| Now with the development of science,technology and economy,high rises,electric equipment and libraries were more and more and their structures and types were more and more complicated.The fire safety of their buildings was paid more attention.Because the different new materials were applied to build the constructions,now the fires were also more complicated than before.Thence,finding and manufacturing new Halon substitutes and study on their fire suppression effectiveness and mechanisms were important and significant in order to suppress the different kinds of fires and protect human life and property.Compared to other kinds of fire suppressant,dry powders had advantages,such as high efficiency,low toxicity and unneeded water and so on.So,dry powders were paid more attention and considered as a kind of high efficient Halon substitute.But now People usually focused on fire extinguishing efficiency of alkali metal salts and ammonium phosphate salts,and the effects of particle sizes and the fire suppression mechanisms have not been studied sufficiently.Thence,in this paper divergences were studied.A new material,magnesium hydroxide(Mg(OH)2)was introduced and its possible application was discussed in this paper in order to protect constructions better.It was analyzed at three aspects including its advantages,physical and chemical properties and fire suppression effectiveness.Mg(OH)2 powder is better because it is cleaner,higher efficiency and lower cost of production,store and transportation.The physical and chemical characteristics of the magnesium hydroxide powders were characterized by SEM and TGA and BET.A comparison of physical properties and chemical properties between magnesium compounds and other common commercial fire suppressant proved that Mg(OH)2 powder absorbed more heat when they decomposed.In a bench-test,the Mg(OH)2 powder is also more efficient than the common commercial BC powder and ABC Powder.The results have proved that Mg(OH)2 powder was a kind of good,clean and high efficient powder to suppress some special building fires,such as high rises,libraries and so on.In this paper the effects of different kinds of magnesium hydroxide on the flame have been also studied by a cup burner.The results are as follows:(I)there is a few influences on the flame height;(2)with.the decrease of powders' size,the flame width first increase.but then decrease;(3)with the decrease of powders' size,the flame flicking frequency increase the theoretical method is applied to analyze the fire suppression imechanisms.The fire extinguishing condition is proposed in a confine space through the damkohler number(Dn),the fire suppression mechanisms are analyzed simply in a confine space.When damkolher number is less than a certain value(De),fire will be extinguished.An experimental apparatus is set up and the fire suppression efficiency and the influence of powders on smoke will be tested in this confine space.The fire-extinguishing ef-ficiency of a new kind of dry powders based on magnesium hydroxide of different particle size was studied through laboratory scale experiments in a confine space of 1*1*lm and a cup burner in this paper.The powders are four different size powders.The results have exhibited that these four kinds of powders are all high efficient for the fire suppression efficiency and there is a threshold value of 5?m for thc fire suppression efficiency of magnesium hydroxide.Possible fire-suppression mechanisms have also been analyzed.In this paper the effects of fire suppressants under different particle sizes on the smoke are studied.And the results exhibited that the powders have a greatly effects on smoke.The generation smoke rate is decreased quickly.The Mg(OH)2 powders were modified by DOPO-VTS.The powders were more efficient which were modified by the 3%DOPO-VTS.In order to investigate the effects of different modified methods on fire suppression effectiveness,three kinds of materials were applied to modify the Mcg(OH):powders.They were DOPO-VTS.DMMP and H3PO2.The results illustrated that the powders modified by DOPO-VTS were more efficient and environmental. |
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