AU727439B2 - Trigger for flame front extinguishing - Google Patents

Description

.i I/UU/U1 28/5/'9 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: TRIGGER FOR FLAME FRONT EXTINGUISHING The following statement is a full description of this invention, including the best method of performing it known to us <Ref:Enid\Sub\Spath.sp3 This invention lies in the field of the extinguishing of flame fronts of the general nature which can arise in the context of explosions, of fireballs, of gas based fires, of coal and other organic material dust based fires, liquid based fires and other fires, especially fires having very high speed propagation fronts. An example is in the field of underground mining where combustible mixtures of gases or of dust with air can give rise to conditions conducive to explosion or the very high speed spread of flame fronts.

A particular application contemplated for this invention is in the extinguishing of fires and explosions in mining, for example, explosions which occur in coal mining due to methane gas and coal dust igniting with surrounding air in an explosive mixture. The invention is, however, not limited to this example of an application.

A methane and/or coal dust based explosion in underground mining is an appalling phenomenon. A flame front can typically advance along an underground tunnel or stope at 100 metres per second, the flame being at approximately 2000'C and accompanied by a pressure shock wave. Heat radiated by the flame front or fireball causes second degree and higher skin burns in humans and human organs may not survive the pressure shock wave which accompanies it. Should :i miners survive the initial effects, the catastrophic depletion of oxygen levels in the stope are likely to result in death due to asphyxiation within a short period following the shock wave.

In order to attempt to deal with such phenomenon the extinguishing of the flame front or fireball within very short periods of time is essential.

For example, it becomes necessary to detect a flame front and extinguish it within 200 milliseconds.

Proposals have been made for the dispersion of the chemical agents with an inert gaseous propellant to "knock-down" or quench a fire or 1 flame front or fireball. Such chemicals may be based on free radical 11 If actions and on physical actions, for example, endothermic reactions to the flame front.

Whereas gases of the halogen family such as halons have been proposed for this type of fire fighting these are preferred not to be used in view of their ozone depletion potential.

An example of a substitute for these types of chemical agents is one styled "NAF S-Ill" (trademark) a product of Sege Stabilimento of Rome, Italy.

The present invention provides a system of dealing with the extinguishing of flame fronts moving at high speed in conditions typical of underground mining conditions including, for example, in particular coal mines.

Despite the very fast speed of propagation of a flame front in conditions such as this it is a remarkable fact that it is within the reach of modern technology to address such events in a manner which effectively douses the flame front and/or explosions. The technology employed has, generally speaking, three main areas, the first is detection of an incipient explosion or fireball or advancing flame front, secondly the deployment of the dousing medium and thirdly the dousing or extinguishing effect of that medium upon the combustion taking place. The technology in each of these areas must complete the respective task within an extremely short time of the order of 0 milliseconds.

With reference to these three main areas of technology, a first aspect of the present invention is concerned area of detection and a second aspect with the area of deployment of the dousing medium.

Apparatus in accordance with a first aspect of this invention comprises a set of detectors selected from optical detectors, fire wire circuits, pressure transducers and others, a control unit providing logic processing of flame front detection and a distribution unit providing extinguishing commands to activate a set of extinguishing units I.r selected from suitable chemically acting, for example, free radical acting, endothermic, thermal capacity and latent heat based physical effects tending to dowse a flame. The detectors are adapted to all provide the detection signals to the control unit, the control unit adapted to analyse the signals received and to make decisions according to the nature of the signals and subject to the nature and locations of the detectors and to provide a command signal to the distribution unit which in turn will distribute commands for the application of extinguishing materials.

A feature of the invention is the use of detectors either singly or in selected combinations in the wave bands of 190 to 230 nanometers (which is not disabled by water), 860 nanometers and 4400 nanometers; suitable software will assess signals from these detectors for the decision to implement dousing of a flame front.

