Abstract:
The present invention relates to improvements to powered air purifying respirators (PAPR). PAPR are known generally for use in polluted environments. A typical PAPR comprises a powered impellor arranged to draw air from the atmosphere, a filter element and a mask to provide the filtered and pressurized air to the user. Embodiments of the present invention place a generator unit, comprising a filter and impellor for pressurizing the air, behind the head of the user, and include components for improving delivery of the air to the user and improving its quality.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to improved breathing apparatus and, particularly, but not exclusively to improvements to powered air purifying respirators. 
       BACKGROUND OF THE INVENTION 
       [0002]    Breathing apparatus such as powered air purifying respirators (PAPR) are known generally, for use in polluted environments. A typical PAPR comprises a powered impeller arranged to draw air from the atmosphere and a filter element through which the air is passed. The impeller positively pressurises the air and transfers it to a users airways via a mask. PAPR devices are used where the environment is heavily polluted or hazardous. Such environments include polluted industrial areas, hospitals and other potentially hazardous environments. 
         [0003]    Conventional PAPRs tend to be bulky, awkward, and uncomfortable to wear. This is a disincentive to their use. Typical PAPRs are difficult to wear and use for long periods. 
         [0004]    The present Applicants have designed a low profile “PAPR” which is less bulky and is more convenient to use. The present Applicant&#39;s PAPR is described in International (PCT) Patent Application No. PCT/AU2010/000902, the disclosure of which is incorporated in this document by reference. 
         [0005]    A need exists for further improvements in PAPRs, to facilitate functionality and comfort. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with a first aspect, the present invention provides a breathing apparatus, comprising an air flow generator, a filter and an airway, the air flow generator being arranged to generate positive pressure air flow, the filter being arranged to filter air entering the breathing apparatus, and the airway being arranged to transport the positively pressurised air and being arranged to connect to a mask for providing the pressurised and filtered air to the airway of a user. 
         [0007]    In an embodiment, the airway includes an airway connector for connecting the airway to the mask, to allow air flow into the mask to the user&#39;s airway. 
         [0008]    In an embodiment, the air flow generator and filter are housed in a generator unit arranged to be positioned remote from the mask. The generator unit may be arranged to be mounted about the users person. In an embodiment, the unit is arranged to be mounted on the shoulder of the user. In another embodiment, the unit may be mounted behind the neck of the user. The unit may be mounted on the head of the user. In another embodiment, the unit may be mounted on a belt. In another embodiment, the unit may be mounted underneath an arm of a user, using a shoulder strap. The unit may be mounted elsewhere about the person of the user. 
         [0009]    In an embodiment, the mask may be removable from the generator unit and airway. In an embodiment the mask may be a disposable mask. In another embodiment, the mask may be cleanable. 
         [0010]    An advantage of the breathing apparatus in accordance with an embodiment, is that the generator unit may be retained, and masks may be disposed of or washed separately. The airway can be plugged into a new mask or a washed mask. At least an embodiment has the advantage that it can be used domestically to cut intake of air pollution in urban areas. For example, it may be used by pedestrians, cyclists and others. 
         [0011]    In one embodiment, air exhaust is via the mask and/or sides of the mask. In a further embodiment, a separate exhaust valve may be provided in the mask. 
         [0012]    In another embodiment, a separate airway is connected to the mask for exhaust. In an embodiment, the separate airway may be provided with a further filter for filtering the exhaust gas before it is exited to the environment. 
         [0013]    The apparatus may be arranged to be used with a disposable mask, as discussed above, or may be arranged to be used with a non-disposable mask. In an embodiment, the breathing apparatus comprises a mask which is intended to be used repeatedly. The mask may be of resilient plastics material such as silicone. In an embodiment, the mask may be arranged to conform with the user&#39;s face. 
         [0014]    In an embodiment, a mask for use with the breathing apparatus incorporates one or more features which facilitate wearing comfort. In an embodiment, the mask has a top portion which is arranged to sit proximate the nose of a user, and the top portion incorporates a resilient structural feature enabling the top part to flex to accommodate the user&#39;s nose. 
         [0015]    In an embodiment, the resilient structural feature comprises a bellows arrangement, arranged to compress and expand. 
         [0016]    In an embodiment, an area arranged to contact the persons face comprises a thinner wall section. The area may also comprise a gel cushion to facilitate comfort against the nose and/or face. 
         [0017]    In an embodiment, the breathing apparatus may comprise a mask which is arranged to surround the mouth of the user but not the nose. In an embodiment, nose plugs extend from a top part of the mouth surrounding mask and are arranged to be inserted within the nostrils of the user. This results in a low profile mask which can advantageously be used with goggles or glasses without the mask getting in the way of the goggles or glasses. In an embodiment, passageways may be provided within the nose plugs to allow air communication between the interior of the mask and the user&#39;s nose. 
         [0018]    In an embodiment, the breathing apparatus comprises a mask which is arranged to surround only the nasal orifices of a user and leave the mouth exposed. The user can therefore still talk and filtered air is still supplied to the nasal passageways for breathing. 
         [0019]    In an embodiment, the breathing apparatus comprises a mask arrangement, comprising a mask scaffold arranged to support a cover. The cover may be relatively soft and flexible. The flexible cover is arranged to cover a person&#39;s nose and/or mouth openings and provide a volume for containing the filtered air. 
         [0020]    In an embodiment, the cover, or a portion of the cover, is not flexible and is arranged to convey sound, so that a user can talk through the mask. 
         [0021]    In an embodiment, the airway comprises airway walls defining an enclosed airway channel. 
         [0022]    In an embodiment, the airway comprises an airway chassis which is arranged to extend to the mask to provide filtered air into the mask. In an embodiment, the airway chassis extends over the front of the mask, openings are provided in the chassis coinciding with openings in the mask, to convey air into the mask. In this embodiment, the chassis may provide additional support for the mask. 
         [0023]    In an embodiment, the filter comprises a filter housing arranged to receive and mount filters. The filters may be replaced from time to time when they have been used. 
         [0024]    In an embodiment, the filter housing comprises a further filter mounting portion, arranged to receive additional filter components to provide extra filtering. 
         [0025]    In an embodiment, the breathing apparatus comprises a pair of arms arranged to extend from the mask or a mask support, to support the breathing apparatus relative to the user. In an embodiment, the arms are arranged to extend to the neck of the user. In an embodiment, the arms may join behind the neck in order to support the breathing apparatus. 
         [0026]    In an embodiment, a separate neck pad may be connected to the arms at points away from the mask, and be used to provide further support to the breathing apparatus when mounted on the user. In an embodiment, supports extend from the arms and comprise hooks arranged to fit over the ears of a user to provide further support. 
         [0027]    In an embodiment, supports extend from the arms and are connected to form a head band arranged to go over the head of the user and provide support. 
         [0028]    In an embodiment, the arms incorporate the airway. 
         [0029]    In an embodiment, the breathing apparatus comprises a pair of arms extending from the mask and connecting to a generator unit arranged, in use, to be mounted via the arms at the rear of the users head. 
         [0030]    In an embodiment, the generator unit is spaced away from the back of the users head to allow the user to tilt their head without interference with the generator unit. In this embodiment, a separate neck support may be provided arranged to abut the neck of the user during use. 
         [0031]    In an embodiment, the breathing apparatus comprises a power supply arranged to provide power to the breathing apparatus. 
         [0032]    In an embodiment, the power supply comprises a battery mounted by the breathing apparatus. 
         [0033]    In an embodiment, the breathing apparatus may comprise a supplementary power supply which can, in use, be added to the breathing apparatus. The supplementary power supply may comprise a power supply mounting arranged to mount a battery. The power supply mounting may be arranged to be mounted to the breathing apparatus. 
         [0034]    In an embodiment, the breathing apparatus comprises a bypass arrangement, which is arranged to enable airflow to bypass the airflow generator in a non-powered mode of the breathing apparatus. This has the advantage of reducing resistance to airflow which may be caused by the airflow generator when it is not operating. This enables a user to still breathe relatively freely, when the airflow generator is not operating. In an embodiment, the bypass arrangement comprises a manifold and bypass valve. 
         [0035]    Some embodiments of the present invention may be utilised primarily for domestic application. Lightweight versions which utilise disposable masks are particularly suited for domestic application. Versions with washable masks that are intended to be used more than once may also be used domestically, however. Embodiments intended for industrial use will likely have more filtering capability and perhaps more powerful motors and heavier masks. Their use domestically is not excluded. 
         [0036]    In an embodiment the breathing apparatus provides a positive air pressure which is slightly above that of the ambient air pressure to ensure that positive air flow occurs in the mask towards the user&#39;s airway to facilitate inhalation. The air pressure will generally not be very great, as the user is able to inhale under their own power and inhalation should not be forced by a large air pressure. In an embodiment, the breathing apparatus provides a pressure internal to the mask of no more than 3 cm of water. 
         [0037]    In an embodiment, the breathing apparatus provides a pressure internal to the mask of between 0.1 and 3.5 cm of water. In an embodiment the pressure provided is between 1 and 2.5 cm of water. In an embodiment, the pressure provided is between 1.5 and 2.2 cm of water. 
         [0038]    In accordance with a second aspect, the present invention provides a mask arranged to surround at least the nose orifices of a user, the mask having a top portion which is arranged to sit proximate the nose of a user, the top portion incorporating a resilient structural feature enabling the top portion to flex to accommodate the user&#39;s nose. 
         [0039]    In an embodiment, the mask is arranged for use with a powered air purifying respirator. 
