Related Rule
Practice Relating to Rule 8. Definition of Military Objectives
Section I. Presence of civilians within or near military objectives
Germany’s Military Manual (1992) states:
Civilians present in military objectives are not protected against attacks directed at these objectives; the presence of civilian workers in an arms production plant, for instance, will not prevent opposing armed forces from attacking this military objective. 
Germany, Humanitarian Law in Armed Conflicts – Manual, DSK VV207320067, edited by The Federal Ministry of Defence of the Federal Republic of Germany, VR II 3, August 1992, English translation of ZDv 15/2, Humanitäres Völkerrecht in bewaffneten KonfliktenHandbuch, August 1992, § 445.