Five workers of two employers (Wastewater Specialties, LLC and Westlake Chemical Lake Charles South) were hospitalized when a flash fire in a vessel occurred. Two employees were on an elevated platform welding a flange onto a 54-inch segment of process piping at the quench tower. Three other workers were engaged in a hydro blasting operation. Employee 1 suffered head trauma, lacerations, and burns. Employee 2 suffered a lower leg/ankle injury. The other workers sustained 2nd and 3rd degree burns to face and torso, and fractures to their arms and legs.