Abstract:
A fire suppression system for a substantially enclosed area comprises: a plurality of solid propellant aerosol generators disposed about the enclosed area for exhausting a fire suppressant aerosol that is substantially void of an ozone depleting material into the enclosed area. Each aerosol generator including an ignition element for igniting the solid propellant thereof. Each ignition element of the aerosol generators being coupled to a fire control unit which is operative to ignite the solid propellant of at least one aerosol generator utilizing the ignition element thereof to exhaust fire suppressant aerosol into the enclosed area. Each aerosol generator preferably includes a container which comprises: a housing including an orifice for exhausting the fire suppressant aerosol; a solid propellant disposed inside of the housing; at least one cover mounted to the housing to seal correspondingly at least one open side thereof; an ignition material coupled to the solid propellant for igniting the solid propellant to produce the fire suppressant aerosol; and at least one baffle disposed integral to the housing to capture non-usable effluent.

Description:
This application claims the benefit of the Provisional application No. 60/323,824 filed Sep. 21, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is directed to fire suppression systems, in general, and more specifically to a fire suppression system and a plurality of aerosol generators for dispensing a fire suppressant material, that is substantially void of an ozone depleting material, promptly into the affected storage area, and a solid propellant container preferably for use therein. 
     It is of paramount importance to detect a fire in an unattended, storage area or enclosed storage compartment at an early stage of progression so that it may be suppressed before spreading to other compartments or areas adjacent or in close proximity to the affected storage area or compartment. This detection and suppression of fires becomes even more critical when the storage compartment is located in a vehicle that is operated in an environment isolated from conventional fire fighting personnel and equipment, like a cargo hold of an aircraft, for example. Current aircraft fire suppressant systems include a gaseous material, like Halon® 1301, that is compressed in one or more containers at central locations on the aircraft and distributed through piping to the various cargo holds in the aircraft. When a fire is detected in a cargo hold, an appropriate valve or valves in the piping system is or are activated to release the Halon fire suppressant material into the cargo hold in which fire was detected. The released Halon material is intended to blanket or flood the cargo hold and put out the fire. Heretofore, this has been considered an adequate system. 
     However, the Halon material of the current systems contains an ozone depleting material which may leak from the storage compartment and into the environment upon being activated to suppress a fire. Most nations of the world prefer banning this material to avoid its harmful effects on the environment. Also, Halon produces toxic products when activated by flame. Accordingly, there is a strong desire to find an alternate material to Halon and a suitable fire suppressant system for dispensing it as needed. 
     For cargo holds of aircraft, a fire in the hold indication requires not only a dispensing of the fire suppressant material, but also a prompt landing of the aircraft at the nearest airport. The aircraft will then remain out of service until clean up is completed and the aircraft is certified to fly again. This unscheduled servicing of the aircraft is very costly to the airlines and inconveniences the passengers thereof. The problem is that some activations of the fire suppressant system result from false alarms of the fire detection system, i.e. caused by a perceived fire condition that is something other than an actual fire. Thus, the costs and inconveniences incurred as a result of the dispensing of the fire suppressant material under false alarm conditions could have been avoided with a more accurate and reliable fire detection system. 
     The present invention intends to overcome the drawbacks of the current fire detection and suppressant systems and to offer a system which detects a fire accurately and reliably, generates a fire indication and provides for a quick dispensing of a fire suppressant, which does not include substantially an ozone depleting material, focused within the storage compartment in which the fire is detected. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a solid propellant container for exhausting a fire suppressant aerosol comprises: a housing having at least one open side and including a multiplicity of orifices for exhausting the fire suppressant aerosol; a solid propellant disposed inside of the housing; at least one cover mounted to the housing to seal correspondingly the at least one open side thereof; an ignition material coupled to the solid propellant for igniting the solid propellant to produce the fire suppressant aerosol; and at least one baffle integral to the housing to capture non-usable effluent. 
     In accordance with another aspect of the present invention, a fire suppression system for a substantially enclosed area comprises: a plurality of solid propellant aerosol generators disposed about the enclosed area for exhausting a fire suppressant aerosol that is substantially void of an ozone depleting material into the enclosed area, each aerosol generator including an ignition element for igniting the solid propellant thereof; and a fire control unit, each ignition element of the aerosol generators being coupled to the fire control unit which is operative to ignite the solid propellant of at least one aerosol generator utilizing the ignition element thereof to exhaust fire suppressant aerosol into the enclosed area. 
