Process Hazards - hdbk10810043

Spontaneous Heating and Pyrophoricity

DOE-HDBK-1081-94

PYROPHORIC METALS

periodically for corrosion. One plant handling zirconium has established the

procedure of disposing of cans containing powder that have been on the shelf for 6

months.

Process Hazards

In general, processing recommendations for zirconium and hafnium are the same.

Handling of zirconium powder, whenever possible, should be under an inert liquid or

in an inert atmosphere. If zirconium or hafnium powder is handled in air, extreme

care must be used because the small static charges generated may cause ignition.

To prevent dangerous heating during machining operations, a large flow of mineral

oil or water-base coolant is required. In some machining operations, the cutting

surface is completely immersed. Turnings should be collected frequently and stored

under water in cans. Where zirconium dust is a byproduct, dust collecting equipment

which discharges into a water precipitation type of collector is a necessity.

Extinguishing Fires in Zirconium and Hafnium

Zirconium and hafnium fires can be extinguished in the same way. Fires exposing

massive pieces of zirconium, for example, can be extinguished with water. Limited

tests conducted by Industrial Risk Insurers have indicated that the discharge of water

in spray form would have no adverse effect on burning zirconium turnings. When a

sprinkler opened directly above an open drum of burning zirconium scrap, there was a

brief flareup after which the fire continued to burn quietly in the drum. When a

straight stream of water at a high rate of flow was discharged into the drum, water

overflowed and the fire went out.

Where small quantities of zirconium powder or fines are burning, the fire can be

ringed with a Class D extinguishing powder to prevent its spread, after which the fire

can be allowed to burn out. Special powders developed for metal fires have been

effective in extinguishing zirconium fires. When zirconium dust is present, the

extinguishing agent should be applied so that a zirconium dust cloud will not form. If

the fire is in an enclosed space, it can be smothered by introducing argon or helium.

Calcium and Zinc

Properties

Calcium

The flammability of calcium depends considerably on the amount of moisture

in the air. If ignited in moist air, it burns without flowing at a somewhat

lower rate than sodium. It decomposes in water to yield calcium hydroxide

and hydrogen, which may burn. Finely divided calcium will ignite

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Pyrophoricity