NFPA 96, “Ventilation Control and Fire Protection of Commercial Cooking Operations”, presents two options for enclosing grease ducts for commercial cooking equipment: the first option is to use continuous fire-rated building component assemblies to enclose the ducts and the second one consists of installing proprietary, fire-rated, field- applied or factory-built grease duct assemblies in accordance with the manufacturer’s instructions. These types of enclosure assemblies are evaluated for their resistance to fire and their ability to protect adjacent combustibles through reduced clearances. Although NFPA 96 references other standards that deal with grease duct assemblies, Sentence 3.6.3.5.(2) requires that CAN/ULC-S144, “Standard Method of Fire Resistance Test – Grease Duct Assemblies”, be used to determine the fire-resistance rating of factory-built and field-applied grease duct assemblies.