Fire Protection for Common Grease Ducts

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Kitchen Ventilation Systems

By Jeff Nocent, P.Eng. (O’Dell Toronto Office)

Working with SpringAir Systems, O’Dell offers complete design and installation services for kitchen fire suppression systems. On any project where we are supplying hoods and fire suppression, we will provide stamped engineering drawings at no additional cost.  All you have to do is ask.

In larger institutional kitchens, there are often multiple hoods connected to a single exhaust fan through a common grease duct system.  Common grease ducts present fire suppression challenges, requiring special attention by the engineer.

A review of the following NFPA standards provides guidance on how to address common grease ducts.

NFPA 96: Standard for Ventilation Control and Fire Protection of Commercial Kitchen Operations

  • Kitchen hoods, makeup air, discharge requirements
  • Grease duct construction, clearances

NFPA 17A:  Standard for Wet Chemical Extinguishing Systems

  • Wet chemical protection methods, coverage areas

In general, grease ducts require additional fire protection when one of the following two conditions exist:

  1. Hoods from two or more separate tenants are connected to a common grease duct system.
  2. Long grease duct runs where the hood collar nozzle will not provide enough coverage area to protect the grease duct. This can occur with one hood if the grease duct run is long enough.

There are two methods available for addressing these conditions. The table below outlines each approach and their inherent pros and cons:

Method 1

All Hoods Fire Suppression Systems Discharge

Method 2

Single Hood/Tenant and Common Grease Duct Systems Discharge

Summary of Components
  • Fire detector in each hood collar.
  • Nozzles above appliances, in each hood collar and bleed valves.
  • Fire detector in each hood collar.
  • Nozzles above appliances, in each hood collar, bleed valves and in the common grease duct.
System Activation
When any single detector or manual pull station is activated:

  • All nozzles on all fire suppression systems for all hoods activate.
  • Hood exhaust fan remains on.
  • All gas and electric power to appliances is cut off to all appliances for all hoods.
When any single detector or manual pull station is activated:

  • For the single specific hood/tenant the detector/pull station was activated:
    • All nozzles activate.
    • Gas and electric power cut off to appliances.
  • Common Grease Duct:
    • All nozzles in the common grease duct activate.
  • Hood exhaust fan remains on.
  • Remaining Hoods/Tenants:
  • All gas and electric power is cut off to all appliances for all hoods.
Pros
  • Simpler Controls.
  • Lower initial cost.
  • Only the hood/tenant with the fire has to clean up the kitchen and appliances.
  • Shorter downtime for cleanup.
  • Less costly cleanup.
  • Once the common grease duct fire suppression is reset, all tenants can operate again.
Cons
  • More time consuming and expensive cleanup.
  • Longer downtime.
  • Tenants not involved in fire have to clean up.
  • False activation (sensor failure, vandalism) causes larger inconvenience.
  • Higher first cost due to slightly more complex design.
  • Must ensure tenants abide by lease requirements to use same installing fire suppression contractor for their space. Education to tenant, follow through by landlord.

 

 

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