Patent Description:
Negative pressure respirators are well known in the art. With respirators of this type, filtered air is drawn into the enclosed space between the inside of the respirator and a wearer's face through a filter system by the wearer's breathing action. When the wearer draws a breath, negative pressure is created in the respirator and air is drawn in through the filter system. When the wearer exhales a breath, spent air leaves the respirator through an exhalation valve and/or back through the filter system.

Although negative pressure respirators are available in many different configurations, and offer many different benefits, they all have one major drawback, that of the uncomfortable build-up of heat and moisture that can sometimes occur inside the respirator. The heat and moisture build-up is caused by the trapping of the wearer's exhaled breath in the cavity created between the respirator and the wearer's face. As the wearer works harder, and/or wears the respirator for extended periods of time, heat and moisture build-up may increase.

Many different solutions have been proposed in the prior art to eliminate, or at least minimise, the problem of heat and moisture build-up inside negative pressure respirators. For example, the addition of exhalation valves, and optimising the operation of these exhalation valves. The design and optimisation of low pressure drop filters and media has also been proposed to alleviate this problem and/or by controlling the filter surface area and filter material pressure drop. Another solution in the prior art is to include pads to absorb the moisture.

A further solution is offered in <CIT> in which a respirator has a blower in fluid connection with the exhalation valve, the blower being operable to draw the wearer's exhaled breath through the valve. This solution presents advantages but also has drawbacks in that the blower applies a constant negative pressure to the exhale valve. This can lead to increased inhalation effort and decreased filter life as a result of the increased flow of air passing through the filter.

It is therefore an object of the invention to deliver the improved cooling effects of the prior art device whilst not unduly reducing filter life or increasing inhalation effort.

Accordingly, a first aspect of the present invention provides a system according to claim <NUM>.

Operating the blower substantially only during the exhale portion of the wearer's respiratory cycle (or a substantial part thereof) delivers significant advantages to the present invention as follows.

Firstly, the volume of air drawn through the filter is reduced. In the prior art device the volume of air drawn through the filter media during inhalation was increased under the action of the blower since both the lungs and the blower were drawing air in through the filter. This is not the case in the present invention. This reduces the load on the filter media and thereby increases the life of the filter under a given load.

Secondly, the power consumed by the blower is significantly reduced by only operating during the exhale breath, or substantially only during the exhale breath. This in turn reduces the size of the battery for a given operating life which reduces the weight of the device. Weight reduction brings improvements in the perceived comfort of the respirator.

Thirdly, inhalation effort of the wearer is reduced since the wearer no longer has to overcome the pressure drop generated by the blower before the inhalation breath starts to deliver air to the lung cavity. This in turn further assists in reducing the temperature and humidity in the respirator through reduced respiratory load on the wearer.

Preferably, the pressure is sensed in a filtered air volume of the personal protection respiratory device.

Alternatively, the pressure is sensed downstream of the exhalation valve.

Alternatively, the pressure is sensed upstream of the inhalation valve.

Preferably, the controller starts the blower when the pressure sensed by the pressure sensor reaches a first predetermined pressure.

Preferably, the controller stops the blower when the pressure sensed by the pressure sensor falls below a second predetermined pressure.

Preferably, the first predetermined pressure and the second predetermined pressure are a common predetermined pressure.

Preferably, the common predetermined pressure is substantially ambient pressure so that the controller starts the blower substantially at the initiation of the wearer's exhale breath and stops the blower substantially at the end of the wearer's exhale breath.

Alternatively, the common predetermined pressure is higher than ambient pressure so that the controller starts the blower momentarily after the initiation of the wearer's exhale breath and stops the blower momentarily before the end of the wearer's exhale breath.

Alternatively, the common predetermined pressure is lower than ambient pressure so that the controller starts the blower momentarily before the initiation of the wearer's exhale breath and stops the blower momentarily after the end of the wearer's exhale breath.

Alternatively, the first predetermined pressure is greater than the second predetermined pressure so that the controller starts the blower momentarily after the initiation of the wearer's exhale breath and stops the blower momentarily after the end of the wearer's exhale breath.

