Pennsylvania Statutes Title 53 P.S. Municipal and Quasi-Municipal Corporations § 24959. Stairs and stairways

All stairs within the building shall be constructed of fireproof material throughout.  Stairways serving for the exit of fifty people must, if straight, be at least four feet wide between railings or between walls, and, if curved or winding, five feet wide, and for every additional fifty people to be accommodated six inches must be added to their width.  In no case shall the risers of any stairs exceed seven and a half inches in height nor shall the treads, exclusive of nosings, be less than ten and one-half inches wide in straight stairs.  In circular or winding stairs the width of the tread at the narrowest end shall not be less than seven inches.