What percentage mixture is recommended for hydrocarbons when using Class A foam?

• A. 1%
• B. 3%
• C. 5%
• D. 8%

Answer: (B)

Class A foam works by forming a stable film on the fuel surface that cools and blankets the material, helping to suppress vapors and keep the fire from reigniting. For hydrocarbons, you want enough foam to spread evenly and maintain that film over the surface. The typical, widely taught dilution is a 3 percent mixture, which provides effective film formation and cooling without wasting concentrate. Using only a 1 percent mix often isn’t enough to sustain the protective film on hydrocarbon fuels, while dilutions like 5 percent or 8 percent tend to be more than necessary for many hydrocarbon scenarios. Always follow the foam manufacturer’s guidelines, but 3 percent is the standard recommendation for hydrocarbons with Class A foam.