Patent Publication Number: US-6042664-A

Title: Aerosol-forming composition for the purpose of extinguishing fires and method for the preparation of this composition

Description:
This application is a division of 08,841,142 filed Apr. 24, 1997 U.S. Pat. No. 5,831,209. 
    
    
     The invention relates to fire-extinguishing technology, in particular the prevention and extinguishing of fires in confined spaces. 
     It is known, for the purpose of extinguishing a fire in a confined space, to create an atmosphere in this confined space which prevents combustion. As a fire-extinguishing agent inert thinning agents are used (carbon dioxide, nitrogen, argon, water vapour), volatile inhibitors, in particular halogen-containing agents, fire-extinguishing powders (A. N. Baratov, E. M Ivanov, &#34;Loschen von Branden in der chemischen und erdolverarbeitenden Industrie&#34;, Moskau, Chemie, 1979) [&#34;Extinguishing fires in the chemical and petroleum processing industry&#34;, Moscow, Chemistry, 1979]. 
     The known methods for the purpose of extinguishing fires in confined spaces using inert thinning agents cannot be used for extinguishing alkali and alkaline earth metals, some metal hydrides and compounds, which contain oxygen in their molecules. 
     In the development of systems for the purpose of extinguishing fires in confined spaces the possibilities are limited owing to the dimensions of the buildings which are to be protected (in the case of buildings with extremely large dimensions it is very difficult to be able to provide a sufficient quantity of gas in a given period of time). Furthermore the possibility of putting persons present in danger of suffocation must also be taken into consideration (therefore signal installations are necessary to indicate the deployment of the extinguishing procedure). 
     Extinguishing fires using halogen-containing compounds likewise has a series of disadvantages. These compositions can have a toxic effect on human beings, since, when a fire is being extinguished, the halogen-containing compounds form thermal decomposition products which have a large corrosive effect. Furthermore confined spaces which are particularly endangered by fire are normally protected by extremely large fire extinguishing systems for extinguishing fires in confined spaces, wherein halogen hydrocarbons are used. Owing to the international standards for the protection of the ozone layer in accordance with the Montreal protocol (1987) the use of the fluoro-hydrocarbons must be halved by the year 1995 and completely eradicated by the year 2000, since these substances comprise a great potential for damaging ozone. 
     Systems are known for the purpose of extinguishing fires in confined spaces, wherein halogen-containing hydrocarbons are used (for example GB-PS 2 020 971). A disadvantage of systems of this type is their harmful effect on the environment. Furthermore systems of this type comprise fairly large dimensions and a fairly large weight so that their efficiency is impaired when extinguishing fires in transport media, e.g. in aeroplanes. 
     A method is known for the purpose of preparing a fire-extinguishing agent, wherein when a charge of a pyrotechnical mass is burnt a mixture of solid particles and inert gases is formed (WO 92/17244). However, the high temperature of the combustive products results in increasing the average ambient temperature in the confined space, which produces a harmful effect on persons therein. Furthermore, when burning pyrotechnical solid combustion fuels, gaseous products (CO, NH 3 , H 2 , CH x , and NO x ), in addition to the primary aerosol products having an extinguishing effect, develop from the incomplete combustion of the organic components, which leads to the environment being polluted by these products. 
     The composition in accordance with the invention achieves the object of providing an ecologically safe composition for the purpose of extinguishing fires in confined spaces. 
     An object of the invention is a pyrotechnical, aerosol-forming composition for the purpose of extinguishing fires in confined spaces, containing potassium nitrate in a quantity of 67-72% by mass, phenolformaldehyde resin in a quantity of 8-12% by mass, and dicyandiamide as the balance, wherein the particles of the potassium nitrate comprise a maximum average particle diameter of 25 μm and accordingly comprise a minimum specific surface area of 1500 cm 2  /g, and the maximum average particle diameter of the phenolformaldehyde resin is 100 μm and the maximum average particle diameter of the dicyandiamide is 15 μm. 
     Preferably the composition in accordance with the invention also contains potassium bicarbonate (KHCO 3 ), potassium benzoate (C 7  H 5  O 2  K) or potassium hexacyanoferrate K 3  [(FeCN) 6  ] having a maximum average particle diameter of potassium-containing material of 15 μm and accordingly having a minimum specific particle surface area of 500 cm 2  /g. The composition contains (in % by mass): 
     
         ______________________________________                                    
potassium nitrate    67-72                                                
dicyandiamide        9-16                                                 
phenolformaldehyde resin                                                  
                     8-12                                                 
potassium benzoate, bicarbonate or                                        
                     4-12                                                 
hexacyanoferrate                                                          
______________________________________                                    
 
