Abstract: At approximately 12:20 a.m. on February 5, 1990, two pipefitters at a Weyerhaeuser facility were removing lines from a liquid chlorine storage tank. A discharge valve had apparently been left open, resulting in a back flow of chlorine and the release of chlorine gas at the point where the pipefitters had removed a section of line. The two workers quickly left the area without harm and notified Employee #2, an operator in the control room. Employees #1 and #3 were working in adjacent areas on liquefaction systems when they were dosed with chlorine gas. They stumbled into the office for help and were given medical care at the facility before being taken to a local hospital. Employee #2, the control room operator, donned a self-contained breathing apparatus (SCBA) and entered the gas release area. He was overcome by chlorine gas because his facepiece hose was improperly connected to the regulator. He was also hospitalized.