Practice Relating to Rule 85. The Use of Incendiary Weapons against Combatants
Section A. The use of incendiary weapons in general
In 2009, in a report on Israeli operations in Gaza between 27 December 2008 and 18 January 2009 (the “Gaza Operation”, also known as “Operation Cast Lead”), Israel’s Ministry of Foreign Affairs stated:
Use of Munitions Containing White Phosphorous
406. During the Gaza Operation, IDF [Israel Defense Forces] forces used munitions containing white phosphorous, which is in common use by militaries worldwide. In particular, IDF used two different types of munitions containing white phosphorous – exploding munitions and smoke projectiles.
407. Exploding munitions containing white phosphorous. A small number of exploding munitions containing white phosphorous were used by the IDF during the Operation as mortar shells fire by ground forces and as rounds from naval vessels. These munitions were fired only at open unpopulated areas and were used only for marking and signalling rather than in an anti-personnel capacity. … No exploding munitions containing white phosphorous were used in built-up areas of the Gaza Strip or for anti-personnel purposes. The restrictions on the use of incendiary weapons under Protocol III (relating to Incendiary Weapons) to the  Convention on Certain Conventional Weapons (“CCW Protocol III”) were observed at all times, even though Israel is not a party to the Protocol (for further elaboration, see below).
409. Smoke projectiles containing white phosphorous. The second and main type of munitions containing white phosphorous employed by the IDF during the Gaza Operation was smoke screening projectiles. …
410. … [S]moke-screening projectiles are designed to create a protective smoke screen for battlefield purposes, and were used exclusively for this purpose by the IDF during the Gaza Operation. The smoke projectiles may, on occasion, produce incidental incendiary effects, but this does not make them incendiary weapons for purposes of international law.
International Law Applicable to the use of Incendiary Weapons
411. The use of munitions containing white phosphorous is not prohibited by any international treaty, including CCW Protocol III. Article I of CCW Protocol III defines “incendiary weapon” as “… any weapon or munition which is primarily designed to set fire to objects or to cause burn injury to persons through the action of flame, heat, or combination thereof, produced by a chemical reaction of a substance delivered on the target.” Article I further expressly excludes from its purview: “… Munitions which may have incidental incendiary effects, such as illuminants, tracers, smoke or signalling systems.”
412. Accordingly, although Israel is not a party to CCW Protocol III, it is clear that the use of munitions containing white phosphorous as a smokescreen is not regulated nor prohibited by it.
414. Although the use of weapons containing white phosphorous for smoke-screening purposes is not prohibited by any international treaty, it is still subject to the applicable norms of the Law of Armed Conflict, including the principles of distinction and proportionality, which regulate the employment of any types of weapons during an armed conflict.
[footnotes in original omitted]
In January 2010, in an update of its July 2009 report on Israeli operations in Gaza between 27 December 2008 and 18 January 2009, Israel’s Ministry of Foreign Affairs stated:
117. This investigation dealt with the use of weapons containing phosphorous by IDF [Israel Defense Forces] forces during the Gaza Operation. The investigation focused on the different types and number of weapons containing phosphorous used during the Operation, the purposes for which they were used, the applicable professional instructions and rules of engagement, and the extent of compliance with those instructions and rules. …
118. The Military Advocate General reviewed the entire record of the special command investigation. …
119. With respect to smoke projectiles, the Military Advocate General found that international law does not prohibit use of smoke projectiles containing phosphorous. Specifically, such projectiles are not “incendiary weapons,” within the meaning of the Protocol on Prohibitions or Restrictions on the Use of Incendiary Weapons [1980 Protocol III to the Convention on Certain Conventional Weapons] because they are not primarily designed to set fire or to burn. The Military Advocate General further determined that during the Gaza Operation, the IDF used such smoke projectiles for military purposes only, for instance to camouflage IDF armour forces from Hamas’s antitank units by creating smoke screens.
[footnotes in original omitted]
In July 2010, in a second update of its July 2009 report on Israeli operations in Gaza between 27 December 2008 and 18 January 2009, Israel’s Ministry of Foreign Affairs stated:
The use of smoke-screening munitions containing phosphorus during the Gaza Operation was also addressed in a special command investigation dedicated to the issue. This investigation determined that the policy of using such munitions was consistent with Israel’s obligations under the Law of Armed Conflict. Nonetheless, following that investigation, the Chief of the General Staff ordered the implementation of the lessons learned from the investigation, particularly with regard to the use of such munitions near populated areas and sensitive installations. As a consequence, the IDF [Israel Defense Forces] is in the process of establishing permanent restrictions on the use of munitions containing white phosphorus in urban areas.