    
     The object described is also achieved by virtue of the method for the preparation of the composition in accordance with the invention, which method comprises providing a solution of phenolformaldehyde resin, mixing the constituents, sieving out, granulating and drying, wherein for the preparation of the solution of the phenolformaldehyde resin a mixture of ethyl alcohol with acetone in a ratio of 30-50:70-50 is used, the powder-form constituents are mixed with the solution of the phenolformaldehyde resin by adding the solution in at least two equal portions until all constituents are distributed in a uniform manner in the whole mass, i.e. until a uniform and stable mass is obtained, the mixture is granulated simultaneously during drying at temperatures of 20-70° C. until a residual content of moisture and volatile constituents of not more than 1% is present and the granulated composition is sufficiently fluid when used. 
     The ratio and the dispersity of the constituents and the method for the preparation of the composition guarantee a more rapid and more complete combustion of the composition and a larger quantity of fine-grain particles and inert gases (CO 2 , N 2 , and H 2  O as vapour) in the aerosol, thus in turn guaranteeing that the composition extinguishes efficiently and thus producing during the extinguishing procedure a toxic level which is acceptable to human beings. 
     The use of fine-grain starting products of the powder-forming components (potassium nitrate, dicyandiamide, potassium benzoate, potassium bicarbonate, potassium hexacyanoferrate) and the use of phenolformaldehyde resin as a lacquer solution in ethyl alcohol/acetone mixture and the use of the method in accordance with the invention for the preparation of the composition render it possible to obtain a final mixture having the necessary technological properties and properties for use, and to reduce the duration of the preparation process and the risk of the said preparation process (the necessity for dangerous operations such as the circulation of air is obviated). 
     The composition in accordance with the invention can be prepared in standard pyrotechnical installations. 
     In table 1 formulations of the composition in accordance with the invention are illustrated in comparison to a known composition and the most important parameters of these compositions are also listed. It is evident from table 1 that the composition in accordance with the invention surpasses the known composition in all parameters listed. 
     In table 2 formulations of the composition in accordance with the invention (No. 11, 14, 16, 17, 18 and 21) are illustrated in comparison to compositions, wherein the quantity and/or the dispersity of the constituents are outside the range in accordance with the invention. It is evident from table 2 that the composition in accordance with the invention comprises a reduced toxic effect. Moreover, for the purpose of extinguishing fires, a lower concentration of extinguishing agent is required. Furthermore the composition in accordance with the invention guarantees a larger quantity of fine-grain particles and inert gases in the aerosol. 
     
                                           TABLE 1                                 
__________________________________________________________________________
                 Concentration of the components (% by mass)              
                                               Nearest Prior Art          
Components, properties of the mixture                                     
                 1    2    3    4    5    6    WO 92/17244                
__________________________________________________________________________
Potassium nitrate                                                         
                 70   70   70   70   70   70   70                         
Dicyandiamide    12   12   12   9    9    9    19                         
Iditol (Phenolformaldehyde resin)                                         
                 --    --  --   --   --   --   11                         
Phenolformaldehyde resin as a                                             
                 11   11   11   11   11   11   --                         
lacquer (solid body)                                                      
Potassium bicarbonate                                                     
                 7    --   --   9    --   --   --                         
Potassium benzoate                                                        
                 --   7    --   --   9    --   --                         
Potassium hexacyanoferrate                                                
                 --   --   7    --   --   9    --                         
Speed of fire (mm/s)                                                      
                 2.1  2.5  2.3  1.8  2.3  2.1  1.5                        
Specific pressure of the pressing                                         
                 1200 1200 1200 1400 1400 1400 2000                       
process*                                                                  
Yield at disperse phase                                                   
                 56   64   62   53   58   57   48                         
(Mol-%)                                                                   
Fire-extinguishing concentration for                                      
                 40   35   35   45   40   40   50                         
Ethanol (g/m.sup.3)                                                       
Concentration of toxic gases                                              
(Vol-%)                                                                   
CO.sub.2         0    0    0    0    0    0    0.018                      
NH.sub.3         0.085                                                    
                      0.080                                               
                           0.078                                          
                                0.070                                     
                                     0.065                                
                                          0.062                           
                                               0.144                      
__________________________________________________________________________
 *for the purpose of attaining coupl. (Coupling) = 0,95 kgf/cm.sup.2      
 
    
     