         [0040]    In accordance with a third aspect, the present invention provides a mask arranged to surround the mouth and/or nose orifices of a user, the mask having an area arranged to contact the person&#39;s face comprising a wall section relatively thinner than the rest of the mask. 
         [0041]    In an embodiment, at least a portion of the area also comprises a gel cushion arranged to facilitate comfort against the user&#39;s face. 
         [0042]    In an embodiment, the mask is arranged for use with a powered air purifying respirator. 
         [0043]    In accordance with a fourth aspect, the present invention provides a mask arranged to surround the mouth of a user but not to surround the nose orifices. 
         [0044]    In an embodiment, the mask comprises a pair of nose plugs extending from the mask and being arranged to be inserted within the nostrils of the user. 
         [0045]    In an embodiment, passageways are provided within the nose plugs to allow air communication between the interior of the mask and the user&#39;s nose. 
         [0046]    In an embodiment, the mask may be arranged for use with a powered air purifying respirator. 
         [0047]    In accordance with a fifth aspect, the present invention provides a mask which is arranged to surround only the nasal orifices of a user and leave the mouth exposed. 
         [0048]    In an embodiment, the mask is arranged for use with a powered air purifying respirator. 
         [0049]    In accordance with a sixth aspect, the present invention provides a mask arrangement, comprising a mask scaffold arranged to support a cover arranged to surround the mouth and/or nose orifices of a user. 
         [0050]    In an embodiment, the mask arrangement is arranged for use with a powered air purifying respirator. 
         [0051]    In accordance with a seventh aspect, the present invention provides a mask arranged to cover the mouth and/or nose orifices of a user and comprising a relatively rigid portion of the mask which enables transmission of sound. 
         [0052]    In embodiments of the present invention, a powered air respirator may comprise a generator unit for generating positively pressurised and filtered air. In one embodiment, the generator unit is mounted in a housing arranged to be positioned, in use, on the back of the neck of the user. 
         [0053]    In accordance with an eighth aspect, the present invention provides a cooling device which is arranged to be used with a powered air respirator having a housing arranged to be mounted at the neck, the cooling device being arranged to be positioned between the neck mounted housing and the neck of the user. 
         [0054]    In an embodiment, the cooling device comprises a pad which can be cooled by refrigeration and placed on a surface of the neck mounted housing, proximate the neck, to keep the neck cool. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0055]    Features and advantages of the present invention will become apparent from the following description of embodiments thereof, by way of example only, with reference to the accompanying drawings, in which; 
           [0056]      FIG. 1  is a block diagram representing components of a breathing apparatus in accordance with an embodiment of the present invention; 
           [0057]      FIG. 2  is a block diagram of an air flow generator and filter unit of a breathing apparatus in accordance with an embodiment of the present invention; 
           [0058]      FIG. 3  is a perspective view of a breathing apparatus in accordance with an embodiment of the present invention; 
           [0059]      FIG. 4  is a sectional view of the apparatus of  FIG. 15 , showing internal components; 
           [0060]      FIG. 5  is a further perspective view of the embodiment of  FIG. 3 , illustrating the mask arrangement disconnected from the rest of the apparatus; 
           [0061]      FIG. 6  is a detail view of the mask arrangement of the embodiment of  FIGS. 3 to 5 ; 
           [0062]      FIG. 7  illustrates a further embodiment of the present invention; 
           [0063]      FIG. 8  is an illustration of a further embodiment of the present invention. 
           [0064]      FIG. 9  is an illustration of a further embodiment of the present invention; 
           [0065]      FIG. 10  is an illustration of a further embodiment of the present invention; 
           [0066]      FIG. 11  is an illustration of a further embodiment of the present invention; 
           [0067]      FIG. 12  is an illustration of a further embodiment of the present invention; 
           [0068]      FIG. 13  is an illustration of a further embodiment of the present invention; 
           [0069]      FIG. 14  is an illustration of a further embodiment of the present invention; 
           [0070]      FIG. 15  is an illustration of a further embodiment of the present invention; 
           [0071]      FIG. 16  is a view of the inside of the mask arrangement of the embodiment of  FIG. 15 ; 
           [0072]      FIG. 17  is an illustration of a further embodiment of the present invention; 
           [0073]      FIG. 18  is a sectional view of the mask arrangement of the embodiment of  FIG. 17 ; 
           [0074]      FIG. 19  is an illustration of a further embodiment of the present invention; 
           [0075]      FIG. 20  is a sectional view of the mask arrangement of the embodiment of  FIG. 19 ; 
           [0076]      FIG. 21  is an illustration of a further embodiment of the present invention; 
           [0077]      FIG. 21A  is an illustration of a “skeleton” which may be used with embodiments similar to the embodiment of  FIG. 21 ; 
           [0078]      FIG. 21B  is an illustration showing a mask utilising the skeleton of  FIG. 21A ; 
           [0079]      FIG. 21C  is a further view of a mask utilising the skeleton of  FIG. 21A ; 
           [0080]      FIG. 22  is an illustration of a further embodiment of the present invention; 
           [0081]      FIG. 23  is an exploded view of parts of the embodiment of  FIG. 22 ; 
           [0082]      FIG. 24  is a representation of a mask cover part of the embodiment of  FIG. 23 ; 
           [0083]      FIGS. 25 and 26  are details of an airway of a breathing apparatus in accordance with an embodiment of the present invention; 
           [0084]      FIG. 27  is a perspective view of a generator unit for use with a breathing apparatus in accordance with embodiments of the present invention, shown with a further filter adapter attached and further filter; 
           [0085]      FIG. 28  is a view of the generator unit of  FIG. 27  showing the filter removed from the further filter adapter; 
           [0086]      FIG. 29  is a perspective view of a breathing apparatus in accordance with a further embodiment of the present invention; 
           [0087]      FIG. 30  is a plan view of a neck support for use with the breathing apparatus of the embodiment of  FIG. 29 ; 
           [0088]      FIG. 31  is a side view of the apparatus of  FIG. 29  shown being worn by a user; 
           [0089]      FIG. 32  is a detail of the embodiment of  FIG. 29 , illustrating connection of a neck support to the breathing apparatus; 
           [0090]      FIG. 33  is a detail of the embodiment of  FIG. 29  showing an alternative connection for a neck support; 
           [0091]      FIG. 34  illustrates a cooling device for use with a breathing apparatus in accordance with an embodiment of the present invention; 
           [0092]      FIG. 35  illustrates the cooling device of  FIG. 34  in position on a breathing apparatus; 
           [0093]      FIG. 36  is a perspective view of a supporting insert for use with a breathing apparatus in accordance with an embodiment of the present invention; 
           [0094]      FIG. 37  is a diagram showing positioning, in use, of the supporting insert of  FIG. 36 ; 
           [0095]      FIG. 38  is a block diagram of an air flow generator and filter unit of a breathing apparatus in accordance with further embodiment of the present invention; 
           [0096]      FIG. 39  is a perspective view of a breathing apparatus in accordance with a further embodiment of the present invention; 
           [0097]      FIG. 40  is a further perspective view of the breathing apparatus of  FIG. 39 , shown with a head support in position. 
           [0098]      FIG. 41  is a disassembled view of the embodiment of  FIG. 40 ; 
           [0099]      FIG. 42  is a further disassembled view of components of the apparatus of  FIG. 40 ; 
           [0100]      FIG. 43  is a disassembled view of further components of the apparatus of  FIG. 40 ; 
           [0101]      FIG. 44  is a perspective view from above and one side of an exhalation filter which may be used with embodiments of the present invention; 
           [0102]      FIG. 45  is a disassembled view of the filter of  FIG. 44 ; 
           [0103]      FIG. 46  is a sectional view of the filter of  FIG. 49 ; 
           [0104]      FIG. 47  is a perspective view of a generator unit for use with a breathing apparatus in accordance with embodiments of the present invention; 
           [0105]      FIG. 48  is a further perspective view of the generator unit of  FIG. 47 , shown with a filter cover open; 
           [0106]      FIG. 49  illustrates the generator unit of  FIG. 47 , with a further filter adapter attached and further filter; 
           [0107]      FIG. 50  shows the generator unit of  FIG. 49 , with the further filter detached from the further filter adapter; 
           [0108]      FIG. 51  is a perspective view from above and one side of the embodiment of  FIG. 39  with the further filter adapter and further filter of  FIGS. 49 and 50  attached; 
           [0109]      FIG. 52  is a detail of the embodiment of  FIG. 39 , showing a connection point for charging of a power source. 
           [0110]      FIG. 53  is a schematic view from the top of a generator unit for use with a filter apparatus in accordance with embodiments of the present invention; 
           [0111]      FIG. 54  is a view from the side of the generator unit  FIG. 53 ; 
           [0112]      FIGS. 55(   a ) and  55 ( b ) show schematic diagrams of embodiments utilising the generator unit of  FIG. 53  and  FIG. 54 , illustrating different attitudes in use; 
           [0113]      FIG. 56  is an exploded view of a rear end of an apparatus in accordance with an embodiment of the present invention illustrating a bypass arrangement; 
           [0114]      FIG. 57  is a detail view of components of a bypass valve for use with the embodiment of  FIG. 56 ; 
           [0115]      FIGS. 58 and 59  are flow diagrams illustrating controlling algorithms for control of a breath responsive arrangement for a breathing apparatus in accordance with an embodiment of the present invention; 
           [0116]      FIG. 60  shows two graphs of mask pressure and motor power during a breathing cycle, and 
           [0117]      FIGS. 61   a  and  61   b  are mask pressure wave forms for operation of an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0118]      FIG. 1  is a block diagram showing components of a powered air purifying respirator (PAPR) system, in accordance with embodiments of the present invention. The PAPR system  1  comprises the following components: 
         [0119]    (a) a mask  2 , which, in use, is arranged to form a closed chamber about the mouth and/or nose orifices of a user. The chamber formed by the mask is arranged to receive purified air which, in this example, is under positive pressure; 
         [0120]    (b) an air flow generator and filter unit  3  (generator unit). In this example, the air flow generator comprises an impeller  4  with power supply (not shown) which is arranged to positively pressurise air drawn in from the outside environment. The generator unit  3  also comprises a filter  5  arranged to filter the air, a control unit  6  for controlling the generator unit  3 , and, in some embodiments, one or more sensors for sensing air pressure/air quality. 
