Patent Publication Number: US-2005140515-A1

Title: Fire suppression system

Description:
The present invention relates to improvements in or relating to fire detection and suppression systems, and is more particularly, although not exclusively concerned with the utilisation of such systems on aircraft.  
      There is an increasing trend in the number of false aircraft cargo alarms. The ratio of false alarm events to actual fire or smoke events is also increasing and is typically of the order of 200 to 1;  
      In addition, the environmental concerns regarding stratospheric ozone layer protection has led to the production of Halon and other chlorofluorocarbons (CFCs) being phased out and hence their use as fire suppression agents. This means that other fire suppression agents need to be developed.  
      In aircraft, water mist fire suppression systems are now being introduced as replacements for CFC-based fire suppression systems. However, water-based systems carry a substantial weight penalty, and the weight of water needs to be reduced to a minimum.  
      U.S. Pat. No. 5,038,867 discloses a system for use in the freight and cargo space of aircraft for fire protection and for extinguishing a fire in such a space. The system comprises two containers which hold fire extinguishing media, for example, media which are liquid under pressure and become gaseous at atmospheric pressure. The system is initialised and triggered by smoke detection in the freight and cargo space and is operated by the aircraft pilot using a trigger switch. Operation of the trigger switch ruptures a safety membrane in one of the two containers in accordance with the location of the fire within the freight and cargo spaces. The fire extinguishing medium then flows from the container into a conduit network which distributes the medium to nozzles in the locality of the fire so that the fire is rapidly extinguished. If necessary, the medium in the other container can also be directed into the same conduit network for deployment through the same nozzles.  
      However, U.S. Pat. No. 5,038,867 is still prone to generating false alarms and the freight or cargo being transported may be damaged by the unnecessary use of the fire extinguishing media.  
      U.S. Pat. No. 4,423,326 discloses a fire or explosion detection system which can discriminate between radiation produced by a source of fire or explosion (e.g. a hydrocarbon fire) and radiation produced by a source which is not detected (e.g. an incendiary ammunition or pyrophoric reaction). The system comprises two detectors connected to a processor, each detector being sensitive to radiation in different wavelength bands, for example, respective narrow wavelength bands centred at 0.96 μm and 4.4 μm. The output from each detector is thresholded and passed to an AND gate. A third input to the AND gate is provided by a signal derived from the rate of change of one of the detector outputs when compared with a reference signal. When the AND gate receives three binary “1” signals, the output of the AND gate changes from binary “0” to binary “1” and if it is maintained for a predetermined period of time, fire or explosion suppression is initiated.  
      U.S. Pat. No. 6,195,011 discloses an early fire detection system which operates in a similar way to U.S. Pat. No. 4,423,326. This system senses two physical quantities relating to a fire, for example, smoke and temperature. When the first physical quantity (smoke) is detected, it is compared to a threshold value. If the threshold is exceeded an alarm condition is set. Similarly, an alarm condition is set when the second physical quantity (temperature) exceeds a threshold value. Further alarm conditions may be set corresponding to rate of change of one or more of the physical quantities and the combined rate of change of both physical quantities. The alarm is triggered in response to a cross-correlation of the set alarm conditions.  
      Both U.S. Pat. No. 4,423,326 and U.S. Pat. No. 6,195,011 utilise at least a two stage detection method prior to triggering operation of a fire suppression system.  
      It is well known to use thermocouple devices for sensing temperature. U.S. Pat. No. 4,904,091 shows a threaded average temperature thermocouple in which a thermocouple is located within a threaded bolt made of a material whose thermal properties are similar to those of material whose temperature is to be sensed. This relies on selecting the correct material for the bolt in order to effectively sense the temperature of a body.  
      U.S. Pat. No. 3,765,242 discloses a re-usable bolt type mounted thermocouple in which the mounting is slotted lengthwise to allow the thermocouple to be replaced and the mounting to be re-used.  
      It is one object of the present invention to provide an improved fire detection and suppression system.  
      It is a further object of the present invention to provide an improved sensing element for use in the improved fire detection and suppression system.  
