GB1597252A - System of protection against fire for an unlimited period of time of a building the framework of which is in incombustible materials - Google Patents

Description

(54) A SYSTEM OF PROTECTION AGAINST FIRE FOR AN UNLIMITED PERIOD OF TIME OF A BUILDING THE FRAMEWORK OF WHICH IS IN INCOMBUSTIBLE MATERIALS (71) We, RAYMOND BASSEM and PETRACHE TELEMAN, respectively of 50 Avenue des Héros, 1160 Brussels and 383 Boulevard De Smet de Nayer, 1090 Brussels, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a system for the protection against fire for an unlimited period of time of a structure whose framework is of incombustible materials, by continuous or discontinuous internal irrigation of the frame with a non-inflammable liquid of high thermal capacity, such as water.

It is known that a fixed installation whose framework comprises metallic elements such as posts, beams, and cross-members of steel is vulnerable to fire. These elements are deformed between 150C and 450"C, and the framework breaks before the temperature reaches 600 "C.

A framework of concrete is generally more expensive than a metal framework, but its resistance to heat is better; it is usually considered that a concrete building exposed to fire can last for some two hours before it collapses.

It is moreover well known that a fixed installation of an incombustible material, when exposed to heat, will perfectly withstand the heat provided that it is lined with a piping network through which passes a cooling fluid such as water, for example; this is the case with furnaces in particular.

Based on this principle, Paul Multin described in French Patent No. 1.225,200 of the 17th April 1959 a system for the protection against fire of fixed installations of incombustible materials, such as the frames of buildings, these frames being provided in their internal space with a metal container filled with a non-inflammable liquid such as water, so that protection against external seats of fire acts from inside by increasing the thermal capacity of the installations. In view of the fact that the internal liquid can be renewed and the calories absorbed can be carried off outside the element protected, thermal capacity is increased indefinitely.

In the case of posts, beams, and crossmembers of concrete which are to be protected against bursting, buckling, and consequently collapse through the action of the heat produced by a seat of fire, these constructional elements are lined wth a piping system filled with water. In the case of a metal framework, the piping system is formed by the framework elements themselves, provided that they have a closed section. Moreover, if automatic nozzles controlled by the fire and connected to the piping system are distributed at judiciously selected points, it will be possible in an advantageous manner to cool the parts affected by the disaster and fight the seat of the fire in its immediate proximity.

The system described is certainly excellent in principle, but it nevertheless has shortcomings which impose limitations and obligations, in the form of expensive checks in particular.

Thus, provision is made for the system to be filled with water and to carry at the top a terraced water tank; the strength of the framework must therefore be designed so as to support these weights as permanent additional loads.

Furthermore, it is known that stagnating water is a medium favourable to the development of microorganisms, algae, etc., which entail the risk of clogging the pipes and nozzles; it is therefore necessary for appropriate inhibiting agents to be mixed with the irrigation water.

Moreover, in order to protect parts of the framework which are exposed to frost an anti-freeze additives is generally provided.

As an alternative, the rupture of the piping system in the event of the freezing of the liquid can be prevented by submerging therein a compressible elastic element (French Patent No. 1,540,322 of the 2nd March 1967 in the name of Etablissements Durafour).

It is also important to prevent the initiation of corrosion of the system at the constant liquid level in the tank and in the liquid level zone in the posts, because if this is not stopped in time there is a risk of reducing the thickness of the system and giving rise to the complete loss of the liquid within a more or less short space of time. It is therefore necessary to avoid the formation of voltaic couples at welds and for this purpose any apparatus, such as a valve, which is connected to the steel piping system must be of a more noble metal than steel and must be electrically insulated from the system.

The tank and the level zone of the posts must be coated internally with a high zinc content paint on the suitably prepared surfaces. The posts must be so designed that at the level of the terrace it is possible to introduce test pieces for checking corrosion, and at a point determined by the internal arrangement of the rooms removable hollow elements of the same metal as the posts, and incorporating a weld made in the same manner as the welding of the structure, must be provided to serve as check samples in respect of the corrosion of the framework.

