Abstract:
A fire extinguishing apparatus ( 10 ) producing a mist of water vapour with a median droplet diameter of between 50 and 500 micron for extinguishing fires in a confined risk area. The mist being generated through nozzles ( 18 ) operating at &lt;2000 kPa (i.e. low pressure). The fire extinguishing apparatus using less than 1.0 litres of water per cubic meter of the risk area in which the fire is contained (i.e. a small volume of water).

Description:
FIELD OF THE INVENTION 
     The present invention relates to a fire extinguishing apparatus and method relying upon a non-flammable liquid, such as water for extinguishing fire including Class A and B fires with a mist formed from a relatively small amount of liquid at a relatively low pressure. The fire extinguishing apparatus intended for use in closed areas, such as, for example, in engine rooms, pump rooms, machinery spaces, computer rooms, storage rooms and the like. More particularly, the present invention relates to a fire extinguishing apparatus intended for use as a replacement for an existing fire extinguishing apparatus based upon the use of the now banned HALON. 
     Hereinafter, the present invention will be described with particular reference to use with liquid being water although it could be used with other non-flammable liquids which absorb heat as they vaporise. 
     BACKGROUND OF THE INVENTION 
     In fighting fires it is known that there are three major contributing factors to the continuation of the fire. These factors are heat, oxygen and fuel and the interrelationship of these factors is shown pictorially in FIG.  6 . Conventionally when extinguishing fires, fire fighters act to remove at least one of the three elements necessary for combustion. Typically, fire fighters use either water, CO 2 , halon, dry chemical or foam. Water acts by removing the heat from the fuel, whilst carbon dioxide works by displacing the oxygen. 
     Another aspect of combustion is a chain flame reaction indicated by a circle which contains the triangle, as shown in FIG.  6 . The chain flame reaction relies upon free radicals which are created in the combustion process and are essential for of its continuation. Halon operates by attaching itself to the free radicals and thus preventing further combustion by interrupting the flame chain reaction. 
     The main disadvantage of water is that considerable amounts of water are required in extinguishing a fire which leads to considerable damage by the water. Also, in some instances suitable quantities of water to extinguish the fire are not available. Carbon dioxide and halon both have the disadvantage that all people must be evacuated from the area in which they are to be used must be evacuated since it will become impossible for the people to breathe. For this reason, fire fighters using these extinguishing agents must use breathing apparatus. Also, for CO 2  and Halon to extinguish the fire any ventilation of the area must be shut down. Halon has further disadvantage that it is highly toxic and very damaging to the environment. For those reasons, the use of halon in extinguishing fires has been banned in most circumstances. 
     The present invention overcomes the above disadvantages by using a non-flammable liquid, such as water, to reduce the heat of the vapour around the fuel, reduce the heat of the fuel, displace the oxygen, and interrupt the flame chain reaction. That is, the liquid attacks all parts of the combustion process except for removing the fuel. The invention is based upon the generation of a relatively fine mist of liquid (referred as a mist), such as water, which displaces the oxygen, and upon heating evaporates and expands to further displace the oxygen. Upon expansion the water mist absorbs heat from the vapour around the fuel and from the fuel. Also, the mist interrupts the flame chain reaction by attaching to the free radicals. The mist also has a smothering effect and a cooling effect upon the fire. For these reasons, the mist has the surprising result that a relatively small amount of water can safely be used to extinguish both A and B class fires as well as electrical fires. 
     The mist generated by the fire extinguishing apparatus of the present invention is not a water on flame scenario. Its operation is more akin to gaseous fire extinguishing mediums such as CO 2  or halon. 
     These surprising results occur due to the very rapid evaporation rate possible with a fine mist of liquid (typically 50-500 microns), the heat absorption characteristics of water as it vaporises, the ability of the fine mist to reduce the convection of heat from the fire to surrounding objects and the ability of the mist to displace oxygen. This is due to the expansion ratio of water from liquid to vapour. 
     With the fire extinguishing apparatus of the present invention a typical fire confined to a room or the like can be entirely extinguished within about 30 seconds with a number of nozzles each spraying about 0.4 litres of water as mist at about 20 bar, with one nozzle per 2.65 m 3 . This is a very small rate of application of water to douse a fire when compared to the prior art. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide a fire extinguishing apparatus which uses a mist generated from non-flammable liquid applied in relatively small volumes to interrupt the combustion process of a fire in a closed space. 
     In accordance with one aspect of the present invention there is provided a fire extinguishing apparatus for extinguishing a fire located in a risk area, the fire extinguishing apparatus comprising: 
     a storage reservoir containing a non-flammable liquid; 
     a spray means for spraying the liquid into the risk area, the spray means forming a mist having a droplet size which enhances the application of the mist to the fire and hence increase the ability for the liquid to extinguish the fire; 
     a propelling means for propelling the liquid out of the storage reservoir and through the spray means under pressure for forming the mist; 
     a sensor means for detecting the presence of a fire in the risk area; 
     a control means in operative association with the sensor means for controlling the propelling means for propelling the liquid out of the storage reservoir. 
     In accordance with another aspect of the present invention there is provided a method for extinguishing a fire, the method comprising the steps of: 
     directing a spray means into the risk area; 
     propelling non-flammable liquid through the spray means under pressure for forming a mist having a droplet size which creates an atmosphere that will not support combustion. 
     Typically, the non-flammable liquid is water. 
     Preferably, the spray means includes a plurality of nozzles interconnected by pipes. 
     Preferably, the mist has a droplet size with a median volume diameter or less than about 500 microns. 
     Typically, the propelling means is a gas contained in the storage reservoir under elevated pressure. Typically, the gas is dry nitrogen. Typically, the gas is pressurised to about 20 bar in the storage reservoir prior to operation of the fire extinguishing apparatus. 
    