      In accordance with one aspect of the present invention, there is provided a temperature sensing device comprising: 
          a bolt assembly;     a nut assembly mountable on the bolt assembly;     a sensor assembly located within the bolt assembly; and     a processing assembly located within the nut assembly, the processing assembly being connectable to the sensor assembly to process signals generated by the sensor assembly in response to temperature.        

      Advantageously, the processing assembly includes an electronics module and means for connecting the electronics module to a remote control unit. The electronics module is capable of storing a unique identification code for the device. The unique identification code may be determined in accordance with the location of the device with respect to a reference position.  
      Preferably, the processing assembly includes at least one indicator unit connected to the electronics module for indicating the operational status of the device. Said at least one indication unit comprises a light emitting diode. Preferably, two light emitting diodes are present, one green and one red.  
      The sensor assembly may comprise a sensor element having a connector portion for connecting with the processing assembly. Ideally, the sensor element comprises a thermocouple, but may comprise a semiconductor temperature sensing element. In either case, the sensor element is preferably mounted in a sheath within the bolt assembly. Advantageously, the sheath comprises a light pipe which transmits light from said at least indicator unit to an external surface of the device, for example, a head portion of the bolt assembly.  
      In accordance with a second aspect of the present invention, there is provided a fire detection system comprising: 
          at least one first detector for detecting the presence of smoke;     at least one second detector for detecting the presence of elevated temperatures; and     processing means connected each of said at least one first and second detectors for receiving signals therefrom indicative of the presence of smoke and elevated temperatures respectively, and for producing an indication of the presence of a fire;     characterized in that each of said second detector means comprises a temperature sensing device as described above.        

      Preferably, the processing means includes first comparison means for determining if the signals from said at least one first detector exceeds a first predetermined threshold, and second comparison means for determining if the signals from said at least one second detector exceeds a second predetermined threshold, the second comparison means being enabled by an output signal from the first comparison means when the first predetermined threshold is exceeded and produces the indication of the presence of a fire when the second predetermined threshold has been exceeded.  
      In accordance with a third aspect of the present invention, there is provided a fire suppression system comprising: 
          a fire detection system as described above;     fire suppression means for suppressing a fire;     control means for controlling the fire suppression means once a signal corresponding to the indication of the presence of the fire has been input.        

      Advantageously, the control means includes comparison means connectable to said at least one second detector for receiving signals therefrom, the comparison means determining if a predetermined threshold has been exceeded and provides a control signal for operating the fire suppression means. It is preferred that the comparison means receives signals from a plurality of second detectors whose signals have exceeded the second threshold in the second comparison means and provides control signals for the fire suppression means in the locality of said plurality of second detectors.  
      Preferably, the fire suppression means comprises a water mist system utilising a plurality of nozzles. 
    
    
      For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which:  
       FIG. 1  illustrates a fastener arrangement in accordance with the present invention;  
      FIGS.  2  to  5  illustrates components of the fastener arrangement of  FIG. 1 ;  
       FIG. 6  illustrates the electronics associated with the nut assembly of  FIG. 5 ;  
       FIG. 7  illustrates the nut assembly if  FIG. 5  in more detail;  
       FIG. 8  illustrates a fire detection system employing the fastener arrangement of  FIG. 1 ;  
       FIG. 9  illustrates fire suppression zone control in accordance with the present invention; and  
       FIG. 10  illustrates a fire detection and suppression system in accordance with the present invention. 
    
    
      The present invention relates to a water mist fire suppression system for aircraft cargo bay compartments which utilises a new fastener. The fastener is modular and can be constructed to fit all aircraft variants, and it serves the purposes of holding an aircraft cargo bay liner panel in situ and providing temperature detection thereby allowing the control of the water mist fire suppression system of which it forms a part.  
      Although the present invention will be described with reference to an aircraft cargo bay fire suppression system and a thermocouple sensor, it will be readily appreciated that the fire suppression system can be employed in other applications, and alternative temperature sensing elements could be employed which meet fastener constraints.  
      Turning now to  FIG. 1 , here a fastener arrangement  10  is shown. The arrangement  10  comprises a bolt assembly  12 , a nut assembly  14  and a removable or integrated temperature sensor assembly  16 . The bolt assembly  12 , the nut assembly  14  and the sensor assembly  16  will be described in more detail below.  
