A firestorm is a fire of such great intensity that it creates and sustains its own wind system.
A wildfire – or multiple wildfires in the same area – can cause a firestorm.
Firestorms occur in nature and have occurred in urban areas. For some historical examples in cities, firestorms occurred in Germany and Japan in WWII as a result of aerial firebombings of Hamburg, Dresden and Tokyo, as well as the atomic bombing of Hiroshima.
A firestorm is created as a result of a “chimney effect,” as heat from a large fire draws in more and more of the air that is surrounding the fire.
Firestorms form for two main reasons:
- Heat rises.
- Nature hates a vacuum. In other words, empty spaces won’t stay empty for long.
It all starts because heat is constantly and quickly rising from the fire. As all this heat and air moves upwards, it leaves behind some empty space. Air from all around the fire rushes in to fill that gap. That movement of air creates a powerful wind called an updraft.
As the updraft mushrooms into the sky, strong inwardly-directed gusty winds develop around the fire, supplying the fire with additional air.
As the firestorm draws in greater quantities of oxygen, it significantly increases combustion, thereby also substantially increasing the production of heat. The intense heat of a firestorm may ignite flammable material at a distance ahead of the fire itself.
This also serves to expand the area and the intensity of the firestorm.
If the fire is big enough, it will form “fire storm clouds,” that can produce lightning, which could set off even more fires. They also generate stronger winds, which fan the fire, making it hotter and helping it spread.
In some cases, the rising air can be so fast it creates a fire whirl, also known as a tornado of fire.
Violent, erratic winds suck anything movable into the fire and as is observed with all intense conflagrations, radiated heat from the fire can melt asphalt, some metals, and glass, and turn street tarmac into flammable hot liquid.
The high temperatures within the firestorm zone ignite most everything that might possibly burn, until the firestorm has consumed so much of the available fuel within the firestorm zone that the wind system drops and the firestorm breaks up into isolated conflagrations.