EP1552860B1 - Foam fire extinguishing system - Google Patents

Abstract

The invention concerns a fire extinguishing system using foam, comprising: a tube (10) designed to be arranged above a space to be protected and capable of being supplied by means of a pressurized water mixture and an emulsifier; and at least one extinguisher nozzle (12) consisting of at least one slot (24) provided in the wall of said tube and an expansion cage (26) configured to receive the liquid jet delivered by said slot and produce foam which is poured onto said space.

Description

The present invention relates to fire protection installations. More particularly, it relates to a fire extinguishing system using a foam that is particularly well adapted to fighting fires in large confined spaces, such as tunnels, car parks or warehouses.

• à réponse rapide, c'est-à-dire réagissant instantanément à une élévation anormale de la température, et
• fiables, c'est-à-dire aussi peu sensibles que possible aux changements de température (gel, ...) mais également aux poussières ou autres salissures risquant de les "aveugler" partiellement ou totalement.

Such an installation must, first of all, be equipped with detectors:

• fast response, that is to say, reacting instantly to an abnormal rise in temperature, and
• reliable, that is to say as insensitive as possible to changes in temperature (frost, ...) but also to dust or other soils that may "blind" partially or totally.

A fire-fighting facility in a large space must also be capable of responding, in a targeted manner, to several fires separated from each other, which is frequent during a fire or when, in a tunnel, a first fire causes chain collisions and new fires. It is therefore vital that the installation intervenes at this location and is not prematurely out of extinction means because it has exhausted too quickly its resources on the first fire.

Due to advances in the field of emulsifiers (generally liquid soaps), foam extinguishing systems have recently developed strongly. The attack of the fire by means of foam is not only more effective than that of a simple installation of water, known as "sprinkler", because it stifles the fire instead of bringing him oxygen, but, moreover, consumes much less water, which is a considerable advantage in tunnels. It will be noted, for example, that a medium expansion installation, well adapted to this kind of space, requires only 1 liter of water to produce some 30 to 40 liters of foam.

• une pluralité de détecteurs thermiques obturant chacun l'extrémité d'un conduit alimenté en air comprimé et réagissant à une élévation anormale de la température ambiante en faisant déboucher ledit conduit à l'air libre,
• un système d'extinction à mousse prenant place au-dessus du secteur à protéger, et
• des moyens de commande qui répondent à une chute de pression résultant de la mise à l'air libre d'au moins l'un desdits conduits par l'alimentation dudit système en un mélange d'eau sous pression et d'émulseur lui permettant de déverser de la mousse d'extinction sur ce secteur.

The document WO 03/041806 describes a fire detection and extinguishing system in a tunnel, which meets the requirements set out above and attacks the fire with foam. This installation comprises a plurality of separate sets each assigned to the protection of a sector of the tunnel and comprising, for each sector:

• a plurality of thermal detectors each closing the end of a duct fed with compressed air and reacting to an abnormal rise in the ambient temperature by opening said duct in the open air,
• a foam extinguishing system taking place over the area to be protected, and
• control means which respond to a pressure drop resulting from the venting of at least one of said conduits by supplying said system with a mixture of pressurized water and an emulsifier enabling it to pour foam on this area.

The main object of the present invention is to provide an improved version of a foam extinguishing system which can equip not only the aforementioned installation but also any existing installation, whether automatic or manual.

• un tube destiné à prendre place au-dessus de l'espace à protéger et pouvant être alimenté à l'aide d'un mélange d'eau sous pression et d'émulseur, et
• au moins une buse d'extinction comportant au moins une fente pratiquée dans la paroi dudit tube et d'une cage à foisonnement disposée pour recevoir le mélange d'eau sous pression et d'émulseur délivré par ladite fente et produire de la mousse qui est déversée sur ledit espace.

