Often we see facilities viewing MOC and PSSR’s management systems as DUPLICATIVE efforts. There is a distinct difference between these two PSM/RMP requirements. Basically, this is how it was so explained to me by Russ Evanston, one of the founding fathers of PSM.
The MOC is a “request” to make a change and the road map to implement that change safely.
The PSSR is the actual verification that the MOC was carried out precisely as the approvers of the MOC prescribed it.
I make a change to a process where I change a process layout, including new valves, piping materials of construction, and an update to an SOP. The MOC is designed to provide a path of what needs to be reviewed/considered in the requested changes.
Once the changes have been made AND BEFORE introducing the Highly Hazardous Chemical (HHC) to the changed process, the PSSR is designed to verify that the change was implemented as prescribed by the MOC.