KARPYSHEV, Alexander Vladimirovich (Olimpiisky pr-t, 28-435 Moscow, 2, 12927, RU)
RYAZANCZEV, Nikolai Nikolaevich (ul. B. Akademicheskaya, 73-1-264 Moscow, 3, 12518, RU)
KARPYSHEV, Alexander Vladimirovich (Olimpiisky pr-t, 28-435 Moscow, 2, 12927, RU)
RYAZANCZEV, Nikolai Nikolaevich (ul. B. Akademicheskaya, 73-1-264 Moscow, 3, 12518, RU)
CLAIMS
1. A fire-extinguishing composition including an aqueous film-forming foam and an addition for suppressing a freezing temperature of the fire-extinguishing composition, is characterized in that a magnesium chloride hydrate is used as an addition, said magnesium chloride hydrate being in the form of an aqueous solution, the components being used in the following ratio in volume percents by the total volume of the fire-extinguishing composition: an aqueous solution of magnesium chloride hydrate - from 85 to 88 wt%, an aqueous film- forming foam - the balance, with the content of magnesium chloride in the fire-extinguishing composition making from about 15% to about 25% by weight of the fire-extinguishing composition.
2. A fire-extinguishing composition according to claim 1 is characterized in that an organofluoric acid based foam former is used as an aqueous film-forming foam.
3. A fire-extinguishing composition according to claim 2 is characterized in that a "PO-6A3F (3%)" foam former is used as a film-forming foam based on organofluoric acids. |
FIRE-EXTINGUISHING COMPOSITION
Field of the invention
The invention relates to the aqueous solutions of the foaming agents based on surface- active substances (SAS) and is designated for extinguishing combustible materials and highly flammable liquids in open areas as well as under conditions where high volume ignition sites are created in the rooms for storage of solutions at low temperatures (down to -35 0 C).
Background of the invention Various kinds of fire-extinguishing compositions are presently known. For example, it is known from the author's certificate SU 865303 (IPC-3: A62D 1/02, issued 23.09.1981) a foaming compound comprising an anionic surface-active substance, water, and an addition: a mixture of calcium chloride and magnesium chloride. The components being used in the following ratio in weight percents: 0.75% to 2.2% by weight SAS; 0.02% to 0.12% by weight calcium chloride; 0.005% to 0.04% by weight magnesium chloride, the balance being water. Addition into the composition of the mixture of calcium chloride and magnesium chloride reduces the fire extinguishing time and minimizes the consumption of the fire-extinguishing composition to thereby increase the fire-extinguishing efficiency of the composition as the whole. It is known from the description in the author's certificate SU 1780774 (IPC-5: A62D
1/00, issued 15.12.1992) a fire-extinguishing composition comprising a hydrated magnesium chloride. An increase in the fire-extinguishing efficiency is achieved in the prior art composition owing to the utilization of water-soluble polar liquids (alcohols, ethers, glycols, amines) for solving bischofite (a natural crystalline salt containing 88-99% by weight MgCl 2 -OH 2 O).
The given composition shows a high fire-extinguishing efficiency, however it may not be utilized for suppressing the fires when it had been stored under low temperature storage conditions. Moreover, because an extremely unstable film is produced, an oxidizer ingress from the environment to a burning surface takes place. It is not improbable that a reignition may occur.
A fire-extinguishing composition known from Patent RU 2157710 Cl (IPC-7: A62D 1/02, issued 20.10.2000) comprises 12% to 24% by weight a surface-active substance, 1.5% to 3.0% by weight a higher fatty alcohol of 6 to 12 carbon atoms, and water. In order to increase
the freeze resistance and reduce the corrosiveness, an ammonium acetate is introduced into the foaming composition in an amount of from about 10% to about 52% by weight.
It should be pointed out that an increase in the prior art composition of the content of ammonium acetate affecting the 'freeze resistance and the corrosiveness of the fire- extinguishing composition results in a reduction of foam stability and, correspondingly, a decrease in the fire-extinguishing efficiency of the foam generated.
