Firebrand Spotting Distance Simulator

Fire & Wind

Wind speed 9 m/s

Firebrand diameter 8 mm

Plume lofting height 35 m

Firebrands / burst 40

Flight Stats

Embers aloft

Spot fires

Max spot distance

0 m

Ignition rate

How it works

A firebrand (ember) released from a convective fire plume is carried by two competing processes: it falls under gravity at its terminal velocity, and it drifts downwind at close to the ambient wind speed. Both responses relax exponentially with a particle response time τ that depends on the ember's size — the same drag physics used in Albini's classic spotting-distance model:

v_t(d) = k·√d            (terminal fall speed, larger embers fall faster)
τ = v_t / g               (response time to gravity/wind)
dv_y/dt = (−v_t − v_y) / τ
dv_x/dt = (U_wind − v_x) / τ
d(t) = d0 − β·t           (diameter shrinks as it burns)

While airborne the ember's diameter shrinks at a steady combustion regression rate β. If it burns down to nothing before it lands, it goes dark — cold ash, no ignition. If it is still glowing when it reaches the ground, it can start a spot fire beyond the main front — the mechanism that lets wildfires jump roads, rivers and firebreaks.

Wind speed — sets the horizontal drift target U_wind; faster wind both throws embers farther and shortens the time available before they hit the ground.
Firebrand diameter — bigger embers have higher terminal velocity (fall faster, less hang time) but also more thermal mass, so they resist burning out; smaller embers float longer but burn out fast. The sweet spot for maximum spotting distance sits in between.
Plume lofting height — how high the fire's convection column carries embers before releasing them into the wind-driven fall; taller plumes mean a longer horizontal transport window.
Launch ember burst — releases a fresh batch from the fire front so you can compare outcomes under the current settings.

Note: the combustion regression rate here is sped up for interactivity — real firebrands typically burn for tens of seconds to a few minutes rather than a few seconds.

Burning firebrand Spot-fire ignition Burnt-out ash

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