Storage and Handling - hdbk10810037

Spontaneous Heating and Pyrophoricity

DOE-HDBK-1081-94

PYROPHORIC METALS

release of large quantities of heat. Tests have shown that very thin chips and fine

turnings could be ignited by a match and heavier chips and turnings by a Bunsen

burner. Coarse chips and turnings 0.79 by 2.7 mm (1/32 by 3/28 in.) or larger may

be considered as difficult to ignite, but unless it is known that smaller particles are

not mixed with the coarser material in significant amounts, it is wise to assume easy

ignition is possible.

Finely divided titanium in the form of dust clouds or layers does not ignite

spontaneously (differing in this respect from zirconium, plutonium, and certain other

metals). Ignition temperatures of titanium dust clouds in air range from 332 to

588 C (630 to 1,090 F), and of titanium dust layers from 382 to 510 C (720 to

950 F). Titanium dust can be ignited in atmospheres of carbon dioxide or nitrogen.

Titanium surfaces that have been treated with nitric acid, particularly with red

fuming nitric acid containing 10 to 20% nitrogen tetroxide, become pyrophoric and

may be explosive.

The unusual conditions under which massive titanium shapes will ignite spontaneously

include contact with liquid oxygen, in which case it may explode on contact. It has

been found that under static conditions spontaneous ignition will take place in pure

oxygen at pressures of at least 2,413 kPa (350 psi). If the oxygen was diluted, the

required pressure increased, but in no instance did spontaneous heating occur in

oxygen concentrations less than 35%. Another requirement for spontaneous heating is

a fresh surface which oxidizes rapidly and exothermically in an oxygen atmosphere.

Storage and Handling

Titanium castings and ingots are so difficult to ignite and burn that special storage

recommendations for large pieces are not included in NFPA 481, Standard for the

Production, Processing, Handling, and Storage of Titanium. Titanium sponge and

scrap fines, on the other hand, do require special precautions, such as storage in

covered metal containers and segregation of the container from combustible materials.

Because of the possibility of hydrogen generation in moist scrap and spontaneous

heating of scrap wet with animal or vegetable oils, a yard storage area remote from

buildings is recommended for scrap that is to be salvaged. Alternate recommended

storage locations are detached scrap storage buildings and fire resistive storage rooms.

Buildings and rooms for storage of scrap fines should have explosion vents.

Process Hazards

Contact of molten metal with water is the principal hazard during titanium casting. To

minimize this hazard, molds are usually thoroughly predried and vacuumed, or inert

gas protection is provided to retain accidental spills.

The heat generated during machining, grinding, sawing, and drilling of titanium may be

sufficient to ignite the small pieces formed by these operations or to ignite mineral oil

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Pyrophoricity