Different application techniques of firefighting foam
Fire extinguishment requires appropriate foam concentrate at the right mixing ratio, foam proportioning and foam discharge equipment with a controlled application rate.
There are 2 main application techniques of applying foam onto a fire, recognised by the European (EN1568) and international (ISO7203) standards.
Forceful or Direct application
In direct attack, the foam is applied directly onto the liquid in fire. The foam will form a foam blanket above the fuel.
Firefighters use a nozzle or a monitor in the "solid jet" position. This allows them to fight the fire from a safe distance, reducing thermal exposure during operation.
Installations such as tank storage or warehouse are using long range monitors or fixed sprinkler heads.
This type of foam application can only be applied onto class B and class F fires, using AFFF (Aqueous Film Forming Foam) or FFF (Fluorine-Free Foam) foam concentrates.
Gentle or Indirect application
Gentle application is mostly used on class B polar solvent liquid fires (water-miscible).
The foam is applied first onto a vertical surface (wall, tank…). The foam then spreads carefully above the burning liquid surface. The foam blanket formed will avoid fuel agitation and foam contamination by the fuel.
Fire departments mostly use gentle application during their operations. Firefighters can raise fuel moisture to protect vegetation or structures and for creating line from which to burn. Gentle application is also used for mobile resource operating tactics.
The foam can also be applied directly onto the liquid using Low, Medium or High expansion. That is the case of most of fixed installations: medium expansion foam box on a tank storage, high expansion foam generator in an engine room...
This indirect application is mandatory to ensure that the foam is not directly absorbed by polar solvent which are water-miscible. It is also suitable to extinguish class B hydrocarbon fires (water-immiscible liquid).
Those 2 foam application methods have the same extinguishing effectiveness.
Chemical action with AFFF foam in direct application
The foam generated by an AFFF foam concentrate has quick drainage property. This allows the rapid formation of a thin fluorine compound film above the hydrocarbon surface.
The film generated is resistant to heat and creates a barrier that prevents hydrocarbon vapours release and burnback.
Chemical action with indirect application
Through the accumulation of foam, a foam blanket is forming above the burning liquid.
This foam blanket is thick and highly resistant to heat. It forms a barrier that prevents from vapours ignition.
In all cases, firefighting foam concentrate can break "the fire triangle" by fuel being isolated from the oxygen supply and a cooling effect.
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