EP0700693A1

EP0700693A1 - Method for extinguishing a fire

Info

Publication number: EP0700693A1
Application number: EP95202438A
Authority: EP
Inventors: Hans Albert Mars; Theodorus Hubertus Hendriks; Nicolaas Bijloo
Original assignee: Nagtglas Versteeg (Deutschland) GmbH; Nagtglas Versteeg BV
Current assignee: AJAX BRANDBEVEILIGING B.V.
Priority date: 1994-09-09
Filing date: 1995-09-07
Publication date: 1996-03-13
Also published as: CA2157949A1; NL9401480A

Abstract

When extinguishing a fire by means of an extinguishing gas, after a fire is detected, the extinguishing gas is supplied under high pressure to the area in which the fire has broken out, with simultaneous displacement of air. In order to prevent gas speeds which are too high, the extinguishing gas is fed, in a first step, into a chamber which is delimited by a porous wall and subsequently, in a second step, is fed via the porous wall to the fire to be extinguished. Preferably, the displaced air is removed at a location which is related to the ratio of the specific weights of air and extinguishing gas.

Description

The invention relates to a method for extinguishing a fire by means of an extinguishing gas, wherein, after a fire is detected, the extinguishing gas is supplied under pressure to the area in which the fire has broken out, with simultaneous displacement of air.
A method of this type, which is disclosed in EP-A 0 496 066, is used in those cases where the use of fluid extinguishing agents is not possible or desirable, because of, for example, the damage to be anticipated as a consequence of the extinguishing fluid. Storage areas for valuable articles such as works of art may be mentioned as an example of such cases. The use of fluid extinguishing agents can also not be considered in the case of electrical and electronic installations, and in the case of some installations in the chemical industry and the like.
The action of extinguishing gas is based either on the principle of a negative catalyst or on the principle of displacement. In the former case, the extinguishing gas contains Halons. However, the use of Halons is no longer permitted under recent environmental legislation and, therefore, for as long as no replacement for Halons is available, use must be made of the displacement principle.
This latter principle is based on the fact that in virtually all cases the ambient air must contain more than 15 % oxygen in order to be able to sustain a fire. Air usually contains 21 % oxygen; however, down to a concentration of 12 %, humans and animals do not suffer from a lower oxygen concentration. On the basis of these data, extinguishing gas installations which are based on this principle are therefore designed in such a way that they are able, within a very short time, to introduce into the protected area an amount of extinguishing gas such that the oxygen concentration in said area falls to a level of between 12 % and 15 %.
Using the displacement principle, a relatively large amount of extinguishing gas is needed to extinguish a fire. Although this amount is introduced into the protected area via several feed elements simultaneously, very high flow rates, which can even approach the speed of sound, nevertheless occur when the gas flows in. With a high inflow of this type, troublesome side effects also arise, such as the entrainment of ambient air, as a result of which powerful air flows can be generated which have the character of a gale.
A further disadvantage of this known method, and in particular of the high inflow speed associated with this method, lies in the extensive mixing which takes place between the air and the extinguishing gas. As a consequence of this, some of the extinguishing gas rapidly disappears from the protected area, as a result of which the displacement effect declines.
Moreover, because of the high air speed, the fire can initially be fanned. This can also lead to dissemination of combustion products, burning materials, hazardous substances and/or infectious substances and the swirling-up of dust, which is particularly disadvantageous in the case of vulnerable articles, such as electronic equipment, works of art, and the like. An inflow of this type is associated with high noise levels, as a result of which communication becomes impossible and panic reactions may occur.
Roofs, walls, floors, windows and doors can also easily be overstressed by the large amounts of extinguishing gas. Furthermore, the displaced air must be prevented from passing on to adjacent areas, which makes the presence of extractors necessary.
Moreover, with the known method, condensation occurs on cold installation components which are in contact with the ambient air. This can be prevented by fitting thermal insulation. However, the outflow facilities cannot be covered, as a result of which condensation cannot be prevented in these areas.
In view of the fact that, with the known method, the extinguishing agent, which consists of a mixture of gas and liquid, is stored in the cryogenic state, the outflow speed must be fairly high in order to allow the extinguishing agent to extract heat from the environment to vaporise the fluid component. Consequently, an (undesirable) mixing of extinguishing agent and ambient air will always take place.
The aim of the invention is, therefore, so to improve the method described above that the said disadvantages are avoided. This aim is achieved in that the extinguishing gas is stored under a high pressure at ambient temperature, in a first step is fed to a chamber which is delimited by a porous wall and subsequently, in a second step, is fed via the porous wall to the fire to be extinguished.
Feeding the extinguishing gas to the protected area in the manner according to the invention has the advantage that, at a high extinguishing gas flow rate and a high feed pressure, the inflow rates remain restricted. The porous wall provides an inflow surface which is so large that it is no longer possible for high local speeds to arise. The noise production remains low. Moreover, the formation of condensation is prevented.
A further advantage of feeding a large amount of extinguishing gas at relatively low speed is the increased effectiveness thereof. This is because the low inflow speeds lead to little mixing of air and extinguishing gas, as a result of which relatively little extinguishing gas is removed from the area with the displaced air.
Preferably, the storage pressure is at least 100 bar; the most preferred range of storage pressures is 150-250 bars.
In this context, the displaced air is preferably removed at a location which is related to the ratio of the specific weights of air and extinguishing gas. Because there is only slight mixing, the extinguishing gas can drive the air uniformly in front of it. By now choosing the feed for extinguishing gas and the discharge for displaced air in a suitable manner, the desired extinguishing effect can already be obtained with relatively little extinguishing gas since hardly any extinguishing gas is lost through the discharge.
According to a first possibility, in this context an extinguishing gas is used which has a specific weight higher than the specific weight of air and discharge of the displaced air takes place at a relatively high level.
According to an alternative, second possibility, an extinguishing gas is used which has a specific weight lower than the specific weight of air and discharge of the displaced air takes place at a relatively low level.
The invention also relates to an area provided with an extinguishing installation for carrying out the method described above, comprising storage means for a stock of extinguishing gas under high pressure and, connected to said stock, a feed element which opens into the area, as well as discharge means for removal of displaced air from said area.
With this arrangement also, according to a first possibility, an extinguishing gas can be used which has a specific weight higher than the specific weight of air, and the discharge means for removal of the displaced air can be located at a relatively high level in the area.
