Slayer Simon, from my knowledge that isn't the way that the activateifused=x and activated=x commands work.
At least they certainly don't normally work that way.
The "x" in both is less of a numeral and more of a truth statement. So if acivateifused=1 then the script will activate the entities "If Used" entry in that entities Properties menu. If it equals 0, then it turns off that activated.
Same thing with the activated=x command--if it is 1, then it will only continue if it has been activated by another entities activateifused command, whereas if it is 0 it will only continue the state if it has not been activated.
I like to do things the longer, more scripted way but the easy way is simple:
1. Right-click on the explosion decal. Where is says "Spawn at Start", choose No. Make sure the decal has a unique name.
2. Place a trigger zone where you want the explosion to appear. Right click the zone and where it says "IfUsed", type in the name of the explosion decal.
Behind the scenes this involves some simple altering of scripts that can be useful if you want to learn how the language works, but if that doesn't matter to you, the above way will do just fine.
Evil has a new name. Demo out now!