    
     BRIEF INTRODUCTION OF HE DRAWINGS 
     An exemplary embodiment of the present invention will now be described with particular reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view, seen from above, of an engine room of a ship shown fitted with a fire extinguishing apparatus in accordance with the present invention; 
     FIG. 2 is a graph showing the fire extinguishing capabilities of the fire extinguishing apparatus of FIG. 1, in a test facility, for extinguishing ignited isopropanol, petrol and diesel; 
     FIG. 3 is a graph similar to FIG. 2 but showing a comparison of the extinguishing capabilities of the fire extinguishing apparatus of FIG.  1  and the use of carbon dioxide on ignited petrol; 
     FIG. 4 is a graph showing typical maximum fire temperature characteristics of fires treated with the fire extinguishing apparatus of FIG. 1; 
     FIG. 5 is a cascade test facility for testing the fire extinguishing apparatus of FIG. 1; and, 
     FIG. 6 is a pictorial representation of the combustion triangle and flame chain reaction circle. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1 there is shown a fire extinguishing apparatus  10  comprising a pressurised container  12 , pipes  14  and  16 , a plurality of nozzles  18 , a plurality of fire detectors  20  and a control panel  22 . 
     Also shown in FIG. 1 is an engine room  100  having a surrounding wall  102  within which is located an engine  104 , fuel tanks  106 , an exhaust pipe  108 , an exhaust muffler  110 , a heat exchanger  112 , and a propeller shaft well  114 . The engine room  100  is a typical layout of the engine room of a ship. 
     The container  12  is typically made from galvanised metal materials and capable of withstanding pressures up to for example 3000 kPa. Typically, the container  12  has a charge of distilled water maintained under pressure by a charge of dry nitrogen. Typically, the container  12  has a capacity between about 5 and 30 litres. However, the container  12  could have virtually any capacity, although by the nature of the operation of the present invention the container  12  may be much smaller than prior art containers. 
     Typically, the pressurised container  12  is located proximate the surrounding wall  102 . The container  12  has a control valve  30  attached to its outlet for controlling the expulsion of the water under pressure from the container  12 . The control valve  30  may be actuated electrically or mechanically and the actuation may be automatic or manual. 
     The pipes  14  and  16  form a plumbing network  36  attached to the flow rate control valve  32  and each carry a plurality of the nozzles  18 . The pipes  14  and  16  and hence the nozzles  18  are strategically located about the engine room  100 , as described hereinafter. Also, the nozzles  18  are oriented in strategic directions from the pipes  14  and  16 . For example, the nozzles  18  are oriented so as to ensure that the pressurised water from the container  12  can be sprayed to all areas of the engine room  100  and to concentrate on areas of higher flame potential. Preferably, the pipes  14  and  16  are oriented about a roof of the engine room  100  and into the propeller shaft well  114 . The nozzles  18  are then oriented downwardly and/or outwardly from the pipes  14  and  16 . Typically, the plumbing network  36  is coupled to the pressurised container  12  by a flexible water way. Typically, the plumbing network  36  has a bore diameter not less than 12 mm. Also, the plumbing network  36  preferably is capable of withstanding internal pressures of at least 3000 kpa. Further, it is preferred that the plumbing network be of a looped design and that there be no ends in the lines of the plumbing network. 
     The nozzles  18  are typically formed from brass or stainless steel and include a swirl chamber and an elongate cone inlet filter. The swirl chamber increases the atomisation of water passing through it and the filter inhibits blockage  6 f the swirl chamber by detritus material. The nozzles  18  typically produce a droplet size between 50 and 500 microns, more particularly between 250 and 400 microns. The spray pattern from the nozzles  18  is typically about 80° at a pressure of 2000 kpa (20 bar). Also, the nozzles  18  typically have a minimum orifice size of about 1 mm 2 . The nozzles  18  use the liquid pressure alone to produce very finely atomised droplets in a hollow cone spray pattern with uniform distribution for achieving high misting performance. The nozzles  18  used in the exemplary embodiment are typically those available under the Registered Trade Mark UNIJET. The following specific nozzles are considered particularly useful: 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 TYPE 
                 FLOW RATE (L/MIN) 
                 PRESSURE (BAR) 
               
