Abstract:
A total flood fire suppression system is provided for transportation tunnels and other human-occupied environments, which employs a selective gas delivery method for supplying a breathable fire-extinguishing agent to a location closest to a fire site. The agent is produced from ambient air at site and stored in high-pressure containers communicating with an addressed gas delivery hose installed throughout a tunnel. When fire is detected, the agent is released from storage containers into the gas delivery hose that simultaneously becomes penetrated or broken in a location next to the fire site, allowing releasing the agent there and extinguishing the fire by totally flooding the affected portion of a tunnel. Additionally, the direction of the agent flow can be controlled by air blocks or inflatable tunnel plugs that, via a signal from a central control station, can inflate and block a tunnel tube in order to redirect the agent flow into the opposite to a block direction.

Description:
[0001]    This application is a continuation in part of:  
         [0002]    U.S. application Ser. No. 09/750,801 “Hypoxic Fire Prevention and Fire Suppression Systems and Breathable Fire Extinguishing Compositions for Human Occupied Environments” filed Dec.28, 2000,  
         [0003]    U.S. application Ser. No. 09/854,108 “Hypoxic Fire Prevention and Fire Suppression Systems with Breathable Fire Extinguishing Compositions for Human Occupied Environments” filed May 11, 2001 and  
         [0004]    U.S. application Ser. No. 09/975,215 “Mobile Firefighting Systems with Breathable Hypoxic Fire Extinguishing Compositions for Human Occupied Environments”filed Oct. 10, 2001 and  
         [0005]    U.S. application Ser. No. 10/024,079 “Hyperbaric Hypoxic Fire Escape and Suppression Systems for multilevel buildings, transportation tunnels and other human-occupied environments” filed Dec. 17, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0006]    The present invention introduces a fire suppression system for transportation tunnels and mines and methods of selective delivery of breathable fire-suppressive composition directly to the location affected by fire. The invented system is mostly suitable for installation in existing automobile and railroad tunnels without interruption of traffic. The system is also suited to provide complete fire safety in mines and other underground facilities, multilevel parking garages, industrial complexes, office and apartment buildings, schools, hospitals, shopping and entertainment centers and other enclosed compartments and environments.  
           [0007]    This invention is an important addition and improvement of the Fire Prevention and Suppression Systems (FirePASS™) described in earlier patent applications provided above.  
         DESCRIPTION OF PRIOR ART  
         [0008]    Tunnel fires have been usually divided into three types based on their order-of-magnitude rate of energy output. They are: small automobile fires (1 MW); medium fires (10 MW); and major and catastrophic fires (100 MW and higher). Small automobile fires are routine incidents, occurring as frequently as weekly in congested urban tunnels. Such reported fires have been universally extinguished without difficulty to date.  
           [0009]    However, the catastrophic fire following a suicidal terrorist attack in a congested traffic tunnel remains to be the most critical scenario, for which emergency services and authorities are unequipped and unprepared. It is relatively uncomplicated to organize and carry out such attack. For instance a regular track can be used, loaded with flammable liquid canisters or pressurized propane gas containers. Such an attack can cause a significant initial structural damage with a consequent catastrophic fire and numerous fatalities.  
           [0010]    Devastating tunnel fires demonstrate that their consequences depend entirely on the tunnel ventilation. Due to the necessity of providing adequate ventilation, a fire in a queue in an urban tunnel with a mixed fire load of passenger cars, buses and trucks could easily develop into catastrophe. Fire services will not be able to tackle these fires until it is too late, because radiant heat and smoke production is too great. This was the case in the last tunnel fire (October 2001, St-Gotthard tunnel), when firefighters could not even enter the tunnel until combustible materials were consumed by fire. Enhanced ventilation can also develop as a result of the chimney effect, as in the London Subway Fire and in the Kaprun disaster.  
           [0011]    Current fire-preventative and fire-suppressive methods are totally insufficient in dealing with catastrophic tunnel fires. Several systems, either installed or contemplated—aside from their effectiveness during normal operations—show little capability of satisfactory operation during a catastrophic fire emergency. These are fire extinguishers, stand pipes, and sprinklers (including water mist sprinklers) with their ancillary systems of water supply and drainage, and different types of ventilation. The standard safety-supporting systems (communication, ventilation, lighting, and escape), primarily support the comfort and well-being of persons in a tunnel during normal operations, but their functions during catastrophic events are insufficient, as was revealed in the Channel Tunnel fire in 1996.  
