Class D agents work primarily by?

Class D fire agents are specifically designed to combat fires involving combustible metals, such as magnesium, titanium, sodium, and potassium. These materials burn at extremely high temperatures and can react violently with water and other common extinguishing agents. The primary function of Class D agents is to form a crust over the fuel.

This crust effectively isolates the burning material from the surrounding oxygen and inhibits the combustion process. By creating this barrier, the agent prevents the release of flammable gases and serves to contain the fire. The formation of a crust is crucial in extinguishing metal fires because it helps manage the extreme heat and potential reactions that could occur if traditional extinguishing methods were employed.

In contrast, while cooling and smothering are methods used in combating many types of fires, they do not address the specific challenges posed by combustible metals. Similarly, diluting chemicals is not a primary function of Class D agents, which are focused on containment and prevention of re-ignition rather than chemical dilution.