Exhaust systems for restaurant equipment require careful design, because grease condenses in the interior of the ducts. Grease accumulations may be ignited by sparks from the cooking appliance or by a small fire on the cooking appliance caused by overheated cooking oil or fat in a deep-fat fryer or on a grill.
If the duct did not have a grease accumulation, cooking appliance fires could often be extinguished before causing appreciable damage.
Fire risk is especially high in frying because cooking oils and fats are heated nearly to their flashpoints
Ducts. The following should be considered when designing a duct system for commercial cooking equipment:
- The system should be designed to minimize grease accumulations, with a minimum air velocity of 1500 ft/min (458 m/min) through any duct.
- Ducts should be arranged with ample clearance from combustible materials to minimize the danger of ignition, incase of fire in the duct.
- Ducts of substantial construction (not lighter than No. 16
Manufacturers Standard Gauge steel or No. 18 Manufacturers Standard Gauge stainless steel) should be used with all seams and joints having a liquid-tight, continuous weld. - Systems should be separated to ensure there is no connection with any other ventilating or exhaust system.
- Ducts should be led directly outside the building, without dips or traps, unless automatic grease removers are employed at the dips and traps.
- Openings should be provided for inspection and cleaning. Dampers should not be installed in any duct system, unless required as part of a grease extractor or extinguishing system.