           [0012]    Automatic fire suppression systems based on water mist may be of little benefit in preventing structural damage to a tunnel and will not be effective in reducing loss of life in the event of a terrorist act followed by a catastrophic tunnel fire. The fire will probably be fully developed before the suppression system would be activated. The explosion can damage the water pipe system before it can create sufficient pressure for sprinklers. There will be a time lag between fire ignition and the activation of the water suppression system, which, in cold climates, must be initially dry. It will take time until pumps are started, valves are opened, and the delivery system piping is filled with water. Vehicular tunnel conditions cannot exploit sprinkler or water mist system strengths and turn most of them to a disadvantage. Tunnels are very long and narrow, often sloped laterally and longitudinally, vigorously ventilated, and never subdivided, so heat will normally not be localized over a fire. A catastrophic, hazardous-material fire will grow and spread hot combustion products far from its origin before sprinkler heads open, especially in colder regions where the water-suppression system is by necessity a dry one. An inordinately large flow of water would be required to deliver an effective spray through all the potentially-open heads to assure application upon the fire itself Besides that, since the fires usually originate from the lower part of a vehicle there will be no efficient fire suppression from sprinklers placed on the ceiling or walls of a tunnel.  
           [0013]    Automatic activation of the sprinklers by active detectors would of necessity be delayed until all traffic could be halted, since even light spray would catch drivers unaware, and would dangerously slicken the roadway. Water squirting from the ceiling of a subaqueous tunnel would suggest tunnel failure and induce panic in motorists. Inadvertent activation is clearly unacceptable. Moreover, discharging water onto a fully developed catastrophic fire within an enclosed tunnel may only increase the danger to the tunnel occupants because of the steam generated when water contacts the fire.  
           [0014]    Available publications and statistical data clearly indicate that currently no adequate and reliable fire-preventative and fire-suppressing technology for traffic tunnels is available anywhere in the world.  
           [0015]    The new fire-safety technology, FirePASS™ (Fire Prevention And Suppression System), recently developed by the inventor and described in previous patent applications provided above, can help resolve the complex problem of fire safety in transportation tunnels, as well as in normally occupied facilities in general. FirePASS™ can minimize structural damage and fatalities in terrorist attacks. This system is effective in the prevention and instant extinguishing of fire of any possible origin and size. It is also absolutely safe for people and is user-friendly, while completely excluding any damage of equipment and property. The system can be referred as related to Total Flood Clean Agent Systems, but it has significant differences from them. The FirePASS™ works by creating a safe human-breathable atmosphere in which nothing can be ignited or burn. This technology employs the Normobaric Breathable Hypoxic Air (NBHA) for prevention and suppression of fire.  
           [0016]    FirePASS technology for tunnels is based on two properties that differentiate it from all other total flood clean agent systems:  
           [0017]    1. The hypoxic generator produces oxygen-reduced air with a preset fire-suppressive, but safe for human breathing, concentration of oxygen. This eliminates the necessity of oxygen monitoring to control the tunnel atmosphere within the range of preset parameters. It also eliminates the complicated and vulnerable electronic feedback circuits that are sensible to structural and fire-related damage.  
           [0018]    2. When in use, the protected space is constantly ventilated with fire-suppressive, breathable hypoxic air. This creates normal or even improved hygienic conditions for occupants of the tunnel while the hypoxic generator produces HEPA-filtered, normal-humidity air. Constant ventilation allows the prompt evacuation of toxic combustion gases without feeding fire with oxygen, which is not possible by any prior art systems.  
           [0019]    As a fire-preventive modality, the environment of normobaric breathable hypoxic air in normally occupied facilities, including railroad tunnels, entirely eliminates the possibility of ignition of all common inflammable materials. As a fire-extinguishing option the effluent discharge of breathable hypoxic air would eliminate fire of any size and origin in seconds, while simultaneously evacuating toxic combustion gases and providing people with fresh breathable air. Smoke evacuation in this way does not feed the fire with oxygen, as in the case of usual forced ventilation with fresh atmospheric air.  
           [0020]    The system can be activated by detection and control equipment for automatic system operation along with providing local and remote manual operation as needed. The system can be engineered for preventive or suppressive mode, as well as a combination of both. FirePASS™ satisfies all critically important properties required for tunnel fire suppression, such as:  
           [0021]    —fire suppression efficiency;  
           [0022]    —reignition quenching;  
           [0023]    —electrical non-conductivity;  
           [0024]    —non-corrosivity to metals;  
           [0025]    —polymeric materials compatibility;  
           [0026]    —stability under long-term storage;  
           [0027]    —toxicity of the chemical and its combustion and decomposition products;  
           [0028]    —speed of dispersion; and  
           [0029]    —safety and occupational health requirements.  
