Abstract: At 12:00 a.m. on March 26, 2021, Employee #2, a supervisor, and Employee #3, a system technician, of 3V Sigma USA Inc. began running batch processes in reactors R-402, R-403 and R-406 of the Gamma chemical plant. During the initiation of the free-radical polymerization reaction, the Gamma control room received successive alarms on pump PT-4009 for low chilled water header pressure. Employees #2 and #3 began troubleshooting in an attempt to cool the reactors. Employee #2 called Employee #1 for assistance. Employee #1 arrived onsite and began helping Employees #2 and #3 troubleshoot. The employees were unsuccessful in stopping the exothermic reaction. Due to high temperature and pressure inside the reactors, methylene chloride vapors escaped through a broken sight glass on R-404 and unsecured hatches on mixing vessels VA-406 and VA-407. Employees #2 and #3 left the Gamma control room due to strong vapors of methylene chloride. They witnessed Employee #1 inside the Gamma plant unresponsive and attempted to retrieve him. Employee #1 was exposed to an IDLH atmosphere of methylene chloride and died of anoxic brain injury, cardiopulmonary arrest, and asphyxiation.