Water on Zirconium Fires

Spontaneous Heating and Pyrophoricity

DOE-HDBK-1081-94

PYROPHORIC METALS

Water on Zirconium Fires

Powdered zirconium wet with water is more difficult to ignite than the dry

powder. However, once ignition takes place, wet powder burns more violently

than dry powder. Powder containing about 5 to 10% water is considered to be

the most dangerous. Small volumes of water should not be applied to burning

zirconium, but large volumes of water can be successfully used to completely

cover solid chunks or large chips of burning zirconium (e.g., by drowning the

metal in a tank or barrel of water). Hose streams applied directly to burning

zirconium chips may yield violent reactions.

Water on Plutonium, Uranium, and Thorium Fires

Water is generally acceptable for use as an extinguishing agent for fires

involving enriched uranium, plutonium, and thorium fires (fissionable

materials). In rare cases where criticality safety considerations preclude the

introduction of moderators such as water, suitable alternative fire protection

measures need to be incorporated into the facility design. Limited amounts of

water add to the intensity of a fire in natural uranium or thorium, and greatly

increase the contamination cleanup required after the fire. A natural uranium

scrap fire can be fought with water by personnel (wearing face shields and

gloves and using long-handled shovels) shoveling the burning scrap into a

drum of water in the open. The hydrogen formed may ignite and burn off

above the top of the drum. The radioactivity hazard of nonenriched uranium is

extremely low (in reality, uranium is a heavy metal poison, although

considerably less toxic than lead). If ingested, plutonium is considerably more

hazardous to humans than uranium.

Water on Magnesium Fires

Although water in small quantities accelerates magnesium fires, rapid

application of large amounts of water is effective in extinguishing magnesium

fires because of the cooling effect of water. Automatic sprinklers will

extinguish a typical shop fire where the quantity of magnesium is limited.

However, water should not be used on any fire involving a large number of

magnesium chips when it is doubtful that there is sufficient water to handle the

large area. (A few burning chips can be extinguished by dropping them into a

bucket of water.) Small streams from portable extinguishers will violently

accelerate a magnesium chip fire.

Burning magnesium parts such as castings and fabricated structures can be

cooled and extinguished with coarse streams of water applied with standard

fire hoses. A straight stream scatters the fire, but coarse drops (produced by a

fixed nozzle operating at a distance or by use of an adjustable nozzle) flow

over and cool the unburned metal. Some temporary acceleration normally

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Pyrophoricity