           [0030]    In its suppressive mode FirePASS™ for tunnels requires sufficient amount of the breathable agent stored in high pressure containers. However, after initial discharge from containers, the agent continues to be produced from ambient air by hypoxic generators and delivered to the site of a fire for as long as needed. The system can be operated by the tunnel operator within established criteria or on the instruction of the Fire Services Incident Operator. A single car fire with no traffic congestion may not warrant its operation. A fully involved or developing car fire resulted from an accident or terror act and spreading to other vehicles may require its activation.  
           [0031]    A hypoxic agent can be used also as a fire-preventive modality in the railroad and funicular tunnels. This application of FirePASS™ technology can be achieved with the help of semi-airtight doors that turn the inner volume of a tunnel into an enclosure, having the atmosphere of NBHA inside. The doors will be opened automatically at the approach of train and closed again after it has passed through. The necessary amount of NBHA in the tunnel will be maintained by continuous compensatory discharge from piping.  
           [0032]    The tunnel-specific configuration of FirePASS™ provides high reliability and efficiency. The system operational reliability cannot be affected by electric power supply failure, because it relies on built-in autonomic compressors and a backup power supply. After the initial agent discharge from pressurized containers the hypoxic generators would be automatically started and will produce sufficient amount of the agent for tunnel ventilation. Due to the addressed delivery of the agent via gas delivery hose the loss of agent is minimized.  
           [0033]    The system is also resistant to structural damage. Thus, even in the case of a major explosion in the tunnel, causing damage to the gas delivery hose and communication cables, the fire-affected area of a tunnel can be flooded and further ventilated with the breathable hypoxic agent.  
           [0034]    An important advantage of the FirePASS™ technology in comparison to all other existing fire-suppressive systems is that its fire-preventative and suppressive agent is produced at site by hypoxic air generators that consume nothing but electric energy. There are no gas transportation and refilling problems, and a low maintenance costs and simple integration in existing structural configurations are the obvious advantages of this technology.  
           [0035]    The equipment for FirePASS™ technology exists in a variety of different prototypes, and can be manufactured and installed in specified applications both for newly-planned tunnels and for retrofitting-existing ones. The system can be periodically tested and exercised; it allows quick response and permits the tunnel operator positive control in the event of a fire. Approximate cost benefit analyses shows that the cost of the system is significantly less than the expected costs of damages, liability, and loss of a vital transportation link that may result from a single catastrophic fire.  
         SUMMARY OF THE INVENTION  
         [0036]    The principal objects of this invention are as follows:  
           [0037]    A method for producing and selectively delivering a breathable fire-suppressive hypoxic composition inside a part of a tunnel or other human-occupied environment affected by fire.  
           [0038]    A method of extinguishing an ongoing fire in a tunnel by releasing a pressurized fire-extinguishing hypoxic composition into a location where fire is detected. This rapidly replaces the contaminated normoxic atmosphere in such an environment with the human-breathable hypoxic fire-extinguishing atmosphere and suppressing any fire at once.  
           [0039]    The provision of equipment that can produce, store and deliver the breathable hypoxic fire-extinguishing composition.  
           [0040]    The provision of a fire suppressant delivery system consisting of an expandable gas delivery hose, fire detectors installed at intervals along the hose&#39;s length and puncturing devices that can puncture the hose in any location where a fire is detected. This will allow the discharge of the fire suppressant from pressurized storage containers and flooding the portion of a tunnel affected by fire. Additional supply of hypoxic agent from hypoxic generators will maintain a fire-extinguishing atmosphere for as long as needed.  
           [0041]    The provision of an inflatable tunnel-blocking device or plug that allows redirecting the fire-suppressant flow towards a direction opposite to the inflated plug. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0042]    [0042]FIG. 1 presents a schematic view of the first preferred embodiment of the Hypoxic Tunnel Fire Suppression System.  
         [0043]    [0043]FIG. 2 shows schematically the design and working principle of the addressed gas delivery system.  
         [0044]    [0044]FIG. 3 shows schematically the working principle of the first embodiment.  
         [0045]    [0045]FIG. 4 illustrates the installation process of the gas-delivery hose inside an existing railroad tunnel tube.  
