ExxonMobil’s Baytown complex, which produces a variety of refinery and chemical products, sits on hundreds of acres about 25 miles east of downtown Houston. The complex contains 27 distinct units, including the hydro-desulfurization unit (HDU), which mixes hydrogen, sulfur, and naphtha. Early on the morning of December 23, 2021, three contractors were in the HDU swapping flange bolts when the pipe holding the flange ruptured. The release of hydrocarbons caused an explosion, which injured the contractors, and a fire, which burned for nearly eight hours. Three ExxonMobil process technicians responded to the fire.