GB2291590A - Dry fire or explosion suppressants - Google Patents

Abstract

The suppressant comprises a flow promoter and sodium or potassium carbonate or hydrogen carbonate where the carbonate or hydrogen carbonate is 0.1 - 20 micron size particulates and is obtained by spray drying a solution thereof. Promoter may be silica. The suppressant may be in the form of loose agglomerations of particles and may be discharged from a container using a gas pressure sufficient to break up the agglomerations.

Description

FIRE AND EXPLOSION SUPPRESSANTS AND METHODS The invention relates to fire and explosion suppressants.

According to the invention, there is provided a dry chemical fire or explosion suppressant, consisting only of a flow promoter and a single one of the following group of compounds: a carbonate or hydrogen carbonate of sodium or potassium; a solution of the compound having been spray-dried to form particles having diameters in the range of 0.1 to 20 micrometers.

According to the invention, there is further provided a method of suppressing fires or explosions, comprising the steps of storing a quantity of a dry chemical suppressant consisting only of a flow promoter and a solution of a carbonate or hydrogen carbonate of sodium or potassium which has been spray-dried to form particles having diameters in the range of 0.1 to 20 microns; and discharging the suppressant into an area to be protected.

According to the invention, there is also provided a method of suppressing fires or explosions, comprising the steps of spray drying a dry substance comprising a solution of a carbonate or hydrogen carbonate of sodium or potassium to form particles having diameters in the range of 0.1 to 20 microns and agglomerations of such particles, adding only a flow promoter to the substance, storing a quantity of the particles and agglomerations in a suppressant container, and discharging the individual particles and agglomerations from the container using gas pressure sufficient at least partially to break up at least some of the agglomerations.

Fire and explosion suppressants embodying the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a schematic diagram of one form of apparatus which may be used to produce the suppressants; Figure 2 is a schematic diagram of one of the suppressant discharge systems; Figures 3 and 4 are views showing the insides of different mixing chambers which may be incorporated in the system of Figure 1; Figure 5 is a view of another of the systems; Figure 6 is a longitudinal cross-section through a delivery tube in the system of Figure 5; Figure 7 is a transverse cross-section through a modified form of the delivery tube of the system of Figure 5; Figure 8 is a schematic view of another of the systems; Figures 9,10 and 11 are views of different nozzle arrangements for discharging the suppressants; and Figure 12 is a schematic view of test apparatus for testing the suppressants.

In accordance with the invention, the suppressants to be described are in the form of dry powders of suitable compounds, examples of which are indicated below, of very small particle size - of the order of 1 micrometre or less, more specifically, in the range of 0.1 to 20 micrometres, preferably 0.1 to 5 micrometers.

Examples of suitable compounds are alkali metal salts such as potassium hydrogen carbonate (KHCO3), potassium carbonate (K2CO3), sodium hydrogen carbonate (NaHCO3) and sodium carbonate (Na2CO3).

A preferred material is potassium hydrogen carbonate (KHCO3) In accordance with a feature of the process, these materials are processed by spray drying to produce the very small particle size.

Such materials, of very small particle size, have been found to have extremely efficient suppressant capabilities. Such suppressants in accordance with the invention are particularly efficient for total flooding applications, where they are discharged into a room or enclosure either directly from a suppressant discharge apparatus or via a pipework distribution system and nozzle. Because of the very small particle size, the suppressant material remains suspended in the atmosphere within the room or enclosure for a substantial period of time, in the manner of a gaseous-type extinguishant. Suppressants in accordance with the invention are very suitable as Halon replacements. In such total flooding applications, the suppressant does not have to be ejected over a relatively long distance. Therefore, "throw" is less important.The suppressant thus consists only of the dry particles and a flow promoter. No additive or other substance to improve throw is used or required.

Potassium hydrogen carbonate is advantageous as a suppressant because it is non-toxic and its reaction products are also nontoxic. It is easily soluble in water and can thus be readily removed after use from areas into which it has been discharged.

As stated above, the suppressants are produced by a spray drying process, of conventional type. Spray drying enables the particle size to be accurately and carefully controlled. As stated above, individual particles are of the order of 1 micrometre and preferably in the range 0.1 to 20 micrometres and advantageously in the range 0.1 to 5 micrometres.

In addition, it is found that the spray-drying process can produce particles which are hollow spheroids or fragments of hollow spheroids, or in the form of spheres within hollow spheres or porous latticed hollow spheres. Such morphology results in increased specific surface area as compared with solid particles of the same diameter; this provides a further increase in suppression efficiency. Moreover, the aerodynamic diameter of such spheroids is lower than would be expected from their physical dimensions and this helps to increase their time of suspension when discharged. They therefore provide an inert atmosphere following actual fire suppression, thus helping to prevent re-ignition of a fire. One form of suitable spray drying apparatus is shown in Figure 1.