     In accordance with yet another aspect of the present invention, a fire suppression system for a plurality of substantially enclosed areas comprises: a plurality of solid propellant aerosol generators disposed about each enclosed area of the plurality for exhausting a fire suppressant aerosol that is substantially void of an ozone depleting material into at least one enclosed area, each aerosol generator including an ignition element for igniting the solid propellant thereof; and a fire control unit for each enclosed area of the plurality, each fire control unit being coupled to the ignition elements of the aerosol generators of the corresponding enclosed area and is operative to ignite the solid propellant of at least one aerosol generator of the corresponding enclosed area utilizing the ignition element thereof to exhaust fire suppressant aerosol into the corresponding enclosed area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sketch of a fire detection and suppression system for use in a storage compartment suitable for embodying the principles of the present invention. 
         FIGS. 2 and 3  are top and bottom isometric views of an exemplary aerosol generator assembly suitable for use in the embodiment of FIG.  1 . 
         FIGS. 4 and 5  are bottom and top isometric views of an exemplary aerosol generator assembly compartment mounting suitable for use in the embodiment of FIG.  1 . 
         FIG. 6  is a block diagram schematic of an exemplary fire detector unit suitable for use in the embodiment of FIG.  1 . 
         FIG. 7  is a block diagram schematic of an exemplary imager unit suitable for use in the embodiment of FIG.  1 . 
         FIG. 8  is a block diagram schematic of an overall fire detection system suitable for use in the application of an aircraft. 
         FIG. 9  is a block diagram schematic of an exemplary fire suppression system suitable for use in the application of an aircraft. 
         FIG. 10  is an isometric view of an exemplary aerosol generator illustrating exhaust ports thereof suitable for use in the embodiment of FIG.  1 . 
         FIG. 11  is an expanded view assembly illustration of the aerosol generator of FIG.  10 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A sketch of a fire detection and suppression system for use at a storage area or compartment suitable for embodying the principles of the present invention is shown in cross-sectional view in FIG.  1 . Referring to  FIG. 1 , a storage compartment  10  which may be a cargo hold, bay or compartment of an aircraft, for example, is divided into a plurality of detection zones or cavities  12 ,  14  and  16  as delineated by dashed lines  18  and  20 . It is understood that an aircraft may have more than one cargo compartment and the embodiment depicted in  FIG. 1  is merely exemplary of each such compartment. It is intended that each of the cargo compartments  10  include one or more aerosol generators for generating a fire suppressant material. In the present embodiment, a plurality of hermetically sealed, aerosol generators depicted by blocks  22  and  24 , which may be solid propellant in ultra-low pressure aerosol generators, for example, are disposed at a ceiling portion  26  of the cargo compartment  10  above vented openings  28  and  30  as will be described in greater detail herein below. 
     In the present embodiment, the propellant of the plurality of aerosol generators  22  and  24  produces upon ignition an aerosol that is principally potassium bromide. The gaseous products are principally water, carbon dioxide and nitrogen. For aircraft applications, each of the aerosol generators  22  and  24  has a large orifice instead of the conventional sonic nozzles. As a result, the internal pressure during the discharge period is approximately 10 psig. During storage and normal flight the pressure inside the generator is the normal change in pressure that occurs in any hermetically sealed container that is subjected to changes in ambient conditions. 
     Test results of aerosol generators of the solid propellant type are shown in Table 1 below. The concept that is used for Extended Twin Operations (ETOPS) up to 540 minutes is to expend a series of aerosol generators of 3½ lbs each for each 2000 cubic feet. This would create the functional equivalent of an 8% Halon 1301 system. At 30 minutes, the concentration would be reduced to the functional equivalent of 4½% Halon 1301. At that point, another aerosol generator may be expended every 30 minutes. Different quantities of aerosol generators may be used based upon the size of the cargo bay. It is understood that the size and number of the generators for a cargo compartment may be modified based on the size of the compartment and the specific application. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Requirements Of Present Embodiment vs. Halon in 2000 Cubic Feet 
               
             
          
           
               
                   
                 Suppression 
                 Design 
                 30 Minute 
               
               
                   
                 Threshold 
                 Minimum 
                 initial Release 
               
               
                   
                   
               
             
          
           
               
                 Fuel Fire 
                 3.5 
                 pounds 
                 4.6 
                 pounds 
                 9.2 
                 pounds 
               
