|This article does not cite any references or sources. (August 2013)|
||The examples and perspective in this article deal primarily with North America and do not represent a worldwide view of the subject. (August 2013)|
A grease duct is a duct that is specifically designed to vent grease-laden flammable vapors from commercial cooking equipment such as stoves, deep fryers, and woks to the outside of a building or mobile food preparation trailer. Grease ducts are regulated both in terms of their construction and maintenance, forming part of the building's passive fire protection system. The cleaning schedule is typically dictated by fire code or related safety regulations, and evidence of compliance must be kept on file by the owner.
Vapors are created when grease is heated to and beyond its vaporization point. As the vapors cool down, the grease condenses and settles on colder surfaces. 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 is not only slippery, but also a highly flammable hydrocarbon. Regardless of what state it is in, vapor, liquid or solid, it ignites easily and burns very rapidly. A fire-resistance rating is intended to certify resistance to an internal grease fire as well as an external fire. Any adjacent firestop must be compatible with the grease duct system.
A proprietary duct system that has its own inherent fire-resistance rating can be used, such as 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. Factory-built designs are UL tested to UL 1978 and UL 2221 (for fire rated models) test standards, are made from lighter gauge stainless steel, and offered in single wall and multiple double wall insulated designs. Typical materials used for fireproofing field fabricated designs are:
- ceramic fibers
- calcium silicate
- vermiculite boards pressed and bonded with sodium silicate
- endothermic materials, sometimes on their own, sometimes in combination with ceramic fiber
In North American unionized construction sites, metallic ducts are typically installed by the sheet metal trade, whereas external wraps are usually installed by the insulators. Inherently fire-resistant systems are likewise installed by the sheet metal trade.
Maintenance and cleaning
Cleaning takes place typically every 3, 6, or 12 months, depending on the nature of the appliances below the exhaust hood. For instance, woks may require grease duct cleaning every 3 months, whereas normal stoves may necessitate the grease duct to be cleaned only every 6 months. Compliance is 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 enabled through the use of approved, fire-resistant access panels.
- Passive fire protection
- Duct (HVAC)
- Pressurisation ductwork
- Smoke exhaust ductwork
- Circuit integrity
- Kitchen exhaust cleaning
- Extractor hood
|Wikimedia Commons has media related to Kitchen Exhausts.|
- UL treatise on wrapping systems
- NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations