Abstract: At approximately 3:15 p.m. on October 19, 1994, Employees #1 through #5 were performing maintenance and mechanical repairs in and around the alkylation and catalytic hydrodesulfurization units. At the same time, another contractor was working with the onsite employer to put an 11C-10 coalescer in service. The contractor removed the lockout/tagout devices from the coalescer's isolation points. As the machine was being started, there was a release of hydrocarbon vapors, which ignited and triggered an explosion and flash fire. Employees #1 through #5 sustained injuries, including a fractured heel, a fractured arm, a strained knee, shoulder lacerations, and a reaction to inhaling chemicals. The onsite employer was not involved with the maintenance or start-up of the coalescer.