               
                 Bulk Load Test 
                 &lt;2.5 
                 pounds 
                 &lt;2.5 
                 pounds 
                 &lt;2.5 
                 pounds 
               
               
                 Container Test 
                 3.5 
                 pounds 
                 4.6 
                 pounds 
                 9.2 
                 pounds 
               
               
                 Aerosol Can 
                   
                   
                 4.6 
                 pounds 
               
               
                 Test 
               
               
                 Halon 
                 25 
                 pounds = 
                 33 
                 pounds = 
                 66 
                 pounds = 
               
               
                 requirement 
                 3% 
                 of Halon 
                 4% 
                 of Halon 
                 8% 
                 of Halon 
               
               
                   
               
             
          
         
       
     
     An exemplary hermetically sealed, aerosol generator  22 ,  24  with multiple outlets  25  for use in the present embodiment is shown in the isometric sketch of FIG.  10 . The aerosol generator  22 , 24  may employ the same or similar initiator that has been used in the US Air Force&#39;s ejection seats for many years which has a history of both reliability and safety. Its ignition element consists of two independent 1-watt/1-ohm bridge wires or squibs, for example. The aerosol generator  22 ,  24  for use in the present embodiment will be described in greater detail herein below in connection with the break away assembly illustration of FIG.  11 . 
     In the top view of FIG.  2  and bottom view of  FIG. 3 , the sealed container  22 , 24  is shown mounted to a base  32  by supporting straps  34  and  36 , for example. The bottom of the base  32  which has a plurality of openings  38  and  40  may be mounted to the ceiling  26  over vented portions  28  and  30  thereof to permit passage of the aerosol and gaseous fire suppressant products released or exhausted from the aerosol generator via outlets  25  out through the vents  28  and  30  and into the compartment  10 . 
     The present example employs four aerosol generators located in two places  22 ,  24  for compartment  10  which are shown in bottom view in FIG.  4  and top view in FIG.  5 . As shown in  FIGS. 4 and 5 , in the present embodiment, each of the four aerosol generators  42 ,  44 ,  46  and  48  is installed with its base over a respectively corresponding vented portion  50 ,  52 ,  54 ,  56  of the ceiling  26 . Accordingly, when initiated, each of the aerosol generators will generate and release its aerosol and gaseous fire suppressant products through the openings in its respective base and vented portion of the ceiling into the compartment  10 . 
     With the present embodiment, the attainment of 240 or 540 minutes or longer of fire suppressant discharge is a function of how many aerosol generators are used for a compartment. It is expected that the suppression level will be reached in an empty compartment in less than 10 seconds, for example. This time may be reduced in a filled compartment. Aerosol tests demonstrated that the fire suppressant generated by the aerosol generators is effective for fuel/air explosives also. In addition, the use of independent aerosol generator systems for each cargo compartment further improved the system&#39;s effectiveness. For a more detailed description of solid propellant aerosol generators of the type contemplated for the present embodiment, reference is made to the U.S. Pat. No. 5,861,106, issued Jan. 19, 1999, and entitled “Compositions and Methods For Suppressing Flame” which is incorporated by reference herein. This patent is assigned to Universal Propulsion Company, Inc. which is the same assignee and/or a wholly-owned subsidiary of the parent company of the assignee of the instant application. A divisional application of the referenced &#39;106 patent was later issued as U.S. Pat. No. 6,019,177 on 1 Feb. 2000 having the same ownership as its parent &#39;106 patent. 
     Referring back to  FIG. 1 , as explained above, each cargo compartment  10  may be broken into a plurality of detection zones  12 ,  14  and  16 . The number of zones in each cargo compartment will be determined after sufficient testing and analysis in order to comply with the application requirements, like a one minute response time, for example. The present embodiment includes multiple fire detectors distributed throughout each cargo compartment  10  with each fire detector including a variety of fire detection sensors. For example, there may be two fire detectors installed in each zone  12 ,  14  and  16  in a dual-loop system. The two fire detectors in each zone may be mounted next to each other, inside pans located above the cargo compartment ceiling  26 , like fire detectors  60   a  and  60   b  for zone  12 , fire detectors  62   a  and  62   b  for zone  14  and  64   a  and  64   b  for zone  16 , for example. In the present embodiment, each of the fire detectors  60   a ,  60   b ,  62   a ,  62   b ,  64   a  and  64   b  may contain three different fire detection sensors: a smoke detector, a carbon monoxide (CO) gas detector, and hydrogen (H 2 ) gas detector as will be described in greater detail herein below. While in the present application a specific combination of fire detection sensors is being used in a fire detector, it is understood that in other applications or storage areas, different combinations of sensors may be used just as well. 