Also known is the prior art the foam former (the author's certificate SU 1790421, IPC-5: A62D 1/00, issued 23.01.1993) containing 6.5% to 7.0% by weight a surface-active substance, 14.0% to 14.6% by weight an OH-based aluminum chloride, 30.0% to 36.5% by weight an ammonium acetate, and water (the balance). For extinguishing the fire sites, an aqueous solution is utilized which contains 2% to 3% by weight a foam former and 20% by weight a magnesium chloride. The fire-extinguishing properties of the composition are maintained upon storage of the composition under the low temperature storage conditions down to -32 0 C for extended periods of time. However, the OH-based aluminum chloride introduced into the composition, renders an increased corrosiveness to the given fire- extinguishing composition, whereby the fire-fighting equipment has a reduced service life.
It should be noted that the prior art fire-extinguishing compositions do not form a stable water film over the entire burning surface, said water film being intended for preventing access of oxygen to combustible materials and vaporization of volatile substances from the burning surface. As a result, the fire extinguishing process is insufficiently effective, and it is not improbable that a reignition and pollution of the atmosphere with toxic substances released during burning process may occur.
The prior art composition closest to the claimed invention is a fire-extinguishing composition described in an international application WO 0147604 (IPC-7: A62D 1/02, issued 05.07.2001). The prior art composition is prepared on the base of an aqueous film forming foam, whereto a 50-60%-aqueous solution of potassium acetate and ethylene glycol or propylene glycol is added in an amount of from 15% to 20% by weight for suppressing the freezing point of the solution. The composition does not freeze at a temperature down to - 5O 0 C. However, a film formation may occur on a burning surface only at temperatures of about -I 0 C. At lower temperatures the film is not generated on the burning surface.
The result is that in the process of extinguishing fire sites, volatile organic vapors evaporate into the atmosphere to cause pollution of the environment with toxic substances, and the access of oxygen to the burning surface leads to an increase in the fire extinguishing time, i.e., a decrease in fire extinguishing effectiveness of the composition.
Disclosure of the invention
The objective of the present invention is formation on the burning surface of a stable thermally resistant water film intended for preventing oxygen ingress from the atmosphere to the ignition site and vaporization of volatile substances from the burning surface into the environment. The fire-extinguishing composition should be stored and utilized without reduction in the fire-extinguishing efficiency in a wide range of low temperatures down to -35 0 C. The invention is further aimed at eliminating the possibility of precipitating the salts in the fire-extinguishing composition in case unpurified tap water is utilized in the process of preparing the solution. The technical result achievable through the implementation of the present invention involves an increase in the efficiency of extinguishing the ignition sites by means of a low- expansion foam and a decrease in the time of extinguishing the ignition sites, when a foam- forming composition is kept at low temperatures (down to -35 0 C), both on horizontal and vertical surfaces due to the generation of a cooling thermally resistant water film and an increase in the hydrostatic stability of the foam.
The given technical result is achievable through the employment of a fire-extinguishing composition including an aqueous film forming foam and an additon designed for suppressing a freezing temperature of the solution. According to the present invention, a magnesium chloride hydrate in the form of an aqueous solution is used as an addition, said components being used in the following ratio in volume percents of the total volume of the fire- extinguishing composition:
- 85% to 88% aqueous solution of magnesium chloride hydrate,
- aqueous film forming foam the balance.
The content of the magnesium chloride in the fire-extinguishing composition makes from about 15% to about 25% by total weight of the fire-extinguishing composition.
Organo fluoric acid based foam formers such as, for example, "PO-6A3F", "Light Water", "Sthamex-AFFF" and other similar foaming agent may be used as aqueous film forming foam.
