Protected lobbies and protected corridors

A protected lobby or protected corridor should be provided to every escape stairway on every storey in a building other than the top storey where – (a) the escape stairway is the only escape stairway serving the building (or part of the building) and the building (or part of the building) has more than one storey above or more than one storey below the storey containing the final exit from the escape stairway; (b) the escape stairway serves a storey more than 18 m above ground level; (c) the building is designed for phased evacuation and the top storey consists exclusively of plant rooms; or (d) the discounting stairway provisions have not been used in calculating escape stair widths as permitted by paragraph 2.64. A protected lobby should also be provided between an escape stairway and a place of special fire hazard, and that lobby should have either not less than 0.4 m2 of permanent ventilation or be protected from the ingress of smoke by a mechanical smoke control system.