Full scale experiments have &en conducted with telephone cables in an attempt to simulate the thermal and atmospheric conditions of a real cable fire. The cables used for the experiments had polyethylene sheathing and were of the same specification and layout as those in the real fire. Temperature, gas concentration, smoke concentration, and hot air velocity were measured and recorded every 15 sec. Thousand pairs of wires were monitored to record the times of their communication stoppages due to fire. Temperatures around the ignition region showed 800 C after 5 min, and the average flame spread over the surface of the cables was about 3 m/min along the tunnel. It was found that the stoppage against time showed a normal distribution with a standard deviation of 2 - 3 min. Based on the comparison of both stoppage behaviors of the experiments and the real fire, the start time and the propagation of the real fire were estimated.