More specifically, the invention relates to a fire extinguishing system using foam, which comprises:

• a tube intended to take place above the space to be protected and which can be fed with a mixture of pressurized water and an emulsifier, and
• at least one extinguishing nozzle having at least one slot in the wall of said tube and an expansion cage arranged to receive the mixture of pressurized water and emulsifier delivered by said slot and to produce foam which is spilled on said space.

• La fente est sensiblement parallèle à l'axe du tube et à l'axe de la cage.
• La buse comporte plusieurs fentes parallèles.
• La cage est réalisée en grillage et comporte une paroi supérieure à section en forme de triangle dont l'arête fait face à la fente, parallèlement à elle, et une paroi inférieure incurvée sensiblement concentrique au tube.
• L'angle au sommet du triangle est sensiblement compris entre 110 et 130°.
• La base dudit triangle a sensiblement la même dimension que le diamètre du tube.
• La base de la partie inférieure de la cage a sensiblement la même dimension que celle du triangle.
• La cage comporte une paroi intermédiaire entre sa paroi supérieure et sa paroi inférieure.
• Cette paroi intermédiaire se prolonge, au-delà de sa jonction avec la paroi supérieure, par une portion qui se termine sensiblement au niveau de l'arête de celle-ci.
• La fente a une largeur comprise entre 0.3 et 1 mm et l'arête du sommet du triangle de la cage est disposée à environ 1 mm d'elle.
• La cage est solidaire d'un collier prenant place autour du tube.
• Le système comporte une pluralité de buses disposées sur le tube de manière à répartir l'arrosage dans tout l'espace à protéger.

This extinguishing system still has the following main features:

• The slot is substantially parallel to the axis of the tube and to the axis of the cage.
• The nozzle has several parallel slots.
• The cage is made of mesh and has a top wall with a triangular section whose edge faces the slot, parallel to it, and a curved bottom wall substantially concentric with the tube.
• The angle at the apex of the triangle is substantially between 110 and 130 °.
• The base of said triangle has substantially the same dimension as the diameter of the tube.
• The base of the lower part of the cage has substantially the same dimension as that of the triangle.
• The cage has an intermediate wall between its upper wall and its lower wall.
• This intermediate wall extends beyond its junction with the upper wall, by a portion which ends substantially at the edge thereof.
• The slot has a width between 0.3 and 1 mm and the edge of the top of the triangle of the cage is disposed about 1 mm from it.
• The cage is secured to a collar taking place around the tube.
• The system comprises a plurality of nozzles disposed on the tube so as to distribute the watering throughout the space to be protected.

• la figure 1 est une représentation schématique d'une installation selon l'invention ;
• les figures 2 et 3 sont des vues en coupe longitudinale et transversale d'une buse à mousse équipant cette installation ; et
• la figure 4 illustre la manière de fixer les cages des buses d'extinction au tube.

Other features of the present invention will emerge from the description which follows, with reference to the appended drawing, in which:

• the figure 1 is a schematic representation of an installation according to the invention;
• the Figures 2 and 3 are views in longitudinal and transverse section of a foam nozzle equipping this installation; and
• the figure 4 illustrates how to fix the cages of the extinguishing nozzles to the tube.

The figure 1 represents very schematically, seen from the ground, a portion of the vault of a road tunnel equipped with an installation using a foam extinguishing system according to the invention.

The installation proposed by way of non-limiting example is divided into sectors of twenty to thirty meters, each comprising a watering tube 10 disposed under the tunnel roof, parallel to the axis AA of the sector concerned, and equipped with foam extinguishing nozzles 12 arranged every three meters or so. These nozzles are directed towards the ground and, in the example shown, aligned along the axis AA.

The installation also comprises a mixer 14 whose inlet E1 is connected to a single pipe of pressurized water 16 running through the tunnel and whose inlet E2 is connected to an emulsifier tank 18 via a control valve 20. The output S of the mixer 14 is connected to the irrigation tube 10 via a control valve 22.

We will now refer to Figures 2 and 3 which show, more precisely, the irrigation tube 10 and the foam extinguishing nozzles 12 according to the invention.