         [0121]    (c) An airway  8  which is arranged to convey positively pressurised air from the generator unit  3  to the mask  2 . 
         [0122]    The mask  3  may comprise any form of mask which can form a closed chamber about the mouth and/or nose orifices of the user. It may comprise a mask which can be separated from the rest of the apparatus and be disposed of. It may comprise a mask which is not intended to be disposable, but instead can be washable. 
         [0123]    Positively pressurised and filtered air from the generator unit  3  is introduced into the air chamber formed by the mask  3  via the airway  20 . Positive pressure within the chamber is advantageous, as it reduces the amount of unfiltered air which may enter the chamber from around the mask edges. 
         [0124]    The mask may be arranged such that when the user exhales, the exhaled air is exhausted from the mask. The mask may be of filter material itself, in which case exhaust may be via the filter material. Alternatively or additionally, exhaust may be via the edges of the mask, surrounding the face. 
         [0125]    In an embodiment, an exhaust valve (see later) may be provided for use with the mask  3 . The exhaust valve may allow exhaust air to escape, when a user is breathing heavily, to relieve the pressure in the air chamber. 
         [0126]    In another embodiment, the airway may include a return air pathway, which receives exhaust air, for exhausting via the further, return airway. In embodiments (see later) a further filter may be provided to filter the exhaled air. 
         [0127]    In embodiments, the generator unit  3  may be mounted in a convenient location, on the user&#39;s shoulder or behind the user&#39;s neck. The generator unit  3  may be placed in different positions and may be of different housing shapes. 
         [0128]    It may be placed under the arm for example, or in a jacket pocket (may be a convenient rectangular shape similar to a smart phone or like device). It may be secured around the back of the neck, for example. It may be positioned on a user&#39;s belt. It may be placed in any other position and the shape may be adapted accordingly. 
         [0129]    The generator unit  3  may be provided in one or more versions. Each version may have different functionality as required by factors such as cost and the desired functionality. 
         [0130]    In one embodiment, only filter and positive air pressure functionality may be required. In this embodiment, the generator unit  3  therefore includes a filter  5  for filtering air, and an impeller  4  for positively pressurising the air. A control unit  6  in this case may be a simple on-off switch. In another embodiment, the control  6 , may include a user setting switch enabling the user to set a level for the impeller  4  and therefore, to decrease or increase the air pressure to the mask. A power supply (not shown in Figures), such as a battery, for the impeller and control is also provided. 
         [0131]    Embodiments of generator units may include variations of the embodiments described in International Patent Application PCT/AU2010/0000902, by the current applicant. 
         [0132]      FIG. 2  is a block diagram showing various components that may be utilized in the generator unit of this embodiment of this invention. As discussed above, some of these components are optional, and what components are included will depend upon factors such as required cost and functionality for the unit. A simple unit may merely comprise a filter, control switch and impeller, as discussed above. Other embodiments may have additional components, providing additional functionality, such as shown in  FIG. 2 . 
         [0133]    The filter  5  may comprise a single type of filter or may comprise a plurality of different types of cascaded filter.  FIG. 2  illustrates a coarse filter  35 , which can remove large particles present in very dusty environments, such as wood cutting workshops. The coarse filter  35  may be low cost synthetic fibre and washable or easily disposable. 
         [0134]    Coarse filter  35  is followed by a prefilter  36 . The prefilter  36  may be made from a suitable synthetic fibre such as polypropylene, and preferably have an efficiency equal to or better than 90% of the particle size of 5 μm and above. 
         [0135]    Prefilter  36  is followed by a HEPA filter  37 . The HEPA filter is a particulate filter. An activated carbon filter  38  may also be included and also photocatalytic filter  39 . The filter array including all filters  35 ,  36 ,  37 ,  38  and  39  would provide very good filter functionality. In a simple embodiment, such as a simple breathing apparatus arranged for use in an urban environment, a single HEPA filter  37  may suffice. 
         [0136]    Different filters  35 ,  36 ,  37 ,  38 ,  39  can be used separately or together depending upon the required application. The filters may be provided in one or more filter units which may be easily removed for disposal and exchange, or for washing. 
         [0137]    The impeller arrangement in the embodiment of  FIG. 2  comprises a motor control and a blower  40  and  41  respectively. A battery pack  42  for power supply is provided, and a battery charger  43  for plugging in to an external power supply for charging the battery  43 . Controller  6  in this embodiment comprises a micro control unit (MCU)  44 . 
         [0138]    The generator unit of  FIG. 2  comprises a heater  45  which may heat cold air to be provided to the mask  2 . In an alternative embodiment a cooler and air conditioner may be provided. Also, in another embodiment, a humidifier may be provided. The breathing apparatus can therefore be adapted for various environments. A cool environment may use a heater, a hot environment may implement a cooler and an air conditioner. 
         [0139]    The embodiment of  FIG. 2  also comprises a negative ion generator  46 , to provide negative ions. 
         [0140]    In the embodiment of  FIG. 2 , sensors  7  are provided, in this embodiment in the form of a flow sensor and/or pressure sensor  47 . The flow or pressure sensor may be placed in or close to the airway  8  to sense the pressure. The pressure may be compared with a user pressure setting, in the MCU  44 , and the blower  41  may be adjusted to vary the pressure. In an embodiment, the MCU  44  may include a control mechanism to sense the rate of change of air flow or pressure and vary the blower  41  accordingly. When a user starts breathing more rapidly, therefore, the blower  41  may be increase to compensate for the increased air requirement. A description of such a feedback control mechanism is given in applicant&#39;s co-pending International (PCT) Patent Application No. PCT/AU2010/0000902, incorporated herein by reference. 
         [0141]    A user interface  48  may be provided for inputting user control, such as pressure settings, heater settings, on/off switch and any other control required. 
         [0142]    The MCU  44  may be programmable, and various software modules may be utilised to vary the functionality. The MCU may operate on upgradable software or program logic to control the flow rate dependent on user setting, and/or environmental conditions and/or sensor data. 
         [0143]      FIG. 3  shows an embodiment of the breathing apparatus in accordance with the present invention. The mask arrangement  150  is connected via airways  160  and  161  (also airways  157  and  158 ) to a generator unit  162 . 
         [0144]    The arrangement of  FIG. 3  is similar to the PAPR apparatus describe in applicant&#39;s earlier patent application PCT/AU2010/000902. It is modified by the mask arrangement  150  (see description of  FIG. 6  later on) and may include any of the other modifications (particularly of the generator unit  162 ) discussed in this specification. 
         [0145]    The generator unit  162  is mounted by a neck component  163  which, in use, is worn at the back of a user&#39;s neck. A neck pad  164  provides a level of comfort for the user. This may be of soft, flexible material. 
         [0146]    Cooperating connector arrangements  165  (an equivalent connector arrangement is on the other side of the apparatus not shown in  FIG. 3 ) operate to connect mask arrangement  150  airway  157  and  158  with airways  160  and  161  leading to the generator unit  162 . The airways  160  and  161  essentially form “arms” that join and support the mask arrangement  150  together with the generator unit  162 . 
         [0147]      FIG. 5  shows an exploded view of the breathing apparatus, showing the mask arrangement  150  separated from the generator unit  162 . The connector arrangement  165  (see  FIG. 5 ) comprises a mask clip  166  and a mask clip receiver  167  arranged to receive the mask clip  166  and retain it. Airways  157  and  158  have plugs  170  and  171  which engage with corresponding sockets  172  and  173  in the airways  160  and  161  respectively. Airways  160  and  161  are resiliently compressible (i.e. they can extend and compress in order to provide some flexibility of the breathing apparatus about the users neck and face, and also to facilitate a good fit) and a ratchet arrangement  175  (equivalent ratchet arrangement is on the other side of  FIG. 5 , not shown) allows for adjustment of the length of the airways  160 ,  161  for comfort and fit. 
         [0148]      FIG. 4  shows a sectional view through the apparatus of the embodiment of  FIG. 3 . A breathing chamber  180  is provided in the space between the face of the user and the shell of the mask  150 . The breathing chamber  180  is isolated from the surrounding environment by virtue of the seal about the face of the user. The airways  157 ,  158 ,  160 ,  161 , when connected provide passageways  181 ,  182  for flow of the air from the generator unit  162  to the mask chamber  180  and back to the generator unit  162  for porting into the environment. Direction of airflow is shown in  FIG. 4  by the white and black arrows. The black arrows indicate air being exhaled and the white arrows indicate pressurised and filtered air being provided to the mask chamber  180 . 
