Abstract:
Deflagration suppression and explosion isolation system ( 10 ) is provided for contained hazardous material. Containment structure ( 12 ) for a highly flammable, particulate or gaseous material is connected by a conduit ( 16 ) to an area ( 14 ) for collection or processing of the material. Normally, the particulate gaseous material is conveyed via the conduit ( 16 ) to the collection or processing area ( 14 ). However, the conduit is of a length and configuration such that upon unforeseen ignition of the material in the containment structure ( 12 ), flame and combustion generated pressure resulting from the incipient explosion in the containment structure can course along the conduit ( 16 ) connected thereto toward the collection or processing area ( 14 ) in the form of a deflagration front that transitions into a detonation stage before reaching the collection or processing area unless adequately suppressed and isolated. A pressure detector ( 18 ) is connected to the containment structure ( 12 ) for detecting a rapid rise of pressure in the containment structure indicative of an incipient explosion. A suppressant device ( 20, 22 ) communicates with the conduit ( 16 ) in disposition to direct a fire suppression agent into the conduit to prevent the flame and combustion generated pressures from the incipient explosion in the containment structure from transitioning from a deflagration stage to a detonation stage in the conduit. A gate valve assembly ( 24 ) is provided in the conduit downstream of the suppressant device ( 20, 22 ) which has a gate member ( 70 ) which is closed in tandem with release of the suppressant agent into the conduit to isolate the flame and combustion generated pressures and thereby prevent the flame and combustion generated pressures from entering the collection or processing area ( 14 ).

Description:
FIELD OF THE INVENTION 
     This invention relates to explosion suppression and isolation apparatus for use with structure which confines highly combustible, flowable material and that is normally conveyed to or from a collection or processing area remote from the structure through an interconnecting conduit. The combustible material presents a hazard in that flame and combustion generated pressures resulting from an unforseen ignition and explosion of the material will rapidly and often destructively be directed into the processing or collection area. 
     The apparatus hereof is operable to prevent the propagating flame front from an explosion transitioning from a deflagration state to a detonation state, and to then isolate and prevent the suppressed flame and deflagration pressures from entering the collection or processing area through the conduit. 
     DESCRIPTION OF THE PRIOR ART 
     Many industrial processes involve handling of highly combustible and therefore very hazardous materials, which are normally confined within containment structure, but are then directed through an interconnecting conduit to another processing or collection area. Exemplary in this respect are machining operations on aluminum and magnesium products which produce very small metal fines. The machining operation often is carried out within structure which confines the metal particles, or the resulting fines can be directed into a vessel for storage until the material is delivered through a conduit or the like to a desired collection point or processing area. Similarly, extremely hazardous, flammable fluids or gases are received or stored in a confinement vessel which is also connected to a processing or collection area by a conduit. 
     The collection or processing area which receives the hazardous metal fines, other types of solid, very small combustible particles, or combustible gaseous or fluid materials is usually spaced some distance from the initial storage or confinement vessel. A conduit is most often used to convey the hazardous flowable material from the containment or storage structure or vessel to the point where it is either collected or further processed. 
     If the highly combustible material in the containment structure or storage vessel ignites as a result of an unforseen event, the propagating flame front resulting from the ignition rapidly transitions from an initial deflagration state to a detonation state within the conduit. Undesirable flame and often destructive pressures may therefore be delivered directly into the collection or processing area through the conduit which connects the containment structure or storage vessel with the collection or processing area. 
     Typically, in view of the volume of highly flammable, flowable materials that must be appropriately contained and then directed via a conduit to a collection or processing area remote from the point of collection or containment, the delivery conduits are of relatively large diameter, e.g., 12 to 24 in. Furthermore, the conveyance structure which for example may comprise of a delivery conduit often includes bends or other obstacles which induce turbulence that substantially contribute to the acceleration of flame propagation. Ignition of combustible material may occur in the confinement structure which also substantially contributes to acceleration of flame propagation by a rapid injection of flame into the interconnecting conduit or pipe. In view of the violent nature of explosions that may occur from containment, storage and conveyance of highly flammable materials as described, as well as others having similar hazardous characteristics, there has been no reliable way to prevent flame transition to detonation and isolation of the combustion flame and pressure from the explosion so that the flame and pressure wave do not enter the defined collection or processing area. 
