(a) Whenever buildings are being erected to a height in excess of sixty (60) feet above grade level, and whenever buildings exceeding sixty (60) feet in height above grade level are being altered, at least one (1) stairway, shall be provided and maintained for access to all floors. In new construction, such stairways shall be installed as soon as practicable.
(b) Until either permanent or temporary stairways are installed, suitable substantial ladders, securely fastened at top and bottom, shall be provided and maintained to provide means of reaching the various levels.
(c) When buildings are occupied during alterations all required means of egress shall be maintained unobstructed except that temporary arrangements for egress may be substituted when approved by the Commissioner.