An aqueous solution of the chosen suppressant material (for example, potassium hydrogen carbonate) is pumped by a pump 2 from a suitable container 3 into a heated chamber 4. The solution of the suppressant material is sprayed into the heated chamber 4 by means of a spray nozzle 5. At the same time, hot air is pumped into the chamber at a high rate through pipes 6, and this causes the sprayed droplets of the suppressant solution to evaporate.

The resulting fine powder falls to the bottom of the chamber 4 and is collected in a receptacle 7 via an outlet 8. The cooled air leaves by filtered outlets 9.

The individual particles produced by the spray drying process may become bound together in loose agglomerations, typically up to 50 micrometres in diameter. Such agglomerations are very porous and therefore have very high specific surface areas, comparable to the specific surface areas of the individual particles. Thus, they have a very low effective aerodynamic diameter. When discharged into the fire zone for suppressant purposes, the agglomerations remain suspended for a long time (many minutes) in the atmosphere within the room or enclosure where suppression is to take place.

The manner in which the suppressants are discharged may be designed to be such that at least some of the agglomerations break up into smaller clusters, linear chains or discrete particles, as will be described in more detail below.

Some possible applications of the suppressants are for suppressing fires or explosion in the following environments: engine bays of vehicles; marine engine compartments; aircraft cargo bays; storerooms and other normally non-occupied rooms; aircraft engine nacelles and dry bays; "grenades" for fire brigade use prior to entering areas of severe flaming combustion; hand extinguishers.

Although potassium hydrogen carbonate is non-toxic, the suppressants are normally most suitable for unoccupied rooms, because of the visual obscuration which the suppressants produce; an exception might be made for the crew compartments of military vehicles.

Various systems, and parts of systems, for discharging the suppressants, and enhancing the disagglomeration effect described above, will now be described with reference to the accompanying drawings.

Figure 2 shows a vessel 10 containing nitrogen or other suitable inert or relatively inert gas under pressure, together with a quantity of the suppressant powder. For example, in one tested version of the system, the vessel 10 has a volume of 2.27 litres and contains nitrogen under pressure at about 200 pounds per square inch (13.79 bar) and between 2 and 20 grams of the suppressant powder. However, pressures up to about 50 bar may be used.

The interior of the vessel 10 is in communication with a mixing chamber 12 through a solenoid-operated valve 14. The mixing chamber 12 has an exit nozzle indicated diagrammatically at 16.

The mixing chamber may, for example, have a volume of 0.6 litres.

When the suppressant is to be discharged, the solenoid valve 14 is operated to move it into the OPEN condition, and the high pressure gas discharges into the mixing chamber 12, carrying with it the suppressant powder. In the mixing chamber, turbulent gas flow occurs which may break up at least some of the agglomerations in the manner explained, and the suppressant is then swept through the nozzle 16 into the fire zone.

In an alternative mode, the system of Figure 2 may be arranged so that the suppressant powder is initially positioned within the mixing chamber 12, instead of being in the vessel together with the high pressure gas. The vessel 10 therefore contains only the gas. When the solenoid valve 14 is moved to the OPEN setting, the high pressure gas enters the mixing chamber 12 and discharges the suppressant in the manner already explained.

Figure 3 diagrammatically shows how the mixing chamber 12 of Figure 2 may incorporate a centrally mounted and positioned baffle plate 18. This prevents the gas and agglomerations from taking a direct path through the chamber 12 and increases the turbulence within the mixing chamber, which is a desirable characteristic.

Figure 4 shows an alternative arrangement for the interior of the mixing chamber 12, in which the gas is directed into the chamber 12 via curved inlet pipes 20 and 22. Again, the effect is to increase turbulence within the mixing chamber 12.

Figure 5 shows a system which could be used for crew bay protection, for example. Here, there is a vessel 22 containing suppressant (150 to 2000 grams of suppressant for example), together with nitrogen or other suitable gas under high pressure.

When a discharge valve 24 is moved to the OPEN setting, the gas and the suppressant are discharged through a delivery tube 26 and a nozzle 28. Advantageously, the delivery tube 26 is arranged to enhance the turbulence of the gas/suppressant powder mixture as it travels to the nozzles. As shown in Figure 6, for example, baffles 30 may be directed part-way across the interior crosssection of the delivery tube 26. Alternatively, and as shown in Figure 7, spiral vanes 32 may be provided for the same purpose.

Figure 8 shows another arrangement suitable, for example, for crew bay protection. Here, the vessel 22 contains only the suppressant powder, and again can contain 150 to 2000 grams, for example, of the powder. A separate, smaller, pressurised chamber 34 is provided which contains high pressure nitrogen. An outlet valve 36 controls the feeding of the high pressure nitrogen through a delivery tube 38 into the lower part of the vessel 22.

