Broadly speaking, a confined space is an area that is large enough for a worker to enter and do work, but that is difficult to get in and out of easily, and not designed or intended for regular occupancy. Examples of potential work spaces that fit this definition include: storage tanks, silos, reaction vessels, enclosed drains, manholes, ship holds, sewers, mines, and many utility or furnace rooms with facility operating systems. While all of these examples can be considered a confined space that professionals often work in, not all confined spaces are the same.
OSHA classifies a confined space in one of two categories: permit required or non-permit required confined spaces.