EP0094757B1 - Respirator - Google Patents

Abstract

The present invention relates to improvements in power assisted positive pressure respirators for use in contaminated atmospheres. The respirator comprises a facepiece 1 having an inlet 3 connected to a pump unit 5 for supplying air to the facepiece which has been filtered by filter means 11 connected to the pump unit inlet. The facepiece is also provided with an outlet provided witha one-way valve 2 which is biased to its closed position and is openable when a predetermined pressure above atmospheric pressure is established within the facepiece. To maximise use of the filter means 11, a one-way inlet valve 13 is provided intermediate the pump unit 5 and the facepiece 1, conveniently at the inlet to the facepiece, which is closed during exhalation by the wearer to thereby cause the pump to be placed in a condition in which, although it continues to operate, no or substantially no air is moved thereby, so that during this period, no or substantially no air is drawn through the filter means 11.

Description

• The present invention relates to improvements in respirators for use in contaminated atmospheres.
• Power assisted respirators for use in dusty atmospheres are known. Such known respirators normally comprise a face piece adapted to cover the mouth and nose of the wearer and having an inlet and an outlet. A first one-way valve means is provided in the outlet which is adapted to open during exhalation by the wearer to permit air to flow out of the face piece when a predetermined pressure differential is established thereacross. The face piece inlet is connected to pump means, which may comprise a fan, for supplying air to the face piece, the air having been filtered by filter means provided in the path of air to the face piece. A second one-way valve means is generally provided between the pump means and the face piece, normally in the face piece inlet, which second valve means closes in the event that the pressure downstream thereof exceeds that upstream thereof.
• In use of such a respirator, the first valve.means is operative to maintain, under normal conditions, a slight positive pressure within the face piece, for example in accordance with British Standard 4558, a pressure of 125 pascals at 85 litres per minute. The pump means is arranged to supply air to the face piece at a constant rate, for example about 120 litres per minute, which is greatly in excess of the average inspiratory requirements of the wearer. U.K. and European Standards require a minimum of 120 litres per minute for four hours in order to sustain a degree of positive pressure within the face piece even at typical peak inhalation rates. In the U.S.A., the relevant Standard requires a minimum flow of 113 litres per minute for tight fitting full face masks and 170 litres per minute for helmets and hoods.
• Because excess air is constantly supplied to the face piece, the inlet and outlet valves are permanently open, the inlet valve (where provided) only closing in the event of failure of the pump to prevent reverse flow of air through the pump and filter.
• Because excess filtered air is constantly supplied to the face piece, the filters are used up much faster than they need to be and indeed only about one third of the capacity of a filter is effectively used for filtering air which is breathed.
• Dust and other particulate material filters have a relatively long life and such inefficient use can be tolerated. However gas and vapour filters, usually in the form of canisters containing granulated activated charcoal, silica gel, molecular sieve material or similar materials, have a much shorter life such that their use in power assisted respirators has not to date been considered practical. As a consequence most gas and vapour filtering respirators are unpowered, the wearer drawing air into the face piece through the filter using the power of his lungs.
• It is also known from U.K. Patent Specification No. 2058577 to provide a respirator comprising a face piece with an inlet and an outlet and first valve means in the outlet as described above. Filtered air is supplied to the inlet of the face piece by pump means comprising a fan. A valve is provided in the path of air flowing from the pump means to the face piece but, in this case, the valve is controlled by a pressure sensor detecting the pressure within the face piece which causes the valve to be closed when the pressure in the face piece exceeds a predetermined level.
• European Patent Specification No. 0066407 also discloses a respirator comprising a face piece having an inlet and an outlet, which are provided with valve means as described above. Filtered air is supplied to the inlet of the face piece by a pump. However, in this case, an inflatable sac is interposed between the outlet of the pump means and the inlet of the face piece. The degree of inflation of the sac is monitored and used to control energisation of the pump so as to reduce the supply of air to the face piece during exhalation by the wearer.
• French Patent No. 1037477 also discloses a respirator comprising a face piece with an inlet and outlet, both provided with valves as described above. The supply of air to the face piece is however provided not by a pump but from a compressed air supply which simultaneously supplies air to a paint spray gun. The valve in the face piece inlet appears to be provided, as described above, to prevent reverse flow of air in the event of failure of the compressed air supply.