A further valve 40 controls the discharge of the suppressant powder through a delivery tube 42 and a nozzle 44. The operation of the valves 36 and 44 is synchronised. The high pressure nitrogen is rapidly discharged into the vessel 22 and causes turbulence within the suppressant powder, thus breaking up at least some of the agglomerations and discharging the suppressant through the opened valve 40, the delivery tube 42 and the nozzle 44. Again, the delivery tube 42 may contain baffles 30 (Fig. 6) or vanes 32 (Fig. 7) or other suitable means for increasing the turbulence.

A suitable nozzle is shown in Figure 9 at 46. The nozzle 46 is conical in shape with an axially directed orifice 48 and transversely directed orifices 50. This type of orifice provides discharge of the suppressant in different directions. The relative size of the orifices 48 and 50 can be varied to vary the amount of suppressant discharged in the different directions.

For example, the orifice 48 may be closed off completely, so that all the suppressant is discharged sideways.

Figure 10 shows a nozzle in which the exit orifice 54 is aligned with an externally mounted barrier 56 against which the discharging suppressant impinges at high speed.

Figure 11 shows a system using gas-mixing. In this case, the high pressure gas containing the suppressant enters along a delivery tube 60 and into a supplementary mixing chamber 62 which is also fed with high pressure gas through a further delivery tube 64. The gas flows impinge on each other and cause break-up of at least some of the agglomerations, the suppressant then being discharged through orifices in a nozzle 66.

Advantageously, the flow promoter comprises finely divided silica added to the suppressant when it is placed in the containers: the silica is typically added in the proportion of 1 to 4k by weight.

Other known additives could be used for the same purpose.

Other methods of discharging the suppressants may be used. For example, instead of using arrangements in which the high pressure gas is pre-stored, the gas may be generated at the time of discharge using a suitable gas generator, such as a pyrotechnic gas generator. Gas generators are relatively low in weight compared with the weight of the vessel suitable for storing gas under pressure.

Tests carried out on systems of the form shown in Figure 2 have indicated that suppressant powders of the types disclosed can be up to ten times more efficient than commercially available suppressants. Figure 12 shows apparatus for carrying out such tests. The test apparatus comprises a test chamber 70 having, in this example, a volume of 287 litres. A pan-fire 72, of standard type and five centimetres in diameter, is positioned within the chamber 70 behind a vertical baffle 74 and underneath a horizontal baffle 76.

A vessel 78, of 0.6 litres in this example, is provided for receiving the suppressant 79 under test, and is connected to a spray nozzle 80 at the top of the test chamber 70. Discharge of the suppressant into the test chamber 70 is controlled by means of pressurised nitrogen which is stored in a cylinder 82. The pressure of the nitrogen from the cylinder 82 is regulated to a standard value, for example 200 pounds per square inch (13.79 bar) by a regulator arrangement 84. The nitrogen under pressure is fed via a valve 85 and a pipe 86 to a reservoir 88 having (in this example) a volume of 2.27 litres. The reservoir 88 is connected to the suppressant-containing vessel 78 via a normally closed solenoid valve 90.

In order to carry out the testing, a measured quantity of the suppressant is placed in the vessel 78. The output valve 85 on the nitrogen cylinder 82 is opened so as to pressurise the reservoir 88 to 200 pounds per square inch (13.79 bar) and the output valve 85 is then closed again. The pan-fire 72 is then lit and allowed to pre-burn for a predetermined time (normally 30 second or 1 minute). At the end of this predetermined time, the solenoid valve 90 is opened, so that the nitrogen under pressure in the reservoir 88 causes the suppressant to be sprayed into the test chamber 70 via the nozzle 80. The time taken to extinguish the pan-fire 72 is then measured. If the time exceeds a predetermined value (e.g. 50 or 60 seconds), the extinguishing action is considered to have failed.Testing is repeated with each different suppressant so as to find the minimum amount of suppressant which will extinguish the fire.

The following Table compares the "suppression efficiency" of various suppressants embodying the invention with other commercially available suppressants. Suppression efficiency is defined as 104 divided by the minimum extinguishing concentration measured in grams per cubic metre of the volume of the test chamber. The minimum extinguishing concentration is the minimum amount of each type of suppressant which, when placed in the vessel 78, extinguishes the pan fire 72.

TABLE Suppressant Particle size Suppression efficiency Ratio (in micrometres) Dessikarb 10-80 273 1.0 Monnex 505 1.8 Furex 219 0.8 K2CO3 less than 44 357 1.3 K2CO3 0.2 - 1.2 1190 4.4 K2CO3 0.4 - 2.8 1064 3.9 KHCO3 0.5 - 7.0 2500 9.2 Dessikarb, Monnex and Furex are trade marks of commercially available suppressants.

The ratio values compare the suppression efficiencies of all the suppressants tested with Dessikarb.