      As shown in  FIG. 1 , the bolt assembly  12  is utilised to retain a portion  18  of a cargo bay liner panel against a bracket  20 , in conjunction with the nut assembly  14 .  
      As shown, the bolt assembly  12  houses part of the sensor assembly  16  within a hollow bolt  22 . The sensor assembly  16  connects with an electronics module  24  housed in the nut assembly  14 . A connector  26  is provided on nut assembly for connecting to a control system (not shown).  
      The bolt assembly  12  includes a hollow bolt  22  which provides an aperture for the sensor assembly  16 , and is shaped at its head end to allow water to drip off. It is preferred that the head end be coated with a material which reduces water surface tension and prevents water collection on its surface. As mentioned above, the bolt assembly  12  functions to retain a cargo bay liner panel  18  in position. However, the nut assembly  14  is required to hold the bolt assembly  12  in place thereby retaining the cargo bay liner panel  18 .  
      The nut assembly  14  houses the electronics module  24  which processes the signals received from the sensor assembly  16 . The module  24  includes a bus transceiver for data transmission between the fastener arrangement  10  and any control system (not shown) to which it is connected. The module  24  also includes built-in test and electronic identification as will be described in more detail below. The nut assembly  14  may also include one or more light emitting diodes (LEDs).  
      The sensor assembly  16  includes a temperature sensor which provides fire detection monitoring for the system (not shown) with which the fastener arrangement  10  is associated. It may include a transparent insulator around a sensor element which also acts as a light pipe to allow the operational status of the sensor element to be indicated through illumination from the nut assembly  14 .  
       FIG. 2  illustrates the bolt assembly  14  with the sensor assembly  16  located within it. As shown, the bolt  22  houses the sensor assembly  16  such that a sensor element  28  extends the length of the bolt  22  but is present at the surface of head portion  30  of the bolt  22  and extends beyond the end of shank portion  32 . Sensor element  28  comprises a thermocouple  34  located within a light pipe  36  and has a connector portion  38  formed in the exposed end of the thermocouple  34 .  
       FIG. 3  illustrates the sensor element  28  in more detail. Components which have been previously described are referenced the same. As shown in  FIG. 3 , the thermocouple  34  extends beyond the light pipe  36  in which it is mounted at both ends. One end of the light pipe  36  includes two locating pegs  40  (only one of which can be seen) which locates in slots formed in the hollow shank portion  32  ( FIG. 2 ) of the bolt  22 . The end of the thermocouple  34  has a connector portion  38  formed in it which extends beyond the bolt  22  and engages with connections in the nut assembly  14 .  
       FIG. 4  illustrates the bolt  22  and, in particular, slots  42  formed in the edge of shank portion  32  of bolt  22 . The head portion  30  of the bolt  22  is selected so that a) it minimises water collection; b) the sensor assembly  18  is not damaged during assembly; and c) a standard nut runner can be used to screw the bolt assembly  12  into the nut assembly  14 . The head portion  30  may also be selected so that it is easily distinguished from the rest of the cargo bolts holding the cargo bay liner panel in place.  
      Naturally, the bolt  22  has mechanical integrity with an equivalent fixture which has a hole extending through the middle thereof.  
       FIG. 5  illustrates the nut assembly  14 , and comprises a nut portion  44  for retaining the bolt  22  in place, and electronics module  24  for processing data received by the thermocouple  34  and for transmitting the data to a control system (not shown) via a data bus connection (also not shown).  
      The electronics module  24  and nut portion  44  are mounted in a housing  46 , and as mentioned above, a connector  26  is provided on the housing  46  of the nut assembly  14  for connecting to the control system (not shown).  
      A suitable connector (not shown) is also present in the housing  46  for connecting with the connector  38  of the sensor element  28  of the sensor assembly  16  once the nut assembly  14  has been attached onto the bolt assembly  12  via nut portion  44  and shank portion  32 . It will be appreciated that at least a portion of the shank portion  32  of the bolt  22  is threaded so as to receive nut portion  44  thereon.  
      The connector is also connected to the electronics module  24  for supplying signals thereto from the thermocouple  34 .  
