There are two (2) classifications of Confined Spaces
1) Permit-Required Confined Space - spaces that may contain or has potential to contain hazardous atmosphere or contains a material that has the potential of engulfing an entrant, also the internal configuration such that an entrant could become trapped or asphyxiated by inwardly converging walls or by a floor which slopes downward and tapers to a smaller cross-section.
2) Non-Permit Confined Space - spaces that do not contain, or with respect to atmospheric hazards, do not have the potential to contain any hazards capable of causing death or serious physical damage.