Fields are effects that can exist on tiles (such as fire, smoke, etc) which might affect items and creatures present there or stepping on it (including the player). All monsters able to dig are immune to fields.
All fields dissipate when their density is equal or below zero.
These fields don't have any significant gameplay effects.
These special tiles serve as sources for other fields to emit from.
These fields can inflict undesirable status conditions on players and mobs that stand in or move through them.