• Finally French Patent Specification No. 785223 discloses a system for providing air to both the face piece and the clothing of a wearer. The face piece is provided with an inlet and an outlet for air, flow of air being controlled by first and second valve means which are mechanically connected together to operate together. Filtered air is supplied to the face piece and the clothing by a pump via a sac which is said to be provided to compensate for the frequency of respiration. The pump apparently operates at a constant rate and is provided with a valved return path for return of excess air from the outlet of the pump to the inlet of the pump.
• According to the present invention there is provided a power assisted respirator comprising a face piece adapted to cover the mouth and nose of the wearer and having an inlet and an outlet, first one-way valve means in the outlet which is adapted to open to permit air to flow out of the face piece when a predetermined pressure differential is established thereacross, pump means comprising a fan connected to the inlet for supplying air to the face piece, filter means for filtering air supplied by the pump means to the face piece, and a second one-way valve means provided in the path of air flowing from the pump means to the face piece and which is adapted to close when the pressure downstream thereof exceeds that upstream thereof, characterised in that said predetermined pressure differential across the first one-way valve means is selected relative to the operating parameters of the pump means so that, during exhalation by the wearer, the pressure downstream of the second one-way valve means exceeds the pressure upstream thereof so that the second one-way valve means is closed and the predetermined pressure differential is established across the first one-way valve means so that the first one-way valve means opens, closing of the second one-way valve means substantially stopping flow of air supplied by the pump means so that the fan of the pump means is placed in a condition such that, although the pump means continues to operate, little or substantially no air is driven thereby, causing little or substantially no air to be drawn through the filter means.
• In a preferred embodiment, the outlet valve means is arranged to open when the pressure within the face piece exceeds about 600 pascals, e.g. as set out in British Standard 4667Part 2 relating to respirators using bottled gas (rather than the much lower operating pressures normally required for power assisted positive pressure respirators). Additionally in this preferred embodiment the pump is arranged to cease or substantially cease pumping effectively when the pressure downstream of the pump and upstream of the inlet valve means is about 600 pascals.
• The pump may optionally be arranged to provide a maximum of about 200 litres per minute and a minimum of 0 litres per minute, depending on demand and the resistance to flow presented by the filter means.
• It has been found that in use of such a system, the proportion of the filter means which is effectively used for filtering air which is then breathed can be increased from one third to at least 80%. The face piece may be a partial or full face mask, or may be in the form of a helmet or hood if adequately sealed to the head, which may be connected by a flexible hose to a unit including the pump and filter means.
• Advantageously the filter means comprise one or more cartridges or canisters of filter material which are removably mounted on the inlet to the pump. The pump preferably comprises a fan driven by a motor which is battery operated so that the assembly is portable.
• An embodiment according to the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
• Figure 1 is a perspective view of an embodiment of respirator in use;
• Figure 2 is a diagrammatic view of the respirator of Figure 1;
• Figures 3 and 4 are perspective views with parts broken away showing the inlet and outlet to the facepiece and the pump unit respectively; and
• Figure 5 is a schematic drawing showing operation of components of the respirator in relation to the respiratory cycle of the wearer.
• The respirator shown in Figures 1 and 2 comprises afacepiece 1 which, as shown, is a full face mask covering the eyes, nose and mouth of the wearer, and which is peripherally sealed to the head of the wearer. Thefacepiece 1 is provided with an outlet provided with a one-way outlet orexhalation valve 2 through which air leaves the mask, and an inlet 3 which is connected by a flexible hose 4 to aunit 5. Theunit 5 is, as shown, supported by a harness on the back of the wearer but may alternatively be mounted by a similar harness on the front of the wearer. Theunit 5 comprises a housing in which a pump unit comprising a fan, for example a centrifugal fan, and a battery operated motor are housed. The housing has anoutlet 8 defining the outlet of the fan and to which the hose 4 is connected, and one or a plurality of, e.g. as shown three,inlets 10 connected to the fan inlet. Each of thehousing inlets 10 is threaded to receive a filter cartridge orcanister 11, which may comprise a particulate filter material and/or a gas or vapour filter material. One such cartridge orcanister 11 may be mounted on the or each or some of theinlets 10 and any unused inlets may be closed by aplug 12.
• It will be appreciated that by increasing the number of cartridges orcanisters 11 provided the rate of flow of air through each cartridge or canister can be reduced, thereby increasing the efficiency of filtering and reducing the resistance to flow of air through the respirator. The motor is connected, as shown, by acable 27 to a separate unit comprising abattery 6 and optionally an off/ on switch 7 controlling power supplied to the motor. Alternatively the battery and, where provided, the switch may be mounted within theunit 5.
• As shown in Figure 2, theoutlet valve 2 is biased to its closed position, for example by a helical spring 14, and so that the valve will only open to permit air to flow out of the facepiece when the air within the facepiece is at a preset pressure above atmospheric pressure, for example so that the valve will open when the pressure within the facepiece is about 600 pascals.
