Fireproof trench for overhead optical cables

A fireproof trench for optical cables combines protective ducts, fire-resistant cable types, and fire-blocking materials to ensure safety and maintain service continuity during fire events.

Trench Design and Construction

For overhead or near-ground optical cable installations, trenches should be excavated to a sufficient depth, typically around 1.65 meters, with a bottom width of 250–300 mm to accommodate cables and protective ducts . The trench bottom should be level and free of stones, and transitions between hard and soft surfaces should be tamped to prevent cable damage . In areas with existing utilities or uneven terrain, DWC (Double Wall Corrugated) pipes or RCC/GI protective pipes can be used to shield the cables .

Fireproof Materials and Accessories

To enhance fire safety, the following measures are recommended:

• Fire-resistant cables: Use cables like Draka FireTuf, which comply with IEC 60331-25 for circuit integrity and IEC 60332-2-3-24C for flame retardancy. These cables maintain performance under high temperatures and are suitable for tunnels, public buildings, and emergency systems .
• Fire-blocking sections: Lightweight intumescent fireproof blocks, fireproof cloth, and metal frames can be installed at trench entrances, tunnels, or overhead bridges. These materials expand under heat to seal cavities, preventing fire spread and protecting the cables .
• Cable trays and covers: Fireproof fiber cloth and openable covers allow easy maintenance while maintaining fire protection .

Installation Considerations

• Cable placement: Lay cables straight along the trench, avoiding sharp bends and minimizing handling .
• Backfilling: Use fine soil or sand to cover the cables, ensuring no sharp objects contact the cable sheath .
• Testing: After installation, perform optical tests to verify signal integrity and ensure no damage occurred during trenching .
• Maintenance: Fireproof sections should allow easy addition or removal of cables without compromising fire protection .

Summary

A fireproof trench for optical cables integrates proper trench depth, protective ducts, fire-resistant cables, and fire-blocking materials. Using standards-compliant cables and accessories ensures circuit integrity during fire events, while careful trenching and backfilling protect the cables from mechanical damage. This approach is suitable for overhead crossings, tunnels, and critical infrastructure installations .