      The electronics module  24  includes a thermocouple amplifier and junction compensation unit  48  coupled to an analogue-to-digital (A/D) converter  50 . The amplifier/compensation unit  48  amplifies the signals received from the thermocouple  34  and passes them to the A/D converter  50  where they are digitised for passing to control electronics/bus transceiver unit  52 . The control electronics/bus transceiver unit  52  also includes a built in test system (BIT) and programmable electronic identification. A standard serial aircraft data bus chip set may be used as the bus transceiver and a field programmable gate array (FPGA) may act as BIT and control electronics of unit  52 . The BIT function provides information relating to whether the sensor assembly  16  is operating within prescribed limits or has failed.  
      The unit  52  may also include an electrical erasable programmable read only memory (EEPROM) as a memory for electronic identification of the sensor assembly  16 . The EEPROM can be programmed via the bus transceiver.  
      The unit  52  may be implemented as a surface mount double sided printed circuit board (PCB) or in a mixed analogue and digital gate array.  
      LEDs may also be included in nut assembly  14  as shown in  FIG. 7 . As before, components which have been described above are referenced the same. In  FIG. 7 , a connector  54  is shown for connecting the sensor assembly  16  to the electronics module  24 , and two LEDs  56 ,  58  which are used to indicate the operational status of the sensor assembly  16 . The connector  54  makes contact with connector  38  of the sensor element  28  in any suitable way which allows the transfer of signals from the thermocouple  34  to the electronics module  24 .  
      As the thermocouple  34  is housed in a light pipe  36 , the light from the LEDs  56 ,  58  can be transmitted from the nut assembly  14  to the head portion  50  of the bolt  22  via the light pipe  36  to provide an indication to maintenance personnel of the operating status of the sensor assembly  16 . The light pipe  36  also acts as a sheath to protect the thermocouple  34  from damage, insulates the sensor or thermocouple  34  from the bolt  22 , and provides mechanical strength to the sensor assembly  16 .  
      A fire detection system in accordance with the present invention will now be described with reference to  FIG. 8 .  FIG. 8  shows a fire detection system  60  which comprises a plurality of sensors  64 ,  66  located in a cargo bay compartment  62  and a fire detection computer  68  connected to the sensors  64 ,  66 , the computer  68  producing an output  74  indicative of a fire in the cargo bay compartment  62  when certain conditions have been met, the output  74  being connected to a warning  76  on the flight deck of the aircraft.  
      Sensors  66  are smoke detectors as are well known in the field, and provide output signals to a smoke discriminating unit  70  in the computer  68 .  
      The sensors  64  are fastener arrangements as described above with particular reference to  FIG. 1 . The sensors  64  are connected to a temperature discriminating unit  72  in the computer  68 .  
      In operation, the computer  68  continuously receives signals from sensors  64 ,  66  but output  74  is not initiated until certain conditions have been met. When smoke is detected by sensors  66  in the cargo bay compartment  62 , signals are provided to smoke discriminating unit  70  and when the signals reach a threshold or trigger level an output signal is provided to the temperature discriminating unit  72 . At the same time as smoke is being detected by sensors  66 , sensors  64  are detecting temperature in the cargo bay compartment  62 . The output signal from the smoke discriminating unit  70  enables signals from sensors  64  to be compared to a threshold or trigger level. Once the threshold or trigger level has been achieved, the temperature discriminating unit provides output  74  indicating that a fire is present in the compartment  62 . The output  74  is passed as a warning  76  to the flight deck where appropriate action is taken to extinguish the fire.  
      The sensors  64 ,  66  are arranged in a suitable grid within the compartment  62  and each sensor is connected to a signal bus for transferring signals from each sensor  64 ,  66  to respective ones of the smoke and temperature discriminating units  70 ,  72  as shown.  
      It will readily be understood that the fire detection system  60  is a two stage or two layer system which requires two separate events to occur prior to triggering the warning signal. It is possible that the warning signal itself may be used to activate fire extinguishing or fire suppression equipment.  
      It is known to use water as a fire extinguishing agent, but as discussed above the quantity of water which is needed to tackle the fire has a serious weight disadvantage if the water is to be used in a flooding system, that is, if all the nozzles are turned on in the cargo bay compartment. Water weight can be reduced by only activating nozzles where the fire threat is located. This is shown in  FIG. 9 .  