The tube 10 is of circular section. Its diameter is typically between 25 and 150 mm and its length is that of the sector, that is to say from twenty to thirty meters in the example described.

The nozzles 12 each consist of a slot 24 formed in the wall of the tube 10 at the vertical axis AA and parallel thereto and a device 26, called foam expansion cage, disposed in front of the slot. Typically, the length thereof is between 60 and 100 mm and its width is about 0.2 to 1 mm depending on the water supply and foam flow required for extinction.

The expansion cage 26 is formed of an upper wall 28, a lower wall 30 and an intermediate wall 32, made by means of a mesh made of stainless steel or plastic whose mesh is between 1 and 3 mm.

The upper wall 28 has a triangular section whose ridge faces the slot 24 parallel to it and is disposed about 1 mm from it. The angle at the apex of the triangle is between 110 and 130 °, while its base has substantially the same dimension as the diameter of the tube 10.

The lower wall 30 is curved, with a center substantially coincident with that of the tube 10. Its base has the same dimension as that of the upper wall 28.

The flat intermediate wall 32 ensures the connection between the upper wall 28 and the lower wall 30. It will be noted that it extends beyond its junction with the upper wall 28 by a portion 34 which ends at the from the edge of it. The distance between the edge and the furthest point of the bottom wall 30 is typically between 30 and 50 mm.

The walls of the cage 26 are advantageously joined by welding or stapling.

As shown in figure 4 , the edge of the upper wall 28 is extended at both ends by a tongue 36 which is welded to a collar 38 which fits around the tube and hangs thereon by means of a loop 40 and a hook 42.

In operation, when a fire is detected, by any means whatsoever, the control valve 22 is opened manually or automatically. A mixture of water and emulsifier whose content, typically from 2 to 5%, was previously adjusted by the regulating valve 20, is sent into the irrigation tube 10.

The slot 24 creates a powerful jet directed on the edge of the upper wall 28. This jet enters the cage 26 and invades it while generating a suction stream which returns air intimately mixing with the particles of liquid.

The mixture then passes through the intermediate wall 32 and the bottom wall 30 with a still sufficient pressure to confine the emulsion and produce a dense foam and heavy enough to cover the floor of the tunnel without being driven by drafts.

It should be noted that the projected jet of water and foam concentrate is sufficiently deviated so that foam is also produced above the cage 26 and passes through the upper portion 34 of the intermediate wall 32, thus adding to the foam ejected from the cage.

In a very interesting and surprising way, experience shows that the cage 26 also has the effect of diverting the jet of foam by 90 °. It is likely that this deviation is due to Coriolis forces. Thus, the foam forms a screen whose plane is substantially perpendicular to the longitudinal axis of the tunnel and which flaps and absorbs the fumes of the fire.

dans laquelle K est un coefficient de forme expérimental, caractéristique de la buse, P est la pression du mélange dans le tube 10 et f est le coefficient de foisonnement défini comme le rapport entre le volume de mousse produite et le volume de liquide.The flow rate Q of the foam produced is given by the formula: $$Q=K\sqrt{P}*f$$

where K is an experimental shape coefficient, characteristic of the nozzle, P is the pressure of the mixture in the tube 10 and f is the expansion coefficient defined as the ratio between the volume of foam produced and the volume of liquid.

• un tunnel de 24 m de long et de 9 m de large ;
• une installation dotée de buses comportant une fente de 80 mm de long et 0,6 mm de large, qui présentent un coefficient K de 26,2 et un foisonnement f de 30 ; et
• un mélange d'eau et d'émulseur circulant à une pression de 3 bars.

We will take as an example:

• a tunnel 24 m long and 9 m wide;
• a plant with nozzles having a slot 80 mm long and 0.6 mm wide, having a K coefficient of 26.2 and an expansion of 30; and
• a mixture of water and emulsifier circulating at a pressure of 3 bar.

The objective of this installation is to produce a thickness of 15 cm of foam per minute and per square meter, evenly distributed on the pavement of the tunnel. This thickness is sufficient to extinguish most fires.

