NZ250329A - Fire extinguishing method using flame suppressing aerosol formed by burning synthetic solid fuel with oxygen - Google Patents

Description

25032ft No.: Date: Priority Date(s): Complete Spcc^ci'.lcn Filed: Cf^ss: . (L ftW^"W:tcR Publication Date: .. .^ .®! P.O. Journs!, No: .. IW£...

NEW ZEALAND PATENTS ACT, 1953 ^ v " 5 JAN 1995 COMPLETE SPECIFICATION A METHOD FOR FIRE EXTINGUISHING We, UUBERETSKOE NAUCHNO-PROIZVODSTVENNOE OBIEDINENIE "SOJUZ", of Russian Federation, Moskovskaya oblast, Dzerzhinsky, uiitsa Sovetskaya, 6, Soviet Union hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- - 1 -(followed by page la) 0 3 2 & - 1fc- A METHOD FOR FIRE EXTINGUISHING The present invention relates to fire prevention equipment and, more specifically, it relates to a method for fire extinguishing.

Most efficiently the present invention can be applied in extinguishing fire 5 catching the enclosed space, e.g. the industrial and civil premises, means of transport etc.

At present frequency of fire incidents increases in proportion to extensive growth of industrial potential. Particularly affected are chemical and gas-and-oil processing industries where accidental blowouts or escapes of the easily inflammable or 10 combustible fluids and gases threaten to explode. Just as worrisome is the fire threat to timber and coal industries.

For centuries fires have been most ravaging at sea. Almost 30 % of all marine accidents are the result of devastating fire. Effective fire fighting has become an urgent problem of safety in navigation.

The prior art method for fire extinguishing relies on supply or delivery into the combustion zone off the gaseous galoid compounds (Halon) which by their fire extinguishing and operational characteristics belong to the group of toxic and ozone-destructing chemicals.

By 2000, their use will have to be totally banned or phased out in accordance 20 with landmark Montreal Protocol (1987) for the protection of the earth's stratospheric ozone layer.

Hence it is necessary to provide an ecologically pure method for fire extinguishing that does not wipe out ozone, and avoids the toxic effects in living beings.

Partly, this problem is solved by the known fire extinguishing method which is ecologically pure (A. N. Baratov, E.N. Ivanov, "Pozharotushenie na predpriatiyakh khimicheskoi i neftepererabatyvayuschei promyshlennosti", 1979, Khimiya, [Moscow], p. 347), comprising supply or delivery into the combustible zone of the gaseous substances or agents that are inert in relation to chemical reactions in the combustion 30 zone, and reduce oxygen content in the air, and also bring down, by consuming a certain amount of heat, the flame temperature below the critical level at which the combustion process discontinues. These agents are represented by carbon dioxide CO2, water vapor H2O, nitrogen N2, and noble gases described as thermal ballasts. The mechanism of their fire extinguishing action is practically the same, while their 35 quantities required for fire extinguishing depend on their thermal and physical aspects based on different values of thermal capacity and conductivity.

Nitrogen, for instance, is used to suppress burning of materials which react with Halons and water with explosion. Carbon dioxide and water vapor are used when halons are economically disadvantageous. 7 ' ~ '—"— j - 5 JAM 1995 I | (N:\LfflP (00069:cg " I 250329 Given the inert relation of the agents to chemical reactions in the combustion zone, their relevant fire extinguishing mass concentration is considerably higher than that of Halons, which explains why the use of such fire extinguishing compounds has become limited in its applicability.

Few years later, widely employed among the known techniques was the method for volumetric extinguishing of fire based on the fire extinguishing powders (A. N. Baratov, L. P. Bogman, "Ognetushaschie poroshkovye sostavy", 1982, Stroizdat [Moscow], pp. 60-62).

