What chemical is primarily used in dry chemical fire extinguishers?

Dry chemical fire extinguishers primarily utilize monoammonium phosphate as the extinguishing agent. This chemical is effective in combating various types of fires, including those fueled by ordinary combustibles, flammable liquids, and electrical materials. Monoammonium phosphate works by interrupting the chemical reaction in the fire, effectively smothering the flames and preventing them from spreading.

In contrast, other options like carbon dioxide, water, and foam each serve different purposes. Carbon dioxide is primarily used in certain classes of fires, particularly electrical fires, as it displaces oxygen but does not provide the same broad range of application as monoammonium phosphate. Water is effective on Class A fires but is not suitable for flammable liquid or electrical fires, as it can spread the fire or conduct electricity. Foam extinguishers are often used for flammable liquid fires but are not considered dry chemical extinguishers since they use a different type of extinguishing agent.

Thus, monoammonium phosphate is uniquely suited for a wide range of fire types, making it the primary choice for dry chemical fire extinguishers.