According to the Occupational Safety and Health Administration (OSHA), confined spaces are defined as spaces that are not designed for continuous human occupancy, have limited means of entry and exit, and are large enough for a person to enter and perform work. Confined spaces can be hazardous due to the presence of dangerous gases, liquids, or solids, or due to the lack of oxygen.
Confined spaces can be divided into two categories: non-permit-required confined spaces and permit-required confined spaces. Non-permit-required confined spaces do not contain any hazards that could cause death or serious injury, while permit-required confined spaces contain one or more hazards that could cause death or serious injury.