         [0046]    [0046]FIG. 5 shows an equipment-installation plan of the invented fire suppression system designed for an existing two-tube railroad tunnel.  
         [0047]    [0047]FIG. 6 shows an additional solution for the controlled delivery of the fire suppressant directly into a necessary section of a tunnel tube.  
         [0048]    [0048]FIG. 7 shows the most effective design of a tube-blocking plug.  
         [0049]    [0049]FIGS. 8, 9 and  10  illustrate the working principle of the gas-flow control system based solely on the inflation of plugs in different situations.  
         [0050]    [0050]FIG. 11 illustrates an alternative method wherein both plugs are closed. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0051]    This invention is based on the Phenomenon of Ignition Suppression and Combustion Elimination in hypoxic breathable air and the Hypoxic Fire Prevention and Suppression System (FirePASS™), being described in previous patent applications..  
         [0052]    [0052]FIG. 1 presents a schematic view of the first preferred embodiment  10  of the Hypoxic Tunnel Fire Suppression System (HTFSS) that is most suitable for automobile and railroad tunnels, mines and underground facilities. The system can be also used in different types of buildings, especially of expanded shape, like the Pentagon building near Washington D.C., having many miles of corridors and underground passageways.  
         [0053]    A tunnel  11  having a gas-distribution hose  12  for selective delivery of hypoxic fire suppressant to any part of the tunnel  11 . Hose  12  is connected, via a release valve, to a gas storage container  13  holding the fire-suppressive composition under high pressure and communicating with a high-pressure compressor  14  and hypoxic generator station  15 .  
         [0054]    When needed, the hypoxic generator station  15  intakes ambient atmospheric air through filter  16  and sends it in compressed form into an air-separation module where a portion of the oxygen is extracted. The oxygen-enriched gas mixture can be disposed of into the atmosphere or, preferably, sent to a fuel-cell power plant that can generate electricity for the object needs. The product remaining after the oxygen extraction is an oxygen-depleted (hypoxic) gas mixture, containing 12% of oxygen and about 88% of nitrogen with traces of other atmospheric gases. The product is further compressed by compressor  14  and sent for storage into high pressure container  13 , ready to be released, as the fire suppressant, into hose  12 .  
         [0055]    Suitable air-separation modules, compressors and containers are available from FirePASS Corporation and Hypoxico Inc. in N.Y. The working principle of these modules has been described in previous patent applications provided above.  
         [0056]    Hypoxic generator station  15  can also employ nitrogen generators that extract 88% nitrogen from ambient air. Alternatively pure nitrogen extracted from ambient air can be mixed in desired proportions with ambient air and provide nitrogen-enriched air for storage in container  13 . However, nitrogen extraction requires preliminary drying of processed air and is more costly and less efficient than hypoxic air generation.  
         [0057]    [0057]FIG. 2 shows schematically the design and working principle of the addressed gas delivery system  20 . The hose  12  is made of any length from a strong, thin synthetic or composite material and can be delivered for installation on a bobbin in collapsed form.  
         [0058]    The upper rim of the hose  12  is permanently attached to a tunnel wall by screws  21 . Screws  22  hold the lower rim so that the rim can be pulled out when hose  12  inflates. This can be achieved by prefabricating a special cut  23  that will allow the lower rim to slide out under screw  22  or by placing a holding bar or profile that will cover the lower rim and press it against the tunnel wall.  
         [0059]    Multiple fire detectors  24  are installed at desired intervals (e.g. 20 meters) alongside the hose  12 . Detectors  24  communicate with a central fire alarm and control station ( 55  on FIG. 5) and allow the precise determination of the location of fire.  
         [0060]    Hose puncturing devices  25  are installed at desired intervals behind the hose  12  (between the hose and the wall of a tunnel). The devices  25  can be initiated by a signal transmitted from a detector  24  or from central station  55  and puncture the hose  12  at controlled location.  
         [0061]    Most recommended are puncturing devices of two types:  
         [0062]    electro-explosive  
         [0063]    thermoelectric.  
         [0064]    An electro-explosive device can be easily and cheaply made by putting a small amount of a plastic explosive in a flat metal can and wiring it directly to the nearest detector  24  and/or to the central alarm and control system  55 . The metal can size can be very small (2-5 cm in diameter) but they can cause an extensive damage to the hose  12  at a desired location. A signal from a detector  24  or central station will initiate an explosion that will puncture or destroy a portion of hose  12 .  
