Creosote Risks in Your Restaurant Kitchen (And Your Chimney)

Reports of fires involving wood-fired pizza and meat smoking ovens are increasing due to the growing number of restaurants that have added this cooking process. According to National Fire Protection Association (NFPA) data, fire departments responded to an estimated average of 7,640 structure fires per year between 2006 and 2010. Three out of five of those fires involved cooking equipment. While we do not know how many of those fires involved wood-fired pizza and meat smoking ovens specifically, we do know that this equipment increases the risk of fire because they produce heat, smoke, grease, flammable debris, and creosote.

The Dangers of Creosote

The chief hazard is creosote buildup. Creosote is made up of condensed volatile gases created by incomplete combustion of wood. Wood smoke mixed with water vapor from cooking forms creosote that clings to the interior of the oven and the exhaust system ductwork. Creosote is highly combustible and is well known for its fire threat in chimneys of wood-burning fireplaces.

Creosote’s flash point (the lowest temperature at which vapors will ignite when given an ignition source like a spark or flame) is surprisingly low at 165-degrees Fahrenheit. All it takes to ignite creosote in hoods, filters, and ducts is a spark, burning ember, or flame that raises the creosote temperature to 165-degrees F.

Creosote’s auto-ignition point (the lowest temperature at which it spontaneously ignites without an external source of ignition) is also surprisingly low at 451-degrees Fahrenheit. The combination of creosote and grease inside the oven and ductwork is easier to ignite than creosote alone and can burn hotter. This becomes more significant when you consider a wood-fired oven could reach temperatures of 800-degrees Fahrenheit and typically maintains temperatures of 300- to 400-degrees Fahrenheit for hours.

Fire Prevention Tips

The only effective way to reduce the fire hazard is to reduce the creosote and grease buildup inside the oven and its exhaust system, which also includes the duct work and the hood if it’s not directly vented. This is done by implementing an effective wood-fired oven cleaning procedure based on NFPA 96 Standard for “Ventilation Control and Fire Protection of Commercial Cooking Operations,” Chapter 14 “Solid Fuel Cooking Operations.” In part, this standard requires that your staff clean the interior of the oven and the fire box daily. If the exhaust system has baffle filters, they must be spark arresting baffle filters and your staff must clean them at least weekly. Your kitchen exhaust cleaning contractor must inspect and clean the exhaust system for the oven monthly, and the exhaust system and ductwork (including vent piping) must be Type #1 as specified in NFPA 96.

In addition, when removing ash from the oven it should be placed in a metal bucket and wetted with water before being disposed of outdoors in a metal trash container with metal cover. Limit the storage of charcoal, wood dust, wood chips, wood pellets and/or wood logs to a one-day supply if it is stored in the same room as the cooking appliance. All solid fuel must be ignited by a match, approved built-in gas flame or other approved ignition source to light the wood fuel – but not a blow torch! Don’t laugh – we’ve seen it before! And never use combustible or ignitable liquids. To suppress an oven fire, have one of these three options: a 1.6 gallon K-Class fire extinguisher, a 2-A-rated water spray fire extinguisher or a water hose with adjusting nozzle capable of producing a fine to medium spray or mist. These should be available for use located within 20-feet.

By understanding the unique risks associated with these solid fuel appliances, restaurant owners can take steps to reduce the threat of building fire hazards associated with their use.

Find more precautionary practices in this blog, 8 Steps to Reduce the Risk of Fire at Your Bar or Restaurant.

-Frank Norton

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