What is implied by the volumetric fire extinguishing is the creation in a limited 10 volume, e.g. a room, a hold, a shop etc. (hereafter referred to as "the protected volume") of a medium that does not feed fire. This is secured by supplying the gaseous agents or aerosols into the protected volume, and their uniform dispersion therein in quantities providing such level of concentration at which both combustion and explosion are impossible. By the zone of combustion is meant a portion or division of space 15 occupied by the visible flame, wherein there happens the chemical process, namely, the interplay or engagement of gaseous agents, i.e. the products of decomposition by fire of the primary materials, with environmental oxygen.

The known method is obtained by supplying into the combustion zone of a medium in the form of powder conveyed by gas under pressure. The compressed 20 powder once ejected, constitutes aerosol that enwraps or encompasses and ultimately suppresses the flame, which is achieved by way of inhibiting the chemical reaction of burning with the help of powder fractions. According to contemporary perceptions, the mechanism of fire extinguishing operation performed by aerosol, contemplates annihilation of the "active centres"" that are responsible for the combustion process 25 generation at conflagration site, on the surface of solid fractures of aerosol. Those "active centres" are represented by atomic particles or molecular fragments (radicals) having free valence, in which case there unfold the branched chain reactions, typical of the combustion process. However, this method for fire extinguishing has limited application due to relatively low dispersiveness of powders. For this reason, it 30 becomes difficult to provide uniform dispersion and continued suspension of the powder aerosol fractions in the protected volume.

Since the powders are manufactured beforehand and are kept for a long time under the compressed gas pressure, they are subject to lumping and coagulation which stand in the way to formation of highly dispersive aerosol to be supplied into the 35 combustion zone. Coarse-grained dispersive powder reveals insufficient fire extinguishing capacity, compared to that of "Halon".

It is an object of this invention to provide a method or fire extinguishing based on suppression of the chemical reaction of burning through re-alignment or re- |N:MIBP100069xg 250329 combination of the flame "active centres" by means of the heterogeneous aerosol particles.

The concept of this invention is accomplished by that supplied into the combustion zone is a medium which interaction or engagement with the flame causes its localization and suppression, said medium being in the form of an aerosol created by burning a synthetic solid fuel which contains oxygen.

Execution of the proposed fire extinguishing method provides suppression of chemical reactions taking place in the combustion zone. A distinguishing feature of aerosol produced by fuel combustion is in its high dispersiveness with particle size of less than 2 mm, which secures large surface of their engagement with the "active centres".

As is known, the "active centres" are represented by atomic particles or radicals having free valence, enabling development of the branched chain reactions, typical for homogeneous combustion. When the "active centres" strike the particles, they are adsorbed by the latter on their surface. In the course of engagement of the particle matter with an "active centre" the latter re-aligns and turns inert. Energy released during this re-alignment or re-combination of the "active centres", is assimilated by the particles prohibiting dissociation of molecules formed as a result of the "active centres" re-combination. And this helps suppress the combustion process.

Aerosol which is produced by fuel combustion is finely dispersive. Kence, the number of particles per cubic measure of medium increases, thus raising the frequency of particles striking the "active centres".

To determine the mass of synthetic fuel with oxygen content the following formula is useful: M = K x V, where V - volume of the combustion zone in cubic meters K - concentration of aerosol in the combustion zone, K = 0.010 - 0.2 kg/cu.m.

The relationship was obtained on the basis of test records.

K value depends on qualities of material set on fire, and also it depends on architecture and hermetic sealing of the protected volume, e.g. an office, a store, a workshop, an aircraft, a vehicle etc. With K < 0.01 kg/cu. m, fire extinguishing is not guaranteed because the summation surface of aerosol particles is inadequate to remove the "active centres". With K = 0.01 -0.2 kg/cu. m, these "active centres" are removed from the flame by aerosol particles. With K > 0.2 kg/cu. m, solid fuel expenditure is essentially inefficient.

