Minecraft wiki entry for Nether_survival, associated text: As mentioned earlier, ghasts shoot deadly fireballs at you when you're in their sight of 100 blocks, so stay alert for incoming fire any time you're in the open, or exposed to open space. Their noises, which sound like crying babies, can give some warning, but their fireballs travel even farther than their sounds, in fact the fireballs travel for one minute before despawning (or until the ghast is dead)., so this isn't a reliable warning. Cobblestone resists the fireballs, which is why you should bring a lot.