Grease Duct Systems - Design for Code Compliance & Fire Safety | Schebler Chimney Systems

Introduction

This tutorial provides a comprehensive guide for designing grease duct systems that comply with fire safety regulations and building codes. Understanding the requirements for these systems is crucial for mechanical engineers and contractors involved in commercial kitchen operations to prevent fire hazards associated with grease buildup.

Step 1: Understand the Types of Kitchen Hoods

• Type 1 Hoods:

  • Designed for cooking processes that produce grease-laden vapors (e.g., frying, grilling).
  • Must be equipped with a fire suppression system.
  • Requires a grease duct system for venting.

• Type 2 Hoods:

  • Used for venting steam, heat, and odors without grease.
  • Do not require a grease duct system.

Step 2: Familiarize with Codes and Standards

• Key Regulations:

  • International Mechanical Code (IMC)
  • National Fire Protection Association (NFPA) 96
  • ASHRAE standards
  • ANSI standards
  • UL 1978 for grease duct testing

• Authority Having Jurisdiction (AHJ): Understand that local codes may vary, so always consult with local code officials to ensure compliance.

Step 3: Design the Grease Duct System

• Material Selection:

  • Use carbon steel (minimum 16-gauge) or stainless steel (minimum 18-gauge) for field-fabricated ducts.

• Fire Rated Shafts:

  • Ducts in multi-story buildings must be enclosed in fire-rated shafts.
  • A one-hour fire rating is required for buildings less than four stories; two hours for taller buildings.

• Zero Clearance Ducts:

  • Factory-built products can be designed for zero clearance, negating the need for fire-rated shafts.

Step 4: Construct the Ductwork

• Field Fabricated Ducts:

  • Ensure all joints are liquid-tight.
  • Follow IMC and NFPA guidelines for construction and insulation methods.

• Factory-Built Ducts:

  • Modular components with mechanical joints reduce the need for field welding.
  • Ensure compliance with UL listings and conduct leakage tests.

Step 5: Install the Grease Duct System

• Slope Requirements:

  • Maintain a slope of at least:
    • ¼ inch per foot for horizontal runs up to 75 feet.
    • 1 inch per foot for runs exceeding 75 feet.
  • Factory-built ducts may have different slope specifications based on UL listings.

• Access and Clean-out Points:

  • Install clean-out access doors every 12 feet for horizontal ducts and on every floor for vertical ducts.
  • Ensure clean-out points comply with both IMC and NFPA regulations.

Step 6: Conduct Testing and Inspections

• Pre-Installation Testing:

  • Perform a light test on field-fabricated ducts to check for leaks before covering.

• Post-Installation Testing:

  • Conduct air pressure tests or water tests to ensure integrity and compliance with safety standards.

Conclusion

Designing and installing grease duct systems requires a thorough understanding of fire safety regulations and building codes. By following the outlined steps, professionals can create systems that enhance fire safety and ensure compliance with local codes. Consider consulting with local authorities and referencing the latest codes to stay updated on any changes.