Abstract:
A fire suppression system is disclosed. The system includes a gaseous extinguishing agent and a liquid extinguishing agent. At least one emitter is in fluid communication with the liquid and gas. The emitter is used to establish a gas stream, atomize and entrain the liquid into the gas stream and discharge the resulting liquid-gas stream onto the fire. A method of operating the system is also disclosed. The method includes establishing a gas stream having first and second shock fronts using the emitter, atomizing and entraining the liquid with the gas at one of the two shock fronts to form a liquid-gas stream, and discharging the stream onto the fire. The method also includes creating a plurality of shock diamonds in the liquid-gas stream discharged from the emitter.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority to U.S. Provisional Application No. 60/864,480, filed Nov. 6, 2006. 
     
    
     FIELD OF THE INVENTION  
       [0002]    This invention concerns fire suppression systems using devices for emitting two or more extinguishing agents in a flow stream projected away from the device onto a fire. 
       BACKGROUND OF THE INVENTION 
       [0003]    Fire control and suppression sprinkler systems generally include a plurality of individual sprinkler heads which are usually ceiling mounted about the area to be protected. The sprinkler heads are normally maintained in a closed condition and include a thermally responsive sensing member to determine when a fire condition has occurred. Upon actuation of the thermally responsive member, the sprinkler head is opened, permitting pressurized water at each of the individual sprinkler heads to freely flow therethrough for extinguishing the fire. The individual sprinkler heads are spaced apart from each other by distances determined by the type of protection they are intended to provide (e.g., light or ordinary hazard conditions) and the ratings of the individual sprinklers, as determined by industry accepted rating agencies such as Underwriters Laboratories, Inc., Factory Mutual Research Corp. and/or the National Fire Protection Association. 
         [0004]    In order to minimize the delay between thermal actuation and proper dispensing of water by the sprinkler head, the piping that connects the sprinkler heads to the water source is, in many instances, at all times filled with water. This is known as a wet system, with the water being immediately available at the sprinkler head upon its thermal actuation. However, there are many situations in which the sprinkler system is installed in an unheated area, such as warehouses. In those situations, if a wet system is used, and in particular, since the water is not flowing within the piping system over long periods of time, there is a danger of the water within the pipes freezing. This will not only adversely affect the operation of the sprinkler system should the sprinkler heads be thermally actuated while there may be ice blockage within the pipes but, such freezing, if extensive, can result in the bursting of the pipes, thereby destroying the sprinkler system. Accordingly, in those situations, it is the conventional practice to have the piping devoid of any water during its non-activated condition. This is known as a dry fire protection system. 
         [0005]    When actuated, traditional sprinkler heads release a spray of fire suppressing liquid, such as water, onto the area of the fire. The water spray, while somewhat effective, has several disadvantages. The water droplets comprising the spray are relatively large and will cause water damage to the furnishings or goods in the burning region. The water spray also exhibits limited modes of fire suppression. For example, the spray, being composed of relatively large droplets providing a small total surface area, does not efficiently absorb heat and therefore cannot operate efficiently to prevent spread of the fire by lowering the temperature of the ambient air around the fire. Large droplets also do not block radiative heat transfer effectively, thereby allowing the fire to spread by this mode. The spray furthermore does not efficiently displace oxygen from the ambient air around the fire, nor is there usually sufficient downward momentum of the droplets to overcome the smoke plume and attack the base of the fire. 
         [0006]    With these disadvantages in mind, devices, such as resonance tubes, which atomize a fire suppressing liquid, have been considered as replacements for traditional sprinkler heads. Resonance tubes use acoustic energy, generated by an oscillatory pressure wave interaction between a gas jet and a cavity, to atomize a liquid that is injected into the region near the resonance tube where the acoustic energy is present. 
         [0007]    Unfortunately, resonance tubes of known design and operational mode generally do not have the fluid flow characteristics required to be effective in fire protection applications. The volume of flow from the resonance tube tends to be inadequate, and the water particles generated by the atomization process have relatively low velocities. As a result, these water particles are decelerated significantly within about 8 to 16 inches of the sprinkler head and cannot overcome the plume of rising combustion gas generated by a fire. Thus, the water particles cannot get to the fire source for effective fire suppression. Furthermore, the water particle size generated by the atomization is ineffective at reducing the oxygen content to suppress a fire if the ambient temperature is below 55° C. Additionally, known resonance tubes require relatively large gas volumes delivered at high pressure. This produces unstable gas flow which generates significant acoustic energy and separates from deflector surfaces across which it travels, leading to inefficient atomization of the water. 
