White phosphorus

Properties and chemistry

White phosphorus is one of several allotropes of the element; other common allotropes include red and black phosphorus with quite different stability and reactivity. The white form is the least stable and most chemically reactive of these allotropes and is typically represented by the molecular formula P4. It ignites readily on contact with air and is usually stored submerged in water to prevent spontaneous combustion. Its combustion yields phosphorus oxides that hydrolyze to acids, producing characteristic acrid fumes.

Uses and examples

Uses fall into two broad classes:

• Military and tactical: munition fillings, artillery and mortar smoke rounds, marking, illumination, and anti-personnel incendiary effects. Because of its smoke-producing and illuminating qualities it has been used as a battlefield obscurant and signal source.
• Civilian and industrial: limited, controlled uses in research, certain specialized pyrotechnics, and as an intermediate in chemical manufacture. Most large-scale civilian applications have been replaced by safer phosphorus compounds.

Readers should note that the physical and tactical effects of white phosphorus — bright flame, thick smoke and deep-burning capability — are often distinguished from other phosphorus compounds and from non-phosphorus incendiaries.

Health, medical effects and safety

White phosphorus is toxic to humans and can inflict severe injuries. Direct contact produces deep thermal and chemical burns that may continue until the material is removed or isolated from air. Inhalation of fumes or ingestion can cause systemic poisoning with multi-organ effects and fatalities in severe exposures. Historically, industrial exposure to white phosphorus caused a distinctive occupational disease involving jaw necrosis. Safe handling requires storage under water, protective equipment and specific burn-care treatment; contaminated clothing must be removed and medical attention sought promptly.

Legal status, controversies and notable incidents

Because of its incendiary and obscurant uses, white phosphorus is subject to international humanitarian law and arms-control discussions. Protocol III of the Convention on Certain Conventional Weapons restricts incendiary weapons and aims to limit their use in civilian areas; authorities and commentators differ on classification and lawful employment. Various reports and investigations have alleged battlefield uses in modern conflicts — including instances reported in 2004 and in 2008–2009 — which generated public concern and legal scrutiny; see reported cases. Discussion of specific incidents is ongoing and often contested among parties and observers.

History and notable facts

White phosphorus played a prominent role in the 19th-century chemical industry and in early pyrotechnics and matches; unsafe exposure in factories produced serious occupational illnesses and led to regulatory changes and the development of safer alternatives. It remains a subject of environmental and humanitarian concern because of its persistence, toxicity and incendiary effects. For general background on the element and its varieties, see material on the element phosphorus and conventional allotropes. For summaries of safety guidance and toxicology references, consult specialized medical and regulatory sources and incident reports; further reading and official investigations are listed elsewhere and summarized by authoritative agencies and review bodies (smoke and effects).

Because of the serious risks white phosphorus presents to people and the environment, its manufacture, storage and use are tightly controlled where it is permitted, and alternatives are often sought in civilian and military practice.