- Grease duct
A grease duct is a purpose-designed duct that is used to vent grease-laden vapours from commercial cooking equipment such as a
stove , "double-decker"pizza oven ,deep fryer orwok 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'spassive fire protection system . Even the cleaning schedule is typically dictated by thefire code and evidence of compliance must be kept on file by the owner.pecial hazard
The grease laden vapors are hot, to begin with. As the vapours 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 vapours 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 inherentchemistry . Regardless of what state it is in, vapour, liquid or solid, it ignites easily and burns very rapidly, necessitating special provisions to accomplish afire-resistance rating based on an internal grease fire as well as an external fire. Special provisions also include the necessity for proof that any adjacentfirestop must be compatible with the grease duct system.Requirements
In North America, grease ducts must be in compliance with NFPA 96 as well as the local
building code s 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. Compliance 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 enabled through the use of approved, fire-resistant access panels. Grease ducts should be kept as short as possible to minimise grease build-up.ystems
A proprietary duct system that has its own inherent fire-resistance rating can be used, or a metallic duct, typically from 16 gauge
sheet metal , all welded, per local codes, which is then externally treated withfireproofing . Typical materials used for fireproofing are:* ceramic fibres
* rockwool
*calcium silicate
*vermiculite board s pressed and bonded withsodium silicate
*intumescent s
*endothermic materials, sometimes on their own, sometimes in combination with ceramic fibreTrade jurisdiction
In North American unionised
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.ee also
*
Passive fire protection
*Duct (HVAC)
*Pressurisation ductwork
*Smoke exhaust ductwork
*Circuit integrity
*Kitchen exhaust cleaning External links
* [http://www.ul.com/fire/wrapping.html UL treatise on wrapping systems]
* [http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=96 NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations]
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