         [0065]    A thermoelectric device can be made even cheaper from a piece of a wire from a nickel-chrome alloy as is used in most electric heaters and stoves. When electric current is applied, such piece of wire would heat up extensively and burn through the material of the hose  12  in a few seconds. Such devices can be preinstalled on an assembly line inside or outside of hose  12  jointly with the connecting electric wire or installed at site. The thermoelectric puncturing devices can be made in a shape of a ring—to provide a round hole, or in linear shape—to cut the hose  12  in two parts.  
         [0066]    The working principle of the gas distribution system  20  can be explained as follows. When a fire is detected by the nearest detector  24 , it sends a signal to the central control station  55  and initiates adjacent puncturing device  25  by applying electric current to an electro-explosive or thermoelectric device that punctures or tears apart hose  12  (FIG. 2A). In some cases device  25  can be initiated only by an operator from a central control station (e.g. in a railroad tunnel when a train on fire stops completely) when alarm from detector  24  is supported by visual information from one of video cameras installed throughout a tunnel. It is always advisable to install video cameras (not shown here) jointly with the system  20 . After hose  12  is punctured, the whole fire-suppression system is initiated and the hypoxic fire suppressant is sent under pressure into hose  12 . The lower rim becomes loose and the hose  12  inflates it to a tubular shape transmitting the breathable fire-suppressive composition at a high velocity to the punctured by device  25  hole and releasing it directly into location affected by fire. After each use, the destroyed portion of the hose  12  can be easily replaced with a new one and attached in place with glue, welding or other fastening method.  
         [0067]    Metal piping certainly can be used instead of the lightweight hose  12 , however it would require much more space and a lot of installation work, which many existing tunnels cannot allow. Moreover, metal piping would require installation of a large amount of gas release nozzles with gas release valves, actuators, initiators and complicated control network. All this will inflate the cost and diminish the reliability of the system significantly.  
         [0068]    [0068]FIG. 3 shows schematically the working principle of the embodiment  10 . Hypoxic generator station  15  intakes ambient atmospheric air through intake filter  16  and separates it into oxygen-reduced (hypoxic) product and oxygen-enriched waste. The oxygen-enriched gas mixture can be disposed into the atmosphere or, preferably, send to a fuel-cell power plant that can generate electricity for the object needs. The product remaining after the oxygen extraction is breathable hypoxic air containing 12% of oxygen by volume and having a fire suppressive property. Therefore the product can be further also called a breathable fire suppression agent or fire suppressant. Three-way valve  31  allows sending the product into high-pressure compressor  14  that, via line  33 , refills containers  13  while release valve  32  is closed. Containers  13  store the product under high pressure (50-300 bar) in amounts sufficient to flood a desired portion of a tunnel: a segment of at least 50 meters is recommended for automobile tunnels and 100 meters for railroad tunnels (smaller segments may apply to mines and other structures). For instance, a railroad tunnel tube with 25 m2 section area would need 2500 m3 of the fire suppressant in order to flood a 100 m segment. In order to store 2500 m3 of suppressant at 100 bar pressure a storage volume of only 25 m3 is required (e.g. 25 containers at 1 m3 each).  
         [0069]    When a fire in a tunnel is detected and the nearest device  25  punctures hole  36  in gas delivery hose  12 , release valve  32  opens as a result of a signal from central control station and releases high-pressure suppressant via a pressure reducing device (not shown here), from high pressure line  33  into line  35  and hose  12 . At this time hypoxic generator station  15  and compressor  14  start working providing more product into line  33 . Hose  12  inflates and releases breathable fire suppressant through the hole  36 , which allows flooding a segment of the tunnel and extinguishing any fire instantly, while providing entrapped people with fresh breathable hypoxic air. The suppressant, released from high pressure becomes very cold, which will provide an additional benefit of thermal absorption and create a positive pressure zone keeping normoxic air away from the flooded zone.  
         [0070]    After all suppressant has been released, valve  31  opens line  34  and hypoxic generator  15  sends additional hypoxic composition directly into hose  12 , via line  35 . The recommended oxygen content in this freshly-made composition is 12%-14%, which will maintain a fire suppressive atmosphere while providing comfortable breathing conditions for people. The supplied flow must be sufficient to keep a positive pressure in the fire zone for as long as needed. In the previous case of a railroad tunnel, a flow of about 400 m3 per minute would be sufficient, provided that all traffic in the tunnel is stopped. This amount can be produced by five hypoxic generators, providing 40m3/min each, that are available from FirePASS Corporation in N.Y., U.S.A.  
