Development And Performances Of Three-Phase Foam Extinguishing Agents For Intensifing Resistance To Oil-Fire

Oils possess flammable and explosive properties so that serious consequences will be caused as soon as fires occur in the large oil stocks.In the domestic and overseas,foam extinguishing agents are the major strategy to put out the oil fires(class B fire).However,the foams generated from the agents readily collapse at high temperatures.Because of the instability of the extinguishing foams and the high re-burning property of the oil,it is necessary to enhance the burning resistance of the extinguishing foams.The three-phase foam extinguishing is an effective technique to improve the extinguishing efficiency.The mixture of extinguishing foam with various powders and its engineering applications is the core and difficulty of the technique.In this work,the surface modification of hollow glass microspheres(HGM)by the silane coupling agent and the mixture of protein foams with solid materials were studied to develop the three-phase extinguishing foams of high burning resistance and high foamability.The extinguishing efficiency of the developed foams was evaluated according to the national technical standards.Furthermore,a corresponding foam discharge device was developed to solve the problems in the mixture and spray of the three-phase foams.The major studies and corresponding results are as follows.HGM were selected as the solid material of the three-phase foam.Their surfaces were modified by propyltriethoxysilane(FSi-8124)and tridecafluorooctyltriethoxysilane(FSi-8261)to improve their lipophobicity.The effects of pretreatment,ultrasonic time,temperature,agitation time,FSi-8124 concentration and FSi-8261 concentration on the HGM lipophobicity were systematically studied.The microstructure and physicochemical parameters of HGM were also studied by scanning electron microscope,thermogravimetric analyzer and contact angle meter.The optimal conditions for the surface modification of HGM were temperature 60 o C,ultrasonic time 2.0 h,agitation time 4.0 h and FSi-8261 concentration 1%(m/m)after their pretreatment.The modified HGM was mixed with protein foams to prepare a novel three-phase foam fire extinguishing agent.The fire extinguishing performances of the prepared agent were tested.The expansion,time for 25% drainage,thermal stability and anti-solubility of the three-phase foams with modified and unmodified HGM were compared.The effects of the contents of the modified HGM and the protein foam fire extinguishing agent and the additive type were also investigated.In addition,the thermal stability of the three-phasefoam with modified HGM and the traditional protein foam was compared under thermal radiation by using an analog device.The results show that the modified HGM effectively improved the foamability of the new three-phase foam fire extinguishing agent and the stability of the three-phase foam.They also slowed down the drainage velocity of the the three-phase foam and increased the time for 25% drainage.At the addition of the modified HGM of 30%,a compact solid coating was formed at the top of the three-phase foam as the foam was heated so that the prepared three-phase foam fire extinguishing agent had good burning resistance.According to the general technical requirements for the foam extinguishing agents(GBT 15308-2006),the experiments for evaluating the burning resistance and fire extinguishing performance of the three phase foam with the modified HGM were carried out in a small-to-medium-size lacquer tray using the traditional protein foam as a reference.The effects of the compsotions and the height of the three-phase foam on its burning resistance and fire extinguishing performance were investigated.The results show that the three-phase foam with the modified HGM and the protein foam had no significant difference in the time for fire extinguishing.However,a compact solid coating was formed at the top of the three-phase foam as the foam was heated,so the three-phase foam had better reburning resistance.A new three-phase foam extinguishing agent was prepared by the leaching liquor from Sapindus and nanosilica.Scanning electron microscope,high-definition digital microscope and foam satbility analyzer were used to characterize the microstructure of nanosilica,the stability,bubble size,expansion and time for 25% drainage level of the three-phase foam.Thermal stability,anti-solubility and burn resistance of the three phase were also studied using the traditional protein foam as a reference.The results show that the concentrated liquor from Sapindus obtained by leaching for 4.0 h and then standing for 8.0 h had a expansion of 8.8 and time for 25% drainage of 367 s,higher than those of the standard protein foam.When the addition of nanosilica was 30%,the foamability of the foaming agent and the thermal stability of the foam at 280?significantly increased.The foam height was about twice of that of the protein foam under the same conditions.Based on the current fire-fighting equipments and the theory of the three-phase foam,a new device for generating the three-phase foam was developed and its spraying angle and distance were measured.The experiments on its application to extinguishing was carried out according to the section of 5.10.5.1.2 in the foam extinguishing agent national standards(GB15308-2006).The results show that the three-phase foam with the modified HGM generated from the negative-pressure type three-phase foam generator had good extinguishing performance and reburning resistance.At the foam content 6% and voluemtric fraction of the modified HGM 15%,the layer of the three-phase foam with themodified HGM generated from the device had good thermal barrier effect and reburning resistance.The results obtained by the large-size lacquer tray was basically consistent with those obtained by the small-size lacquer tray.