Experience has moreover shown that the system described is not completely reliable, because it may occur that faulty tightness of the framework, due to a fortuitous cause, will give rise to the imperceptible but inevitable loss of the liquid provided as protection. Furthermore, the system lacks flexibility in the sense that any subsequent modification or extension of the fixed installation may make it necessary for the contractor to empty the framework - and then refill it, with all the inconvenience that that entails, and this will be so even for the slightest additional welding.

Starting from the same principle of irrigation of a piping network described above in the case of furnaces, for example, a reliable and convenient system has now been conceived for the protection against fire of structures having frameworks of incombustible materials, such as steel and concrete, by internal irrigation, with the aid of a non-inflammable liquid such as water, this system differing from that described in French Patent No. 1,225,200 mainly in that the hollow framework to be irrigated is permanently empty except in the case of fire.

Consequently, it is no longer necessary to provide a tank filled with liquid at the top of the building; the framework will therefore no longer be subjected to permanent additional loads due to the weight of the irrigation liquid.

Since the system proposed provides empty and dry hollow elements, all problems of corrosion, freezing, and biological contamination will be eliminated and there will be free choice in respect of the liquid which is most suitable. In general, this liquid will be water without any additive, such as town water, or else rainwater stored in a tank situated at the base of the structure. This liquid could optionally be an aqueous solution or suspension of a suitable fire extinguishing product or any non-inflammable liquid having high thermal capacity and suitable for extinguishing flames.

With a view to producing according to the invention an irrigation system adapted to preserve in an unlimited manner the framework of a structure exposed to fire, hollow elements of steel or concrete are connected together so that the framework may form either a single irrigation system or an arrangement of separate systems capable of being supplied with liquid from a common source.

If it is required to protect a structure by means of a single system, the framework must be composed of tubular metal elements and in communication with one another, since the elements will all be filled with liquid in the event of a fire.

If on the other hand it is desired to provide individual protection by their own irrigation system for each of the storeys or each group of contiguous storeys of a multi-storey building, it will be ensured that the vertical elements of the framework are protected against the risk of fire while they are empty; this is the case particularly for the columns of the building. which also serve to supply the storeys separately. These columns must necessarily be in the form of steel tubes connected by metal stirrups, enclosed in concrete.

It is known that any element of a fixed installation which is internally provided with liquid can withstand fire; this resistance is obviously durable and even unlimited if the irrigation liquid is constantly renewed, that is to say if the liquid circulates.

According to the invention two types of systems providing protection by circulation of liquid in the event of fire will in general be considered, depending on whether the source of liquid is a system of distribution of water under pressure or else a reserve of water which is to be placed under pressure; this reserve is advantageously constituted by rainwater.

If so desired, the system may comprise various nozzles, particularly sprinkler heads adapted to spray the rooms and even the seats of fires selectively with water, so that the water can provide protection for an unlimited period of time not only to the framework but also to structures which are not irrigated and to the contents of the rooms. According to the first system of protection, the irrigation system water coming from the pressurised supply flown directly to the drains, in the second system the water comes from a tank and generally circulates in a closed circuit. A subsidiary supply coming from a pressurised water supply system is obviously also provided to make good losses of water due, among other causes, to discharge from the sprinklers and thus to maintain a constant level in the tank.

This subsidiary supply is all the more indispensable if the irrigation water flows to the drains. It will readily be realised that if the first type of fire protection system is provided, any piping system attacked will first be filled with water, but there will be no circulation of water as long as the fire remains small; if on the other hand the fire extends, the temperature of the room may rise to a level at which the sprinkler heads must open automatically and spray the room from above. The circulation initiated in this manner will continue until stopped by hand.

Whatever the type of system selected, means must obviously be provided to evacuate the air contained in the system; according to the invention the system is provided with air bells which are mounted on the piping system and with the aid of which the piping system attached by the fire is filled with liquid without forming air pockets and without loss of liquid. The air bells will advantageously be mounted on the opposite top ends of the system to that where the liquid enters. As used herein the term "air bell" means an air vent which may be bell-shaped but need not necessarily be that precise shape provided it fulfils the same function.

Another means of evacuating the air consists in providing the piping system with bent overflow pipes whose open end is directed towards an external part for example the roof of the building. As soon as the liquid is forced into the system it drives out the air, fills the system. and flows freely from the overflow pipe on the roof so as to water and protect the latter.

