Abstract:
Apparatus for use in delivery of gas capable of combustion that incorporates a safety valve unit. The safety valve unit closes the flow path of the gas from the source upon occurrence of a fire. The safety valve unit has a valve body, a valve head resiliently biased towards a valve-closure position and a fusible retainer that holds the valve member in a valve open position. The valve body defines a fluid flow passage between an outlet and the valve head. Within the fluid flow passage there is an elongate link member which extends from the valve head to the foot. The foot engages the fusible retainer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT Application No. PCT/GB2007/004872 titled Apparatus and Instruments for Handling Gas and Incorporating a Safety Valve Unit, filed Dec. 19, 2007 which claims priority to Great Britain Application No. 0709683.7 filed May 21, 2007, which claims priority to Great Britain Application No. 0625585.5 filed Dec. 21, 2006. 
     FIELD OF THE INVENTION 
     The invention relates to gas handling and distribution and in particular to a gas handling apparatus incorporating a safety valve. 
     RELATED ART 
     Disclosed herein is an apparatus and instrument for handling gas capable of combustion or of supporting combustion, and incorporating a safety valve unit and is specifically, but not exclusively, concerned with such apparatus and instruments as are used in association with respirators for supplying oxygen to patients both in hospitals, by emergency services, and more particularly in the domestic environment where awareness of the danger resulting from the use of an oxygen enriched environment may not be so readily appreciated. 
     The provision of supplementary oxygen for patients suffering from acute respiratory disorders is becoming more widespread. The delivery of such oxygen to the patient is usually effected by an interface such as a nasal cannula, a face mask or even an endotracheal tube. The oxygen is supplied to the interface unit by flexible plastic tubing from a source of oxygen. 
     Oxygen may be supplied in one of three ways, namely in compressed form in cylinders, from concentrators which extract oxygen from the atmosphere, or as liquid oxygen in a Dewar flask. Such sources are coupled typically via a plastic line to a face mask, nasal cannula or endotracheal tube. 
     Clinical experience, and experience in the home has established that the risk of fire when using such oxygen delivery apparatus is particularly significant since the exposure of the apparatus to a combustion igniting event such as an electrical short circuit, a faulty cooking element, open flames such as candles, matches or cigarettes can result in ignition with a flame starting as an external fire supported by oxygen leaking from the delivery apparatus, and then moving to the interior of the tubing and migrating rapidly upstream towards the oxygen source. The fire hazard resulting from the use of oxygen delivery apparatus is exacerbated in the domestic environment, where such therapy is ever more frequently utilised, because the use of the oxygen is not supervised by health care workers, and even the presence of mandatory smoke detectors, fire alarms and other such safety equipment, cannot mitigate the risks due to the rapidity of conflagration once triggered. The risk of catastrophic fires, especially due to careless use of such apparatus, is very much higher in the case of patients who smoke since there is a temptation for the patient to discard the oxygen delivery mask or cannula, leaving it lying in the vicinity, whilst a cigarette is smoked. Most oxygen delivery apparatus is set to deliver oxygen continuously at a rate determined by the needs of the patient, and removal of the delivery interface from the patient&#39;s airways does not cause the delivery of oxygen to cease. In such circumstances an oxygen-enriched atmosphere can build up around the patient, investing any bedding or furnishing materials, and preparing the environment for a catastrophic conflagration upon ignition by even the smallest spark. 
     There is therefore a need for apparatus and/or procedures to prevent or avoid fire occurring as a result of material ignited in an oxygen-enriched environment, in the proximity of the patient using such a respirator. 
     Further, the patient interface component of respiratory equipment such as facemasks and nasal cannulas are usually disposable and therefore there is a great incentive for any safety equipment associated with it to be inexpensive and easy to install. There is also a requirement for any safety valve units to be so formed that they do not weigh down on a supply line and pull on connections causing them to become loose, and also so that that a safety valve unit connected close to a mask or nasal cannula does not cause the patient undue discomfort due to its weight. Although it is known to provide safety valves for inserting in a gas delivery line, the present invention seeks to address the problem by devising a way in which a safety valve can be effectively and easily incorporated into a component of the system whilst remaining accessible for checking and easy replaceability. 
