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, were 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.