By Todd Hohbein, Deputy Fire Marshal, Utah State Fire Marshal’s Office

As seen in the IKECA, Spring 2016 Journal

It is almost a certainty that, at some point during your career in the fire service, you will be asked to inspect a kitchen hood and its fire suppression system.  Nearly every restaurant has one as does almost every school, hospital, and correctional facility.

The most commonly performed fire inspection of a kitchen hood fire-suppression system involves inspecting the nozzles, hood, and filters and witnessing a trip test of the system, activated by the manual pull station and/or a fusible link.  Although this certainly covers the intended basic operation of the system, if you stop at that point, you’re neglecting the hood’s most important function: to safely and efficiently remove grease from the kitchen itself. If grease-laden vapors are not properly extracted and exhausted through the ductwork, the chances of a kitchen fire increase significantly due to the accumulation of combustible grease, the clogging of the exhaust system, and the real potential for grease to drip through the exhaust ductwork and collect in other parts of the building.

To prevent this from happening, the International Mechanical Code (not the fire code) spells out extremely specific requirements for the grease exhaust ductwork from the point at which it leaves the hood system and continues through the building to an exhaust termination point. If you, working in tandem with your local building inspector, conduct a thorough exhaust ductwork inspection before the ceiling is finished and the system hidden from view, you can locate and have corrected many deficiencies that otherwise would have contributed to the chances of a serious kitchen fire.

The 2012 IMC, Section 506, details the requirements for commercial kitchen hood ventilation ducts and exhaust equipment. I highly recommend you purchase the 2012 IMC Code and Commentary, bound together as one book. The commentary features numerous photos, diagrams, and schematics that are essential to understanding the fire safety requirements for both simple and complex hood ventilation installations. Here is a brief overview of the things you as a fire inspector need to be looking for when you look “beyond the hood”:

  1. Proper welding: Joints, seams, and penetration of grease ducts are required to have a continuous weld to prevent grease and residue from leaking from the duct interior. Sheet metal locking joints, rivets, screws, or any mechanical connectors are prohibited, save for the three exceptions to IMC 506.3.2. Many contractors simply use sheet metal locking joints in hopes that the building or fire inspector is not aware of the weld requirement, which saves them from having to do a significant amount of hot work.
  2. The light test: Prior to the use or concealment of any portion of a grease duct system, a leakage test should be performed. So very few building inspectors know about it, and even fewer conduct this test. The ductwork contractor is required to pass a 100-watt lightbulb through the entire section of ductwork to prove that all welded joints are liquid tight. Obviously, if the bright light shines through any portion of the ductwork in a darkened room, grease would be able to leak out of those holes and gaps as well (IMC 506.3.2.5).
  3. Bracing and support: Grease duct bracing and supports shall be of noncombustible material, and bolts, screws, and rivets Looking Beyond the Hood: Inspecting Grease Exhaust Ductwork in Type I Hood System Installations – Part 1 By Todd Hohbein, Deputy Fire Marshal, Utah State Fire Marshal’s Office Figure 1. Many fire inspectors never look past this view of a hood system. Figure 2. Accumulated grease in an exhaust duct in dire need of cleaning. THE IKECA JOURNAL SPRING 2016 | PAGE 15 shall not penetrate duct walls. Simply put, ductwork is to be cradled or hung from supports, but supports cannot be attached to the ductwork by means that penetrate the duct wall. If they were, you would eventually see grease leakage at the points of penetration (IMC 506.3.3).

That brings us to the point at which the ductwork penetrates an exterior wall or ceiling/roof assembly. There is a whole host of additional codes that deal with that particular instance and the requirements for the exhaust fan and termination point itself. We will discuss an overview of those requirements next. Be safe and inspect thoroughly!

* Editor’s note – Other accepted codes call for access at the change of direction

Todd Hohbein serves the Utah State Fire Marshal as a Fire Cause and Arson Investigator. Deputy Fire Marshal Hohbein has served in this capacity for sixteen years. He previously worked for the Nebraska State Fire Marshal’s Office. Deputy Hohbein is an ICC Certified Fire Marshal, Fire Inspector II, Fire Plains Examiner, Building Plans Examiner, and Building Inspector. Todd is also a CFI, CFEI and CVFI. Inspecting kitchen hood systems and exhaust installations is one of his favorite responsibilities as a fire inspector. Deputy Hohbein resides in sunny southern Utah with his wife and three children, and can be reached at