Evolution 11 — Foam Stream Operations

Overview

Foam operations add a layer of complexity to pump operations that catches many operators off guard. The in-line eductor requires a specific inlet pressure to properly proportion foam concentrate into the water stream — typically 200 PSI at the eductor inlet for most models. Too little pressure and the eductor won't pick up concentrate, producing a plain water stream that is useless against flammable liquid fires. Too much pressure and the foam ratio is wrong, wasting concentrate and producing an ineffective stream. The eductor itself creates significant back-pressure — its pressure loss runs roughly a third of the inlet pressure (about 65 PSI at a 200 PSI inlet), which is why the inlet requirement is so high. The pump supplies that inlet pressure, plus the friction loss in any hose between the pump and the eductor; the eductor's own loss is already inside the 200 PSI and is not added again. Foam operations also have a time component — the foam tank is finite (usually 20-30 gallons), and even at a lean 0.3% Class A rate with 95 GPM flow it depletes steadily, so the operator has to track the remaining supply.

Training Objective

Produce a properly proportioned foam stream using an in-line eductor, maintaining the correct inlet pressure for proper eduction. The operator must account for eductor back-pressure in the PDP calculation and maintain stable pressure for consistent foam quality throughout the evolution.

Skills Practiced

• Foam eductor operation, setup, and inlet pressure requirements
• Inlet pressure calculation: the eductor's required inlet pressure plus any hose before it
• Foam proportioning awareness — Class A (0.1–1%) and Class B (1%, 3%, 6%) rates
• Maintaining stable pressure for consistent foam quality over time
• Class A vs Class B foam considerations and application differences
• Foam tank capacity awareness and duration calculation
• Understanding eductor back-pressure and why it sets the inlet requirement
• Recognising improper eduction by stream appearance

Setup

Hydrant supply with an in-line foam eductor connected at the pump discharge and a 1¾" handline (150 ft, 95 GPM) beyond it. The eductor requires 200 PSI inlet pressure, and roughly a third of that (about 65 PSI) is lost across the eductor itself. Class A foam concentrate at 0.3% proportioning rate. The operator must deliver the precise inlet pressure the eductor requires; the hose and nozzle beyond the eductor run on what is left after its loss, which is why it needs 200 PSI.

Scenario

A wildland-urban interface exposure protection operation. The attack crew has deployed an eductor on a handline to apply Class A foam to structures threatened by an advancing wildfire. The pump operator must deliver the exact pressure for proper foam proportioning. Inconsistent pressure means inconsistent foam — and inconsistent foam means inadequate protection for the structures.

What to Expect

The simulation judges the pressure at the eductor inlet, which sits at the pump discharge. You are scored on the pressure you calculate and the pressure you hold over the last 10 seconds before you finish, so bring the line to a steady 200 PSI and finish there. Foam proportioning is scored too, and it falls with every second the line flows without the foam turned on. The foam tank level depletes during the evolution, so the operator must monitor the remaining supply.

Tips

• Eductors are pressure-sensitive — even 5 PSI of fluctuation affects foam quality
• Know the required inlet pressure for your department's eductors before starting — most require 200 PSI
• Foam operations typically require higher pump pressures than standard handlines due to eductor back-pressure
• Maintain steady throttle — fluctuations break the foam/water ratio and waste concentrate
• Know your foam rate. At this drill's 0.3% Class A rate, 95 GPM draws about 0.29 gallons of concentrate a minute, so a 30-gallon supply lasts about 105 minutes of flow — and the panel's foam gauge drains at that same rate, so expect it to move slowly over a seven-minute drill. A Class B eductor at the standard 3% draws about 2.85 gallons a minute and empties the same tank in about 10 minutes — track the gauge through the drill
• After the evolution, the eductor and hose must be flushed with clean water — foam concentrate is corrosive