By Todd Hohbein, Deputy Fire Marshal, Utah State Fire Marshal’s Office
As seen in the IKECA, Fall 2016 Journal
In the last issue, we discussed the necessity of conducting a thorough inspection and test not only of the fire suppression system in the kitchen hood exhaust system, but also of the grease exhaust ductwork itself. In this issue, we look at the importance of inspecting the exhaust termination point: that point at which the exhaust ductwork penetrates an exterior wall or roof assembly and forcibly exhausts grease-laden vapors into the surrounding atmosphere.

The International Mechanical Code (IMC) regulates exhaust termination points in great detail. Why? Because if they’re not installed properly, hot, grease-laden vapors can be blown onto rooftops, the exterior walls of buildings, sidewalks and roads, pedestrians, or, worse, sucked back into the building through HVAC fresh air intakes or building openings. Not only does any one of those scenarios create a slick and disgusting mess, it can also create dangerous health hazards to occupants and coat the exterior portions of a building in highly combustible grease.

To ensure the particulars of the exhaust termination point are properly installed and assembled, the prudent fire inspector needs to look for the following items:

A standard rooftop-mounted, dual exhaust termination point over a large institutional kitchen

The grease has to go somewhere (IMC 506.3.13.1 and 506.3.13.2: Basics of the approved locations for the exhaust termination point):

Obviously, the grease cannot exhaust inside the building; it’s going to pass through either an exterior side wall or a roof/ceiling assembly. If it is located above the roof, the code tells us the discharge opening at the top of the exhaust fan shall not be less than 40 inches above the surface of the roof (see figure 1). If the discharge opening passage is through the exterior wall, the mechanical code tells us the smoke, grease, gases, vapors, and odors from the discharge cannot create a public nuisance or fire hazard. Although that sounds a bit vague and subjective, later sections of the code offer specific distances and measurements. Regardless, the IMC states that other exterior building openings cannot be located within three feet of the exhaust termination point.

The grease has to be kept away from people and building surfaces:

We’ve all driven by the old bowling alley in town that has stains on the side of the exterior wall from 40 years of hamburger grease oozing down the wall because the exhaust fan is worn out and/or was never properly installed. IMC 506.3.13.3 gives us specific distances for termination locations at both walls and rooftops. The exhaust outlet must be at least 10 feet away horizontally from adjacent buildings and property lines. This is primarily in the code to protect other building owners and tenants who probably don’t want grease all over their windows and walls. In addition, the exhaust must be at least 10 feet above the joining grade level. The sentence in the code protects pedestrians and customers who do not wish to be deep fried as they travel along a public way in an urban environment. In a crowded downtown restaurant setting, this distance becomes very significant. Most importantly, the exhaust outlet must be at least 10 feet horizontally and at least three feet vertically from any air intake openings into any building. No one wants to have thick, grease-laden vapors blowing out of their air conditioning register.

Properly hinged upbeats fan with flexible cable

Looks pretty good… but something is missing

The exhaust fan must be properly installed and equipped:

If the roof-mounted exhaust fan is in the right spot, far away that’s great. However, if the fan is incapable of being cleaned and maintained, it won’t be long before the room service and exterior walls are covered in dripping grease. IMC 506.5.2 and 506.5.3 detail four extremely important requirements for a blast fan. First, the fan has to have a drain outlet and collection point for the grease that is too heavy to be blown into the atmosphere. Typically, you will see this as a small, rectangular metal box with piping running from the top of it to the base of the fan. This rectangular box is a grease reservoir and is used to collect the runoff from the exhaust fan. It is common for these reservoirs to be missing or simply not installed by the ductwork contractor. Keep a sharp eye out for them as they provide a valuable service to the system. Second, the fan must be hinged (see figure 2) so that it and the ductwork below it can be easily cleaned by service personnel. Third, in addition to the hinge, the electrical power source serving the fan must have flexible, weatherproof cable to permit inspection and cleaning (see figures 1 and 2).

Fourth, the ductwork itself must extend at least 18 inches above the roof surface. This, again, is a commonly misinterpreted and misunderstood code requirement. To understand it and to simplify, look at figures 1 and 2 again. You’ll notice that the pink-colored ductwork actually extends out of the roof surface a good distance before attaching to the bottom of the exhaust fan. On that particular installation, when I first conducted the initial fan inspection, the ductwork only extended 12 inches above the roof surface. After meeting with the contractors and explaining the code requirement, they added an additional six inches of stainless duct to pass inspection. To review, the very top of the exhaust fan must be at least 40 inches above the roof surface. Included in that 40-inch measurement can be the 18 inches that the ductwork must extend above the roof surface as well.

Look for the commonly missed items:

Take a closer look at figures 1, 3, and 4. Notice anything missing? That’s right, the two exhaust fans you saw in figure 1, located on the rooftop of a newly constructed building, never had their grease drain outlet and reservoir installed. This system was allegedly ready for “final” inspection. Had the fire or building inspector never taken the time to climb onto the roof and look at the fans, the cardboard boxes full of metal pieces would’ve eventually become saturated with grease, fallen apart, and dropped their contents down into the spinning fan blades, destroying the system and possibly causing a seized motor and subsequent rooftop fire.

Not only is it common for the grease reservoir to be missed, often times the contractor wants to do a cut-and-run job, get paid, and get out. This kind of carelessness can result in the exhaust fan being much too close to building openings, not having the required hinges and flex conduit, or being too close to the surface of the roof or wall.

Oh there it is! The grease reservoir is still in the original cardboard packaging and has never been installed!

As always, if the fire inspector takes his or her time and does a thorough, competent inspection, items such as the ones listed in points 1 through 4 can be easily inspected and checked not only for their presence, but for their proper installation. It may take a little time to climb up the roof access ladder, squeeze through that hatch, and take a few measurements, but the rooftop fire you may prevent from happening could save countless lives and hundreds of thousands of dollars in damages. Be safe, and inspect thoroughly!
PHOTO CREDIT: Photos courtesy of Todd Hohbein