     SUMMARY 
     According to the present invention there is provided apparatus for use in delivering a gas capable of combustion or of supporting combustion incorporating a safety valve unit for closing the flow path of the gas from the source thereof upon the occurrence of a fire. 
     In a preferred embodiment of the invention, the safety valve unit is formed as a removable assembly having a connector nozzle by which the apparatus is connectable to the gas delivery line thereof. 
     Likewise it is preferred that the safety valve unit is removably connectable to the body of a component of the gas delivery apparatus or an ancillary unit associated therewith and connected in line with the gas delivery path of the apparatus. The said component part or ancillary unit may be, for example, a gas flow meter, a flow or pressure regulator, a patient interface (in the case of oxygen delivery respiratory support apparatus). 
     The safety valve unit itself may comprise a valve body, a valve member having a valve head resiliently biased towards a valve-closure position and a fusible retainer holding the valve member, against the bias, in a valve-open position, the valve body defining a fluid flow passage, between an outlet and the said valve head, within which is an elongate link member extending from the valve head to a foot, which engages the fusible retainer. 
     The elongate link member may be a generally laminar or flat element. Alternatively the elongate member may take the form of a substantially cylindrical element or a tapered cylindrical element. The elongate link member may be integral with the valve head or, alternatively, may be a separate element. 
     The valve head may further include a sealing member. The sealing member and the valve head may be arranged to co-operate such that the sealing member seals against the wall of the fluid flow passage when the valve member is in the closure position. The sealing member may take, for example, the form of a substantially spherical ball element, and the valve head may be shaped to seat the sealing member. 
     Alternatively, the valve head may have an annular recess and an annular sealing member disposed therein to form a seal between the valve head and the wall of the fluid flow passage when the valve member is in the valve closure position. 
     At least a portion of the surface of the valve head may be formed of a suitable material, to form a seal between the valve head and the wall of the fluid flow passage when the valve member is in the valve closure position. The whole of the head itself may be formed from such a material. Alternatively, the sealing member may be formed of a suitable material for form a seal against the wall of the fluid flow passage when the valve member is in the valve closure position. 
     The foot may comprise at least one lateral protrusion. However, the foot may comprise two or more lateral protrusions, which are preferably diametrically opposed across a plane of symmetry of the elongate link member. 
     The fusible retainer may be in the form of an inwardly directed annular flange arranged to retain the foot of the valve member within the hollow body. The fusible retainer may be formed from heat susceptible material, which may be selected from thermoplastic materials, solder and waxes. In a preferred embodiment the fusible retainer is formed from a thermoplastic material, such as, for example, polyvinylchloride (PVC). 
     The valve member may be resiliently-biased by a coiled compression spring mounted within the hollow body and compressed between an internal annular rim provided by the valve body and an annular shoulder of the valve head. 
     In another aspect, the present invention provides apparatus in which the foot comprises at least one lateral protrusion. 
     Valves according to the present invention may be adapted to connect directly to a component part of or ancillary unit associated with the gas delivery apparatus. The safety valve unit may, for example, be directly connectable to a Flowmeter. 
     In such valves the means for securing the body of the valve to a component part of or ancillary unit associated with the gas delivery apparatus comprises a hollow tubular spigot for introduction into an opening in the body of the said component or ancillary unit, gas-tight sealing means on the said spigot and means for retaining the spigot in position within the opening in the said body. The said means for retaining may comprise one or more lateral projections for forming a bayonet type coupling. Alternatively, the said means for retaining comprises a screw threaded portion for engaging a corresponding screw thread in the opening. 
     The present invention also encompasses a respiratory support apparatus incorporating such a safety valve. 
     Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. By way of example only, embodiments of the present invention are described in relation to the accompanying drawings, in which: 
         FIG. 1  is a front view of a flowmeter incorporating a safety valve unit in accordance with the present invention; 
         FIG. 2  is a perspective view of a nasal cannula delivery respiratory support system incorporating safety valves in accordance with the principles of the present invention; 
         FIG. 3  is a perspective view of a face mask patient interface device for a respiratory support system incorporating a safety valve in accordance with the present invention; 
         FIG. 4  is a perspective view of a safety valve in accordance with the present invention, adapted to fit onto a component part or ancillary unit of gas delivery apparatus; 
         FIG. 5  is a perspective view of an alternative form of safety valve unit adapted to fit a component part or ancillary unit of gas delivery apparatus; 
         FIG. 6  is an axial section through a further safety valve unit formed in accordance with the principles of the present invention; and 
         FIGS. 7 ,  8  and  9  are perspective views of alternative forms of safety valve unit in accordance with the present invention, adapted to fit onto a component part or ancillary unit of gas delivery apparatus; and 
         FIG. 10  is an exploded perspective view of the safety valve unit of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings and particularly to  FIG. 1 , there is shown a flowmeter generally indicated  11 , intended to form part of gas delivery apparatus adapted as respiratory support system for delivering oxygen from a source (not shown) which is connected by a flexible line generally indicated  12  to an inlet nozzle  13  projecting from a generally cylindrical body  14  of the flowmeter. 
     From the body  14  of the flowmeter projects a control knob  15  which is turnable to control the rate of flow of gas through the unit. Projecting upwardly from the body  14  is a hollow, cylindrical flow-indicator body  16  having a transparent window  17  through which the interior passage of the indicator body  16  can be observed. Within this passage is located a lightweight ball generally indicated  18 . In use of the flow indicator gas arriving at the inlet  13  is passed up the interior passage  17  within the indicator body  16 , carrying with it the lightweight ball  18 . The gas is then passed down a passage (not shown) back to the body  14  from where it exits through an outlet generally indicated  19 . The outlet  19  is formed as a safety valve  20  having an outlet nozzle  21  to which can be connected a flexible line generally indicated  22  leading to the delivery outlet of the gas delivery apparatus, which may, in the case of respiratory support apparatus, be a nasal cannula device as shown in  FIG. 2 , or a facemask as shown in  FIG. 3 . 
     The safety valve  20  is one having a heat-sensitive element located in the connector nozzle  21  which, should the patient initiate a fire at the delivery end of the apparatus, for example by smoking, detect the rise in temperature as the flame front approaches along the line  22  and fuse to allow a valve element within the unit  20  to close thereby isolating the flowmeter  11  and the remainder of the delivery apparatus, including, especially, the source of combustion-supporting gas (usually oxygen) from the fire. 
       FIG. 2  illustrates the delivery end of the apparatus a part of which is shown in  FIG. 1 , this comprising two parallel flexible lines  23 ,  24  which lead from the single line  22  (by means of a branching or twinning device (not shown)) which are held together by means of a sleeve  25 . End portions  26 ,  27  of the lines  23 ,  24  are formed into a loop and connected, via respective safety valves  28 ,  29  to a nasal cannula  30  of known type having two parallel outlet nozzles  31 ,  32  which are, in use, introduced into respective nostrils of a user. The safety valves  28 ,  29 , like the valve  20  in the embodiment of  FIG. 1 , act to detect a rise in temperature indicating that a fire has started, and close to isolate the remainder of the system from the source of the fire. By positioning the valves  28 ,  29  close to the nasal cannula  30  a rapid response to the initiation of a fire can be achieved. In an alternative embodiment, not shown, these valves may be positioned further down the lines  26 ,  27  or in the sections  23 ,  24  of the lines upstream of the sleeve  25 . 
     In the embodiment of  FIG. 3  the line  22  is shown connected by a safety valve  33  to a facemask  34  having a normal configuration with a padded rim  35  and elasticated retaining band  36 . 
     As with the safety valves  28 ,  29  of the embodiment of  FIG. 2 , the valve  33  senses a rise in temperature indicating that a fire may have started and closes communication with the line  22 . This is particularly important in circumstances where, for example, the respiratory support apparatus of which the facemask or nasal cannula (in the embodiment of  FIG. 2 ) are used in the home without close clinical supervision since a forgetful patient may remove the mask or cannula and place it on the bed or chair next to him or her, and then engage in some activity, such as smoking, lighting candles or the like which might cause ignition of the gas leaking from the open end of the delivery apparatus. It will be appreciated that, in the majority of cases, the oxygen delivered through the line  22  is emitted at a metered rate suitable for the patient during inhalation, but continues during exhalation at the same rate so that the atmosphere around the patient becomes oxygen-enriched whilst the apparatus is in use, and, of course, should the delivery outlet be put down away from the patient, the flow of gas continues unabated unless turned off at a main control valve. 
