Abstract: At approximately 10:40 a.m. on April 2, 2019, the housing of a three-inch Y-strainer of an isobutylene line that fed into reactor K8 ruptured and isobutylene was released, forming a vapor cloud. Three employees responded to mitigate the isobutylene vapor in the reactor area. As Employee #1 was at an old control room area and Employee #2 was approaching a tank farm area away from reactors K8 and K9, Employee #3 activated the fire water monitor located next to the hot oil area on the West side of the main control room. Shortly after 10:50 a.m., the isobutylene vapor cloud ignited, causing an explosion. Fire spread to a dry storage area. Employee #1 suffered injuries that affected his upper extremity and brachial artery on his right side, killing him. Employees #2 and #3 sustained thermal burns, which they were hospitalized and received treatment.