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.

A known improvement to the device of <CIT> is to control the blower so that the blower so that the blower preferably only operates during the exhale breath. This has the advantage that the user no longer needs to overcome the blower during the inhale stroke. While this reduces the inhalatory effort over known devices, the user must still overcome the pressure drop delivered by the filter medium. This can be significant dependent on the type of filter in use and the extent of the respiratory effort of the user. <CIT> resp. <CIT> disclose most of the features of the independent claim <NUM>.

It is therefore an object of the disclosure to deliver the improved cooling effects of the prior art device while reducing the inhalation effort required to overcome the filter pressure drop.

Accordingly, the present invention provides a personal protection respiratory device that defines a filtered air volume in a filtered air cavity adjacent to the face of a wearer and comprises at least one exhalation valve and at least one inhalation valve said inhalation and exhalation valves being one-way diaphragm valves; wherein the personal protection respiratory device further includes a powered apparatus that is either permanently or releasably connected thereto. The powered exhaust apparatus comprises:.

Operating the blower selectively to draw air through the exhalation valve during user exhalation or draw air through the inhalation valve during user inhalation (or a substantial part thereof) delivers significant advantages to the present disclosure as follows.

Firstly, the inhalation effort of the user is reduced since the pressure drop generated by the filter is at least in part, but potentially entirely, compensated by the blower. In the prior art device the user must generate sufficient back pressure to overcome the filter pressure drop before any air flow passes through the filter. This additional pressure must be maintained throughout the inhalation in order for the user to draw sufficient air into the lung cavity to meet physiological demand. This is not the case in the present disclosure where the blower overcomes the pressure enabling the user to breath "normally", that is to say breath as if the filter was not present in the air flow path to the lungs. This is a significant advantage where heavy duty filters with a significant pressure drop are required.

Secondly, it is possible to operate the blower so as to achieve a positive pressure in the filtered air volume when averaged over the respiratory cycle. This reduces the risk of the filtered air volume becoming compromised by leakage of ambient air between the filter and the user's face during use. This increases the efficacy of the respiratory device.

Preferably, the controller starts the first blower and stops the second blower when the pressure sensed by the pressure sensor falls below a first predetermined pressure or the rate of change of pressure reaches a first predetermined rate.

Preferably, the controller stops the first blower and starts the second blower when the pressure sensed by the pressure sensor falls below a second predetermined pressure or the rate of change of pressure reaches a second predetermined rate.

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 first blower and stops the second blower substantially at the initiation of the wearer's exhale breath and stops the first blower and starts the second blower substantially at the end of the wearer's exhale breath.

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

Preferably, the first and second blowers further comprise an inlet, a motor, a fan, and an outlet.

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.

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

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

While the respirator <NUM> illustrated in <FIG>, <FIG>, <FIG>, and <FIG> is indicative of those sold under the trade designation "<NUM> Series" from <NUM> Company, St. Paul, MN, of gas, vapor and particulate respirators, the exhaust apparatus <NUM> can be utilized 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, vapors 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 utilize a filter which prevents the inhalation of contaminants, particles, gases and vapors from the air inhaled by the wearer. Some common examples of this type of respirator are those commercially available under the trade designations "<NUM> Series", "<NUM> Series", and "<NUM> Series" from <NUM> Company, which are reusable respirators or tight-fitting hood facepiece respirators.

Disposable respirators, such as those commercially available from <NUM> Company under the trade designations "<NUM> Series" 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 those commercially available from <NUM> Company under the trade designations "<NUM> Series", "<NUM> Series" 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 half mask to which filters can be attached using bayonet connectors, which is commercially available from <NUM> Company under trade designation "<NUM> Series".

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>, an exhaust apparatus <NUM> is shown 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 a housing <NUM> defined by upwardly extending section indicated generally at <NUM> which houses the inlet <NUM>, outlet <NUM> and blower <NUM>. The housing <NUM> also 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 center of mass of the device to sit most closely to the center 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 optimize 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> 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.

Tuming 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 filters, such as those series of filters commercially available from <NUM> Company under the trade designations "<NUM> Series", "<NUM> Series" or "<NUM> Series". 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 half mask series, such as those commercially available under the trade designation "<NUM> Series" from <NUM> Company.

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>. While 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>. 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>.

