Firestorm

This article is about fires. For other uses, see Firestorm (disambiguation).

A firestorm during the 1988 Yellowstone fires

A firestorm is a conflagration which attains such intensity that it creates and sustains its own wind system. It is most commonly a natural phenomenon, created during some of the largest bushfires and wildfires. The Black Saturday bushfires, the Great Peshtigo Fire and the Ash Wednesday fires are examples of firestorms, as is that following the 1906 San Francisco Earthquake. Firestorms can also be deliberate effects of targeted explosives such as occurred as a result of the aerial bombings of Hamburg, Dresden, Tokyo, the atomic bombing of Hiroshima.

Mechanism

See also: Thermal column

Firestorm: fire (1), updraft (2), strong gusty winds (3)

A firestorm is created as a result of the stack effect as the heat of the original fire draws in more and more of the surrounding air. This draft can be quickly increased if a low level jet stream exists over or near the fire. As the updraft mushrooms, strong gusty winds develop around the fire, directed inward which supply the fire with additional air. This would seem to prevent the firestorm from spreading on the wind, but the tremendous turbulence also created causes the strong surface inflow winds to change direction erratically. This wind shear is capable of producing small tornado- or dust devil-like circulations called fire whirls which can also dart around erratically, damage or destroy houses and buildings, and quickly spread the fire to areas outside the central area of the fire. A firestorm may also develop into a mesocyclone and induce true tornadoes. Probably, this is true for the Peshtigo Fire.

The greater draft of a firestorm draws in greater quantities of oxygen, which significantly increases combustion, thereby also substantially increasing the production of heat. The intense heat of a firestorm manifests largely as radiated heat (infrared radiation) which ignites flammable material at a distance ahead of the fire itself. This also serves to expand the area and the intensity of the firestorm. Violent, erratic wind drafts suck movables into the fire, while people and animals caught close or under the fire die for lack of available oxygen.^{[citation needed]} Radiated heat from the fire can melt asphalt, metal, and glass, and turn street tarmac into flammable hot liquid. The very high temperatures replicate the conditions of a smelting furnace,^{[citation needed]} where anything that might possibly burn does so readily, until the firestorm runs out of fuel.

Besides the enormous ash cloud produced by a firestorm, under the right conditions, it can also induce condensation, forming a pyrocumulus cloud or "fire cloud". A large pyrocumulus can grow into a pyrocumulonimbus and produce lightning, which can set off further fires. Apart from forest fires, pyrocumulus clouds can also be produced by volcanic eruptions.

In Australia, the prevalence of eucalyptus trees that have oil in their leaves results in forest fires that are noted for their extremely tall and intense flame front. Hence the bush fires appear more as a firestorm than a simple forest fire. Sometimes, emission of combustible gases from swamps (e.g., methane) has a similar effect. For instance, methane explosions enforced the Peshtigo Fire.

In cities

The same underlying combustion physics can also apply to man-made structures such as cities during war or disaster.

Firestorms are thought to have been part of the mechanism of large urban fires such as the Great Fire of Rome, the Great Fire of London, the 1871 Great Chicago Fire, and the fires resulting from the 1906 San Francisco earthquake and the 1923 Great Kantō earthquake.^{[citation needed]} Firestorms were also created by the firebombing raids of World War II in cities like Hamburg, and Dresden.

City / Event	Date of the firestorm	Notes
Bombing of Hamburg (Germany)	27 July 1943	46,000 dead.
Bombing of Dresden (Germany)	13 February 1945	maximum of 25,000 dead.
Firebombing of Tokyo (Japan)	9–10 March 1945	Firestorm covering 16 square miles (41 km2). 267,171 buildings destroyed, 83,793 dead. The most devastating air raid in history with destruction greater than the Atomic bombing of Hiroshima, although with fewer casualties.
Atomic bombing of Hiroshima (Japan)	6 August 1945	Firestorm covering 4.4 square miles (11 km2). The proportion of firestorm victims who survived the initial blast can never be known.

Firebombing

Braunschweig burning after aerial firebombing attack in 1944.

Firebombing is a technique designed to damage a target, generally an urban area, through the use of fire, caused by incendiary devices, rather than from the blast effect of large bombs. Such raids often employ both incendiary devices and high explosives. The high explosive destroys roofs making it easier for the incendiary devices to penetrate the structures and cause fires. The high explosives also disrupt the ability of firefighters to douse the fires.

