Which of the following is NOT a basic method by which foam may be proportioned?

• A. Eduction
• B. Blending
• C. Batch-mixing
• D. Premixing

Answer: (B)

Foam proportioning relies on delivering a defined concentrate-to-water ratio, which is achieved through three standard methods: eduction, batch-mixing, and premixing. Eduction uses a Venturi or eductor to draw concentrate into the water stream as it flows, creating the foam solution on the go. Batch-mixing mixes the concentrate with water in a dedicated tank to make a ready-to-discharge foam solution. Premixing pre-dilutes the concentrate with water in advance in a separate tank so the foam solution is already prepared for use.

Blending is not a basic method because it would involve mixing concentrate with water in a less controlled, downstream manner, often at the nozzle or within piping without a proper metering device. This makes the ratio highly sensitive to flow and pressure changes, leading to inconsistent foam quality and performance. The reliable, repeatable ratios relied on in firefighting are achieved by eduction, batch-mixing, or premixing, not by blending.