Final answer:
The National Institute for Occupational Safety and Health (NIOSH) researches toxicity levels and human tolerance levels of hazardous substances to protect workers' health and safety.
Step-by-step explanation:
The purpose of the National Institute for Occupational Safety and Health (NIOSH) is to conduct research on the toxicity levels and human tolerance levels of hazardous substances in order to protect workers' health and safety. NIOSH plays a crucial role in identifying and studying the health effects associated with exposure to toxic chemicals in workplace and environmental settings. By researching and establishing safety standards and guidelines, NIOSH aims to prevent and ameliorate the adverse effects of chemical, physical, or biological agents on living organisms.