• A one-way inlet valve 13 is mounted in the inlet 3 of the facepiece and is openable to permit air to flow from the pump to the facepiece. Thevalve 13 may, for example, be a flap valve and is unbiased so that the valve will close as soon as the pressure downstream thereof within the facepiece exceeds that upstream thereof within the hose 4.
• The rate and throughput of thepump unit 5 are selected so that, during exhalation by the wearer, the pressure within the facepiece will build up to a point where it exceeds that in hose 4. At this point, thevalve 13 will close. Closure ofvalve 13 causes an immediate build-up of pressure within hose 4 and this build-up of pressure is arranged so that thepump unit 5 will be placed in a condition in which, although it continues to operate, it ceases or substantially ceases to drive air into the system and therefore to draw air through the filters. Additionally, during exhalation,valve 2 will open to permit exhaled air to flow out of the facepiece and this may take place at about the same time as closure ofvalve 13.
• Towards the end of exhalation, the pressure within the facepiece will fall causingvalve 2 to close and causingvalve 13 to open, when the pressure falls below that in hose 4. At this point the pump will start to operate effectively again to supply to the facepiece the air required for inhalation.
• Thus by suitable selection of the operating pressure of theoutlet valve 2 in relation to exhalation pressure and the pump characteristics, the effective operation of the pump can be made to vary with the breathing cycle of the wearer. This then reduces the amount of air which is drawn into the facepiece through the filters and which is not then breathed so that a point can be reached where at least 80% of the life of the filters is used for-filtering air which is then inhaled.
• Figure 5 shows schematically the presently preferred operation of thepump unit 5 and inlet andoutlet valves 12 and 2 in relation to the respiratory cycle of the wearer. As shownvalves 13 and 2 open and close at about the same points in the respiratory cycle, although these points may be relatively displaced.
• As shown, the facepiece includes aninner mask 15 which closely surrounds the nose and mouth of the wearer and is provided with one or more one-way inlet valves 16. These valves may for example be flap valves which are unbiased and serve to prevent flow of exhaled air into the total volume of the facepiece so as to limit the amount of exhaled air which may be re-breathed. However, if the inner mask is sufficiently well sealed to the wearer's face to prevent leakage around the edges,valve 13 may be omitted, the or eachvalve 16 performing its function.
• Figures 3 and 4 show preferred embodiments of thevalves 2,13 and thepump unit 5. As shown in Figure 3, thevalve 13 is a flap valve comprising aflexible disc 20 which is seated over aseat 21 surrounding an opening in the passage of inlet 3 to the facepiece, and lifts fromseat 21 to allow air to flow into the facepiece when the pressure in the facepiece is lower than that in the hose 4. Theoutlet valve 2 comprises a flap valve comprising arigid disc 22 which seats against anoutlet seat 23 surrounding an outlet opening and is biased to its closed position by helical spring 14 which bears against thedisc 22 and a part of the housing around the outlet. Air exits from the valve throughopenings 24 communicating with the opening inseat 23.
• Thepump unit 5 shown in Figure 4 comprises amotor 26 connected bycable 27 to the battery and to theshaft 28 of acentrifugal fan 29 whose outlet is connected tooutlet 8 provided by the unit housing. The fan inlet is connected, as shown, to threeinlets 10 provided by the housing, each of which is threaded to receive a filter canister orcartridge 11. One, two or three cartridges or canisters may be used and any unused inlets may be closed by aplug 12.
• In a preferred embodiment of the above described respirator, theoutlet valve 2 is arranged, as previously mentioned, to open when the pressure in the facepiece is about 600 pascals. Theinlet valve 13 closes as soon as the pressure within the facepiece exceeds that within the hose 4, which is generally when the pressure within the facepiece is about 600 pascals, and thefan 29 is arranged to provide up to about 200 litres per minute depending on demand. At the point at whichvalve 13 closes, the pressure in the hose 4 will be about 600 pascals but just below the pressure in the facepiece, and at these pressures, the fan will then be placed in a condition in which, although it continues to rotate, no or substantially no air flows therethrough and specifically no air is drawn thereby into the unit housing and through the filter cartridges or canisters.
• It will be appreciated that the above pressures and flow rates are exemplary only and that they may be higher or lower depending on the particular requirements for the facepiece.
• It will also be appreciated that, while the invention has been described above in terms of a respirator comprising a full face mask, it is equally applicable to partial face masks and to facepieces in the form of hood or helmets which are adequately sealed to the head of the wearer. Additionally, while in the above described respirator, thevalve 13 is placed in the inlet to the facepiece, this valve may be provided at any convenient point intermediate the fan and the facepiece. It will further be appreciated that, although the above described respirator has particular application to gas and vapour filtering, it is of course equally applicable to dust or particulate material filtering because an increase in the efficiency of use of any such filter is beneficial.

