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24 FEDA News & Views continued on page 28 Foster Frable Wood and Solid Fuel Cooking is Hot— Sometimes Too Hot By Foster Frable Jr., Clevenger Frable LaVallee fosterf@cfldesign.com T he popularity of wood-burning and coal pizza ovens, rotisseries, and grills has soared over the past five years. A solid fuel grill is the "hot" thing with many chefs and the ability to cook with wood has become a restaurant sta- tus symbol. The hotter/bigger/bolder the fire the better, and in some trendy restaurants, whole kitchens or cooking suites are being designed to use solid fuel for grilling, baking, and broiling. Unfortunately, the passion for solid fuel cooking has created some installations that are unsafe and/or have created prob- lems for operators due to undesirable smoke or odor (aroma). Newly enacted codes that place restrictions on ventila- tion and other installation issues reflect this trend. Ventilating wood-burning (solid fuel) cooking operations must serve two func- tions. They need to capture and contain the contaminants generated by the cook- ing process, which consists of the same components as with electric or gas, i.e., smoke-expanded hot air, moisture (water and fat), and combustion effluent (CO and CO2). Solid fuel ventilation also must function as a chimney because of the relief air flow needed to conduct the convected air temperature differentials and sustain the draft to support the com- bustion process. The Science Behind Creosote Wood burns in different stages. When a fire is initially set, a lot of oxygen is required to keep the fire burning until sufficiently retained heat is avail- able to support the combustion process through the drafting of convected air. As the wood burns down into coals and the fire continues to be stoked, reject- ed radiant heat levels will be generated along with the increase of retained heat in the bed of the fire. As a result, the fire burns longer and generates a more even temperature. However, reducing the amount of oxygen (as in damping down a fire to retain proper tempera- ture) allows unburned gases and particu- lates to escape from the combustion pro- cess. As these hydrocarbons cool down and travel up through the exhaust duct/ stack, they become dense and drop out of the air stream. During the process, they solidify and adhere to the duct walls in the form of creosote. Creosote develops in three forms, black flake (soot), solid and crusted black mass (similar to hardened epoxy resin), and a gooey clear-to-brown liquid (simi- lar to sap). It's the black flaky substance that is most likely to ignite and is often set aflame by sparks generated when the fire is first lit, and embers carry over when fires are stoked. In many cases, cre- osote can literally explode upon ignition. The second form of creosote (solid crusted black) will also burn intensely and is highly susceptible to the same condition of ember carry-over. The third form of creosote (although more liquid and staid) is considerably less flammable. Creosote is highly flammable and will ignite without direct contact to flame or can spark with temperatures as low as 165° Fahrenheit (which is over 235° F less than the flash point of grease). This creates additional hazards to the ventilating process that is not normally considered with the heat sources such as natural gas, electricity, or steam. Fire risk from creosote can be created by solid fuel charbroilers, rotisseries, pit barbeques, ovens, and smokers, including those that have dual-fuel gas and wood. In this situation, wood chips or logs are only intended to add flavor or drama to open kitchens. In some respects, adding wood chips to a gas charbroiler under a convectional Type I grease hood can be more risky then an all-wood broiler with a dedicated hood and exhaust duct. Reducing the Risk Embers and burning creosote can eas- ily escape and set fire to wood shingle or tar roofs. Several factors can reduce the accumulation of flammable creosote in the wood cooking process: -If the wood can be burned faster and hotter (versus dampening it down once a bed of coals has been achieved), it significantly reduces the creosote out- put because the hydrocarbons are con- sumed during the combustion process. Unfortunately, this can adversely affect cooking temperatures and the consump- tion of wood. ➤ Seasoned wood will burn cleaner and will minimize the creosote discharge because seasoned wood requires less heat to be completely consumed during combustion. ➤ Chimney sweeps (in lieu of duct- work cleaners) should be consid- ered for maintenance of the duct line because they use different tech- niques, tools, and chemicals than tra- ditionally used with strictly grease laden deposits. ➤ Careful attention to collecting