During extinguishing of the fire sites with the use of the claimed composition, the foam delivered from a fire-extinguisher is fed to the burning site to flow down and form on the burning surface a water film covered from above with a foam emulsion. The film generated on the burning surface is adapted for sealing the surface from the fuel vaporization and ceasing the access of an oxidizer to the surface of the burning liquid. The film also facilitates in
cooling of the fire site surface. The result is that the flame extinguishing process is intensified and, accordingly, the fire extinguishing time is reduced.
The film forming foam former in conjunction with the aqueous solution of magnesium chloride hydrate at a predetermined percent content of said components enables the fire sites to be effectively suppressed owing to the stabilized generation of a film on the burning surface, when the composition is kept under low temperature conditions.
Preferable examples of embodiment of the invention
In order to produce a fire-extinguishing composition, an aqueous solution of magnesium chloride hydrate should be preliminarily prepared, said solution having a density of 1.21d=0.01 g/cm 3 and a volume no more than 300 /. The salt solution is mixed in a mixing reservoir furnished with an agitator, Prior to preparing the aqueous solution, unpurified tap water and a magnesium chloride hydrate are fed into the mixer. The water is initially fed into the mixer in an amount of M H 0 , with following feeding of the magnesium chloride hydrate (for example, magnesium chloride hexahydrate MgCl 2 -OH 2 O). The magnesium chloride hydrate and the water are fed in approximately equal parts:
M MgCl 1 6H 2 O K ^H 2 O > where M MsCli 6Hi0 is the weight of magnesium chloride hydrate, kg; M H 0 is the weight of water fed, kg. The desired component ratio in the solution is provided by weight dosing. The volume of the aqueous solution of magnesium chloride hydrate to be prepared is calculated from the formula:
T/ _ MgCl 2
QH 1
O H 2
U ^ H 2
O ^ ■, η yr v -n p ~ 1,21 ~ ' H
'° L J
' where
M MgC ι 2 &H ^ 0 « M Hi0 is the weight of the magnesium chloride hydrate, kg;
M H 0 is the weight of water fed into the mixer, kg.
It is also permitted that the aqueous solution of magnesium chloride hydrate be prepared with the use of a volumetric method for dosing of the components used. In this case, the water is initially fed in a volume of V w 0 « 0,626V (V is a full volume of a solution to be obtained).
The magnesium chloride hydrate is then fed until a full volume V of the solution is reached.
This method is, however, connected with the need for precise maintaining the water temperature and the temperature of the magnesium chloride hydrate in the range of 18±2°C.
The component composition of the magnesium chloride hydrate was checked by determining the density of the obtained solution with the help of an aerometer. An average density of the solution was determined on the basis of the results of three measurements. The measurement error should constitute ±0.01 g/cm 3 , i.e., the density of the resultant aqueous solution of the magnesium chloride hydrate should be within in range of (1.2 to 1.22) g/cm .
After producing a required amount of the aqueous solution of magnesium chloride hydrate, the fire-fighting equipment is to be charged, with fire-extinguishing apparatuses, portable fire-extinguishing units, mobile fire-extinguishing installations, and the like being used as fire-fighting equipment. To do so, 85% to 88% of magnesium chloride hydrate solution (by the total volume of composition) is initially fed into a reservoir to be charged, with following adding, respectively, 12% to 15% of the preliminarily prepared aqueous film- forming foam. Such a succession of feeding the components to be mixed allows foaming of the solution in the fire-extinguisher reservoir to be decreased. The magnesium chloride content in the fire-extinguishing composition is maintained in the range of (15 to 25)% by total weight of the fire-extinguishing composition.
Various prior art foam formers such as "Sthamex-AFFF 3%" (the manufacturer is German company "Dr. Sthamer-Hamburg"), "PO-6A3F" which may be used in three modifications: "PO-6A3F (1.5%)", PO-6A3F (3%)", and "PO-6A3F (6%)" (the manufacturer is Russian Closed Joint Stock company "EGIDA-PTV"), "Light Water" (the manufacturer is USA company "3M") and other similar film forming foam formers may be used as aqueous film forming foam formers.
