Abstract: On November 3, 1991, I.S.T. Mechanical was removing a blind from a 10 in. flange on the line from the depropanizer overhead condensers (8-E-35 A/B) to the depropanizer overhead receiver (8-C-13) under fresh air. The flange was parted and some vapors escaped. The flange was closed and the decision was made to connect a water hose to a 3/4 in. bleeder valve located upstream from the flange and put a water seal in the piping between the flange and the receiver. Employees were setting the gasket when the water seal was lost and a hydrocarbon cloud was released. Paramedics and emergency crews of Mobil Oil Corp. responded to the accident and treated I.S.T. employees. Employees #1 through #3 were brought to Little Company of Mary in Torrance, CA, and treated for chemical burns of the feet and inhalation of vapors.