Such vestibules consist of merely a set of inner doors and a set of outer doors, the intent being to reduce air infiltration to the building by having only one set of doors open at any given time.
Such vestibules consist of merely a set of inner doors. Such vestibules consist of a set of outer doors. Outer doors are the intent. This intent is being to reduce air infiltration to the building by having only one set of doors open at any given time.