It was the 18th November 1987, just after rush hour,  7.30 pm, but the central London Piccadilly, Hammersmith and Circle and Victoria lines of the London Underground were still very busy. A passenger noticed a fire under a wooden escalator on the Piccadilly line and called the police. It was only the size of a cardboard box, but the police evacuated the station anyway and called the London Fire Brigade. What happened next was totally unexpected and revealed not only the usual inadequacies in training and preparation but also a physical effect of fires that had never been studied before: the so - called Trench Effect.