Before utilization, the fire-extinguishing composition was kept within 30 days at a temperature of -35 0 C. The efficiency in extinguishing the fire sites carried out with the use of the given fire-extinguishing composition is supported by the examples which follow.
Example No 1
For charging a 6 / volume fire-extinguisher, a film forming foam former in an amount of 0.8 / (6 / x 0.133) and an aqueous solution of magnesium chloride hydrate in an amount of 5.2 / (6 / x 0.867) were utilized. In order to obtain 5.2 / of the aqueous solution of magnesium chloride hydrate, 3.25 kg of unpurified tap water and 3.042 kg of the magnesium chloride hydrate (MgCl 2 -OH 2 O) were initially fed into the mixer. The desired component ratio in the solution was provided by weight dosing. The accuracy of the aqueous solution of magnesium
chloride hydrate with regard to a desired component concentration was checked by measuring the density of the resultant solution with the help of an aerometer. The density of the produced solution was 1.21 g/cm 3 .
The resultant 5.2 / of the aqueous solution of magnesium chloride hydrate were then charged into the fire-extinguisher (86.7% by total volume thereof) and 0.8 / of a aqueous film- forming foam was added. In the example under consideration a synthetic fluorinated film- forming "PO-6A3F (3%)" foam of Russian manufacturer (a Closed Joint Stock company "EGIDA-PTV") was used in accordance with the Specification TU 24 1279-002 -49888 190- 98. The given foam former is characterized as an incombustible, explosion-proof, moderately hazardous substance of the 3 rd class hazard according to the Standard GOST 12.1.0007. No flash temperature exists in an open crucible. A spontaneous ignition temperature is above a boiling temperature.
The "PO-6A3F" (3%) foam former has the following properties: 1. the outer appearance - a homogeneous liquid free of precipitate and breaking;
2. the density at the temperature of 2O 0 C from 1 ,000 to 1 ,200 kg/m 3 ;
3. the kinematic viscosity at the temperature of 2O 0 C no more than 200 mm 2 /s;
4. pH = 6.5 ... 10.0;
5. the degree of expansion of the low-expansion foam used with water no more than 20;
6. the hydrostatic stability of the low-expansion foam used with water more than 60 s;
7. the time for extinguishing of n-heptane with the low-expansion foam at the intensity of feeding a working solution (0.059±0.002) //(m 2 -s) no more than 120 s.
The fire-extinguishing composition obtained had the following characteristics: - the content of magnesium chloride in the fire-extinguishing composition 20.6% by weight of the composition;
- the degree of expansion of the foam 10;
- the hydrostatic stability of the foam 23 min;
- the time for extinguishing of n-heptane at the intensity of feeding the working solution (0.059±0.002)l/(m 2 -s) 35 s;
- the storage temperature for the fire-extinguishing composition -35 0 C.
As seen from the above listed characteristics, utilization of the claimed composition reduces the time of extinguishing the n-heptane in comparison with the pure foam former of
the "PO-6A3F (3%) grade at the identical intensity of feeding the working solution (0.059±0.002) Z/(m 2 -s).
In order to prepare the aqueous solution of magnesium chloride hydrate, the hexahydrate magnesium chloride MgCl 2 -OH 2 O was used. The fire-extinguishing composition did not exhibit salt precipitation. For the purpose of comparison, the initial solution of the "PO-6A3F (3%)" foam former grade free of additions was utilized.
For each experiment the foam was prepared by aerating 100 ml of the premix solution in a cylindrical steel reservoir within 20s. The resultant foam was supplied by means of a pressurized air through a pipeline from the reservoir onto the surface of a burning liquid (n- heptane). The foam flow rate was varied by changing the air flow rate.