A further feature in accordance with the invention has been the placement of detectors in a mining stope in an anticipated up-stream position in relation to an advancing flame front by a calculated distance from an array of bottles with extinguisher material in them under pressure. This spacing between the detectors and the extinguishing materials is calculated in accordance with anticipated speeds of approach of a flame front to provide for the efficient dowsing and safe dowsing of the flame front, preventing any risk of it passing through the flame dowsing area.

The invention is, however, also applicable in areas other than a flame front advancing down a stope at high speed. For example, the invention can be applied as a safety measure mounted upon underground mining machinery, such as continuous miners.

It will be understood that the dousing medium can in broad principle comprise any substance which has the capacity and properties to extinguish combustion in the form of an explosion or a flame front and these media are generally classifiable into liquids, gases, powders and foam. Substances in these various classifications exhibit various speeds or rates of extinguishing and in the very short total time frame 4 I permitted effectively to deal with the kind of events discussed the rate of extinguishing must be carefully addressed. Before, however, the extinguishing process can commence there is required the deployment of the material in the necessary space, the time required for this event to occur is a material consideration affecting the choice of the extinguishing substance. Thus if the triggering and release for deployment is relatively speaking slow then an extinguishing medium has to be selected which is exceptionally fast acting. It is an unfortunate fact that the exceptionally fast extinguishing media tend to be more expensive and are often characterised by endothermic chemical activity rather than the more simple thermal activity, for example, of a water spray or stone dust. Conversely if the deployment can be speeded up less expensive substances can be used.

A deployment practice adopted in this field is to provide the extinguishing medium under very high pressure in a high pressure steel bottle with a triggering mechanism to trigger release of the substance from the bottle from which it is then sprayed at very high velocity into the region in which the extinguishing effect is required. For example, it may be designed to spray a "curtain" across a mine tunnel or stope to arrest a very high velocity flame front progressing along that space.

The twin requirements of leak free containment of the substance o under very high pressure and on the other hand a very rapid and "reliable release of that substance after what may be a very long period of monitoring are mutually contradictory and the reconciling of these has given rise to considerable difficulty. A solution which has been adopted is to seal the material under high pressure within the bottle behind a membrane which is fitted across an outlet passage from the bottle, the membrane to be broken when it is required to release the substance. Although this approach addresses significant requirements it has introduced a disadvantage in that the membrane S. fragments into shrapnel which, driven by the very high pressure material such as gas is dangerous and would cause serious injury to any persons unfortunate enough to be in the area at the instant of triggering.

The invention therefore provides a valve for use with a pressurized container of a flame-dowsing substance in a flame front extinguishing system, said valve including: a valve body containing a passage which is adapted to communicate with the container; a piston retained in a sealing position within the passage by a sear and movable by pressure in the container to an opening position wherein the container is vented through the passage, when released from the sealing position by actuation of the sear; and a pyrotechnic trigger mechanism including an electronically ignited charge and a pin adapted to actuate the sear on ignition of the charge thereby to release the piston to move in the passage in the valve body to the opening position.

The term "sear", originally used for a catch in a gun-lock mechanism released by pressure on a trigger, is here used in the sense of a mechanical 15 catch which when moved releases a retained component. The sear may goo: include a shaft intersecting the passage and partially flattened so that the shaft :0 0 is rotatable to a position whereby the piston is free to move in the passage.

0:0. Preferably, the passage includes a cylinder in which the piston is movable, having a first portion in which the piston seals and a second portion of larger 0o: 20 diameter than the first portion in which the piston is non-sealing and to which oego the piston moves during opening, the piston finally moving into an enlarged chamber to allow high velocity discharge of a substance under pressure from the container.

The pyrotechnic trigger mechanism may include a cylinder with the pin 25 projecting therefrom and containing the charge, an electrical fuse adapted to ignite the charge to drive the pin outwardly relative to said cylinder, and an electrical connection to the fuse.

It is preferred that the pyrotechnic trigger mechanism is one of two simultaneously triggerable pyrotechnic trigger mechanisms for redundancy, and therefore enhanced reliability.

