Abstract: Employees #1 through #6 were engaged in maintenance work at a refinery, near the #2 HDS/Reformer unit hydrotreater #16, a unit that fractionated, hydrotreated, and reformed raw naphtha. The unit was being run in normal operations mode. The 16-D-2 prefractionator overhead receiver was a used, 6 ft by 10 ft horizontal pressure vessel, first fabricated in 1976 with no code plate and then returned to a different service at the refinery in 1989. The vessel was operating at 110 psig and 118 degrees F when it split open catastrophically along a thinned top section and dumped its contents of sour naphtha, liquefied petroleum gas, and other light hydrocarbons from an elevated platform down into the unit. Employees #1 through #6, some employed by the refinery and some by a contractor, observed the vessel failure and product release, which they took to be steam. A few seconds later, the released hydrocarbons ignited explosively. The ensuing fireball was taller than the unit's process columns and stretched out into adjacent units. Employees #1 thru #6 fled from three different points and suffered burns ranging in severity from minor to critical. Employee #7 was painting in the area and sustained injuries as he scrambled to escape to an adjacent storage tank farm. Subsequent investigation revealed numerous serious violations of the employer's process safety management procedures and practices, its emergency response program (i.e., communication and containment), and personal protective equipment program. The mechanical integrity inspection, documentation, and repair practices for this recycled pressure vessel were found seriously lacking over its operating lifetime.