Safety system for road tunnels in case of fire.

The present patent application for industrial invention relates to a safety system for road tunnels in case of fire.

As it is known, the main hazard factor in the use of road tunnels is related to the fact that fire can start inside a tunnel, possibly for a breakdown or an accident affecting one or more vehicles in transit.

In such a case the personal safety of individuals can be endangered not only by flames at very high temperature, but also by the emission of burning air currents, toxic fumes and by the progressive reduction of oxygen due to the action of fire.

In view of the above - and especially in case of very long tunnels - individuals, including those situated at a long distance from the point where the fire has started, can easily perish because of the aforementioned collateral effects of fire.

Moreover, big fires normally cause severe damages to the bearing structure of the tunnel due to the so-called "oven effect" generated inside it.

In fact, the high temperatures generated inside the tunnel can easily weaken the bearing structure of the tunnel, causing severe structural damages that may cause the collapse of lateral walls and vault.

The studies that have been carried out so far about such an unfortunate phenomenon have led to the development of solutions that cannot be considered as fully satisfactory.

In some cases fire-resistant protective coatings have been mounted inside tunnels; in some cases, one or more parallel tunnels for service purposes have been constructed near or under a road tunnel, divided from it by means of a large number of emergency fire doors.

In such a case, individuals who are escaping from fire should take shelter, through the nearest door, inside the so-called safety tunnels and through the safety tunnels they should reach the nearest exist, while being protected against fire, smoke, high temperature and lack of oxygen.

A careful evaluation of the traditional solutions shows that, whereas they seem to be suitable to contain the front of the fire and protect the bearing structures of the road tunnel, the aforementioned fire-resistant coatings do not ensure effective prevention against the inevitable propagation of very hot toxic currents and against the lack of oxygen.

From such a view point the creation of said parallel evacuation tunnels seems to be a more effective solution. However, such a solution is extremely expensive, is not viable for existing tunnels and does not guarantee protection of the bearing structures of the main tunnel.

A careful examination of prior art and relevant drawbacks has led to devise the new system of the invention, which seems to be able to satisfy the different requirements related to a potentially catastrophic phenomenon such as a fire in a long road tunnel.

The installation of the invention is characterized by reasonable installation and maintenance costs. Moreover, it can be installed both in new and existing tunnels and finally it provides effective protection of both individuals and bearing structures of the tunnel affected by fire.

It must be noted that the system of the invention has been developed starting from the fact that it is normally impossible to attack big fires inside road tunnels with extinguishing liquid or water.

In such a case, the action of the fire brigade is basically impossible due to the high temperatures that are generated in the fire area, the total lack of visibility and the long distance between the mouth of the tunnel and the area affected by fire.

Moreover, it would be impossible to carry out an effective action with extinguishing substances by means of automatic fire-fighting systems, not only because of their high installation and management costs, but also because, due to the low capacity of said extinguishing substances, these systems would immediately fail (and stop operation) because of flames and of the very high temperature, approximately 900 °C, generated by them. In view of the above consideration, the present invention is based on the selective activation of extractor units in the specific section of the tunnel affected by fire in order to extract flames and fumes and convey them outside the tunnel.

To that end the flames and fumes are taken inside a specific evacuation conduit where they are exposed to the action of a series of spraying nozzles that produce jets of water.

Such jets are capable of reducing the temperature of fumes down to

100°C, that is to say the water evaporation temperature.

In such a way the evacuation conduit, and more generally the entire structure of the tunnel along which said evacuation conduit is developed, will be affected by a "reasonable" temperature that will not generate severe structural damages.

At the same time the system of the invention provides for the selective activation of additional spraying nozzles that generate jets of water towards the walls and vault of the tunnel in order to maintain their temperature at the acceptable threshold value of about 100°C.

Moreover, it must be noted that the activation of said extraction of fumes and flames (and consequent depression) spontaneously attracts external air through the mouth of the tunnel until the point where fire has started.

It is worthless saying that such a current of fresh air loaded with oxygen guarantees high visibility in the internal space and allows individuals not only to continue on breathing normally, but also to direct themselves towards the opening of the tunnel for a faster and safer evacuation, by simply moving in opposite direction to the air current flow coming from outside.