     In addition, at least one IR imager may be disposed at each cargo compartment  10  for fire detection confirmation, but it is understood that in some applications imagers may not be needed. In the present embodiment, two IR imagers  66   a  and  66   b  may be mounted in opposite top corners of the compartment  10 , preferably behind a protective shield, in the dual-loop system. This mounting location will keep each imager out of the actual compartment and free from damage. Each imager  66   a  and  66   b  may include a wide-angle lens so that when aimed towards the center or bottom center of the compartment  10 , for example, the angle of acceptance of the combination of two imagers will permit a clear view of the entire cargo compartment including across the ceiling and down the side walls adjacent the imager mounting. It is intended for the combination of imagers to detect any hot cargo along the top of the compartment, heat rise from cargo located below the top, and heat reflections from the compartment walls. Each fire detector  60   a ,  60   b ,  62   a ,  62   b ,  64   a  and  64   b  and IR imagers  66   a  and  66   b  will include self-contained electronics for determining independently whether or not it considers a fire to be present and generates a signal indicative thereof as will be described in greater detail herein below. 
     All fire detectors and IR imagers of each cargo compartment  10  may be connected in a dual-loop system via a controller area network (CAN) bus  70  to cargo fire detection control unit (CFDCU) as will be described in more detail in connection with the block diagram schematic of FIG.  8 . The location of the CFDCU may be based on the particular application or aircraft, for example. A suitable location for mounting the CFDCU in an aircraft is at the main avionics bay equipment rack. 
     A block diagram schematic of an exemplary fire detector unit suitable for use in the present embodiment is shown in FIG.  6 . Referring to  FIG. 6 , all of the sensors used for fire detection are disposed in a detection chamber  72  which includes a smoke detector  74 , a carbon monoxide (CO) sensor  76 , and a hydrogen (H 2 ) sensor  78 , for example. The smoke detector  74  may be a photoelectric device that has been and is currently being used extensively in such applications as aircraft cargo bays, and laboratory, cabin, and electronic bays, for example. The smoke detector  74  incorporates several design features which greatly improves system operational reliability and performance, like free convection design which maximizes natural flow of the smoke through the detection chamber, computer designed detector labyrinth which minimizes effects of external and reflected light, chamber screen which prevents large particles from entering the detector labyrinth, use of solid state optical components which minimizes size, weight, and power consumption while increasing reliability and operational life, provides accurate and stable performance over years of operation, and offers an immunity to shock and vibration, and isolated electronics which complete environmental isolation of the detection electronics from the contaminated smoke detection chamber. 
     More specifically, in the smoke detector, a light emitting diode (LED)  80  and photoelectric sensor (photo diode)  82  are mounted in an optical block within the labyrinth such that the sensor  82  receives very little light normally. The labyrinth surfaces may be computer designed such that very little light from the LED  80  is reflected onto the sensor, even when the surfaces are coated with particles and contamination build-up. The LED  80  may be driven by an oscillating signal  86  that is synchronized with a photodiode detection signal  88  generated by the photodiode  82  in order to maximize both LED emission levels and detection and/or noise rejection. The smoke detector  74  may also include built-in test (BIT), like another LED  84  which is used as a test light source. The test LED  84  may be driven by a test signal  90  that may be also synchronized with the photodiode detection signal  88  generated by the photodiode  82  in order to better effect a test of the proper operation of the smoke detector  74 . 
     Chemical sensors  76  and  78  may be each integrated on and/or in a respective semiconductor chip of the micro-electromechanical system (MEMS)-based variety for monitoring and detecting gases which are the by-products of combustion, like CO and H 2 , for example. The semiconductor chips of the chemical sensors  76  and  78  may be each mounted in a respective container, like a TO-8 can, for example, which are disposed within the smoke detection chamber  72 . The TO-8 cans include a screened top surface to allow gases in the environment to enter the can and come in contact with the semiconductor chip which measures the CO or H 2  content in the environment. 
