by Yevgeny ZHEGROV, Dr. Sc. (Tech.), head of department, SOYUZ Federal Center of Dual Technologies (town of Dzerzhinsky)
To begin with, it would clearly be no exaggeration to say that almost each and every scientific and technical innovation "pops up on the surface" in its own individual way. Some are the products of the combined efforts of whole teams of researchers, while others are a mere "stroke of good luck" and others still can best be described by a Russian saying which can be literally translated as "There would be no luck, had it not been for a stroke of bad luck." And here is just one case in point.
The late 1980s in this country saw the start of a campaign of conversion of what we call our military and industrial complex. It boasted a truly vast R&D potential by any standards and many of its factories and plants had no problems switching to non-military or what we call "peaceful" applications. One of them is now called the SOYUZ Federal Center of Dual Technologies (FTSDT) * . For more than half a century of its history its experts were engaged in R&D work on different types of gunpowder and solid rocket fuel (SRF). Studies of the SRF combustion mechanism proved that it can be intensified (catalyzed) with the help of various additives, or suppressed, or inhibited. The latter property was used in several types of nameless powders and SRF. With the start of the conversion campaign this latter phenomenon provided the basis for a very novel SOYUZ product-aerosol fire fighting systems. In the first half of the 1990s experts of the Center developed special compositions-on the basis of nameless artillery powder and rocket fuel- which produce, as they bum, aerosols with a high content of activated inhibitor. This new chemical substance helps extinguish fires.
A similar fire-fighting method on the basis of freon became very common at one time. It later turned out, however, that it is not effective enough and also affects the ozone layer of the atmosphere.
In their work on new fire-fighting methods Center experts were proceeding from two important factors. In the first place, most fires occur in the air and consume oxygen as oxidizer. Secondly, flammable materials as a rule mostly consist of carbohydrates which means that the decisive role belongs to the reactions of oxidation of hydrogen and carbon oxide. If and when these reactions are inhibited, the flame zone is suppressed and the combustion stops completely.
As it turned out, in the development of fire-fighting compositions
* See: "New Chapter of Old Glory" in the same issue. - Ed.
specialists were facing an even more complicated task than in the production of nameless powder. What was needed was not just to suppress the secondary reaction of combustion in the air of powder combustion products which were not fully oxidized, but to do away with flame completely.
Strange as this may be, flameless powder and fire extinguishing compositions have much in common and differ mainly by the levels of the inhibitor additives, which is only 6 percent in the first case and 60 to 70 percent in the second. And since these additives perform in every concrete case similar functions-suppressing the combustion reaction in the flame zone - they have identical chemical nature, being compounds of alkaline metals.
As a result of prolonged experiments, the authors of the new project picked up potassium nitrate (KNO 3 ) as their final choice. And now let us try and see what was behind this choice.
As has been mentioned already, combustion is a chain of consecutive chemical reactions. If this chain is broken, the process comes to an end. Getting into the flame zone, potassium atoms gain extra energy and undergo excitation (chemists would say that this metal has a relatively low ionization potential) and actively "intervene" into on-going reactions and thus break the chain. Apart from that, potassium nitrate is chemically compatible with powder, which means that side reactions take place between them which means that the mixture does not "deteriorate".
And there is one more point. For the aerosol to "go into action" its components must catch fire themselves - something that can happen only in the presence of oxygen. Sufficient amounts of it are present in potassium nitrate, and, apart from that KNO 3 is much less toxic than, let us say, chlorates or perchlorates.
In other words, the main conditions for the flame extinguishing mixtures were identified. They must contain maximum levels of inhibitor additives; all of their components should be non-toxic; their basic properties must be preserved over long periods of storage and in a broad range of temperatures. With all of these requirements being met, the new aerosols turned out to be very effective. For example, using them for putting out fires of such easily flammable liquids as benzine or acetone, a mixture concentration of only 0.02-0.03 kg/m 3 is quite enough, which is 10 times as effective as the best of freons. And low levels of carbon monoxide (CO) and NO and NO 2 in the products of combustion made it possible for biophysicists to refer these mixtures to the category of "low-risk" chemicals.