Tuming now to <FIG>, the exhaust apparatus <NUM> and respirator <NUM> are shown schematically. The fan <NUM> is shown in a different position to in <FIG> and a single filter cartridge <NUM> is shown for clarity.

<FIG> shows a first embodiment of a respirator <NUM> in use with an exhaust apparatus <NUM> according to the present disclosure. The exhaust apparatus <NUM> has a housing <NUM> (not shown for clarity) similar to that shown in <FIG> but reconfigured to house the following features of the disclosure.

It will be appreciated that, like the exhaust apparatus <NUM> of <FIG>, the exhaust apparatus of the present disclosure is intended for use with a negative pressure respiratory mask <NUM> as described and defined above. That is to say, the term 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 utilize a filter which prevents the inhalation of contaminants, particles, gases and vapors from the air inhaled by the wearer.

The housing defines an air duct in the form of inlet <NUM>, an air duct in the form of outlet <NUM>, an outlet blower <NUM> and an inlet blower <NUM>. The housing <NUM> also houses a battery <NUM> and a controller <NUM>.

A filter cartridge <NUM> is attached to the respirator mask <NUM> at inlet <NUM>. An inhalation valve <NUM> is positioned within inlet <NUM> on the inside of the respirator mask <NUM>. The inhalation valve <NUM> opens as a wearer <NUM> draws an inhaled breath. An exhalation valve <NUM> is positioned within the outlet. The exhalation valve <NUM> opens when a wearer <NUM> expels an exhaled breath. The inhalation valve <NUM> and exhalation valve <NUM> are one-way diaphragm valves.

Similar to that shown in <FIG>, the respiratory mask <NUM> has a conformable gasket or seal <NUM> which generally encloses the wearer's mouth and nose. The mask <NUM> defines a filtered air cavity <NUM>.

The outlet blower <NUM> has a motor (not shown for clarity) which drives an outlet fan <NUM> and which is powered by the battery <NUM> and is in communication with, and controlled by, the controller <NUM>. Similarly, the inlet blower <NUM> has a motor which drives an inlet fan <NUM> and which is powered by the battery <NUM> and is in communication with, and controlled by, the controller <NUM>. The blowers <NUM>, <NUM> collectively forma blower assembly.

The wearer's breathing cycle is detected by measuring the pressure of the filtered air volume in the filtered air cavity <NUM> via a pressure sensor <NUM> in communication with the controller <NUM>.

The exhaust apparatus is configured and arranged so that in use the first blower operates throughout the wearer's exhale breath, or a substantial period thereof, and does not operate throughout the wearer's inhale breath, and the second blower operates throughout the wearer's inhale breath, or a substantial period thereof, and does not operate throughout the wearer's exhale breath.

Accordingly, in some embodiments, the controller <NUM> is able to continuously monitor the pressure in the cavity <NUM> and control the blowers <NUM>, <NUM> via the motors in order to ensure that the inlet fan <NUM> is only operating during the inhale breath of the wearer <NUM>, or a substantial period thereof, and that the outlet fan <NUM> is only operating during the exhale breath of the wearer <NUM>, or a substantial period thereof. This reduces the inhalatory effort required in order to overcome the pressure drop across the filter as will be described in further detail below.

<FIG> shows a second embodiment of a respirator <NUM> in use with an exhaust apparatus <NUM> according to the present disclosure which has two filters <NUM> as opposed to the single filter <NUM> of the first embodiment as shown in <FIG>. The exhaust apparatus <NUM> has a housing <NUM> similar to that shown in <FIG> but reconfigured to house the following features of the present disclosure. The housing defines an air duct in the form of first and second inlets <NUM>, each of which is associated with a filter <NUM>, an air duct in the form of outlet <NUM>, an outlet blower <NUM> and an inlet blower <NUM>. The housing <NUM> also houses a battery and a controller (which are not shown for clarity). The blowers <NUM>, <NUM> collectively forma blower assembly.

The filter cartridges <NUM> are attached to the respirator mask <NUM> at inlets <NUM>. Inhalation valves <NUM> are positioned on the inside of the respirator mask <NUM>. The inhalation valves <NUM> open as a wearer <NUM> draws an inhaled breath. An exhalation valve <NUM> is positioned within the outlet <NUM>. The exhalation valve <NUM> opens when a wearer <NUM> expels an exhaled breath. The inhalation valves <NUM> and exhalation valve <NUM> are one-way diaphragm valves.

