Trench effect

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The trench effect (partly borrowed from the English trench effect ) is a superposition of two well-known but different phenomena: the Coandă effect from the flow dynamics and the flashover from the fire dynamics. The trench effect was discovered in 1988 during an investigation into a fire at King's Cross St. Pancras train station , in which 31 people were killed the previous year.

Description of the phenomenon

The Coandă effect is the tendency of a rapidly moving stream of air to be deflected from a nearby surface. The air flow is thereby bound to the surface orientation.

The flashover is a sudden ignition of pyrolysis gases, which are caused by the heating of surfaces in the fire room. With this ignition, all flammable surfaces of a fire area are spontaneously on fire.

The trench effect occurs when a fire burns near a steep surface. The flames do not strive upwards, as one would expect, but lie on the surface according to the Coandă effect. The flames heat up the surface above the fire to such an extent that, on the one hand, pyrolysis gases are exuded and, on the other hand, the ignition temperature of the surface is reached. Then, in accordance with the flashover theory, an ignition occurs, in which suddenly the entire inclined surface is on fire. The flames shoot like a flamethrower over the upper end of the inclined plane, creating enormous temperatures. This can ignite the room above the slopes.

discovery

The rift effect has not been known for very long. When the devastating fire broke out in London's King's Cross St. Pancras Underground Station in 1987, it was impossible to explain how an initially small fire on an escalator with wooden steps could lead to a sudden burst of flame that ignited the hall above and many people cost life. A computer simulation showed the previously unknown rift effect, which the programmers initially saw as a simulation error. Only different models of the escalator were able to prove that there was an ignition effect that was unknown until then.

literature

  • Keith Moodie : The King's Cross Fire: Damage Assessment and Overview of the Technical Investigation. In: Dougal D. Drysdale (Ed.): King's Cross Underground Fire (= Fire Safety Journal. Volume 18, No. 1, 1992, Special Issue , ISSN  0379-7112 ). Elsevier Applied Science, Barking 1991, pp. 13-33, doi: 10.1016 / 0379-7112 (92) 90045-E .
  • Keith Moodie, Stuart F. Jagger : Results and Analysis from the Scale Model Tests. In: The King's Cross Underground Fire. Fire Dynamics and the Organization of Safety. Papers presented at a Seminar held on July 1, 1989 (= IMechE Seminar Publication. 2, 1989). Mechanical Engineering Publications , London 1989, ISBN 0-85298-705-6 , pp. 27-40.
  • Alan F. Roberts : A Correlation of the Eyewitness Accounts and Results of the Scientific Investigation. In: The King's Cross Underground Fire. Fire Dynamics and the Organization of Safety. Papers presented at a Seminar held on July 1, 1989 (= IMechE Seminar Publication. 2, 1989). Mechanical Engineering Publications , London 1989, ISBN 0-85298-705-6 , pp. 41-48.
  • S. Simcox , NS Wilkes , IP Jones : Computer Simulation of the Flows of Hot Gases from the Fire at King's Cross Underground Station. In: Dougal D. Drysdale (Ed.): King's Cross Underground Fire (= Fire Safety Journal. Volume 18, No. 1, 1992, Special Issue ). Elsevier Applied Science , Barking 1991, pp. 49-73, doi: 10.1016 / 0379-7112 (92) 90047-G .
  • Yajue Wu , Dougal D. Drysdale : Study of upward flame spread on inclined surfaces (= HSE Contract Research Report. No. 122). Health and Safety Executive Books , Sudbury 1996, ISBN 0-7176-1289-9 , digital version (PDF; 1.48 MB) .