fire Resistance of equipment
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 are 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, which 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.