Which extinguishing method is ineffective against Class D fires?

Class D fires involve combustible metals such as magnesium, titanium, and sodium, which react violently with water. Cooling with water is ineffective and can actually exacerbate the situation, leading to explosive reactions that could endanger firefighters and exacerbate the fire.

In contrast, methods such as smothering with special agents or using dry chemical extinguishers are designed specifically for extinguishing Class D fires. These agents do not react negatively with the burning metals and can form a barrier that effectively starves the fire of oxygen or interrupts the combustion process. Additionally, using sand or dirt can help to smother the fire by covering the combustible metals, further preventing oxygen from fueling the fire.

Thus, water is ineffective for Class D fires due to the potential for hazardous reactions, making it crucial for firefighters to utilize appropriate extinguishing methods tailored for these specific types of fires.