         [0149]    The generator unit comprises a filter unit  185  to receive and filter inhaled air. The filter unit  185  may comprise a number of different types of filter as discussed previously, such as pre-filter, HEPA filter and others, depending upon the type of filtering required for the environment in which the breathing apparatus is to be used. An impellor unit  186  pressurises the air and forces it in the direction indicated by the arrows. The exhaled air may be ported via a further filter unit  187 , to avoid pathogens from the user, for example, being ported into the environment. A software controlled control unit  188  may control the impellor  186  and other aspects of the breathing apparatus. A power supply  189  in the form of a battery is also provided in the generator unit. 
         [0150]    The breathing apparatus may also comprise one or more pressure flow and/or temperature sensors. By monitoring breathing patterns of the user the control unit  188  is able to control the flow rate of the air delivered to the mask chamber  180 . The control unit may operate on upgradable software or program logic to control the flow rate dependent on user settings, environmental attributes and/or sensor data. 
         [0151]    The breathing apparatus of this embodiment may include one, more or all of the other components which are shown and described above with reference to  FIG. 2 . A valve arrangement, such as described with reference to  FIGS. 46 ,  47 ,  48 , may be used as valve  156 . An optional communication module consisting of a microphone, voice signal processing/noise cancelling and a Bluetooth module can be implemented in this embodiment (and other embodiments). The purpose is to be able to speak quietly and clearly while wearing the mask. The microphone is ideally located within the neck component  162 . Alternatively, it can be fitted inside the mask. A noise cancelling and Bluetooth module is fitted in the neck component  162 . Noise from the motor and environmental noise is cancelled and a voice is enhanced. The voice is converted to an audio stream and is transmitted to a suitable Bluetooth enabled device, such as speaker or smartphone nearby, wirelessly. Thus voice communication is made easy without taking off the mask. When wearing a Bluetooth earplug or headphone, the user can make a phone call in a whisper even in a noisy environment. With the Bluetooth module, a smartphone can be used as a remote control device to the respirator (using an “App” for example) and it is also possible to download software, retrieve respirator usage information, alerts, warnings for filter replacement, etc. 
         [0152]      FIG. 6  is perspective view of a mask arrangement in accordance with an embodiment of the present invention. The mask arrangement of this embodiment comprises mask structural features which facilitate comfort for the user and also effectiveness of the mask. The mask  150  of this embodiment comprises a face contacting cushion  151  which is arranged to surround the periphery of the mask, and, in use, contact the user&#39;s face. This cushion  151  may be arranged to be relatively flexible and softer than the rest of the mask and may even be made of different material. A portion  152  of the cushion arranged to contact the upper part of the face and the nose bridge is arranged to be thinner than the rest of the cushion  151  to facilitate comfort. 
         [0153]    The top portion  153  of the mask is provided with a flexible bellows arrangement  154  which allows the cushion  153  to flex. Bellows arrangement  154  forms a resilient structural feature of the mask  150 , which again improves comfort and conformity to the user&#39;s face in use. 
         [0154]    A lower portion of the mask  155  mounts a valve  156 , which ports air from the mask  150  when the pressure inside the mask  150  exceeds a predetermined level. 
         [0155]    Airways  157  and  158  are, in this embodiment, integral with the mask  150 . Airway  157  conveys pressurised and filtered air from the generator unit  162  to the mask and airway  158  conveys exhaled air from the mask back to the generator unit where it may be filtered before being ported. 
         [0156]    The features associated with the mask, such as the resilient structural feature and the thinner wall section are not limited to a mask with an integral airway such as shown in  FIG. 6 . The airway may be separate and may be of any of the type shown above and in the following described embodiments, for example, or any other type. 
         [0157]      FIGS. 7 through 13  illustrate various forms of breathing apparatus in accordance with embodiments of the present invention. 
         [0158]    Referring to  FIG. 7 , a PAPR in accordance with a further embodiment of the present invention is illustrated. The PAPR  50  comprises a generator unit  51 , an airway  52  and a combined mask and eye protector arrangement  53 . The generator unit  51  and airway  52  may comprise components similar to those discussed above in relation to the previous embodiments, and no further description will be given here. The airway is a single airway  52  from the generator unit  51  to the mask  53 . There is no return airway as in the embodiment of  FIG. 3 . The generator unit  51  is mounted on the shoulder. 
         [0159]    The mask and eye protector arrangement  53  comprises a mouth and nose mask  54  and an eye protector  55  in the form of a pair of goggles secured by a strap  56  passing over the ears and behind the neck in use. Alternatively, the strap  56  may comprise a pair of supports which merely pass over the ears. 
         [0160]    In this embodiment, the goggles  55  are secured to the mask  54 . And may be able to be separated from the mask  54  for cleaning. The mask  54  is secured by a strap  57  arranged to pass behind the neck. The mask  54  is, in this embodiment, not a disposable mask, but a mask of washable material, such as silicone. A portion  58  of the mask is relatively flat and rigid and may carry sound waves, so that the user can speak through it. 
         [0161]    In this embodiment, the generator unit  51  is worn on the shoulder, and there is a single airway  52  for providing filtered and pressurised air to the mask  54 . Exhaled air, may escape the mask  54  via filter material and/or an exhaust valve (not shown). 
         [0162]    A further embodiment is shown in  FIG. 8 . The PAPR  60  of this embodiment comprises a generator unit  61  which, in this embodiment, comprises a neck mounted housing which extends around the back of the user&#39;s neck and has a rest portion  62  which rests on the user&#39;s shoulders. The airway  63  in this embodiment comprises a pair of airway limbs  64 , only one of which is shown in the Figure, the other airway  64  passes around the other side of the neck and joins the generator unit  61  on the opposite side of the user (not shown). The structure of the airway  63  is generally similar to a structure of the airway of the embodiment of  FIGS. 3 to 5 . 
         [0163]    The PAPR  60  also comprises a mask, which in this embodiment is covered by a decorative mask cover  65 . Decorative mask cover  65  may comprise material which is attached to the unit  61  and also to a headband  66  at attachment points  67 . The cover  65  in this embodiment is intended to provide aesthetic appeal. The decorative mask cover  65  also provides protection from the environment for the face. This is very important, particularly in a number of countries where it is felt to be important to shield the face from the environment. For example, the decorative cover may be effective in shielding the face from the effect of UV radiation. 
         [0164]    In use, pressurised and filtered air is provided by the airway  64  into a mask (not shown) underneath the cover  65 . On the other side of the user (not shown) the second limb  64  of the airway transports exhaled air away from the mask and back to the unit  64 . The exhaled air is ported from the unit  61 . The unit  61  in this embodiment includes an exhaled air filter, which filters the exhaled air, as well as including filters for filtering air taken in to the apparatus. Having an exhaled air filter in this fashion means that any viruses or bacteria that the user may be carrying will not be ported into the environment, or at least porting of such pathogens into the environment will be reduced. 
         [0165]      FIG. 9  illustrates yet another embodiment of the invention. The breathing apparatus  70  of this embodiment comprises a mask and glasses unit  71 . The mask  72  comprises a nose bridge  73  which extends upwardly to integral glasses support  74 , which support protective lenses  75 ,  76 . The support  74  comprises a pair of arms  77 ,  78  which extend behind the ears of the user to support the arrangement. The arms  77 ,  78  may be rigid plastics or, in an alternative embodiment, may comprise a flexible strap which passes around the back of the head of the user. The breathing apparatus  70  also comprises an airway  79  and a generator unit  80 , which is similar to the generator unit and airway of the embodiment of  FIG. 8 . The mask  72  includes a flat, relatively rigid portion  81  which allows sound to carry. 
         [0166]      FIG. 10  illustrates a further embodiment of a breathing apparatus in accordance with the present invention. 
         [0167]    The breathing apparatus  90  of this embodiment comprises a mask arrangement  91  which includes a frame  92  which supports the mask  93  and also supports eyewear  94 , comprising a pair of integral lenses  95  and  96 . A headband  97  is attached to the frame  92  at top portions  98  and  99 . The headband  97  extends over the back of the head of the user in use to secure the mask arrangement about the face of the user. The frame  92  forms a full face mask covering the nose and mouth of the user and supporting the eyewear  94 . The mask  92  has a flat relatively rigid portion  100  for carrying sound. The frame  92  may be relatively flexible so as to conform with the contours of the user&#39;s face. 
         [0168]    The generator unit  101  and airway  102  are similar in form to the embodiment of  FIG. 8 . 
         [0169]      FIG. 11  is a side view of further embodiment of a breathing apparatus  110  in accordance with the present invention. In this embodiment the generator unit  111  is arranged to sit at the back of the neck of the user in use. A head strap  112  is connected to a top portion  113  of the generator unit  111 . The head strap  112  reaches up from the back of the neck to the back of the head and is integral with a mask strap  113  which passes round either side of the head and is attached to side portions  114  (there is another side portion  114  on the other side of the user&#39;s face not shown in this drawing) of the mask arrangement  110 . The mask strap  113  and head strap  112  work together to support the entire breathing apparatus  110 . 
         [0170]    The mask arrangement  120  comprises a framework  116  which forms a top portion  117  of the mask and has side portions  118  (other side portion  118  on the other side of the head, not shown in this drawing) which connects the top portion  117  of the mask arrangement  110  and the generator unit  111 . The framework, at least the portions  118 , are of relatively flexible material so that the entire apparatus  110  may be passed over the head of the user and secured in position. 