It is necessary that aerosol contains oxides or carbonates or phosphates of metals or their mixtures. It has been established by experiment that the said compounds are remarkably "akin" to the "active centres", which means that frequency of the (N:\UBP|00069:cg 250329 O i— LO ; o* r~. ;m l> ;5^ i IJ ;lO 1 ;"active centres" re-alignment in relation to the said compounds is high. In other words, the chain reactions of combustion are interrupted more often. Hence, to suppress the combustion process, smaller amount of aerosol will be required. ;It is preferred that the metals are selected from group I of the periodic system 5 (law) because their compounds are less toxic, abundantly present in nature, comparatively cheap, and, as stated, remarkably "akin" to the "active centres". ;Highly dispersive aerosol needs cooling before it is supplied to the combustion zone. At lower temperatures aerosol requires less time to suppress fire because in this case the process of balancing or equalizing the irregularity of aerosol concentration in 10 relation to a height off the protected volume, is accelerated, said irregularity being caused by elevating power existing by virtue of aerosol and environment temperature difference. ;Aerosol is cooled down to below critical temperature of conflagration or blasting of the explosive gas mixtures. It is recommended to perform cooling at a rate 15 of at least 400 degrees per second. ;When the cooling of aerosol is done at a rate > 400 degrees per second, it remains highly dispersive for several tens of minutes due to suppression of coagulation, which results in greater efficiency of fire suppression. It is preferred that introduced into aerosol should be such gaseous medium that is inert in relation to the combustion 20 process, selected from the group of C02, N2, H20, He, Ar, or their mixtures in proportion to mass of at least 1:30. ;As a result, owing to the fact that oxygen content in the combustion zone is brought down as the inert medium is supplied into the said zone, the synthetic fuel mass with oxygen content, which is used to suppress fire, reduces. ;25 The object of the present invention will become more fully apparent from the following description of its particular embodiments and accompanying drawing, wherein: ;Fig. 1 is a schematic longitudinal section of the chamber in which diesel oil combustion and fire extinguishing process take place according to the invention; 30 Fig. 2 is a diagrammatic representation "a" of time-measured temperature curve of diesel oil combustion, and similar representation "b" of time-measured temperature curve related to combustion of solid fuel with oxygen content, having mass of 1.230 kg; ;Fig. 3 is a diagrammatic representation "a" of time-measured temperature 35 i curve of diesel oil combustion, and similar representation "b" of time-measured temperature curve related to combustion of solid fuel with oxygen content, having mass of 2.370 kg; ;Fig. 4 is a diagrammatic representation "a" of time-measured temperature curve of diesel oil combustion, and similar representation "b" of time-measured t ;J ;(N:\UBP100069:cg ;250329 ;- 5 ;»r> ;cr: ;*3 temperature curve related to combustion of solid fuel with oxygen content, having mass > 2.370 kg.

EMBODIMENT I A method for fire extinguishing according to the invention was accomplished 5 in a special chamber 1 (Fig. 1) having volume of 60 cu. m, which is representative of conventional premises intended for fire protection. Inside chamber 1, there is a drip cup or pan 2 filled with diesel oil, having combustion surface of 1 sq. m, and placed on support 3. Incandescent filament 4 serves to ignite diesel oil. Inside chamber 1 hold, placed on slip (stapel) 5 there is an aerosol generator which comprises a cylindrical 10 body 7 with orifice 8, containing solid fuel with oxygen content, for instance, in the form of cylinder. Incandescent filament 10 provides ignition of solid fuel 9. Walls 11 of chamber 1 are made of reinforced concrete. To imitate deficiency of hermetic sealing, there is a metal gate 12 which can be moved in the longitudinal direction in order to ensure variable entrance area of the ventilating clearance 13. Temperature 15 levels in zone 14 of diesel oil combustion are controlled with the help of thermocouples (not shown in diagram), said thermocouples being used also to control aerosole temperatures (not shown in diagram).