For purposes of clarity, the description of the invention continues with reference to the enclosed drawings, which are intended for purposes of illustration only and not in a limiting sense, wherein:

- Figure 1 is a general diagrammatic view of a tunnel provided with the system of the invention, sectioned with a longitudinal plane;

- Figure 2 is a partial enlarged view of Fig. 1 ; - Figure 3 is a sectional view of the tunnel with a transversal plane;

- Figure 4 is a perspective view of a section of the tunnel.

Referring to the enclosed figure, the system of the invention comprises a series of segment-shaped barriers (1 ), preferably made of metal, and adapted to be mounted in vertical position with regular spacing on the top of the vault of a tunnel (G).

Obviously, the lower horizontal border of said barriers (1 ) must be disposed at a height higher than the maximum height of lorries.

Said barriers (1 ) are designed to originate a sequence of identical compartments (C) for the entire length of the tunnel (G), each of them bordered by a consecutive pair of barriers.

It must be noted that said barriers (1 ) are centrally provided with a hole with large section crossed by a corresponding conduit (2), preferably made of metal, which extends for the entire length of the tunnel (G).

Said conduit (2) is provided with a regularly spaced series of windows with openable doors (3); it being provided that each window is basically disposed at the centre of one of said compartments (C) defined by two consecutive specimens of barrier (1 ).

A series of nozzles (4) is mounted with regular spacing inside the conduit (2) for forced distribution of water delivered by a pipe (5).

Said barriers (1 ) are also provided with holes with lower section, adapted to be crossed by additional pipes (6) supplied with water, preferably pressurized water, and provided with corresponding series of spray nozzles (7) directed towards the walls and the vault of the tunnel (G).

Said pipes (6) are connected, by means of corresponding branches (8) that extend towards the road bed (S) with a plurality of fire hoses (9), each of them being a fire-fighting station that also comprises a tank of extinguishing liquid (9a).

Sensors of known type (10) are installed in each of said compartments (C) to detect fire and fumes.

Outside each end of the tunnel (G) the main conduit (2) is fitted to an extractor unit (1 1 ), near which a water tank (12) is provided and associated to a pump assembly (13) to supply pressurized water from the tank (12) to both the first pipe (5) contained inside said main conduit (2) and the specimens of second pipe (6) provided outside the latter.

Finally, it must be noted that the conduit (2) is centrally provided with a partition (20) to create two semi-conduits on the right and left-hand side, each of them being served by a corresponding extractor unit (1 1 ) and a pump assembly (13).

After describing the structure of the system of the invention, it is necessary to illustrate the automatic operation mode in case of a fire.

Considering that the tunnel (G) is divided in consecutive compartments

(C) by said barriers (1 ), it appears evident that the fire refers to one of said compartments (C).

Based on the above consideration, it must be noted that the system of the invention reacts to a similar event within the specific compartment (C) that is directly affected by the fire.

In particular, the activation of the operational procedure of the system is originated by the sensors (10) when they detect flames and fumes in the corresponding compartment (C).

Said sensors (10) send the information to the management and control unit of the system of the invention that immediately enables the opening of the door (3) of the conduit (2) of the compartment (C) directly affected by the fire by means of a suitable actuator.

On the other side, the doors (3) of the other compartments (C) of the tunnel (G) remain closed, with the aid of the depression determined inside the main conduit (2) further to the opening of the single door.

Simultaneously, the electronic management and control unit activates one of the two extractor units (1 1 ) provided outside the tunnel (G): more precisely, the extractor unit (1 1 ) situated at a shorter distance from the compartment (C) affected by the fire.

In such a way, in view of the combined effect of the opening of said door (3) and the actuation of the extractor unit (1 1 ) connected to it, the conduit (2) acts as a sort of forced chimney (or extractor hood) with respect to flames and fumes.

Moreover, it must be noted that the activation of the extractor unit (1 1 ) corresponds to the activation of the pump assembly (13) that takes water from the tank (12) and forces it into the first pipe (5) provided inside the main conduit (2) in such a way to favour the distribution of highly-pressurized jets of water in all of the spray nozzles (4).

Evidently, said jets of forced water can reduce fumes and temperature of combustion gases (down to the maximum threshold value of 100° C, which corresponds to water evaporation temperature) transferred into the main conduit (2) through the open door (3).

First of all, the considerable temperature reduction (with respect to the approximate temperature of fire of 900° C) is designed to protect the structure of the main conduit (2) against deformation induced by excessive heat and manage the flow of fumes and gases during the final evacuation of the tunnel (G).

