What is the primary agent used in dry chemical fire extinguishers?

The primary agent used in dry chemical fire extinguishers is ammonium phosphate. This compound is effective because it works by forming a barrier between the fuel and the oxygen in the air, which helps to extinguish fires. Ammonium phosphate is particularly effective on Class A (ordinary combustible materials such as wood and paper), Class B (flammable liquids), and Class C (electrical fires) fires.

When the dry chemical is discharged, it blankets the burning material, cooling the fuel and preventing re-ignition. This versatility makes ammonium phosphate a widely used suppressant in various fire situations, differentiating it from other options like water, carbon dioxide, or fluoride. Each of those agents has its specific applications and limitations; for example, water is not effective on flammable liquid fires and can sometimes exacerbate them. Hence, ammonium phosphate stands out as the primary agent specifically used in dry chemical fire extinguishers for its broad effectiveness across different fire classes.