Study On Flame Suppression Mechanism Of Powdered Halon Replacements

Fire accidents not only endanger human life and property,but also have a huge impact on the global environment and ecological.The study of fire extinguishing agents with high-efficiency has always been an important research topic in the field of safety science.Halon fire extinguishing agents have been eliminated and banned due to the destruction of atmospheric ozone layer.Therefore,it is imperative to research new types of fire extinguishing agents with high-efficiency and environment-friendly.The research of fire extinguishing agent should not only pay attention to the agent itself,but also analyze the fire extinguishing efficiency and the suppression mechanism.Based on these,this article studied fire extinguishing agents containing metal,fluorine and phosphorus elements.The burning velocity and the minimum fire extinguishing time were used to evaluate the extinguishing efficiency.The fire suppression mechanism were also analyzed.The main works include four parts:(1)The physical and chemical suppression ef-fects of NaHCO₃ fire extinguishing powder were decoupled through the physical heat-sink model.(2)The physical inhibition effect of silica and the chemical inhibition ef-fect of fluorine were combined into a new type of fluorine-containing silica powder fire extinguishing agent.The morphology,extinguishing efficiency and suppression mech-anism were systematically analyzed.(3)The silica,water and phosphorus-containing compound was combined to synthesis dry water fire extinguishing agents with differ-ent phosphorus content.Then the extinguishing efficiency and suppression mechanism were studied theoretically and experimentally.(4)Theoretical study on the suppression effect of Fe(C₅H₅)₂.The physical heat-sink model was used to calculate the physical suppression effect of NaHCO₃.The burning velocity which measured by experiment was compared with the model value to verify the physical heat-sink model.Based on the decomposition of NaHCO₃ in flame,NaOH was used to analyze the chemical suppression effect of NaHCO₃.The chemical suppression effect was explored under different initial tem-perature and pressure.Given the effective decomposition parameter of powder,the influence of particle size on the suppression effect was analyzed.The result showed that the particle size directly affected the effective volume of NaOH in flame,so the size had a huge impact on the chemical suppression.When the particle size was large,the suppression mechanism was controlled by thermodynamics,the suppression mainly came from physical effect.When the particle size was small,the suppression mecha-nism was controlled by kinetics,the chemical inhibition was dominant.The physical and chemical suppression effects of the fire extinguishing agent were equally impor-tant,the combination of these two effects could further enhance the fire extinguishing efficiency.Combining F-containing groups and SiO2 powder,a new type of powder fire ex-tinguishing agent SiO2-F was synthesized.Through the two-step reaction process(co-condensation and amidation reactions),trifluoroacetyl(CF3CO)and SiO2 were con-nected into SiO2-F powder.The minimum extinguishing concentration and burning ve-locity were used to evaluate the fire extinguishing efficiency.SiO2-F powder showed better fire extinguishing efficiency than NaHCO₃ and SiO2.The TG experiment was utilized to simulate the decomposition behavior of powder in the flame.The suppres-sion mechanism was divided into two parts:the physical suppression caused by the heat absorption of solid materials;the chemical suppression caused by scavenging free radicals of fluorinated groups.The physical suppression effect occupied about 23.1%of the total suppression effect,which was an indispensable part of the entire suppres-sion mechanism.CF3CO could effectively consume free radicals to suppress flames,especially the OH groups.In general,the suppression effect of SiO2-F powder was the result of the combined effect of physical and chemical suppression.A new type of phosphorus acid dry-water fire extinguishing agent(SiO2-P)was synthesized,which comtained H3PO4,H20 and SiO2.Considering the dispersion and uniformity of the agent,we determined the preparation conditions and prepared four SiO2-P powders with different H3PO4 content.The minimum extinguishing time of SiO2-P powder was measured to evaluate the extinguishing efficiency by the oil-pool-fire extinguishing test.The result showed that the SiO2-P has good fire extinguishing effect.Based on the TG experiment and GA algorithm,the decomposition reaction and kinetic parameters of SiO2-P powder were determined.The decomposition mechanism was used to simulate the influence of powder on burning velocity and free radicals(H,O and OH).The result indicated that the powder could consume a large amount of free radicals through the synergistic inhibition of H2O and H3PO4.The burning velocity was reduced greatly.Furthermore,the study of dry-water containing DMMP(SiO2-DMMP)was conducted under the conditions of lean-burn and normal equivalence ratio.The re-sult showed that SiO2-DMMP which contained 10%DMMP solution could effectively avoid the combustion enhancement effect of DMMP under lean-burn condition.This was because the inhibition of H2O could neutralize the combustion enhancing effect of DMMP.Furthermore,the SiO2-DMMP powder also exhibited good suppression effect under the normal equivalent ratio.Finally,the flame suppression characteristics of Fe compounds were studied and Fe(C₅H₅)₂ was selected as the main research object.Given the special molecular struc-ture of Fe(C₅H₅)₂,we determined the kinetic parameters of the decomposition reactions and constructed the detailed reaction mechanism of Fe(C₅H₅)₂.Based on the mecha-nism,the influence of Fe(C₅H₅)₂ on the burning velocity of methane/air flame,flame temperature and free radicals were analyzed.In the condition of stoichiometric com-bustion and fuel-rich {??1),Fe(C₅H₅)₂ exhibited high flame suppression ability.In the condition of extremely lean-burn(?<0.55),Fe(C₅H₅)₂ exhibited combustion enhancement effect.When equivalent ratio was between the two parts,Fe(C₅H₅)₂ en-hanced combustion firstly and then suppressed combustion.The H,O and OH radicals in the flame also showed a similar trend.This was due to the competition between the flammability of hydrocarbon groups(such as C5H5)and the inhibition effect of Fe-containing radicals.Further,the effect of Fe-containing radicals in the flame was stud-ied.There were many cyclic reactions between various Fe-containing radicals and they could be transformed into each other.In this process,they consumed a large amount of O,H and OH free radicals.