In which the ductwork leaves the compartment from which it serves (shown in blue) it need to retain integrity and insulation fire ratings for the same timeframe as the compartment through which it passes. Huge obtain panels are strategically put through the entire duct system, enabling complete cleaning and inspection. https://collincuixl.laowaiblog.com/35906046/rumored-buzz-on-grease-tight-extract-ductwork