Sometimes, water won’t put the fire out.

The Warren Fire Department practiced Wednesday with a foam system intended to put out flammable liquid fires. A layer of foam can separate the liquid fuel from the air it needs to burn.

A trailer hauled behind an engine carried three 55-gallon drums of foam concentrate, a “master stream” launcher, and various connections, to the department’s practice tower off of Harmar Street. The master stream has an effective range of about 75 feet.

Seven firefighters practiced with the system Wednesday, using both hoses and the master stream to deliver foam to the target.

There is a technique to applying the foam to a fire – just shooting it at the blaze won’t put the fire out. Firefighters practiced bouncing it and rolling it to form a membrane of the thickness needed to prevent air from getting to the fuel.

The fire-fighting foam costs $55 per gallon. To save money, firefighters used practice foam on Wednesday.

The system mixes water pumped through hoses of various sizes with the proper amount of foam concentrate and air to deliver a three-percent solution to hydrocarbon (typically gasoline) or polar solvent (gasoline with at least 10 percent ethanol) fires.

“We have enough foam concentrate to blanket 2,500 square feet of a flammable liquid that would be classified as a polar solvent or about 5,000 square feet of a hydrocarbon spill,” Warren Fire Department Chief Sam Pascuzzi said.

“It gives us the ability to make an initial response,” he said.

In the event of a larger flammable liquid fire, the department could start the process and await the arrival of another department – Warren County All-Hazards and United Refining both have foam systems.

Ethanol is increasingly being added to gasoline.

“If you don’t have the right type of foam, the alcohol reacts with the foam blanket, degrades it, and allows air to come back into contact with the fuel,” Pascuzzi said. “That’s why we wanted to make sure we had foam that could be used on gasoline that contains ethanol.”

The department used a grant of $8,000 to first purchase the foam system in 2010.