Hood Cleaning Inspections

Every year in the United States there are over 8,000 eating establishment fires, with most of the fires originating from the commercial kitchen cooking area.

This is too often due to kitchen exhaust hood systems that are neglected after installation, which only increases the risk of a more damaging and dangerous fire. 

While proper maintenance of the kitchen exhaust hood system is the owner responsibility, NFPA 96 requires schedule inspections in order to determine if a kitchen hood system has gone from acceptable to dangerous.  
 
When you’re inspecting a kitchen exhaust hood system, it’s good to have a list to keep from forgetting anything. This safety article is provided to ensure that authorities having jurisdiction (AHJs) are aware of all aspects of a commercial kitchen exhaust hood system that should also be on your checklist. As you go through a site, check items off and ask questions:

When was the kitchen exhaust system last cleaned? 

Can I see the fan?  Is there grease buildup? Is there horizontal ductwork?  Your inspection can mean the difference between life and death.

However, the scary truth is that your checklist might not be complete, and that could make you and the owner feel a false sense of security.

Let the Inspection Begin!

The first place to start is with the establishment documentation of cleaning. This should include paperwork detailing the date of the most recent cleaning and frequency along with any deficiencies the cleaning company may have encountered and may include photo documentation. Keep in mind when inspecting kitchen exhaust hood systems what type of cooking equipment used.  

NFPA 96 provides guidelines for inspections based on specific kitchen operations.  Systems that utilize solid fuel, like wood, charcoal, and pitch, should be inspected monthly.  High-volume cooking operations, like 24-hour char-grilling, frying or wok cooking sites should be inspected quarterly.  Moderate-volume cooking operations like banquet halls should be inspected semi-annually.

Low-volume cooking businesses, like churches, day camps, and senior centers, need to be inspected annually.
NFPA 96 also requires that if a kitchen exhaust hood system needs cleaning, it should be done by a certified kitchen exhaust cleaner acceptable to the authority having jurisdiction (AHJ).

Standards also require that a sticker, usually found on the hood, should display the name of the cleaning or servicing company, the name of the person who performed the work, and the date of the system last cleaning.

The Hood: What Lies Beneath Perhaps the most overlooked area in a commercial kitchen inspection is the kitchen exhaust hood system.  

Vapors carrying grease can compromise the kitchen exhaust hood system, and one wrong spark can allow a fire to travel from the frying pan and into the building.

If a hood’s exterior looks dirty or if there is a heavy accumulation of grease, it does not necessarily mean the system is not regularly cleaned remember, it depends on the cooking style, although it may indicate that the kitchen exhaust hood system requires more frequent cleaning.

As you inspect the hood, make sure to look beyond the obviously visible system elements by removing the filters and looking at the plenum area. This area is usually a good indicator of how the rest of the system looks inside, as it accumulates the grease vapors and directs it further into the duct work.

The filters should be made of steel or a listed equivalent material, and should be removable for cleaning.  There should not be any gaps in the filters or missing filters, but if there are, this problem might have been created by the establishment’s kitchen staff; however, that is also usually a good indicator that the system is need of some serious cleaning.  

Duct work:  

The Path to Safe Haven or Home to a Fiery Future external portions only account for about 25-30% of the exhaust system, so a thorough inspection must be of the entire exhaust system, beyond the hood and into the ductwork and fans.
Therefore, another item to inspect while looking into the plenum area is trying to look past it and into the duct work.

Duct work is crucial to carrying those vapors out of the cooking area, although in the event of a fire, the duct should be able to contain the fire and prevent the flames from escaping into the building. Generally found at the top of the plenum is the entrance to the system duct run, often called the “throat.”  

There may be more than one throat depending on the size of the hood and each one should be inspected as the equipment used under each location varies and determines the amount of grease that is generated. A flashlight should be used to look from the plenum area up into the duct collar or throat of the duct.  

Remember that the ideal situation is to have a clear view of the fan blades that help carry the vapors away.  If you can only see steel and grease, that may be the sign of a serious problem.

Determining the rate of grease accumulation and how often a system should be cleaned is crucial. Using a tool such as or similar to the IKECA Depth Gauge Comb can provide an organized and specific method to determine the rate of grease buildup.

If a system established cleaning frequency is questionable, take photo validation of the duct area and equipment during the visit using a gauge comb to determine if the system is at or above the cleaning-required depth of 0.078.” If the ducts are found to have above that level of buildup, verify the last cleaning date and recommend that they contact their certified exhaust cleaners and schedule a cleaning. 

Also discuss with the owner that they consider changing how frequently the equipment is cleaned.As for the ducts themselves, according to NFPA 96, they must be a liquid-tight, continuous external weld so that any potential fires are contained and safely conveyed out of the building.

Ducts must also be constructed of and supported by carbon steel at least 0.054 inches thick, or with stainless steel at least 0.043 inches.  

Ask if the owner or person responsible knows the construction and parameters of their duct work. Access Doors: Getting In So Fire Doesn’t Get Out According to NFPA 96, access doors must meet the 1500 degree (Fahrenheit) rating and be grease-tight.  All access panels to the ductwork must also comply with the following standards set down by NFPA 96: Signage that reads  “Access Panel Do Not Obstruct” Openings at the sides or top of the duct and at changes of direction.  

Hoods with dampers should also have an access panel to allow for inspection and cleaning within 18 inches of the damper. With horizontal ducts, look for at least one 20 x 20 inch opening to allow for entry; although if this is not possible, then there ought to be openings large enough to enable access to clean every 12 feet along the duct work.  

If the duct is vertical and personnel entry is impossible, access to clean the interior ought to be provided on every floor. Some ducts might be difficult to access, however they still need inspection, whether they span 5 feet or 50 feet.

A lot of grease buildup in the ductwork is fuel for a future fire, and leads to significantly greater damage.Inaccessible ducts pose the same problem, if not a greater one.  

If no one knows where the access door to the duct is, that is a red flag that the system is not undergoing proper cleaning or perhaps has never been cleaned after installation.  Regardless of the duct work length, find out where the access doors are and open them for a thorough check.

Systems that feature a rooftop fan should open from the fan on a hinge, allowing for an easy point of access to look at the conditions of the duct work.  If there is no hinge, and the fan cannot be opened, find out how and if the system is cleaned, ask for proof.