Related Rule
Practice Relating to Rule 8. Definition of Military Objectives
Section I. Presence of civilians within or near military objectives
The Military Manual (1993) of the Netherlands considers that:
Acts such as the manufacturing and transport of military materiel in the hinterland certainly do not constitute a direct participation in hostilities. In addition, it has to be borne in mind that the fact that civilians are working in, for example, a weapons factory does not convert such an industrial object into a civilian object. Such a case has to be assessed in the light of the definition of a military objective. 
Netherlands, Toepassing Humanitair Oorlogsrecht, Voorschift No. 27-412/1, Koninklijke Landmacht, Ministerie van Defensie, 1993, p. V-5.