With reference to this operational step, it must be noted that each of said extractor unit (1 1 ) is provided with an extraction chamber (1 1 a) with water bath towards which the fumes and gases extracted from the tunnel (G) are conveyed by the conduit (2) through the passage section liberated by opening the door (3).

It must be noted that during this step the extraction chamber (1 1 a) also acts as separation cyclone for the mixture of steam, water and fumes coming from the conduit (2).

The water bath contained inside the extraction chamber (1 1 a) holds the solid hazardous particles contained in said mixture and makes them precipitate by gravity on the bottom of said water bath, whereas the gaseous component, now depurated, can be reintroduced without risks into the atmosphere through suitable evacuation chimneys.

Moreover, it must be noted that, in addition to enable the supply of the pipe (5) contained in the main conduit (2), the pump assembly (13) simultaneously activates the supply of the pipes (6) outside the main conduit (2).

In such a way the spray nozzles (7) fitted into the second pipes (6) are induced to distribute highly-pressurized jets of water towards the vault and the walls of the tunnel (G), which are certainly useful to reduce the temperature of both vault and walls to prevent structural damages or collapse.

All of the above conditions that originate from the activation of the system of the invention guarantee that the areas of the tunnel (G) near the fire can be maintained at a relatively low, in any case bearable temperature, also because the tunnel (G) receives a significant flow of cool and clean air from outside, which is extracted inside the nearest opening because of the depression created by the system.

In fact, such a flow of fresh air contributes to reduce the temperature of the combustion gases and prevents propagation of smoke and toxic fumes along the tunnel (G), thus allowing for safe evacuation of individuals in the tunnel (G) and easy action of fire brigade.

Once they have reached the active centre of the fire, the fire brigade can advantageously use said fire hoses (9) and adjacent tanks of extinguishing liquid (9a) provided in the tunnel (G).

Certainly the presence of said fire-fighting tools inside the tunnel (G) eliminates the difficulties and risks for fire fighters involved in transporting the appropriate equipment from outside, thus allowing for their effective and prompt action, including by means of simple motorcycles.

Referring to Fig. 1 , it must be also considered that the conduit (2) is preferably provided, at approximately half of its length, with a partition (20) that forms two independent semi-conduits on the right and left-hand side, each of them being served by a corresponding extractor unit (1 1 ) and pump assembly (13).

Such a separation of the conduit (2) guarantees that in each of said semi-conduits (left and right) the extraction effect of flames and fumes is additionally favored, and the possibilities of hazardous losses of load along the conduit (2) are reduced.

On the other hand, in order to obtain the same technical-functional result, two mobile partitions (not shown in the enclosed figures) can be provided alternatively in correspondence with each end of the conduit (2).

In such a case, should fire originate inside the tunnel (G), the electronic unit designed to operate the system of the invention will determine which mobile partition will remain open and which mobile partition will be closed to obstruct the passage section of the conduit (2).

Obviously, the mobile partition to be maintained in open position will be the one near the end of the conduit (2) nearest to the fire point; this is done to guarantee, also in this case, the maximum efficacy of the flow originated by the activation of the extractor unit (1 1 ) adjacent to it.

In view of the above considerations, it appears evident that the possible absence of the partitions of the conduit (2) can be compensated - for the best efficacy of said extraction effect of flames and fumes - with the simultaneous activation of both extractor units (1 1 ) mounted at the two ends of the tunnel (G).

It is worthless saying that all the aforementioned components of the system and the necessary cables that are not expressly illustrated herein shall be made in such a way to ensure maximum protection and resistance in such a critical environment such as a closed space attacked by fire.

According to a preferred embodiment of the present inventive idea, the entire operation cycle of the system of the invention is automatically controlled by an electronic management and control unit that is suitably interfaced with sensors (10), with actuators that control the opening of the doors (3), with extractor units (1 1 ) and with pump assemblies (13).

However, the system of the invention can also manually operated, it being provided in such a case that the sensors (10) are only designed to inform the specific compartment (C) attacked by the fire; further to such information, the operators will take action and in rapid sequence will open the corresponding door (3) and activate the corresponding extractor unit (1 1 ) and pump assembly (13).

Without leaving the inventive scope of the present invention, it must be noted that the conduit (2) can have any type of section and can be installed, rather than on top of the vault of the tunnel (G), in correspondence with a lateral wall of the vault, provided that the selective extraction windows are directed towards the top of the tunnel.