Sealing at the base of the vertical shaft cable tray

The base of a vertical shaft cable tray should be tightly sealed using fire-resistant materials, waterstops, and proper firestop systems to prevent fire, smoke, and water penetration.

Fireproof Sealing Requirements

When a vertical cable tray passes through a shaft, the opening at the base must be sealed with firestopping materials in accordance with design and code requirements. Openings should be free of visible cracks or voids, and for large gaps, a fire-resistant backing plate should be installed before sealing . Firestop materials can include fire-rated boards, mineral wool, firestop packs, or firestop mastic, and gaps between the materials and cables should not exceed 1 cm², with packing thickness of at least 24 cm .

Waterstop and Threshold Considerations

At floor level or slab penetrations, a waterstop of at least 50 mm in height is recommended to prevent water ingress into the shaft . The base of the shaft should have a threshold to support the tray and provide a secure surface for sealing. Proper alignment and positioning of the tray facilitate both installation and maintenance .

Firestop Systems and Materials

Several tested firestop systems are suitable for cable tray penetrations:

• Panel seals: Protect both single and bundled cables, including optical fibers, and their supporting structures, with fire resistance up to 120 minutes .
• Soft seals and sealbags: Flexible solutions for retrofitting or frequent cable replacement, providing flame- and smoke-tight sealing .
• Fire protection mortars: Swell upon curing to fill gaps around cables and prevent cracks, ensuring high integrity and fire resistance . These systems are tested according to standards such as DIN 4102-9, EN 1366-3, BS 476 Part 20, and UL 1479 .

Installation Best Practices

• Ensure floor and wall finishes are completed and shaft doors are installed before sealing .
• Place firestop packs in an orderly sequence, sealing all gaps inside and around metal trunking both internally and externally .
• Cover plates should be square, evenly painted, and dimensionally consistent to close the opening .
• Maintain earthing continuity for the cable tray system, using bonding jumpers and connecting to the main earthing busbar .

Performance Considerations

The effectiveness of the sealing depends not only on the material but also on the construction process. Poor installation or gaps can accelerate the spread of smoke and flames due to the chimney effect in vertical shafts . Properly installed fireproof seals provide thermal insulation, smoke containment, and structural integrity during fire events . By following these guidelines, the base of a vertical shaft cable tray can be effectively sealed to meet fire safety, smoke containment, and water ingress prevention requirements.