Duct access doors are a fundamental part of every commercial kitchen exhaust system. Why? Because duct access doors help facilitate the cleaning, maintenance, and inspection of exhaust systems. And this helps to keep fats, oils, and grease from accumulating on the surfaces of your ductwork. Understanding how grease gets into your ductwork in the first place is helpful in understanding the importance of duct access doors.
How does grease get into your ductwork?
Commercial kitchens create varying levels of grease exhaust. Solid fuel cooking, grills, wok cooking and high volume fryer operations all create a greater volume of grease exhaust. But even low volume cooking operations will eventually have to deal with traces of fats, oil, grease and dirt building up over time on the surfaces of ventilation ducts.
Highly flammable creosote build-up from solid-fuel cooking such as a wood burning pizza oven can create a particularly hazardous situation when combined with other grease deposits. According to the National Fire Protection Association (NFPA), the combination of creosote and grease in exhaust ducts can be easier to ignite than creosote alone, and can burn even hotter.
Even if you use the appropriate hood filters, a certain amount of grease will find its way in. During cooking, fats, oils, and grease become vaporized and are drawn up into your exhaust system.
Much of the grease will accumulate on the hood and the grease filter. But some of the grease vapor will escape through the filter into your ductwork. We’ll explain later why this is one of the most important reasons to install duct access doors. But first, lets learn more about what can happen when grease accumulates in your ducts.
What happens when grease accumulates in your exhaust ducts?
Grease deposits in your exhaust ducts are highly flammable and pose a major fire risk. One report says that when not regularly cleaned, as much as 3 inches of grease can easily accumulate along the bottom of a horizontal section of ductwork.
If a flare-up produces high flames or intense enough heat, the combustible grease deposits in your duct can ignite. According to the NFPA, most restaurant fires begin with a cooking appliance and flare up into the exhaust duct system.
Duct grease fires can be very damaging and dangerous. They travel so rapidly that they often don’t provide sufficient enough heat to activate the fusible links of a fire suppression system.
As duct grease fires spread quickly throughout the exhaust system, they also put adjacent areas of the building including other floors and the roof at risk for fire. Easily burning at 1,500°F or more within minutes, radiant heat from duct fires can even ignite combustible material outside the duct.
Once they start, duct grease fires are hard to stop. Their exact location is hard to pinpoint and extinguish. They are also very susceptible to re-ignition and break out.
So the best way to deal with a grease duct fire is to stop it before it starts. And you do that by keeping your exhaust ducts clean of grease and oil. This is why duct access doors play a key part in your defense against fire hazards in your commercial kitchen.
How do duct access doors help keep grease out of your ductwork?
Sometime it’s what you can’t see that is the most dangerous. Even if the rest of your kitchen is spotless, your ducts might be harboring layers of built up fats, oils, and grease.
Ducts must be cleaned and maintained to ensure both safety and adequate ventilation in your commercial kitchen. Properly placed NFPA compliant duct access doors make it easier and safer to thoroughly clean and inspect both horizontal and vertical exhaust ducts.
Am I required to install duct access doors?
The NFPA 96 Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations requires all commercial kitchen exhaust systems to have duct access doors. Having the right equipment will greatly reduce your risk of grease related fires, but keep in mind that your duct access doors must meet the minimum requirements of NFPA 96 and be installed in accordance with NFPA fire codes.
All horizontal and vertical ducts must be provided with access. On horizontal ducts, at least one 20 inch x 20 inch opening must be provided. If an opening of that size is not possible, openings large enough to permit thorough cleaning must be provided at 12 feet intervals.
Duct access doors must be constructed of the same material and thickness as the duct (typically 16-gauge carbon steel or 18-gauge stainless steel). All duct access doors must have a gasket or seal that is rated to at least 1,500°F and be grease-tight. Any fasteners used to secure the access panel must be carbon steel or stainless steel and may not penetrate the duct wall.
Which duct access door is right for me?
Choosing a duct access door shouldn’t be hard, but with so many styles to choose from, it can be helpful to get some expert advice before making a purchase. Check out our Duct Access Door Comparison video to learn more about the various options available.
If you aren’t sure which duct access doors are the best fit for your exhaust system, call 877.394.9731 to speak with one of our product specialists. To view our entire selection of duct access doors visit us online at www.HoodFilters.com.