:state=0,activated=0:state=10,activate=1,triggerforce=500
:state=10,activated=1,plrusingaction=1:rundecal=0,sound=audiobank\user\explosion.wav,timerstart,plraddhealth=-100,state=20
:state=20,timergreater=8000:destroy
Okay, here is what is wrong.
You start as being activated=0, so in state=0 you are starting off by activating the entity and moving to state=1
There in state=1 you check for activated=1 which we know is true, and plrusingaction=1 then you take action.
If you try your setup again and shoot your wall, then all you need to do to see your effect is to hit the enter key.
But we both know that is not what you want.
After testing again and hitting your enter key, you'll see what I mean.
Now, according to what you said you wanted it to do then this may be better...
:state=0,activated=0:state=10,triggerforce=500
:state=10,activated=1:rundecal=0,sound=audiobank\user\explosion.wav,timerstart,plraddhealth=-100,state=20
:state=20,timergreater=8000:destroy
All I did was remove the activate=1 action from state=0
and I removed the plrusingaction=1 condition from state=1
Try that and see if you get better results.