For centuries water has been the weapon of choice in fire protection. But in certain types of fires, water is at best ineffective and a catalyst at worst. To fight oil and other flammable liquid fires, fire suppression foam was found to be the best way to extinguish these highly dangerous blazes.
In its simplest form, fire protection foam is a stable mass of tiny air filled bubbles. It is made up of water, air, and some type of foam concentrate. Fire suppression foam was invented back in 1902 by Russian chemist and engineer Aleksandr Loran.
Loran worked near the Russian oil fields and was looking for a way to put out oil fires that were hard to extinguish. He mixed sodium bicarbonate and aluminum sulfate with water and tiny amounts of licorice which was used to stabilize the bubbles. Since then, foam technology has greatly expanded but the underlying principle has remained unchanged.
Fires burn because of the presence of four different elements: heat, fuel, oxygen, and a chemical chain reaction. The removal or interference of any of those elements is usually enough to extinguish a fire. Foam accomplishes this in the following ways:
– Foam is able to blanket a fuel fire because it is lighter than the burning liquid and smothers the fire
– Foam extinguishes the fire by cooling the fuel source and any nearby metal objects
– Foam separates the ignition source or flames from the fuel surface
– Foam suppresses vapors that can easily spread combustion.
There are two popular types of fire suppression foam that are in wide use today near severely flammable liquids.
High Expansion Foam
Invented in the early 1950’s and originally designed to fight fires in coal mines, HEF works mainly by separating, insulating, and suppressing effects. It has a higher proportion of air and larger bubbles which make HEF a dryer foam compared to other types.
Today it is most commonly used in confined areas that need to be filled quickly because of the presence of highly combustible liquids like aircraft hangars. High expansion foam generators are required to outfit a facility and will allow for complete foam flooding in minimal time. The water content is also so low in HEF that water damage is drastically lowered.
Aqueous Film Forming Foam
Developed by the United States Navy in the mid 1960’s, AFFF has a couple of unique features that make it popular in hydrocarbon fuel fire suppression. As the foam is used to extinguish a fire, an aqueous film is formed over the fuel source stopping evaporation and preventing the fire from reigniting. There is also a self-healing capability where even if the film is punctured by falling debris of firefighting activities, it rapidly reseals itself.
AFFF can also be used as a preventative measure where highly flammable liquids could be exposed to an ignition source. One such event happened in 1987 in Fairfax Virginia. A bulldozer ruptured an underground gas line sending thousands of gallons of dangerously flammable liquid and vapors over an entire community.
Nearby airports and military facilities provided 4,375 gallons of AFFF to insure that the spill would not turn into an inferno. Officials were amazed that nothing was able to spark the gas and that no lives were lost.
For more information on fire suppression foams and protection systems, check out our blog!