I am say this just to make the game more realistic I'm not sure if you know this but it real life c-4 is detonated by electricity not fire is=f you use fire on c-4 then it would just sizzle not explode I know that in tpt it is denotated by both i'm just saying it should only detonate it with electricity if this is not possible because it would mess up saves thats fine too.
I think temperature of exlosion must be higher. Over 1000 degrees, because explosive must be able to break metal, C4 like it is now cant destroy anything.