I don't think so... chests can withstand attacks from creepers, fire, and lava. So I don't ghasts can destroy them.
I can't remember but I heard it in general chat, some other people confirmed it was possible. I have never tested it as it would be griefing.
It is impossible for a creeper to break a locked chest period. The only way a locked chest can be destroyed is a SR mod or admin removes the sign, Or the player who owns it removes the sign. There is no other way for the chest/lock to be destroyed. I can say this for a fact because I did personally very extensive testing on it when it first came out.
Yes, ive seen in the wild (after it was lava-greifed) a chest with a sign still floating above it even without the block behind it...The chest was also floating...So no matter what it seems to stay the same--Locked
Creepers and explosives can destroy non locked chests! If it is locked by JustinGuy's magical lock then it can't be destroyed by anything but YOU!
I will be honest, I did not try it with a ghast, but did test with creepers / tnt / etc and they all use the same explosion event so it should be fine
even if they do get destroyed, ghast blasts arent that powerful, just put a 2nd layer of wall behind the chest and youll be fine
Creeper Blast = TNT and all other explosions are inferior. If they can withhold creeper and tnt they can withstand other creatures. I thought though that it had to do with the player not its environment. It would only make sense.