Claims (38)

1. A dry chemical fire or explosion suppressant, consisting only of a flow promoter and a single one of the following group of compounds: a carbonate or hydrogen carbonate of sodium or potassium; a solution of the compound having been spray-dried to form particles having diameters in the range of 0.1 to 20 micrometers.

2. A suppressant according to claim 1, in which the compound is a hydrogen carbonate.

3. A suppressant according to claim 2, in which the compound is potassium hydrogen carbonate.

4. A suppressant according to any preceding claim, in which the respective diameters of the particles are in the range 0.1 to 5 micrometers.

5. A suppressant according to any preceding claim, at least partially in the form of loose agglomerations of individual particles.

6. A suppressant according to claim 5, in which the loose agglomerations are about 50 micrometers or less in diameter.

7. A suppressant according to any preceding claim, in which the flow promoter is silica.

8. A suppressant according to any preceding claim, in which at least some of the particles are hollow spheroids or fragments thereof.

9. A suppressant according to any preceding claim, in which at least some of the particles are in the form of spheres within hollow spheroids or fragments thereof.

10. A suppressant according to any preceding claim, in which for at least some of the particles their aerodynamic diameter is substantially less than their physical diameter

11. The use as a fire or explosion suppressant of a suppressant according to any preceding claim.

12. The use according to claim 11, in a total flooding application.

13. The use according to claim 11 or 12, in which the suppressant is discharged using high pressure gas.

14. A method of suppressing fires or explosions, comprising the steps of: storing a quantity of a dry chemical suppressant consisting only of a flow promoter and a solution of a carbonate or hydrogen carbonate of sodium or potassium which has been spray-dried to form particles having diameters in the range of 0.1 to 20 microns; and discharging the suppressant into an area to be protected.

15. A method according to claim 14, in which the stored suppressant is at least partially formed of individual said particles bound in loose agglomeration, and in which the discharging step at least partially breaks up at least some of the agglomerations at or immediately before discharge of the suppressant.

16. A method according to claim 14 or 15, in which the particles have diameters in the range of 0.1 to 5 microns.

17. A method according to any one of claims 14 to 16, in which at least some of the particles are hollow spheroids or fragments thereof.

18. A method according to any one of claims 14 to 17, in which at least some of the particles are in the form of spheres within hollow spheroids or fragments thereof.

19. A method according to any one of claims 14 to 18, in which for at least some of the particles their aerodynamic diameter is substantially less than their physical diameter.

20. A method according any one of claims 14 to 19, including the step of forcibly discharging the suppressant under high gas pressure.

21. A method according to claim 20, in which the gas pressure is applied to the suppressant in turbulent conditions within a chamber, from which the suppressant is discharged by the pressure.

22. A method according to claim 20 or 21, in which the gas pressure drives the suppressant along a delivery tube for discharge therefrom, the tube incorporating means for increasing turbulence.

23. A method according to claim 21, including the step of increasing the turbulence in the chamber.

24. A method according to claim 21 or 22, in which the suppressant material is carried by the gas into the chamber.

25. A method according to any one of claims 21,23 and 24, in which the suppressant is pre-positioned in the chamber and the gas pressure is subsequently applied to the chamber.

26. A method of suppressing fires or explosions, comprising the steps of (a) spray drying a dry substance comprising a solution of a carbonate or hydrogen carbonate of sodium or potassium to form particles having diameters in the range of 0.1 to 20 microns and agglomerations of such particles, (b) adding only a flow promoter to the substance, (c) storing a quantity of the particles and agglomerations in a suppressant container, and (d) discharging the individual particles and agglomerations from the container using gas pressure sufficient at least partially to break up at least some of the agglomerations.

27. A method according to claim 26, in which the particles have diameters in the range of 0.1 to 5 microns.

28. A method according to claim 26 or 27, in which the agglomerations are about 50 micrometers or less in diameter.

29. A method according to any one of claims 26 to 28, in which at least some of the particles are hollow spheroids or fragments thereof.

30. A method according to any one of claims 26 to 29, in which at least some of the particles are in the form of spheres within hollow spheroids or fragments thereof.

31. A method according to any one of claims 26 to 30, in which for at least some of the particles their aerodynamic diameter is substantially less than their physical diameter.

32. A method according to any one of claims 26 to 31, in which the gas pressure is produced by pre-stored gas under pressure.

33. A method according to claim 32, in which the gas is stored in the suppressant container.

34. A method according to claim 32, in which the high pressure gas is stored in a separate container and is allowed to enter the suppressant container when the said discharge is to occur.

35. A method according to any one of claims 26 to 31, in which the gas pressure is generated immediately prior to discharge of the suppressant.

36. A fire or explosion suppressant, substantially as described.

37. The use as a fire or explosion suppressant, substantially as described.

38. A method of suppressing fires or explosions, substantially as described with reference to the accompanying drawings.