RU2019214C1 - Method of volumetric fire extinguishing by extinguishers - Google Patents

Abstract

FIELD: fire extinguishing. SUBSTANCE: method involves providing inhibitory action of surface of condensed aerosol phase on flame, with aerosol being produced in the process of combustion of solid fuel; preliminarily placing solid fuel in volume to be protected so that additional displacers and extinguisher conveyance devices are not required. Solid fuel may be ignited by fire initiator as well as by special igniting device. When specific fire extinguishing system based on solid fuel is designed, solid fuel weight is determined in accordance with formula M=K V, where K≥ 10 g/m³ is fire extinguishing concentration of solid-fuel aerosol composition; V is volume of object to be protected. Fire extinguishing effect may be increased by cooling solid fuel combustion products. EFFECT: increased efficiency and enhanced reliability in operation. 3 cl, 2 tbl, 4 dwg

Description

 The invention relates to fire fighting equipment, mainly to preventing and extinguishing a fire in a confined space. In modern fire extinguishing, volumetric extinguishing is based on creating an environment in the protected volume that does not support combustion. Inert extinguishing agents use inert diluents (carbon dioxide, nitrogen, argon, water vapor), volatile inhibitors - halogen-containing substances, powder extinguishing agents (A.N. Baratov, E.M. Ivanov Fire extinguishing at the enterprises of the chemical and oil refining industry. M: Chemistry, 1979, pp. 80-126).

 Known methods of volumetric extinguishing with inert diluents do not allow them to be used to extinguish alkali and alkaline earth metals, some metal hydrides and compounds in the molecules of which oxygen is included. When installing volumetric extinguishing systems, there are limited possibilities of the method for the size of the protected rooms (with a very large volume of the room it is difficult to supply the required amount of gas in an acceptable amount of time), it is necessary to take into account the possibility of injuring people caused by suffocation (signaling devices warning about putting the extinguishing system into operation are required )

 Quenching by halide-containing compounds (freons) has a number of disadvantages. These substances can have a toxic effect on humans, the products of their thermal decomposition, which are formed during fire extinguishing with chladones, are characterized by high corrosivity. In addition, the most fire hazardous areas are traditionally protected by powerful volumetric fire extinguishing systems that use freon. However, the implementation of international measures for the protection of the ozone layer of the Earth in accordance with the Montreal Protocol (1987) will require a reduction in the use of the said chladones as substances with high ozone-depleting potential by half by 1995 and a complete ban on their use by 2000.

 The main disadvantage of using fire extinguishing powders during volumetric fire extinguishing is their tendency to caking and clumping, while the ability of the powders to transport through pipelines and form a fire extinguishing cloud is lost. In addition, these formulations have high consumption rates.

A known method of extinguishing using a redox system and its burning energy for the evaporation of compounds of type C ₆ Br ₆ , and extinguishing action carried out by vapors containing bromine, and the dispersed phase is not used (US patent N 3972820, CL A 62 C 1/00 , 1976).

However, the known method of extinguishing does not provide a sufficient extinguishing effect, since vapors containing bromine rise and collect in the upper part of the protected volume due to the high temperature, thereby reducing the effect of inhibiting the combustion zone by these vapors, based on the removal of active centers from the reaction zone ( atoms and radicals) responsible for the development of the combustion process. The extinguishing concentration of the extinguishing agent carried out in this way is 128 g / m ³ .

 The aim of the invention is to increase the efficiency and simplification of the fire fighting process.

This goal is achieved by the fact that in the known method, based on the creation in a protected volume of a medium that does not support combustion, quenching is carried out by an inhibitory effect on the flame of the surface of the condensed phase of an aerosol generated by the combustion of solid fuel placed in advance in a protected volume and ignited from a fire or using a special incendiary device, and the mass of fuel burned is selected from the ratio
M = ^K. V
where V is the volume of the protected object;
K ≥ 10 g / m ³ - fire extinguishing concentration of solid fuel combustion products.

 In addition, the resulting aerosol can be pre-cooled.

 The condensed phase of the aerosol resulting from the combustion of solid fuel as a result of gravitational forces settles on the fire, which increases the effectiveness of the inhibitory effect on the flame. The main act of inhibition is the heterogeneous recombination of oxygen atoms and other radicals and atoms on the surface of aerosol solid particles.

Preliminary toxicological assessment of fire extinguishing concentrations of solid fuel (composition PAS-11) showed that the combustion products of PAS-11 at K = 40 g / m ³ in terms of toxic effects are lower than that of freon, and the environment formed during the extinguishing is characterized as portable.

 No technical solutions containing signs associated with the application of the effect of inhibiting the flame of a fire source by the condensed phase of solid fuel combustion products for volumetric fire fighting were found. A series of experiments was conducted under model and natural conditions in order to determine the fire extinguishing efficiency of the PAS-11 solid propellant aerosol composition, consisting of a mixture of potassium nitrate and potassium peroxide cured on an epoxy bond.

