What is the minimum specific gravity of foam concentrate that will not mix with water?

• A. 1.10
• B. 1.20
• C. 1.05
• D. 1.15

Answer: (D)

When foam concentrate is heavier than water, it tends to separate rather than fully dissolve or emulsify with the water. In practice, to ensure the concentrate will not mix with water under typical storage, dilution, and temperature conditions, a minimum specific gravity around 1.15 is used as the threshold. This means a concentrate with a specific gravity of 1.15 or higher will reliably not mix with water, making 1.15 the smallest value in the given options that guarantees non-mixing. Values closer to 1.0, like 1.05 or 1.10, may still mix under some conditions, while a higher value like 1.20 also won’t mix but isn’t the minimal threshold.