Fireproofing and Sealing Openings in Vertical Shaft Cable Trays

Vertical shaft cable trays must be fireproofed using fire-rated materials, proper sealing techniques, and fire-resistant coatings to prevent fire spread and ensure compliance with safety standards.Firestopping RequirementsWhen cable trays pass through vertical shafts, walls, or slabs, all openings must be tightly sealed with firestopping materials to maintain the integrity of fire-rated barriers. Common materials include fire-rated boards, firestop packs, firestop mastic, and fire-resistant mineral wool. For large openings, a fire-resistant backing plate should be installed before sealing. Gaps between firestop packs and cables should not exceed 1 cm², and packing thickness should be at least 24 cm. All gaps inside and around metal trunking must be sealed both internally and externally, and cover plates should be square, evenly painted, and properly fitted .Fireproof Cable Tray MaterialsCable trays used in vertical shafts should be fire-resistant. Options include galvanized steel, stainless steel, fire-resistant coated trays, and flame-retardant plastic composites. Surfaces can be coated with fire-retardant paint to slow flame spread and increase heat resistance. Fire barriers can be installed within trays to isolate different fire zones, ensuring that flames do not propagate along the tray .Installation and Sealing TechniquesFirestop Packs and Putty: UL-listed systems, such as 3M firestop pillows or moldable putty, can be used to seal openings around cable trays. The number of pillows depends on tray size, and putty sticks are applied to ensure complete coverage .Slab Penetrations: At floor or slab penetrations, provide 20–30 mm of firestopping and install a fire-support plate at the top. Waterstops of at least 50 mm height are recommended at floor level .Sequence: Firestopping is typically performed after cable routing, grounding, and waterproofing steps to ensure proper installation and accessibility for maintenance .Heat Dissipation ConsiderationsTo prevent overheating, use perforated or wire mesh trays to improve airflow and maintain adequate clearance between cables. This ensures that fireproofing measures do not compromise the thermal performance of the cable system .Coating and AcceptanceFireproof cable trays should undergo a coating process to enhance fire resistance, corrosion protection, and durability. Steps include cleaning, rust removal, primer application, and topcoat application. Coatings must comply with national safety standards, and the thickness should meet design specifications. Acceptance inspections verify that the trays meet fireproofing and durability requirements .SummaryProper fireproofing of vertical shaft cable trays involves:Selecting fire-resistant tray materials.Using UL-listed firestop packs, putty, or mastic to seal openings.Installing fire-support plates and waterstops at slab penetrations.Applying fire-retardant coatings and performing acceptance inspections.Ensuring adequate heat dissipation through perforated or mesh trays. Following these measures ensures compliance with fire safety standards, prevents fire spread, and maintains the long-term reliability of electrical installations.