     The present invention also comprehends safety valves adapted to be fitted directly to the body of a pressure regulator, flowmeter or other item of a gas delivery system. In the embodiment of  FIG. 4 , a safety valve, generally indicated  37  is formed in two parts,  38 ,  39  which can be fitted together, for example, by screwing. The part  38  comprises substantially a hollow cylindrical spigot having an open or mouth end  40  with a circumferential annular groove in its vicinity, housing an o-ring seal  41 . A major portion  42  is threaded, and a radial hand grip  43  is provided at the end remote from the mouth  40  to assist not only in securing the safety valve  37  in position on the component to which it is intended to be fitted, but also to assist in connecting the second component  39  thereto. This second component  39  comprises a generally cylindrical body portion  44  with two opposite radially projecting luggs  45 ,  46  serving as hand grips, and having a hollow nozzle  47  in axial alignment with the hollow spigot. A typical interior construction of the safety valve will be described in more detail in relation to  FIG. 6 . 
     Turning now to  FIG. 5 , the further embodiment comprises a main body portion  48  from which projects a nozzle  49  corresponding in function to the nozzle  47  in the embodiment of  FIG. 4 . 
     Projecting radially from the body  48  are two radial projections  50 ,  51  which form part of a generally electicle enlargement of the body  48  and serve as a hand grip for fitting and removing the safety valve. Projecting axially in the opposite direction from the nozzle  49  is a hollow tubular spigot  52  which, like the embodiment of  FIG. 4 , has an open mouth  53  and an o-ring seal  54  housed in a circumferential annual groove adjacent to the open mouth end  53 . 
     Projecting laterally from the cylindrical body of the spigot  52  is a radial boss  55  which, when the valve is fitted to a component in the gas delivery system, engages within an axial slot and, upon turning of the body  48  by means of the luggs  50 ,  51  forms a bayonet-type coupling within the apparatus. 
     Turning now to  FIG. 6  shows an exemplary interior structure for the safety valve. It is to be understood, however, that the interior structure of the safety valves referred to in the embodiments of  FIGS. 1 to 5  may not necessarily be identical to this and that other safety valve configurations, for example that known from the applicants own earlier patent application number GB0624524.5 may be employed. 
     In  FIG. 6  it can be seen that the valve shown has a body  56  with a cylindrical main body portion  57  from which projects a nozzle  58  in one direction and a hollow spigot  59  in the other. The open end of the spigot  59  receives an annular cap  60  with a central opening  61  which defines an annular shoulder  62  the function of which is to engage one end of a spring  63  which urges a valve shutter  64  towards a valve-closure position as will be explained in more detail below. 
     The opposite end of the spring  63  acts upon the valve shutter member  64  which is mounted within the valve body  57 . The valve shutter member  64  comprises a head  65  integrally formed with an elongate link member  66  which extends through the nozzle  56  and terminates in a foot  67 . The elongate link member  66  is generally planar while the head  65  has a conically tapering neck portion  68 , shaped to correspond with an annular valve seat  69  formed on the internal surface of the body  57 . The head  65  has an annular recess  70  defined between the neck portion  68  and a shoulder  71 . 
     The end of the spring  63  bears against the shoulder  71  and the recess  70  accommodates a resilient sealing o-ring  72 , the function of which is described below. 
     The foot  67  of the elongate link member  66  bears against a fusible retaining member in the form of a collar  73  which is mounted at the exit end of the nozzle  58 . The retaining collar  73  has a sleeve portion  74  and an annular end portion  75 . The sleeve portion  74  fits within the open end of the nozzle and has lugs which form a snap fit with rim recess on the inside surface of the body. The annular end portion  75  provides a radially inwardly extending shoulder or rim  76  against which the foot  67  bears. 
     The retaining collar  73  is formed of a material which is sensitive to heat and softens or fuses at the temperatures such as may be caused by flashback and/or ignition of a gas. At the same time, the material must have sufficient strength that, in use, it retains its structural integrity within the exit end of the nozzle section against the compressive force of the spring  63  acting thereon by way of the valve member  65 , the link  66  and the foot  67 . Suitable materials are some thermoplastics such as, for example, polyvinylchloride (PVC), and materials such as waxes and lead free solder. 
