What ratio is considered a safe mixing practice when using different types of foam?

When it comes to mixing different types of foam concentrates, it is generally advised against mixing them at all due to the potential for chemical reactions that can compromise their effectiveness. Different foam types are formulated with specific properties designed for various fire scenarios, and mixing them can produce unexpected results, such as reduced performance or inadequate fire suppression capabilities.

In fire service protocols, the best practice is to use foam concentrates as directed by the manufacturer and stick to one type of foam for firefighting applications. Therefore, the notion that "mixing is not advised" aligns with industry standards and recommendations for maintaining the integrity and effectiveness of foam agents.

The other ratios presented represent inappropriate mixing practices, which could lead to ineffective foam solutions. Hence, one should always adhere to using a single type of foam concentrate as specified for the task at hand.