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grease duct


PART 1: COVID-19 Restaurant Shutdowns & The Dangers of >72 Degrees in a Grease Duct

Eric Dyer

The abrupt closing of full-service restaurants and bars across the United States caused most of these businesses to immediately cancel all upcoming services, including hood cleaning and fire suppression inspections.

Additionally, a lot of takeout restaurants that remained open failed to schedule these services citing "decreases" in business

Regardless of the operational status of their kitchens, one truth remains the same: all their exhaust systems are loaded with more than three months of grease buildup. This article will examine the impacts of that buildup and the potential implications of it.

Why 72°?
72° is important in grease ducts because of the components of exhaust grease:

  • Liquids - unsaturated fats from plant & fish oils
  • Solids - saturated fats from animals
  • Trans fats - created by altering liquid fats to become solids (like margin), or when plant-based cooking oil is heated

During cooking, all these fats are liquefied, aerosolized, and pulled through the kitchen exhaust system at the molecular level. As they pass through the system, they cool, collect, and return to a form of their natural state. Because the majority of fats are from animal & trans fats, most of the grease reforms as a solid throughout the system.

Note: Solid fats liquefy at 72°F.

Weather Impacts
The timing of Covid-19 caused our restaurants to close during the cooler spring months.

This meant the temperature inside of those exhaust systems was cooler than room temperature. However, as the temperature rises outside, it will also rise inside of grease ducts as well, but at a higher rate.

Unventilated ducts can reach temperatures exceeding 125° and over 150° on the roof. Just imagine what that does to solid fats.

Note: Under normal conditions restaurant exhaust fans are running 18-24 hrs/day pulling cool kitchen air through the system. However, kitchens are closed and exhaust fans are not running. So no cool air has been moving through the ducts for most of the past month.