Effects of interlayer distance and cable spacing on flame characteristics and fire hazard of multilayer cables in utility tunnel

Fire safety of utility tunnel, which is significantly affected with cables, has arouse public concern. This work experimentally investigated influences of interlayer distance (d) and cable spacing (s) on flame characteristics and fire hazard of multilayer cables in utility tunnel. Larger interlayer distance leads to higher flame height but lower flame width. The flame width decreases with an increase in cable spacing, while the flame height increases first and then reduces. The flame height reaches the highest value when s = 1.0 cm. Flame spread rate (v(f)) progressively increases from bottom layer to the top when d = 4.5-7.0 cm, while the trend is inverse for d = 9.5-10 cm v(f) over the middle layer presents the lowest value when s = 1.0-2.5 cm, while v(f) gradually reduces from the bottom layer to the top for s = 3-4 cm. The maximum temperature of the pyrolysis zone of top cable layer gradually decreases as d rises, but rises in the bottom layer. When s = 1.0-2.5 cm, the highest temperature is observed in the middle cable layer, while in the top layer when s = 3-4 cm.