A system for exhausting flue gases in a tunnel

Abstract

 According to the invention, a system for carrying away flue gases from a fire in a tunnel (1) comprises a duct (2) provided with a plurality of hinged doors or gates (3), which each are kept closed against a spring force by means of a lock with thermostatic release.
The hot flue gases will hereby release locks and open the dampers (3) at the fire zone concerned and convey the flue gases via the dampers into the duct (1), from where they are evacuated from the tunnel by means of fans.

Description

The prior art

[0001] The invention relates to a system for exhausting and thereby carrying away flue gases and hot air from a fire in a tunnel via a damper into a discharge duct which extends in the tunnel, and through which the flue gases and the hot air are discharged.

[0002] Tunnels are characterized by being elongated cavities which have an opening at both ends, and which have a cross-sectional area that is relatively small in relation to their length. In most tunnels, there is frequently a natural draught which ensures a reasonable supply of oxygen. Tunnels are frequently used for the transport of carriages, cars, trains, passengers, etc., or as passages for cables and other permanent installations. Frequently, tunnels contain large amounts of combustible substances.

[0003] In connection with fires, the draught in the tunnel and the amount of fuel mean that a fire of relatively great intensity can easily occur. The hot fire gases can be distributed only over a relatively small cross-section in a elongated pipe, where a relatively large amount of air is to be moved to give room for the hot fire gases, and as a result of this the temperatures in the tunnel risk getting very high in connection with relatively small fires, which can therefore spread relatively rapidly and become very violent.

[0004] Also, fire gases will rapidly fill the tunnel with thick and stifling gases which make it difficult to evacuate the tunnel in a fire and carry out a safe and efficient rescue operation.

[0005] Extinguishing systems for fire fighting in tunnels based on the spreading of water or water mists have been developed and are installed in tunnels today. These systems are relatively expensive. They require supply of extinguishing medium, and, depending on the required water pressure and the required water amount, these systems also need a relatively great supply of energy.

[0006] In connection with the evaporation of water in connection with the extinguishing with water, water vapour is produced, the oxygen potential in the tunnel air is reduced, the combustion of the combustion gases is reduced, and the temperature of the combustion gases is reduced. Condensation of water vapour in the tunnel causes the visibility to be reduced considerably. So does the increased amount of non-combusted fire gases, which also results in an increased concentration of stifling CO and Nx gases in the tunnel atmosphere, and the cooling of the fire gases causes the thermal buoyancy of the gases to be reduced, as a result of which these will fill the entire cross-section of the tunnel even for relatively short tunnels and corridors.

[0007] Tunnels are frequently vented of car smoke, etc. by fans which are positioned close to the ceiling of the tunnel. Arranging them in rows near the ceiling ensures that the gases are conveyed away near the ceiling of the tunnel without too great mixing with the air which is present at lower levels in the tunnel cross-section.

[0008] These systems are relatively inexpensive to install and are efficient against car smoke, but insufficient in case of tunnel fires with a much greater concentration of fire gases and water vapour, which, particularly in case of long tunnels, risk getting mixed with the rest of the air in the tunnel.

[0009] It has been attempted to solve this by installing an extra tunnel ceiling above the tunnel ceiling proper, the space between the two ceilings being separated by a ceiling system with inclined slats. The angle of inclination of the slats may be adjusted to the direction of ventilation and in a few cases also the ventilation pressure and the air speeds. Smoke and gases, etc. may hereby be discharged from the utility cross-section of the tunnel and be discharged in the extra ceiling space without any mixing between the gases which are being discharged and the air in the utility tunnel.

[0010] This method, too, requires a relatively great ventilating system and will have a relatively great power consumption because of the large amount of air which is to be transported in the relatively large cross-section of the ceiling space. Because of the cost of construction, etc., this solution is best suited for tunnels which have been designed in advance for this venting solution.

[0011] US 6 478 672 discloses a system for discharging flue gases comprising a duct which is provided with slats which may be remote-controlled so that a plurality of slats in the fire area may be pivoted to open, thereby providing a communication to the duct through which the flue gases may be exhausted.

[0012] For this system to operate, remote-controlled equipment has to be mounted, comprising signal generators to pivot the dampers, including a power supply for the pivoting mechanism of the dampers. This is therefore a relatively expensive system to manufacture and install, since it requires installation of remote signal generators, pivoting means for the dampers and associated power supply, wiring systems, etc.

The object of the invention

[0013] The object of the invention is to make the exhaustion more efficient, while making the system inexpensive to produce as well as to install, and this is achieved according to the invention in that the duct is provided with gates in the form of hinged doors which each are kept closed against a spring force by means of a lock with thermostatic release, so that a local temperature increase in the tunnel automatically releases the door or doors which are located above the scene of fire concerned.