Claims (7)

1. A power assisted respirator comprising a face piece (1) adapted to cover the mouth and nose of the wearer and having an inlet (3) and an outlet, first one-way valve means (2) in the outlet which is adapted to open to permit air to flow out of the face piece when a predetermined pressure differential is established thereacross, pump means (5) comprising a fan (29) connected to the inlet (3) for supplying air to the face piece, filter means (11) for filtering air supplied by the pump means to the face piece, and a second one-way valve means (13) provided in the path of air flowing from the pump means to the face piece and which is adapted to close when the pressure downstream thereof exceeds that upstream thereof, characterised in that said predetermined pressure differential across the first one-way valve means (2) is selected relative to the operating parameters of the pump means (5) so that, during exhalation by the wearer, the pressure downstream of the second one-way valve means (13) exceeds the pressure upstream thereof so that the second one-way valve means (13) is closed and the predetermined pressure differential is established across the first one-way valve means (2) so that the first one-way valve means (2) opens, closing of the second one-way valve means (13) substantially stopping flow of air supplied by the pump means (5) so that the fan (29) of the pump means (5) is placed in a condition such that, although the pump means (5) continues to operate, little or substantially no air is driven thereby, causing little or substantially no air to be drawn through the filter means (11).

2. A respirator as claimed in claim 1, characterised in that the second one-way valve means (13) is mounted in the inlet (3) of the face piece.

3. A respirator as claimed in claim 1, characterised in that the second one-way valve means (13) is mounted intermediate the outlet of the pump means (5) and the inlet (3) of the face piece.

4. A respirator as claimed in any one of the preceding claims, characterised in that the second one-way valve means (13) comprises a flap valve which is unbiased so as to close as soon as the pressure downstream thereof exceeds that upstream thereof.

5. A respirator as claimed in any one of the preceding claims, characterised in that the first one-way valve means (2) is a flap valve which is biased to its closed position.

6. A respirator as claimed in any one of the preceding claims, characterised in that the pump means (5) is connected to the face piece by a flexible hose (4) and is adapted to be carried by the wearer.

7. A respirator as claimed in any one of the preceding claims, wherein the face piece (1) covers the eyes as well as the mouth and nose of the wearer.

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