Abstract: On December 8, 1997 a leak developed in a hydrofluoric acid check valve, spilling approximately 25-35 gallons of 70 percent hydrofluoric acid in the basement of the Zenith Electronics-Rauland Plant in Melrose Park, IL. A number of employees working in the basement area were exposed to acid vapors to the extent that an emergency evacuation was initiated at the plant. The plant critical processes and pipes were shut down shortly after the evacuation. Employees #1, #2, and #3 were hospitalized after receiving doses of inhalation high enough to require hospitalization. Two employees were kept 24 hours for observation and then released. One employee was kept for 43 hours and then released. Employees #1, #2, and #3 were interviewed after coming back to work at Zenith. All were doing fine. The plant was closed down for three days and a subcontractor, Clean Harbor, was contracted to clean up the initial spill. Zenith maintenance personnel changed the defective valve. The activity of the contracted spill response team on site was observed from outside the regulated area the day after the incident. It appeared to the CSHO, after questioning the on-scene incident commander of Clean Harbor, the clean-up activities, PPE, and methodologies, that these were executed following federal regulations and using good judgment. The CSHO did not initiate an inspection of Clean Harbor.