     More specifically, in the present embodiment, the semiconductor chip of the CO sensor  76  uses a multilayer MEMS structure. A glass layer for thermal isolation is printed between a ruthenium oxide (RuO 2 ) heater and an alumina substrate. A pair of gold electrodes for the heater is formed on a thermal insulator. A tin oxide (SnO 2 ) gas sensing layer is printed on an electrical insulation layer which covers the heater. A pair of gold electrodes for measuring sensor resistance or conductivity is formed on the electrical insulator for connecting to the leads of the TO-8 can. Activated charcoal is included in the area between the internal and external covers of the TO-8 can to reduce the effect of noise gases. In the presence of CO, the conductivity of sensor  76  increases depending on the gas concentration in the environment. The CO sensor  76  generates a signal  92  which is representative of the CO content in the environment detected thereby. It may also include BIT for the testing of proper operation thereof. This type of CO sensor displayed good selectivity to carbon monoxide. 
     In addition, the semiconductor chip of the H 2  sensor  78  in the present embodiment comprises a tin dioxide (SnO 2 ) semiconductor that has low conductivity in clean air. In the presence of H 2 , the sensor&#39;s conductivity increases depending on the gas concentration in the air. The H 2  sensor  78  generates a signal  94  which is representative of the H 2  content in the environment detected thereby. It may also include BIT for the testing of proper operation thereof. Integral heaters and temperature sensors within both the CO and H 2  sensors,  76  and  78 , respectively, stabilize their performance over the operating temperature and humidity ranges and permit self-testing thereof. For a more detailed description of such MEMS-based chemical sensors reference is made to the co-pending patent application bearing Ser. No. 09/940,408, filed on Aug. 27, 2001 and entitled “A Method of Self-Testing A Semiconductor Chemical Gas Sensor Including An Embedded Temperature Sensor” which is incorporated by reference herein. This application is assigned to Rosemount Aerospace Inc. which is the same assignee and/or a wholly-owned subsidiary of the parent company of the assignee of the instant application. 
     Each fire detector also includes fire detector electronics  100  which may comprise solid-state components to increase reliability, and reduce power consumption, size and weight. The heart of the electronics section  100  for the present embodiment is a single-chip, highly-integrated conventional 8-bit microcontroller  102 , for example, and includes a CAN bus controller  104 , a programmable read only memory (ROM), a random access memory (RAM), multiple timers (all not shown), multi-channel analog-to-digital converter (ADC)  106 , and serial and parallel I/O ports (also not shown).The three sensor signals (smoke  88 , CO  92 , and H 2    94 ) may be amplified by amplifiers  108 ,  110  and  112 , respectively, and fed into inputs of the microcontroller&#39;s ADC  106 . Programmed software routines of the microcontroller  102  will control the selection/sampling, digitization and storage of the amplified signals  88 ,  92  and  94  and may compensate each signal for temperature effects and compare each signal to a predetermined alarm detection threshold. In the present embodiment, an alarm condition is determined to be present by the programmed software routine if all three sensor signals are above their respective detection threshold. A signal representative of this alarm condition is transmitted along with a digitally coded fire detection source identification tag to the CFDCU over the CAN bus  70  using the CAN controller  104  and a CAN transceiver  114 . 
     Using preprogrammed software routines, the microcontroller  102  may perform the following primary control functions for the fire detector: monitoring the smoke detector photo diode signal  88 , which varies with smoke concentration; monitoring the CO and H 2  sensor conductivity signals  92  and  94 , which varies with their respective gas concentration; identifying a fire alarm condition, based on the monitored sensor signals; receiving and transmitting signals over the CAN bus  70  via controller  104  and transceiver  114 ; generating discrete ALARM and FAULT output signals  130  and  132  via gate circuits  134  and  36 , respectively; monitoring the discrete TEST input signal  124  via gate  138 ; performing built-in-test functions as will be described in greater detail herebelow; and generating supply voltages from a VDC power input via power supply circuit  122 . 
     In addition, the microcontroller  102  communicates with a non-volatile memory  116  which may be a serial EEPROM (electrically erasable programmable read only memory), for example, that stores predetermined data like sensor calibration data and maintenance data, and data received from the CAN bus, for example. The microcontroller  102  also may have a serial output data bus  118  that is used for maintenance purposes. This bus  118  is accessible when the detector is under maintenance and is not intended to be used during normal field operation. It may be used to monitor system performance and read detector failure history for troubleshooting purposes, for example. All inputs and outputs to the fire detector are filtered and transient protected to make the detector immune to noise, radio frequency (RF) fields, electrostatic discharge (ESD), power supply transients, and lightning. In addition, the filtering minimizes RF energy emissions. 
