A grease duct is a duct that is connected to the Kitchen Exhaust hood and is specifically designed to vent grease, smoke and other harmful contaminants from commercial cooking equipment to the outside of a building. Grease ducts are regulated both in terms of their construction and maintenance, forming part of the building’s passive fire protection system. Even the cleaning schedule is typically dictated by the local fire codes and evidence of compliance must be kept on file by the owner.
Grease laden vapors are hot to begin with. As the vapors cool down, the grease settles on colder items. It is thus important for occupational safety and health as well as compliance with local fire codes to vent such vapors outside the kitchen and outside the building where the kitchen is located. Grease, of course, is not only slippery, but also highly flammable. In fact, it qualifies as a hydrocarbon due to its inherent chemistry. Regardless of what state it is in, vapor, liquid or solid, it ignites easily and burns very rapidly, necessitating special provisions to accomplish a fire-resistance rating based on an internal grease fire as well as an external fire. Special provisions also include the necessity for proof that any adjacent firestop must be compatible with the grease duct system.
In North America, grease ducts must be in compliance with National Fire Protection Association (NFPA) 96 (NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations) as well as the local building codes and fire codes. Cleaning takes place typically every 3 months, 6 months, or annually, depending on the nature of the appliances below the hood. For instance, woks require quarterly grease duct cleaning, whereas normal stoves may necessitate the grease duct to be cleaned only every 6 months.
The Compliance with code must be proven through certificates issued by the cleaning and maintenance contractors. Purpose-designed fire suppression systems inside the hoods must also be routinely maintained. Proper cleaning must be on time, fire-resistant access panels. Grease ducts should be kept as short as possible to minimize grease build-up.
A proprietary duct system that has its own inherent fire-resistance rating can be used, or a metallic duct, either field fabricated or UL certified factory-built designs. Field fabricated is typically made from 16-gauge carbon steel, all welded, per local codes, which is then externally treated with fireproofing.