December 2019, ScientificAmerican.com 65The Laboratory Fire Whirl
Smallscale vortices of fire generated in the
laboratory have shed light on the physics of fire
tornadoes. These burn fuel several times faster
than nonrotating fires, for example, and are
remarkably efficient at conserving energy, which
enables them to live long.Spinning Up
The rotation in the air that gets gathered up
into a fire tornado can come from various
sources, including wind dragging along the
ground. The resulting vortices are horizontal,
but the hot air from the wildfire, being buoyant,
streams upward, pulling on one (or more) so
that it stands on its end. The burning gases
in the fire plume heat up the air so that it
accel erates upward, stretching and consoli
dating the fire whirl into a long, thin tube.
As the vortex thins, it spins up, like an ice skater
pulling his or her arms in, until a tall, tightly
spinning column of fire forms.Illustration by Bryan Christie Design
© 2019 Scientific American