PHOSPHORUS (WHITE OR YELLOW)

PHOSPHORUS (WHITE OR YELLOW)

White or yellow phosphorus is a flammable, toxic, corrosive, wax-like, transparent, nonmetallic solid with a disagreeable odor similar to garlic; it will spontaneously ignite in air as it approaches its autoignition temperature. For this reason the product is kept in a vacuum, in an atmosphere of inert gas, or under water to keep it from igniting. Among its synonyms are element phosphorus, phosphorus, WP, white phosphorus, and yellow phosphorus.

It has a specific gravity of 1.82 and an atomic weight of 31 It has an autoignition temperature of 86°F, melts at 1 1 1.4°F, boils at 536°F, and is not soluble in water. Its CAS (Chemical Abstract Services) number is 7723-14-0; its STCC (Standard Transportation Commodity Code) number is 4916140 (white or yellow, dry) and 191614 1 (white or yellow, in water); its I N/NA (United Nations/North America) designation is 1381 (dry or under water or in solution) and 2447 (molten liquid); its CHRIS (Chemical Hazard Response Information System) designation is PPW; its NFPA (National Fire Protection Association) 704 Rating is 3-3-1; its RTECS (Registry of Toxic Fffects of Chemical Substances) designation is TH3500000 (dry) and TH3505000 (in water); its DOT (U.S. Department of Transportation) classification is flammable solid; and its IMO (International Maritime Organization) designation is flammable solid, 4.2. Its atomic symbol is P.

Phosphorus exists in three allotropic forms: white (or yellow), red, and black. Red phosphorus, which is much less reactive, is made from white phosphorus that has been heated to 464°F w ith a catalyst. Red phosphorus will ignite at 500°F and is fairly stable. Black phosphorus also is made from white phosphorus, is less reactive, and will ignite at temperatures above 752°F.

White phosphorus is unquestionably the most dangerous of the three allotropes (an allotrope is a different form of the same element). It oxidizes rapidly in the presence of air or other oxidizer, generating heat as it does so, enough to raise its temperature to that at which it will ignite violently. Although ignition of white phosphorus may not be instantaneous on contact w ith air in ambient temperatures below 86°F, spontaneous ignition most certainly w ill occur as the material reaches 86°F unless responders intervene to exclude oxygen and cool the phosphorus.

While some references do not list elemental phosphorus as “pyrophoric,” the material nevertheless behaves consistently with the literal definition of that word, “ignites spontaneously in air.” Semantics aside, it is essential that the responder understand the speed at w hich white phosphorus can and often will ignite. Phosphorus begins to oxidize at temperatures below 86°F: if particle size is small enough, its temperature will rise rapidly and it will ignite at ambient temperatures below 86°F. Remember that when it comes to hazardous materials, it is always best to err on the side of conservatism.

When not burning, phosphorus w ill evolve dense, toxic, phosphorous fumes with a vapor density of 4.27, corresponding to a molecular weight of 123.88, which indicates a molecular formula of P4. When white phosphorus burns in air, the combustion products include multiple oxides of phosphorus, probably mostly phosphorus pentoxide and phosphorus trioxide. All oxides of phosphorus, collectively referred to as POx are very toxic materials and must be avoided.

Once white phosphorus begins to burn in air, it may be extinguished only by the exclusion of air, usually bycovering it with water or a firefighting foam. Application of wet soil or sand also is recommended. After extinguishment, the spilled phosphorus must be kept wet to prevent reignition. White phosphorus fires are very frustrating to emergency responders because even after one has been extinguished, it will reignite as soon as the remaining white phosphorus is reexposed to air, generating large amounts of toxic combustion products.

Any contact of the skin by phosphorus will cause very deep thermal burns. A large enough piece of phosphorus. if not removed, will burn completely through a hand or foot. Indeed, one of its uses is in antipersonnel explosives where white phosphorus is spread by an explosive device, causing severe injury and/or death when it contacts a human.

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