Road Tunnels Manual

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9.3. Resistance of equipment to fire

In terms of resistance to high temperatures, tunnel equipment and cables can be broadly grouped as either fire-rated or unprotected.

Protected equipment and cables with variable levels of resistance to fire include, for example:

  • fire-resistant cables capable of withstanding 950°C for 3 hours (CWZ specification);
  • LS0H cables: 250°C for 3 hours;
  • ventilation fans: 250°C for 1 or 2 hours

Unprotected items of equipment such as traffic signs, cameras and public address (PA) speakers have working temperatures typically up to 50°C, and are likely to fail at relatively low temperatures. Materials include:

  • luminaires - laminated glass (fluorescent) or toughened glass (SON); aluminium alloy or steel housings (working temperatures for SON luminaires typically about 120°C)
  • traffic signs - polycarbonate screens, stainless steel housings
  • cameras - lenses, aluminium housings
  • public address (PA) horn speakers - glass-reinforced polyester (GRP).

Critical temperatures for materials used in such unprotected items include:

  • polymer-based materials such as polycarbonate will melt at temperatures in the region of 150°C and ignite at temperatures in the order of 300-400°C;
  • silicone sealing - working temperatures typically go up to 200-250°C;
  • glass - working temperatures for toughened glass are typically up to 250-300°C, cracks may develop at temperatures greater than 600°C;
  • aluminium alloy - softens at 400°C and melts at 660°C.

All fittings used for the fixing of equipment to the structures should be considered in terms of their behaviour in fires.

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