     The internal surface of the body  57  defines the annular shoulder  69  which is of generally frusto-conical form. The tapered annular shoulder is arranged to be engaged by the O-ring  72  in the event of fusing of the collar  73 , due to its exposure to excessive heat, for example, due to fire or explosion in its vicinity. 
     In use the safety valve of the present invention is fitted between the circuit from a pressurised gas supply such as that commonly used in the home for those requiring oxygen to assist a patient&#39;s breathing, and a respiratory support device, such as a mask or nasal cannula. The gas supply may be in the form of an oxygen cylinder which provides oxygen for enrichment of normal oxygen intake by admixture with ambient air, or may be in the form of a source of oxygen-enriched air, both being under pressure. The pressure of the supply to the patient is regulated by suitable pressure regulators (not shown). The valve unit according to the invention is, in use, positioned so as to ensure that in the event of the oxygen or oxygen-enriched air igniting, this supply can be cut off quickly. To this end, if the collar  73  softens in the event of increased temperature to an extent such that it weakens sufficiently no longer to resist the force of the spring  63 , the spring will overcome its resistance, thereby moving the valve member immediately to urge the sealing ring  72  against the annular shoulder  69 , thereby closing the valve unit. 
       FIGS. 7 ,  8  and  9  share various features with the forms of safety valve unit shown in  FIGS. 4 and 5 . The safety valve unit of  FIG. 7  is an alternative version of the safety valve unit of  FIG. 5  and the safety valve unit of  FIG. 8  is an alternative version of the safety valve unit of  FIG. 4 . The same numbering conventions have therefore been used in relation to these figures where appropriate. In the embodiment of  FIG. 9 , the safety valve, generally indicated  37  is formed in two parts,  38 ,  39  which can be fitted together, for example, by screwing. The part  38  comprises substantially a hollow cylindrical portion having an open or mouth end  40 . The second component  39  comprises a generally frustroconical body portion  44  and has a hollow nozzle  47  in axial alignment with the hollow cylindrical portion  38 . 
       FIG. 10  is an exploded perspective view of the safety valve unit of  FIG. 8 . It will be appreciated that it illustrates an alternative exemplary interior structure for the safety valve. 
     It can be seen in  FIG. 10  that the valve shown has a body  56  with a cylindrical main body portion  57  from which projects a nozzle  58  in one direction and a hollow spigot  59  in the other. As described in relation to  FIG. 6 , the open end of the spigot  59  receives an annular cap  60  with a central opening which defines an annular shoulder (not shown) the function of which is to engage one end of a spring  63  which urges a valve shutter  64  towards a valve-closure position as will be explained in more detail below. 
     The opposite end of the spring  63  acts upon the valve shutter member  64  which is mounted within the valve body  57 . The valve shutter member  64  comprises a head portion  65  integrally formed with a substantially cylindrical tapered elongate link member  66  which, in use, extends through the nozzle  56  and terminates in a foot portion  67 . The elongate link member  66  is generally cylindrical and tapered. The head portion includes a cup shaped seat (not shown) formed to receive a substantially spherical ball sealing element  77 . 
     The end of the spring  63  bears against the sealing element  77 , the function of which is described below. 
     The foot  67  of the elongate link member  66  bears against a fusible retaining member in the form of a collar (not shown) which is mounted at the exit end of the nozzle  58 . The retaining collar has a sleeve portion and an annular end portion as described in relation to  FIG. 6 . The sleeve portion fits within the open end of the nozzle and has lugs which form a snap fit with rim recess on the inside surface of the body. The annular end portion  75  provides a radially inwardly extending shoulder or rim against which the foot  67  bears. 
     The retaining collar is formed of a material which is sensitive to heat and softens or fuses at the temperatures such as may be caused by flashback and/or ignition of a gas. At the same time, the material must have sufficient strength that, in use, it retains its structural integrity within the exit end of the nozzle section against the compressive force of the spring  63  acting thereon by way of the valve member  65 , the link  66  and the foot  67 . Suitable materials are some thermoplastics such as, for example, polyvinylchloride (PVC), and materials such as waxes and lead free solder. 
     The internal surface of the body  57  defines the annular shoulder  69  which is of generally semihemispherical form. The tapered annular shoulder is arranged to be engaged by the sealing element  77  in the event of fusing of the collar, due to its exposure to excessive heat, for example, due to fire or explosion in its vicinity.