Wherever the ductwork leaves the compartment from which it serves (proven in blue) it must preserve integrity and insulation fire rankings for a similar period of time because the compartment by which it passes. Promat has developed self-supporting systems without having a metal liner, such as PROMATECT®-Advertisement, PROMATECT®-L500 and MASTERBOARD®, https://daltoniynbo.daneblogger.com/35938926/the-2-minute-rule-for-grease-tight-extract-ductwork