         [0171]    The mask arrangement  120  also comprises a relatively rigid front portion  119  which allows sound to carry. An airway  121  connects the generator unit  111  to a chamber about the mouth and nose of the user formed by the mask arrangement  120 . An equivalent airway (not shown) is positioned on the other side of the head to receive exhaled air, in a similar fashion to the apparatus of  FIG. 8 . 
         [0172]      FIG. 12  illustrates yet a further embodiment of the present invention. The breathing apparatus  130  of this arrangement has a mask arrangement  131  which comprises a full face mask  132  which extends over the nose and over the chin. A head strap  133  is attached to top portions  134  of the mask arrangement (the other top portion  134  is on the other side of the head, not shown in this drawing), and extends over the back of the head to secure the arrangement. A pad  135  is attached to the head strap  133  at the back of the head. 
         [0173]    The breathing apparatus includes a generator unit  136  which sits at the back of the head and is secured by elasticated straps  137  (a strap  137  is also on the other side of the head, not shown in this drawing) which are attached to the mask arrangement  130  at side portions  138  (other side portion  138  on the other side of the head, not shown in this drawing). Airways  139  (other airway on the other side of the head) connect the mask  132  with the generator unit  136 . 
         [0174]    A further embodiment of a breathing apparatus is shown in  FIG. 13 . The breathing apparatus  140  in this embodiment comprises a mask arrangement  141  comprising a mask  142  which extends from the bridge of the nose to underneath the chin of a user. The apparatus  140  includes a behind neck mounted generator unit  143  and airways  144  from both sides of the head (airway on the other side is not shown in this drawing). 
         [0175]    Vent arrangement  145  is provided at the front of the mask. The vent arrangement comprises holes  146  in the mask material and filter material under those holes, filtering exhaled air. 
         [0176]    In this embodiment, filtered and pressurised air is provided to the mask arrangement  140  via the airway  144  and exhaled air returns to the generator unit  143  via other airway (not shown) on the other side of the head and is ported via a filter for the exhaled air. If the pressure in the mask rises, some exhaled air may be ported via the vents  146 . 
         [0177]      FIG. 14  illustrates a further embodiment of a breathing apparatus in accordance with the present invention, generally designated by reference numeral  200 . The breathing apparatus  200  is a variation on the embodiment of  FIGS. 3 to 5 . The breathing apparatus  200  comprises a generator unit  162  and airways  160  and  161  (not shown) which are the same as the embodiment of  FIGS. 3 to 5 . No further description will be given of these components. 
         [0178]    The breathing apparatus  200  comprises a mask arrangement  201  which comprises a low profile nose portion  202 . The low profile nose portion  202  is arranged to encompass the nasal orifices of a user, without covering the upper portion of the nose of the user. This allows the user to wear relatively large eye gear such as goggles  204 , without the goggles  204  being interfered with by the low profile mask. 
         [0179]    The mask arrangement  201 , with low profile nose portion  202 , may be used with variations which do not include the generator unit mounted at the back of the neck. For example, the generator unit may be mounted elsewhere and attached to the mask arrangement  201  via different types of airways, such as those described above. 
         [0180]      FIGS. 15 and 16  illustrate a further embodiment of the present invention. The breathing apparatus  210  of this embodiment comprises a neck mounted generator unit  162  with airways  160  and  161 . These airways and the generator unit  162  have the same components as the embodiments of  FIGS. 3 and 5 , and no further description will be given. 
         [0181]    The mask arrangement  211  of this breathing apparatus  210 , however, is a hybrid mask arrangement. It comprises a mouth covering portion  212  and nasal plugs  213 ,  214  which are arranged to engage with the nasal passageways of the user. 
         [0182]    In more detail, the mouth portion  212  comprises a cushion  215  which is arranged to surround the mouth of the user, and the mask arrangement  211  forms a breathing chamber  216  about the mouth of the user. Airways  217 ,  218  communicate with the chamber  216  and also with the airways  160 ,  161  in the neck portion of the breathing apparatus  210 . 
         [0183]    The nasal plugs  123 ,  124  have passageways  219 ,  220  which communicate with the chamber  216 . Nasal plugs  219 ,  220  sit in the nostrils, and the user can therefore breath the filtered and pressurised air through the nasal plugs  213 ,  214 , as well as via the mouth and mask chamber  216 . 
         [0184]    The nasal shield portion  221  of the mask arrangement  211  extends over the nasal plugs  213 ,  214 , to shield them and also extends over the bottom part of the user&#39;s nose in use. 
         [0185]    This hybrid mask arrangement  211  results in a low profile mask with a low profile shield part  221  which also allows goggles and other heavy eyewear to be worn with the breathing apparatus  210 . 
         [0186]    The mouth cushion  215  may be formed from relatively soft, flexible material, such as silicone, for comfort. 
         [0187]    As with other embodiments, the mask arrangement  211  is not limited to use with a neck component mounted generator  162 , and the generator unit may be mounted elsewhere and different airways may be used with a mask arrangements similar to or the same as  211 . 
         [0188]    A variation of the embodiment of  FIG. 15  and  FIG. 16  comprises a mask arrangement which does not include the nose plug shield  221 . In this embodiment, the nose plugs merely extend from the top of the mask portion  212  to the nose of the user, and are unshielded. 
         [0189]      FIGS. 17 and 18  illustrate a further embodiment of a breathing apparatus in accordance with the present invention, generally designated by reference numeral  230 . This embodiment includes a neck mounted generator unit  232 . An airway  232  from the generator unit  231  attaches to an airways chassis  233 . Note that an equivalent airway  232  is provided on the other side of the user that cannot be seen in this drawing. The airway chassis  233  is a relatively rigid component that passes around the face of the user and connects to airways  232 , so that there is air passage through to the mask arrangement  235  from the generator unit  231 . 
         [0190]    In this embodiment, the mask  235  covers the nose orifices only of the user and allows the users mouth to be free, so that they can communicate for example. 
         [0191]      FIG. 18  shows a sectional view of the mask  235  showing a chamber  236  formed by the mask via which the pressurised and filtered air reaches the nasal passageways of the user. 
         [0192]    The chassis  233  is engaged to the mask body  235  as shown. A resilient cushion  237  is formed at the top part of the mask  235  to cushion against the nose bridge of the user and against the face. A second cushion portion  238  is formed to cushion against the upper lip of the user. 
         [0193]    This embodiment is advantageous in that a user of the mask  235  may continue to speak, eat or drink, while still receiving filtered and pressured air via the nasal passageways. 
         [0194]    This nose mask arrangement  235  and air chassis  233  embodiment may be used (on adaption) with any of the generator units described above, or any other generator unit, whether placed behind the neck or elsewhere about the user. 
         [0195]    The relatively rigid chassis  233  operates in this embodiment to support the mask  235  against the face of the user. 
         [0196]      FIGS. 19 and 20  illustrate a further embodiment of a breathing apparatus in accordance with the present invention, designated generally by reference numeral  240 . 
         [0197]    The breathing apparatus  240  comprises a generator unit  162  and flexible air ducts  160  which are the same as the arrangement of  FIGS. 15 to 16 . No further description will be given of these components. 
         [0198]    The mask arrangement  241  of this embodiment comprises a mask  242  which is arranged to cover only the nose openings of the user. In operation, the mouth of the user is uncovered. The mask arrangement also comprises airways  243 ,  244  which engage with airways  160  and define conduits which can convey air to and from a mask chamber  245  defined by the mask  242 . The mask  242  comprises face engaging cushions  246  (nose cushion) and  247  (upper lip cushion) to engage the face of the user. These cushions may be made of relatively soft material, such as soft silicone. 
         [0199]    The mask arrangement  241  also comprises a visor  250  which is connected to the mask  242 . In this embodiment a nose piece  251  of the visor is connected to a slot extending in the mask  242 . The nose piece  252  may be able to be disengaged from the slot to remove the visor  250 . In another embodiment the nose piece  251  may be permanently secured to the mask  241  or may be integral with it. The visor  250  in this embodiment comprises protective lenses  254 ,  255 . A strap  256  is attached to the visor  250  and extends around the back of the head to secure the visor  250 . 
         [0200]    An optional communications component  260  is provided with this embodiment. The communication component  260  engages with a slot  261  on the lower part of the mask  241  and extends downwardly from the mask so that a microphone or the like  263  is positioned proximate the mouth of the user. An appropriate wireless link may be provided e.g. Bluetooth™ for linking to communications. 
         [0201]    The user can advantageously communicate as their mouth is free, including communicating via a coms link provided in the mask via item  260 . 
         [0202]    The mask  241  also includes an extending portion  265  which extends downwardly from the mask to partially cover the mouth. 
         [0203]      FIG. 21  illustrates yet a further embodiment of a breathing apparatus, generally designated by reference numeral  270 . A breathing apparatus  270  comprises a neck component mounted generator unit  271  which is connected by airways  272  which are integral with a mask arrangement  273 . Another airway  272  extends on the other side of the user, but is not shown in this drawing. 
