Effect of technology of obtaining on the properties of dry water fire extinguishing powder with sodium bicarbonate

Abstract

Dry water can be classified as an effective and environmentally safe means of extinguishing fire. Dry water is formed by high-speed mixing of hydrophobic fumed silica and water, resulting in a coating of silica nanoparticles on the water droplets. At high temperatures, the silica shell is destroyed and finely dispersed water is released for extinguishing the fire.

The article studies the effect of the technology of obtaining dry water material from hydrophobic methylsilica, water and the addition sodium bicarbonate of various concentrations on the texture and properties of the of the resulting dry water powder.

Dry water fire extinguishing powder was obtained by mixing the components at the speed of 15,000 rpm for 10 s. Samples were made containing 10 wt. % methyl silica 2; 4; 6; and 8 wt. % sodium bicarbonate and the appropriate concentration of water. Adding 2 and 4 wt. % NaHCO₃ to preliminarily prepared dry water results in a cream-like material; at concentrations of 6 and 8 wt. % the formation of a two-phase system - of a suspension of methyl silica in water and an aqueous solution of sodium bicarbonate is observed. When adding an aqueous solution of NaHCO₃ with a concentration of 2; 4; and 6 wt. % to methyl silica, separation into two phases is also observed; at the NaHCO₃ concentration of 8 wt. %, a wet coarse powder is formed. With the simultaneous mixing of all components, a dry water powder is obtained. The bulk density is 0.321; 0.299; 0.276; and 0.271 g/cm³ for samples with 2; 4; 6; and 8 wt. % of sodium bicarbonate, respectively. Dry water without sodium bicarbonate admixture has a bulk density of 0.343 g/cm³.

The fire extinguishing properties of the obtained dry water powders were studied by spraying them onto a layer of burning gasoline A-92 on the water surface. The time to complete extinguishing of the fire and the consumption of the substance per unit area of burning were determined. It has been found out that when using dry water fire extinguishing powder, which was obtained by simultaneously mixing all components, for extinguishing gasoline, the time of extinguishing gasoline and the costs of extinguishing it decrease with increasing concentration of NaHCO₃ and amount to 2; 4; 6 and 8 wt. % 5.2; 4.9; 4.3;3.8 s and 0.373; 0.370; 0.313; 0.217 g/cm³, respectively. For dry powder without impurities, these values are 7 s and 0.137 g/cm³, respectively. Powders suitable for extinguishing fire, which were obtained by another technology, have much worse fire-extinguishing properties. The texture of the material affects the consumption of dry water powder to extinguish gasoline - more time and consumption of powder for extinguishing the fire.