Foam is the tool most of us reach for first on a fuel fire, and for good reason. But a fuel fire that’s moving, dripping or spraying doesn’t play by the same rules as a pool sitting on the ground. If you treat a running fuel fire like a spill fire, it will keep beating you no matter how much agent you put on it.

Know which fire you’re looking at

Most fuel fires we train on are pool fires. The fuel is lying on a flat surface, it’s burning off the top and it isn’t going anywhere. That’s what foam was made for. Lay down a blanket, let it flow across the surface, cut off the vapors and the fire goes out.

A running fuel fire is different. The fuel is falling from a ruptured wing tank, leaking out of an engine, running down a fuselage or spraying from a pressurized line. The fire isn’t just on the ground. It’s in the air, on the vertical surfaces and all along the path the fuel is traveling.

Here’s the problem. Foam works by sitting on top of the fuel. It can’t form a blanket on a stream of fuel falling through the air. You can bury the pool underneath in foam, and the fire above it keeps burning and keeps feeding new fuel into the fire you just put out.

Agent choice matters

This is where a lot of crews get frustrated. They flow foam, they knock down the ground fire, and then the whole thing lights back up from the fuel still coming down. They think they did something wrong with the stream. Usually they picked the wrong agent for that part of the fire.

A dry chemical agent attacks the fire differently. It interrupts the chemical reaction of combustion, so it can knock down flame in the air and on surfaces where foam has nothing to hold on to. What it doesn’t do is secure the fuel. Dry chem knocks it down, but it leaves no blanket behind. Once the agent drifts away, any hot surface or ignition source can light it right back up.

That’s why the two agents work best together. Dry chemical knocks down the running and falling fire. Foam secures the pool on the ground and keeps it from reigniting. That’s the whole idea behind a twin-agent attack, and a lot of ARFF apparatus carry both for exactly this reason. If your crew only ever trains with one agent at a time, they’ll never learn how the two work as a team.

Stop the source

The most important thing on a running fuel fire usually isn’t the agent at all. It’s the fuel supply. As long as fuel keeps flowing, you’re fighting a fire that is being refilled faster than you can put it out.

That might mean shutting down an engine, closing a valve, plugging a leak or simply getting the aircraft or vehicle crew to shut off the fuel system. It might mean you can’t stop it and you have to protect a rescue path until the fuel runs out. Either way, somebody on that crew needs to be thinking about the source from the first minute, not after the third time the fire comes back.

When I’m running this on a training ground, I want to hear crews talking about a few things before they ever open a nozzle:

• Where is the fuel coming from, and can we stop it?
• Which part of this fire is on the ground, and which part is in the air?
• Who has dry chem, who has foam, and how are we working together?
• Once it’s out, how are we keeping it out?

If a crew can answer those questions out loud, they’re going to fight the fire with their heads instead of just their hands.

Train it the way it shows up

A pan fire is a great tool. It teaches stream placement, foam application and crew movement. But if every fuel fire your people ever see in training is sitting flat in a pan, that’s the only fire they know how to fight.

The mistake I see most is crews who have never seen a fire behave like this until the day it counts. If you have a prop that can produce a running or falling fuel fire, use it, and use it safely within your live-fire standards. If you don’t, talk it through, walk it on an aircraft or a tabletop, and make crews explain how their attack would change. A firefighter who’s thought it through once is a lot better off than one who’s seeing it for the first time on a real incident.

The bottom line

Foam is a blanket. It’s outstanding on a fuel fire that sits still, and it’s nearly useless on fuel that’s falling through the air. Know the difference when you size it up. Use dry chemical to knock down what’s running, use foam to secure what’s on the ground, and go after the fuel source as hard as you go after the flame. Train it the way it really shows up, so your crew isn’t learning it for the first time when it’s for real.

Stay safe, and train like it matters.

Eric Makowski