EP1512435B1 - Method and apparatus for extinguishing metal fires - Google Patents

Abstract

Method for extinguishing metal fires involves application of a completely waterless liquid extinguishing agent which reacts with the burning metal, by bonding the air oxygen and forming an incombustible compound. The extinguishing agent is sprayed as multiple fine jets from above onto the source of fire. An independent claim is also included for an extinguishing device for use in the above method.

Description

Metal fires, fire class D fires (magnesium alloys, aluminum alloys, lithium alloys, sodium, etc.) are still a major fire-fighting problem to this day. The reason for this is the heavy reactivity of these metals (especially if they are alkali metals) ) with already smallest amounts of water. To accelerate the combustion process already sufficient in the environment high humidity.

Metals which are suitable for metal fires are in detail the alkali metals sodium, potassium, lithium and cesium, further the metals magnesium, calcium and barium, all of which also react violently with water, and the metals aluminum, cerium, iridium, niobium and Palladium and also magnesium oxide.

Due to the increased technical use of such metal alloys, for example, especially in the automotive sector, the problem of firefighting amplified considerably, especially since of chips that are incurred in the cutting shaping of components made of such alloys, a significant fire risk. Automobile manufacturers are currently working worldwide to increase the use of magnesium components in vehicles such as engines, transmissions, axles, doors, etc. As a result, traffic accidents involving such vehicles today and particularly in the future pose an increased risk of fire, posing a significant problem that rescue teams are currently unable to target such fires. The fire brigades have until today no suitable extinguishing agent to be able to take action against fires of this kind effectively.

The combustion temperatures of the above metal alloys are well over 2000 degrees Celsius. This leads to the dissociation of the water molecules, which are split into hydrogen and oxygen when they meet with water. This splitting can lead to oxyhydrogen gas formation, which means an additional hazard potential.

When extinguishing metal fires with extinguishing agents known today one does not speak of an actual extinguishing process, but only of a covering, which is related to the nature of extinguishing agents used to date. The currently used extinguishing agents are salt (sodium chloride-potassium chloride), extinguishing powder fire class D, sand and gray castor chips. Thus, only a covering of the burning metal can be made. An extinguishing process as such is currently not possible with all these extinguishing agents. But if the burning metal is only covered by the extinguishing agent, the deletion process can take several hours, even days. This represents an untenable condition for metal processors.

The use of previously known extinguishing powder also has the disadvantage that contamination of the production equipment occurs to a very high degree when a fire is to be extinguished in the area of a production plant. This requires lengthy and complex cleaning work and therefore large downtime of expensive manufacturing equipment. Furthermore, the dust formation during firefighting with powder also results in a corresponding health risk for the firefighting personnel, since the fine powder dust remains in the lungs after inhalation and can no longer be excreted.

Also Graugrußspäne as a cover for metal fires have significant shortcomings in handling. Large German car manufacturers hold large amounts of gray cast iron chips for possible metal fires. However, a significant problem associated with gray cast iron shavings is the occurrence of corrosion associated with atmospheric oxygen. If these rusty chips are applied to, for example, burning magnesium chips, this in turn can lead to undesired reactions. These occurring reactions are due to the iron oxide (rust has the chemical formula FeO (OH)). With strong heating, water is released, and this released from the iron oxide water in turn leads to corresponding reactions with the magnesium.

A similar problem arises with the extinguishing agent sand, since it must be kept in an absolutely dry state. Dampy sand leads to the same phenomena as oxidized gray castor chips.

The invention is therefore based on the object to provide a method for extinguishing metal fires, with which the indicated problems can be avoided at least to a considerable extent.

This object is achieved according to the invention by the method specified in claim 1. An apparatus for carrying out the method according to the invention is the subject of the independent device claim.

The invention operates in contrast to the prior art with a liquid extinguishing agent, which is completely anhydrous and thereby not subject to the risk of fire acceleration in water-reactive metals. The liquid extinguishing agent also has no components which contain a risk potential due to dissociation or other reactions during the extinguishing process.

The liquid extinguishing agent used in the method according to the invention consists essentially of polydimethyl siloxane with solids and perfluoro-polyether. It is therefore constructed so that it contains no water components. This makes it possible to extinguish the metal fires described above, without causing the dissociation of water or hazardous reactions during the deletion process.

The extinguishing principle of this liquid extinguishing agent based on the fact that the polydimethyl siloxane leads to silicate formation, which is triggered by the thermal decomposition of the alkali metals or the alkali metal compounds and the presence of oxidizing oxygen.