In view of the fact that the system according to the invention provides for the piping systems to be empty and dry except in the event of a fire, it must be possible to empty and dry them once they have been used for protection purposes. To this end the piping systems are provided at their base with a drain tee which can be opened, and through the action of the air bells or overflow pipes provided at the top of the piping systems the liquid can flow off; a hot air blower can then be connected to the open drain tees in order to dry the wet piping.

According to the invention the system is provided with automatic control means connected to a fire detection device, for the purpose of introducing the protective liquid into the piping systems, and also with manual means guarding against failure of the automatic control system.

If the source of liquid is a pressurised distribution supply, the means of flooding and a system is a motorised valve; the safety means is a manual cock branched off from the said valve.

If the source of liquid is a reserve tank, the means of forcing the liquid into the piping system is a booster pump submerged in the liquid in the tank; the safety means is a manual switch connected in parallel to the automatic control of the pump.

The detection device connected in parallel to the mains and to an emergency unit comprises detectors sensitive to heat, smoke, and gas and/or to radiation, such as infrared or ultraviolet radiation, and socalled thermovelocimetric detectors (i.e.

detectors which emit a signal when a temperature increase is higher than a selected value within a given time interval) fixed on the piping systems intended to receive the liquid. The electric output signals of the detectors are received by an indicator panel provided with conventional warning devices and time delay means to retard the automatic operation of the irrigation in the event of a false alarm.

In view of the fact that the hollow framework elements according to the invention are normally permanently empty and dry, the structure of any system can be modified at will without jeopardizing the required protection. It will thus be possible to fix, particularly by simple welding, all accessories necessary for the completion of a building, namely suspension systems for false ceilings, ducting, hydraulic piping and electric wiring, and also to incorporate in the system double jackets to be filled with liquid and adapted to cool either tanks for inflammable materials, such as fuels, for example, or safes for the protection of valuables against fire and against the danger of breaking-open by cutting with a blowlamp, while in addition it will be possible to add to the systems at any time a calculated number of so-called sprinkler head nozzles in order to provide additional protection and make it possible to extinguish the seat of a fire.

According to the present invention we provide a system of protection against fire for an unlimited period of time for a structure having a framework of incombustible materials by internal irrigation of the said framework with the circulation of a non-inflammable liquid of high thermal capacity, the said framework comprising either tubular metal elements or concrete elements in which metal pipes are embedded, the said elements being connected by their hollow portions to one another and optionally to other hollow structures in order to form either a single irrigation system or an arrangement of separate irrigation systems, characterised in that each irrigation system is connected to a source of liquid, particularly a public supply watermains system or a reserve tank situated at the bottom of the structure, by way of a pipe containing respectively either a closed motorised valve or an electric booster pump at rest, and each piping system is provided with fire detectors connected to a general electric panel connected in parallel to the electrical mains and to an autonomous emergency generator set and is equipped with fire alarms and automatic time lag relay devices adapted to control either the opening of the valve or the starting-up of the pump after a predetermined period of time, so that the piping system remains empty and dry in normal times and so remains on appropriate external intervention within the predetermined period of time in the event of a false alarm but can be completely filled with the said liquid in the event of a fire, the complete evacuation of the air contained in the system being effected by at least one air bell (as herein defined) or one bent overflow pipe mounted at the top of the system.

As a precaution against failure of the automatic devices the system may contain either a valve branched off from the motorised valve and adapted to be opened manually, or a manual switch connected in parallel to the automatic control of the pump.

According to one embodiment of the invention the system contains so-called sprinkler head nozzles mounted judiciously on the irrigation systems and capable of pouring jets of liquid either onto the parts of the structure which are not internally irrigated in order to cool them when the structures are exposed to fire, or onto the seats of the fire.

In order to provide protection against fire for the upper structures of the building, such as the roofing, the system contains bent overflow pipes fixed on the piping systems with their open end directed towards the said structures in order to spray them with liquid, while the liquid thus poured out and collected by gutters and down pipes can be conducted either to the drain or to the liquid reservoir.

