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PART 2: COVID-19 Restaurant Shutdowns & The Dangers of >72 Degrees in a Grease Duct

Eric Dyer

Exhaust System Design Code Requirements
When restaurants are constructed, they must meet numerous fire and safety requirements. One requirement is that horizontal grease ducts shall be installed so that grease cannot collect in any portion thereof, and the system shall slope 2% toward the hood or toward an approved grease reservoir. If the duct exceeds 75' in length, the slope shall not be less than 8.3%.

Bad Upon Bad
Every restaurant kitchen exhaust system has an area that accumulates more buildup than other sections. Sometimes the grease gets baked onto these sections and hardens. And if those sections were difficult to access (or inaccessible) prior to the shutdown, they can cause the newly liquified fat flows to get stuck. This can lead to complete ductwork blockages, or at a minimum disrupt airflow once cooking is re-established in the kitchen.

These airflow disruptions can lead to dramatic increases in temperature in the ductwork and smoke buildup in the kitchen. Under the right conditions, this alone can lead to kitchen exhaust fires.

Grease Acts as a Thermal Shield to Fire and Heat Sensors
Another concern is that the fat flow can coat and insulate the fire suppression links and internal heat sensors. This would cause the emergency extinguishing systems to fail to function at the correct temperature and could allow a fire to grow before activating the automatic system.

Grease Filter Failure
These fat flows could also lead to mounds of grease build up on the backside of hood filters. Once the cooking surfaces are relit, this buildup could completely liquefy and pour through the filters onto the hot surfaces below. If this flow found an open flame, a waterfall of fire leading straight back into the hood could be created. Under the worst of circumstances, this would lead to a complete exhaust system fire spreading throughout the entire building.

Single vs Multi-level Buildings
Does your kitchen have horizontal ductwork? In my seventeen years of hood cleaning experience, I know that 99% of restaurant kitchens have horizontal ductwork regardless of the building design. If you are unsure, remove your hood filters and look up the vertical openings. If you can see straight up to the exhaust fan you don’t. Otherwise, you have horizontal ductwork.

RECOMMENDATIONS

  • Have the kitchen hoods cleaned before reopening. It is the only way to ensure your kitchen hood exhaust system is safe and certified to protect your business.
  • Have the hood fire suppression system, all extinguishers, and all other emergency equipment inspected and serviced before reopening to ensure everything is operational and ready to handle any emergency situation.

These are all minor expenses compared to the devastating costs of a fire, or the loss of life for a first responder, employee, customer, or tenant living above a restaurant. Be safe and be well!

 

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