         [0008]    Systems which use only an inert gas to extinguish a fire also suffer certain disadvantages, the primary disadvantage being the reduction in oxygen concentration necessary to extinguish a fire. For example, a gaseous system that uses pure nitrogen will not extinguish flames until the oxygen content at the fire is 12% or lower. This concentration is significantly less than the known safe breathable limit of 15%. Persons without breathing apparatus exposed to an oxygen concentration of 12% have less than 5 minutes before they lose consciousness for lack of oxygen. At oxygen concentration of 10% the exposure limit is about one minute. Thus, such systems present a hazard to persons trying to escape or fight the fire. 
         [0009]    There is clearly a need for a fire suppression system having an atomizing emitter that can discharge both liquid and gaseous extinguishing agents and which operates more efficiently than known resonance tubes. Such an emitter would ideally use smaller volumes of gas at lower pressures to produce sufficient volume of atomized liquid particles having a smaller size distribution while maintaining significant momentum upon discharge so that the liquid particles may overcome the fire smoke plume and be more effective at fire suppression. 
       SUMMARY OF THE INVENTION  
       [0010]    The invention concerns a fire suppression system comprising a gaseous extinguishing agent and a liquid extinguishing agent. At least one emitter is used to atomize and entrain the liquid extinguishing agent in the gaseous extinguishing agent and discharge the gaseous and liquid extinguishing agents on a fire. A gas conduit conducts the gaseous extinguishing agent to the emitter. A piping network conducts the liquid extinguishing agent to the emitter. A first valve in the gas conduit controls pressure and flow rate of the gaseous extinguishing agent to the emitter. A second valve in the piping network controls pressure and flow rate of the liquid extinguishing agent to the emitter. A pressure transducer measures pressure within the gas conduit. A fire detection device is positioned proximate to the emitter. A control system is in communication with the first and second valves, the pressure transducer and the fire detection device. The control system receives signals from the pressure transducer and the fire detection device and opens the valves in response to a signal indicative of a fire from the fire detection device. The control system actuates the first valve so as to maintain a predetermined pressure of the gaseous extinguishing agent within the gas conduit for operation of the emitter. 
         [0011]    Preferably, the emitter comprises a nozzle having an inlet connected with the gas conduit downstream of the first valve and an outlet. A duct is connected in fluid communication with the piping network downstream of the second valve. The duct has an exit orifice positioned adjacent to the outlet. A deflector surface is positioned facing the outlet in spaced relation thereto. The deflector surface has a first surface portion oriented substantially perpendicularly to the nozzle and a second surface portion positioned adjacent to the first surface portion and oriented non-perpendicularly to the nozzle. The liquid extinguishing agent is dischargeable from the orifice, and the gaseous extinguishing agent is dischargeable from the nozzle outlet. The liquid extinguishing agent is entrained with the gaseous extinguishing agent and atomized thereby forming a liquid-gas stream that impinges on the deflector surface and flows away therefrom onto the fire. 
         [0012]    Preferably, the deflector surface is positioned so that the gaseous extinguishing agent forms a first shock front between the outlet and the deflector surface, and a second shock front is formed proximate to the deflector surface. The duct is positioned and oriented such that the liquid extinguishing agent, discharged from the exit orifice, is entrained with the gaseous extinguishing agent proximate to one of the shock fronts. The deflector surface may also be positioned so that shock diamonds form in the liquid-gas stream. 
         [0013]    The invention also encompasses a method of operating a fire suppression system. The system has an emitter comprising a nozzle having an inlet connected in fluid communication with a pressurized source of gaseous extinguishing agent and an outlet. A duct is connected in fluid communication with a pressurized source of liquid extinguishing agent. The duct has an exit orifice positioned adjacent to the outlet. A deflector surface is positioned facing the outlet in spaced relation thereto. The method comprises: 
         [0014]    (a) discharging the liquid extinguishing agent from the exit orifice; 
         [0015]    (b) discharging the gaseous extinguishing agent from the outlet; 
         [0016]    (c) establishing a first shock front between the outlet and the deflector surface; 
         [0017]    (d) establishing a second shock front proximate to the deflector surface; 
         [0018]    (e) entraining the liquid extinguishing agent in the gaseous extinguishing agent to form a liquid-gas stream; and 
         [0019]    (f) projecting the liquid-gas stream from the emitter. 