To determine the required aerosole concentration in the given volume in order to ensure fire extinguishing at the combustion site, the solid fuel mass quantities were 20 varied. Voltage applied to incandescent filament produced conflagration and burning of diesel oil placed in drip pan 2. Once the combustion process becomes steady, say in 20 seconds, voltage is applied to incandescent filament 10 to ignite solid fuel 9 having mass of 1.230 kg on the physical scale. Aerosol generated by fuel 9 combustion is mixed with air and fills up the whole volume of chamber 1. Upon termination of the 25 generator 6 operational period, the suppression of flame in zone 14 of diesel oil combustion could not be achieved, as is evident from diagrams "a" and "b" (Fig. 2): both representing a curve that crosses axis (t) of abscissae at two points. Points al, a2 correspond to the beginning and the end of diesel oil combustion, while points bl, b2 reflect the beginning and the end of burning the solid fuel with oxygen content. Time 30 consumed till termination of diesel fuel combustion (point a2) essentially exceeds that of solid fuel burning (b2) which corresponds to the period of its complete burn-down. In this case, aerosole concentration equals 0.020 kg/cu. m, which is inadequate to extinguish fire because the summation surface of its particles have turned out to be incapable of removing the "active centres". Then the solid fuel mass was increased. 351 With 2.370 kg mass of solid fuel, the flame in zone 14 of diesel oil combustion was localized and suppressed. Point a2 and b2 on abscissae axis coincided (Fig. 3) reflecting the termination of diesel oil and solid fuel combustion. Aerosole combustion in this case reached 0.040 kg/cu. m. ; i j io j i (N:\U8P|00069:cg 250329 In consequence of the above examination it may stated that this concentration of aerosol is adequate for fire extinguishing. Aerosol which filled the measure of chamber 1 (Fig. 1) has the following composition: gaseous oxygen (O2), nitrogen (N2), carbon dioxide (CO2), water vapor (H2O), and condensed particles of sodium chloride (NaCl) and sodium carbonate (Na2C03), said particles not exceeding 2 mm. The "active centres", namely atoms and radicals O, H, OH, CO responsible for combustion process development, descend on the surface of the said condensed particles and interact or engage with them; in which case there are created molecular particles that are incapacitated for the work function of the combustion "active centres".

Further concentration of aerosol in chamber 1 affords faster suppression of fire in the combustion zone. As is shown in diagrams "a" and "b" (Fig. 4), point a2 which represents the time of termination of diesel oil combustion, is placed on abscissae axis nearer to the point of reference than b2 which corresponds to the time of termination of solid fuel burning. This indicates that higher concentration of aerosol > 0.040 kg/cu.m results in excessive expenditure of solid fuel with oxygen content.

EMBODIMENT H A method according to the invention is applied in view of fire, for instance, in the machine-room of a watercraft due to oil conflagration. In its enclosed volume, synthetic solid fuel is burnt to generate aerosol filling the measure of the machine-room. The solid fuel is in the form of pots placed in the machine-room, their mass being calculated on the basis of formula; M = K x V, where V - volume of the combustion zone, e.g. 1300 cu.m; K - aerosol concentration, e.g. 0.040 kg/cu.m.

Fuel is inflamed either with ignition device placed in each shop with pots, or from the fire source itself.

Aerosol which filled the measure of the machine-room has the following composition: gaseous oxygen (O2), nitrogen (N2), carbon dioxide (CO2), water vapor (H2O), and condensed particles of potassium chloride (KC1), sodium chloride (NaCl), sodium carbonate (Na2C03), potassium sulphate (K2SO4). The "active centres", namely atoms and radicals O, H, OH, CO responsible for combustion process development, descend on the surface of the said condensed particles and interact or engage with them; in which case there are created molecular particles incapacitated for the work function of the "active centres". Energy released during the re-alignment or re-combination of the "active centres", is assimilated by the particles prohibiting dissociation of molecules formed.

The above process affords suppression of fire in the machine-room. In this case, oxygen content which is filled up with aerosol, practically does not diminish, and so there is no impact against respiration.

