The National Institute for Occupational Safety and Health (NIOSH) estimates that millions of workers may be exposed to hazards in confined spaces each year. The Institute’s investigations of confined space injuries and fatalities indicate that workers usually do not recognize that they are working in a confined space and that they may encounter unforeseen hazards. Testing and monitoring of the atmosphere is not performed, and rescue procedures are seldom planned. NIOSH’s definition of a confined space is “a space which by design has limited openings for entry and exit; unfavorable natural ventilation which could contain or produce dangerous air contaminants, and which is not intended for continuous employee occupancy.”