The valve may be provided with a component connected to the valve body hich component includes a buffer adapted to receive the piston in a shock- 6 absorbing manner to reduce rebound of the piston after opening of the valve.

The buffer may include a hollow cone with an integral base. The piston may have a flange which, as the piston approaches the buffer, hooks under an elastomeric shoulder included in said component so that the piston is retained by said component without rebounding. There may be secured between the valve body and the said component, a distribution "fan" including a stack of coaxial rings separated by spacers thereby to define peripheral outlets for material vented from the container.

In any of the forms disclosed above, the valve may be provided with a diffuser head or "fan" through which the substance in the container is deployable by operation of the valve.

It is particularly preferred to provide apparatus for extinguishing flame fronts including: a set of detectors selected from at least optical detectors, fire wire circuits, pressure transducers; a control unit providing logic processing of 15 the detector outputs for flame front detection; a set of one or more extinguishing units which include pressurized containers containing a flame dowsing substance; and a distribution unit, wherein a said extinguishing unit includes a valve in any one of the forms disclosed above for venting the substance contained in the said extinguishing unit to tend to dowse the flame 20 front, the said valve being operable by the distribution unit in response to a command from the control unit.

The said flame dowsing substance may be selected from suitable substances which are chemically acting endothermic, or which are based on .thermal capacity or latent heat effects. The said flame dowsing substance may 0 25 be selected from gases, extinguishing powder, water or stone dust.

The detectors may be placed in a mining stope or tunnel in an anticipated upstream position in relation to an advancing flame front by a calculated distance from an array of the extinguishing units.

The said valve of the or an extinguishing unit may be connected by a branch connection to a nozzle.

Within the scope of the invention is a method for extinguishing a flame front using apparatus according to any one of the forms disclosed above, which method includes assessing detection signals from the said detectors by means of a computer controlled by software, making a decision to deploy a flame dowsing substance and issuing a command signal which results in actuation of extinguishing units. A computer programmed to execute this method is also within the scope of the invention.

The invention will be more fully described by way of examples with reference to the accompanying drawings in which: Figures 1 to 7 are referred to in the description of example of tests conducted in relation to the invention, Figures 1,3, 4 and 5 showing arrangements of apparatus, and Figures 2, 6 and 7 showing graphical representations, *"o Figures 8 to 37 show valve and trigger mechanisms, Figures 8 to 34 showing components, and Figure 35 an assembly of a first trigger and valve, in which Figure 8 is a perspective view of a valve and trigger mechanism in accordance with the invention attached to a steel bottle containing high pressure extinguishing gas, Figure 9 is a partial sectional elevation of the valve and trigger device 20 with attached deployment baffles, Figure 10 is a side elevation of the means shown in Figure 9, Le.

Figures 11 to 17 are various views of the body of the valve mechanism, Figure 11 being a section on Section AA of Figure 12, e *e eoo15 eo e .o o o Figure 12 being a rear elevation, Figure 13 being a side elevation, Figure 14 being a front elevation, Figure 15 being a section on BB in figure 11, Figure 16 being a-plan view, Figure 17 being a section on CC in figure 14, Figure 18 is an axial section of the piston used in the body, Figure 19 is a view of the sear, Figure 20 is an end on view of the sear with attached detent which is acted on by the trigger, Figures 21 to 24 show components of the trigger mechanism, Figure 21 showing the pin, Figure 22 showing the cylinder in which the pin moves, Figure 23 showing the chamber for the pyrotechnic charge, and Figure 24 showing the end closure for the chamber access hole for the electric fuse, Figures 25 to 28 showing an adaptor for the valve housing for the case where the medium is to be directed to a nozzle, Figure 25 being an axial section of the adaptor body, Figure 26 being a plan view of the adaptor, Figure 27 being an underneath view of the adaptor, Figure 28 being a closure cap for the adaptor, Figures 29 and 30 showing shock absorbing components for the piston which are mounted in the adaptor, figure 29 showing a cone and figure 30 showing a socket, Figures 31 to 34 showing an enclosure housing used for the valve and trigger mechanism, Figure 31 showing a section on AA of figure 32, Figure 32 showing an elevation on a left half of the housing, Figure 33 being a plan view on a right half of the housing, and Figure 34 being an elevation on the right half of the housing, Figure 35 is an axial cross sectional elevation of the valve with trigger mechanism in accordance with an embodiment of the invention, and Figures 36 and 37 an assembly of a second trigger and valve.

