What primary factor should be assessed when choosing firefighting foam?

When selecting firefighting foam, the primary factor to assess is the type of fire being fought. Different types of fires require specific foam agents tailored to their characteristics. For instance, Class B foams are specifically designed to combat flammable liquid fires, while Class A foams are effective for ordinary combustibles. Understanding the nature of the fire—whether it involves hydrocarbons, polar solvents, or other combustible materials—directly influences the effectiveness of the foam used. Choosing the right foam based on the type of fire ensures that firefighters can control and extinguish the blaze more efficiently and safely, maximizing their efforts during an emergency situation.