         [0204]    The mask arrangement  273  in this embodiment comprises a relatively thin layer of silicone  274  laid over and supported by a polycarbonate chassis  275 . The chassis comprises a support frame  276  which extend into the airway  272  of the breathing apparatus (see  FIG. 21A  which shows the support frame  276  separate from the mask arrangement. It also comprises a central supporting member  277  which forms a curved plate supporting the thin silicone layer  274 . This is clearly shown in  FIGS. 21   b  and  21 C. In  FIG. 21   b , the silicone layer  274  has been cut away in the area of the supporting member  277  apart from at the edges  277   a  which are sealed to the supporting member  277 . Because the supporting member  277  is quite rigid, it supports the user speaking through the mask at this point. In  FIG. 21C , the silicone layer has not been cut above the supporting member  277 , but this will still be rigid enough to support speech. The supporting member supports a silicone skin  274  which may be relatively thin and flexible. The polycarbonate chassis may be manufactured by three dimensional printing. The airways  272  may also be manufactured in this way and the airways  272  may be integral with the chassis  275 , forming “arms” which extend backwards from the mask and connect the generator unit. The silicone  274  may also comprise a silicone cushion  278  about the mouth and nose of the user, for comfort. 
         [0205]    The silicone layer  274  may be relatively thin compared with the mask of the preceding embodiment and may include one or more relatively rigid layers to enable transmission of sound when a user speaks. The thin silicone also has the advantage of lighter weight. 
         [0206]    Referring to  FIG. 22 through 24 , a composite mask apparatus  280  is illustrated, which includes a mask  281  and a decorative cover  282  for the mask. The breathing apparatus  280  includes a neck component  283  which is similar in form and function to the generator unit of  FIGS. 3 to 5 . Fastening means, in the form of clips  284  and  285  attach airway component  286 ,  287  to airways for the generator unit  283 . The airway components  286 ,  287  include plugs  288 ,  289  which cooperate with corresponding sockets (not shown) in the generator unit  283  airways. Ports  290  are formed at the end of airways  286 ,  287  distal from the generator unit  283 . These ports cooperate with orifices  292 ,  293  in a inner silicone mask  281 . 
         [0207]    Note that, in an alternative embodiment, the mask may be of other material than silicone or rubber, and may be of porous filter material. 
         [0208]    The inner mask  281  also comprises vent holes  294 ,  295  which are arranged to receive exhaust valves  298 ,  299 . 
         [0209]    The outer cover  282  comprises ports  296 ,  297  which correspond to exhaust ports  294 ,  295  when the outer cover  282  is placed in position over the mask. Exhaust valves  298 ,  299  fit into ports  296 ,  297 . They also assist in securing the outer cover  282  to the mask  281 . In an alternative embodiment, components  298  and  299  may not be exhaust valves, but may merely be plugs, sealing exhaust ports  295 ,  294 . 
         [0210]    The cover  282  also comprises slots  300  in the cover which may be for decorative purposes, which may also allow venting of air where the mask  281  is of porous material. 
         [0211]    The inner mask  281  is shaped to cover the mouth and nasal passages of the user. Airways  286 ,  287  convey filtered and pressurised air to the mask (airway  286 ) and from the mask (airway  287 ) back to the generator unit  283  where the expired air may be exhausted via an exhaust filter. If pressure in the mask increases, further exhaust air may be vented via the exhaust valve&#39;s  298 ,  299  and/or mask material. 
         [0212]    The outer cover  282  may facilitate aesthetic appeal of the breathing apparatus. The cover may include patterns, colours, and the like for aesthetic appeal. A plurality of such covers may be available, so that the user can change them, to vary the aesthetics of the breathing apparatus  280 . The cover may also provide a function of protecting the user&#39;s face from the environment. In Particular, these covers may be very popular where it is usual and important to protect the complexion from the effects of UV radiation, for example. 
         [0213]    In the above embodiment, the inner mask covers the nose and mouth. Various embodiments may only cover one of the nose or mouth. Further, covers such as the cover  282  may be used with other embodiments of the mask apparatus that have been described here. Covers may be varied in shape so as to operate with each embodiment. 
         [0214]    The generator unit for the embodiment of  FIGS. 22 to 24  is not limited to a neck component such as illustrated in the drawings but may be provided by other types of generator units positioned anywhere on the body. 
         [0215]      FIGS. 25 and 26  illustrate an alternative embodiment of a connector mechanism  310 , for connecting an airway of a generator unit to an airway of a mask arrangement, for any of the embodiments described herein. 
         [0216]    The connector arrangement  310  comprises a male connector component  311  which is mounted on the mask arrangement airway  312 . The male component  311  has a pair of fingers  313 ,  314  which extend towards the generator unit airway  315  in use. Fingers  314 ,  313  are arranged to be inserted into a corresponding female member  316  mounted on the generator unit airway  315 . The fingers  313 ,  314  include heads  317 ,  318  projecting distally and being arranged to engage with slots  319 ,  320  in the female member  316 . The fingers  313 ,  314  are resilient so that they lock into the female member slots  319 , 320  the connector arrangement may be released by pressing the projecting portion  317 ,  318  in the slots  319 ,  320  and pulling the male member  311  away from the female member  315 . 
         [0217]    In the above embodiments, there are a number of breathing apparatus which include a generator unit comprising a housing arranged to be mounted at the neck of the user. The housing may contain an airflow generator, filter, and other components. In some environments, particularly hot ones, wearing such a neck mounted unit may result in some discomfort. In an embodiment, a cooling device is provided to facilitate comfort of such a neck mounted unit.  FIGS. 36 and 37  illustrate an embodiment of the cooling device. 
         [0218]    The cooling device, generally designated by reference numeral  350  comprises a cooling insert  351 . The cooling insert  351  comprises a material which is arranged to maintain coolness. The insert  351  is, in use, placed in a refrigerator for a time until it cools sufficiently. The cooling device  350  also comprises a cover  352  which is arranged to receive the cooling insert  351  within the cover  352  via opening  353 . The cover  352  has a velcro attachment at the back (not shown) which is arranged to fit to a corresponding velcro pad on the neck unit of a breathing apparatus in accordance with an embodiment of the present invention, see  FIG. 37 . 
         [0219]    In operation, the cooling device  350  maintains coolness of the neck of the user, promoting comfort. 
         [0220]    The breathing apparatus of embodiments of the present invention include flexible airways for conveying filtered and pressurised air to the mask and conveying air from the mask (in some embodiments). Because the airways are flexible (see  FIGS. 3 and 5 , for example, where the airways are a flexible bellows) there is some potential for them to kink and close in operation. In order to prevent this, the present applicants have developed an insert, see  FIGS. 36 and 37 . The plastics insert  360  comprises a base  361  and a pair of fingers  362 ,  363  extending perpendicularly from the base. In operation, the base of the insert sits within an airway  370  and maintains the airway open even if it kinks. This is because the insert  360  by virtue of the fingers  362 ,  363  cannot lie flat and will maintain the airways in an open condition. 
         [0221]    Referring to  FIGS. 27 and 28 , there is illustrated a further filter adapter  500  which is arranged to be mounted to a generator unit  501  to receive further filter units, such as filter unit  502 . Generator unit  501  may be the same or similar to generator units used in other embodiments of this invention, such as generator unit  162  of  FIGS. 15 to 22 . It may contain the same componentry. It will be used with an airway and mask arrangement in accordance with any of the embodiments discussed above or following. 
         [0222]    In some circumstances, it may be required to use additional filter capability, which may require larger and bulkier filters to be added to the apparatus. For example, for extremely harsh environments with irritating or poisonous gases possibly present, gas filters may be required. Filter unit  502  may contain the appropriate filter and can be added to the generator unit  501  by using the filter adapter  500 . The filter unit slots into the adapter  500 , in the direction of the arrows  503 . 
         [0223]    The further filter unit  502  may be used in addition to filters already mounted in the generator unit  501 , or in place of. 
         [0224]    Enhanced filter functionality allows apparatus in accordance with embodiments of the present invention to be used in very harsh environments, such as hazardous gaseous environments, and even in military applications. 
         [0225]      FIGS. 47 through 52  show more detailed views of generator unit  501  with a slightly modified filter adapter  500   a  and further filter unit  502   a.    
         [0226]      FIGS. 47 and 48  show the generator unit  501  configured for use with standard filters, and showing how to replace filter units. 
         [0227]    The generator unit  501  comprises a housing  510  within which the components of the generator unit (filters, impellers for powered air, control electronics and other components) are mounted. The housing mounts a touch control pad  511  which includes touch buttons  512  and displays  513  allowing the user to enter control parameters (e.g. air flow and/or pressure control, temperature, etc.). The control pad  511  may take any convenient configuration. 
         [0228]    A door  515  is mounted at the rear of the housing  510  and can be opened (shown opened in  FIG. 48 ) to allow access to the housing  510 , in particular to remove and replace filter cartridges  516 . Filter cartridge  516  may contain a plurality of cascaded filters such as a HEPA filter, particle filter and any other filter, as discussed above. In the configuration as shown in  FIG. 59 , the filter cartridge  516  comprises an inhalation filter  517  (which may contain a plurality of cascaded filters, or may be only one type of filter) and also an exhalation filter  518 . 
         [0229]    The surface area of filter cartridge  516  is similar on the outside  516   a  and the inside  516   b , at least as the filter area being presented at  516   a  and  516   b . Having similar or equal areas of filter intake and outlet results in the filter material being used more efficiently. 
         [0230]    The inhalation filter  517  is at the intake of the generator unit  501  (operation is the same as inhalation filter  185  shown in  FIG. 14   a  and described above). Exhalation filter  518  is placed to receive output airflow and filter exhaled air (same as filter  187  of  FIG. 14   a , described above). The exhalation filter  518  may, in embodiments, also include a plurality of cascaded filters. 
         [0231]    Filters  517  and  518  are mounted on a backing  519  and the cartridge  516  is arranged to slot into a receptacle  520  in the generator unit housing  510 . Door  515  is then closed as shown in  FIG. 47 . 