According to a second possibility, an extinguishing gas can be used which has a specific weight lower than the specific weight of air, and the discharge means for removal of the displaced air can be located at a relatively low level in the area.
The discharge outlets in the area can be provided with a seal which is breakable under the effect of overpressure in the area, for example a breakable membrane. A seal of this type prevents any outside influences, for example, the effects of weather, from being able to reach the protected area during normal operations.
A possible embodiment of the discharge facility comprises a weight-loaded overpressure valve with a breakable membrane, for example made of plastic film, on both the inlet side and the outlet side. When a set overpressure is exceeded, the membranes are broken. The excess air can then escape to the outside via the overpressure valve, the pressure thus being kept substantially equal to the atmospheric pressure. When the feed of extinguishing gas ceases, the non-return valve closes to a sufficient extent to prevent the escape of extinguishing gas to the outside and the ingress of oxygen-rich air. As long as the membranes have not been broken, they provide good thermal insulation and a good vapour-tight and dust-tight seal.
The invention also relates to a feed element for feeding extinguishing gas into an area as described above, comprising a chamber with an inflow opening for the extinguishing gas, and a porous wall for releasing extinguishing gas from the chamber.
The extinguishing gas fed under high pressure expands in the chamber, as a result of which the rate of flow decreases. The extinguishing gas then flows at moderate speed via the porous wall into the area to be protected. A further advantage is that the drop in temperature which occurs during expansion remains relatively slight, with the result that there is no ice formation. Only a layer of rime is deposited, which sublimes without dripping phenomena, such as would occur on the thawing of ice deposits.
Preferably, the inflow opening has an adjustable restriction for controlling the flow rate of the extinguishing gas. On feeding the extinguishing gas via elements, the restrictions can in each case be so adjusted that a feed of extinguishing gas uniformly distributed over all elements takes place.
According to a preferred embodiment, the porous wall is cylindrical and closed at one end by an end baffle, whilst it has an end baffle containing an inflow opening at the opposing end.
Furthermore, the porous wall is preferably made of sintered stainless steel. A material of this type is well able to resist corrosion; there is then also hardly any risk of blocking, even during the prolonged period in which the installation has to remain ready for use. Moreover this material can be subjected to mechanical stress without any problems. A further advantage is the predictable and readily reproducible porosity.
Incidentally, other sintered materials, such as sintered bronze, can also be used. It is also conceivable to use ceramic materials, on condition that the mechanical stresses allow this.
The feed element can also have two separate inflow openings, each with its own restriction. The twin feed not only offers the possibility of mixing different extinguishing gases and so feeding these simultaneously, but also makes it possible to inject water into the extinguishing gas. Retaining the low-pulse feed, the atomised water will rapidly vaporise and expand. As a consequence of this, not only will the air be displaced rapidly but, at the same time, as a consequence of the vaporisation of the water, heat will also be withdrawn from the environment and the object to be extinguished.
The feed element of porous material is also suitable for low-pulse atomisation of a liquefied gas, such as carbon dioxide, which leads to a much more effective oxygen displacement and cooling. This latter application is also suitable as water-saving cooling in production processes.
A further advantage is that, despite the low temperature of the feed element, no condensation of water vapour on the feed element takes place because, during feeding of the extinguishing gas, the feed element is completely surrounded by extinguishing gas in which virtually no water vapour is present. Ambient air can come into contact with the feed element only after the feed of extinguishing gas has ceased. As a result of the feed of dry extinguishing gas, the moisture content of the ambient air is appreciably lower than before. A thin layer of rime forms on the feed element and sublimes without forming drips.
A feed element made of sintered material has been used previously and has been described in EP-A 0 496 066. However, in this case the feed element serves only for very fine dispersion of the mixture of liquid and gaseous extinguishing gas (argon stored under cryogenic conditions; pressure 15 to 40 bar) in order to promote rapid vaporisation of the liquid argon. However, the outflow speeds reached with this arrangement are appreciably higher than those according to the invention and indeed must be so in order to be able to achieve the target rapid vaporisation. The described advantages of the low outflow speeds (with respect to restriction of mixing with ambient air and condensation) are not achieved with the known feed element.
The invention will be explained in more detail below with reference to an illustrative embodiment shown in the figures.
Figure 1 shows a vertical cross-section through an area provided with an extinguishing gas installation according to the invention.
Fig. 2 shows a cross-section through the feed element according to the invention.
The area 1 shown in Figure 1, in which an object, which is not indicated in more detail, to be protected against fire is located, is provided with two feed elements 2 according to the invention for extinguishing gas. Said feed elements are connected in a known manner via piping 3 and valve 4 to a holder 5. A large amount of extinguishing gas under high pressure is stored in said holder 5.
As soon as fire is detected in the area 1, for example via detection means which are known per se and are not shown, the valve 4 is opened, likewise in a known manner which is not shown, after which the extinguishing gas flows under high pressure and at high speed to the feed elements 2.
As shown in Figure 2, said feed elements 2 comprise a chamber 6 surrounded by a porous, cylindrical wall 7. Said porous cylindrical wall can be made, for example, of sintered stainless steel. A wall 8 is located at one end of the chamber 6 and a wall 9, provided with a feed 10, is located at the other end. Upstream of said feed 10, there is a restriction 11, which is adjustable in such a way that an identical flow rate can be obtained through both feed elements 2.
The extinguishing gas expands in the chamber 6, with a decrease in pressure and speed. The extinguishing gas then flows at a moderate speed into the area 1.
In the illustrative embodiment shown, the extinguishing gas has a specific weight which is higher than the specific weight of the air initially present in the area 1. As, moreover, the extinguishing gas flows in at a moderate speed, as a result of which there is hardly any mixing with the air, the extinguishing gas will initially collect at a low level 12 in the area 1. The extinguishing gas front 13 drives the air present in the area 1 before it, in such a way that the air can flow away uniformly through the discharge outlets 14 provided in the area 1. The air flow is indicated by the arrows 15.
The advantage of this method is that hardly any extinguishing gas is lost through the discharge outlets 14, such that an extinguishing effect can be achieved with minimum amounts of extinguishing gas. A further advantage is that high flow speeds hardly occur in the area 1, as a result of which the objects located in said area remain spared and hardly any dissemination of hazardous or infectious substances will occur.