         [0020]    The method may also include establishing a plurality of shock diamonds in the liquid-gas stream. 
         [0021]    The liquid extinguishing agent may be entrained with the gaseous extinguishing agent proximate to one of the shock fronts. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIGS. 1 and 1A  are schematic diagrams illustrating exemplary embodiments of dual extinguishment fire suppression systems according to the invention; 
           [0023]      FIG. 2  is a longitudinal sectional view of a high velocity low pressure emitter used in the fire suppression system shown in  FIG. 1 ; 
           [0024]      FIG. 3  is a longitudinal sectional view showing a component of the emitter depicted in  FIG. 2 ; 
           [0025]      FIG. 4  is a longitudinal sectional view showing a component of the emitter depicted in  FIG. 2 ; 
           [0026]      FIG. 5  is a longitudinal sectional view showing a component of the emitter depicted in  FIG. 2 ; 
           [0027]      FIG. 6  is a longitudinal sectional view showing a component of the emitter depicted in  FIG. 2 ; 
           [0028]      FIG. 7  is a diagram depicting fluid flow from the emitter based upon a Schlieren photograph of the emitter shown in  FIG. 2  in operation; and 
           [0029]      FIG. 8  is a diagram depicting predicted fluid flow for another embodiment of the emitter. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0030]      FIG. 1  illustrates, in schematic form, an example dual extinguishment fire suppression system  11  according to the invention. System  11  includes a plurality of high velocity low pressure emitters  10 , described in detail below. Emitters  10  are arranged in a potential fire hazard zone  13 , the system comprising one or more such zones, each zone having its own bank of emitters. For clarity, only one zone is described herein, it being understood that the description is applicable to additional fire hazard zones as shown. 
         [0031]    The emitters  10  are connected via a piping network  15  to a source of pressurized liquid extinguishing agent  17 . Examples of practical liquid agents include synthetic compounds such as heptafluoropropane (sold under the tradename Novec™ 1230), bromochloro-difluoromethane and bromotrifluoromethane. Water is also feasible, and especially de-ionized water for use near charged electrical equipment. De-ionized water reduces electrical arcing due to its low conductivity. 
         [0032]    It is preferred to control the flow of liquid to each emitter  10  using individual flow control devices  71  positioned immediately upstream of each emitter. Preferably the individual control devices include a flow cartridge and a strainer to protect the flow cartridge and the emitter. The flow cartridge operates autonomously to provide a constant flow rate over a known pressure range and is useful to compensate for variations in water pressure at the source as well as frictional head loss due to long pipe runs and intervening joints such as elbows. Proper operation of the emitters, described below, is ensured by controlling the flow at each emitter. A liquid control valve  19  may be used to control the flow of liquid from the source  17  to the emitters  10 , with fine control of the flow rate managed by the individual flow control devices  71 . 
         [0033]    The emitters are also in fluid communication with a source of pressurized gaseous extinguishing agent  21  through a gas conduit network  23 . Candidate gaseous extinguishing agents include mixtures of atmospheric gases such as Inergen™ (52% nitrogen, 40% argon, 8% carbon dioxide) and ArgoniteTM (50% argon and 50% nitrogen) as well as synthetic compounds such as fluoroform, 1,1,1,2,2-pentafluoroethane and 1,1,1,2,3,3,3-heptafluoropropane. The gaseous extinguishing agent may be maintained in banks of high-pressure cylinders  25  as shown in  FIG. 1 . Cylinders  25  may be pressurized up to 2,500 psig. For large systems which require large volumes of gas, one or more lower pressure tanks (about 350 psig) having volumes on the order of 30,000 gallons may be used. Alternately, large volume high pressure tanks (for example 30 cubic feet at a pressure of 2600 psi) may also be used. In a further practical embodiment, shown in  FIG. 1A , the gaseous extinguishing agent may be stored in a single tank  73  common to all emitters  10  in all of the fire hazard zones  13 . 
