloses a number of filters 38, 40 with varying pore sizes for capturing different types of airborne matter. When the user inhales, air is drawn into the filter housing 36, through the sequential filters, 38, 40 and then through two 22mm hoses 42. The hoses 42 are connected to the face mask. As the air filtration is achieved externally to the face mask, the four filter windows of the face mask described above are blocked off with polyethylene sheets that clip into place and provide a substantially airtight seal. The lower two of these polyethylene sheets have input connections (not shown) in the form of screw fit holes. The hoses 42 from the external filter housing 36 screw into these input connections to allow filtered air to pass directly into the Flow Zone cavity 3 and be inhaled by the user. Exhaled air is released via the high-flow exhalation valves 10 as described above. Straps (not shown) are provided on the external filter housing 36 to allow the user to wear the housing 36 like a backpack. This external filter system is of particular use over extended periods of time, e.g. by cycle couriers and patrolling policeman, due to the increased capacity of the external filters 38 relative to the mask filters 8.

In a particular variation of the above Example, a face mask is provided as defined above with the exception that no filter windows are provided in the frame. Instead, two hose connectors form part of the frame which receive the 22mm air hoses from the external filter system.

Example 2

Referring to the figures, a face mask is provided, wherein the mask is a half-mask and is in contact with the face of the user 1a via a deformable hollow seal 4a made of silicone. As is discussed below, the seal 4a also comprises an air valve and a core of open cell foam; the seal 4a is thus deformable in such a way that allows its shape to be manipulated to match the contours of the face of the user 1a. The seal 4a is also attached to a frame 6a around its circumference, the frame 6a being composed of thermoplastic polyurethane to provide a strong, resilient and flexible supporting structure for the mask. The frame 6a is spaced away from the face of the user 1a by the seal 4a, meaning that a cavity (known as the Flow Zone) 3a is formed between the face of the user 1 a and the frame 6a.

The frame 6a supports four sequential filters 8a with different pore sizes for capturing different types of airborne matter; these filters 8a are held in place by two filter cassettes (44) that clip into, and are visible through, two windows in the frame 6a (see Fig. 6), and thus air passes easily from the external environment into the Flow Zone 3a when the user inhales. The air is filtered as it passes through the sequential filters 8a in the cassettes. Therefore, the user breathes in only filtered air from the Flow Zone 3a.

The frame 6a also comprises two further windows that each support a high-flow exhalation valve 10a (see Fig. 7). These valves are formed of a housing 20a that extends through the mask, meaning that corresponding windows are cut out of the frame 6a. The valve housing (20a) is formed of two pieces joined by a living hinge 46. This makes it easy to remove of the valves 10a and replace the diaphragms 16a. The valves 10a also comprise a mesh covered window 13a to prevent the passage of insects and the like.

The high-flow exhalation valve 10a further comprises a lightweight 0.8mm thick silicone diaphragm 16a that falls under gravity into its closed position wherein it is in contact with a valve seat 18a situated on the valve housing 20a. The valve seat 18a is tapered to further reduce the cracking pressure required to move the diaphragm 16a from its closed position into its open position (both positions being illustrated in Fig. 7). The diaphragm 16a is suspended by a shaped neck 48. The valve 10a is open when the user exhales and closed when the user inhales. Thus, inhaled air is forced to pass through the filter material 8a. The air inlet of the exhalation valve 10a is smaller in diameter than the air outlet; this results in reduced resistance as air is exhaled through the valve 10a. The low cracking pressure of the diaphragm 16a, coupled with the low resistance arrangement of the exhalation valve 10a, results in a high flow capacity of approximately 5 litres per second.

The high flow capacity of the exhalation valves 10a ensures that the filters 8a do not become damp with humid exhaled air, as the air is efficiently expelled. The Flow Zone cavity 3a also helps to ensure that the filters remain dry and effective, since in use the face of the user is not in contact with the filters 8a.

The frame 6a also supports a supporting strap 14a. The supporting strap 14a functions to secure the mask to the head of the user. Velcro® is provided on the free ends of the supporting strap 14a and the free ends are secured to each other toward the rear of the head of the user. This ensures the mask remains on the face of the user when in use.