               
                   
                   
               
             
             
               
                   
                 TN-4 
                 0.65 
                 20 
               
               
                   
                 TN-6 
                 0.83 
                 20 
               
               
                   
                 TN-8 
                 0.96 
                 20 
               
               
                   
                 TN-10 
                 1.06 
                 20 
               
               
                   
                   
               
             
          
         
       
     
     The nature and size of the nozzles  18  to be used in a particular engine room  100  (or other risk area) depends upon a number of factors and can be calculated as shown in example 1. 
     EXAMPLE 1 
     To determine the quantity and type of nozzles  18  to use the following calculations can be performed. 
     The calculation is performed according to the following glossary of terms: 
     G.V.—the gross volume which represents the volume of the risk area (height H×width W×length L); 
     N.V.—the nett volume which represents the gross volume of the risk area minus all solid objects within it; 
     W.R.—water required which represents the amount of water required in litres to be introduced into the risk area; 
     N.N—the number of nozzles required to spray the mist into the risk area in a substantially uniform manner; 
     90FR—a ninety second flow rate which represents the volume of water which flows through each nozzle  18  in 90 seconds at 20 bar (typically 1.26 litres); 
     C.F.—a compensating factor which we have developed through experimentation for each flow rate of nozzle  18  as shown below: 
     2.8 for TN-4 type nozzle  18   
     2.1 for TN-6 type nozzle  18   
     1.8 for TN-8 type nozzle  18   
     1.1 for TN-10 type nozzle  18   
     W.V.—water volume in cubic metres (i.e. W.R./1000) 
     P.V.—potential vapour which represents the expansion ratio of vaporisation of water, namely 1700 * W.V.; 
     P.F.B.—potential fuel by-products due to combustion and represents the amount of CO 2  and H 2 O which are released as gases during combustion of the fuel, for example 212 grams of C 15 H 32  (diesel) produces about 1525 litres of CO 2  and H 2 O under complete combustion, and about 1284 litres of CO 2  and H 2 O for a similar mass of C 8 H 10  (xylene petrol); 
     The water capacity and the number of nozzles  18  required is then represented by the following formula: 
     W.R.=N.V./C.F. 
     N.N.=W.R./90FR 
     Thus given a risk area 7 m×4 m×1.7 m, with 3 obstructions one of which is 1 m×1 m×1 m and the other two obstruction being 1.8 m×0.9 m×0.8 m, and using nozzles  18  of the type TN-6 the number of nozzles  18  required is determined as follows: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 G.V. = 
                 7 × 4 × 1.7 
               
               
                 = 
                 47.6 m 3   
               
               
                 N.V. = 
                 G.V. − (1 × 1 × 1 + 2 × (1.8 × 0.9 × 0.8)) 
               
               
                 = 
                 47.6 − 3.492 
               
               
                 = 
                 44.008 m 3   
               
               
                 W.R. = 
                 44.008/2.1 
               
               
                 = 
                 20.9 l 
               
               
                 N.N. = 
                 20.9/1.26 
               
               
                 = 
                 16.58 nozzles 
               
               
                   
               
             
          
         
       
     