     Each fire detector may have BIT capabilities to improve field maintainability. The built-in-test will perform a complete checkout of the detector operation to insure that it detects failures to a minimum confidence level, like 95%, for example. In the present embodiment, each fire detector may perform three types of BIT: power-up, continuous, and initiated. Power-up BIT will be performed once at power-up and will typically comprise the following tests: memory test, watchdog circuit verification, microcontroller operation test (including analog-to-digital converter operation), LED and photo diode operation of the smoke detector  74 , smoke detector threshold verification, proper operation of the chemical sensors  76  and  78 , and interface verification of the CAN bus  70 . Continuous BIT testing may be performed on a continuous basis and will typically comprise the following tests: LED operation, Watchdog and Power supply ( 122 ) voltage monitor using the electronics of block  120 , and sensor input range reasonableness. Initiated BIT testing may be initiated and performed when directed by a discrete TEST Detector input signal  124  or by a CAN bus command received by the CAN transceiver  114  and CAN controller  104  and will typically perform the same tests as Power-up BIT. 
     A block diagram schematic of an exemplary IR imager suitable for use in the fire detection system of the present embodiment is shown in FIG.  7 . Referring to  FIG. 7 , each imager is based on infrared focal plane array technology. A focal plane infrared imaging array  140  detects optical wavelengths in the far infrared region, like on the order of 8-12 microns, for example. Thermal imaging is done at around 8-12 microns since room temperature objects emit radiation in these wavelengths. The exact field-of-view of a wide-angle, fixed-focus lens of the IR imager will be optimized based on the imager&#39;s mounting location as described in connection with the embodiment of FIG.  1 . Each imager  66   a  and  66   b  is connected to and controlled by the CAN bus  70 . Each imager may output a video signal  142  to the aircraft cockpit in the standard NTSC format. Similar to the fire detectors, the imagers may operate in both “Remote Mode” and “Autonomous Mode”, as commanded by the CAN bus  70 . 
     The imager&#39;s infrared focal plane array (FPA)  140  may be an uncooled microbolometer with 320 by 240 pixel resolution, for example, and may have an integral temperature sensor and thermoelectric temperature control. Each imager may include a conventional digital signal processor (DSP)  144  for use in real-time, digital signal image processing. A field programmable gate array (FPGA)  146  may be programmed with logic to control imager components and interfaces to the aircraft, including the FPA  140 , a temperature controller, analog-to-digital converters, memory, and video encoder  148 . Similar to the fire detectors, the FPGA  146  of the imagers may accept a discrete test input signal  150  and output both an alarm signal  152  and a fault signal  154  via circuits  153  and  155 , respectively. The DSP  144  is preprogrammed with software routines and algorithms to perform the video image processing and to interface with the CAN bus via a CAN bus controller and transceiver  156 . 
     The FPGA  146  may be programmed to command the FPA  140  to read an image frame and digitize and store in a RAM  158  the IR information or temperature of each FPA image picture element or pixel. The FPGA  146  may also be programmed to notify the DSP  144  via signal lines  160  when a complete image frame is captured. The DSP  144  is preprogrammed to read the pixel information of each new image frame from the RAM  158 . The DSP  144  is also programmed with fire detection algorithms to process the pixel information of each frame to look for indications of flame growth, hotspots, and flicker. These algorithms include predetermined criteria through which to measure such indications over time to detect a fire condition. When a fire condition is detected, the imager will output over the CAN bus an alarm signal along with a digitally coded source tag and the discrete alarm output  152 . The algorithms for image signal processing may compensate for environmental concerns such as vibration (camera movement), temperature variation, altitude, and fogging, for example. Also, brightness and contrast of the images generated by the FPA  140  may be controller by a controller  162  prior to the image being stored in the RAM  158 . 
