The place the ductwork leaves the compartment from which it serves (revealed in blue) it should manage integrity and insulation fire rankings for the same period of time given that the compartment through which it passes. CE & UKCA marked Ducts that cross inside the escape corridor (shown in blue) https://grease-tight-extract-duct01223.estate-blog.com/36045009/a-secret-weapon-for-grease-tight-extract-ductwork