A substance ispyrophoric (fromAncient Greek:πυροφόρος,pyrophoros, 'fire-bearing') if it ignites spontaneously in air at or below 54 °C (129 °F) (for gases) or within 5 minutes after coming into contact with air (for liquids and solids).^[1] Examples areorganolithium compounds andtriethylborane. Pyrophoric materials are oftenwater-reactive as well and will ignite when they contact water orhumid air. They can be handled safely in atmospheres ofargon or (with a few exceptions)nitrogen.Class Dfire extinguishers are designated for use in fires involving metals but not pyrophoric materials in general. A related concept ishypergolicity, in which two compounds spontaneously ignite when mixed.

The creation ofsparks from metals is based on the pyrophoricity of small metal particles, and pyrophoric alloys are made for this purpose.^[2] Practical applications include the sparking mechanisms inlighters and various toys, usingferrocerium; starting fires without matches, using afiresteel; theflintlock mechanism in firearms; andspark testing ferrous metals.

Small amounts of pyrophoric liquids are often supplied in a glass bottle with apolytetrafluoroethylene-linedseptum. Larger amounts are supplied in metal tanks similar to gas cylinders, designed so a needle can fit through the valve opening. A syringe, carefully dried and flushed of air with aninert gas, is used to extract the liquid from its container.

When working with pyrophoric solids, researchers often employ a sealedglove box flushed with inert gas. Since these specialized glove boxes are expensive and require specialized and frequent maintenance, many pyrophoric solids are sold as solutions, or dispersions inmineral oil or lighterhydrocarbon solvents, so they can be handled in the atmosphere of the laboratory, while still maintaining an oxygen- and moisture-free environment. Mildly pyrophoric solids such aslithium aluminium hydride andsodium hydride can be handled in the air for brief periods of time, but the containers must be flushed with inert gas before the material is returned to the container for storage.

• White phosphorus
• Alkali metals, especiallypotassium,rubidium,caesium, including the alloyNaK
• Finely divided metals (iron,^[3]aluminium,^[3]magnesium,^[3]calcium,zirconium,^{[citation needed]}uranium,titanium,tungsten,bismuth,hafnium,thorium,osmium,neodymium)
• Some metals and alloys in bulk form (cerium)
• Alkylated metalalkoxides or nonmetalhalides (diethylethoxyaluminium, dichloro(methyl)silane)
• Potassium graphite (KC₈)
• Metalhydrides (sodium hydride,lithium aluminium hydride,uranium trihydride)
• Partially or fully alkylated derivatives of metal and nonmetal hydrides (diethylaluminium hydride,trimethylaluminium,triethylaluminium,butyllithium), with a few exceptions (i.e.dimethylmercury andtetraethyllead)
• Copper fuel cell catalysts (zinc oxide,aluminium oxide)^[4]
• Grignard reagents (compounds of the form RMgX)
• Usedhydrogenationcatalysts such aspalladium on carbon orRaney nickel (especially hazardous because of the adsorbed hydrogen)
• Iron(II) sulfide: often encountered in oil and gas facilities, where corrosion products in steel plant equipment can ignite if exposed to air
• Lead andcarbon powders produced from decomposition oflead citrate^[5][6]
• Uranium, as shown in the disintegration ofdepleted uranium penetrator rounds into burning dust upon impact with their targets; in finely divided form it is readily ignitable, and uranium scrap from machining operations is subject to spontaneous ignition^[7]
• Neptunium
• Several compounds ofplutonium are pyrophoric, and they cause some of the most serious fires occurring inUnited States Department of Energy facilities^[8]
• Petroleum hydrocarbon (PHC) sludge

• Diphosphane
• Metalorganics of main group metals (e.g.aluminium,gallium,indium,zinc,cadmium, etc.)
• Triethylborane
• tert-Butyllithium
• Diethylzinc
• Triethylaluminium

• Nonmetalhydrides (arsine,phosphine,^[i]diborane,germane,silane)
• Metal carbonyls (dicobalt octacarbonyl,nickel carbonyl)

• US Dept. of Energy Handbook, "Primer on Spontaneous Heating and Pyrophoricity" (archived)
• "List of pyrophoric materials". Archived fromthe original on 2015-07-09.
• "Pyrophoric Chemicals Guide"(PDF).Environmental Health and Safety. University of Minnesota. Archived fromthe original(PDF) on 31 October 2014. Retrieved27 March 2021.