How to fireproof and seal cable trays in vertical shafts

Fireproof cable trays in vertical shafts are sealed using a combination of fire-rated rock wool panels, intumescent sealants, fire pillows, and fire mortar to ensure airtight, fire-resistant compartmentation.

Key Materials

• Fire Batts (Fire-Rated Rock Wool Panels): High-density slabs cut to fit around cables, filling all gaps. Small remaining gaps are sealed with intumescent sealant, which swells under heat to maintain fire integrity .
• Fire Pillows: Flexible, removable bags filled with intumescent graphite, ideal for areas where cables are frequently added or removed. They can be repositioned without breaking the seal .
• Fire Mortar: Special fire-rated powder mixed with water and applied around cables in vertical shafts. Once dry, it behaves like concrete and contains intumescent powder that swells to seal cracks .
• Firestop Mastic and Putty: Used to seal smaller gaps around metal trays or conduit penetrations, ensuring complete coverage and adherence to surfaces .

Installation Process

1. Prepare the Shaft: Ensure floor and wall finishes are complete, and shaft doors are installed. Large openings may require a fire-resistant backing plate before sealing .
2. Position Cable Trays: Install trays and route cables according to design, leaving appropriate gaps for fireproofing materials .
3. Apply Fire Batts or Fire Pillows: Cut fire batts to fit tightly around cables, filling all voids. For removable solutions, stack fire pillows around and between cables .
4. Seal Remaining Gaps: Use intumescent sealant or firestop mastic to fill any small gaps (<1 cm²) between cables and the shaft wall or tray .
5. Fire Mortar for Vertical Shafts: For multi-story shafts, pour or trowel fire mortar at each floor level around descending cables. Allow it to dry completely to maintain fire compartmentation .
6. Cover Plates: Install square, consistent cover plates over openings where required, ensuring a uniform, airtight seal .

Best Practices

• Maintain Packing Thickness: Firestop packs or batts should have a minimum thickness of 24 cm for large openings .
• Sequence and Layout: Arrange firestop materials in an orderly sequence to facilitate installation and future maintenance .
• Regular Maintenance: Every time new cables are added, the fireproof seal must be re-established, especially in vertical shafts, to prevent fire spread .
• Compliance: Use UL-listed or certified firestop systems appropriate for the wall or slab type, and follow manufacturer instructions for fire ratings and installation .

Performance Considerations

• Properly installed fireproof seals prevent the chimney effect, which can rapidly spread fire and smoke in vertical shafts .
• The combination of thermal insulation, smoke sealing, and structural integrity ensures that the fireproofing system maintains its performance under fire conditions .
• Gaps or improperly sealed penetrations significantly reduce fire resistance and can compromise building safety . By following these materials, methods, and best practices, vertical cable tray shafts can achieve effective fireproof sealing, maintaining both safety and compliance with fire protection standards.