Cal/OSHA General industry 5157(b), and Cal/OSHA Construction 1951 Definition: Permit-required confined space or permit space means a confined space that has one or more of the following characteristics:

  1. Contains or has a potential to contain a hazardous atmosphere
  2. Contains a material that has the potential for engulfing an entrant;
  3. Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor which slopes downward and tapers to a smaller cross-section, or
  4. Contains any other recognized serious safety or health hazard.