Which type of fire extinguisher should NOT be used on Class D fires?

Using water on Class D fires is not advisable because Class D fires involve combustible metals, such as magnesium, titanium, or sodium. These metals can react violently with water, potentially leading to explosive reactions that exacerbate the fire and create a hazardous situation.

When fighting a Class D fire, it's essential to use specialized extinguishing agents specifically designed to smother or cool the burning metals without causing a reaction. Common choices for these types of fires include dry powder extinguishers made for metal fires, which can effectively smother the flames and prevent oxygen from reaching the burning material.

In contrast, dry chemical extinguishers and carbon dioxide extinguishers work well on various fire classes but are not designed specifically for metals. Foam is also ineffective on Class D fires, as it could introduce water and increase the risk of a violent reaction. Thus, the use of water is firmly discouraged in the context of Class D fires, highlighting the importance of selecting the right type of extinguisher based on the materials involved in the fire.