The example of sodium gives, for example, the following reaction formula:

R - [(CH ₃ ) ₂ Si- O- Si (CH) ₃ ) ₂ ] _n + 2n Na + 1 / 2n O ₂ -> 2n R- (CH ₃ ) ₂ Si- O ₂ (-) + 2n Na (+)

where R denotes the radical and n denotes the length of the polymer chain.

Generally speaking, the reaction formula is: $$\mathrm{polydimethylsiloxane}+\mathrm{alkali\; metal}+\mathrm{oxygen}\to \mathrm{Dimethyl\; silicate\; of\; the\; alkali\; metal}$$

• Verbrauch des verbrennungsfördernden Sauerstoffs,
• Verbrauch des brennenden Alkalimetalls, und
• Ausbildung einer verglasungsähnlichen Schicht über dem Brandherd.

This silicate formation produces three effects that are significant for the extinguishing effect:

• Consumption of combustion-promoting oxygen,
• Consumption of the burning alkali metal, and
• Formation of a glazing-like layer over the fire.

The first two effects, namely the consumption of oxygen and the consumption of alkali metal, minimize the available amount of combustible substance, and the latter effect, namely the formation of a glazing-like layer above the source of the fire, at the same time inhibits the entry of new atmospheric oxygen , Furthermore, due to the relatively good heat conduction, the glass-like layer forming forms contributes to rapid cooling of the fire.

The abovementioned proportions of solids to the polydimethyl siloxane may be, for example, melanin or boron and should not exceed 10% of the volume. These solids are helpful in masking the source of the fire to stop unwanted reactions.

As mentioned above, the liquid extinguishing agent may also contain perfluoro-polyether. This is not involved in the silicate formation reaction described above, but has a strong cooling effect, which is known to fire fighting extremely important.

wobei I die Löschintensität, V die Löschmittelmenge (Löschmittelvolumen), t die Löschzeit (Aufbringungsdauer), und A die Brandoberfläche ist.For the process according to the invention, it is also essential to apply the liquid extinguishing agent carefully metered onto the burning metal. If the liquid extinguishing agent to violently, for example, in surge form or full jet form, applied, for example, to burning or liquid sodium, it may possibly come to a reaction with the liquid metal, with the result that the fire is no longer manageable. It is also essential that when applying the liquid extinguishing agent to the burning metal, such as magnesium, the amount of extinguishing agent supplied is in a certain proportion to the mass of the metal, so that no undesirable reactions of the burning metal can be caused. The extinguishing intensity I as amount of extinguishing agent applied per unit time can be defined as follows: $$\mathrm{Extinguishing\; intensity\; I}\mathrm{=}{\mathrm{V}}_{\mathrm{extinguishing\; Media}}\mathrm{/}{\mathrm{t}}_{\mathrm{deleted}}\mathrm{\times }{\mathrm{A}}_{\mathrm{fire}}$$

where I is the erasing intensity, V is the amount of extinguishing agent (extinguishing agent volume), t is the extinguishing time (application time), and A is the firing surface.

These criteria are taken into account by applying the liquid extinguishing agent in the form of fine extinguishing agent jets to the source of the fire according to the method of the invention.

Since the liquid extinguishing agent described above has a relatively high viscosity of 100 to 350 mPa.s, in the method according to the invention, this requires the application of a correspondingly high pressure to produce the fine extinguishing agent jets, if they are to have a good throwing distance.

The extinguishing device according to the invention for carrying out the method according to the invention operates at an operating pressure of at least 10 bar. This can be achieved with the liquid extinguishing agent a throw of about 4 m, which means a greater security for the user during the deletion. Previously known metal fire extinguishers (powder extinguishers) have a throw of only a maximum of about 0.5 m, so that the user is at risk because of the immediate proximity to the fire to a high degree.

The serving for carrying out the method extinguishing device according to the invention may be a working with supercharged fire extinguisher with an extinguishing agent container in which the liquid Extinguishing agent is subjected to the corresponding operating pressure, an extinguishing agent hose and an extinguishing agent head having a nozzle assembly through which a plurality of fine extinguishing agent jets are generated, which are preferably directed somewhat perpendicular to the fire hearth surface. The working pressure of the extinguishing device should, as already mentioned, preferably be at least 10 bar to preferably about 34 bar.

The invention will be described in more detail below with reference to the accompanying drawing, which schematically shows a person with a fire pistol of the extinguishing device according to the invention, wherein the extinguishing agent hose shown broken and the extinguishing agent container is omitted for clarity.

