Bizarre Natural Phenomena Vol. 40 - When Fire Starts Spinning Around (Firewhirls)

Image from: flickr.com

Whirlwinds are really common, spinning vortexes can be viewed everywhere. Now, let's heat it up a bit, what about... flambé whirlwinds?

Something like this you mean?

Image from: commons.wikimedia.org - Author, J. Patrick Fischer - License

Yeah, but instead of a crème brûlée picture a flaming bushfire with a spinning air column in front of it and there you have it:

A fire whirl!

Image from: commons.wikimedia.org

Fire whirls are not so common as whirlwinds and occur during raging fires. When a bushfire is burning, the surrounding air is heated up. And when this mass of hot air meets with currents that blow around the area of the fire, then it is uplifted and starts twirling. 

In more details: Columns of air are fueled by the heat generated from the bushfire (more usually). Winds blowing around the burning spot cause these hot updrafts to twist, the thinner the column the faster it will spin. This hot whirlwind will have a core of fire (with a diameter of 1 to even 10 meters) and a pocket of air around it, spinning. The fire will also produce combustible gases (from the plants that are brutally lost in the fire). Those gases will be sucked by the firewhirl but they cannot ignite unless enough oxygen is present (something more possible up higher from the burning ground). Temperatures within the burning core may reach up to 1000 °C, bearing the danger of re-igniting hot ashes and causing a new fire to rise.

We need hot and dry weather for a firewhirl to form. Present shears (a flow vertical to another: for example a strong wind getting in touch with the hot flows created by the fire) also help to their formation; but in cases of large bushfires, firewhirls are able to form regardless of the presence of shears. When a firewhirl appears, it won't get taller than 2-10 meters and won't live more than a couple of minutes, but those minutes might do great damage spreading the fire and putting firefighters' lives at risk.

I come with a lot of names

Fire devils, fire tornadoes, firenadoes, fire swirls and fire twisters are used to describe the above phenomenon, although the different names imply a difference in magnitude and behavior.

• A fire devil with a diameter of 1-10 meters has little or no impact on how the fire expands and rotates at a velocity of less than 22 miles/hour, they are natural to every fire.
• A fire whirl has a diameter of 10-30 meters and rotates at speeds of  22-67 miles/hour. These guys form when topography, fire characteristics and meteorological factors mix up to give a more dangerous whirlwind form. They can affect the spread of the fire and are dangerous for firefighters.
• A fire tornado's diameter can be from 30-300 meters and rotate at a speed of even 90 miles/hour. When a fire tornado is formed it can pose a great threat to firefighters.
• A fire storm is as bad as it sounds, with a diameter from 300 meters to 3 kilometes and winds that blow up to 400 miles/hour, it is a preview of a Hades' barbeque party.

A need for better understanding

Their unpredictable nature makes firewhirls a firefighter's worst nightmare. In the past, casualties have been reported from firewhirls. Scientists need to study the behavior and formation of them in order to predict their "behavior" and protect people. 

References

nationalgeographic.com
wildfiretoday.com
wikipedia.org
australiangeographic.com.au

Thank you so much for your time!

Until my next post,
Steem on and keep smiling, people!