Kitchen Exhaust Fans

By Author: Oleg Tchetchel
Total Articles: 31
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NFPA 96 Ventilation Standard provides the minimum fire safety requirements related to the design, installation, operation, inspection, and maintenance of all public and private cooking operations except for single family residential usage. The requirements include, but are not limited to, all manner of cooking equipment, exhaust hoods, grease removal devices, exhaust ductwork, exhaust fans, dampers, fire extinguishing equipment and all other components or systems that are involved in the capture, containment and control of grease-laden cooking residue. The provisions of this standard are considered necessary to provide a reasonable level of protection from loss of life and property from fire and explosion. This standard is intended to be applied as a whole.

Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations not provide safe design and operation if parts of it are not enforced or are arbitrarily deleted in any applications. The authority having jurisdiction shall determine compliance with this standard an d authorize any deviations from it in all applications.

Cooking equipment ...
... that produces smoke or greaseladen vapors shall be equipped with an exhaust system that complies with all the equipment and performance requirements of this standard. All such equipment and performance also needs to be maintained per the requirements of this standard during all periods of operation. Specifically, the cooking equipment, hoods, ducts, fans, fire suppression systems and special grease collection or energy control equipment are to be kept in good working condition.

Airflows throughout all components of the system must be maintained at intervals necessary to keep the operating conditions of the equipment at the proper levels. All interior surfaces of the exhaust system shall be reasonably accessible for cleaning and inspection purposes. Except where enclosures are required, hoods, grease removal devices, exhaust fans, and ducts shall have a clearance of at least 18 inches to combustible material, 3 inches to limited combustible material and 0 inches to non-combustible material. (See Fig. 1a - 1e.) This is only a guideline and there are several exceptions to these.

Ultimately, the authority having jurisdiction (AHJ) has the final say in the acceptance or rejection of the installation. In the event of a fire within the exhaust system, the system must be inspected by qualified personnel and approved by the AHJ to determine whether the system is structurally sound, capable of maintaining their fire protection function, and suitable for continued operation. Clearances can be reduced by the installation of field applied or factory built grease duct enclosures. These must demonstrate that they provide sufficient mechanical and structural integrity, resiliency and stability when subjected to expected building environmental conditions, duct movement under general operating, and fire conditions. A drawing of the exhaust system installation along with a copy of operating instructions for subassemblies and components used in the exhaust system, including electrical schematics, shall be available on the premises.

Upblast fans with the motors surrounded by the airstream shall be hinged, supplied with a flexible weatherproof electrical cable and a hold open retainer for servicing and cleaning, and be listed for this use. Inline fans shall have the motor located outside of the airstream and have the belts and pulleys protected from the airstream by a greasetight housing. The fan must be securely bolted to the flanges of the exhaust duct using stainless steel bolts, nuts, lock washers and gasketing rated for 1500o F. Flexible connectors are not be used. If the design or positioning of the fan allows grease to be trapped, a grease drain directed to an accessible grease receptacle, not exceeding 1 gal, must be supplied.

Inline fans shall be located in an easily accessible area to allow for service and removal. Utility set exhaust fans, if installed at the rooftop termination point, shall meet the requirements for rooftop termination installations. If the fan is installed in a building, it shall be accessible for service and removal. The fan must be connected with flanges to the exhaust duct and securely bolted. Fans shall have a drain directed to a grease receptacle.

The air velocity through a duct may not be less than 1500 feet per minute. Exhaust air volumes for hoods must be of a sufficient level to provide for the capture and removal of the grease-laden cooking vapors. The exhaust system in a hood must continue to operate after the extinguishing system has been activated unless a fan shutdown is required by a listed component in the ventilation system or by the design of the extinguishing system. It shall not be required to restart the hood exhaust fan when the extinguishing system is activated if the exhaust fan and all cooking equipment served by the fan had previously been shut down. Master kitchen exhaust ducts that serve multiple tenants shall include provisions to bleed air from the outdoors or adjacent spaces into the master exhaust duct in order to maintain the minimum air velocity required in the master duct. This bleed air duct shall connect to the top or side of the master exhaust duct and have a fire damper at least 12 inches from the exhaust duct connection. The damper must be adjustable in order to regulate the volume of air into the master duct. A bleed air duct shall not be used for the exhaust of greaseladen vapors. Unused tenant exhaust connections into the master exhaust duct that are not being used as bleed air connections are to be disconnected and sealed.

Oleg Tchetchel
Ventilation Engineer
Buffalo Fan Co.
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