Diagram 9.3 Ductwork passing through protected escape routes – method 2 or method 3

NOTE:
Ventilation ducts which serve other parts of the building should not supply or extract air directly to or from a protected escape route.
Ductwork enclosed in fire resisting construction classified EI X in accordance with BSEN13501-2 (fire exposure from the duct side), or fire resisting ductwork classified EIS X in accordance with BS EN 13501-3, where X is the fire resistance rating (in minutes) of the walls of the protected escape route
See para 9.16