What happened

Two contract workers opened the wrong flange on mislabeled piping, releasing more than 27,000 pounds of toxic hydrogen sulfide gas; the two contractors were killed and 13 other workers were hospitalized, while Deer Park and Pasadena issued shelter-in-place orders. The CSB found refinery operators had failed to clearly label the equipment or follow written procedures. This was an accidental industrial incident, not an attack.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.