     It has been proposed to protect a processing or collection area which normally receives the highly flammable material from the containment structure or storage vessel, by providing equipment for directing a suppressant agent into the material-conveying conduit downstream of the containment structure or vessel. A detector in that proposal is located to sense ignition of the combustible material ahead of the location where a suppressant agent is delivered into the conduit. In the case of deflagrations of highly flammable materials originating in the containment area adequate suppressant agent cannot be effectively delivered to a large diameter delivery conduit at the necessary rate and for a duration to prevent transition of the deflagration to a detonation state. Likewise, it has not heretofore been feasible to mechanically block entry of flame and combustion generated pressure produced by an explosion of highly combustible material from entering the collection or processing area to be protected when the deflagration has transitioned to detonation velocities. Conversely, it is not possible to place a mechanical isolation device at a location ahead of the distance where a deflagration can transition to a detonation and still provide sufficient time to effect closing of the valve. 
     In order for an explosion to occur, a fuel and oxidizer mixture within the flammable limits of the fuel must be exposed to an ignition source of adequate strength to initiate combustion. If the flammable material is contained in a structure or is in an elongated pipe or conduit, immediately upon ignition, an explosion will propagate from the ignition point into the unburned fuel and oxidizer mixture. A spherical flame front is first formed which continues to grow until the confining walls are reached. A pressure wave is also generated, which travels at the speed of sound of the mixture it is propagating into. At this point in time, the flame front and the pressure wave are traveling at different speeds, with the pressure wave traveling much faster than the flame front. 
     Once the flame front has reached the wall of the pipe or conduit, it changes from spherical form to an essentially planar front. As the planar flame front continues to propagate down the length of the pipe, it begins to elongate and the surface of the flame increases. As the surface area increases, the burning rate increases and as a result, the flame propagation velocity increases. This stage of an incipient explosion initially involves a phenomena known as “deflagration,” which may be defined as conditions where the pressure wave and flame front are traveling separately, the pressure wave is traveling at the speed of sound, and flame front propagation involves heat transfer. 
     The pressure wave and the flame front eventually coalesce into a shock wave. If propagation continues, the energy of the pressure wave is sufficient to cause localized explosions. At the point where the pressure wave is strong enough to initiate the combustion reaction, the explosion phenomena becomes known as “detonation.” In the initial stages, the detonation wave will propagate into a precompressed mixture of fuel and oxidizer, known as “over-driven detonations.” The over-driven detonation will catch up to the foremost pressure wave and become a stable detonation with a constant velocity. A stable detonation wave consists of a pressure wave closely coupled with a flame front such that the energy released by the flame front supports the pressure wave. 
     Therefore, in a typical explosion in a conduit, the deflagration stage may be followed immediately by detonation. At each stage of an explosion, magnitude of pressure, rate of pressure rise, flame velocity and relative location of flame front to the pressure front, are different, depending upon the material that is susceptible to exploding, the point of ignition, and the nature of the conduit along which the flame is propagating. 
     In the deflagration region of an incipient explosion, pressures experienced increase from 0 bar g up to no more than about 10 to 12 bar g. In the detonation region, pressures can varying from about 20 up to as much as 80 bar g. Flame velocity in the deflagration region is usually of the order of 100 to 300 m/s, while flame velocity in the detonation region typically will rise to a level of about 1500 to 2500 m/s. 
     The size of the particles of the combustible flowable material has an effect on the overall explosion phenomena, as does the diameter of the conduit through which the products of combustion are flowing. Pipes of larger diameter provide smaller heat sinks than smaller diameter pipes or conduits. The longitudinal configuration of the conduit also affects the propagation phenomena. Obstacles and bends in the pipe or conduit can exert turbulence which in turn will effect flame surface area and cause faster transition to detonation. Where ignition occurs in a closed vessel or containment structure, it is known as “prevolume” ignition. This leads to initially higher flame propagation speed, faster transition to detonation, and higher pressure generation. 
     The goal of explosion protection is to suppress the deflagration stage of the explosion, preventing the deflagration phenomena from transitioning into detonation phenomena, and block the flame and combustion generated pressures from entering a protected area at the end of the conduit or pipe opposite the containment structure or storage vessel that normally receives the hazardous material. In the case of highly flammable and hazardous flowable materials such as aluminum and magnesium particles, other similar metal fines, or gases such as hydrogen, this goal has not heretofore been realized. 
     SUMMARY OF THE INVENTION 
     The present invention provides deflagration suppression and explosion isolation apparatus for preventing flame and combustion generated pressures resulting from explosion of a highly flammable, flowable material in a containment structure or a storage vessel from entering a collection or processing area that normally receives the material or is the sources of the material via a conduit interconnecting the structure or vessel and the collection or processing area. 
     The overall deflagration suppression and explosion isolation system includes containment structure, which may for example comprise a storage vessel or compartment, for confining a flowable, highly combustible material which presents a fire and explosion hazard, such as aluminum or magnesium dust, certain highly flammable organic materials, and gases such as hydrogen. An elongated conduit connected to the structure normally conveys flowable material to or from the structure to a collection or processing area remote from the containment structure. The conduit is typically of a length and configuration longitudinally thereof that upon unforseen ignition of the material in the structure, flame can course along the conduit in the form of a deflagration front that transitions into a detonation state before reaching the material collection or processing area. 
     A suppressant device communicating with the conduit is in disposition to direct a fire suppressant agent into the conduit. A detector associated with the structure and conduit is operable to sense ignition of the material in the structure and to activate the suppressant device to deliver suppressant agent into the conduit. The suppressant unit is located on the conduit along the length thereof in disposition to begin introducing suppressant agent into the conduit before the flame has reached its location. 
     An isolation assembly connected to the conduit ahead of the collection and processing area and after the suppressant unit is operable in association with the suppressant device to ;prevent flame and combustion generated pressure from entering the collection or processing area via the conduit. Isolation of the collection or processing area is preferably accomplished through provision of a gate valve connected to the conduit downstream of the suppression agent delivery device which has a valve plate normally in unblocking relationship to the conduit, but that can rapidly move into a position fully blocking the conduit upon detection of an incipient explosion by the ignition detector. In a preferred form of the invention, the suppressant device includes a vessel for storing a quantity of a powder suppressant under gas pressure, a rupture disc normally preventing release of suppressant from the suppressant vessel, and a gas cartridge unit operable to produce a gaseous discharge sufficient to rapidly rupture the disc upon receipt of an activation signal from the incipient explosion detector. In that same preferred form of the invention, the gate valve also is provided with a gas cartridge unit which is operable to produce a gaseous discharge which effects rapid closing of the gate of the gate valve when the incipient explosion detector detects ignition of the highly flammable material in the containment structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an essentially diagrammatic view of deflagration suppression and explosion isolation apparatus in accordance with the preferred embodiment of the invention and illustrating containment structure for a highly flammable, flowable material, a collection or processing area spaced from the structure, a conduit interconnecting the structure and the area, and a deflagration suppression device, and an explosion isolation assembly connected to the conduit; 
     FIG. 2 is a cross-sectional view taken substantially on the line  2 — 2  of FIG. 1, looking in the direction of the arrows; 
     FIG. 3 is a fragmentary, enlarged, partial cross-sectional view of one of the suppressant agent delivery devices illustrated in FIG. 2; 
     FIG. 4 is a side view of the products of combustion isolation assembly depicted in FIG. 1; and 
     FIG. 5 is a cross-sectional view along the lines  5 — 5  of FIG. 4, looking in the direction of the arrows. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A system  10  is shown essentially in diagrammatic form in FIG. 1 for containing highly combustible, flowable material, and for directing the material to or from a collection or processing area. In FIG.1, the material is shown as being contained in structure  12  identified as a containment process vessel. Structure  12  may vary according to a particular industrial application. For example, structure  12  may consist of a compartment in which metal grinding machines or other processing equipment are housed. Alternatively, structure  12  may take the form of a pressure vessel in which highly flammable, flowable material is stored. In particular, a typical containment vessel may be of steel, having a nominal thickness of the order of one inch where the combustible material is particularly hazardous, such as aluminum or magnesium fines, and have an interior volume of about five cubic meters. 
     A collection or processing areal  4  which receives the highly flammable material from structure is  12  is shown diagrammatically and labeled “PROTECTED AREA” in FIG. 1, and may comprise for example a conventional bag house collector, a cyclone-type collector, or structure for collection and then reprocessing of metal dust. A conduit  16  extends between and interconnects structure  12  and the protected area  14 . Although the conduit  16  is shown diagrammatically as extending directly between structure  12  and protected area  14  with two 90° bends, it is to be understood that the depiction in FIG. 1 is for illustrative purposes only, and the actual longitudinal configuration of conduit  16  will vary from installation to installation, depending upon the distance between structure  12  and area  14 , as well as the dictates of the plant layout. In typical industrial applications of the deflagration suppression and explosion isolation apparatus of this invention, conduit  16  generally will be a relatively large diameter type of the order of 12 to 24 inches in diameter and will have multiple bends. A 16-inch diameter pipe is often used for this purpose. 