According to another embodiment of the invention a system may be provided with double jackets which will be internally irrigated with a circulation of liquid in order to provide protection against fire and optionally also against burglary involving the use of heat, particularly against cuttingopen by means of a blowlamp, structures of the building such as tanks or strongrooms and safes which respectively contain inflammable materials and explosive materials or valuables. The term "double jackets" means having hollow walls capable of being internally flooded with water under the specified conditions.

According to a further embodiment of the invention the pipes connecting the piping systems to the source of irrigation liquid are each equipped with at least one manual valve and a drain tee which can be used for emptying the liquid contents from an irrigated piping system after a fire and then for drying the wet system with hot air, while an isolatable portion of each pipe also makes it possible to check the functioning of the automatic irrigation devices without wetting the entire piping systems.

The accompanying drawings illustrate by way of example two particular forms of construction of the fire protection system according to the invention.

Figures 1 and 2 show hollow metal framework elements; Figures 3 and 4 show hollow concrete framework elements, and Figures 5 to 7 are partial views of hollow frameworks according to the invention.

If it is sufficient to provide a structure with temporary protection against fire in order to enable firemen to attack the seats of the fire, the framework may be composed for example of reinforced concrete columns supporting an arrangement of hollow beams and cross-members of steel which are internally irrigated with liquid. If on the other hand the framework is intended to withstand fire indefinitely, the pillars must also be internally irrigated.

The pillar 1 (Figure 1) is a closed steel section 2 which is square, rectangular, or circular in shape and whose openings are closed by welded end pieces 3 and 4. The pillar may be composed of a single section or of a plurality of elements 5, 6 whose previously drilled adjacent end pieces 7, 8 are joined by bolts 9. A flange 10 for subsequent connection to the liquid supply is welded to the base of the column.

In order to form the horizontal portion of the framework use is made of similar horizontal elements 11 (Figure 2) having drilled bases and connected together to form a duct, the first horizontal element being fixed to the pillar by its end piece 12 by welding, riveting, or bolting in such a manner that a hole 13 in the pillar communicates with a hole 14 in the end piece. A similar procedure is adopted for the cross-members connecting two beams together. If the hollow horizontal structure contains piping, these elements are fixed by flanges.

The hollow steel pillars of the type described above obviously afford the least expensive protection, but they do not make it possible to construct easily an irrigation system composed of separate systems for a multistorey building.

Even if the supplying of these systems through closed metal sections grouped to form pillars were contemplated, only a part of the pillars intended for the protection of a zone of the framework threatened by the fire would be irrigated, but there would be a danger that the remainder would undergo deformation and even destruction because it would be exposed locally to the fire.

If it is desired to provide protection against fire for an indefinite time for common supply columns for separate systems, use must be made of metal columns enclosed in concrete and composed of elements 15 (Figure 3), 16 (Figure 4). For the purpose of producing these, connection flanges 19 are welded on steel tubes of the same length and of square section 17 (Figure 3) or round section 18 (Figure 4); the pipes are grouped together and plates 20 are welded to their ends, whereupon the pillars are formed by pouring concrete 21. In both cases the pipes are surrounded by metal stirrups 22.

The pipes therefore constitute the reinforcement for the concrete and will be advantageous to use identical elements for an arrangement comprising a plurality separate piping systems. In the case of a fourstorey building, for example, which has to be independently protected against fire, a pillar 15 will be formed (Figure 3) of elements bolted together by their end pieces 20 after the precaution has been taken of burning holes 23 by means of a torch in the end pieces in order to ensure the continuity of the supply columns, the connection flanges 19 being suitably oriented for the purpose of connection of the rising columns to the various horizontal framework units.

In order to simplify the drawings, in Figures 5 and 6, relating to buildings to be protected against fire for an indefinite time, only one storey is shown in each case, but it is quite obvious that the building in question may comprise a large number of storeys to be protected simultaneously, and consequently the pillars supplying liquid to the different storeys will be of the type illustrated in Figures 3 and 4; on the other hand, when it is required to protect such a building only with the aid of a single liquid piping system, or if there is only a single storey, the pillars will be of the type shown in Figure 1.