The tunnel floor having an area of 9 x 24 = 216 m ² , the desired foam flow rate is 216 x 0.15 = 32.4 m ³ / min.

A single nozzle, sized as described above, produces: $$\mathrm{26}\mathrm{,}\mathrm{2}\mathrm{\times }{\mathrm{3}}^{\mathrm{1}\mathrm{/}\mathrm{2}}\mathrm{\times }\mathrm{30}\mathrm{=}\mathrm{1}\mathrm{,}\mathrm{351}{\mathrm{m}}^{\mathrm{3}}\mathrm{/}\mathrm{min\; of\; foam}\mathrm{.}$$

Thus, the installation must have 32.4 / 1.351 = 24 nozzles.

The mixing rate flowing in the spray tube will be 26.2 * 3 ^1/2 * 24 = 1089 L / min. For a mixture comprising 5% of emulsifier, the water flow must therefore be 1034 L / min.

It should be noted that the calculation example given above does not take into account the pressure drops caused by the piping. For a finer calculation, it is possible to calculate the pressure differences between two adjacent nozzles caused by the pressure drops and thus to differentiate the flow of foam produced by each nozzle.

The present description has been made with reference to a tube 10 whose slots 24 are all aligned vertically of its axis AA. It goes without saying that, depending on the size of the tunnel, it may be advantageous, for a better distribution of the foam, to shift the staggered slots, for example, at 45 ° with respect to the vertical diameter of the tube. Of course, the cages are always centered on the slots.

It goes without saying that, for a wide tunnel, the installation may comprise two or three parallel tubes distributed under the vault.

Furthermore, to increase the foam flow produced, each nozzle may have a plurality of slots centered on the crown edge of the triangle of the cage, for example, three 0.2 mm slots separated by 2 mm.

Thus is proposed an inexpensive foam extinguishing system, easy to install, compact and particularly effective.

Claims (12)

1. A fire extinguishing system using foam, characterized in that it comprises:

   - a tube (10) designed to be arranged above a space to be protected and capable of being supplied by means of a pressurized water mixture and an emulsifier, and

   - at least one extinguisher nozzle (12) consisting of at least one slot (24) formed in the wall of said tube and an expansion cage (26) configured to receive the pressurized water mixture and the emulsifier delivered by said slot and produce foam which is poured onto said space.
2. The system according to claim 1, characterized in that said slot (24) is substantially parallel to the axis of the tube (10) and the axis of the cage (26).
3. The system according to one of claims 1 and 2, characterized in that said nozzle comprises a plurality of parallel slots (24).
4. The system according to one of claims 1 to 3, characterized in that said cage (26) is made in a grid and comprises:

   - an upper wall with a triangle-shaped section (28), the edge of which faces said slot (24), parallel thereto, and

   - a curved lower wall (30) substantially concentric to the tube (10).
5. The system according to claim 4, characterized in that the angle at the apex of said triangle is substantially between 110 and 130°.
6. The system according to one of claims 4 and 5, characterized in that the base of said triangle has essentially the same dimension as the diameter of the tube (10).
7. The system according to claim 6, characterized in that the base of said lower portion (30) has essentially the same dimension as that of said triangle.
8. The system according to claim 7, characterized in that said cage (26) comprises an intermediate wall (32) between the upper wall (28) and the lower wall (30).
9. The system according to claim 8, characterized in that said intermediate wall (32) extends, beyond its intersection with the upper wall (28), by a portion (34) which ends essentially at the edge.
10. The system according to one of claims 1 to 9, characterized in that said slot (24) has a width between 0.2 and 1 mm and in that said edge is arranged approximately 1 mm from it.
11. The system according to one of claims 1 to 10, characterized in that said cage (26) is integral with a fastening collar (38) arranged around the tube (10).
12. The system according to one of claims 1 to 11, characterized in that it comprises a plurality of nozzles (12) arranged on said tube (10) so as to distribute the watering in the space to be protected.

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