reference will now be made in detail to some possible embodiments of the invention , examples of which are outlined in this description . according to one embodiment , a fire extinguishing agent configured to extinguish a class d fire and one or more other classes of fires such as , for example , a class a fire and / or a class b fire , may include a foam and one or more inert gases combined with the foam . for example , the foam may include a foam marketed by tyco international ltd . as “ ansul target - 7 ®” foam . the use of other foam agents known to those having skill in the art is contemplated . some embodiments may include foam agents that do not include foams based on fluorocarbon chemistry , such as , for example , aaaf - type foams . the one or more inert gases may include , for example , helium , neon , argon , krypton , xenon , and / or radon . for example , the fire extinguishing agent may include a conventional fire fighting foam gasified with , for example , helium and / or argon , although neon , krypton , and / or xenon may be included in the fire extinguishing agent . the foam and the one or more inert gases may be combined via any method known to those having skill in the art , such as , for example , via combining in a nozzle of a fire extinguisher agent delivery apparatus and / or combining in a fire extinguisher agent mixing conduit . the fire extinguishing agent may be applied to a fire via any methods and / or devices known to those having skill in the art . according to some embodiments , the foam and the one or more inert gases may be combined in a ratio corresponding to about 60 gallons of foam - generating solution per 400 cubic feet of inert gas . other ratios are contemplated . most classes of fires , including class d fires , require fuel , an oxidizer , and heat in order to sustain combustion . unlike most other classes of fires , however , class d fires can sustain combustion by liberating necessary oxidizers from otherwise stable compounds , such as , for example , co 2 and / or halon ®. furthermore , unlike many common classes of fires , metal and / or metal compound fires may burn in oxidizers other than oxygen , such as , for example , chlorine , fluorine , and / or nitrogen . class d fires , however , cannot burn in an inert atmosphere . the family of “ true ” inert or noble gases includes helium , neon , argon , krypton , xenon , and radon . many of the inert gases may be currently thought to be too rare to be economically viable for use in a fire extinguishing agent . further , radon is radioactive . as a result , helium and argon are two inert gases that currently appear to be desirable for use in a fire extinguishing agent according to some embodiments . attempting to extinguish fires including burning metal ( s ) and / or metal compound ( s ) ( e . g ., class d fires ) using one or more inert gases alone , however , may be very difficult . for example , attempting to use an inert gas alone to deprive such a fire of its oxidizer may not be effective because maintaining coverage may be difficult since helium is lighter than the surrounding atmosphere and will quickly float off , and argon is heavier than the surrounding air and will tend settle away from the area of deployment . furthermore , the use of conventional foams to extinguish burning metal ( s ) and / or metal compound ( s ) has proven substantially ineffective , for example , because the water in the foam reacts with the metals to liberate hydrogen and because of the extreme heat of class d fires , the fire &# 39 ; s reaction will continue and use the air and / or nitrogen in the foam as an oxidizer , and the fire will continue to burn . the combination of foam and inert gas may be effective because when water in the foam reacts with the metal , a hydroxide radical ( not oxygen or any other oxidizer ) is liberated during the reaction . hydrogen is also liberated , but in the absence of an oxidizer ( no air or nitrogen is used to generate the foam ), the fire is starved out . the foam may serve to trap the inert gas and keep it positioned where it most effectively acts to extinguish the fire . other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein . it is intended that the specification and examples be considered as exemplary only , with a true scope and spirit of the invention being indicated by the following claims .
a fire extinguishing agent may include a foam and at least one inert gas combined with the foam . a method of extinguishing a fire including a burning metal and / or a burning metal compound and also including a burning plastic material and / or a burning paper material may include combining a foam and at least one inert gas to form a fire extinguishing agent , and applying the fire extinguishing agent to the fire .