USCG Firefighting License Practice Exam 2025 - Free Firefighting License Practice Questions and Study Guide

Dry chemical extinguishers primarily extinguish Class B fires by breaking the chain reaction that occurs in the combustion process. Class B fires involve flammable liquids or gases, and one of the crucial elements that sustain a fire is the chemical reaction between the burning material and the oxygen in the environment.

The dry chemical agent, often sodium bicarbonate or monoammonium phosphate, works effectively by interrupting this chain reaction. When the dry chemical is deployed on the fire, it produces a non-flammable gas that coats the fuel and inhibits the ongoing combustion process, thus stopping the fire from burning.

This method is particularly effective because it can quickly bring an active fire under control by eliminating the chain reaction. While other methods, such as cooling or oxygen dilution, can sometimes play a role in fire suppression, the primary action of dry chemical extinguishers is to target the chemical reaction portion of the fire triangle.