         [0071]    [0071]FIG. 4 illustrates the convenience of the installation of the gas-delivery hose  12  inside an existing railroad tunnel tube. A bobbin  41  is mounted on a railroad platform slowly moving through the tube  42 . Two workers can walk on the benchwall and attach hose  12  to the tube wall with screws or other fixtures. All necessary wiring, detectors  24  and devices  25  are incorporated in a plastic tape  44  that is attached to the wall prior to hose  12  or can be installed separately.  
         [0072]    [0072]FIG. 5 shows an equipment-installation plan of the invented fire suppression system designed for an existing two-tube railroad tunnel in N.Y., wherein most of the equipment is installed in a ventilation shaft building  51 .  
         [0073]    High-pressure gas containers  13  contain breathable hypoxic fire suppressive composition under 100 bar pressure ready to be released into pressure reducing device  53  and on of the pipes  54 . When in operation, hypoxic generator  15  intakes ambient air though the intake filter  16  and sends hypoxic air, after partial oxygen extraction, into high-pressure compressor  14  that can refill containers  13  when needed. The system is controlled by central computerized control station  55  under constant supervision of an operator.  
         [0074]    [0074]FIG. 6 shows an additional practical solution for controlled selective delivery of the fire suppressant into a required section of the same railroad tunnel tube  61  having two existing ventilation shaft buildings  62  and  63  equipped as shown on FIG. 5. This system can redirect the flow of the agent in the tunnel simply by plugging up air blocks  64  or  65 . The blocks or plugs  64  and  65  can be made in a variety of configurations from light materials that can block air but not a train.  
         [0075]    [0075]FIG. 7 shows the most effective design of plug  72  installed in a special box  71  placed at each end of the tunnel tube  61 . Plug  72  that can be inflated in case of emergency, providing a complete blockage of the tunnel entrance. The inflatable plug  72  is made from a lightweight strong synthetic material and can be easily deflated by cutting through or removing a plug from it. The purpose of the inflatable tunnel plug  72  is simply to prevent air movement in order to control the direction of the agent flow, and it can in no way prevent a train from moving in or out. Plug  72  can be inflated using a device similar to one used in automobile bags or just from a small container with compressed air or nitrogen. Other pyrotechnical or chemical devices can provide for inflation as well. The inflation is initiated, when needed, by a signal from the central control station  55 .  
         [0076]    [0076]FIG. 8, 9 and  10  illustrate the working principle of the gas flow control system based solely on the inflation of plugs  72  and  73  in different situations.  
         [0077]    When a fire starts in a middle section of a tunnel as shown on FIG. 8, the suppressive agent is released from the gas storage containers in the station  63 . The agent is directed to the fire site simply by inflating plug  73 , via a signal from control unit  55 . FIG. 9 shows a fire in the first section of the tube  61 . In this case, the fire suppressant is released from the station  62  and plug  73  blocks the tube  61  in the final section, directing the agent flow into the fire-affected area. Fire becomes extinguished, smoke is removed from the tunnel and the area becomes ventilated with the fresh breathable gas mixture for as long as needed.  
         [0078]    [0078]FIG. 10 illustrates similar situation with a fire in the last section of the tube  61 . Plug  72  inflates and the fire suppressive agent is released from station  63 , flooding the fire site instantly and providing breathable atmosphere for trapped people. It is recommended that a train with a fire on board stop completely in order to provide most efficient suppression.  
         [0079]    [0079]FIG. 11 illustrates an alternative method wherein both plugs  72  and  73  can be closed while smoke and excessive suppressant sent from station  63  can be removed via a ventilation shaft in station  62 .  
         [0080]    Tunnel plugs can be used effectively in a combination with the addressed gas delivery system shown on FIG. 2. This will ensure that the fire suppressant flow could be redirected in the required direction if the situation changes. In longer tunnel tubes, multiple tunnel plugs can be installed in different sections of a tunnel in order to achieve faster fire extinguishing results and to use fire suppressant more effectively. Such a plug or a blocking device can be made as an inflatable, expandable, erectable, moveable or falling barrier that will substantially block air movement through it. An inflatable plug made of a lightweight synthetic material, a moveable or closeable gate or shield, a droppable curtain or other air-blocking means can be used as well. The plugs can be also rapidly inflated and deflated by a blower controlled by an operator at the control station according to a situation during a tunnel fire. This will make the system very reliable and easy to control.