Which extinguishing agent is NOT used for Delta fires?

Delta fires, also known as Class D fires, involve combustible metals such as magnesium, sodium, or titanium. The correct answer to the question is that AFFF (Aqueous Film-Forming Foam) is not used for extinguishing Delta fires.

AFFF is primarily designed for use on Class A (ordinary combustibles) and Class B (flammable liquids) fires. Its chemical makeup and design render it ineffective and potentially hazardous when applied to combustible metals, as it can react with them and lead to explosive situations or re-ignition.

In contrast, water in fog patterns can sometimes be effective against certain types of metal fires by cooling, though it may not be universally recommended over all others. CO2 is often used for its suffocating properties but is not effective against all metal fires. Dry chemical powders, especially those specifically designed for Class D fires, are effective because they smother the fire and form a barrier between the combustible metal and any oxygen, thus preventing re-ignition.