Because the density of the foam former working solution does not substantially differ from that of water, it had been accepted in the course of experiments that the volume of the solution in liters was numerically equal to the weight thereof in kilograms. The weight of the consumed solution was defined by weighing the reservoir together with the foam before and after each of the experiments.
The comparison of the foam former solution comprising the aqueous solution of magnesium chloride hydrate and the premix solution of the "PO-6A3F (3%)" foam former was performed on the basis of the following criteria.
1. Degree of expansion is the ratio of a resultant volume of the foam to the total volume of the solution. The degree of foam expansion in the examples under consideration was defined as a ratio of the foam layer height in the reservoir to the foam former layer thickness in the reservoir before the foam was produced.
2. Hydrostatic stability. The hydrostatic stability was evaluated on the basis of the time during which 50% of the liquid was released from the foam. 3. Critical intensity of feeding the solution. The evaluation was based on the foam disintegration intensity under the fire extinguishing conditions.
The value of foam disintegration intensity was defined from the formula characterizing the dependence of the time for extinguishing of n-heptane in the reservoir upon the intensity of feeding the fire-extinguishing composition. The intensity J of feeding the solutions was calculated from the formula:
J = m 0 -m ]
S R r B
where mo H nij is the weight of reservoir with the foam before and after extinguishing the fire site, kg;
S R is the area of reservoir, m 2 ;
TE is the extinguishing time, s.
The extinguishing time X E depends upon the foam feeding intensity and hydrostatic foam stability ratio.
4. Extinguishing efficiency. The evaluation was based on the ratio of time and consumption of the fire-extinguishing composition for ceasing the burning process on the area unit of the fire site.
For evaluation of the extinguishing efficiency, the fire site extinguishing index P E1 was used:
1
1 P EI = ■ q s -τ τ where q $ is the specific flow rate of the solution, 1/m 2 ,
T T is the extinguishing time at the selected feeding intensity, s.
The obtained results are presented in the Table No 1.
Table No I
Example No 2
A 61 volume fire-extinguisher was charged with a fire-extinguishing composition comprising 5.28 / (6/ x 0.88) of the aqueous solution of magnesium chloride hydrate and 0.72/
(61 x 0.867) of the synthetic film-forming fiuorinated "Sthamex-AFFF (3%)" foam former delivered by German company "Dr. Sthamer - Hamburg". The "Shtamex-AFFF (3%)" foam
former is produced on the base of a surfactant - tenzide. The "Sthamex-AFFF" foam former is adapted for extinguishing of class A fires and class B fires by the virtue of creating a gas- tight film on the burning surface. The given foam former is stable and resistant to thermal radiation of combustibles having high content of polar additions such as alcohol. Depending on the desired quality, the foam former concentrate was mixed with unpurified tap water in the volumes of from 3% to 6%.
The foam former solution had the following characteristics:
1. the outer appearance - a homogeneous liquid free of precipitate and breaking ;
2. the hydrostatic stability of the foam 310 s; 3. the density at temperature of 2O 0 C 1,045 kg/m 3 ;
4. pH=6.5...8.5;
5. the degree of foam expansion 10;
6. the freezing resistance down to - 15 0 C;
7. the time for extinguishing of n-heptane at the intensity of feeding the working solution (0,059+0,002) //m 2 -s 79 s.
The aqueous solution of magnesium chloride hydrate was prepared in the manner similar to that of the example N° 1.
The obtained fire-extinguishing composition had the following characteristics:
- the content of magnesium chloride 25% by weight of the fire-extinguishing composition;
- the density of the resultant solution 1.22 g/cm 3 ;
- the degree of expansion of the foam 10;
- the hydrostatic stability 25 min;
- the time for extinguishing of n-heptane at the intensity of feeding the working solution (0.059±0.002)//(m 2 -s) 35 s.
The storage temperature for the resultant fire-extinguishing composition at which the composition kept its properties for an extended period of time was -35 0 C.
