Storage and Handling - hdbk10810034

PYROPHORIC METALS

DOE-HDBK-1081-94

Spontaneous Heating and Pyrophoricity

Scrap magnesium chips or other fines (finely divided particles) may burn as the result

of ignition of waste rags or other contaminants. Chips wet with water, water soluble

oils, and oils containing more than 0.2% fatty acid may generate hydrogen gas.

Chipswet with animal or vegetable oils may burn if the oils ignite spontaneously.

Fines from grinding operations generate hydrogen when submerged in water, but they

cannot be ignited in this condition. Grinding fines that are slightly wetted with water

may generate sufficient heat to ignite spontaneously in air, burning violently as

oxygen is extracted from the water with the release of hydrogen.

Storage and Handling

The more massive a piece of magnesium, the more difficult it is to ignite, but once

ignited, magnesium burns intensely and is difficult to extinguish. The storage

recommendations in NFPA 480, Standard for the Storage, Handling, and Processing

of Magnesium (hereinafter referred to as NFPA 480) take these properties into

consideration. Recommended maximum quantities of various sizes and forms to be

stored in specific locations are covered in this standard. Storage buildings should be

noncombustible, and the magnesium should be segregated from combustible material

as a fire prevention measure.

With easily ignited lightweight castings, segregation from combustible materials is

especially important. In the case of dry fines (fine magnesium scrap), storage in

noncombustible covered containers in separate fire resistive storage buildings or

rooms with explosion venting facilities is preferable. For combustible buildings or

buildings containing combustible contents, NFPA 480 recommends automatic

sprinkler protection to assure prompt control of a fire before the magnesium becomes

involved.

Because of the possibility of hydrogen generation and of spontaneous heating of fines

wet with coolants (other than neutral mineral oil), it is preferable to store wet scrap

fines outdoors. Covered noncombustible containers should be vented.

Process Hazards

In machining operations involving magnesium alloys, sufficient frictional heat to

ignite the chips or shavings may be created if the tools are dull or deformed. If

cutting fluids are used (machining of magnesium is normally performed dry), they

should be of the mineral-oil type that have a high flash point. Water or water-oil

emulsions are hazardous, since wet magnesium shavings and dust liberate hydrogen

gas and burn more violently than dry material when ignited. Machines and the work

area should be frequently cleaned and the waste magnesium kept in covered, clean,

dry steel or other noncombustible drums which should be removed from the

buildings at regular intervals. Magnesium dust clouds are explosive if an ignition

source is present. Grinding equipment should be equipped with a water-spray-type

Pyrophoricity

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