Exactly where the ductwork leaves the compartment from which it serves (shown in blue) it need to keep integrity and insulation fire rankings for the same time frame since the compartment through which it passes. Promat has created self-supporting systems and not using a steel liner, such as PROMATECT®-AD, PROMATECT®-L500 https://fire-resisting-ductwork-i90123.theobloggers.com/43400757/detailed-notes-on-fire-resisting-ductwork-insulation