Recognizing a Confined Space

A confined space is defined as a place:
a) That Is partially or fully enclosed
b) That Is not both designed and constructed for continuous human
occupancy, and
c) Where atmospheric hazards may occur because of its construction,
location, or contents, or because of work that is done in it.
All three criteria have to be met before a space is defined as a confined space.

Here is more information on each of the criteria.
Partially or fully enclosed
Because air cannot move freely in and out of a partially or fully enclosed space, there is a potential for a hazardous atmosphere to be generated inside. This is especially true for spaces such as vaults, tanks, pits, trenches, or manholes.

Not designed and constructed for continuous human occupancy
Confined spaces are not designed or constructed for people to work in them on an ongoing basis. They are usually designed and constructed to store material, transport products, or enclose a process. But occasionally, some work must be done inside the space.

Atmospheric hazards
A hazardous atmosphere is one which contains any of the following:
 an accumulation of flammable, combustible, or explosive agents
 less than 19.5% or more than 23% oxygen, or
 an accumulation of atmospheric contaminants that could result In acute (short-term) health effects which pose an immediate threat to life, or o interfere with a person’s ability to escape unaided from a confined space.