The outlet blower <NUM> has a motor (not shown for clarity) which drives an outlet fan <NUM> and which is powered by the battery and is in communication with, and controlled by, the controller. Similarly, the inlet blower <NUM> has a motor which drives an inlet fan <NUM> and which is powered by the battery and is in communication with, and controlled by, the controller.

The wearer's breathing cycle is detected by measuring the pressure of the filtered air volume in the filtered air cavity <NUM> via a pressure sensor in communication with the controller.

Accordingly, in some embodiments, the controller is able to continuously monitor the pressure in the cavity <NUM> and control the blowers <NUM>, <NUM> via the motors in order to ensure that the inlet fan <NUM> is only operating during the inhale breath of the wearer <NUM> or a substantial period thereof, and that the outlet fan <NUM> is only operating during the exhale breath of the wearer <NUM>, or a substantial period thereof. This reduces the inhalatory effort required in order to overcome the pressure drop across the filter as will now be described in further detail below.

Tuming now to <FIG> which show a third embodiment of a respirator <NUM> in use with an exhaust apparatus <NUM> according to the present disclosure, in particular the exhaust apparatus is for connection to respirators, such as those commercially available from <NUM> Company under the trade designation "<NUM> Series", and has two filters <NUM> arranged on either side of a respirator mask <NUM>.

The mask <NUM> has a see-through face mask <NUM> surrounded by a conformable gasket or seal <NUM> which generally encloses the wearer's face. The mask <NUM> additionally has a conformable gasket or seal <NUM> (see <FIG>) which encloses the wearer's mouth and nose. The mask <NUM> defines a filtered air cavity <NUM> within the seal <NUM>.

The apparatus <NUM> has an air duct in the form of first and second inlets <NUM>, each of which is associated with a filter <NUM>, an air duct in the form of first and second outlets <NUM>, an outlet blower <NUM> and an inlet blower <NUM>. The apparatus <NUM> also has a battery and a controller (which are not shown for clarity). The blowers <NUM>, <NUM> collectively form a blower assembly.

The filter cartridges <NUM> are attached to the respirator mask <NUM> at inlets <NUM>. An inhalation valve <NUM> (see <FIG>) is positioned within the inlet blower <NUM>. The inhalation valve <NUM> opens as a wearer <NUM> draws an inhaled breath. First and second exhalation valves <NUM> are positioned at the fluidic entrance to the first and second outlets <NUM> as shown in <FIG>. The exhalation valves <NUM> open when a wearer <NUM> expels an exhaled breath. The inhalation valve <NUM> and exhalation valves <NUM> are one-way diaphragm valves.

The outlet blower <NUM> has a motor <NUM> which drives an outlet fan <NUM> (see <FIG>) and which is powered by the battery and is in communication with, and controlled by, the controller. Similarly, the inlet blower <NUM> has a motor <NUM> which drives an inlet fan <NUM> (again, see <FIG>) and which is powered by the battery and is in communication with, and controlled by, the controller.

Accordingly, in some embodiments, the controller is able to continuously monitor the pressure in the cavity <NUM> and control the blowers <NUM>, <NUM> via the motors in order to ensure that the inlet fan <NUM> is y only operating during the inhale breath of the wearer <NUM>, or a substantial period thereof, and that the outlet fan <NUM> is only operating during the exhale breath of the wearer <NUM>, or a substantial period thereof. This reduces the inhalatory effort required in order to overcome the pressure drop across the filter as will now be described in further detail below.

Referring to <FIG>, it will be noted that the filters <NUM> are positioned substantially rearwardly of the face mask <NUM>. This presents the advantage to the user of minimizing the extent to which the filters impair the field of vision.

<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 preferably only be 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 known exhaust apparatus <NUM> as described in <FIG>. 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.

However, it will be noted that the magnitude of the inhalatory pressure in the mask cavity <NUM> as represented by line <NUM>, which peaks at point Z, remains considerable as the device of <FIG> preferably does not provide any assistance to the user during the inhalation breath.

