Related Rule
Practice Relating to Rule 84. The Protection of Civilians and Civilian Objects from the Effects of Incendiary Weapons
Belgium’s Law of War Manual (1983) defines incendiary weapons in accordance with Article 1 of the 1980 Protocol III to the Convention on Certain Conventional Weapons and states:
The use of such [incendiary] weapons against persons is prohibited because they cause unnecessary suffering, but their use against military objectives, such as bunkers, tanks, depots, etc. is permitted. However, if these military objectives are located inside a civilian concentration, their use is prohibited, except when the object is clearly separate from the concentration of civilians and all precautions are taken to avoid any loss of life among the civilian population and any damage to civilian objects. Their use against forests is also prohibited, except when they constitute a military objective or are used to conceal combatants or other military objectives. 
Belgium, Droit Pénal et Disciplinaire Militaire et Droit de la Guerre, Deuxième Partie, Droit de la Guerre, Ecole Royale Militaire, par J. Maes, Chargé de cours, Avocat-général près la Cour Militaire, D/1983/1187/029, 1983, p. 38.