The flame front burns down each fuse segment at a roughly constant linear rate v set by the fuse's own black-powder core, so the delay before the next cracker in the string ignites is a straight length-over-speed calculation, slowed by moisture in the fuse:
t_ignite(k→k+1) = L / v_eff
v_eff = v_burn · (1 − 0.6 · humidity)
p_transfer = contact · (1 − 0.7 · humidity), clamped
At every splice the flame has to physically bridge from the spent charge of one cracker to the exposed powder core of the next fuse — a step that fails constantly in real quickmatch strings when the wrap is loose or damp, which is why this simulation rolls a genuine pass/fail there instead of guaranteeing the fire always continues. A successful splice heats the next charge's trapped gas faster than the crimped paper tube can vent it, so pressure spikes until the casing bursts — the pop — releasing hot expanding gas that, if the next splice holds, relights the process one cracker further down the line.
- Fuse burn rate — the fuse's intrinsic propagation speed.
- Splice contact quality — tighter wraps transfer heat faster and more reliably.
- Humidity — slows the burn front and starves marginal splices of the heat needed to jump — a real cause of dud strings.
- Fuse segment length — longer runs mean a longer burn time, and longer for a weak flame to smoulder out, per hop.
- View — drag the scene to pan, scroll/pinch to zoom along the string.