Which class of solvents requires a foam proportioning percentage of 6%?

The correct choice highlights that polar solvents require a foam proportioning percentage of 6%. This is essential because polar solvents, such as alcohols and certain solvents like acetone, can mix with water and do not offer the same fire suppression benefits as non-polar solvents, which are more easily extinguished with standard foam solutions.

Using a foam proportioning percentage of 6% specifically targets the challenges posed by polar solvents, as they need a more robust foam to effectively suppress flames and prevent re-ignition. This higher percentage aids in the formation of a thicker blanket of foam, which is better at preventing vapors from rising and helps to smother the fire more effectively.

Contrast this with non-polar solvents, which typically require a lower percentage of foam; Class D solvents, which involve combustible metals and require specialized extinguishing methods; and Class A solvents, which are generally extinguished using water and may not need foam at all. Thus, understanding the properties and behaviors of these different classes of solvents is crucial for effective fire suppression strategies.