Related Rule
France
Practice Relating to Rule 18. Assessment of the Effects of Attacks
France’s LOAC Manual (2001) provides:
Those who plan or decide upon an attack shall … refrain from deciding to launch any attack which may be expected to cause incidental loss of civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be excessive in relation to the concrete and direct military advantage anticipated. 
France, Manuel de droit des conflits armés, Ministère de la Défense, Direction des Affaires Juridiques, Sous-Direction du droit international humanitaire et du droit européen, Bureau du droit des conflits armés, 2001, p. 49; see also p. 89.