Abstract: On November 3, 1991, Employee #1 was overseeing IST employees who were changing the bundles of drums on the downward flow of light n-hydrocarbons from the Deprop tower to the Reflux drum. For preventive measures, IST employees placed isolation blinds above and below the drum. In addition, the system was shut down, purged with nitrogen, and drained. Once the bundles in the drums were replaced, IST employees began to remove the blinds. Working under fresh air (required by Mobil Oil Refinery), they removed the bottom blind. As they removed the upper blind, vapors, which were being released through the flange and were being suppressed by water, dramatically increased. As Employee #1 stepped forward to tell IST employees to close the flange, he stepped into a cloud of butane gas, approximately 15 feet in diameter. He was immediately overcome, blacked out, and fell to the ground, striking his head on a bleeder valve. An emergency crew arrived on scene and performed first aid. Employee #1 was brought to Little Co. of Mary, in Torrance, CA, and was treated for chemical burns and abrasions of the buttocks, shoulder, and lower extremities.