Affliction, Explosive, and Heart Attack

[Aldric]

A 1d or something attack with Fragile (Explosive) as symptoms should not be immediately lethal unless the target is already wounded.
Make it a Malediction with No Signature and you can just stare at something for a few seconds to make it Explosive, and some more to actually make it explode. Increase number of dices to make the process faster.

But if you just want to blow something up instantly, just buy an Innate Attack with ex and enough damage, bonus points if you make it a follow up