Transit disaster in
London, 18 November 1987.
31 people died and over 60 were injured in a fire in the King's Cross Underground station. The fire started when a still-burning cigarette butt fell into a crevice in an escalator from the Piccadilly Line platform. While that escalator burned, flammable gases were produced over the course of the next 15 minutes. These gases were then ignited in a flash fire that spread through multiple escalators and the station concourse.
The disaster was exacerbated by the fact that trains continued arriving virtually every minute, adding to the transient load and making reliable evacuation extremely difficult. Use of wood as a construction material also contributed (as wood is obviously flammable). Among the most significant results were a smoking ban in the entire Tube system, and a change to non-flammable flooring materials in Tube cars (carriages).
Sources:
http://www.floormaster-plus.com/kingscross.htm
http://www.sos.se/SOS/PUBL/REFERENG/9003030E.htm