How much foam is added to a water extinguisher?

The proper amount of foam to add to a water extinguisher, particularly for enhancing its effectiveness against Class A fires, is 1 ounce. This quantity allows the water extinguisher to be more effective in suppressing fires involving ordinary combustibles such as wood, paper, and textiles. The addition of foam creates a blanket over the burning materials, effectively cooling and smothering the fire while helping to prevent re-ignition.

Using foam in water extinguishers specifically improves the performance for Class A applications by providing better burn-back resistance. In contrast, the other options do not accurately reflect the appropriate quantity or application for the foam in water extinguishers. Class B and Class C fires pertain to flammable liquids and electrical fires, respectively, which do not require the same foam integration as Class A fires. Therefore, the focus remains on the correct approach for the type of materials being extinguished with the added foam.