Interior stairways, lifts and escalators (other than those entirely contained within the machinery spaces) and enclosures thereto. In this contex, a stairway which is enclosed only at one level is to be regarded as a part of the space from which is not separated by a fire door. Stairways penetrating only one level are required to be enclosed in “A” class bulkheads at one level. If penetrating more than one level, the requirement is for complete enclosure at all levels.