         [0034]    Valves  27  of cylinders  25  (or tank  73 ) are preferably maintained in an open state in communication with a high pressure manifold  29 . Gas flow rate and pressure from the manifold to the gas conduit  23  are controlled by a high pressure gas control valve  31 . Pressure in the conduit  23  downstream of the high pressure control valve  31  is measured by a pressure transducer  33 . Flow of gas to the emitters  10  in each fire hazard zone  13  is further controlled by a low pressure valve  35  downstream of the pressure transducer. 
         [0035]    Each fire hazard zone  13  is monitored by one or more fire detection devices  37 . These detection devices operate in any of the various known modes for fire detection, such as sensing of flame, heat, rate of temperature rise, smoke detection or combinations thereof. 
         [0036]    The system components thus described are coordinated and controlled by a control system  39 , which comprises, for example, a microprocessor  41  having a control panel display (not shown), resident software, and a programmable logic controller  43 . The control system communicates with the system components to receive information and issue control commands as follows. 
         [0037]    Each cylinder valve  27  is monitored as to its status (open or closed) by a supervisory loop  45  that communicates with the microprocessor  41 , which provides a visual indication of the cylinder valve status. Liquid control valve  19  is also in communication with microprocessor  41  via a communication line  47 , which allows the valve  19  to be monitored and controlled (opened and closed) by the control system. Similarly, gas control valve  35  communicates with the control system via a communication line  49 , and the fire detection devices  37  also communicate with the control system via communication lines  51 . The pressure transducer  35  provides its signals to the programmable logic controller  43  over communication line  53 . The programmable logic controller is also in communication with the high pressure gas valve  31  over communication line  55 , and with the microprocessor  41  over communication line  57 . 
         [0038]    In operation, fire detectors  37  sense a fire event and provide a signal to the microprocessor  41  over communication line  51 . The microprocessor actuates the logic controller  43 . Note that controller  43  may be a separate controller or an integral part of the high pressure control valve  31 . The logic controller  43  receives a signal from the pressure transducer  33  via communication line  53  indicative of the pressure in the gas conduit  23 . The logic controller  43  opens the high pressure gas valve  31  while the microprocessor  41  opens the gas control valve  35  and the liquid control valve  19  using respective communication lines  49  and  47 . Gaseous extinguishing agent from tanks  25  and liquid extinguishing agent from source  17 , are thus permitted to flow through gas conduit  23  and liquid piping network  15  respectively. Preferred liquid extinguishing agent pressure for proper operation of the emitters  10  is between about 1 psig and about 50 psig as described below. The flow cartridges or other such flow control devices  71  maintain the required liquid flow rate. The logic controller  43  operates valve  31  to maintain the correct pressure of gaseous extinguishing agent (between about 29 psia and about 60 psia) and flow rate to operate the emitters  10  within the parameters as described below. For a ½ inch emitter tests show nitrogen supplied at pressure of 25 psi and a flow rate of 150 scfm is effective. 
         [0039]    The dual extinguishing agents discharged by the emitters  10  work together to extinguish the fire in the presence of an oxygen concentration of no lower than 15%. This is significantly better than various gas only systems such as those which use nitrogen and require a reduction of oxygen concentration of 12% or lower before the fire will be extinguished. It is advantageous to maintain an oxygen concentration of at least 15% if possible, as 15% is a known safe level and provides a breathable atmosphere. In action, the gaseous extinguishing agent reduces the fire plume temperature to the critical adiabatic temperature of the fire. (This is the temperature at which the fire will self-extinguish.) In addition to lowering the fire plume temperature, the gaseous component acts to decreases the oxygen concentration as well. The liquid extinguishing agent acts as a heat sink to absorb heat from the fire and thereby suppress it. 
         [0040]    Upon sensing that the fire is extinguished, the microprocessor  41  closes the gas and liquid valves  35  and  19 , and the logic controller  43  closes the high pressure control valve  31 . The control system  39  continues to monitor all the fire hazard zones  13 , and in the event of another fire or the re-flashing of the initial fire the above described sequence is repeated. 
         [0041]      FIG. 2  shows a longitudinal sectional view of a high velocity low pressure emitter  10  according to the invention. Emitter  10  comprises a convergent nozzle  12  having an inlet  14  and an outlet  16 . Outlet  16  may range in diameter between about ⅛ inch to about 1 inch for many applications. Inlet  14  is in fluid communication with a pressurized supply of gaseous extinguishing agent, for example, the cylinders  25  (see also  FIG. 1 ), that provides the gaseous extinguishing agent to the nozzle at a predetermined pressure and flow rate. It is advantageous that the nozzle  12  have a curved convergent inner surface  20 , although other shapes, such as a linear tapered surface, are also feasible. 