         [0232]    In some embodiments there may be no exhalation filter  518  on the filter cartridge  516 . In some embodiments, the airflow does not return to the generator unit  501  for exhalation (see later on), and may be exhaled via a valve elsewhere or via a porous mass (e.g. a filter mask). 
         [0233]    The door  515  is hinged to the housing  510  via a hinge  521 . The hinge  521  comprises a hinge pin  522  mounted within a pair of cylindrical passages  523 ,  524  in the housing  510  and also running through a cylindrical passageway  525  at one end of the door  515 . At the other side of the door  615  from the hinge  521  is a release pin  526  which can be actuated to a release position (shown in  FIG. 48 ) so that the door  515  can be opened. The pin  526  and door  515  are shown in the closed position in  FIG. 47 . 
         [0234]    The release pin  526  is slideable within a pathway  517  formed by a pair of lugs  528 ,  529  on the housing  510 , the lugs  528 ,  529  defining cylindrical holes  531 ,  532  to receive the pin  526 . The door  515 , at its end corresponding to the position of the pin  526  has a lug  530  which defines a cylindrical passageway  531  which sits between lugs  529  and  528  when the door is closed and is arranged to receive the pin  526  therein in order to fasten the door  515  closed. 
         [0235]    In order to retain the pin  526 , the pin is secured to a spring  535  which is arranged to move within a slot  536  in the housing  510  in parallel with the movement of the securing pin  526 . The spring  535  is bent at  538  and which interferes with the slot within which it moves to retain the pin closed when the pin is in the position shown in  FIG. 47 , by interference fit. 
         [0236]    The door  515  can be entirely removed from the housing  510 , in order to mount the filter adapter ( 500  in  FIGS. 28 and 500   a  in  FIGS. 49 and 50 ). The pin  522  of the hinge  521  is removed by unscrewing using an alien key (not shown). The locking pin  526  is opened at the other side of the door  515  and the door can then be completely removed. 
         [0237]    Referring to  FIGS. 49 and 50 , these show the filter adapter  500   a  secured to the generator unit housing  510 . The filter adapter  500   a  comprises a frame  520   a  having sides  521   a  defining a front opening  522   a  in use arranged to fit over the opening  520  of the generator unit housing  510  and a rear opening  523   a  which is arranged to receive the further filter unit  502   a.    
         [0238]    The filter adapter  500   a  extends the dimensions of the generator unit so it can receive a large further filter unit such as  502   a . The further filter unit can communicate with opening  520  in the generator unit housing  510  and therefore with airways  181  and  182  ( FIG. 14   a ). 
         [0239]    The filter adapter  500   a  in  FIGS. 49 and 50  is secured to the generator unit  501  via the hinge  521  and locking pin arrangement  526 . Further adapter  500   a  comprises a receiving element  530   a  arranged to receive the locking pin  526  and a hinge arrangement  523   a  arranged to receive the hinge pin  522 . The filter adapter  500   a  also comprises a latch arrangement, comprising a latch  550  on the bottom of the housing  520   a  and a hinged latch  551  on the top of the housing  520   a.    
         [0240]    The filter unit  502   a  comprises a housing  555   a  mounting the filter  556   a . The filter housing  555   a  is provided with projections  580  on the top and the bottom of the housing  555   a  (the bottom projections cannot be seen in the drawings but are the same as the top projections). These projections fit into slots  557  on the top  551  and bottom  550  latches of the filter adapter  500   a . This is shown in  FIG. 49 . The top latch  551  is hinged on the filter adapter housing  528  by hinges  558 . The bottom latch  550  is not hinged. 
         [0241]    In operation, filter unit  502   a  is pushed into the opening  523   a  until the bottom projections  556   a  fit into slots  557  of the bottom latch  550 . The top latch  551  is hinged open and then closed about the hinge so that the slots  557  receive the top projections  556   a , as shown in  FIG. 49 , in order to secure the further filter unit  502   a  to the generator unit  501 . Gaskets  560  are provided in the filter adapter  500   a  to seal the filter adapter to the further filter unit  502   a . Alternatively, gaskets are provided on the filter housing  555   a.    
         [0242]    The filter unit  502   a  may include a powerful filter, such as a gas filter. It may include any other type of filter. 
         [0243]    The filter unit  502   a  may include an inhalation filter and an exhalation filter, so that exhaled air can also be filtered (see  FIG. 4 ). 
         [0244]    In another embodiment, the exhaled airway path  182  may be sealed and exhaled air may be exhaled out of the sides of the mask or via a separate exhalation valve (e.g. a valve at the front of the mask or elsewhere). In this embodiment,  502   a  may be an inhalation filter only. 
         [0245]      FIG. 51  shows a perspective view of a mask arrangement in accordance with an embodiment of the present invention with the further filter adaptor  500   a  fitted. A latch arm  590  is shown mounted to the arrangement by a hinge  591 . The latch arm acts in operation (as shown in  FIG. 51 ) to secure the top latch  551  in position. 
         [0246]      FIG. 52  shows an underside view of the apparatus of  FIG. 51 . A charging point  595  is arranged to receive the plug of a charger  596  in order to recharge the battery of the arrangement. 
         [0247]    Referring to  FIGS. 56 and 57 , a bypass arrangement which can be used in embodiments of the present invention, generally designated by reference numberal  800 , is illustrated. 
         [0248]    In some cases, the airflow generator may be inoperable. This may be either because it is faulty, or the user chooses to operate the breathing apparatus in a non-powered mode, or for any other reason. 
         [0249]    When the airflow generator is not operating, the air pathway passing through the air generator can result in resistance to airflow, which could make it difficult for the user to breathe. 
         [0250]    The bypass arrangement provides a bypass pathway by which air can flow when the airflow generator is not working, which avoids air flowing via the airflow generator. 
         [0251]    The bypass arrangement comprises a manifold  801  which has a first pathway  802  which allows airflow via the airflow generator. It also has a second pathway  803  which includes a bypass valve  804 . When the airflow generator is operating, the valve  804  is closed. 
         [0252]    When the airflow generator is not operating, the pressure differential is such that the user can breathe via the valve  804  and the bypass passageway  803 . 
         [0253]    In all of the above embodiments that include a circular airway (such as the embodiment of  FIGS. 3 to 5 , the exhalation path may be sealed and air may exit the apparatus via a further exhalation valve. 
         [0254]    The ability to add a further filter (in addition or instead of filters already contained within the generator unit  501 ) provides further functionality for apparatus in accordance with embodiments of the present invention. 
         [0255]      FIGS. 27 and 28  show an alternative embodiment of filter adapter  500 . This embodiment may be integral with the housing  510  of the generator unit  510  or may merely slot in a receiving opening in the housing  501  without requiring locking pin and hinge arrangement. 
         [0256]    The further filter unit  502  is arranged to slot into a rear opening  523  of the filter adapter  500 . The filter unit housing  555  is of slightly different configuration to the filter unit housing  555   a  of  FIGS. 49 and 50  embodiment. The housing  555  includes a pair of lugs  560  and  561  which are arranged to sit in corresponding receiving slots  562  and  563  in the filter adapter  500 , as shown in  FIG. 27 . 
         [0257]    A further embodiment will now be described with reference to  FIGS. 38 to 46 . This embodiment is a modification of the embodiment of  FIGS. 3 to 5 . Modifications include the addition of a head support arrangement  630 , a modified exhalation valve  601  and a modified airflow pathway compared to the embodiment of  FIGS. 3 to 5 . The airflow pathway is not “circular” via inhalation limb  160  and exhalation limb  161 . Instead, exhalation air pathway  161   a  is closed and exit of air occurs via exhalation valve  601 . A further modification comprises a supplementary power supply mounted by supplementary power supply pack  600 . 
         [0258]    Referring to  FIGS. 38 through 46 , the same reference numerals have been used for components equivalent to those already described with reference to  FIGS. 3 to 5 , and no further description will be given of these components. 
         [0259]    Referring to  FIG. 40 , the airflow pathway in this embodiment is generally as indicated by arrows A, B, C and D. Airflow is “in” via the generator unit (mounting impeller and filters)  162 , around to the mask via limb  160  (arrows B and C) and “out” via the exhalation valve  601  (arrow D). Limb  161   a  is blocked by a partition (not shown) sitting within airway  161   a.    
         [0260]    The exhalation filter  601  currently mounted at mask  150   a  is shown in detail in  FIGS. 47 and 48 . The exhalation valve  601  comprises a valve base  620 , which provides a valve seat  640 . A valve actuator  621  comprising a disc  641  and projecting arm  651 . The projecting arms  651  sits within a sleeve  652  within the valve base  620  and is retained by a spring  653  so that the disc  641  is biased to sit against the valve seat  640  and close the valve passageways  653  which communicate with the air chamber within the mask  150   a.    
         [0261]    A filter mount  622  comprising annular discs  655 ,  656  bracketing a perforated surface  657  to form an annular slot  658  for receiving the filter  623 . Disc  656  has an opening  659  facing air passageways  653  and receiving the valve actuator  621  disc  641 . 
         [0262]    The exhalation filter  623  may be a HEPA filter or any other type of filter arranged to prevent particles being exhaled into the atmosphere (e.g. virus particles attached to droplets, bacteria etc.). 
         [0263]    A filter cover  624  having a perforated outer rim  660  to allow the air to escape, covers the valve arrangement. 
         [0264]    In operation, when a user exhales in the mask, the air pressure increases sufficiently to move the valve disc  621  against the force of the spring  653  to open the communication between the air passageway  653  so that air is exhaled via the filter  623  perforation  660  in the cover. When the pressure drops the spring  653  closes the valve. 