Of particular importance is the nozzle arrangement or nozzle configuration on the extinguishing gun 1 of the extinguishing device according to the invention. The extinguishing pistol 1 has a nozzle head 2 in the form of a projecting from the extinguishing gun longer tubular body. Whose front end portion 3 may, as seen in the drawing, be angled slightly upwards, for example, about 30 °, and know on its underside a variety of fine outlet nozzles for generating thin extinguishing agent jets, which is substantially perpendicular to the extinguishing head end piece. 3 escape.

Thus, what is important in extinguishing metal fires, the extinguishing gun be held so that the extinguishing agent impinges almost vertically from above the fire. This applies both when the extinguishing gun is held substantially directly over the fire, so even if the extinguishing gun is held obliquely upward that a throw of the extinguishing agent beam is achieved by a few meters and the extinguishing agent beam in the arc and then turn about perpendicular to the burning metal from above.

The nozzle configuration of the extinguisher according to the invention also allows effective extinguishing on metal working machines in which metal fires occur, since the extinguishing agent can be effectively introduced into the narrowest column of machines in which burning metal chips can be located.

As stated above, since a metal fire, e.g. burning and possibly liquid sodium, must be very carefully treated with extinguishing agent, the flow rate for a metal fire extinguisher may be a maximum of about 301 / min. Working pressure of the extinguisher and nozzle configuration must therefore be coordinated so that you get a suitable flow rate, because only then the correct extinguishing success can be achieved.

Preferably, the extinguisher is designed so that it can be quickly refilled by the operator and immediately ready for use.

The invention described above thus brings considerable advantages in the fight against metal fires. By using the liquid extinguishing agent for fire class D, the extinguisher can be very simple and operate. The fire is carefully dosed with extinguishing liquid by the special nozzle configuration. As a result, a wetting of the surface takes place, so a deletion process in the true sense, and also the fire and adjacent surfaces is cooled by the liquid extinguishing agent.

Due to the liquid extinguishing agent metal fires can be targeted deleted, which was not possible until today. Especially for personnel on production machines, it is now possible to spontaneously extinguish fires of metal shavings, etc. as quickly as possible and accurately. Thus, the ever present in metal fires always existing danger is effectively countered that located nearby other machines or plants are also set on fire due to the high combustion temperatures of the metals, because so far with metal fire extinguishing these fires could not be effectively deleted.

By using the liquid extinguishing agent eliminates the hitherto when using extinguishing powder very problematic heavy contamination of manufacturing machinery and equipment, so far the major downtime and cleaning work of manufacturing machines can be largely avoided.

Claims (9)

1. A process for extinguishing metal fires by applying an extinguishing agent to the seat of the fire, characterised in that a totally water-free liquid extinguishing agent is used which reacts with the burning metal while binding the air oxygen and forming a non-flammable compound, and that the liquid extinguishing agent is applied to the seat of the fire substantially from above in the form of a multiplicity of fine jets of the extinguishing agent.
2. The process according to claim 1, characterised in that polydimethylsiloxane is used as the liquid extinguishing agent.
3. The process according to claim 2, characterised in that the liquid extinguishing agent also contains a proportion of solids such as melamine and/or boron in a proportion of up to approx. 10 %.
4. The process according to claim 2 or 3, characterised in that the liquid extinguishing agent also contains perfluoropolyether.
5. A fire extinguisher for carrying out the process according to one of claims 1 to 4, which fire extinguisher has an extinguishing gun (1) with a nozzle head (2, 3) having a plurality of small outlet nozzles arranged adjacent to one another, which generate substantially parallel fine jets of extinguishing agent.
6. The fire extinguisher according to claim 5, wherein the extinguishing head (2) is an approximately tubular body with an approximately flat end piece (3) protruding from the extinguishing gun (1), in which the nozzles are arranged on one side so that the extinguishing agent jets emerge approximately perpendicular to the orientation of the end piece.
7. The fire extinguisher according to claim 6, characterised in that the end piece (3) of the tubular extinguishing head (2) is angled slightly upwards in relation to the remaining tubular body of the extinguishing head (2).
8. The fire extinguisher according to one of claims 5 to 7, characterised in that the working pressure is approximately 10 to 34 bar.
9. The fire extinguisher according to one of claims 5 to 8, characterised in that it is a refillable pressure device having a container for the liquid extinguishing agent, said container having for the liquid extinguishing agent a separate filler opening that can be closed pressure-tightly.

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