I've been trying to figure out a way to break or destroy the planks in the death valley pack and if I hit the plank with a hammer it registers the collision or hit but does nothing else, I've tried checking the health of the entity with a "if g_Entity[e]['health'] = 0 then Destroy( e ) end" in the _main section of my script.

I've also tried graphix_explosion.lua script but still does nothing, am I trying to destroy something that can't break or destroy?

Firstly that Lua snippet won't work as it would need to be == 0. Also say <= 0 as the health could drop below 0. (there used to be a bug such that when the health was 0 or below the script no longer gets called btw, not sure if that was ever fixed)

Secondly if you want entities to be breakable then they need to be made that way in the first place. i.e. they need to have some sort of animation frames built in and a script that drives the animation to mimic the breaking action. None of the stock objects are made this way.

Destroy( e ) should remove the entity from the map but you can also use Hide(e) to simply make it invisible (that way you can re-used that entity elsewhere on the map with appropriate scripting) and CollisionOff(e) to remove it's physical body.

As Amen pointed out the mesh should be ready to be breaking in GG or GGMax.
https://www.youtube.com/watch?v=DPkOQ4kqgP4

@ RoadKill
This stuff is too old I did it ages ago, but it might help as a starting point.
It works fine, I just tested it minutes ago in GG.

https://youtu.be/plM-zHibbkY