How many seconds does afterburn damage last?
Solution 1:
According to the creation kit, the taper duration (how long the spell lasts after it's cast) for each of the fire spells is:
Flames: .1 Seconds
Firebolt: 1 Second
Fireball: 2 Seconds
Incinerate: 1 Second
Fire Storm: 4 Seconds
Testing on a few giants, this seems about right. Flames dies out almost immediately. Firebolt and Incinerate last the same length, Fireball and Fire Storm last longer.
The non-direct spells list taper durations of:
Fire Rune: 1 second spell duration, 1 second taper
Flame Cloak: 60 Second duration (time on self), 2 second taper
Wall of Flame: 1 second spell duration, 2 second taper