I'm curious as to what mechanism drives the "death on explosion" ability of Flame Atronachs.

For starters, I couldn't find the spell that is used to create the effect. And worse yet, nothing under Flame Atronachs' actor entries suggests anything that would make it work. There are no scripts attached to the atronachs, nothing in spell list, etc.

Can someone shed some light on how this works?

In the attronatch script, there is a line: AtronachUnsummonDeathFXS.Play(selfRef) , that activates FXAtronachFireDeathExplosion . It's not a spell. Is an explosion (explosions are in the CK in the special effects category)