Although simple incendiary bombs have been used to destroy buildings since the start of gunpowder warfare, World War II saw the first use of strategic bombing from the air to destroy the ability of the enemy to wage war. London, Coventry and many other British cities were firebombed during the Blitz. Most large German cities were extensively firebombed starting in 1942 and almost all large Japanese cities were firebombed during the last six months of World War II. However as Sir Arthur Harris, the officer commanding RAF Bomber Command from 1942 through to the end of the war in Europe, pointed in his post war analysis, although many attempts were made to create deliberate man made firestorms during World War II few attempts succeed:

"The Germans again and again missed their chance, ... of setting our cities ablaze by a concentrated attack. Coventry was adequately concentrated in point of space, but all the same there was little concentration in point of time, and nothing like the fire tornadoes of Hamburg or Dresden ever occurred in this country. But they did do us enough damage to teach us the principle of concentration, the principle of starting so many fires at the same time that no fire fighting services, however efficiently and quickly they were reinforced by the fire brigades of other towns could get them under control."

—Arthur Harris, 

According to David Hafemeister firestorms occurred after about 5% of all fire-bombing raids of World War II (but he does not explain if this is a percentage based on both Allied and Axis raids, or combined Allied raids, or U.S. raids alone). The [American] National Fire Protection Association stated in a 2005 report that there were only 3 major fire storms resulting from Allied conventional bombing campaigns during World War II: Hamburg, Dresden and Tokyo. They go on to quote Glasstone and Dolan:

based on World War II experience with mass fires resulting from air raids on Germany and Japan, the minimum requirements for a fire storm to develop are considered by some authorities to be the following: (1) at least 8 pounds of combustibles per square foot of fire area, (2) at least half of the structures in the area on fire simultaneously, (3) a wind of less than 8 miles per hour at tJte time, and (4) a minimum burning area of about half a square mile.

—Glasstone and Dolan (1977).

See also

• Wildfire

References

• American National Fire Protection Association (2005), Scawthorn, Charles; Eidinger, John M.; Schiff, Anshel J., eds., Fire Following Earthquake, Issue 26 of Monograph (American Society of Civil Engineers. Technical Council on Lifeline Earthquake Engineering), American Society of Civil Engineers Technical Council on Lifeline Earthquake Engineering (illustrated ed.), ASCE Publications, p. 68, ISBN 978-0-7844-0739-4 
• Gess, Denise; Lutz, William (2003) [2002], Firestorm at Peshtigo: A Town, Its People, and the Deadliest Fire in American History, ISBN 978-0-8050-7293-8 
• Glasstone, Philip J.; Dolan, eds. (1977), ""Chapter VII — Thermal Radiation and Its Effects", The Effects of Nuclear Weapons (Third ed.), United States Department of Defense and the Energy Research and Development Administration, pp. 299, 200, § "Mass Fires" ¶ 7.58, http://www.fourmilab.ch/etexts/www/effects/eonw_7.pdf#zoom=100 
• Frankland, Noble; Webster, Charles (1961), The Strategic Air Offensive Against Germany, 1939–1945, Volume II: Endeavour, Part 4, London: Her Majesty's Stationary Office, pp. 260–261 
• Hafemeister, David W, ed. (1991), Physics and Nuclear Arms Today, Issue 4 of Readings from Physics Today (illustrated ed.), Springer, p. 24, ISBN 978-0-88318-640-4 
• Harris, Arthur (2005), Bomber Offensive (First, Collins 1947 ed.), Pen & Sword military classics, p. 83, ISBN 1-84415-210-3 
• Kartman, Ben; Brown, Leonard (1971), Disaster!, Essay Index Reprint Series, Ayer Publishing, p. 48, ISBN 978-0-8369-2280-6 
• McRaney, W.; McGahan, J. (6 August 1980), Radiation dos reconstruction U.S. occupation forces in Hiroshima and Nagasaki, Japan, 1945–1946 (DNA 5512F) — Final Report for Period 7 March 1980-6 August 1980, Science Applications, Inc, p. 24, archived from the original on 24 June 2006, http://web.archive.org/web/20060624185903/http://www.dtra.mil/toolbox/directorates/td/programs/nuclear_personnel/docs/DNATR805512F.pdf 
• Neutzner, Matthias; et all (2010), Abschlussbericht der Historikerkommission zu den Luftangriffen auf Dresden zwischen dem 13. und 15. Februar 1945, Landeshauptstadt Dresden, p. 70, http://www.dresden.de/media/pdf/infoblaetter/Historikerkommission_Dresden1945_Abschlussbericht_V1_14a.pdf, retrieved 7 June 2011 
• Pyne, Stephen J. (2001), Year of the Fires: The Story of the Great Fires of 1910, Viking-Penguin Press, ISBN 0-670-89990-9 
• Weaver, John; Biko, Dan, Firestone Induced Tornado, http://rammb.cira.colostate.edu/visit/fire/video/fire_tornado.html, retrieved February 2012