Model tests were carried out in a special chamber 1 (see Fig. 1) with a volume of 68 l, in which a cuvette 2 was located with a flammable liquid that was flammable by means of a spiral 3, and a sample of solid fuel 4, which was flammable from a spiral 5. Ignition and extinguishing processes were observed through transparent end cap 6 and controlled by thermocouples. Isopropyl alcohol (C ₃ H ₈ O) was used as fuel. The quenching time of alcohol was calculated from the moment the solid fuel sample was ignited until the flame disappeared above the cell. From experiment to experiment, the mass of a sample of solid fuel varied. The main test results are given in table 1.

Preliminary experiments showed that in a hermetically sealed chamber, the alcohol in the cuvette spontaneously extinguishes after 30-40 s due to oxygen burnout, in the presence of an air flow through the hole in the chamber end, stable combustion continued until the alcohol burned out completely, this happened after 120 s (experiment 1). Quenching experiments (experiment 2-5) with a change in the mass of solid fuel showed that the quenching time is 3-4 s. The extinguishing concentration was 40 g / m ³ or 3% of the mass of air in the volume, which is at the level of the best results obtained previously. At a concentration of less than 40 g / m ³ (experiment 5), the quenching of the burning site did not occur.

For experimental verification of the effectiveness of fire extinguishing by the combustion products of aerosol solid fuel under natural conditions, an aerosol generator and a special box (60 m ^{3 in} volume) were developed, which is close to natural premises to be protected from fire.

 The aerosol generator (see figure 2) consists of a housing 1, an output nozzle 2, an igniter 3. The aerosol generator is equipped with a charge 4 of individual pieces of a fire extinguishing composition. Depending on the number of pieces, the charge mass may vary. Ignition comes from an electric coil.

Boxing (see figure 3) for field testing is a room with dimensions of 3x3, 6x6 m and has a ventilation hole 1 with a changing area. The size of the volume and the lack of complete tightness brings it closer to the full-scale premises, in which it is necessary to prevent or extinguish fires in real conditions. Combustion center 2, in this case a pan with alcohol, had a combustion surface of 1 m ² and was ignited by an electric spiral 3. The aerosol generator 4 was ignited by an electric spiral. In the box, temperature sensors were installed to assess the distribution of temperature in the volume. The process of burning and extinguishing was recorded by filming and the readings of thermocouples installed in the alcohol combustion zone and the aerosol generator.

A typical curve of the temperature of the combustion zone (curve a) and the combustion products of the aerosol generator (curve b) is shown in Fig. 4. It can be seen that after the stationary combustion process T ₁ = 20 s was established, a signal was sent to ignite the aerosol generator. Upon reaching the concentration of solid fuel combustion products required for extinguishing, the flame of the combustion zone fades and its temperature drops at time T ₂ = 40 s. The difference T ₂ -T ₁ = T _t determined the time of extinguishing the flame.

 The test results in a box with different mass of the generator charge are given in table 2.

From the data given in Table 2 (experiments 1-5), it is seen that the minimum fire extinguishing concentration of solid fuel combustion products required for extinguishing is 40 g / m ³ , which is on a par with model experiments in a volume of 68 l. It should be noted that the efficiency of fire extinguishing by solid fuel combustion products is significantly increased if they are pre-cooled (for example, with an inert gas - nitrogen). The nitrogen consumption in experiment 6 was 2.2 kg / s, while it was found that the minimum concentration of combustion products for extinguishing decreased by 2.5 times and amounted to 20.5 g / m ³ .

From experiments it was found that when developing a specific solid-fuel fire extinguishing system, the mass of solid fuel is determined by the formula
M = ^K. V
where K ≥ 10 g / m ³ - fire extinguishing concentration of fire extinguishing solid propellant aerosol composition;
V is the volume of the protected object.

Using the proposed method of volumetric fire extinguishing with solid fuel aerosol formulations provides an increase in extinguishing efficiency compared to the existing method (the possibility of obtaining a fire extinguishing concentration of 40 g / m ³ at 128 g / m ³ in the prototype). The absence of gases harmful to human life in the products of solid fuel combustion is confirmed by experimental verification. The absence of ozone-depleting substances in the combustion products of solid fuels is evident from the thermodynamic calculation of the composition of gases and the condensed phase below.

Gas phase, mol.% O ₂ 21.62 N ₂ 74.7 CO ₂ 1.6 H ₂ O 0.5
The condensed phase, wt.% KCl 0,17 K ₂ CO ₃ 1,43

Claims (3)

 1. THE METHOD OF VOLUME EXTINGUISHING OF EXTINGUISHING COMPOSITIONS, based on the creation of a medium in a protected volume that does not support combustion, characterized in that, in order to increase efficiency, the extinguishing is carried out by an inhibitory effect on the flame of the surface of the condensed aerosol formed during the combustion of solid fuel placed in advance in protected volume and flammable from the fire source or using a special incendiary device. 2. The method according to claim 1, characterized in that the mass of fuel burned is selected from the ratio
M = K
where V is the volume of the protected object;
K ≥ 10g / m ³ - fire extinguishing concentration of solid fuel aerosol composition.  3. The method according to claim 1, characterized in that the resulting aerosol is pre-cooled.

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