Vertical Opening 4 : Any hole that penetrates one or more floors of a building, e. g. , a stairway, elevator, or conveyor, or duct for heating, ventilation, and utility lines
Ralph W. Burklin & Robert G. Purington, Fire Terms: A Guide to Their Meaning and Use, National Protection Association, Boston, MA 1980 USA. (Guide: Meaning and Use, Nat Prot Association Fr Srvc - Amer) {457}