     N.N.=17 NOZZLES 
     NB: Always round up to the nearest whole number i.e. in this case N.N. is 17 an the volume of water required W.R. must be adjusted accordingly (i.e. W.R. in this example is 21.4 litres). 
     The fire detectors  20  include a fixed temperature fire detector  40  and a rate of rise fire detector  42 . The fixed temperature  40  typically includes a bimetallic strip with an extension rod which elevates a diaphragm to make a contact when the ambient temperature increases above a predetermined temperature. Typically, the fixed temperature is between 60 and 100° C. The rate of rise fire detector  42  typically includes a diaphragm and an air chamber, wherein the chamber leaks air through a fence tube in the diaphragm at relatively low rates of rise in temperature but which causes raising of the diaphragm to make a contact at relatively high rates of rise of the fire temperature. Typically, the rate of rise fire detector  42  is set to be active when the rate of rise in temperature is greater than about 9° C. per minute. 
     The detectors  20  also typically include smoke detectors. The smoke detectors are preferably located so as to detect air flowing out of the risk area to sense any smoke entrained in the air. 
     The control panel  22  is located so as to be easily accessed during a fire. For example, the control panel  22  may be located on the outside of the surrounding wall  102  of the engine room  100 . The control panel  22  includes a wiring fault detection monitoring system and an activation system. The fault detection monitoring system monitors the wiring to the fire detectors  20  and the control valves  30  and  32  for open circuits, short circuits and unstable wiring conditions. The control panel  22  also senses the pressure in the pressurised container  22  and issues an alarm in the event that the pressure falls below a predetermined pressure. The activation system is of the “detonator” type which causes the control valves  30  and  32  to release the pressurised water from the container  12 . Typically, the control panel  22  includes a mist release push button having a lift cover placed over it. The mist release push button is required to be activated to manually release the water from the container  12 . The control panel  22  is also connected to visual and audible alarms located in the engine room  100 . 
     In use, the fire extinguishing apparatus  10  is installed into a risk area, such as the engine room  100 , by first calculating the number of nozzles required, the type of nozzles to use and the volume of water required for example as shown in Example 1. The nozzles  18  are then spaced about the engine room  100  along the pipes  14  and  16  to the pressurised container  12  via the control valves  30  and  32 . The control panel  22  is located on the outside of the engine room  100  and wired into the fire detectors  20  and the control valves  30  and  32  and the audible and visual alarms. 
     In the event of a fire or rapid increase in temperature in the engine room  100  the fire detector  40  or  42  is triggered to initiate the control panel  22  to operate the control valves  30  and  32  to release water under pressure out of the container  12 . The pressurised water passes along the pipes  14  and  16  to the nozzles  18 . The water passes through the filter and swirl chamber of the nozzles  18  and forms a fine mist having a median droplet diameter between 250 and 500 microns. The median droplet diameter is an expression of the droplet size in terms of the volume of the liquid and is a value where 50% of the total volume of the liquid sprayed is made up of droplets with diameters larger than the median valve and 50% smaller than the median value. 
     The following test procedures were performed in a test rig situated in a forty foot cargo container having its access doors open at one end and with a plurality of the nozzles  18  located mid way up the side walls of the container. Flammable fuel was placed in a tray located on the floor of the container intermediate of the length of the container. The results of the tests are as follows: 
     TEST 1 Purpose: VISUAL DEMONSTRATION—ISOPROPANOL 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 EXTINGUISHING MEDIUM 
                 WATER MIST 
               
               
                   
                 FUEL 
                 ISOPROPANOL 
               
               
                   
                 AMOUNT OF FUEL USED 
                 3 l 
               
               
                   
                 SURFACE AREA OF FIRE 
                 0.636 m 2   
               
               
                   
                 DETECTION TIME 
                 5 s 
               
               
                   
                 NOZZLE SIZE 
                 HF-16 
               
               
                   
                 ORIFICE SIZE 
                 1.1 mm 
               
               
                   
                 CAPACITY EACH NOZZLE AT 20 BAR 
                 0.683 l/min 
               
               
                   
                 CAPACITY ALL NOZZLES AT 20 bar 
                 16.4 l/min 
               
               
                   
                 WATER PRESSURE 
                 2000 kpa (20 bar) 
               
               
                   
                 SPRAY ANGLE 
                 84° 
               
               
                   
                 NUMBER OF NOZZLES 
                 24 
               
               
                   