In figure 1 a particular test set up is illustrated. In an underground mining stope 1 a methane charge was place in the end of the tunnel at 2 with a curtain 3 simply to facilitate containing the methane until the moment of commencement of the test. The remainder of the tunnel was charged with coal dust and at a position 82 metres from the methane store, the position being indicated at 4, a test set up for extinguishing a flame front was produced.

In this test the advancing flame front was finally put out at a distance of 105 metres, that is 0,3 seconds after the sensor triggered the flame.

In this regard figure 2 shows a graphical representation of test results on a further test dealing with a 9% methane explosion. In this case the flame front was suppressed and a coal dust explosion was stopped. This is indicated in the four sets of graphs on figure 2. In the graphs the abscissa is time and the ordinate is a measure of flame intensity.

Figure 3 shows the set up of extinguishing units used in the test described with reference to figure 1. At the position of 82 metres in the test tunnel an array of gas bottles was provided containing the extinguishing material. These were bottles containing extinguishing chemical at a pressure of 62 bars, the design of the bottles allowing them to be opened within 5 milliseconds and to remain open for a 120 millisecond discharge of material. This was a chemical capable of providing a 75% cooling effect by physical processes and 25% by free radical or similar chemical processes. It must be mentioned than an alternative extinguishing material or an additional extinguishing material which can be used in the context of this invention includes water. Here water could be pressurised, for example, to 100 bar or more to provide the necessary high velocity discharge.

Referring again to figure 3 the discharge nozzles were angled towards the expected approach of the flame front and they were distributed around the stope to spread the supply of extinguishing material and completely enclose the cross section of the stope with a curtain of extinguishing material within milliseconds. In this experiment an optical sensor was used capable of detecting a flame front within approximately 1 millisecond. The optical detectors were placed at a ool° position that within 40 milliseconds the flame front would pass from the sensors to the extinguishing barrier allowing for the expected ,speed of 100 metres per second of the flame front. The UV range of detection was 178 nanometres.

A preferred range for UV detection is between 190 and 230 nanometers because water is transparent to this part of the spectrum so that there is no danger of condensation droplets or residual washing water "blinding" the detectors. Also this band width ignores anything behind glass, i.e. glass is opaque to it, allowing spurious actuations by lights, etc. to be avoided.

A further preferred detection according to the invention is to combine this UV detection with far infra red detection; the reason for this is that formation of CO 2 produces a peak at 4 400 nanometers. This allows increased reliability of detection if both signals are required by the logic to actuate dowsing.

It must be mentioned that in accordance with this invention it is furthermore possible to provide more than one extinguishing barrier area if it is desired or required to provide greater levels of security of the extinguishing.

Figure 4 schematically shows an apparatus set up in accordance with this invention. This apparatus comprises various bottles 5, 6, 7 and 8 each illustrated here by way of example with different kinds of delivery nozzles. A control unit 9 which conducts logic processing of signals received from detectors, a distribution unit 10 which sends command signals distributed to the various extinguishers when a decision is made by the control unit 9, an emergency switch 11 is provided and wires 12 and 13 may lead to, for example, optical detectors or other forms of detectors, wires 14 lead to a fire wire which can be used also as a detector. According to the nature and location of these detectors the control unit can be programmed to s •process signals received from them according to desired or required logic to provide assured signals and also fail safe signals which are ~free from false alarms.

