What is the minimum clearance to combustible construction for commercial grease duct systems serving a Type I hood?

The minimum clearance to combustible construction for commercial grease duct systems serving a Type I hood is 18 inches. This requirement is established to reduce fire hazards that may arise from the extremely hot air and grease vapor that these systems carry. The 18-inch clearance provides a safety buffer that minimizes the risk of ignition from heat transfer or flammable materials that could be present in adjacent structures.

Grease ducts can accumulate flammable deposits over time, making it essential to maintain a safe distance from combustible materials. The code standards that govern these installations are formulated based on the need to prevent fire hazards in kitchen environments, where grease buildup is a common occurrence. Thus, ensuring a distance of 18 inches helps to provide a safer operating environment in commercial kitchens using Type I hoods.