Fire Tornadoes: How and When Do They Form?
23 September 2018
Wildfires have burned about 7.3 million acres across the U.S. this year compared to an average of 5.8 million acres for the equivalent period over the last 10 years. Scientists are trying to unlock the secrets of how fires spread, in hopes of keeping them away from people and property. One particularly dramatic example of the growing threat they're studying: fire tornadoes.
A tornado of fire has recently captivated the interest of million of users, why? It swallowed up and destroyed a firefighter's hose in British Columbia.
Footage of the incredible incident was filmed by on-duty firefighter MC Schidlowsky. Her crewmates can be seen struggling to pull the hose back from the swirling winds as it is pulled more than 100 ft into the air.
Writing on Instagram, Ms Schidlowsky said "Fire tornado destroyed our line."
"It threw burning logs across our guard for 45 minutes and pulled our hose 100 plus ft in the air before melting it. That's definitely a first."
A fire whirl – also commonly known as a fire devil, or, (in many cases erroneously), as a fire tornado, firenado, fire swirl, or fire twister – is a whirlwind induced by a fire and often made up of flame or ash. They usually start with a whirl of wind or smoke. Fire whirls may occur when intense rising heat and turbulent wind conditions combine to form whirling eddies of air. These eddies can contract into a tornado-like vortex that sucks in burning debris and combustible gases.
Fire whirls are sometimes colloquially called fire tornadoes, but are not usually classifiable as tornadoes as the vortex in most cases does not extend from the surface to cloud base. Also, even in such cases, even those fire whirls are not classic tornadoes, in that their vorticity derives from surface winds and heat-induced lifting, rather than a tornadic mesocyclone aloft.
A fire whirl consists of a burning core and a rotating pocket of air. A fire whirl can reach up to 2,000 °F (1,090 °C). Often, fire whirls are created when a wildfire or firestorm creates its own wind, which can turn into a vortex of fire. This causes the tall and skinny appearance of a fire whirl's core.
Most of the largest fire whirls are spawned from wildfires. They form when a warm updraft and convergence from the wildfire are present. They are usually 10–50 meters tall, a few meters wide, and last only a few minutes. However, some can be more than a kilometer tall, contain winds over 160 km/h, and persist for more than 20 minutes.
Fire whirls can uproot trees up to 15 metres (49 ft) tall. These can also aid the 'spotting' ability of wildfires to propagate and start new fires as they lift burning materials such as tree bark. These burning embers can be blown away from the fireground by the stronger winds aloft.
REFERENCES: MC Schidlowsky, Wikipedia
|Written by: Laura Cozzo|