Alternatively, the second predetermined pressure is greater than the first predetermined pressure so that the controller starts the blower momentarily before the initiation of the wearer's exhale breath and stops the blower momentarily before the end of the wearer's exhale breath.

The blower further comprises an inlet, a motor, a fan, and an outlet.

Preferably, the exhaust apparatus further comprises an attachment means for releasably connecting the blower to the at least one exhalation valve.

Preferably, the exhaust apparatus is generally L-shaped comprising an upwardly extending portion and rearwardly extending portion.

Preferably, the rearwardly extending portion houses a battery for powering the blower.

Preferably, the personal protection respiratory device is selected from a group consisting of disposable, reusable, half mask, full face, particulate, gas and vapour and tight-fitting hood respirators.

A second aspect of the present invention provides a method of controlling the exhaust apparatus of any preceding claim, including the steps of:.

The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which:.

<FIG> is an exploded view of an exhaust apparatus according to the present invention indicated generally at <NUM>. The apparatus <NUM> is able to connect or otherwise engage to or with a personal protection respiratory device <NUM>, either in a permanent fashion or in a releasable manner as will be described in further detail shortly.

Whilst the respirator <NUM> illustrated in <FIG>, <FIG>, <FIG>, and <FIG> is indicative of the <NUM>™ <NUM> Series of gas, vapour and particulate respirators, the exhaust apparatus <NUM> of the present invention can be utilised with any negative pressure respiratory device <NUM>. The skilled person will appreciate that the term "respirator" or "respiratory mask", as used interchangeably herein, is intended to mean a breathing device worn to prevent the inhalation of hazardous substances, particles, vapours or noxious gases. The term "negative pressure respiratory mask" is intended to cover any respirator in which the air pressure inside the mask becomes lower than the ambient air pressure when the wearer inhales.

A negative pressure respiratory mask <NUM> as described herein is used to mean any form of respirator intended to fit the face of the wearer <NUM> in a substantially sealed configuration causing the air inhaled and exhaled by the wearer <NUM> to pass through a filter body or a filter portion of the respirator or exhalation valve). Negative pressure respiratory mask <NUM> can be full or half facepiece mask, depending upon the hazard of concern. Again, these masks utilise a filter which prevents the inhalation of contaminants, particles, gases and vapours from the air inhaled by the wearer. Some common examples of this type of respirator are manufactured by <NUM> Company located in St. Paul, Minnesota, and include the <NUM>™ <NUM>, <NUM> and <NUM> Series of reusable respirators or tight-fitting hood facepiece respirators.

Disposable respirators, such as the <NUM>™ <NUM> and <NUM> Series of cup-shaped and flat-folded products, are lightweight single-piece respirators that employ a filter media which removes particulates and mists from the air stream as the wearer draws a breath. The entire unit is designed to be discarded after some extended period or a single use or single shift, depending on the contaminant. Filtering facepieces, such as the <NUM>™ <NUM>, <NUM> and <NUM> Series are generally reusable products and which can have replaceable filter cartridges. Typically one or two cartridges attach securely to half mask or full facepiece which has built into it a corresponding number of valves for inhalation, and usually one for exhalation.

The personal protection respiratory device <NUM> that is illustrated in <FIG> is a <NUM>™ <NUM> half mask to which filters can be attached using bayonet connectors.

Referring to <FIG> and <FIG>, a pair of filter cartridges (not shown for clarity) are attached to the respirator mask <NUM> at respective inhalation ports <NUM>. Each of the inhalation ports <NUM> has a respective inhalation valve <NUM> (shown in <FIG>) on the inside of the respirator mask <NUM> which open as a wearer <NUM> draws a breath. The face mask <NUM> has an exhalation valve <NUM> with a one-way exhalation valve diaphragm <NUM> (shown in <FIG>) which open as a wearer <NUM> expels a breath. The mask <NUM> is held in position on the wearer's head by adjustable straps <NUM> (shown only in <FIG> and <FIG>).

The respiratory mask <NUM> has a conformable gasket or seal <NUM> which generally encloses the wearer's <NUM> mouth and nose. Since a good seal is needed to ensure filtration of the containments, one drawback in the prior art is that sometimes an uncomfortable build-up of heat and moisture is noticed by the wearer <NUM> inside the respirator <NUM>. As the wearer <NUM> works harder, and or wears the respirator <NUM> for extended periods of time, heat and moisture build-up can occur. The heat and moisture build-up is caused by the trapping of the exhaled breath in the cavity created between the respirator <NUM> and the wearer's <NUM> face.

