The enclosure comprises: a partition (1) of panels (2) provided with longitudinal grooves (3) and a space for mounting a door (6); and a door (6) comprising: an upper box (7); and two vertical posts (9) with vertical guides (30) for moving a closing element (10), in addition to longitudinal channels (15) defining passages, with the longitudinal grooves (3), for housing fastening elements (16, 17) that can be vertically moved between a position wherein the door (6) is held and a position wherein the door (6) is released. The door comprises means for ensuring peripheral tightness in the closed position.