       FIG. 9  shows a cargo bay compartment  62  in which a plurality of water nozzles  78  are located. A fire is located in an area  80  and a fire control zone  82  surrounds the area  80 . Here, only four nozzles  84  are activated to suppress or extinguish the fire. In this arrangement, it is necessary to measure the temperature at a sufficiently small grid spacing to determine if a nozzle is to be activated or not.  
      Water weight can be further reduced if the nozzles are only activated in bursts when the temperature exceeds a predetermined level. In such a system, the fastener arrangements  10  will need to be spaced in a grid. Furthermore, if the water is applied as a directed fine mist even less water is required.  
      A fire suppression system  100  utilising the fire zone control of  FIG. 9  is shown in  FIG. 10 . In  FIG. 10 , a cargo bay compartment  102  includes a plurality of smoke detectors  104 , a plurality of temperature sensors  106  and a plurality of water nozzles  108 . As shown, the smoke detectors  104  are located centrally within the compartment  102 , and the temperature sensors  106  are arranged in a grid around the water nozzles  108 . In the embodiment shown, there are four temperature sensors  106  for each water nozzle  108 . It will, however, be appreciated that any other suitable number of temperature sensors  106  can be associated with each water nozzle  108 . Similarly, any suitable number of smoke detectors  104 , temperature sensors  106  and nozzles  108  can be provided in the compartment  102 .  
      The sensors  104 ,  106  are connected to a fire detection and suppression computer  110  which determines if there is a fire and suppresses the fire when armed by the aircraft crew. The computer  110  includes a smoke discriminating unit  112  which determines if the level of smoke in the compartment  102  exceeds a threshold or trigger level, and provides an output signal for a temperature discriminating unit  114  when the threshold or trigger level has been exceeded. The temperature discriminating unit  114  is connected to the temperature sensors  106  in the compartment  102  and receives signals therefrom indicative of elevated temperatures at one or more locations within the compartment  102 . When the temperature in one or more location exceeds a threshold or trigger level, an output signal  116  is provided indicative of the presence of fire in the compartment  102  and the location(s) of the fire within the compartment  102 . This is similar to the fire detection system  60  as previously described with reference to  FIG. 8 .  
      The output signal  116  is used to alert the crew via a warning on the flight deck and the crew then arms the fire suppression system as shown by block  118 . Arming the fire suppression system provides an input to the computer  110  and initiates activation of the suppression system (box  120 ). The output signal  116  is also fed directly to box  120  so that the location of the fire is available for the suppression system. Once activated, a further temperature discriminating unit  122  determines if a threshold or trigger level has been exceeded. If it has, an output signal is provided to nozzle activation unit  124  which activates the nozzles  108  in one or more areas where the threshold level has been exceeded for a burst period, e.g.  4 s. After each burst has ended, the temperature discriminating unit  122  is reactivated and the process is repeated. It will be appreciated that the nozzle activation unit  124  is connected to the water supply (not shown) and each nozzle  108  so that control of the water mist can be achieved.  
      Although two temperature discriminating units  114 ,  122  are shown, it will be understood that a single unit could be utilised to sense/detect the temperature exceeding one or more threshold or trigger levels.  
      It will be appreciated that the threshold or trigger levels utilised in the temperature discriminating units  114 ,  122  may be the same or may be different in accordance with a particular application.  
      In accordance with the present invention, the fastener arrangement  10  can be implemented in the fire detection system of  FIG. 8  and the fire detection and suppression system of  FIG. 10 .  
      The fastener arrangement  10  has the advantage of combining a cargo bay liner panel fastener with a temperature sensor. Because of its modular construction, different bolt assemblies, nut assemblies and sensor assemblies can be combined for different applications. The optional provision of the light pipe allows a maintenance engineer or the like to determine whether the sensor is operating properly or not when they are in the compartment or in situ according to the particular application.  
      Advantageously, fire detection false alarm rates can be improved using the fastener arrangement of the present invention by providing two layer protection.  
      The fastener arrangement of the present invention is simple, robust and is compatible with existing fasteners. Moreover, the arrangement is easy to assemble, is of low cost both in manufacturing and maintenance.