Experimental study on fire performance of optical cables used in utility tunnel: Influence of cable spacing and heat flux

Optical cable is an important part of modern telecommunications infrastructure. In this study, cone calorimeter experiments are conducted on the optical cables which are widely being applied in utility tunnels in China. The coupling effect of the spacing between optical cables (8, 10, 12, 15 mm) and the heat flux (30, 40, 50 kW/m²) on fire performance of optical cables is studied. It is highlighted that the optical cables conform to the ignition time model of the thermally thin material. The ignition time of the optical cables decreases when increasing the heat flux. When the heat flux is 30 kW/m², the ignition time of the optical cable with different spacing varies greatly. When the heat flux is greater than 30 kW/m², the difference in the ignition time between the optical cable samples with different spacing is small. Furthermore, the average mass loss rate of the optical cables increases when increasing either the heat flux or the spacing between optical cables. The heat release rate of the optical cables also increases when increasing either the heat flux or the spacing between optical cables. The curves of the heat release rate versus time show two peaks, the second one being significantly smaller.