In Figures 5 and 6 the pillars are given in the reference numeral 24 and the horizontal arrangement of beams and cross-members is given the reference 25.

The two embodiments of the invention differ essentially only in respect of the manner in which they are supplied with irrigation liquid, that is to say respectively from a rainwater tank 26 (Figure 5) and from a town water supply mains 27 (Figure 6), and in respect of the fact that the roof 28 (Figure 5) of the construction is considered to be valuable.

The top part of the piping system is therefore surmounted by bent overflow pipes 29 (Figure 5), whereas the corresponding portion of the other system is provided with air bells 30 (Figure 6); one of the nozzles or sprinkler heads 31 with which any irrigation system may be equipped is also shown in this drawing.

Each system is equipped with a number of fire detectors 32 (Figures 5 and 6) connected electrically to the corresponding station of an indicator light panel 33, the detectors either opening or closing an electric contact with the aid of a current supply 34 coming either from the mains or from an autonomous emergency generator, in the event of fire.

An acoustic alarm 35 and a telephone line 36, which is advantageously connected to a fire station, may also be connected to this panel.

For each station the panel 33 also contains a time lag relay which is activated in the event of an alarm. If it is found that the signal given by the detectors is a false alarm, the alarm is terminated and the relay thus deactivated. If the alarm is genuine, the relay supplies a voltage 37 within a predetermined period of time.

In the case of the embodiment shown in Figure 5 the means of supplying the liquid to a system is a booster pump 38 submerged in the liquid 39 and intended to drive the liquid into a pipe 40 provided with a non-return valve by way of a permanently open valve 41; the pipe is connected to a pipe 42 connected to the supply pillars 24.

In the event of a fire the voltage 37 beings the pump 38 into operation; the liquid rises into the pillars 24, completely fills the elements of the unit 25 and overflows onto the roof through the pipes 29. The liquid 39 discharged flows off by way of gutters 43, is received by troughs 44, and returns to the tank by way of down pipes 45, which may be of plastics material and which are protected against the fire by the liquid passing through them.

An additional supply system connected to the town water supply may optionally be provided in order to maintain the level of water in the tank.

A drain tee 46, which is normally closed and which is fixed on the pipe 40, is opened after a fire in order to empty the system into the tank, whereupon hot air is blown into the tee in order to dry the system.

In order to guard against the failure of the time lag relay, a manual switch 47 is provided. which is for example of the movable tee type and which is fed by the mains or the emergency unit and connected in parallel to the output 37 of the relay.

In order to check the installation without filling the piping systems, the output 37 is activated by means of the switch 47 in order to operate the pump 38, after the valve 41 has been closed and the drain tee 46 opened.

In the case of the embodiment shown in Figure 6 the supply source 27, the town water mains, is connected to the supply pillars 24 by a pipe 48 provided with a motorised valve 49 which is normally closed.

Downstream of the motorised valve the pipe is also provided with a drain cock 50, a manual valve 51 which ispermanently open, and a drain tee 52, the elemnts 50 and 52 being closed. A normally closed manual valve 53 is branched off from the pipe 48.

When a time lag relay corresponding to a system exposed to fire is activated the voltage 37 should open the valve 49. In the event of failure, the valve 53 is opened manually and the system filled with liquid.

Circulation will continue until the valve 53 and possibly the valve 51 are closed.

In order to empty the system the drain cock 50 is opened after the valve 51 has been opened, whereupon the drain tee 52 is opened and hot air is blown into the system in order to dry it.

In order to check the operation of the motorised valve 49 without filling the system the elements 51 and 53 are closed and the drain cock 50 opened; the motorised valve 49 is then activated so that the water coming from the mains 27 flows through the drain cock.

An embodiment of the invention which is intended to illustrate the principle of a system providing protection by means of separate irrigation piping systems is given in Figure 7, which shows diagrammatically in plan a rectangular framework WXYZ composed of metallic elements of the type shown in Figure 1, which are mounted on posts.

The single source of supply is a town water distribution mains 27 connected to the framework as described in connection with Figure 6, except that the pipes 48, given the general reference R, are taken direct to each separate piping system.

The framework is a grid of sections or sections laid end to end and disposed along the length and width of the framework, the lines designating the sections, each interruption of a line symbolising the closing of a section by a welded plate as described in Figure 1, and each square representing a post of concrete or steel.

