39. A shaft is an enclosed space extending through one or more stories of a building connecting a series of openings therein, or any story or stories and the roof, and includes exterior and interior shafts whether for air, light, elevator, dumbwaiter or any other purpose.
40. A stair is a flight or flights of steps together with any landings and parts of public halls through which it is necessary to pass in going from one level thereof to another.
41. A firestair is a fireproof stair, enclosed in fireproof walls, within the body of the building which it serves, to which access may be had only through self-closing fireproof doors.
42. A firetower is a fireproof stair, enclosed in fireproof walls, without access to the building from which it affords egress other than by a fireproof self-closing door opening on a communicating balcony or other outside platform at each floor level.
43. A fire escape is a combination of outside balconies and stairs providing an unobstructed means of egress from rooms or spaces in a building.
44. Window dimensions shall always be taken between stop beads or, if there are no stop beads, between the sides, head and sill of the sash opening.