Smoke leakage (S): The duct shall not Possess a leakage exceeding 5 m³/h for each 1 m² of inner area spot. This shall be relevant to the floor space of the duct through the perforated plate to the tip with the duct because of the inlet nozzles. Fire resistant board https://grease-tight-extract-duct02234.tinyblogging.com/grease-tight-extract-ductwork-no-further-a-mystery-80655290