The framework is thus formed of 17 separate systems which are supplied separately.

The system A is U-shaped, its bottom branch stopping at 54; the branch WZ is in communication with the two side branches at 55 and 56 and is closed at 57. A pipe 58 coming from the supply R is connected to the middle branch WZ at 59, so that the water coming from the supply in the event of a fire detected by the detectors 32 (Figure 6) fills the system A, following the paths marked by the arrows. The same applies to the systems B and C.

The system D comprises a branch 59'-60, two opposite branches 60-61 and 60-62 to which are attached 11 parallel closed sections. The system is fed through a pipe 63 connected at 59', so that the sections 64 to 74 are filled with liquid as far as their ends.

In order to evacuate the air, all these ends are provided with air bells 30 (Figure 6). All the systems from A to P and the so-called technical system T, in which the controls are grouped together, are equipped in the same manner.

It is advantageous for the systems to be provided with sprinkler heads 31 (Figure 6).

As long as the heat of the framework elements does not reach the critical temperature the systems contain irrigation water, and there is therefore no circulation.

Beyond that temperature the sprinkler heads open and the circulation of water commences.

It is obvious that sprinkler heads are not provided in rooms reserved for delicate and expensive equipment and that other means of extinguishing the seats of fire must be provided.

The invention is of course not limited to the embodiments which have been described above and illustrated as examples, and modifications may be made to it without departing from its scope.

WHAT WE CLAIM IS: 1. A system of protection against fire for an unlimited period of time of a structure whose framework is of incombustible materials, by internal irrigation of the framework with the circulation of a non-inflammable liquid of high thermal capacity, the said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. tank by way of down pipes 45, which may be of plastics material and which are protected against the fire by the liquid passing through them. An additional supply system connected to the town water supply may optionally be provided in order to maintain the level of water in the tank. A drain tee 46, which is normally closed and which is fixed on the pipe 40, is opened after a fire in order to empty the system into the tank, whereupon hot air is blown into the tee in order to dry the system. In order to guard against the failure of the time lag relay, a manual switch 47 is provided. which is for example of the movable tee type and which is fed by the mains or the emergency unit and connected in parallel to the output 37 of the relay. In order to check the installation without filling the piping systems, the output 37 is activated by means of the switch 47 in order to operate the pump 38, after the valve 41 has been closed and the drain tee 46 opened. In the case of the embodiment shown in Figure 6 the supply source 27, the town water mains, is connected to the supply pillars 24 by a pipe 48 provided with a motorised valve 49 which is normally closed. Downstream of the motorised valve the pipe is also provided with a drain cock 50, a manual valve 51 which ispermanently open, and a drain tee 52, the elemnts 50 and 52 being closed. A normally closed manual valve 53 is branched off from the pipe 48. When a time lag relay corresponding to a system exposed to fire is activated the voltage 37 should open the valve 49. In the event of failure, the valve 53 is opened manually and the system filled with liquid. Circulation will continue until the valve 53 and possibly the valve 51 are closed. In order to empty the system the drain cock 50 is opened after the valve 51 has been opened, whereupon the drain tee 52 is opened and hot air is blown into the system in order to dry it. In order to check the operation of the motorised valve 49 without filling the system the elements 51 and 53 are closed and the drain cock 50 opened; the motorised valve 49 is then activated so that the water coming from the mains 27 flows through the drain cock. An embodiment of the invention which is intended to illustrate the principle of a system providing protection by means of separate irrigation piping systems is given in Figure 7, which shows diagrammatically in plan a rectangular framework WXYZ composed of metallic elements of the type shown in Figure 1, which are mounted on posts. The single source of supply is a town water distribution mains 27 connected to the framework as described in connection with Figure 6, except that the pipes 48, given the general reference R, are taken direct to each separate piping system. The framework is a grid of sections or sections laid end to end and disposed along the length and width of the framework, the lines designating the sections, each interruption of a line symbolising the closing of a section by a welded plate as described in Figure 1, and each square representing a post of concrete or steel. The framework is thus formed of 17 separate systems which are supplied separately. The system A is U-shaped, its bottom branch stopping at 54; the branch WZ is in communication with the two side branches at 55 and 56 and is closed at 57. A pipe 58 coming from the supply R is connected to the middle branch WZ at 59, so that the water coming from the supply in the event of a fire detected by the detectors 32 (Figure 6) fills the system A, following the paths marked by the arrows. The same applies to the systems B and C. The system D comprises a branch 59'-60, two opposite branches 60-61 and 60-62 to which are attached 11 parallel closed sections. The system is fed through a pipe 63 connected at 59', so that the sections 64 to 74 are filled with liquid as far as their ends. In order to evacuate the air, all these ends are provided with air bells 30 (Figure 6). All the systems from A to P and the so-called technical system T, in which the controls are grouped together, are equipped in the same manner. It is advantageous for the systems to be provided with sprinkler heads 31 (Figure 6). As long as the heat of the framework elements does not reach the critical temperature the systems contain irrigation water, and there is therefore no circulation. Beyond that temperature the sprinkler heads open and the circulation of water commences. It is obvious that sprinkler heads are not provided in rooms reserved for delicate and expensive equipment and that other means of extinguishing the seats of fire must be provided. The invention is of course not limited to the embodiments which have been described above and illustrated as examples, and modifications may be made to it without departing from its scope. WHAT WE CLAIM IS:

