Fireproof sealing of cable trays penetrating the ceiling slab

Cable tray penetrations through ceiling slabs must be sealed with fire-resistant materials such as intumescent sealants, firestop packs, or fire-rated foams to maintain fire integrity and prevent smoke spread.

Key Principles

When cable trays penetrate a ceiling slab, the opening must be tightly sealed to maintain the fire-resistance rating of the slab and prevent fire and smoke from spreading between floors. The seal should be continuous, without cracks or voids, and compatible with the materials of the slab and cable tray ( ).

Recommended Materials

• Intumescent Sealants: Acrylic or silicone-based intumescent sealants expand when exposed to heat, blocking fire and smoke. Products like FireStop Intumescent Acrylic Graphite 682 are suitable for cable penetrations and start expanding at around 200°C ( ).
• Firestop Packs and Mineral Wool: For larger openings, fire-resistant mineral wool or firestop packs can be used as backing material before sealing with a mastic or foam ( ).
• Fire-Rated PU Foam: Fire-rated polyurethane foams, such as Fire Rated Gunfoam B1 187, provide thermal insulation and fire resistance for cable penetrations ( ).
• Fire Barrier Putty: Moldable putty, such as 3M Fire Barrier Moldable Putty+, can be used for retrofitting or sealing multiple cables in a single penetration ( ).

Installation Guidelines

1. Prepare the Opening: Ensure the slab and cable tray are clean and free of debris. For large openings, install a fire-resistant backing plate to support the sealant or packing material ( ).
2. Apply Firestop Material: Fill the gap around the cable tray with the chosen firestop material. For intumescent sealants, use a caulking gun to apply evenly. Ensure the gap between cables and sealant does not exceed 1 cm² ( ).
3. Seal Internally and Externally: All gaps inside and around metal trays or conduits must be sealed both internally and externally to maintain fire integrity ( ).
4. Cover Plates: Use square, consistent cover plates to close the opening, ensuring a neat finish and additional protection ( ).
5. Waterstop Considerations: For penetrations in electrical shafts, a waterstop of at least 50 mm may be required at floor level, with 20–30 mm of firestopping above the slab penetration ( ).

Compliance and Testing

• Follow EN 1366-3 for penetration seals, especially for mixed penetrations with multiple cables or pipes ( ).
• Ensure the firestop system is tested and approved for the specific cable type, tray configuration, and slab thickness.
• Temporary sealing during construction can use removable intumescent pillows or sleeves, which are replaced with permanent firestopping after installation ( ).

Practical Tips

• Keep openings as small as practicable to reduce fire risk ( ).
• Use intumescent materials for areas where heat exposure is expected, as they expand to fill gaps and maintain fire resistance.
• For retrofits, select products that allow easy installation without removing existing firestops, such as moldable putty or flexible foam ( ). By following these guidelines, cable tray penetrations through ceiling slabs can achieve effective fireproofing, maintain structural fire integrity, and comply with building regulations.