Abstract: At 9:25 a.m. on January 23, 2019, eight employees were preparing the Alkyl Second Stage Acid Settler Level Column for maintenance. They depressurized the level column and hooked-up one end of a Durco stainless steel flexible hose to the Mag Tech Level Column and the other end to the flare (M-H Acid Circulation Pump Flare Connection). Three employees were adding blinds to the flange as well as removing old bolts, inserting new bolts, and tightening them onto a flange when they smelled a very strong ammonia-like odor that took their breath away. The employees started to cough and they felt a burning in their throat and lungs. Five of the eight employees were hospitalized for exposure to hydrofluoric acid.