Abstract: At approximately 2:00 p.m. on February 2, 1995, Employee #1, a pipe inspector for Purity Systems, was working in Building R of Quad l at Lam Research. On the second floor of the building, machines are tested before they are sent to semiconductor manufacturers. Gases are used in the semiconductor fabrication process and the gas supply pipes come from the sub-fab on the first floor of Building R. At the time of the accident, some of these pipes were in use and others were being installed. Employee #1 was alone in the sub-fab testing an inactive pipe when he smelled chlorine gas and immediately left the building. Approximately 20 minutes later, he felt a burning sensation in his throat. He was sent to Valley Medical Center, San Jose, CA, examined, and released the same day.