Figure 5 shows another example of apparatus in accordance with this invention. Once again the apparatus comprises bottles 16 and 17 containing extinguishing chemicals, a control unit 18, a power supply •19, an array of sensors 20 to 23 and wiring harnesses which can connect the various components appropriately.

se Figure 6 is a graphical representation of an advancing flame front 3o under conditions of no extinguishing. As will be seen the flame front moves at very high speed in that it will cover a distance of .I Th depth of h approximately 180 metres in about 1,2 seconds. The depth of the flame front can be seen also to vary in a random manner.

Figure 7 shows a similar flame front which has been extinguished by apparatus in accordance with the invention. Here it will be seen that in a period of approximately 0,3 milliseconds the flame front has been extinguished.

The necessary very high speed of opening of a bottle under pressure containing extinguishing material can be achieved in any one of three different alternative possibilities, for example. A first may be a squib and toggle arrangement whereby with the release of an over-centred toggle a squib is released from the neck of the bottle. A second possibility is a so-called tear membrane where a membrane which will sustain the pressure can be torn and will then open under pressure very, very fast. A third possibility is to use a piston and O-rings, the piston again being allowed to pop out with the action of an over-centre toggle or sear. In all cases opening within, for example, 5 milliseconds is found to be approximately suitable and they may be allowed to remain open for periods up to 300 milliseconds for a large stope or tunnel.

Where optical or UV sensors or, for example, milli-Geigy counter sensors are combined with other sensors, for example, fire wires, point detectors and the like potentially at different locations, the necessary logic combinations can be programmed into the control unit.

It may be necessary to sensitise a fast detector in this context.

Figure 8 shows an example of an arrangement which comprises a steel bottle 25 which is able to hold the extinguishing material or medium under very high pressure. This is screwed on to the valve body which body together with the trigger mechanism is enclosed within a housing 26. At the lower end of the housing 26 there is connected a diffuser 27 which will deploy the extinguishing or dowsing substance or medium in a 3600 sheet and may thus be strategically mounted, for example, in a mine tunnel to deploy the sheet across the area of the tunnel to stop an advancing flame front.

A gland 28 is provided for the connection of an electric lead which will carry an electrical current which will trigger the mechanism to release the substance. The electric current in turn will be activated by a suitable electronic means upon the detection of an advancing flame front and in regard to these aspects reference is again made to the aforesaid provisional specification. The gland 28 can in fact accommodate a cable which will carry duplicated signals for the benefits of redundancy and thus greater reliability of triggering.

The main focus of the present invention as has been stated is the valve with associated trigger mechanism which is contained inside the housing 26.

Figure 9 shows the housing 26 with one half of the housing removed to reveal the valve body 29 inside the trigger mechanism 30 and figure 10 shows the housing 26 and diffuser 27 in end elevation.

The screw threaded neck 31 which screws into the bottle 25 is seen and in figure 11 the piston 32 is seen in an open position in which substance under pressure in the bottle would be released for deployment by the diffuser 27.

S" The diffuser which is a subsidiary feature of the invention comprises a flange 33 which can be screwed into the valve body at its lower end 0 and vanes 34 (one is shown in figure 9 but two are shown in figure 8) together with a base deflector 35 and a bottom closure 36 which provide for the 3600 deployment of the substance in the bottle. Base 36 can also carry suitable shock absorbing means for the piston 32, for example, as are shown in figures 29 and The valve body 29 to which the invention is primarily directed is o shown in more detail in figures 11 to 17. It will be seen that the body comprises a passage 37 which by being screwed via the neck 31 into the bottom of the bottle communicates with the container for the substance under pressure. A piston (shown in figure 18) can move within the passage 37 between a sealing position to an opening position. A pyrotechnic trigger mechanism (the mechanism shown in figure 9) can be duplicated, screwed into the holes 38 and 39 (figures 14 and 17) (the functional inter-relationship of the I 1 components will be more fully described with reference to figure The passage 37 comprises a frustoconical portion 40 which leads to a narrow cylindrical portion 41 in which the piston is able to seal, followed by an enlarged cylindrical portion 42 at which the seal is lost once the piston is moved to that position and an enlarged portion 43 which constitutes the beginning of a chamber which is completed by the adaptor shown in figures 25 to 28 for connection to a nozzle for deploying of the substance. A hole 44 carries the sear which is shown in figure 19, the hole 44 intersecting partially with the passage 42 and the sear having a flattened off portion which will be described with reference to figure 19 to provide the means of either retaining the piston or releasing the piston. Recesses 45 and 46 are let into the outer surfaces of the body on either side to house a detent in each recess which is shown in figure 20 and both detents are attached to the sear shaft. Holes or threaded holes 47 and 48 are provided for the insertion of adjustment screws to adjust the limits of the release position of the detent and hence of the sear. Holes 49 and 50 are provided for connection to pressure monitoring means which can continuously monitor the pressure of substance available in the bottle 25 to provide warning signals if the pressure drops below the **..minimum requirement.

