White Phosphorus Munition

Smoke production and intense combustion are the principal properties exploited in white-phosphorus munitions: the same substance can provide battlefield obscuration or serve an incendiary purpose.[1] Smoke screens limit an opponent’s field of vision and can disrupt optical tracking and targeting.[3] Military applications also include signalling, marking targets, and illumination.[2]

White phosphorus is a highly reactive and toxic form of phosphorus that can ignite in air at approximately 35°C (95°F).[5] Its reactivity requires storage under water or another inert liquid.[5] Contact with burning material can cause severe skin burns, while its heat can ignite vegetation and other flammable objects.[3]

A munition’s chemical contents alone do not determine whether it is a chemical weapon: white-phosphorus weapons whose primary effect depends on incendiary properties rather than toxicity are not chemical weapons under the definition used by the Chemical Weapons Convention.[4] This distinction concerns the mechanism of the weapon’s effects, rather than an absence of injury hazards.[1][4]

White phosphorus has been used militarily since World War I, both as an incendiary agent and to generate smoke screens or signals.[1] Its use has extended across aircraft bombs, artillery and mortar projectiles, air-to-ground rocket warheads, landmines, and hand- and rifle-grenades.[1] Projectiles containing the substance have served both incendiary and smoke-screening or smoke-marking purposes.[1]

During Operation Cast Lead, fought from 27 December 2008 to 18 January 2009, Israel used white-phosphorus munitions in forms that included exploding munitions and smoke-screening projectiles.[6][7] The Israeli government’s account distinguished a small number of exploding shells used by ground and naval forces for marking and signalling in open, unpopulated areas from the smoke shells that constituted the main white-phosphorus munitions used during the operation.[7] That account also described one use in an open area to uncover tunnel entrances.[7]

A precautionary decision to stop using the exploding munitions was made on 7 January 2009, although a subsequent Israeli investigation identified two further marking uses after that date.[7] The decision did not amount to a simultaneous end to the acknowledged use of white-phosphorus smoke projectiles.[6]

In April 2013, the Israeli army announced that it would replace white-phosphorus shells with shells based entirely on gas, without specifying a retirement date.[8] In 2023, the IDF stated that its principal smoke shells did not contain white phosphorus, while acknowledging that it still possessed some white-phosphorus smoke shells.[9] It described operational considerations and availability as factors affecting the choice of smoke munition.[9]

Battlefield obscuration uses the dense white smoke generated when phosphorus burns in air to reduce visibility.[1] By limiting observation, a screen can interfere with an opponent’s optical tracking and targeting.[3] During the 2008–09 Gaza operation, the stated purpose of Israel’s white-phosphorus smoke shells was to screen ground forces from observation and anti-tank units.[7] The Israeli operational account described air-burst deployment using delay fuses at least 100 metres above the ground.[7]

One documented smoke-projectile design was a 155-mm howitzer-fired canister shell timed to burst in the air and disperse approximately 160 white-phosphorus-impregnated felt wedges in a fan-shaped pattern.[10] The wedges ignited on contact with air and emitted smoke until their phosphorus was exhausted or deprived of air.[10] This design distributed smoke-producing material rather than relying on a single point of combustion.[10]

Incendiary applications exploit the substance’s ability to start fires in vegetation or other combustible material.[3] Burning vegetation in open areas can expose concealed military compounds, tunnel shafts, bunkers, or weapons.[3] Other military applications use the visible smoke for marking and signalling rather than destruction.[1] White phosphorus has also been used for illumination.[2]

The distinction between these purposes is reflected in the range of delivery systems: aircraft bombs, artillery and mortar rounds, rocket warheads, mines, and grenades have all contained white-phosphorus formulations.[1] A projectile containing the substance may therefore be used for smoke screening or smoke marking as well as for an incendiary purpose.[1] Israel’s account of its Gaza smoke shells acknowledged incidental incendiary effects while maintaining that their purpose was screening, not attacking personnel or destroying buildings.[7]

Burning particles can remain hazardous after initial deployment because they may be difficult to extinguish and can reignite when dry.[1] In Gaza, dispersed felt wedges remained active for periods reported as long as 21–24 days after discharge, and children were subsequently injured after contact with them.[10] Smoke emission continued while phosphorus remained available and exposed to air.[10]

Deep burns are a major consequence of burning phosphorus contacting skin.[1] Particles that remain alight can damage muscles and deeper tissues, potentially causing permanent loss of motor function.[1] Embedded phosphorus can also produce systemic toxic effects, including potentially lethal injury to the liver, heart, kidneys, and blood-generating organs.[1]

Medical accounts from the 2008–09 Gaza conflict described deep tissue and organ damage that was not always apparent initially, with some wounds worsening after patients left hospital.[11] Doctors also described fragments that continued to smoke when bandages were removed.[11] The reported treatment involved keeping the material wet and removing embedded particles and affected tissue.[11]

Weapon classification distinguishes thermal destruction from poisoning: incendiary weapons such as napalm and phosphorus are not classified as chemical-warfare agents when their destructive power is primarily thermal.[12] Smoke-producing obscurant rounds likewise are not viewed as chemical weapons merely because chemicals generate their smoke.[12] For white-phosphorus weapons specifically, the relevant distinction is whether their primary effect depends on incendiary properties rather than toxicity.[4]

International humanitarian law requires assessment of attacks under distinction, proportionality, and precautions, including feasible steps to verify targets and minimize incidental civilian casualties and damage.[13] Those obligations apply to choices of weapons and methods of attack, not only to whether a weapon type is expressly prohibited.[13] Legal assessment of white-phosphorus use consequently involves its manner of employment as well as the classification of the munition.[13][14]

Protocol III of the Convention on Certain Conventional Weapons restricts attacks with incendiary weapons, including attacks involving civilians and military objectives within concentrations of civilians.[14] The United States executive branch has interpreted white phosphorus as outside the protocol’s incendiary-weapon definition; Israel’s position similarly excludes smoke projectiles with incidental incendiary effects, while recognizing that other laws of armed conflict still apply.[14][7] Israel is not a party to Protocol III.[2]

The 2009 Gaza fact-finding inquiry criticized white-phosphorus use in built-up areas and recommended consideration of further controls, while acknowledging that the substance was not generally prohibited under international law.[11] At the UNRWA compound on 15 January 2009, at least seven container shells struck or discharged substantially within a site sheltering 600–700 civilians and containing substantial fuel stores; the inquiry concluded that feasible precautions had not all been taken.[11] Israel maintained that the shells screened forces from anti-tank crews, reported three injuries and property damage, and said smoke-projectile use in that area stopped after the incident.[7] The inquiry also criticized use around al-Quds and al-Wafa hospitals.[11]

In October 2023, Human Rights Watch alleged white-phosphorus use in Gaza and Lebanon; the reporting carried an independent-verification caveat, and the IDF denied the Gaza accusation.[2] In June 2024, further allegations concerned residential buildings in five southern Lebanese communities; the underlying investigation reported no evidence of burn injuries but accounts suggesting possible respiratory damage.[15] Israel maintained that its use was for screening rather than targeting civilians.[15] The IDF also stated that procedures barred use in built-up areas except in exceptional circumstances, reflecting a 2013 undertaking whose two exceptions were disclosed only to the Supreme Court.[9]