What is the chemical composition of a soda-acid type fire extinguisher?

A soda-acid type fire extinguisher utilizes a chemical reaction between sodium hydrogen carbonate (also known as baking soda or sodium bicarbonate) and sulfuric acid [1]. The extinguisher typically contains a solution of sodium hydrogen carbonate in a main cylinder, with a separate glass vial or compartment containing concentrated sulfuric acid. When the device is activated—often by striking a plunger or inverting the canister—the acid mixes with the bicarbonate solution. This reaction produces sodium sulfate, water, and a significant volume of carbon dioxide gas [1]. The rapidly expanding carbon dioxide acts as a propellant, forcing the water out through the nozzle to extinguish the fire. While sodium carbonate can also react with acids to produce carbon dioxide, the standard historical and chemical design of the 'soda-acid' extinguisher specifically employs sodium hydrogen carbonate [1].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Uses of Baking soda > p. 31