     A pressure detector  18  mounted on structure  12  is mounted on and monitors the pressure inside of vessel structure  12 . Detector  18  is operable to detect a rise in pressure within the structure  12  indicative of an incipient explosion. The detector  18  is connected to a controller (not shown) which, upon receipt of a signal from detector  18 , is operable to send electrical activation signals to deflagration devices  20  and  22  mounted on conduit  16  in adjacent relationship to structure  12 . The controller which is sensitive to detection of a pressure rise in structure  12  indicative of an incipient explosion, also sends electrical actuating signals to the explosion isolation gate valve assembly  24  also mounted on conduit  16 . Although a preferred embodiment of the invention utilizes a pressure detector  18  which is operable to detect a rise in pressure within structure  12 , it is to be understood that other types of conventional detectors may be employed to detect the onset of an incipient explosion. 
     Viewing FIG. 2, it can be seen that each of the devices  20  and  22  include a suppressant storage vessel  26  for containing a quantity of a dry suppressant agent in powdered form, such as sodium bicarbonate. A cylindrical end extension  28  integral with vessel  26  and communicating with the interior thereof is internally threaded at the outermost end thereof for removably receiving a flanged, externally threaded tubular fitting  30 . A prebulged, domed rupture disc  32  is trapped between the innermost end of fitting  30  and an internal circular shoulder of extension  28  for normally closing the passage defined by end extension  28 . It can be seen from FIG. 3 that disc  32  is preferably oriented such that the concave surface thereof faces the interior of pressure vessel  26 . 
     Extension  28  of each of the storage vessels  26  is connected to and communicates with the interior of conduit  16  on opposite sides thereof. As is evident from FIG. 2, the connection between each vessel  26  of devices  20  and  22  and respective opposite sides of conduit  16  takes the form of conventional piping  34  of overall L-shaped configuration. A quantity of a pressurized gas such as nitrogen is provided in each of the vessels  26  for forcing the solid suppressant agent out of a corresponding vessel  26  upon rupture of a respective disc  32 . 
     Although a detonator may be used to release suppressant from a bottle containing suppressant agent that is maintained under pressurized nitrogen, a preferred construction comprises a gas cartridge unit  36  mounted on the extension  28  of each of the vessels  26  in direct communication with the interior of a respective extension. To that end, extension  28  of each vessel  26  has a tubular element  38  affixed to the outer side wall thereof and which is in alignment with an opening  40  in the side wall of a respective extension  28 . A sleeve  42  is carried within each tubular element  38  and supports a gas-generating cartridge  44  which rests against a prebugled rupture disc  46  normally closing the interior passage through sleeve  42 . The cartridge  44  may contain a gas-generating propellant formulation that, for example, may comprise a combination of potassium perchlorate, nitroglycerine, nitrocellulose, and lead thiocyanate, having a minimum auto-ignition temperature of about 325EF and a DOT classification of 1.4s and a UN classification of 0323. The quantity of smokeless powder contained within cartridge  44  should be adequate to generate gaseous products of combustion to rupture disc  46  as well as disc  32 . A tubular end closure  48  is threaded into extension  38  of each of the devices  20  and  22 , and serves to lock cartridge  44  in place. Electrical wires  50  are connected to the cartridge unit  44  and to the controller which receives an actuating signal from detector  18 . 
     The explosion isolation gate valve assembly  24  mounted on conduit  16  and which is shown in greater detail in FIGS. 4 and 5, may be of the type illustrated and described in application Ser. No. 09/373,087 filed Aug. 12, 1999, assigned to the Assignee hereof, and entitled “Gas Cartridge Actuated Isolation Valve,” now U.S. Pat. No. 6,131,594, which is incorporated herein by specific reference thereto. As illustrated and described in the &#39;087 application &#39;594 patent], gate valve assembly  24  is also of a type actuated by a gas cartridge unit. 
