Duct system should be capable of resisting the ravages of fire for a period of time, so as to perform its intended function.Ducts can be classified as Duct A - exposed to external fire Duct B - exposed both External & internal fire Duct system must satisfy all the relevant performance criteria of stability, integrity and insulation.Duct works fall in to following categories. Ventilation and air conditioning Natural smoke extract Fan assisted smoke extract pressurization of escape routes and fire fighting lobbies Fast and interrupted smoke extraction during fire, preventing spread of smoke is a key factor in protection of ducts. Fire rating of the duct shall be achieved using Fire Rated constructions / protection to the duct work.