The seal 4a of the face mask is prepared using a silicone extrusion method. As illustrated in Fig. 8, this method produces a tubular silicone toroid with a square cross-section of 1mm thickness 22a, comprising a lumen 24a filled with open cell low density polyether foam. The seal 4a is then fitted with a push button valve 26a for controlling the volume of air held in the lumen 24a at any given time. The open cell foam is resilient and is naturally biased to an expanded state whereby it occupies the maximum volume possible. Thus, the open cell foam in the lumen 24a expands to ensure that the largest volume of air possible is maintained in the lumen 24a when the valve 26a is in its open position. When fitting the face mask, the seal 4a is pressed against the face of the user, causing the seal 4a to deform and mould to the contours of the face of the user, while air is expelled from the seal 4a through the valve 26a.

In order to achieve the bespoke shape of the seal 4a required for a given user’s face, the user opens the valve 26a by pressing on the valve stem 30a. This moves a spring 32a that is otherwise biased to keep the valve 26a in its closed position. The user then presses the face mask against his/her face causing the seal 4a to deform and air to be expelled through the valve 26a. Once the seal 4a is properly moulded to the face of the user, the user can release the valve stem 30a to close the valve 26a, causing the seal 4a to be set in its deformed state.

In order to reset the seal 4a from its deformed state, the user must remove pressure from the seal 4a (e.g. by removing the mask or changing its position of their face) and then open the valve 26a by pressing the valve stem 30a to allow the foam to expand. The user can then release the valve stem 30a to close the valve 26a.

The seal 4a is attached to the frame 6a by way of a U-channel 34a in the silicone extrusion. The U-channel 34a envelopes the outer rim of the frame 6a ensuring that the seal 4a is securely attached to the frame 6a along the entire circumference on its toroid. Additionally, two barbs (not shown) are provided on the frame 6a; one on the front of the frame 6a near the outer rim and the other on the rear of the frame near the outer rim. These barbs help secure the frame 6a within the U-channel 34a of the silicone seal extrusion by providing an interference fit of the frame 6a to the seal 4a.

In use, the face mask provides a means of protecting the user from air pollution, wherein a number of air pollutants are captured by the filters 8a and are thus prevented from being inhaled by the user. The user is able to assess whether the filter(s) need changing by opening the filter cassette 44 and observing a portion of the filters under the support rib that are not involved in filtering air when the mask is in use. By comparing the unused filter colour with the colour of the portion of filter(s) involved in air filtration, the user is able to determine whether the filter(s) are saturated with pollutants and need to be changed.

As illustrated in Fig. 5, an external filter housing 36 encloses a number of filters 38, 40 with varying pore sizes for capturing different types of airborne matter. When the user inhales, air is drawn into the filter housing 36, through the sequential filters, 38, 40 and then through two 22mm hoses 42. The hoses 42 are connected to the face mask. As the air filtration is achieved externally to the face mask, the two windows in the frame 6a that contain the filter cassettes 44 are blocked off with polyethylene sheets having input connections (not shown) in the form of screw fit holes. The hoses 42 from the external filter housing 36 screw into these input connections to allow filtered air to pass directly into the Flow Zone cavity 3a and be inhaled by the user. Exhaled air is released via the high-flow exhalation valves 10a as described above. Straps (not shown) are provided on the external filter housing 36 to allow the user to wear the housing 36 like a backpack. This external filter system is of particular use over extended periods of time, e.g. by cycle couriers and patrolling policeman, due to the increased capacity of the external filters 38 relative to the mask filters 8a.

Claims

1. A face mask comprising a face seal, wherein the seal comprises an envelope defining a lumen containing an open cell foam core, and wherein the seal comprises one or more valves that control the passage of air to and from the core of the seal.