(NVUBPl00069:cg 25032 EMBODIMENT III Another embodiment of the invention is obtained by cooling aerosol before it is supplied to chamber 1, say down to 900 K by means of its ingression/passage through the familiar heat exchanger. The volume of chamber 1, the dimensions of drip pan 2 with diesel oil contained therein, the quantity of solid fuel 9 with oxygen content (2.370 kg) as well as the procedure followed to inflame diesel oil and extinguish fire are similar to those in embodiment I.

The distinguishing feature lies in the fact that during the supply of cooled aerosol having greater density of gas run (phase) into the said chamber 1, the process of balancing or equalizing the aerosol concentration in relation to a height of the said chamber is accelerated. As a result, the flame in the combustion zone 14 is getting suppressed 9 seconds earlier than in embodiment I (Fig. 3).

EMBODIMENT IV A method for fire extinguishing is accomplished according to this invention in chamber 1 (Fig. 1) equipped with a supply system which is inert in relation to the process of gaseous medium combustion, e.g. nitrogen. The procedure of aerosol delivery is same as in embodiment I. The distinguishing feature is afforded by the medium set on fire which is represented by isopropylalcohol having mass of up to 32 kg. Time required for complete burn-down is 20 minutes. To extinguish the same only by nitrogen N2, 20 kg of niiiogcr. will have to be supplied to chamber 1. In order to extinguish the burning isopropylalcohol in chamber 1 by aerosol only, said aerosol should be generated by combustion in chamber of solid fuel with oxygen content, having mass of 2.5 kg. Within 5 seconds of alcohol ignition, when the flame becomes steady, first the highly dispersive aerosol generated by combustion of solid fuel with oxygen content, is supplied, then, in 10 seconds. - gaseous nitrogen N2. 11 kg for 1.5 seconds. Owing to nitrogen N2 delivery, the concentration of oxygen O2 in chamber 1 has come down. As a result alcohol combustion has terminated 22 seconds earlier than if the fire extinguishing were to be carried out only by aerosol. The required quantity of solid fuel has reduced to 1.26 kg. Accordingly, the fire extinguishing efficiency has grown two-fold.

!N:\UBP100069.cg

Claims (9)

250329 - S - WHAT/lfWE CLAIM IS 4MMS-

1. A method for fire extinguishing comprising supply into a combustion zone 14 of a medium such that engagement with flame causes localization and suppression of the latter, characterized in that the medium is represented by a aerosol 5 created by burning an synthetic solid fuel with oxygen content 9.

2. A method for fire extinguishing according to claim 1, characterized in that the mass of said synthetic solid oxygen-containing fuel 9 is determined by formula:

M = K . V, where V = volume of the said combustion zone 14/in and K = concentration of the said aerosol in the said combustion zone 14, K = 0.010 - 0.2 kg/cu.m. io 3. A method for fire extinguishing according to claim 1, characterized in that the aerosol includes oxides or carbonates or chlorides or sulphates or phosphates of metals or their mixtures.

4. A method for fire extinguishing according to claim 3. characterized in that metals are selected from group I of the periodic system. 15

5. A method of fire extinguishing according to claims 1, 3, 4, characterized in that the aerosol is cooled before it is supplied to the combustion zone 14.

6. A method for fire extinguishing according to claim 5, characterized in that aerosol is cooled down below the critical temperature of inflammation or blasting of explosive gas mixtures. 20

7. A method for fire extinguishing according to claim 5, characterised in that the aerosol is cooled down at a rate of at least 400 degrees per second.

8. A method for fire extinguishing according to claim 1, characterized in that introduced into the aerosol is a gaseous medium that is inert in relation to the combustion process, selected from the series of C02> H^O, He, Ar, or 25 their mixtures in proportion to mass of at least 1:30.

9. A method for fire extinguishing when performed substantially as herein described with reference to any example thereof. D.-Tr".1 T'r'iS D£V OF y—*9 : V-W — r J AC—Ni t o rOri Tine APPLlCAiSl fS |N:\ueP)00069;C9