A confined space is any area that is not intended for human occupancy and that also has the potential for containing a dangerous atmosphere. A confined space:
- Is large enough for a worker to enter and perform assigned work;
- Has limited entries and exits;
- May contain a hazardous atmosphere, arising from chemicals, sludge or sewage;
- Is constructed so that anyone who enters could be asphyxiated or trapped by walls or floor that converge to a small cross-section, such as a hopper;
- Contains a material, such as sawdust or grain, that could engulf anyone who enters.
Examples of a confined space include a tank, vessel, vat, silo, bin and vault.
Others which are less obvious can be equally dangerous like open- top tanks and vats (particularly where heavier than air gases or vapours may be present), closed and unventilated rooms, or furnaces and ovens in which dangerous accumulation of gases can build up because of restricted air circulation even though the door is left open.