                                           TABLE 2                                 
__________________________________________________________________________
Concentration of component, % by mass,                                    
(average particle diameter, μm)                                        
                        Toxic effect*                                     
                                Fire-extinguishing                        
        Phenolformal-   Dead,                                             
                           Paralysed,                                     
                                concentration                             
                                        Level of discharge                
No.                                                                       
   KNO.sub.3                                                              
        dehyde resin                                                      
               Gas-Aerosol-former                                         
                        %  %    g/m.sup.3                                 
                                        into the aerosol,                 
__________________________________________________________________________
                                        %                                 
 1 60 (˜320)                                                        
        15 (˜360)                                                   
               25 (˜340) DCDA**                                     
                        79 100  48      76                                
 2 67 (&lt;25)                                                               
        10 (&lt;100)                                                         
               23 (˜340) DCDA                                       
                        0  4.2  36      88                                
 3 50 (&lt;25)                                                               
        8 (˜360)                                                    
               32 (˜340) DCDA                                       
                        100                                               
                           100  42      80                                
 4 67 (&lt;25)                                                               
        18 (&lt;100)                                                         
               15 (˜340) DCDA                                       
                        0  58.3 38      84                                
 5 60 (&lt;25)                                                               
        8 (&lt;100)                                                          
               32 (˜340) DCDA                                       
                        100                                               
                           100  40      84                                
 6 70 (&lt;25)                                                               
        5 (˜360)                                                    
               25 (&lt;15) DCDA                                              
                        0  12.5 36      86                                
 7 70 (&lt;25)                                                               
        15 (&lt;100)                                                         
               15 (&lt;15) DCDA                                              
                        0  4.2  34      90                                
 8 70 (&lt;25)                                                               
        18 (&lt;100)                                                         
               12 (&lt;15) DCDA                                              
                        0  16.7 36      90                                
 9 60 (&lt;25)                                                               
        15 (&lt;100)                                                         
               25 (&lt;15) DCDA                                              
                        79 79.2 42      80                                
10 58 (&lt;25)                                                               
        5.5 (&lt;100)                                                        
               36.5 (&lt;15) DCDA                                            
                        79 100  56      78                                
11 69 (&lt;25)                                                               
        12 (&lt;100)                                                         
               17 (&lt;15) DCDA                                              
                        0  4.2  26      97                                
12 65.5 (&lt;25)                                                             
        14 (&lt;100)                                                         
               20.5 (&lt;15) DCDA                                            
                        0  17.4 28      95                                
13 68 (&lt;25)                                                               
        13 (&lt;100)                                                         
               19 (&lt;15) DCDA                                              
                        0  4.2  26      96                                
14 70 (&lt;25)                                                               
        11 (&lt;100)                                                         
               19 (&lt;15) DCDA                                              
                        0  0    24        99.3                            
15 54 (&lt;25)                                                               
        12 (&lt;100)                                                         
               34 (&lt;15) DCDA                                              
                        100                                               
                           100  120     68                                
16 70 (&lt;25)                                                               
        11 (&lt;100)                                                         
               12% (&lt;15) DCDA +                                           
                        0  0    27      97                                
               7% (&lt;15) KB                                                
18 69 (&lt;25)                                                               
        8 (&lt;100)                                                          
               11% (&lt;15) DCDA                                             
                        0  0    23      98                                
               12% (&lt;15) KHCF                                             
19 75 (&lt;25)                                                               
        10 (&lt;100)                                                         
               15% (&lt;15) DCDA                                             
                        12.5                                              
                           100  40      90                                
20 76 (&lt;25)                                                               
        15 (&lt;100)                                                         
               9% (&lt;15) DCDA                                              
                        14.7                                              
                           100  44      85                                
21 72 (&lt;25)                                                               
        10 (&lt;100)                                                         
               18% (&lt;15) DCDA                                             
                        0  0    26      97                                
__________________________________________________________________________
 *The results are obtained from experiments conducted on white mice, which
 were subjected for a period of 15 minutes to a concentration of 60       
 g/m.sup.3 and were monitored thereafter for a period of 2 weeks.         
 **DCDA  dicyandiamide                                                    
 KB  potassium benzoate                                                   
 KBC  potassium bicarbonate                                               
 KHCF  potassium hexacyanoferrate                                         
 
    
    
    
     EXAMPLE 1 
     Extremely favourable results are obtained when using the composition in accordance with the invention and the method for the preparation thereof, if the following formulation (% by mass) is used: 
     
         ______________________________________                                    
potassium nitrate with a specific                                         
                        70                                                
particle surface area of 2000 cm.sup.2 /g                                 
dicyandiamide with an average                                             
                        12                                                
particle size of 12 μm                                                 
phenolformaldehyde resin as 50%                                           
                        11                                                
solution in a mixture of ethyl alcohol and                                
acetone in the ratio of 50:50                                             
(calculated as a solid body)                                              
potassium benzoate with a                                                 
                        7                                                 
particle surface area of 600 cm.sup.2 /g                                  
______________________________________                                    
 
    
     The preground powder-form constituents (potassium nitrate, dicyandiamide, potassium benzoate) are poured into a mixer and mixed for 10 minutes. Then a phenolformaldehyde resin solution is added in three equal portions. The contents of the mixture are mixed for 5 minutes in each case after the addition of the corresponding portion of the phenolformaldehyde resin. The mixing is performed at a temperature of 40° C., with an opened cover. The mixture thus obtained is emptied from the mixer and passed through a sieve into a granulator whilst being continuously aerated with hot air at a temperature of 40° C. The predried granulate is laid in bands in layers 2-3 cm thick and is dried up to 1% for the purpose of removing any further moisture and volatile constituents. The total time spent mixing and granulating amounts to approximately 1 hour. 
     The mixture thus obtained can be dried still further in a pressed state, if the amount of moisture and volatile constituents exceeds 1%. 
     The pyrotechnical, aerosol-forming composition in accordance with the invention and the method for the preparation thereof render It possible to charge aerosol fire-extinguishing generators therewith and with the aid of said extinguishing generators to extinguish in an effective manner a fire of gaseous, liquid and solid combustible materials in stationary confined spaces, in transport media in rail and road traffic, on ocean-going and river ships, in aeroplanes, also including blow-by devices for example in aeroplane engines, and likewise to detect fires and to prevent the transition from a fire in specialist manufacturing installations to an explosion in the storage areas and in production plants which are endangered by fire and explosion.