It's basic science, don't throw water/ice into/on hot things. This is because steam is created faster than it can escape, causing pressure and things to explode.
There's a few videos where people tried to fry food on rocks, moisture trapped in rocks either cracked the rock or made an explosion. This works the other way around if you pour or place things cold quickly on the rock.
Anyway, it was explained the barrier will stop humans out but keep spirits in, obvious now he is a some sort of great spirit since he can be seen by humans and can see chibis spirits.
Zero probably will get stuck there or find a way to dispell the barrier.