القاعدة ذات الصلة
Spain
Practice Relating to Rule 47. Attacks against Persons Hors de Combat
Section C. Quarter under unusual circumstances of combat
Spain’s LOAC Manual (1996) states that when the conditions of combat make it impossible to treat prisoners of war properly and to evacuate them (e.g. isolated special operations, small units, mass capture which exceeds the possibility of the unit in question), the prisoners must be released and all feasible precautions must be taken to ensure their safety. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Publicación OR7-004, 2 Tomos, aprobado por el Estado Mayor del Ejército, Division de Operaciones, 18 March 1996, Vol. I, § 7.4.c.
Spain’s LOAC Manual (2007) states:
When the conditions in which the hostilities are being conducted prevent prisoners of war from being treated as required and evacuated (isolated action by special operation forces or small units, the capture of large numbers of prisoners of war that the detaining unit does not have the capacity to handle, etc.), they must be released and all feasible precautions taken to ensure their safety.  
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 7.4.c; see also § 8.3.c.
Upon ratification of the 1977 Additional Protocol I, Spain interpreted the term “feasible” as meaning that “the matter in question is feasible or possible in practice, taking into account all the circumstances prevailing at the time, including humanitarian and military aspects”. 
Spain, Interpretative declarations made upon ratification of the 1977 Additional Protocol I, 21 April 1989, § 3.