A brief discussion on Foam in the Fire Service.

Class A Foam is used on Class A fuels.
Class B foam is used on Class B fuels.

As in life, these are two very different fire classes. The two foams are also very different. They may come in the same looking bucket, and make the same white bubbles on the ground, but they are very different chemistries and designed for very different missions. They are not compatible, nor are they interchangeable.

Making foam is a very simple task – water + soap + air.
There are numerous variations in the makeup (consistency) of the foam. Knowing which variation to use when requires good equipment, training and practice. Using the wrong consistency at the wrong time makes for very unhappy firefighters and possibly a very unhappy situation.

There are 4 levels of effectiveness in firefighting.

The bottom level is water. High surface to mass ratio (STMR) – inefficient heat absorption; high surface tension – no penetration; repels carbon – won’t stick.

Next up is Foam solution – water + concentrate.
Reduced surface tension – improves penetration. Carbon loving – it sticks horizontal, but not vertical. Still has high SMTR. Only slight improvement in heat absorption.

Next level up is Aspirated Foam – better than solution since it is in a bubble format – the bubbles result in an increased STMR for better heat absorption. These bubbles are fragile and cannot be applied at long distance – low energy.

Top level is CAF – penetrates, sticks, ultimate heat absorption (this is what firefighting is all about), high energy, small, strong bubbles – long reach.