On April 15, 2014, Employee #1, a maintenance technician employed by Solarworld Industries America Inc., and Coworker #1, a tool operator in the plant’s fabrication area, was working at the employer’s solar cell manufacturing facility. Coworker #1 had submitted a work order to repair a leak of liquid hydrofluoric acid (HF). HF is used in the manufacture of solar cells in a process similar to that for making semiconductor wafers. The acid runs through double-contained plastic pipes that travel through a maintenance tunnel under the production floor, referred to as the Sub-Fab. There are low point drain boxes (liquid traps) at various points in the system to enclose valves. These drain boxes have sensors connected to alarms. A leak sensor on one of the low point drain boxes (#3CVB-310-2-6) in the Sub-Fab alerted Coworker #1 to a leak in the HF piping system. Coworker #1 tracked the leak and submitted a work order for the needed repair. Employee #1 arrived to perform the repair. Coworker #1 led Employee #1 to the leaking drain box and then moved out of the way. Employee #1 attempted to tighten the fittings on the valves within the drain box. He determined that the threads were stripped on one of the fittings.