                 NUMBER OF EFFECTIVE NOZZLES 
                 14 TO 16 
               
               
                   
                 MEDIAN DROPLET SIZE 
                 375-400 MICRONS 
               
               
                   
                 TIME TO EXTINGUISH 
                 23 s 
               
               
                   
                 RATE OF ABSORPTION 
                 21.7° C./s 
               
               
                   
                   
               
             
          
         
       
     
     The number of nozzles  18  which were effective was less than the total number of nozzles  18  since the doors of the container where open. 
     TEST 2 Purpose: VISUAL DEMONSTRATION—PETROL 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 EXTINGUISHING MEDIUM 
                 WATER MIST 
               
               
                 FUEL 
                 PETROL 
               
               
                 AMOUNT OF FUEL USED 
                 3 l 
               
               
                 SURFACE AREA OF FIRE 
                 0.636 m 2   
               
               
                 DETECTION TIME 
                 3 s 
               
               
                 NOZZLE SIZE 
                 HF-16 × 16 
               
               
                   
                 HF-32 × 8 
               
               
                 ORIFICE SIZE 
                 HF-16 = 1.1 mm 
               
               
                   
                 HF-32 = 1.5 mm 
               
               
                 CAPACITY EACH NOZZLE AT 20 bar 
                 21.8 l/min 
               
               
                 WATER PRESSURE 
                 2000 kpa (20 bar) 
               
               
                 SPRAY ANGLE 
                 HF-16 = 84° 
               
               
                   
                 HF-32 = 91° 
               
               
                 NUMBER OF NOZZLES 
                 24 
               
               
                 NUMBER OF EFFECTIVE NOZZLES 
                 16 
               
               
                 MEDIAN DROPLET SIZE 
                 HF-16 = 375-400 
               
               
                 micron 
                 HF-32 = 350-375 micron 
               
               
                 TIME TO EXTINGUISH 
                 13 s 
               
               
                 RATE OF ABSORPTION 
                 1.123° C./s 
               
               
                   
               
             
          
         
       
     
     TEST 3 Purpose: VISUAL DEMONSTRATION—DIESEL 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 EXTINGUISHING MEDIUM 
                 WATER MIST 
               
               
                   
                 FUEL 
                 DIESEL 
               
               
                   
                 AMOUNT OF FUEL USED 
                 3 l 
               
               
                   
                 SURFACE AREA OF FIRE 
                 0.363 m 2   
               
               
                   
                 DETECTION TIME 
                 12 s 
               
               
                   
                 NOZZLE SIZE 
                 HF-16 
               
               
                   
                 ORIFICE SIZE 
                 1.1 mm 
               
               
                   
                 CAPACITY EACH NOZZLE AT 20 bar 
                 0.683 l/min 
               
               
                   
                 CAPACITY ALL NOZZLES AT 20 bar 
                 16.4 l/min 
               
               
                   
                 WATER PRESSURE 
                 2000 kpa (20 bar) 
               
               
                   
                 SPRAY ANGLE 
                 84° 
               
               
                   
                 NUMBER OF NOZZLES 
                 24 
               
               
                   
                 NUMBER OF EFFECTIVE NOZZLES 
                 24 
               
               
                   
                 MEDIAN DROPLET SIZE 
                 375-400 MICRONS 
               
               
                   
                 TIME TO EXTINGUISH 
                 6 s 
               
               
                   
                 RATE OF ABSORPTION 
                 0.33° C./s 
               
               
                   
                   
               
             
          
         
       
     
     TEST 4 Purpose: COMPARISON OF MIST WITH CO 2   
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 EXTINGUISHING MEDIUM 
                 WATER MIST 
               
               
                   
                 FUEL 
                 PETROL 
               
               
                   
                 AMOUNT OF FUEL USED 
                 2 l 
               
               
                   
                 SURFACE AREA OF FIRE 
                 0.636 m 2   
               
               
                   
                 DETECTION TIME 
                 5 s 
               
               
                   
                 NOZZLE SIZE 
                 HF-16 
               
               
                   
                 ORIFICE SIZE 
                 1.1 mm 
               
               
                   
                 CAPACITY EACH NOZZLE AT 20 bar 
                 0.683 l/min 
               
               
                   
                 CAPACITY ALL NOZZLES AT 20 bar 
                 16.4 l/min 
               
               
                   
                 SPRAY ANGLE 
                 84° 
               
               
                   
