Firestorm

Principle of the firestorm: The fire (1) creates rising hot air (2), which draws in fresh air via the suction effect (3)

A firestorm is the chimney effect in large area fires , in which hot air rises above the seat of the fire due to the development of intense heat and the resulting suction draws fresh air. With this chimney effect, there is thus a positive feedback - the supply of fresh air further fans the fire.

description

Firestorms are favored by the basin-shaped terrain and by a fan-shaped system for the initial fires , with the tip of the fan pointing in the direction from which the wind is coming.

A firestorm can only arise after a large, contiguous source of fire has formed, e.g. B. through the merging of individual small fires, large forest fires or fires of entire city districts and cities. For example, some area bombings in the air war of World War II led to fire storms. The roofs of the buildings were covered by the combined dropping of high-explosive bombs and incendiary bombs , so that the incendiary bombs could ignite wooden components inside. By destroying the window panes, additional air got to the fire sites and enabled the fire to spread rapidly, especially in the case of narrow, winding old town buildings that were largely made of wood. At the same time, the destruction caused by the high-explosive bombs made it more difficult for the rescue workers to advance in the streets blocked by rubble, and there was also the destruction of pipes and the collapse of the (extinguishing) water supply.

In order to optimize the effect of incendiary bombs on inner-city construction methods typical for Germany, replicas of German tenements were built on the Dugway Proving Ground (“ German Village ”) in 1943 . The critical minimum values for the formation of a firestorm are given as 39 kilograms of combustible substance per square meter (8 pounds per square foot) and an area of approx. 1.3 square kilometers (0.5 square miles).

They were also observed following atomic explosions - the two atomic bombs dropped on Hiroshima and Nagasaki and above-ground nuclear weapons tests .

A large firestorm can also spin and then form a cyclone . Fire storms are generally not considered actively extinguishable. They usually only end when the available combustible material has been used up.

The meteorological environment can favor their formation, e.g. B. Before the firestorm in Hamburg in the summer of 1943 it was particularly hot and dry. Heavy bombardments of cities do not necessarily have to generate a firestorm, as the examples in Berlin, Munich and Nagoya show : Even attacks spread over a long period of time could not generate a feedback effect; especially not if there was sufficient extinguishing capacity on site and the development was not dense enough.