[0014] The function of the opening of the individual damper plates will hereby be autonomous, as only the most important dampers will open and only in dependence on the temperature which exists around the dampers concerned.

[0015] This ensures that exhaustion will always take place in the hottest area and also that the ventilation, i.e. the exhaustion, will be effective, since the capacity is utilized fully to remove the dangerous gases concerned and the heat which are generated by a fire.

[0016] When, as stated in claim 2, the release mechanisms in the individual dampers also control the ventilation, the exhaustion may be optimized in response to the need.

[0017] When, as stated in claim 3, the release mechanisms are used for signalling for fire fighting, such as activation of sprinkler and mist nozzles, the fire fighting will be concentrated to the zones where the fire is to be fought.

[0018] When, as stated in claim 4, water mist is supplied to the hottest and most smoke-filled places in the duct, these will cool the gases, and the ventilation capacity is thereby increased, just as a certain precipitation of the smoke particles will take place in the water mist.

[0019] When, as stated in claim 5, the duct is cooled externally in the hot zone by means of water mist, the temperature in the duct may be kept low.

[0020] Finally, it is expedient, as stated in claim 6, to mount axial fans in the entire cross-section of the duct, since this makes it possible to generate a small positive pressure for effectively driving the gases through the duct.

The drawing

[0021] Examples of systems according to the invention will be described more fully below with reference to the drawing, in which

fig. 1

shows a perspective view of a tunnel with an exhaustion system according to the invention,

fig. 2

shows a section of the duct with a damper with a release mechanism,

figs. 3b-e

show examples of release mechanisms according to the invention,

fig. 4

shows a perspective view of a system with fire fighting equipment, and

fig. 5

shows a system with water mist equipment.

Description of exemplary embodiments

[0022] Fig. 1 shows an example of a tunnel 1 in which an exhaustion system according to the invention is installed at the top, said system comprising a duct 2 which is provided with a plurality of openings with dampers 3, and which is provided with vent openings 4 which each are provided with suction fans (not shown).

[0023] Fig. 2 shows a section of the duct 2 in the form of a sectional view with a damper 3 which is mounted on the side of the duct 2.

[0024] The damper 3 is mounted by a bracket 7 with springing which acts on the damper with a constant spring force for opening, which will keep the damper open if it is not held back by a locking mechanism which, at a predetermined temperature, will be released thermally to open so that the spring-loaded damper 3 will open automatically for passage to the interior of the duct.

[0025] Fig. 2 shows an example of a locking mechanism consisting of a pawl system 10 which is kept in its locked position by a release element 11, and where springs 9 are mounted such that these springs pull the pawls 10 back when the thermal release element 11 is released, whereby the damper will open automatically.

[0026] The thermal release element 11 may be a liquid-filled glass ampoule, a meltable member, a bimetallic member or a piece of alloyed material and the like.

[0027] The duct 2 is thermally insulated 8 so that heating from the hot fire gases inside and outside and in particular heating of the air in the duct is reduced.

[0028] Fig. 3b shows an example of an embodiment of the locking mechanism, where it is affected for release by a compression spring 15.

[0029] Fig. 3c shows an example of a mechanism which is heat-released by a thermal release element, which is released electrically by means of a detonator 12 consisting of a pyrotechnical charge which affects a piston or other device, which removes the thermal release element 11 when the pyrotechnical charge is ignited by an electrical pulse, whereby the locking pawl 10 is released.

[0030] Fig. 3d shows an example of a mechanism which activates an electrical switch 13 when the thermal element 11 is released so that it may be used for electrical control of e.g. fans in the duct or similar extra equipment, which will be described later.

[0031] Fig. 3e shows a mechanism where the pawl system 10 affects a hydraulic or pneumatic valve 14 so that this automatically opens or closes when the pawl is activated. This may be used for automatically activating extinction systems and/or cooling systems independently of electrical connections, as will be described later.

[0032] Fig. 4 shows an example of a tunnel 1 in which a venting duct system corresponding to the one shown in fig. 1 and a fire fighting system are installed, which may be a water and/or foam-based sprinkler system with open sprinklers, or a water mist system with or without addition of additives to the water supply.

[0033] The fire fighting system consists of a water supply which, in the case shown, is in the form of a reservoir 18, a pump system 17 and one or more supply pipes 16, which are connected with a branch pipe 19 connected via a valve 21 with one or more nozzle pipes with open nozzles 20, which for each branch pipe covers a predetermined area of the tunnel in which the fire zone is present.

[0034] Supply pipes and branch pipes may be pressurized, and the valves 21 prevent liquid from reaching the nozzles, or branch pipes and supply pipes may be without pressure and be pressurized only when the heat from a fire releases one or more of the locking mechanisms and thereby activates a switch which opens the dampers 3 above the fire and simultaneously open the valve closest to the open damper 21 and the two adjacent valves 21 and starts the pump 17, if this is not started automatically by a pressure drop in the supply pipe 16.