As illustrated in <FIG> and <FIG>, and in further detail in <FIG>, the present invention defines an exhaust apparatus <NUM> having a housing <NUM> with a generally L-shaped form. The exhaust apparatus <NUM> includes an inlet <NUM> (see <FIG>) and an outlet <NUM> (see <FIG>). The outlet <NUM> is formed in a side surface of the housing <NUM>. Positioned inside housing <NUM> between the inlet <NUM> and the outlet <NUM> is a blower <NUM> which in use draws air out of the respiratory device <NUM>. The blower <NUM> has a motor <NUM> which drives a fan <NUM>. The motor <NUM> is powered by a battery <NUM>, which will be described in further detail shortly with reference to <FIG>.

The apparatus <NUM> has an upwardly extending section indicated generally at <NUM> which houses the inlet <NUM>, outlet <NUM> and blower <NUM>. The apparatus <NUM> has a rearwardly extending section indicated generally at <NUM> which houses the battery <NUM> and a controller <NUM> (shown in <FIG>). The positioning of the battery <NUM> (a relatively heavy component of the device <NUM>) in the rearwardly extending section <NUM> allows the centre of mass of the device to sit most closely to the centre of mass of the head. This improves the comfort of the apparatus by minimizing the moment of inertia of the device as the user <NUM> moves his or her head during use.

To operate the apparatus, a switch mechanism <NUM> is accessible to the wearer <NUM>. The switch mechanism <NUM> can have a simple on/off mode of operation or can include a variable adjustment so that the wearer <NUM> can optimise the desired blower speed, and hence, cooling effect based upon the environmental conditions, the task the wearer <NUM> is undertaking, and the wearer's personal choice. Alternatively the settings may be preconfigured by connection to managing software on a PC via USB connection port <NUM>. The connection port <NUM> also serves as a charging port for the battery <NUM>.

In use a cooling effect is achieved by the exhaust apparatus <NUM> as follows. When the wearer <NUM> inhales a breath, "cooler" ambient air is drawn into the respiratory mask <NUM> either though the filter cartridges and inlet ports <NUM> as shown in <FIG> and <FIG> in the case of a reusable mask, or through, for example, a filter portion or filtering mask body of the respirator, in the case of a disposable mask. Heat and moisture build-up is then caused by trapping the exhaled breath in the cavity created between the respirator <NUM> and the wearer's <NUM> face. When operated, the exhaust apparatus <NUM> of the present invention draws this warm and moist air out through the exhaust valve <NUM> during the exhale breath and reduces the exhalation breathing resistance, as described below. This produces a noticeable cooling benefit for the wearer <NUM> without placing a respiratory burden on the inhale breath or reducing the life of the filter.

Turning now to <FIG>, the exhaust apparatus <NUM> is shown connected to the respirator <NUM>. The mechanism for connection will be described in further detail below. <FIG> shows in greater detail the inlet ports <NUM> which are defined by port walls <NUM> which have bayonet fitting <NUM> of known design. The bayonet fittings <NUM> are provided to connect to the <NUM>™<NUM>, <NUM> or <NUM> series of filters. However, it will be appreciated that alternative attachments mechanisms such as the DIN threaded filters may be provided in order to accept differing types of filters. Furthermore, an integral cartridge may be provided in line with the <NUM>™<NUM> series half masks without departure from the invention.

The inlet <NUM> of the exhaust device <NUM> is shaped to releasably connect by way of an interference fit to the shape and dimensions of the respective exhaust valve <NUM> situated on the respiratory mask <NUM>. Whilst the exhaust apparatus <NUM> described herein in relation to <FIG> connects by way of an interference fit, the skilled person will appreciate that any form of releasable connection to the exhaust valve <NUM> is possible, including, for example, connection by way of a screw thread, snap fit engagement, bayonet, quick release mechanism etc. The above list is in no way intended to be limiting and exhaustive.

