Overview:
Operations was in the process of depressuring a cooler that had a suspected leak. The operator was using a steam hose to thaw some ice that had accumulated in an elbow. This steam also cleared a blockage in the upstream isolation valve, allowing for an uncontrolled release of H2S. One operator was in the immediate area and was able to egress safely.
Prior to the event, operations had tightened the drain valve, which appeared closed, followed by the removal of the drain plug off the elbow. The lower elbow had visual ice accumulation. In order to depressurize the cooler, operations required a length of hose to tie the line into flare. Due to the ice in the elbow, the decision was made to steam the elbow to clear the ice. When the operator added steam to the elbow, the line heated up, inevitably allowing for the blockage in the valve to free. The valve then allowed sour product at up to 6,200 kPa of 1.5% H2S to be released to atmosphere.