Insights into the particle diameter and base chosen for dry powder fire extinguishing agents

Abstract

Sodium bicarbonate and potassium bicarbonate are commonly used as the bases of dry powder fire extinguishing agents. However, the choices of particle diameter and base are still not obvious, bringing difficulties to the design of fire extinguishing agents. Through the study on thermal decomposition kinetics, it was found that the smaller the particle size, the faster the decomposition rate of dry powder agents. For instance, if the D90 of sodium bicarbonate is reduced from 46.2 to 1 μm, the decomposition rate triples. As determined by thermal decomposition experiments, the residues after a fire could be bicarbonates, carbonates, and mixtures. The residue solutions' pH shows that carbonates are more alkaline than bicarbonates, and potassium salts are more alkaline than sodium salts. The corrosion tests on four common metals reveal that the residues of potassium bicarbonate after a fire could accelerate the electrochemical corrosion of metal surfaces, especially aluminum alloys. This research identifies the ideal particle diameter and supports the choice of alkali metal salts for the design of dry powder agents.