As an alternative to releasable connection described above, it may be desirable to utilize a direct permanent connection between the device <NUM> and the respiratory mask <NUM>, not according to the invention. Such connection might be by welding, adhesive or other known attachment mechanism such as attachment by screw as will be described in further detail shortly.

Referring now to <FIG> and <FIG> the motor <NUM> is shown mounted within the upwardly extending section <NUM> of the exhaust apparatus <NUM>. The motor <NUM> drives a shaft <NUM> which in turn drives the fan <NUM>. When operative, the fan <NUM> draws air from the filtered air cavity (indicated generally at <NUM> in <FIG>) of the respirator <NUM> past the valve <NUM> and expels the air through the fan scroll <NUM> which is connected to the outlet <NUM>. In this way operation of the motor <NUM> is able to draw air from the cavity <NUM> and expel it to atmosphere. The motor <NUM> is powered by the battery <NUM> which is situated in the rearwardly extending section <NUM>. Directly above the battery <NUM> is a controller <NUM> in the form of a microprocessor on PCB. The controller <NUM> is programmed to control the motor <NUM> is response to the wearer's breathing cycle.

The wearer's breathing cycle is detected by measuring the pressure of the filtered air volume in the filtered air cavity <NUM>. This is achieved via a pressure port <NUM> (see <FIG>) in the respirator <NUM>. The pressure port <NUM> is in fluid communication with a pressure conduit <NUM> in the device <NUM>. The pressure conduit is defined by a connector <NUM> and a pipe <NUM>, the two ends of which <NUM>', <NUM>" are shown in <FIG>. The connector <NUM> has an orifice <NUM> in fluid communication with the pressure port <NUM>. The connector <NUM> seals against the forward face of the respirator <NUM> under the action of screw <NUM> (a second corresponding screw on the opposite side of the device <NUM> is not shown for clarity and by virtue of the cross-sectional view of <FIG>) which passes through a hole <NUM> in the connector <NUM>. The screw <NUM> also acts to supplement the interference fit between the exhaust apparatus <NUM> and the respirator <NUM> to mechanically attach the apparatus <NUM> to the device <NUM>. The second end <NUM>" of the pipe <NUM> is connected to a pressure transducer <NUM> (shown only in <FIG>) which detects the pressure and sends a signal to the controller <NUM>. It is conceivable within the scope of the application that the pressure generated by the wearer's breath could be measured at a position other than in the filtered air volume. For example the pressure could be detected downstream of the exhalation valve. This would remove the necessity for the connector <NUM> and pressure port <NUM> and their sealed interface. Alternatively the pressure could be sensed upstream of the inhalation valve at the inhalation ports <NUM>.

Accordingly, the controller is able to continuously monitor the pressure in the cavity <NUM> and control the blower <NUM> via the motor <NUM> in order to ensure that the fan is, essentially, only operating during the exhale breath of the wearer <NUM>. This operation will now be described in further detail.

<FIG> shows a representation of pressure in, and flow rate through, the filtered air cavity in the prior art device of <CIT>. The dashed line <NUM> represents the flow rate through the mask and the solid line <NUM> represents the pressure in the mask cavity when the device is switched off. The flow rate naturally oscillates about zero as the wearer breaths in cool air through inhale breath B and breaths out hot air through exhale breath A. With the device switched on, the flow rate remains unchanged as the wearer continues to breathe the volume of air required to match respiratory demand. However, the pressure line drops to the extended dashed line <NUM> as the fan operates to maintain a negative pressure in the mask throughout both the inhale and exhale breath. This can only achieved by pulling additional air through the filters during the inhale stroke. This additional volume of air is driven by the additional negative pressure shown in the hatched area <NUM>. The additional flow volume through the filter limits filter life. Furthermore, the additional negative pressure must be overcome by additional respiratory effort if the same flow rate is to be maintained. This additional respiratory effort may itself cause increased respiratory load resulting in an increased breathing rate.

