The Hazard Evaluations and Technical Assistance Branch of NIOSH conducts field investigations of possible health hazards in the workplace. These • investigations are conducted under the authority of Section 20(a)(6) of the Occupational Safety and Health Act of 19.70, 2S U;S.C. 669(a){6) which authorizes-the Secretary of Health• and Human Services, following •a written request from any employer or authorized representative of employees, to determine whether any substance normally found in the pla~e of employment has potentially toxic effects in such concentrations .as used or found. .