A confined space has limited or restricted means for entry or exit, and it is not designed for continuous occupancy. These spaces include, but are not limited to underground vaults, tanks, storage bins, manholes, pits, silos, process vessels, and pipelines.
OSHA uses the term "permit-required confined space" to describe a confined space that has one or more of the following characteristics:
contains or has the potential to contain a hazardous atmosphere
contains a material that has the potential to engulf an entrant
has walls that converge inward or floors that slope downward and taper into a smaller area which could trap or asphyxiate an entrant
or contains any other recognized safety or health hazard, such as unguarded machinery, exposed live wires, or heat stress