     Gate valve assembly  24  includes a valve body  52  presenting a flow passageway  54  aligned with conduit  16 . A gate unit  56  forming a part of valve body  52  has a shiftable, apertured, plate-type gate member  58 . An actuator  60  forms a part of the assembly  24 , and includes a gas-generating cartridge or unit  62  which is the same type as gas-generating unit  36 . 
     The valve body  52  includes a pair of upright, spaced apart, interference plates  64 ,  66  cooperatively defining an upright internal chamber  68 . The gate unit  56  includes an elongated, upright, metallic gate member or plate  70  which is situated within the chamber  68  and is designed for up and down shifting movement therein. As shown, the plate  70  has a circular aperture  72  therethrough which is of the same size as plate openings  74  and  76  in body plates  64  and  66  respectively. As those skilled in the art will appreciate the gate member  70  is shiftable between a valve open position as shown in FIG. 5, wherein the aperture  72  is in registry with openings  74  and  76 , and a valve closed position, wherein the gate member  70  is shifted downwardly so that the aperture  72  is fully out of register with openings  74  and  76 , thus blocking flow through conduit  16  at the position of the assembly  24 . 
     The actuator  60  includes an upright, tubular piston cylinder  78  having a base  80  provided with a vertical through-bore, as well as an annular top fixture  82 . The base  80  is secured to plates  64  and  66 , whereas the top fixture  82 , surmounting the upper end of cylinder  78 , is attached to the base  80  by means of long shank connectors  84 . The top fixture  82  has a threaded bore for receiving cartridge unit  62 . The cylinder  78 , base  80  and top fixture  82  cooperatively define an internal piston chamber  86 . An elongated piston rod  88  is secured to the upper end of gate member  70  and extends into chamber  86 . A circular piston  90  is secured to the uppermost end of rod  88  is slidable within the chamber  86 . 
     The gas-generating cartridge unit  62  may be identical to gas cartridge unit  36 , and is threadably connected to top fixture  82  in communication with the chamber  86  via passage  92  in fixture  82 . The unit  62  has a gas cartridge  96  which is the same as cartridge  36  in that the smokeless powder formulation is as previously described with respect to cartridge  36 , with the understanding that a sufficient quantity of the powder is provided to actuate and shift gate member  70  in accordance with the operating parameters specified herein. Unit  62  also has a prebulged rupture disc identical to disc  46 . Housing  94  connected to the outer ends of gas cartridge unit  62  contains electrical controller components which are operably coupled directly to the detector  18  or, alternatively, to the controller previously described that is actuated by detector  18 . 
     Normally, the particulate or gaseous material contained in structure  12 , whether it be a compartment or pressure vessel as previously described, is directed into area  14  via conduit  16  as a result of operation of a blower which provides positive pressure to the interior of structure  12 , or a negative pressure inside of structure  12  by virtue of the blower being located within area  14 . Solid particulate material, such as aluminum or magnesium fines, when received in area  14  is either collected by suitable conventional bag structure, or a cyclone, or is directed to equipment for processing of the metal particles. On the other hand, a gaseous product, such as hydrogen, may either be exhausted, or collected for use. Alternatively, the flow of particulate and/or gaseous material may flow from area  12  toward structure  12  presenting a similar hazard. 
     However, if the detector  18  detects a rise in the pressure within structure  12  indicative of ignition of the combustible material contained in structure  12 . The incipient explosion detected by detector  18  triggers operation of the devices  20  and  22  as well as the gate valve assembly  24 . In the case of the suppression of the deflagration suppression devices  20  and  22 , the electrical signal generated as a result of detection of a pressure rise within structure  12  by detector  18 , and which derives from the controller which is connected to or is a part of detector  18 , is directed to each of the gas cartridges  44 , thus effecting actuation of each of the cartridges. Pressurized gas generated by the cartridges  44  in each of the gas cartridge units  36  causes rupture of respective rupture disc  46  thus permitting the gaseous products from cartridge  44  to enter the interior of end extension  28 . The gas pressure from cartridge  44  also functions to immediately rupture disc  32 . 
