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, forest fires, 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 Dresden, Hamburg, Stalingrad, Tokyo, the atomic bombing of Hiroshima[1] (but not Nagasaki) and The Blitz during World War II.
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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.[2] Probably, this is true for the Peshtigo Fire.[3]
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. 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, 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.[3][4]
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. Firestorms were also created by the firebombing raids of World War II in cities like Stalingrad, Tokyo, Kobe, Hiroshima, Hamburg, and Dresden.
| City / Event | Date of the firestorm | Notes |
|---|---|---|
| Great Fire of London | 2 September 1666 – 5 September 1666 | Most of the City of London was destroyed, though few fatalities recorded (this affected a much smaller area than that covered by modern London). |
| 1871 Great Chicago Fire Peshtigo Fire Port Huron Fire |
8 October 1871 | Hundreds killed in Chicago from 8 October to 10 October; up to 2,500 killed in Peshtigo, Wisconsin; others killed in similar fires in Holland and Manistee, Michigan. |
| 1906 San Francisco Earthquake | 18 April 1906 | Also known as the "Ham and Eggs Fire," the fire became uncontrollable because of water mains damaged in the quake. |
| Great Fire of 1910 | 20–21 August 1910 | Also known as the "Big Burn" and the "Big Blowup": 87 killed (including one entire Forest Service Fire crew of 28 men), at least 3 towns were partially burned in two days of firestorms; about 3 million acres (12,000 km2) of forest lands in 4 U.S. western states is estimated to have burned. Smoke reached as far as New England and fallout ash was found on snowfields in Greenland.[5] |
| 1923 Great Kantō earthquake | 1 September 1923 | 140,000 dead, most of them in firestorms in Tokyo and the port city of Yokohama. Total damages amounted to 40% of the GNP of that year. |
| Black Friday (1939) | 13 January 1939 | 71 people died, Almost 2,000,000 ha (4,942,000 acres) burnt. Over 1,300 homes,69 sawmills and a total of 3,700 buildings were destroyed. |
| Second Great Fire of London | 29/30 December 1940 | Particularly heavy bombing raids (as part of The Blitz) caused a firestorm affecting the City and other parts of London. |
| Bombing of Stalingrad | 23–26 August 1942 | 955 dead, 1,181 wounded, most of the city reduced to rubble |
| Bombing of Hamburg (Germany) | 27 July 1943 | 45,000 dead |
| Bombing of Kassel (Germany) | 23 October 1943 | 10,000 dead |
| Bombing of Braunschweig (Germany) | 15 October 1944 | 2,600 dead |
| Bombing of Darmstadt (Germany) | 11 September 1944 | 12,300 dead |
| Bombing of Heilbronn (Germany) | 6 December 1944 | 6,500 dead |
| Bombing of Dresden (Germany) | 13 February 1945 | 25,000–135,000 dead |
| Bombing of Pforzheim (Germany) | 23 February 1945 | 17,000 dead |
| Firebombing of Tokyo (Japan) | 9 March 1945 | 120,000 dead |
| Bombing of Würzburg (Germany) | 16 March 1945 | 5,000 dead |
| Firebombing of Kobe (Japan) | 17 March 1945 | 8,841 dead |
| Atomic bombing of Hiroshima (Japan) | 6 August 1945 | 90,000+ dead, though partly due to attendant nuclear explosion |
| Oakland Firestorm of 1991 | 20 October 1991 | 25 dead, $1.5 billion in damages |
| Black Saturday bushfires | 7 February 2009 contained 6 March 2009 | 173 people died , 400 individual fires, 450,000 ha (1,100,000 acres) burnt, Over 3,500 structures destroyed |
Early in World War II many British cities were firebombed, a particularly notable raid was the Coventry Blitz on 14 November 1940. During the Coventry Blitz the Germans pioneered several innovations which were to influence all future strategic bomber raids during the war.[6] These were: The use of pathfinder aircraft with electronic aids to navigate, to mark the targets before the main bomber raid; The use of high explosive bombs and air-mines (blockbuster bombs) coupled with thousands of incendiary bombs intended to set the city ablaze. The first wave of follow-up bombers dropped high explosive bombs, the intent of which was knock out the utilities (the water supply, electricity network and gas mains), and to crater the road – making it difficult for the fire engines to reach fires started by the follow-up waves of bombers. The follow-up waves dropped a combination of high explosive and incendiary bombs. There were two types of incendiary bombs: those made of magnesium and those made of petroleum. The high explosive bombs and the larger air-mines were not only designed to hamper the Coventry fire brigade, they were also intended to damage roofs, making it easier for the incendiary bombs to fall into buildings and ignite them. Arthur Travers Harris, commander of RAF Bomber Command, wrote after the war "Coventry was adequately concentrated in point of space [to start a firestorm], but all the same there was little concentration in point of time",[7] so a firestorm was not ignited. They did not have the numbers or size of aircraft (they only had a twin-engine bomber).
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It was not until later in the war when Bomber Harris also known as "Butcher" Harris and the RAF managed sufficient concentration of bombers over one target close to simultaneously that a firestorm could be ignited. For example during the Dresden raid on 13 February 1945, first attack was carried out entirely by No. 5 Group, using their own low-level marking methods and tactics. The pathfinders marked the Ostragehege stadium as the initial aiming point and each bomber fanned out from that point releasing their bombs at slightly different preassigned times on slightly different preassigned trajectories. The first bombs of No. 5 Group were released at 22:14 (CET) with all but one bomber releasing all their bombs within two minutes. The fan shaped area of destruction that the 244 Lancaster bombers created was one and a quarter miles (2.01 km) long and at its extreme about one and three quarters miles (2.82 km) wide.[8][9] This raid by the RAF, with follow up raids by more RAF bombers and bombers of the USAAF, caused one of the most devastating and infamous firestorms in history.
One of the most terrifying firestorms resulted from one bombing raid against Hamburg, on 27 July 1943, shortly before midnight. A number of factors combined to give the enormous destruction that followed; the unusually dry and warm weather, the concentration of the bombing in one area and that the city's firefighters were unable to reach the initial fires — the high explosive "Cookies" used in the early part of the raid had prevented them getting into the center of the city from the periphery where they were working on the results of the 24th. The bombings culminated in the spawning of the so-called "Feuersturm" (firestorm). Quite literally a tornado of fire, this phenomenon created a huge outdoor blast furnace, containing winds of up to 240 km/h (150 mph) and reaching temperatures of 800 °C (1,470 °F). It caused asphalt on the streets to burst into flame, cooked people to death in air-raid shelters, sucked pedestrians off the sidewalks like leaves into a vacuum cleaner and incinerated some eight square miles (21 km2) of the city. Most of the 40,000 casualties caused by Operation Gomorrah happened on this single night.
In 1945, Tokyo had an average 103,000 inhabitants per square mile and peak levels as high as 135,000 per square mile, the highest density of any industrial city in the world. With firefighting measures inadequate to the task, 15.8 square miles (41 km2) of the city were destroyed on a night when fierce winds whipped the flames and walls of fire blocked tens of thousands fleeing for their lives. An estimated 1.5 million people lived in the burned out areas.[10]
Nuclear weapons can also create firestorms in urban areas. This was responsible for a large portion of the destruction at Hiroshima.