Turning now to <FIG>, the chart shows a representation of pressure in, and flow rate through, the filtered air cavity of the exhaust apparatus <NUM> of the present invention in use with the respirator120. The dashed line <NUM> once again represents the flow rate through the mask <NUM> and the solid line <NUM> represents the pressure in the mask cavity <NUM>. To the left of the centerline X-X the exhaust apparatus <NUM> is switched off and to the right it is switched on. With the exhaust apparatus <NUM> switched off the pressure oscillates about zero subject to the larger maximal negative pressure resulting from the pressure drop across the filters. With the device switched on, the pressure line rises from its low point Z towards zero as the wearer inhales through the filters. As the wearer breaths in through the filter, the controller <NUM> monitors the rise in pressure in the cavity <NUM> via the pressure conduit <NUM>. When the controller detects a predetermined pressure in the cavity <NUM>, in this instance P<NUM> (equal to zero), the controller <NUM> controls the motor <NUM> to initiate the blower <NUM>. This pulls air from the cavity <NUM> in order to assist the breathing of the wearer. The blower <NUM> continues to operate until such time as the pressure in the cavity <NUM> falls below the predetermined P<NUM> at which point the controller stops the motor <NUM>.

The extent of exhale breath assist may be varied by decreasing the predetermined pressure, as indicated by PD, or increasing the predetermined pressure, as indicated by PI. PD delivers a cooler feel to the wearer and PI a warmer feel. It is conceivable that this variation in cooling effect could be controlled by the wearer in response to the operating conditions.

It will be appreciated that whilst <FIG> depicts the same predetermined pressure at the beginning and the end of the exhalation breath, that is to say PD, for example, remains constant throughout the exhalation breath, it is conceivable within the scope of the invention that the blower <NUM> could be started at a first predetermined pressure and stopped at a second predetermined pressure. In the situation where the first predetermined pressure were greater than the second predetermined pressure, the controller would start the blower momentarily after the initiation of the wearer's exhale breath and stop the blower momentarily after the end of the wearer's exhale breath. In the situation where the second predetermined pressure were greater than the first predetermined pressure, the controller would start the blower momentarily before the initiation of the wearer's exhale breath and stop the blower momentarily before the end of the wearer's exhale breath.

<FIG> shows an idealized representation of the pressure plots. In reality the blower is controlled in real time in order to best approximate the desired predetermined pressure value. A number of factors affect this control. Firstly, the pressure drop across the exhale valve will vary from valve to valve. Accordingly the motor may be required to work harder to achieve a predetermined value, say PI, across a narrow exhale valve orifice, than it might across a larger orifice exhale valve.

Claim 1:
A system comprising:
a personal protection respiratory device (<NUM>) that defines a filtered air volume adjacent to the face of a wearer (<NUM>) and comprises an exhalation valve (<NUM>), and
an exhaust apparatus (<NUM>) comprising a housing (<NUM>) and a blower (<NUM>) positioned inside the housing between an inlet (<NUM>) and an outlet (<NUM>) thereof and comprising a fan (<NUM>) and a motor (<NUM>) which drives the fan (<NUM>), the exhaust apparatus being connected to the personal protection respiratory device (<NUM>) such that the inlet (<NUM>) of the exhaust apparatus (<NUM>) is releasably connected to the exhaustion valve (<NUM>) situated on the respiratory device (<NUM>) and such that the blower (<NUM>) is in fluid connection with the exhalation valve (<NUM>), wherein the blower (<NUM>) is responsive to the wearer's respiratory cycle to draw a substantial portion of the wearer's exhaled breath from the filtered air volume of the respirator device through the exhalation valve (<NUM>) of the respirator device and pass the inlet (<NUM>) of the exhaust apparatus and to expel the wearer's exhaled breath out through the outlet of the exhaust apparatus and thus to atmosphere,
wherein the exhaust apparatus (<NUM>) further comprises:
a controller (<NUM>),
a pressure sensor (<NUM>) for sensing a pressure generated by the wearer's breathing cycle and sending a pressure signal indicative of the pressure to the controller (<NUM>),
the controller (<NUM>) being in communication with the pressure sensor (<NUM>) and the blower (<NUM>),
wherein the controller (<NUM>) operates the blower (<NUM>) in response to the pressure signal, and
wherein, in response to the wearer's respiratory cycle, the blower (<NUM>) operates throughout the wearer's exhale breath, or a substantial period thereof, and does not operate throughout the wearer's inhale breath, or a substantial period thereof.