Claims

Method for extinguishing a fire by means of an extinguishing gas, wherein, after a fire is detected, the extinguishing gas is supplied under pressure to the area in which the fire has broken out, with simultaneous displacement of air, characterised in that the extinguishing gas is stored under a high pressure at ambient temperature, in a first step is fed to a chamber which is delimited by a porous wall and subsequently, in a second step, is fed via the porous wall to the fire to be extinguished.
Method according to claim 1, wherein the storage pressure is at least 100 bar.
Method according to Claim 1 or 2, wherein the storage pressure is between 150 bar and 250 bar.
Method according to Claim 1, 2 or 3, wherein the displaced air is removed at a location which is related to the ratio of the specific weights of air and extinguishing gas.
Method according to Claim 4, wherein an extinguishing gas is used which has a specific weight higher than the specific weight of air and discharge of the displaced air takes place at a relatively high level.
Method according to Claim 4, wherein an extinguishing gas is used which has a specific weight lower than the specific weight of air and discharge of the displaced air takes place at a relatively low level.
Area provided with an extinguishing installation for carrying out the method according to one of the preceding claims, comprising storage means for a stock of extinguishing gas under high pressure and, connected to said stock, a feed element which opens into the area, as well as discharge means for removal of displaced air from said area.
Area according to Claim 7, wherein an extinguishing gas is used which has a specific weight higher than the specific weight of air, and the discharge means for removal of the displaced air are located at a relatively high level in the area.
Area according to Claim 7, wherein an extinguishing gas is used which has a specific weight lower than the specific weight of air, and the discharge means for removal of the displaced air are located at a relatively low level in the area.
Area according to Claim 7, 8 or 9, wherein each discharge outlet is provided with a seal which is breakable under the effect of overpressure in the area.
Area according to Claim 10, wherein the seal comprises at least one breakable membrane.
Feed element for feeding extinguishing gas into an area according to one of Claims 7-11, comprising a chamber with an inflow opening for the extinguishing gas, and a porous wall for releasing extinguishing gas from the chamber.
Feed element according to Claim 12, wherein the inflow opening has an adjustable restriction for controlling the flow rate of the extinguishing gas.
Feed element according to Claim 12 or 13, wherein the porous wall is cylindrical and closed at one end by an end baffle, and has an end baffle containing an inflow opening at the opposing end.
Feed element according to Claim 14, wherein the inflow opening has an adjustable restriction.
Feed element according to one of Claims 12-15, wherein the porous wall is made of sintered stainless steel.
Feed element according to one of Claims 12-16, wherein two separate inflow openings are provided, each with its own restriction.