Calculation of fireproofing and sealing holes for cable trays

Material calculation for fireproofing cable trays depends on tray size, penetration type, and selected firestop products, including firestop packs, intumescent sealants, and fire-rated foams.

Key Considerations

1. Identify the Penetration Type and Size
   • Measure the cable tray dimensions and the opening in the wall or slab. For example, a 4” x 12” tray typically requires an opening 1.5” larger on all sides, resulting in a 7” x 15” opening for firestopping purposes .
   • Determine whether the penetration is through a concrete wall, gypsum wall, or slab, as fire rating requirements differ (e.g., 3 HR F-rating for concrete, 1–2 HR for gypsum), .
2. Select Appropriate Firestop Materials
   • Firestop Packs/Pillows: Medium self-locking pillows (e.g., 3M FSP-SLP-M) are used to fill gaps around cables. The number of pillows depends on the opening size and tray type .
   • Intumescent Sealants: Acrylic or latex-based sealants (e.g., FireStop Intumescent Acrylic Graphite 682) expand under heat to block smoke and fire .
   • Fire-Rated Foams: One-component polyurethane foams (e.g., Fire Rated Gunfoam B1 187) can fill larger voids and adhere to multiple surfaces .
   • Mineral Wool or Fire-Rated Boards: Used as backing for large openings to support sealants and maintain fire resistance .
3. Calculate Material Quantities
   • Firestop Packs: Determine the gap area around the tray. Each pillow typically covers a specific volume; for example, a medium pillow may fill a 1–2 in³ gap. Count pillows to fill the total gap area, ensuring no gap exceeds 1 cm² .
   • Sealant: Measure the perimeter of the opening and multiply by the recommended bead thickness (usually 10–20 mm) to calculate the required volume of intumescent sealant .
   • Foam: For larger voids, calculate the cubic volume of the gap and select foam cans based on manufacturer coverage rates.
4. Installation Guidelines
   • Install backing plates for large openings before applying firestop materials .
   • Pack pillows or mineral wool tightly around cables, leaving minimal voids.
   • Apply sealant or foam evenly over the surface, ensuring complete coverage and adherence.
   • Maintain minimum packing thickness (e.g., 24 mm for firestop packs) and waterstop height at slab penetrations (50 mm recommended), .
5. Verification and Compliance
   • Ensure all materials are UL or EN listed for the specific penetration type.
   • Check that the installation meets the required F-rating and T-rating for fire resistance .
   • Perform visual inspection to confirm no visible cracks or voids and that cover plates are properly installed .

Example Calculation

For a 4” x 12” ladder tray through a concrete wall:

• Opening: 7” x 15”
• Gap area: approximately 1.5” around the tray
• Firestop packs: 2–3 medium pillows per opening
• Moldable putty: 2 sticks per opening
• Intumescent sealant: bead along the perimeter (~0.5 m length, 10 mm thickness)
• Optional backing plate: 1 fire-resistant plate for large openings . By following these steps, you can accurately estimate the materials needed for fireproofing cable tray penetrations while ensuring compliance with fire safety standards.