                 NUMBER OF NOZZLES 
                 24 
               
               
                   
                 NUMBER OF EFFECTIVE NOZZLES 
                 24 
               
               
                   
                 MEDIAN DROPLET SIZE 
                 375-400 MICRONS 
               
               
                   
                 TIME TO EXTINGUISH 
                 12 s 
               
               
                   
                   
               
             
          
         
       
     
     This is hereinafter referred to as the “mist test”. 
     TEST 5 Purpose: COMPARISON OF MIST WITH CO 2    
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 EXTINGUISHING MEDIUM 
                 CARBON DIOXIDE 
               
               
                   
                 FUEL 
                 PETROL 
               
               
                   
                 AMOUNT OF FUEL USED 
                 2 l 
               
               
                   
                 SURFACE AREA OF FIRE 
                 0.636 m 2   
               
               
                   
                 DETECTION TIME 
                 5 s 
               
               
                   
                 QUANTITY OF CO 2   
                 32 kg 
               
               
                   
                 NUMBER OF NOZZLES 
                 6 
               
               
                   
                 NUMBER OF EFFECTIVE NOZZLES 
                 6 
               
               
                   
                 TIME TO EXTINGUISH 
                 17 s 
               
               
                   
                   
               
             
          
         
       
     
     This is hereinafter referred to as the “CO 2  test”. 
     In the test procedures each of the fuels was ignited and allowed to flame up for between 25 to 60 seconds, after which time the fire extinguishing apparatus  10  was activated to extinguish the fire. The temperature inside the container was monitored from the time of ignition of the fuel until after extinguishing of the fire produced thereby. These results are shown graphically in FIGS. 2 and 3. FIG. 2 relates to tests 1 to 3, and tests 4 and 5 are shown graphically in FIG.  3 . An arrow indicated “I” represents the point in time at which the fuel was ignited and an arrow indicated “E” indicates the point in time at which the fire was extinguished. 
     The result of each of the tests of the fire extinguishing apparatus  10  is that the fire was extinguished in a relatively short period of time and typically less than the 25 seconds. It should also be noted, particularly as shown in FIG. 3, that the temperature reducing effect of the fire extinguishing apparatus  10  is greater than that of carbon dioxide. This occurs because as the temperature in the risk area increases the volume of the water mist increases dramatically as it changes state from water mist to water vapour. Water vapour has a volume which is 1700 times greater than the volume of the water from which it was produced. Hence, the water vapour further displaces the oxygen from the risk area and inhibits the risk area from maintaining combustion. Also, in the change of state of the water from liquid to gas it absorbs heat 540 times greater than that of the liquid phase. Further, the increase in temperature of the risk area decreases the specific gravity of the water which increases its velocity, decreases its droplet size and increases the flow of the water throughout the risk area. That is, the water mist is more effective with increase in temperature of the risk area. This does not usually occur with other fire fighting mediums. 
     In FIG. 4 there is shown a graph of temperature versus time showing the minimum operational characteristics of the fire extinguishing apparatus  10 . The graph shows a pre-burn period denoted P, a stabilising temperature period denoted ST (which is typically 90 seconds) and at the end of which the fire extinguishing apparatus  10  is activated. Thereafter, the fire is extinguished within an extinguishing period denoted E which is typically less than 60 seconds and the container  12  is fully discharged within a discharge period denoted D which is typically greater than 90 seconds. During the pre-burn period the risk area typically reaches a temperature in excess of 300° C., which temperature is maintained during the temperature stabilisation period ST. Typically, the temperature in the risk area is reduced to 60% of the temperature in the stabilised temperature period ST before the container  12  is fully discharged. Typically,the final temperature within the risk zone is less than 250° C. The tests shown in FIGS. 2 and 3 show that these results are achievable with the fire extinguishing apparatus  10  of the present invention. 
     The abovementioned test were conducted using a cascade apparatus  200  shown in FIG.  5 . Th cascade tray  204  is designed to simulate fuel leaking onto a hot manifold. The cascade apparatus  200  comprises a relatively large box tray  202  having an area of approximately 1 square metre, a flat cascade tray  204  having a surface area of approximately 0.5 square metres, upon which is located a relatively small box tray  206 . The small box tray  206  has a plurality of holes  208  for allowing diesel from the box tray  206  to fall onto the flat cascade tray  204 . The cascade tray  204  has legs  210  spacing it above the tray  202 , and the tray  206  has legs  212  spacing it above the cascade tray  204 . Typically, the tray  202  has petrol and/or isopropanol located in it. In use, the cascade tray  204  becomes extremely hot and causes ignited fuel from the tray  206  to explode and be projected off the cascade apparatus  200 . 
     A further test of the fire extinguishing apparatus  10  of the present invention was conducted in a risk area having a volume of 500 m 3  (10 m×10 m×5 m) with 190 of the same nozzles  18  as used in the previous test. In this test 90 litres of fuel was used having an area of 7 m 2 . The fuel was contained in the cascade tray  204  and 6 other trays including pool fires and a diesel oil pressure fire (representing a fire from a ruptured fuel line). All of the trays were ignited and allowed to burn for two minutes before activation of the fire extinguishing apparatus  10  of the present invention. 
     During the test it was observed that the colour of he combustion by-products changed from thick black to white immediately the fire extinguishing apparatus  10  was started. The results of the test was that all of the fires were extinguished within 30 seconds and observers walked into the risk area before the completion of the 90 second period over which the mist is released into the risk area. The observers experienced no difficulty in breathing during that time. It appears from this test that the fire extinguishing apparatus  10  lead to suppression of smoke and causes combustion by-products to fall out of the air. 
     The fire extinguishing apparatus  10  of the present invention has the advantage that it can use water mist to fill a risk area so as to interrupt the flame chain reaction in the combustion cycle so as to prevent combustion within the risk area. Also, the water vapour has the effect of greatly reducing the heat within the risk area and displacing oxygen within the risk area due to the change in the state of the water from a liquid to a vapour (mist). Hence, the fire extinguishing apparatus  10  of the present invention has the surprising result that it can use a relatively small quantity of water to extinguish a flame caused by a relatively large quantity of highly flammable liquid. In Table 1 there is shown a comparison of the benefits of the fire extinguishing apparatus  10  of the present invention (referred to as MISTEX) with conventional fire extinguishing systems. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 COMPARISONS 
               
