A system for detecting a leak in a duct is disclosed, including a sheath covering a duct section, a fluid concentrating device and a sensor. The sheath is attached to a boundary portion of the duct section and forms an inner space between an outer surface of the duct section and the sheath. The fluid concentrating device has an opening through the sheath connecting the inner space to an external space outside the sheath. The inner space is sealed except for the opening through the sheath. The sensor is stationed outside the opening of the fluid concentrating device and is configured to detect fluid flow from the inner space through the opening at a level corresponding to a duct leak in a pre-burst condition.