Investigation On Fire-fighting Foam Based On Mixture Of Hydrocarbon And Silicone Surfactants

Aqueous film-forming foam(AFFF)is a kind of high-efficiency fire-fighting foam used to extinguish flammable liquid fuel fire.It has been widely used in many civilian and military facilities,such as oil-field,oil-depot,ships,airport and the places that store large oil materials.Recently,the application of conventional AFFF has been severely restricted due to the serious environmental hazard caused by fluorocarbon surfactants,the key component in conventional AFFF.Nowadays,major manufacturers of long-chain fluorocarbons have ceased or cease the production and sale of fluorocarbons,replacing them with alternative short-chain substances.However,it does not provide adequate biocompatibility of derived foaming agents and do not allow to classify them as safe even in the near future.The present study focuses on the replacement of fluorocarbons with the mixture of hydrocarbon and silicone surfactants in order to develop environmentally friendly fire-fighting foam.Firstly,silicone surfactants with excellent surface activity and hydrocarbon surfactants with different charge are selected.Aqueous solutions of respective binary mixtures of a non-ionic silicone surfactant with anionic,cationic,and non-ionic hydrocarbon surfactants were prepared for evaluation of their surface activity and foam properties.The findings show that the addition of the silicone surfactant results in a decrease in surface tension for aqueous solutions of the hydrocarbon surfactants.The critical micelle concentration(CMC)of the hydrocarbon surfactants is also changed by the additive silicone surfactant.Additionally,clear foam synergistic effects were observed in the mixtures of silicone and hydrocarbon surfactants,regardless of the ionic types of the hydrocarbon surfactant.The foam stability of the hydrocarbon surfactant was shown to generally improve with the increasing concentration of the silicone surfactant.Even so,aqueous solutions of different ionic hydrocarbon surfactants in the presence of the silicone surfactant will give different foam stabilities.The results of the present study are meant to provide guidance for the practical application of foams generated by the mixtures of the silicone and hydrocarbon surfactants.Then,carboxymethylcellulose,xanthan gum,triethanolamine and lauryl alcohol,are chosen as foam stabilizers of AFFF to synthetize AFFF formulation concentrates.The properties of foam solution,foam drainage,foam spreading,fire extinguishing performance and burn-back performance of AFFF containing different foam stabilizers are deeply evaluated.The results indicated that film-forming property and foam spreading property are decreased by the addition of the foam stabilizers.Foam stability of AFFF can be enhanced by the addition of carboxymethylcellulose and xanthan gum but reduced by the addition of triethanolamine and lauryl alcohol.The AFFF containing 0.4%xanthan gum shows the optimal foam stability,but the AFFF containing 0.3%xanthan gum shows the optimal fire extinguishing performance.This indicates that fire extinguishing efficiency is affected by multiple factors.In selecting foam stabilizers we need to be trading off factors such as film-forming property,foam stability and foam spreading property.Finally,the formulations of fluorine-free fire-fighting foam are determined based on the results of the study of mixture of silicone and hydrocarbon surfactants and the results of the study of foam stabilizers.The properties of foam solution,foam drainage and foam spreading of fluorine-free fire-fighting foam are studied and compared with that of AFFF.The formulations with excellent foam stability and foam spreading property are selected,and the fire extinguishing performance and burn-back performance of these formulations are evaluated.The results show that the stability of fluorine-free foam is much higher than that of AFFF.The decrease in foam expansion ratio results in the acceleration of foam drainage.The spreading of fluorine-free foam on the surface of heptane is slower than that of AFFF.The decrease in foam expansion ratio or the increase in foam flowrate leads to a rapid spreading of fluorine-free foam and AFFF.Theoretically,fluorine-free foam can spread on the surface of heptane as rapidly as AFFF by decreasing expansion ratio or increasing foam flowrate.The fire extinguishing and burn-back performance meet the requirement of Chinese national standard and better than that commercial AFFF formulation.