     In addition, the imager may have BIT capabilities similar to the fire detectors to improve field maintainability. The built-in-tests of the imager may perform a complete checkout of its operations to insure that it detects failures to a minimum confidence level, like around 95%, for example. Each imager  66   a  and  66   b  may perform three types of BIT: power-up, continuous, and initiated. Power-up BIT may be performed once at power-up and will typically consist of the following: memory test, watchdog circuit and power supply ( 164 ) voltage monitor verification via block  166 , DSP operation test, analog-to-digital converter operation test, FPA operation test, and CAN bus interface verification, for example. Continuous BIT may be performed on a continuous basis and will typically consist of the following tests: watchdog, power supply voltage monitor, and input signal range reasonableness. Initiated BIT may be performed when directed by the discrete TEST Detector input signal  150  or by a CAN bus command and will typically perform the same tests as Power-up BIT. Also, upon power up, the FPGA  146  may be programmed from a boot PROM  170  and the DSP may be programmed from a boot EEPROM  172 , for example. 
     A block diagram schematic of an exemplary overall fire detection system for use in the present embodiment is shown in FIG.  8 . In the example of  FIG. 8 , the application includes three cargo compartments, namely: a forward or FWD cargo compartment, and AFT cargo compartment, and a BULK cargo compartment. As described above, each of these compartments are divided into a plurality of n sensor zones or cavities # 1 , # 2 , . . . , #n and in each cavity there are disposed a pair of fire detectors F/D A and F/D B. Each of the compartments also include two IR imagers A and B disposed in opposite corners of the ceilings thereof to view the overall space of the compartment in each case. Alarm condition signals generated by the fire detectors and IR imagers of the various compartments are transmitted to the CFDCU over a dual loop bus, CAN bus A and CAN bus B. In addition, IR video signals from the IR imagers are conducted over individual signal lines to a video selection switch of the CFDCU which selects one of the IR video signals for display on a cockpit video display. 
     In the present embodiment, the CFDCU may contain two identical, isolated alarm detection channels A and B. Each channel A and B will independently analyze the inputs from the fire Detectors and IR imagers of each cargo compartment FWD, AFT and BULK received from both buses CAN bus A and CAN bus B and determine a true fire alarm and compartment source location thereof. A “true” fire condition may be detected by all types of detectors of a compartment, therefore, a fire alarm condition will only be generated if both: (1) the smoke and/or chemical sensors detect the presence of a fire, and (2) the IR imager confirms the condition or vice versa. If only one sensor detects fire, the alarm will not be activated. This AND-type logic will minimize false alarms. This alarm condition information may be sent to a cabin intercommunication data system (CIDC) over data buses, CIDS bus A and CIDS bus B and to other locations based on the particular application. Besides the CAN bus interface, each fire detector and IR imager will have discrete Alarm and Fault outputs, and a discrete Test input as described herein above in connection with the embodiments of  FIGS. 6 and 7 . As required, each component may operate in either a “Remote Mode” or “Autonomous Mode”. 
     As shown in the block diagram schematic embodiment of  FIG. 8 , the Cargo Fire Detection Control Unit (CFDCU) interfaces with all cargo fire detection and suppression apparatus on an aircraft, including the fire detectors and IR imagers of each compartment, the Cockpit Video Display, and the CIDS. It will be shown later in connection with the embodiment of  FIG. 9  that the CFDCU also interfaces with the fire suppression aerosol generator canisters, and a Cockpit Fire Suppression Switch Panel. Accordingly, the CFDCU provides all system logic and test/fault isolation capabilities. It processes the fire detector and IR Imager signals input thereto to determine a fire condition and provides fire indication to the cockpit based on embedded logic. Test functions provide an indication of the operational status of each individual fire detector and IR imager to the cockpit and aircraft maintenance systems. 
     More specifically, the CFDCU incorporates two identical channels that are physically and electrically isolated from each other. In the present embodiment, each channel A and B is powered by separate power supplies. Each channel contains the necessary circuitry for processing Alarm and Fault signals from each fire detector and IR imager of the storage compartments of the aircraft. Partitioning is such that all fire detectors and IR imagers in both loops A and B of the system interface to both channels via dual CAN busses to achieve the dual loop functionality and full redundancy for optimum dispatch reliability. The CFDCU acts as the bus controller for the two CAN busses that interface with the fire detectors and IR imagers. Upon determining a fire indication in the same zone of a compartment by both loops A and B, the CFDCU sends signals to the CIDS over the data buses, for eventual transmission to the cockpit that a fire condition is detected. The CFDCU may also control the video selector switch to send an IR video image of the affected cargo compartment to the cockpit video display to allow the compartment to be viewed by the flight crew. 