             
          
           
               
                   
                 SPRINKLER 
                 HALON 
                 CO 2   
                 MISTEX 
               
               
                   
                   
               
             
          
           
               
                 NON-TOXIC 
                 YES 
                 NO 
                 NO 
                 YES 
               
               
                 EXTINGUISH 
                 NO 
                 YES 
                 YES 
                 YES 
               
               
                 A &amp; B CLASS FIRES 
               
               
                 ENVIRONMENTALLY 
                 YES 
                 NO 
                 NO 
                 YES 
               
               
                 FRIENDLY 
               
               
                 REQUIRED 
                 YES 
                 NO 
                 NO 
                 NO 
               
               
                 FIRE PUMP 
               
               
                 LIGHT WEIGHT 
                 NO 
                 YES 
                 NO 
                 YES 
               
               
                 SERVICE 
                 NO 
                 NO 
                 NO 
                 YES 
               
               
                 ACCESSIBLE BY 
               
               
                 CREW 
               
               
                 HIGH HEAT 
                 YES 
                 NO 
                 NO 
                 YES 
               
               
                 ABSORPTION 
               
               
                 COST 
                 NO 
                 YES 
                 NO 
                 YES 
               
               
                 EFFECTIVENESS 
               
               
                 RUNNING TIME 
               
               
                 (IN-BUILT SAFETY) 
                 N/A 
                 NO 
                 NO 
                 YES 
               
               
                 NO EVACUATION 
                 YES 
                 NO 
                 NO 
                 YES 
               
               
                 PLAN REQUIRED 
               
               
                 SERVICE AND REFILL 
                 N/A 
                 NO 
                 NO 
                 YES 
               
               
                 COST 
               
               
                 EFFECTIVENESS 
               
               
                 EFFECTIVE IN SEMI- 
                 YES 
                 NO 
                 NO 
                 YES 
               
               
                 VENTILATED AREAS 
               
               
                   
               
             
          
         
       
     
     Modifications and variations such as would be apparent to a skilled addressee are considered within the scope of the present invention. For example, a heat absorber and fuel emulsifier such as, for example, a liquid under the trade mark PHIREX could be added to the water to increase its fire extinguishing capabilities. Also, any form of fire detector could be used in the fire extinguishing apparatus, such as, for example, radioisotope based fire detectors, ionic chamber detectors, beam detectors, ultraviolet detectors or the like.