After that our experts faced another and no less difficult task of designing the appropriate fire extinguishers. The thing is that the aerosol produced has a very high temperature - about 1,500 0 to 1,700 0 C - and in putting out fires this should not be more than 250 0 to 300 0 C. The SOYUZ specialists solved this problem by using specially designed cooler attachments. They helped develop a whole family of what they called generators of fire extinguishing aerosols. These can be used for extinguishing burning gases, liquids, sold materials and even electrical equipment. And the aerosol itself possesses some important characteristics: it does no cause metal corrosion, does not harm to paper, fabrics or objects of art, and, strange as it may sound, even to foodstuff's (like grain, flower or farm fodder).
More than 30 types of such generators are available now, each with some specific design modifications. Depending on the applications, one can choose extinguishers with different charge volumes, rate of aerosol flow and jet direction (unilateral, bilateral, radial or multidi-
rectional). Such generators can be permanently attached to the protected objects (indoor premises, automobiles, railway cars, etc.) or can be thrown into a fire like a hand grenade or a mortar shell.
These units have a metal shell which contains one or several round charges of special aerosol material, an electric activator or a fire cord, and a solid cooler. Such charges can be "triggered" in several ways. First is known as thermochemical in which the generator is placed in such a way that one end of a polymer fire cord (rate of combustion 100-200 mm/sec) extends into the protected area. In case of fire it ignites as soon as the temperature exceeds 170 0 C and "activates" the device.
Another - thermoelectric mechanism, is based on the thermal effect of electric current of 6-36 V and 0.1-2 Amps which is fed to special charges that catch fire when heated. This method has made it possible to develop automatic fire extinguishers which respond to different kinds of signals, such as temperature, smoke, spectral changes, etc.
Finally, there is what we call the thermodynamic trigger mechanism used in generators of the "hand grenade" type. Used here are primer caps which are easily triggered off (by pulling out a ring).
At the present time the SOYUZ Center turns out 18 types of MAG aerosol generators and also PURGA generators of 13 types. Both of these units feature ecological "cleanness", rapid action (fire is put out in 5-10 sec) and high reliability The units boast simple design and their installation and operation do not cause any problems on the part of the user.
In the process of fire extinguishing there is practically no damage to the surface of the objects involved and any traces of sediments can be simply wiped off with a wet cloth or cleaned by a fire extinguisher.
The area of application of such generators is very wide. For example, MAG units with a high rate of flow of aerosol (operation time of 3-5 sec) are meant for uses on transport and objects with considerable losses of pressure. Another unit of the same model with the rate of aerosol escape of 1-1.5 kg/sec, are installed in large premises and the MAG-B units (with supersonic rate of discharge) we used for the fire protection of oil and gas wells. Installed on fuel supply lines they
can either prevent or localize an explosion.
Units of the PURGA type are meant for another range of applications. Since their one-second volume of aerosol discharge is 5 to 7 times less and the time of operation is longer in about the same proportion, they can be used on objects with low drops of pressure and low-strength structural elements (glass and partitions) which can collapse even at insignificant impacts.
All of these various models have small size and low weight. Five of them only weigh more than 15 kilos. The heaviest one is MAG-17 (weight of generator 55 kg, diameter - 490 mm and length-285 mm) and it can be used for the fire protection of premises of up to 140 m 3 .
The new fire extinguishers have all passed the standard tests and have received general approval as demonstrated by 30 Russian and international patents. They have been certified in the United States, Italy, Spain, Australia, Kazakhstan, Great Britain, Hungary and Cyprus and they are currently being used in Germany, China, Yugoslavia and Malaysia. These fire extinguishers won a Silver Medal at the 1993 Brussels Show "Eureka-93".
And the Russian experts, meanwhile, keep up their research in this important field. Some time ago specialists of the Center committed what they call a fire-and-blast retarder, or preventer.
This is a generator which sprays the aerosol through two side nozzles at supersonic velocities. Within a matter of seconds it can put out fire or prevent an explosion at any or both sides of some technical unit or equipment.
Tests have also been successfully completed of a modification of the MAG fire extinguisher for use on diesel railway engines and electric engines (TEP-70 and VL-65). A PURGA KO2-ZHG unit has been specially designed for new highspeed passenger trains of the SOKOL type. Another novelty is a revolver-type mobile generator with a set of aerosol cartridges which will keep "firing" until a fire is extinguished. Work is now in progress on extra powerful fire extinguishers on the basis of jet motors.
Prepared by Arkady MALTSEV
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