Every firefighter learns it early: you don’t put a straight stream on a burning liquid. Hit a pan of flaming grease or a fuel spill with plain water and you don’t put it out — you spread it. The water sinks, the burning fuel rides on top, and now the fire is bigger and moving. Class B fires — flammable and combustible liquids — don’t play by the rules that work on an ordinary structure fire.
Why Class B is a different animal
A Class A fire burns a solid that stays put. A Class B fire burns a liquid that flows, pools, floats, and throws vapor. Back in Week 4 we covered three-dimensional fires — fuel running down a surface or falling from a height — and why a foam blanket fails when there is no flat pool to cover. Class B is where that problem lives. The fuel will not hold still long enough to be blanketed, and the vapor coming off it is what actually burns.
That is the whole challenge. You are not fighting the liquid, you are fighting the vapor it releases — and anything that does not stop the vapor just buys a few seconds before the fire finds it again.
Why the mix goes to 3%
F-500 EA is metered at 1% for Class A and steps up to 3% for Class B, C, D, K, and lithium-ion. The higher concentration is not arbitrary. On a flammable liquid, the agent has more fuel to surround — it has to encapsulate the hydrocarbon molecules themselves, wrapping each one so it can no longer release flammable vapor. At 3%, there is enough agent in the water to do that across a moving, vaporizing fuel. This is Encapsulator Technology from Hazard Control Technologies, the manufacturer of F-500 EA — not a blanket laid on top, but a chemical change to the fuel itself.
“NFPA 18A-compliant F-500 EA can mitigate two-dimensional and three-dimensional Class A, B, C, D, and lithium-ion battery hazards.”
Where foam runs into trouble
Foam suppresses a Class B fire by floating a blanket over the pool to hold the vapor down and keep oxygen out. On a flat spill with no wind and no movement, it works. But the moment the fuel is three-dimensional — flowing off a tank, dripping through a rack, running down a slope — there is no surface to blanket, and the fire keeps feeding. And the fluorine-free foams that departments are moving to as they leave AFFF behind often need more product, not less, to hold a Class B fire.
“Many fluorine-free foams do not perform as effectively as their predecessors. In some cases, they require 2-3x the application rate of AFFF to combat two-dimensional Class B hazards.”
Encapsulation does not depend on a surface. It works molecule by molecule, so it handles the flowing, three-dimensional Class B fire that a blanket cannot cover — and because the fuel is encapsulated rather than merely smothered, it does not re-release vapor and flash back the instant the blanket breaks.
What it means on the fireground
Class B shows up everywhere a department runs: vehicle fires, fuel storage, generator and transformer oil, solvent and process fires at industrial sites. A fluorine-free agent that shuts down both the pooled spill and the flowing fuel, cools fast, and leaves no forever-chemical runoff to clean up is a different tool than a foam that only works when the fire holds still.
“F-500 EA is fluorine-free, biodegradable, and non-corrosive, allowing your department to adopt a more environmentally responsible fire suppression solution without compromising performance or safety.”
Water alone spreads a Class B fire. Foam covers it and hopes the blanket holds. Encapsulation takes the fuel out of the fight.
Next week we move into industrial hazards — the plants, data centers, and energy-storage sites where Class B and lithium-ion risks live under one roof, and why hazard protection there is a discipline of its own.
On-site training is available for your department or facility. Contact us at ControlHazards.com to schedule yours.