2. A face mask according to claim 1, wherein face mask is a half mask.

3. A face mask according to any preceding claim, wherein the face mask is for a cyclist.

4. A face mask according to any preceding claim, wherein the envelope is tubular.

5. A face mask according to any preceding claim, wherein the envelope is toroidal.

6. A face mask according to any preceding claim, wherein the envelope comprises a silicone material.

7. A face mask according to any preceding claim, wherein the envelope is made of a silicone material.

8. A face mask according to any preceding claim, wherein in use the seal passes under the chin of the face of the user.

9. A face mask according to any preceding claim, wherein the one or more seal valves comprise a valve stem.

10. A face mask according to any preceding claim, wherein the one or more seal valves are rotary valves.

11. A face mask according to any preceding claim, wherein the seal is mounted on a frame, and wherein only the seal contacts the face of the user.

12. A face mask according to claim 11, wherein the frame comprises a polyethylene material.

13. A face mask according to either claim 11 or 12, wherein the frame is made of a polyethylene material.

14. A face mask according to either claim 11 or 12, wherein the frame is made of a thermoplastic polyurethane.

15. A face mask according to any of claims 11-14, wherein the frame accommodates one or more removable air filters.

16. A face mask according to claim 15, wherein the one or more removable air filters comprise a filter that captures airborne material above 100 microns in diameter.

17. A face mask according to either claim 15 or 16, wherein the one or more removable air filters comprise a filter that captures airborne material above 10 microns in diameter.

18. A face mask according to any of claims 15-17, wherein the one or more removable air filters comprise a filter that captures airborne material above 2.5 microns in diameter.

19. A face mask according to any of claims 15-18, wherein the one or more removable air filters comprise a fine filter that captures airborne material above 0.3 microns in diameter.

20. A face mask according to any of claims 11-19, wherein the frame accommodates one or more exhalation valves that allow the passage of air out of the mask.

21. A face mask according to claim 20, wherein the one or more exhalation valves comprise a valve body with an air inlet and an air outlet, the air inlet comprising a diaphragm that opens to allow the passage of exhaled air and closes to block the passage of inhaled air, and wherein the diameter of the air inlet is sufficiently smaller than the diameter of the air outlet.

22. A face mask according to either claim 20 or 21, wherein the one or more exhalation valves provide a peak air flow rate capacity of approximately five litres per second.

23. A face mask according to either claim 21 or 22, wherein the one or more exhalation valves comprise a valve cap mounted on the air outlet of the valve body, and wherein the valve cap acts to secure the one or more removable air filters to the frame.

24. A face mask according any of claims 20-23, wherein the one or more exhalation valves comprise a mesh-covered window in the air outlet.

25. A face mask according to any of claims 15-24, wherein the face mask comprises a portion of filter that is not involved in air filtration, and wherein comparison of the colour of this portion with the colour of a portion of filter material involved in air filtration can be used as a filter change indictor.

26. A face mask according to claim 25, wherein the portion of filter that is not involved in air filtration is visible through a transparent window in the frame.

27. A face mask according to any of claims 11-14, wherein the frame is connected to an external housing via one or more air hoses.

28. A face mask according to claim 27, wherein the one or more air hoses are 22mm in diameter.

29. A face mask according to either claim 27 or 28, wherein the housing is a backpack.

30. A face mask according to any of claims 27-29, wherein the housing accommodates one or more removable air filters in fluid connection with the face mask via the one or more air hoses.

31. A face mask according to claim 30, wherein the one or more removable air filters comprise a filter that captures airborne material above 100 microns in diameter.

32. A face mask according to either claim 30 or 31, wherein the one or more removable air filters comprise a filter that captures airborne material above 10 microns in diameter.

33. A face mask according to any of claims 30-32, wherein the one or more removable air filters comprise a filter that captures airborne material above 2.5 microns in diameter.

34. A face mask according to any of claims 30-33, wherein the one or more removable air filters comprise a fine filter that captures airborne material above 0.3 microns in diameter.

35. A method of fitting a face mask as defined in any preceding claim, comprising opening a seal valve, pressing the face mask against the face of a user, in order to deform the seal to match the face of the user, and closing the valve.

36. A method of resetting a face mask as defined in any of claims 1-34, comprising opening a seal valve, allowing the open cell foam core to recover into its expanded configuration, and closing the valve.

37. A method according to either of claims 35 or 36, wherein a supporting means is mounted on the face mask and is used to secure the face mask to the head of the user.