Foam solution is defined as:

• A. The final foam after air introduction.
• B. The mixture of foam concentrate and water before adding air.
• C. The amount of foam concentrate used.
• D. The result of mixing the appropriate amount of foam concentrate with water; foam solution exists between the proportioner and the nozzle or aerating device that adds air to create finished foam.

Answer: (D)

Foam solution is the liquid blend of foam concentrate and water at the proper proportion that flows from the proportioner toward the nozzle or aerating device. It exists in the system between the proportioner and the device that adds air to create finished foam. It isn’t the concentrate by itself, nor the foam after air has been introduced. The key idea is that foam solution is the aeration-ready liquid in the line, at the designed ratio, before air is mixed in to produce the finished foam.