In general, Hellfighter U is a school about the correct use of fire fighting foam, said chief instructor Frank Bateman. It might be more correct to refer to it as a fire school focusing on liquids that vaporize, causing problems with industrial processes.
“Foam isn’t the all-purpose, only-need-one agent solution to your problems,” Bateman said. “There are times that foam really doesn’t work well on liquids or gases.”
However, foam is the main focus at Hellfighter U because it is the only mechanism that, with proper use, firefighters can use upon arrival to prevent a fire, he said.
“With dry chemical, once a fire is going you can put it out, especially the three-dimensional spraying liquid type fire,” Bateman said. “It will even put out a pooling fire. But it provides no cooling or vapor suppression.”
Re-ignition is quite likely if the fuel itself is still vaporizing, he said. And that brings us back to foam.
“What foam does is essentially lower the surface tension of water so it can be more effective against fire,” Bateman said.
“Take a freshly waxed car hood. Water applied to the surface will bead. But if that water contains a wetting agent, the beads have no ability to hold together. It will spread out across the entire surface.
“That’s what a Class A foam does,” Bateman said. “It does not provide a blanket, although some say it will. And while it does provide a blanket on a Class B fire, it does not provide a good one. It has no film in it. It does not have any burn back capability to prevent re-ignition.”
A Class A fire involves ordinary combustibles such as wood, paper or anything that leaves an ash. Class B fires are fueled by flammable or combustible liquids. Depleting the oxygen supply works best against Class B fires.
If Class A foam is the only foam available, use it. But never turn your back on any Class B fire freshly extinguished using Class A foam. Water quickly drains out of Class A foam. Hopefully, a high quality AR-AFFF (alcoholresistant aqueous film-forming foam) can be obtained instead.
Basically, Class A foam is a hydrocarbon surfactant. That puts it in the same category as most dishwashing detergent. Class A foam has no fluorine content, which is the basis for all effective Class B foams.
“There is big talk about fluorine free foams,” Bateman said. “However, there is nothing that’s been shown to replace the high quality AR-AFFF to date. Stay tuned. I’m sure that will change. But I am not going to send somebody in with fluorine free foams as they exist now.”
Ignition of a Class B fire is a matter of fuel vapor mixture. Bateman cites a California refinery explosion many years ago. An over fill of an internal floating roof tank pushed product out the vents to pool around the base.
Downwind, outside the refinery property, a driver is mystified that the engine on her car has stalled. With the air so rich in hydrocarbon fumes, there is not enough fresh air available to sustain ignition. Meanwhile, an alarm has sounded in the control room and two operators have been dispatched to the overfilled tank to investigate.
“The woman tells herself, ‘I’m going to try the engine one more time,’” Bateman said. “Unfortunately, the fumes had thinned out enough where there was now an ignitable mixture of product and air.”
The resulting explosion not only killed the woman outside the refinery fence, but the two operators driving to the scene with their windows down.
Class B foam is designed to prevent this scenario, Bateman said. However, as a solution, foam blankets are never permanent. Heat and wind limit performance when it comes to smothering vapor.
“Wind will dry out the bubbles,” Bateman said. “It will push them in an accordion-like manner. The bubbles will start to ravel and accumulate at the far end of the pooling area. So you have to be ever watchful for when it is time to replenish the blanket.”
Because the specific gravity of a product such as gasoline is less than water, it will rise to the top as the foam blanket breakdown. Even a small source of vaporization can result in total ignition.
“There’s no such thing as a partially extinguished flammable liquid fire,” Bateman said.
If the product is ethanol instead of gasoline, the ethanol and water become a solution. Diluting ethanol to the point that it will not ignite is no easy thing. Remember that the solution created becomes a hazardous material and must be disposed of in its entirety.
AR-AFFF is the weapon of choice against ethanol because it is approved not only for gasoline but polar solvents. Many plants and refineries that have no polar solvent still prefer AR-AFFF because of its improved performance on hydrocarbon. Or, they have mutual aid partners that do handle polar solvents.
All foams used in industrial fire fighting today require foam concentrate, water, air and mechanical agitation. Still, the foam bubble created can be a fragile thing.
“Me and a zillion of my buddies hit this liquid surface,” Bateman said. “We’re traveling, traveling and putting out the fire as we go. Then we hit this thing. It could be a berm or tank wall. It stops us. If it’s been impinged by fire for some period of time, it’s probably pretty hot.”
Those first arriving bubblse go pop, sacrificed to cool the heated exposure. When the temperature falls below 212 degrees Fahrenheit, the bubbles survive and begin to adhere, creating a foam blanket. However, the sacrificed bubbles are now contributing to the rising volume beneath that blanket.
“Don’t squander foam,” Bateman said. “It’s precious. Keep it for when you need it. You are at your least effective at the beginning of an incident in almost every case.”