For which class of fire would water extinguishing agents typically be ineffective?

Water extinguishing agents are typically ineffective for Class D fires, which involve combustible metals such as magnesium, sodium, and potassium. These metals can react violently with water, potentially leading to an explosive situation or further exacerbation of the fire. Instead of cooling or smothering the fire, water in this case can create additional hazards, making it crucial to use specialized extinguishing agents designed to handle combustible metal fires, such as dry powder agents that do not react with the burning metal.

In contrast, water is generally effective for Class A fires, which involve ordinary combustible materials like wood, paper, and cloth, as it effectively cools and dampens these materials. For Class B fires, which involve flammable liquids and gases, water can often be ineffective or dangerous because it can spread the fire, although certain situations might allow for water to be used in combination with other methods. Class C fires, arising from electrical equipment, require the avoidance of water until the electricity is turned off to prevent electrocution, but water itself does not inherently react with the fire in the way it does with combustible metals.