The resultant solution containing 25% magnesium chloride by weight of the fire- extinguishing composition was compared with the initial aqueous solution of the film-forming "Shtamex-AFFF (3%)" foam. The conditions for preparing the solutions to be compared and the evaluation criteria corresponded to those of the example Ns 1. The obtained results are represented in Table No 2.
Table No 2
Example No 3
A 61 volume fire-extinguisher was charged with 5.1/ (6/ x 0.85) of the aqueous solution of magnesium chloride hydrate and 0.9/ (6/ x 0.15) of the "Light Water" foam former solution based on fluorinated acids, the said foam former being delivered by American company "3M" (Minnesota Mining and Manufacturing Co).
The "Light Water" foam former is an aqueous solution of a liquid surfactant concentrate based on fluorine compounds, said solution being designed for producing of a stable foam layer on the burning liquid surface for sealing thereof.
The foam former free of magnesium chloride hydrate has the following characteristics:
1. the hydrostatic stability of the foam 4-5 min;
2. the density at the temperature of 2O 0 C (from 1.01 to 1.16) • 10 3 kg/m 3 ;
3. the kinematic viscosity at the temperature of 2O 0 C no more than 30-35 mm 2 /s; 4. pH=6.5...8.5;
5. the concentration of the working solution 3 to 6 wt%;
6. the surface tension 17.5 mN/m;
7. the degree of foam expansion 6 to 10;
8. the hydrostatic foam stability 5 min; 9. the time for extinguishing of n-heptane at the intensity of feeding the working solution (0,059±0,002)//(M 2 -S) 150 s.
The resultant fire-extinguishing composition including the magnesium chloride hydrate had the following characteristics:
- the content of magnesium chloride 15% by weight of the fire-extinguishing composition; - the degree of foam expansion 10;
- the hydrostatic stability 25 min.
The storage temperature for the obtained fire-extinguishing composition, at which the composition kept the fire-extinguishing properties for an extended period of time was -35 0 C.
The obtained solution containing 25% of magnesium chloride by weight of the fire- extinguishing composition was compared with the initial aqueous solution of the "Light Water" foam former free of additions. The results of the comparative analysis are represented in Table No 3.
Table No 3
As seen from the present comparative analysis (see Tables No 1 to 3), adding of the magnesium chloride hydrate (MgCl 2 -OH 2 O) did not affect the foaming capacity of the solution. The degree of expansion of the foam former provided at identical conditions did not change.
The investigations have shown that the low-expansion foam based on the aqueous solution of magnesium chloride hydrate, at other factors being the same, has a higher hydrostatic stability as compared to that of the initial foam former solution. It has also been found that the fire-extinguishing composition including the aqueous film-forming foam former and the magnesium chloride hydrate provides for a higher fire-extinguishing capacity characterized by a shorter time needed for extinguishing of n-heptane.
It has been found in the course of comparative tests that a maximal efficiency in the extinguishing of fire with the use of a foam, when an initial aqueous solution of a film-forming foam former of "PO-6A3F", "Sthamex-AFFF", "Light Water" or other grade foam formers free of additions were utilized, was achieved at a significantly greater feeding intensity than with the utilization of a fire-extinguishing composition including a foam former and an aqueous solution of magnesium chloride hydrate. The desired intensity of feeding an initial foam former solution is about twice as large as the intensity of feeding a composition including a foam former solution and a magnesium chloride hydrate. Furthermore, it has been found that the utilization of unpurified tap water for preparing of a fire-extinguishing composition did not result in the precipitation of salts at a prolonged storage of the composition within the fire-extinguisher under low temperature conditions.
It also follows from the experimental data obtained that the claimed fire-extinguishing composition keeps its excellent fire-extinguishing performance after a prolonged storage under low temperature conditions (down to -35 0 C) and may be used in fire-fighting equipment of various designation for extinguishing of highly flammable burning liquids and other combustible materials under various climatic conditions.