1. A system of protection against fire for an unlimited period of time of a structure whose framework is of incombustible materials, by internal irrigation of the framework with the circulation of a non-inflammable liquid of high thermal capacity, the said

framework comprising either tubular metallic elements or concrete elements in which metal pipes are embedded, the said elements being connected by their hollow portions to one another and optionally to other hollow structures in order to form either a single irrigation system or an arrangement of separate irrigation systems, characterised in that each irrigation system is connected to a source of the said liquid, particularly a public supply water-mains or a reserve tank situated at the bottom of the structure, by a pipe containing respectively either a closed motorised valve or an electric booster pump at rest, and in that each system is provided with fire detectors connected to a general electric panel which is connected in parallel to the electric mains and to an autonomous emergency generator set and is equipped with fire alarms and automatic time lag relay devices adapted to control either the opening of the valve or the operation of the pump after a predetermined period of time, so that the system remains empty and dry in normal times and so remains an appropriate external intervention within the predetermined period of time in the event of a false alarm but can be completely filled with the said liquid in the event of fire, the complete evacuation of the air contained in the system being effected by at least one air bell (as hereinbefore defined) or bent overflow pipe mounted at the top of the system.

2. A system according to Claim 1, characterized in that in order to guard against failure of the automatic devices it is provided either with a value branched off from the motorised valve and adapted to be opened manually or a manual switch connected in parallel to the automatic pump control.

3. A system according to Claim 1, char acterized in that it contains so-called sprink ler head nozzles mounted judiciously on irrigation systems and capable of discharg ing jets of liquid either on to structures of the building which are not internally irri gated in order to cool them when these structures are exposed to fire, or onto seats of fire.

4. A system according to Claim 1, char acterized in that for the purpose of protect ing top structures of the building, such as roofs, against fire, it is provided with bent over-flow pipes fixed on the systems with their open end directed towards the said structures in order to discharge liquid onto them, while the liquid thus discharged, which is collected by gutter and down pipes, can be carried either to the drain or to a liquid reservoir.

5. A system according to Claim 1, char acterized in that a system may be provided with double jackets (as herein defined) for internal irrigation with circulation of liquid in order to protect against fire, and possibly also against burglary involving the use of heat, particularly by cutting-open by means of a blowlamp, structures of the building such as tanks or strongrooms and safes containing respectively inflammable materials and explosive materials or valuables.

6. A system according to Claim 1, characterized in that the pipes connecting the piping systems to the source of irrigation liquid are each equipped with at least one manual valve and a drain tee, which valve and tee can be used in order to empty an irrigated piping system of its liquid contents and then to dry the wet system with hot air, while an isolatable portion of each pipe also makes it possible to check the operation of the automatic irrigation devices without wetting the entire piping systems.

7. A system according to claim 1 substantially as hereinbefore described with reference to the drawings.