Carbon Microspheres

PYROPHORIC METALS

DOE-HDBK-1081-94

Spontaneous Heating and Pyrophoricity

Carbon Microspheres

Specially formulated extinguishing powders are generally used to suppress fires

involving metals. Because of the reaction many metals have with water,

sprinklers and the use of other water-based agents are not appropriate and, in

some cases, quite dangerous. However, many of the special agents for metal

fires are at times unsatisfactory because they are corrosive, applied manually

rather than by an extinguishing system, capable of clogging extinguishing

nozzles, and expensive.

Studies have been undertaken to examine the effectiveness of carbon

microspheres or microspheroids to extinguish fires involving alkali metals,

such as sodium, sodium-potassium, and lithium. These microspheres are

petroleum-coke-based particles with a diameter of approximately 100 to 500

microns. The particles possess high thermal conductivity, chemical inertness,

and excellent flow characteristics and are capable of being directed onto fires

from dry-chemical-type extinguishers and conventional nozzles.

Tests have shown that carbon microspheres compare favorably in performance

to other metal extinguishing agents. In particular, experiments with carbon

microspheroids incorporating neutron absorbers have been effective in

extinguishing fires involving nuclear fissionable materials, such as uranium

metal powder. The excellent flow characteristics and noncoking properties of

these microspheres suggest an effective way to extinguish radioactive metal

fires within the inert atmosphere glovebox enclosures used in the nuclear

industry.

Graphite Powder

Graphite powder (plumbago) has been used as an extinguishing agent for metal

fires. Its action is similar to that of G-1 powder in that the graphite acts as a

coolant. Unless the powder is finely divided and closely packed over the

burning metal, some air does get through to the metal and extinguishment is

not as rapid as with G-1 powder.

Sand

Dry sand has often been recommended as an agent for controlling and

extinguishing metal fires. At times it seems to be satisfactory, but usually hot

metal (such as magnesium) obtains oxygen from the silicone dioxide in the

sand and continues to burn under the pile. Sand is seldom completely dry.

Burning metal reacting with the moisture in the sand produces steam and,

under certain conditions, may produce an explosive metal-water reaction. By

Pyrophoricity

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