The piston is shown in figure 18 which comprises a conical head 51 **for good gas flow on release (see figure 9) two grooves 52 and 53 which contain O-rings 54 and 55 for sealing on the walls of the cylindrical portion 41 of the passage 37 in the valve body. A cylindrical flange 56 serves the important function of engaging with detents (see figure 35) while the piston is being retained in the sealing position and the flange 57 provides stability for the piston. A •***"conical hole 58 within the piston provides for inter-action with shock absorbing means which is shown in figures 29 and As shown in figure 19 the sear 59 is a shaft which fits into the hole 44 of the valve body and has a flattened portion 60 which corresponds precisely with the walls of these cylindrical portion 42 of the passage 37 through the valve body. Squared off ends 61 and 62 provide for connection of two detents, one at either end of the sear shaft, of which one is shown in figure As shown in figure 20 the detent 63 has a squared off hole 64 which fits irrotationally on the squared off portions 61 and 62 of the detent shaft and a face 65 which is presented towards the pin of the trigger mechanism which is shown in figures 21 to 24.

As shown in figure 21 the pin 65 is located inside the cylinder 66 shown in figure 22. Thereafter a pyrotechnic charge is charged into the body 67 shown in figure 23 which is screw connected on to the cylinder 66. Then the pyrotechnic charge is enclosed by means of a cap 68 shown in figure 24 with an electrical fuse inserted via the hole 69 and providing lead wires which can be connected to suitable electronic equipment to provide a triggering electrical pulse. There are two such pyrotechnic fuses provided in the apparatus, one on either side of the sear shaft 59 and both can be triggered simultaneously to provide greater reliability against the possibility of a faulty charge.

S:Figure 25 shows an adaptor 70 which can be screwed at its screw :i threaded neck 71 into the screw threaded portion 43 (figure 11) of the valve body to connect the adaptor to the valve body. The 0 adaptor has a side opening 72 to which can be screw connected a =i suitable nozzle. A closure base 73 can be screw threaded into the portion 74 of the adaptor to close off the bottom. The base 73 can be provided with certain safety release apertures for extreme pressure conditions. A shock absorbing component shown in figure 28A comprises a pin 75 on a base 76 with an elastomeric substance 77 of el conical shape around the pin 75 having a base impact portion 78.

*el° The elastomeric portion 77, 78 is shown also in figure 29 and it is 00: dimensioned to correspond to the tapering hole 58 in the piston (figure 18).

In addition an elastomeric socket 79 is mounted on the base 73 around the conical portion 78 and has an inwardly directed flange which receives the reduced diameter portion 81 of the valve shown in figure 18 when the valve is driven into the open position after having been released by the sear, the very high pressure of the material in the container driving it downwards.

The components shown in figures 29 and 30 thus provide a shock absorbing function to prevent rebounds of the piston.

The outer housing for the valve body and trigger mechanism is shown in figures 31 to 34, comprising two halves which are bolted together around the body which is shown in figures 11 to 17.

