 The Barnes signalman had forgotten about the freight train and used his release key to clear the signals.A contributory factor was the failure of the circuit breakers supplying the traction current to the section to trip when the collision occurred – the subsequent arcing and fire caused most of the fatalities.The official report concluded that the current drawn by the short-circuit (approx 5700 A) was only slightly higher than the trip current (5000 A), and the breakers failed to trip due to poor response speed and stiffness of operation.