[0035] Fig. 5 shows a tunnel 1 corresponding to the one shown in fig. 1, where a water cooling system and a drain system for the plant are installed. The water cooling system is typically a water mist system which distributes a water mist 23 in the duct 3. The water cooling system comprises a water supply 28 for one or more nozzle pipes 27, on which a plurality of water mist nozzles 32 inside the duct 2 are mounted, and which are distributed in the entire length of the duct.

[0036] The water cooling system may have nozzles which are closed by a thermal release element, and which open individually when it is subjected to a temperature higher than a predetermined release temperature of the release element, or it may consist of open nozzles which automatically distribute water mist when they are pressurized with water. Valves and water supply for the water cooling system may be activated automatically when a locking mechanism, as shown in figs. 2 and 3, is activated.

[0037] The system pipe is provided with drain pipes 25 on which a drain valve is mounted, which may consist of flap 29 affected by a spring 30 such that the flap is kept closed against the drain pipe 25, whereby supply of air to the duct from the drain pipe may be prevented. When the drain pipe 25 is filled with water, the force F on the flap 29 becomes greater than the closing force, and the water may be drained from the drain pipe, the water in the drain pipe serving at the same time as a plug preventing air from being admitted into the duct 2 from the drain pipes.

[0038] The mode of operation will be described now.

[0039] In case of a fire in the tunnel, the hot flue gases from a fire will ascend and surround the duct over the scene of fire. When the temperature of the hot fire gases locally reaches the release temperature of the thermal release elements 11, the heat-sensitive release element or elements 11 are released locally, whereby the locking mechanism for the dampers automatically opens on the dampers which are present in the heat-affected area.

[0040] The fans are started at the same time, which are present in the duct system, and which will be mounted inside the duct in very long tunnels. A particularly efficient ventilation may be achieved by installing axial fans which cover the entire cross-sectional area of the tunnel, thereby increasing the efficiency and allowing a small positive pressure to be established in the duct for effective driving-off of the flue gases.

[0041] The fans may be activated automatically by means of a switch mounted on the thermal locking device on the individual dampers.

[0042] A simple exhaustion systems for mounting in tunnels is established in the same manner. The system carries away only the hot flue gases from the scene of fire, which reduces the requirement with respect to the capacity of the ventilation and thereby also the power consumption of the system.

[0043] The invention moreover ensures physical separation between the hot fire gases and the utility air in the tunnel. Therefore, it may advantageously be combined with an active water mist or sprinkler extinction system, thereby ensuring improved visibility and air quality in the tunnel during a fire.

[0044] This facilitates the evacuation and the fire fighting work. The system also reduces the possibilities of flashover and thereby a tendency of fire spreading in the tunnel, since the hot fire gases are driven-off and cooled.

[0045] A special variant of the invention is when the system comprises an internal water cooling system, where the hot gases in the vent pipe are cooled by a water mist which binds the particles of the fire gases to the water, whereby this water may be drained automatically via drain pipes on which drain valves are mounted for automatic draining of the system.

[0046] In connection with long tunnels, a special variant of the invention is a system with internal water mist cooling and cleaning of the fire gases which may be combined with axial venting in the tunnel ceiling, so that the individual length of the duct sections may be reduced and the venting from these is partially taken over by venting systems already installed.

Claims

1. A system for exhausting and thereby carrying away flue gases and hot air from a fire in a tunnel via a damper into a discharge duct which extends in the tunnel, and through which the flue gases and the hot air are discharged, characterized in that the duct (2) is provided with gates in the form of hinged doors (3) which each are kept closed against a spring force by means of a lock (9-11) with thermostatic release, so that a local temperature increase in the tunnel (1) automatically releases the door or doors (3) which are located above the scene of fire concerned.

2. A system according to claim 1, characterized in that the release mechanism simultaneously activates the ventilation to ensure sufficient exhaustion.

3. A system according to claim 1 or 2, characterized in that the release mechanism simultaneously releases an extinction system at the location concerned in the tunnel (1).

4. A system according to claims 1-3, characterized in that the release mechanism simultaneously activates a water mist system (27, 32) for cooling the gases and the air in the duct (2) by spreading water mist (33) in the duct (2).

5. A system according to claims 1-4, characterized in that the release mechanism simultaneously activates a water mist system for cooling the external parts of the duct (2) by means of water mist.

6. A system according to any one of claims 1-5, characterized in that the ventilation takes place by means of axial fans mounted in the duct (2), said fans essentially filling the entire cross-sectional area of the duct (2).

Drawing