Tuming now to <FIG> in which the chart shows a representation of pressure in, and flow rate through, the filtered air cavity of the first, second and third embodiments of respirators of the present disclosure. The dashed line <NUM> once again represents the flow rate through the mask <NUM>, <NUM>. The solid line <NUM> represents the pressure in the mask cavity <NUM>, <NUM>, <NUM>. To the left of the centerline X-X the exhaust apparatus <NUM>, <NUM>, <NUM> is switched off and to the right it is switched on. With the exhaust apparatus <NUM>, <NUM>, <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 controller detects a negative pressure in the cavity <NUM>, <NUM>, <NUM> the controller controls the motor to initiate the blower <NUM>, <NUM>, <NUM>. This pulls air through the filters <NUM>, <NUM>, <NUM> into the cavity <NUM>, <NUM>, <NUM> in order to assist the inhalation breath of the wearer. As a result the rise in pressure in the cavity <NUM>, <NUM> increases rapidly as indicated by the pressure line <NUM> rising rapidly from its low point Z towards zero as the wearer inhales through the filters <NUM>, <NUM>, <NUM>. As the wearer breaths in through the filter, the controller <NUM> monitors the rise in pressure in the cavity <NUM>, <NUM>, <NUM>. When the controller detects a predetermined pressure in the cavity <NUM>, <NUM>, <NUM> in this instance P<NUM> (equal to zero), the controller cuts power to the blower <NUM>, <NUM>, <NUM> and initiates the blower <NUM>, <NUM>, <NUM>. This pulls air from the cavity <NUM> in order to assist the exhale breath of the wearer. The blower <NUM>, <NUM>, <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 switches power back to the blower <NUM>, <NUM>, <NUM>.

In this manner the pressure in the cavity is maintained as close to zero pressure as possible in order to provide the user with a natural feeling of breathing in and out without the heat build-up associated with an unassisted exhale breath and without the need to overcome the pressure drop across the filter during the inhale breath. This significantly increases the comfort and safety experienced by the user.

It is conceivable within the scope of the disclosure that the controller could control the blowers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> in the manner described above in order to achieve an average pressure greater than atmospheric. Line <NUM>' in <FIG> represents such a situation where the predetermined pressure at which the controller switches power to the blowers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> in increased to PI. This provides the advantage of maintaining a positive pressure within the cavity <NUM>, <NUM>, <NUM> which serves to minimize the risk of unfiltered air passing into the cavity between the mask and the face of the wearer.

Claim 1:
A personal protection respiratory device (<NUM>; <NUM>) that defines a filtered air volume in a filtered air cavity (<NUM>; <NUM>; <NUM>) adjacent to the face of a wearer (<NUM>) and comprises at least one exhalation valve (<NUM>; <NUM>; <NUM>) and at least one inhalation valve (<NUM>; <NUM>; <NUM>), said inhalation and exhalation valves being one-way diaphragm valves; wherein the personal protection respiratory device further includes a powered apparatus (<NUM>; <NUM>; <NUM>) that is either permanently or releasably connected thereto, the powered apparatus comprising:
a first air duct (<NUM>; <NUM>; <NUM>) in fluid connection with the at least one exhalation valve,
a second air duct (<NUM>; <NUM>; <NUM>) in fluid connection with the at least one inhalation valve,
a first blower (<NUM>; <NUM>; <NUM>) associated with the first air duct, and
a second blower (<NUM>; <NUM>; <NUM>) associated with the second air duct,
the first and second blowers (<NUM>, <NUM>; <NUM>, <NUM>; <NUM>, <NUM>) for selectively directing air through the first and second ducts, respectively, and being responsive to the wearer's respiratory cycle so that, in use,
the first blower draws a substantial portion of the breath exhaled by the wearer through the at least one exhalation valve and out through the first duct, and
the second blower draws a substantial portion of the air inhaled by the wearer through the second duct and in through the at least one inhalation valve;
wherein
the first blower operates throughout the wearer's exhale breath, or a substantial period thereof, and does not operate throughout the wearer's inhale breath, and
the second blower operates throughout the wearer's inhale breath, or a substantial period thereof, and does not operate throughout the wearer's exhale breath; and
wherein the exhaust apparatus further comprises:
a controller (<NUM>),
a pressure sensor (<NUM>) for sensing a parameter generated by the wearer's breathing cycle and sending a signal indicative of the parameter to the controller,
the controller being in communication with the sensor and the first and second blower,
wherein the controller operates the first and second blower in response to the signal, and wherein the parameter is pressure, the signal is a pressure signal and the pressure that is sensed is the pressure of the filtered air volume in the filtered air cavity of the personal protection respiratory device.