A term used in Occupational Safety and Health Administration (OSHA) safety regulations to define an area which workers may be required to enter but which, because of its size, shape, or location, can present safety hazards. The inside of a gasoline storage tank, for example, is designated as a “confined space.”

Certain containment sumps may also meet the definition of a confined space. Safety regulations may require that workers who enter such a space be equipped with safety lines, breathing devices, etc.