         [0265]    This type of valve can be used for any of the embodiments described in the present invention. If allows exhaled air to be filtered so that contaminants, will not be exhaled. 
         [0266]    Referring to  FIG. 38 , in order to enable use of the PAPR for extended periods of time, a supplementary power supply is provided. A supplementary power supply arrangement  600  comprises a pouch  670  ( FIGS. 40 ,  41  and  42 ) having an opening  671  and walls  672  forming a pouch arranged to receive a power pack unit  672 . The power pack unit comprises ( FIG. 38 ) a rechargeable battery pack  673 , a battery charger  674 , a micro-control unit  675  for controlling battery charging and a user interface  676 . The connector  677  is arranged to connect the power pack unit  672  to the generator unit  162 . 
         [0267]    A flap of material  678  extends from the pouch  670  and, in use, is arranged to fit between the neck pad  164  and generator unit  162  in order to retain the pouch  670  in position. The flap  678  may include fastening means such as velcro and complementary fastening means may be provided on the neck pad  164   a  or a surface of the generator unit  162 . Alternative connection means to Velcro could be buttons, buckles or any other connection means. The fabric of the pocket may be any flexible material, neoprene or leather for example. The pocket may have an opening or transparency to allow visibility of a battery indicator. An alternative to having an opening at the top for the battery pouch could be an opening at the side so the battery could just be slid in. 
         [0268]    The embodiment of  FIGS. 38 to 46  also includes a support in the form of a headband  630 , to provide further support of the apparatus in use. 
         [0269]    The headband  630  is in the form of a fabric webbing having a portion  680 , which is webbed, and which is arranged to sit on top of the user&#39;s head in use. A pair of straps  681  and  682  extend from the webbed portion  680  and support connectors  631  and  632 . Connectors  631  and  632  are arranged to receive lugs  684  provided on the sides of connector arrangement  165 , so that the support  630  supports the apparatus in use (see  FIG. 40 ). 
         [0270]      FIG. 43  is an exploded view of the generator unit  162  of this embodiment, showing components in slightly more detail than  FIGS. 3 to 5 . Generator unit housing comprises a bottom base portion  611  and a top portion  613  that mount componentry when the base and top are closed. They also comprise a cover  610  which fits over the filter unit  185  and has perforations  700  to allow entry of air. Portion  187   a  of filter unit  185  does not have any exhalation filter as in this embodiment exhalation is via exhalation valve  601 . In other embodiments, an exhalation filter may be provided and the airway  161  opened. 
         [0271]    The housing  611 ,  613  mounts within it the onboard power supply  189 , the control unit  188  and the impeller unit  186 . 
         [0272]    The control unit  188  comprises a printed circuit board  690  which mounts the components. A cover to the printed  6  circuit board  616  may be provided for heat dissipation. The cover  616  may also include a humidifier arrangement such as described in the Applicant&#39;s earlier application. 
         [0273]    Impeller  186  is mounted on mounting  165  and air is drawn into the airway  160  via the impeller mounting  615  passageway  691 . 
         [0274]    The top part  612  of the generator unit housing comprises a control pad  613  and control pad cover  614 . 
         [0275]    The neck pad  164   a  is modified from the version of  FIGS. 3 to 5  and may comprise a cooling arrangement such as described with reference to  FIGS. 34 and 35 . 
         [0276]    A plastic insert  360  is provided (as described with reference to  FIGS. 36 and 37 ) for maintaining airway  160  open. 
         [0277]    Cover  700  may be removed in operation and a further filter adapter such as described with reference to  FIGS. 27 and 28  and  FIGS. 47 to 52  may be utilised. 
         [0278]    A further embodiment of a breathing apparatus in accordance with the present invention will now be described with reference to  FIGS. 29 through 33 . 
         [0279]    With the “neck mounted” generator unit embodiments, such as those described within reference to  FIGS. 2 to 5  and  40  to  48 , for example, the generator unit  162  is mounted tightly against the back of the neck. In some circumstances, this can make it difficult for the user to move their head freely and could cause some discomfort if worn for a very long duration. 
         [0280]    The embodiment shown in  FIG. 29  has the same componentry as embodiments of  FIGS. 3 to 5  or  39  to  46 , and no further description will be given of these components. The breathing apparatus  900  of  FIG. 29  is, however, elongated as compared with other embodiments so that the generator unit  162   a  is spaced away from the back of the neck. See particularly  FIG. 31 . A neck pad  901  is arranged to fit against the back of the neck in use, an adjustment bracket is mounted on the air way  902  and  903  (adjustment bracket reference numeral  905 ). The adjustment bracket  905  supports the neck pad  901  using buttons  906  which fit into the holes  907  on the bracket  905 . Note that bracket  905  will be on both air ways  902  and  903 . This means the affixing the neck pad  901  is illustrated in  FIG. 32 . 
         [0281]    An alternative method of affixing user&#39;s an integrated air clip  910  which is fixed to the air ways  902 ,  903  and the neck pad  901  has a strap  911  which fits through a buckle  912  on the air clip. 
         [0282]    In this embodiment, the generator unit  162   a  is spaced from the back of the neck. A pivot point  915  is created which allows the user to tilt their head. The generator unit  162   a  is free to move without inhibiting neck movement. 
         [0283]    A further embodiment of an adjusted position generator unit is illustrated in  FIGS. 53 to 55 . The generator unit shown, reference numeral  162   b  is arranged, in use to be supported by the shoulders of the user (see  FIGS. 55   a  and  55   b ). The generator unit  162   b  may support a gas filter cartridge  920 . 
         [0284]    A central portion of the generator unit  162   b , is contoured ( 921 ) to follow the contour of the neck and shoulder. A larger weight can be comfortably supported by the shoulders than the neck. It enables comfortable, long term wearing of the breathing apparatus and the ability to be able to tilt the head comfortably. 
         [0285]    As discussed above, embodiments of the breathing apparatus of the present invention may implement a breath responsive control, so that the air pressure may vary with the breathing rate. The motor power (fan motor) may also vary during the breathing cycle. In any breathing cycle, there is a breathing interval, a pause where there is no breathing, and exhalation interval. 
         [0286]    Breath responsive embodiments of the present invention may take into account rate of breathing as well as varying motor control during a breathing cycle. 
         [0287]    Referring to  FIGS. 58 through 61 , embodiments of the present invention implement a responsive flow control algorithm consisting of control functions for the exhalation positive air pressure (EPAP) and the inhalation positive air pressure (IPAP). In the EPAP control function (see  FIG. 59 ) a breath responsiveness program is implemented, the program detecting the start of inhalation at the end of the EPAP state and calculating boost pressure based on the product of the breathing effort and the user gain setting to be used for the IPAP state following the EPAP state. The cycles of the EPAP and IPAP repeat breath by breath. 
         [0288]      FIG. 58  and  FIG. 59  are flow diagrams showing the control algorithms.  FIG. 60  shows graphs comparing mass pressure with motor power.  FIGS. 61A and 61B  show the mask pressure waveforms during the breathing cycle. 
         [0289]    The breath responsiveness control program is based on the product of the breathing effort and the user gain setting (the user may manually set what air pressure they wish to have). The higher the product, the higher the responsiveness. Breathing effort is calculated by measuring the pressure drop in a defined period after the mask pressure goes below the set pressure point for the EPAP. The gain setting is user selectable, the higher setting leading to higher sensitivity of the blower output to the breathing effort.  FIGS. 58 and 59  illustrates steps for the breath responsiveness control.
       For a given Gain setting, the higher the pressure dips at the start of the inhalation, the higher the breathing effort.   For a given Gain setting, if the breathing effort is sufficiently large, the blower tends to reach its maximum capacity.   With a higher Gain setting, the same breathing effort can lead to higher flow responsiveness, for saving breathing effort.   With a higher Gain setting, the pressure dips at the start of the inhalation is relatively less, thus the minimum mass pressure is higher and more suitable for higher exertion work or for persons with higher lung capacities while it may be felt irritating for lower lung capacities.   With higher Gain setting, average IPAP pressure is higher at a cost of more battery consumption.   For light work, or for persons with lower lung capacities, a lower Gain setting may be more comfortable and the blower may be quieter and the battery will last longer.       
 
         [0296]    For embodiments of the present invention, the mass pressure range is from 0.1 cm H 2 o to 3.5 cm H 2 o. Target EPAP pressure may be from 0.5 cm 1 cm H 2 o. The target inhalation pressure is variable depending on breathing effort and user comfort setting, and is higher than 1 cm H 2 o and up to 3.5 cm H 2 o. 
         [0297]    As discussed above, control of the breathing apparatus may include software control. Software control may include:
       Predictive software to predict when the filter is blocked. As the resistance of the filter becomes higher, the blower may have to work harder.   Blower flow capability checking. Utilising a built-in flow meter provides a way for the user to check the flow capability of the respirator before each use.   Altitude compensation for filter blockage detection capable up to plus or minus 3000 meters.   Auto pressure sensor zero offset calibration.   Manual pressure sensor zero offset calibration.   Low battery audible alarm.   Breath responsiveness settings.   Internal battery charger and indication.   Filter blockage detection both during breathing and mask off.   Air temperature control (heating and cooling).   Air humidity control.   User access to usage info via Bluetooth, such as use hours, breathing rate, filter usage, title volume, etc.       
 
         [0310]    It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention.