Safe/Kill Volumes
First, the absolutes:
Kill volumes have highest priority. If you enter an immediate kill volume (that is, not the soft kind) then you are dead. If you enter a soft kill volume, then you are "out of bounds." Being out of bounds starts your ten-second countdown for you to get back in bounds.

Safe volumes are the opposite. If at least one safe volume is on the map, then you are in trouble if you are not inside at least one of them. If any of the safe volumes are immediate, then you will die as soon as you are not inside a safe volume. If all of the safe volumes are "soft," then you are out of bounds and your timer will count down.

Typically you want to make one large soft safe volume over the playable area of your map, and then fill in trouble spots with soft kill volumes. And if you have some kind of falling-to-death area, cover that with an immediate kill volume.
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