The OSH Act which created OSHA also created the National Institute for Occupational Safety and Health (NIOSH) as a research agency focusing on occupational health and safety. NIOSH is not a part of the U.S. Department of Labor.
OSHA federal regulations cover most private sector workplaces. The OSH Act permits states to develop approved plans as long as they cover public sector employees and they provide protection equivalent to that provided under Federal OSHA regulations. In return, a portion of the cost of the approved state program is paid by the federal government.