     Rupture of disc  32  allows the nitrogen in each of the suppressant storage vessels  26  of both of the devices  20  and  22  to force the dry powder suppressant stored therein through respective piping  34  directly into conduit  16  on opposite sides thereof. The devices  20  and  22  are preferably positioned along conduit  16  in sufficiently spaced relationship from containment structure  12  to result in release of the dry suppressant into conduit  16  on opposite sides thereof, just prior to arrival of the flame generated by ignition of the material in the containment structure  12  and which travels along conduit  16  from the pressure source in structure  12 . A finite, although very short, period of time is required for the rise in pressure in containment structure  12  to be sensed by detector and for the detector to respond to a predetermined pressure, usually no more than about 1 to 2 to 10 m/s. Furthermore, a short time period, only a few milliseconds, is required for the gas cartridge  36  to be activated and for the rupture discs  46  and  32  respectively to be ruptured by gas pressure from cartridge  36 . Finally, a short interval of time is required for the released suppressant agent to traverse respective pipes  34  and into opposite sides of the conduit  16 . Accordingly, when locating suppressant devices  20  and  22 , the sum of the respective time intervals for delivery of the suppressant agent into the interior of conduit  16  should be accounted for, given the speed at which the flame produced by ignition of the combustible material in containment structure  12  will be traveling along conduit  16  from containment structure  12  until it reaches the locale of suppressant agent delivery pipes  34  connected to conduit  16 . The suppression devices will be located such that they will discharge prior to the arrival time of the flame front. Generally, this will be within the range of about 1 to 5 meters along the length of conduit  16  away from the point of connection of the conduit to containment structure  12 . 
     The gas cartridge unit  62  of gate valve assembly  24  is also actuated at the same time of actuation of the gas cartridge unit  36 . The powder in cartridge  96  is ignited, thus producing a pressurized gaseous discharge which is directed into the interior of cylinder  78  via passage  92 . The gas pressure within cylinder  78  above piston  90  drives the piston downwardly as shown in FIG. 5 thereby exerting force on the piston rod  88  connected to the gate member  58 . Shifting of piston  90  and the associated piston rod  88  causes the gate member  58  to be moved into full closing relationship to openings  74  and  76  thereby closing off flow of materials through conduit  16 . As previously indicated, the amount of the gas generating charge in cartridge  96  should be adequate to cause the gate member  70  to be moved into full closing relationship to the passage through conduit  60 , within a time interval of about 3 to 5 ms for each inch of diameter of conduit  16 . 
     Accordingly, gate valve assembly  24  should be located in conduit  16  downstream of suppression devices  20  and  22  a distance such that the gate member  70  is fully closed before the pressure wave of the products of combustion produced by burning of the contained material in structure  12  and which is traveling along the length of conduit  16 , reaches the vicinity of gate valve assembly  24 . In the example above, the spacing between suppression devices  20  and  22  and gate valve assembly  24  will be in the range of about 5 to 10 meters. 
     Limitation of the pressure wave to a level of no more than about 12 to 13 bar in conduit  16 , as opposed to the 30 bar level of the pressure wave experienced without suppression devices  20  and  22 , allows the gate member  70  to fully close off conduit  16  and not allow flame and pressure from the incipient explosion of the material in containment structure  12  to enter the collection or processing area  14 . 
     Thus, area  14  will be fully protected from an explosion that may have occurred in the containment structure  12 . Without the provision of the suppression devices  20  and  22  which deliver suppressant agent into the conduit  16 , the flame and pressure wave generated by ignition of highly flammable material such as aluminum or magnesium fines in containment structure  20  and traveling along the length of conduit  16  would be of such velocity and magnitude that the products of combustion would undergo a transition from a deflagration stage to a detonation stage. Therefore, the gate member  70  could not be placed such that it would close fully before the arrival of the detonation flame front. Furthermore, in the case of fires resulting from ignition of highly flammable materials such as aluminum, magnesium and hydrogen, as examples, the pressure wave from detonation of the material in conduit  16  would be of a sufficiently high level to cause limited physical displacement of the gate member  70  axially of conduit  16  and thereby allow leakage of flame and pressure past the seals of gate valve assembly  24  on each side of the gate member or plate  58 . 
     It has been determined, for example, that upon ignition of confined aluminum particles the pressure wave will reach a level of at least about  30  bar in conduit  16  downstream of containment structure  12 . By introducing the suppressant agent into conduit  16  ahead of, the time of arrival of the flame front at the piping  34  forming a part of each of the suppressant devices  20  and  22 , it has further been determined that when the suppressant agent is supplied from a  9  liter explosion suppressant vessel containing sodium bicarbonate as the suppression media, the suppressant agent lowered the pressure wave to a level of no more than about  12  to  13  bar within conduit  16  beyond the suppressant devices  20  and  22 .