The assembly drawing in figure 35 shows the key components in the valve body with the trigger mechanism. As shown in figure 35 the body 29 contains a passage 37 which is connectable by means of the screw thread 31 to communicate with the container of a substance such as the gas under high pressure, a piston comprising a conical portion 51, grooves 52 and 53 containing O-rings 54 and 55, a cylindrical shoulder 56 and land 57. The piston may move as a valve from a sealing position in which it is illustrated in figure 35 to an opening position at the bottom of the adaptor 70. A pyrotechnic trigger mechanism comprises a pin 65 located in a cylinder 66 which o has a closure cap 67 with a cap 68 from which an igniting fuse wire 82 is led. An identical second pyrotechnic trigger mechanism is provided for the device but not illustrated in this drawing as it is a sectional elevation and the other pyrotechnic device is located in the part which is sectioned off and removed from this view. The pin 65 is able to act against a detent 63 on the face 65 of the detent. The sear 59 has a flattened surface 60 which, when the sear is turned in S"I the position shown bears against the cylindrical flange 56 to hold the piston in the closed position. When the pyrotechnic trigger mechanism 66 to 68 is fired the pin 65 is shot partially out of the mechanism and engages the face 65 of the detent 63 pushing it 30O across in an anti-clockwise direction in the view of figure 35 and thus rotating the sear in that direction so that it disengages with the cylindrical shoulder flange 56 and then the piston 51 is able to be pressed downwardly in the direction indicated by arrow 83 onto the shock absorbing cone 77 and pad 78 and rubber surround 79. The flange 57 of the piston then hooks under the shoulder 84 of the surround 79 and the components 77 and 79 exercise a shock absorbing effect so that the piston is retained at the bottom and does not rebound. This then allows gases to exit from the adaptor 70 at the hole 72 as indicated by the arrow 84, the valve then being in the position indicated broadly by the broken lines Figures 36 and 37 show another trigger and valve device 90 attached to a distribution fan 91; it also shows an enhanced shock absorbing cone 92 and pad 93, a pressure sensor 94 to monitor pressure in the gas bottle being maintained, improved connection arrangements and a refilling nipple 96.

The cone 92 has been made hollow as shown at 114 which reduces its inertia with the result that a tendency for the cone to be torn off its base 97 when the piston 98 hits it is eliminated. A thicker pad 93 also helps.

The pressure sensor is shown in cross section in figure 37, it comprises a cylinder 98 in which a piston 99 can move against :*loading by a spring 100; a flange 101 of the piston acts against plungers 102 which actuate a micro switch 103 which closes an 20 electrical circuit at terminals 104. This can be set to give a warning if the pressure in the gas bottle drops below a threshold.

The refilling nipple 96 then allows the gas to be replenished without having to dismantle or disturb the device.

Passages 105 and 106 allow communication respectively to the pressure sensor and nipple.

:The new gases used to avoid CFC criticisms have been found to require more stringent sealing arrangements and connections between the bottle 107 (only the bottom part of a bottle is shown) and the valve mechanism. This has been provided for by the use of encircling clamps 95 (only partially shown) and 0 ring seals being duplicated at the high pressure joint.

Fan type gas delivery means 91 comprises a series of rings 108 assembled in a stack by means of bolts 109 with spacers 110; directionality can be built into the sack by substituting for the spacers closing arcs on one side covering as many degrees of arc as required; this structure thus gives versatility to allow an installation to be adapted to local requirements.

In the example shown in these figures 36 and 37 the remaining parts are the same as in the previous embodiment and reference is made to the descriptions of figures 9 to 35; this includes the functionally O important sear shaft 111, the two detents 112 and two trigger mechanisms 113 (which by redundancy provide heightened reliability) o:ee and the piston 98.

*to 6 :0 *The trigger and valve assemblies of figures 8 to 37 can be used in the apparatus of figures 1 to 7.

While preferred embodiments of the invention have been described, it will be appreciated that various changes may be made within the scope of the eepo -°}invention, and all such changes are intended to be included in the e eaccompanying claims.

"Comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims (4)

1. A valve for use with a pressurized container of a flame-dowsing substance in a flame front extinguishing system, said valve including: a valve body containing a passage which is adapted to communicate with the container; a piston retained in a sealing position within the passage by a sear and movable by pressure in the container to an opening position wherein the container is vented through the passage, when released from the sealing position by actuation of the sear; and a pyrotechnic trigger mechanism including an electronically ignited charge and a pin adapted to actuate the sear on ignition of the charge thereby to release the piston to move in the passage in the valve body to the opening position.

2. A valve according to claim 1, wherein the sear includes a shaft intersecting the passage and partially flattened so that the shaft is rotatable to a position whereby the piston is free to move in the passage.

3. A valve according to claim 1 or 2 wherein the passage includes a cylinder in which the piston is movable, having a first portion in which the piston seals and a second portion of larger diameter than the first portion in which the piston is non-sealing and to which the piston moves during opening, and wherein the piston finally moves into an enlarged chamber to allow high

60000. S velocity discharge of a substance under pressure from the container.

4. A valve according to any one of claims 1 to 3 wherein the pyrotechnic trigger mechanism includes a cylinder with the pin projecting therefrom and containing the charge, an electrical fuse adapted to ignite the charge to drive the pin outwardly relative to said cylinder, and an electrical connection to the fuse. 19 A valve according to any one of claims 1 to 4 wherein the pyrotechnic trigger mechanism is one of two simultaneously triggerable pyrotechnic trigger mechanisms for enhanced reliability. 6. A valve according to any one of claims 1 to 5 provided with a component connected to the valve body which component includes a buffer adapted to receive the piston in a shock-absorbing manner to reduce rebound of the piston after opening of the valve. 7. A valve according to claim 6 wherein the buffer includes a hollow cone with an integral base. 8. A valve according to claim 6 or 7 wherein the piston has a flange which, as the piston approaches the buffer, hooks under an elastomeric shoulder included in said component so that the piston is retained by said component without rebounding. 9. A valve according to any one of claims 6 to 8 including, secured between the valve body and the said component, a distribution fan which includes a stack of coaxial rings separated by spacers thereby to define peripheral outlets for material vented from the container. 0 01. :9000: 10. A valve according to any one of claims 1 to 7 provided with a diffuser o a* head or distribution fan through which the substance in the container is S• deployable by operation of the valve. 11. Apparatus for extinguishing flame fronts including: a set of detectors selected from at least optical detectors, fire wire circuits, pressure transducers; a control unit providing logic processing of the detector outputs for flame front detection; a set of one or more extinguishing units which include pressurized containers containing a flame dowsing substance; and a distribution unit, wherein a said extinguishing unit includes a valve according to any one of claims 1 to 10 for venting the substance contained in the said extinguishing unit to tend to dowse the flame front and said valve is operable by the distribution unit in response to a command from the control unit. 12. Apparatus according to claim 11 wherein a said flame dowsing substance is selected from suitable substances which are chemically acting endothermic, or which are based on thermal capacity or latent heat effects. 13. Apparatus according to claim 11 or 12 wherein a said flame dowsing substance is selected from gases, extinguishing powder, water or stone dust. 14. Apparatus according to any one of claims 11 to 13 wherein the detectors are placed in a mining stope or tunnel in an anticipated upstream position in relation to an advancing flame front by a calculated distance from an array of the extinguishing units. 15. Apparatus according to any one of claims 11 to 14 wherein a said valve of an extinguishing unit is connected by a branch connection to a nozzle. :16. A method for extinguishing a flame front using apparatus according to any one of claims 11 to 13, which includes assessing detection signals from said detectors by means of a computer controlled by software, making a °decision to deploy a flame dowsing substance and issuing a command signal which results in actuation of extinguishing units. *Gooo*: 17. In apparatus for detecting and extinguishing a flame front, a computer programmed to execute a method according to claim 16. 18. Apparatus substantially as described herein with reference to Figure 21 19. Apparatus substantially as described herein with reference to Figure 36. DATED this 18th day of September 2000 HELMUTH SPATH WATERMARK PATENT AND TRADE MARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA SKP:DHS:VRH P7952AU00.DOC 0. 000* *00 0.*0