Rich Swierczyna, Senior Engineer
With the rise of exhibition and front-of-house cooking, solid fuel appliances are gaining a foothold in commercial kitchens, most notably in establishments like pizzerias and BBQ restaurants. These appliances are fueled by highly combustible material such as charcoal, briquettes, mesquite, or hardwood. Many restaurant operators prefer this method of cooking for the unique charred or smoked flavoring it lends popular food items such as pizzas, beef brisket, sausages, etc., that other types of fuel, like natural gas, do not provide. However, even though this cooking method imparts a desirable flavor, the process poses great fire and health risks making proper ventilation particularly imperative to the restaurant operator.
Nationwide, the International Mechanical Code (IMC) and Uniform Mechanical Code (UMC) models typically govern the installation of commercial kitchen appliances. For California, the California Mechanical Code (CMC) is based off the UMC. In either case, the model codes refer to National Fire Protection Association (NFPA) 96 for the installation, operation, and maintenance of the equipment. In general, for safe operation and maintenance, the ventilation of solid fuel cooking appliances must be separate from all other cooking appliances. The exemption to the requirement is if solid fuel is only used for flavoring. The major point of contention has always been the definition of cooking with solid fuel vs. flavoring with solid fuel. How can an operator tell the difference?
The ASHRAE 154 standard on kitchen ventilation has the most conservative approach. It defines a solid fuel appliance as an appliance that combusts solid fuel such as wood, charcoal, or coal to provide all or part of the heat for the cooking process. It defines a solid fuel flavoring cooking appliance as an appliance that uses an energy source other than solid fuel to provide all of the heat for the cooking process, but combusts solid fuel solely for the purpose of imparting flavor to the food being cooked, e.g. a natural gas combination oven with a “smoker box” attachment. Essentially, if solid fuel is involved in any point of the cooking process, it is considered a solid fuel operation and requires a separate exhaust system.
However, the model codes typically rely on NFPA 96 which is more specific in determining the difference between solid fuel for flavoring and solid fuel for cooking. The CMC refers to Solid-Fuel Cooking Equipment as “cooking equipment that utilizes solid fuel” [NFPA 96:18.104.22.168]. This equipment includes ovens, tandoori charcoal pots, grills, broilers, rotisseries, barbecue pits, or other types of cooking equipment that derive all or part of its heat source from the burning of solid cooking fuel. The ventilation requirements of these appliances have been recently revised. Solid fuel cooking equipment requires a separate exhaust system with two notable exceptions: (1) If it is installed under a water-wash hood listed under UL300 (i.e., cooking equipment not requiring automatic fire-extinguishing equipment) or (2) If the solid fuel is used for flavoring only. For the second exception, the code limits the size, amount, and rate at which solid fuel is consumed by the appliance. This is to minimize the amount of available fuel in case of a fire. The solid fuel must be contained in a smoker box and the box must be protected by the fire suppression system. Spark arresters must be placed before the grease filters to minimize the passage of airborne sparks and embers into plenums and ducts. Sparks and embers can ignite built up creosote (a by-product of solid fuel combustion) in the exhaust ducts. Creosote adheres to the exhaust duct walls and because of its low flashpoint, poses a severe fire hazard. Monthly duct cleaning as recommended in the code should be strictly followed.
Incidentally, Demand Controlled Kitchen Ventilation (DCKV) is not recommended for solid fuel cooking. The cooking and thermal plume generated during cooking and ready-to-cook conditions are too similar to allow for any airflow modulation or potential energy savings.
The code clearly defines the parameters for the installation, operation, and maintenance of solid fuel appliances. However, vigilant oversight is necessary. During follow up inspections, inspectors have often found more than the allowable amount of solid fuel used as fuel instead of flavoring. As we have seen, there is a fine line between the definitions, but the results of too much solid fuel can be disastrous.