Halon applied to a Sodium Fire
Halon contains three Fluorine atoms in its molecule. It is this Fluorine that can energetically react when applied to a Class D metal
Fluorine is a better oxidizer than oxygen. When exposed to the heat of a fire the Fluorine is liberated and rapidly oxidizes the metal to create a very hot fire.
Here is an example of a sodium fire and its reaction with Halon.
A small piece of sodium about one half inch square set on fire.
Application of Halon to the fire results in a significant reaction.
Proposed replacement agents for Halon, such as DuPont FM-200 has seven Fluorine atoms. Although Cargo Foam is water based and will also react with certain metal fires it has the benefit of Argon. Argon promotes the formation of a hydrate layer around the metal that is burning. This has the effect of sealing in the reaction and preventing it from spreading.