         [0042]    A deflector surface  22  is positioned in spaced apart relation with the nozzle  12 , a gap  24  being established between the deflector surface and the nozzle outlet. The gap may range in size between about 1/10 inches to about ¾ inches. The deflector surface  22  is held in spaced relation from the nozzle by one or more support legs  26 . 
         [0043]    Preferably, deflector surface  22  comprises a flat surface portion  28  substantially aligned with the nozzle outlet  16 , and an angled surface portion  30  contiguous with and surrounding the flat portion. Flat portion  28  is substantially perpendicular to the gas flow from nozzle  12 , and has a minimum diameter approximately equal to the diameter of the outlet  16 . The angled portion  30  is oriented at a sweep back angle  32  from the flat portion. The sweep back angle may range between about 15° and about 45° and, along with the size of gap  24 , determines the dispersion pattern of the flow from the emitter. 
         [0044]    Deflector surface  22  may have other shapes, such as the curved upper edge  34  shown in  FIG. 3  and the curved edge  36  shown in  FIG. 4 . As shown in  FIGS. 5 and 6 , the deflector surface  22  may also include a closed end resonance tube  38  surrounded by a flat portion  40  and a swept back, angled portion  42  ( FIG. 5 ) or a curved portion  44  ( FIG. 6 ). The diameter and depth of the resonance cavity may be approximately equal to the diameter of outlet  16 . 
         [0045]    With reference again to  FIG. 2 , an annular chamber  46  surrounds nozzle  12 . Chamber  46  is in fluid communication with a pressurized liquid supply, for example, the liquid extinguishing agent source  17  of  FIG. 1  that provides the liquid extinguishing agent to the chamber at a predetermined pressure and flow rate. A plurality of ducts  50  extend from the chamber  46 . Each duct has an exit orifice  52  positioned adjacent to nozzle outlet  16 . The exit orifices have a diameter of about 1/32 inch to about ⅛ inch. Preferred distances between the nozzle outlet  16  and the exit orifices  52  range between about 1/64 inch to about ⅛ inch as measured along a radius line from the edge of the nozzle outlet to the closest edge of the exit orifice. Liquid extinguishing agent flows from the pressurized supply  17  into the chamber  46  and through the ducts  50 , exiting from each orifice  52  where it is atomized by the flow of gaseous extinguishing agent from the pressurized gas supply that flows through the nozzle  12  and exits through the nozzle outlet  16  as described in detail below. 
         [0046]    Emitter  10 , when configured for use in a fire suppression system, is designed to operate with a preferred gas pressure between about 29 psia to about 60 psia at the nozzle inlet  14  and a preferred liquid extinguishing agent pressure between about 1 psig and about 50 psig in chamber  46 . 
         [0047]    Operation of the emitter  10  is described with reference to  FIG. 7  which is a drawing based upon Schlieren photographic analysis of an operating emitter. 
         [0048]    Gaseous extinguishing agent  85  exits the nozzle outlet  16  at about Mach 1 and impinges on the deflector surface  22 . Simultaneously, liquid extinguishing agent  87  is discharged from exit orifices  52 . 
         [0049]    Interaction between the gaseous extinguishing agent  85  and the deflector surface  22  establishes a first shock front  54  between the nozzle outlet  16  and the deflector surface  22 . A shock front is a region of flow transition from supersonic to subsonic velocity. Liquid extinguishing agent  87  exiting the orifices  52  does not enter the region of the first shock front  54  in this mode of operation of the emitter. 
         [0050]    A second shock front  56  forms proximate to the deflector surface at the border between the flat surface portion  28  and the angled surface portion  30 . Liquid extinguishing agent  87  discharged from the orifices  52  is entrained with the gaseous extinguishing agent  85  proximate to the second shock front  56  forming a liquid-gas stream  60 . One method of entrainment is to use the pressure differential between the pressure in the gas flow jet and the ambient. Shock diamonds  58  form in a region along the angled portion  30 , the shock diamonds being confined within the liquid-gas stream  60 , which projects outwardly and downwardly from the emitter. The shock diamonds are also transition regions between super and subsonic flow velocity and are the result of the gas flow being overexpanded as it exits the nozzle. Overexpanded flow describes a flow regime wherein the external pressure (i.e., the ambient atmospheric pressure in this case) is higher than the gas exit pressure at the nozzle. This produces oblique shock waves which reflect from the free jet boundary  89  marking the limit between the liquid-gas stream  60  and the ambient atmosphere. The oblique shock waves are reflected toward one another to create the shock diamonds. 
