Phosphine

PYROPHORIC GASES AND LIQUIDS

DOE-HDBK-1081-94

Spontaneous Heating and Pyrophoricity

Phosphine

Phosphine (PH3) is a highly toxic colorless gas. This chemical is very dangerous, with

an ignition temperature of 212 F, often igniting spontaneously. Phosphine gas readily

combines with nitrates, halogens, and metals to form very explosive and volatile

compounds. Specifically, phosphine reacts violently with air, BCl3 , Br2 , Cl2 , ClO,

Hg(NO3)2, NO, N2O, NCl3, -NO3, N2O, HNO2, O2, (K+NH3), and AgNO3. In

addition, at elevated temperatures, phosphine decomposes, emitting highly toxic fumes

of POx, which react vigorously with oxidizing materials. It possesses the characteristic

putrefying odor of a mixture of garlic and decaying fish. Prolonged exposure to very

low concentrations will cause chronic poisoning, characterized by anemia, bronchitis,

gastro-intestinal disturbances, and visual, speech, and motor difficulties.

Silane

Silane (SiH4 ), also know as silicon tetrahydride, is a colorless gas with a putrid odor.

It and its compounds (e.g., disilane Si2H8) can ignite in air and react violently with

chlorine (Cl2 ). The presence of other hydrides as impurities causes ignition always to

occur in air. However, 99.95% pure silane ignites in air unless emerging at very high

gas velocities, whereas mixtures of up to 10% silane may not ignite. Hydrogen

liberated from its reaction with air (atmospheric oxygen) often ignites explosively.

Silanes react violently with chlorine and bromine. All silanes should be considered

pyrophoric until they are properly characterized. Halon should not be used as an

extinguishing agent on silane fires.

Extinguishing Pyrophoric Gas Fires

Pyrophoric gases may spontaneously explode at high gas release rates. For fires

involving flammable gases, the best procedure is to stop the flow of the gas before

attempting extinguishment of the fire. To extinguish the fire while allowing continued

flow of the gas is extremely dangerous; an explosive cloud of gas/air mixture may be

created that, if ignited, may cause far more damage than the original fire.

Extinguishing the flame using carbon dioxide or dry chemical may be desirable to

allow immediate access to valves to shut off the flow of gas, but this must be done

carefully. In many cases, it will be preferable to allow continued burning, while

protecting exposures with water spray, until the flow of gas can be stopped. Since

many pyrophoric gases react violently with halogens, Halons should not be used as

extinguishing agents.

Pyrophoric Gas Storage and Dispensing Areas

Pyrophoric gas cylinders in storage or dispensing areas should be provided with the

following safeguards:

Pyrophoricity

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