Other Combustible Metal Extinguishing Agents

Spontaneous Heating and Pyrophoricity

DOE-HDBK-1081-94

PYROPHORIC METALS

Other Combustible Metal Extinguishing Agents

Foundry Flux

In magnesium foundry operations, molten magnesium is protected from contact

with air by layers of either molten- or crust-type fluxes. These fluxes, which are

also used as molten metal cleaning agents, consist of various amounts

ofpotassium chloride, barium chloride, magnesium chloride, sodium chloride,

and calcium fluoride. The fluxes are stored in covered steel drums. When

applied to burning magnesium, these fluxes melt on the surface of the solid or

molten metal, excluding air. The thin layer of protection can be provided by

properly applying relatively small amounts of flux.

Fluxes are valuable in extinguishing magnesium spill fires from broken molds

or leaking pots and in controlling and extinguishing fires in heat treating

furnaces. In open fires, the flux is applied with a hand scoop or a shovel. Areas

of furnaces that are difficult to reach can be coated by means of a flux throwing

device similar to those used to throw concrete onto building forms.

While fluxes would rapidly extinguish chip fires in machine shops, such use is

not recommended. The fluxes are hygroscopic and the water picked up from

the air, combined with the salt, causes severe rusting of equipment.

Copper Powder

Advances in the science of alternative propulsion systems have led to the

development of copper powder as a viable extinguishing agent for combustible

metals. Work sponsored by the Naval Sea Systems Command was conducted

to evaluate the adequacy of existing lithium fire suppression agents and to

develop new agents should deficiencies exist.

Copper powder was found to be superior to known lithium fire extinguishing

agents in extinguishing capacity. The dry powder is of uniform particle size

and extinguishes a lithium fire more quickly and efficiently than existing

agents. The process of extinction is by formation of a copper-lithium alloy,

which is nonreactive and forms preferentially on the surface of the molten

lithium. The alloy becomes an exclusion boundary between air and the molten

metal, preventing reignition and promoting cooling of the unreacted lithium.

Copper powder can be applied from hand-portable extinguishers. The nominal

charge for each extinguisher is 14 kg (30 lb); it is 68 and 160 kg (150 and

350 lbs) for wheeled units, as well as fixed systems. Argon is used as the

propellant. The method of application is similar to that of other metal fire

powders, in that the fuel surface is coated with the copper powder in an initial

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Pyrophoricity