         [0051]    Significant shear forces are produced in the liquid-gas stream  60 , which ideally does not separate from the deflector surface, although the emitter is still effective if separation occurs as shown at  60   a . The liquid extinguishing agent entrained proximate to the second shock front  56  is subjected to these shear forces which are the primary mechanism for atomization. The liquid extinguishing agent also encounters the shock diamonds  58 , which are a secondary source of atomization. 
         [0052]    Thus, the emitter  10  operates with multiple mechanisms of atomization which produce liquid particles  62  less than 20 μm in diameter, the majority of the particles being measured at less than 10 μm. The smaller droplets are buoyant in air. This characteristic allows them to maintain proximity to the fire source for greater fire suppression effect. Furthermore, the particles maintain significant downward momentum, allowing the liquid-gas stream  60  to overcome the rising plume of combustion gases resulting from a fire. Measurements show the liquid-gas stream having a velocity of about 7,000 ft/min 18 inches from the emitter, and a velocity greater than 1,700 ft/min 8 feet from the emitter. The flow from the emitter is observed to impinge on the floor of the room in which it is operated. The sweep back angle  32  of the angled portion  30  of the deflector surface  22  provides significant control over the included angle  64  of the liquid-gas stream  60 . Included angles of about 120° are achievable. Additional control over the dispersion pattern of the flow is accomplished by adjusting the gap  24  between the nozzle outlet  16  and the deflector surface. 
         [0053]    During emitter operation it is further observed that the smoke layer that accumulates at the ceiling of a room during a fire is drawn into the stream of gaseous extinguishing agent  85  exiting the nozzle and is entrained in the flow  60 . This adds to the multiple modes of extinguishment characteristic of the emitter as described below. 
         [0054]    The emitter causes a temperature drop due to the atomization of the liquid extinguishing agent into the extremely small particle sizes described above. This absorbs heat and helps mitigate spread of combustion. The flow of liquid extinguishing agent entrained in the flow of gaseous extinguishing agent replace the oxygen in the room with gases that cannot support combustion. Further oxygen depleted gases in the form of the smoke layer that is entrained in the flow also contributes to the oxygen starvation of the fire. It is observed, however, that the oxygen level in the room where the emitter is deployed does not drop below about 15%. The liquid extinguishing agent particles and the entrained smoke create a fog that blocks radiative heat transfer from the fire, thus, mitigating spread of combustion by this mode of heat transfer. The mixing and the turbulence created by the emitter also helps lower the temperature in the region around the fire. 
         [0055]    The emitter is unlike resonance tubes in that it does not produce significant acoustic energy. Jet noise (the sound generated by air moving over an object) is the only acoustic output from the emitter. The emitter&#39;s jet noise has no significant frequency components higher than about 6 kHz (half the operating frequency of well known types of resonance tubes) and does not contribute significantly to atomization. 
         [0056]    Furthermore, the flow from the emitter is stable and does not separate from the deflector surface (or experiences delayed separation as shown at  60   a ) unlike the flow from resonance tubes, which is unstable and separates from the deflector surface, thus leading to inefficient atomization or even loss of atomization. 
         [0057]    Another emitter embodiment  101  is shown in  FIG. 8 . Emitter  101  has ducts  50  that are angularly oriented toward the nozzle  12 . The ducts are angularly oriented to direct the liquid extinguishing agent  87  toward the gaseous extinguishing agent  85  so as to entrain the liquid in the gas proximate to the first shock front  54 . It is believed that this arrangement will add yet another region of atomization in the creation of the liquid-gas stream  60  projected from the emitter  11 . 
         [0058]    Fire suppression systems using emitters and dual extinguishing agents according to the invention achieve multiple fire extinguishment modes which are well suited to control the spread of fire while using less gas and liquid than known systems which use water. Systems according to the invention are especially effective and efficient in ventilated fire conditions.