     A block diagram schematic of an exemplary overall fire suppression system suitable for use in the present embodiment is shown in FIG.  9 . As shown in  FIG. 9 , Squib fire controllers in the CFDCU also monitor and control the operation of the fire suppression canisters, # 1 , # 2 , . . . #n in the various compartments of the aircraft through use of squib activation signals Squib # 1 -A, Squib # 1 -B, . . . , Squib #n-A and Squib #n-B, respectively. Upon receipt of a discrete input from a fire suppression discharge switch on the Cockpit Fire Suppression Switch Panel, the respective squib fire controller fires the initiater in the suppressant canisters, as required. Verification that the initiaters have fired is sent to the cockpit via the CIDS as shown in FIG.  8 . The CFDCU may include BIT capabilities to improve field maintainability. These capabilities may include the performance of a complete checkout of the operation of CFDCU to insure that it detects failures to a minimum confidence level of on the order of 95%, for example. 
     More specifically. the CFDCU may perform three types of BIT: power-up, continuous, and initiated. Power-up BIT will be performed once at power-up and will typically consist of the following tests: memory test, watchdog circuit verification, microcontroller operation test, fire detector operation, IR imager operation, fire suppressant canister operation, and CAN bus interface verification, for example. Continuous BIT may be performed on a continuous basis and will typically consist of the following tests: watchdog and power supply voltage monitor, and input signal range reasonableness. Initiated BIT may be performed when directed by a discrete TEST Detector input or by a bus command and will typically perform the same tests as Power-up BIT. 
     The exemplary aerosol generators  22 ,  24  of the present embodiment will now be described in greater detail in connection with the break away assembly illustration of FIG.  11 . The assembly is small enough to mount in unusable spaces in the storage compartment, e.g. cargo hold of an aircraft, and provides an ignition source for the propellant and a structure for dispensing hot aerosol while protecting the adjoining mounting structure of the aircraft, for example, from the hot aerosol. A modular assembly of the aerosol generator supports and protects the fire suppressant propellant during shipping, handling and use by a tubular housing  180 . The modular design also allows the assembly to be used on various sized and shaped compartment or cargo holds by choosing the number of assemblies for each size. This assembly may be mountable within the space between the ceiling of the cargo hold and the floor of the cabin compartment as described in connection with the embodiment of FIG.  1 . In the assembly, the propellant may be supported by sheet metal baffles that capture non-usable effluent and force the hot aerosol to flow through the assembly allowing them to cool before being directed into the cargo hold through several exhaust orifices or ports  25 . These ports  25  are closed by a hermetic seal, which provides the dual purpose of protecting the propellant from the environment as well as the environment from the propellant. An integral igniter is included in the assembly, which meets a 1-watt, 1-amp no-fire requirement. 
     Referring to  FIG. 11 , more specifically, the assembly comprises a substantially square tube or housing  180  which may have dimensions of approximately 19″ in length and 4″ by 4″ square, for example. The tube  180  supports the rest of the assembly. Several holes are stamped in one wall of the tube or housing  180  to provide mounting for mating parts and ports  25  that are used to direct the fire suppressant aerosol into the cargo hold. Two extruded propellants  182  which may be approximately 3⅓ pounds, for example, are mounted flat to surfaces of two sheet metal baffles  184 , respectively. The baffles  184  are in turn mounted vertically within the square aerosol generator such that a gap between the top of the baffles  184  and the inside of the tube  180  exists to allow the hot aerosol to flow over the baffles  184  and out the ports  25  in the tube. Two additional baffles  186  cover the sides of the tubular housing  180 . The baffles also capture non-useful effluent. One side of the assembly is closed with a snap-on cap  187  which has a port  188  to secure a through bulkhead electrical connector  190 . The other side of the assembly is also closed with another snap-on end cap  192 . Inside the assembly attached to a face of each of the propellants  182  is a strip of ignition material that is ignited by an igniter. The electrical leads of the igniter are connected to the through bulkhead electrical connector in order to provide the ignition current to the igniter. 
     While the present invention has been described herein above in connection with a storage compartment of an aircraft, there is no intended limitation thereof to such an application. In fact, the present invention and all aspects thereof could be used in many different applications, storage areas and compartments without deviating from the broad principles thereof. Accordingly, the present invention should not be limited in any way, shape or form to any specific embodiment or application, but rather construed in breadth and broad scope in accordance with the recitation of the claims appended hereto.