The vessel you are viewing is part of a PSM Covered process. I have blacked out pipe and vessel labeling, as it does not matter what the HHC/EHS is or the type of process. Pay close attention to the sight glass column in the center of the picture. The process vessel shown has a safe upper level of 80%. Exceed the safe upper level and liquid is sent to a compressor, which will result in a catastrophic failure of the compressor and a catastrophic release of the HHC. So why is ISA-84 needed?