My non-HAZOP-expert experience is that PSVs or other relief devices are not considered in the HAZOP methodology. They would be listed as a HAZOP recommendation when it is determined there is a loss of mechanical integrity. Manual valves would be failed "open or left open, human error" or "closed or left closed, human error" depending on their normal position. So, yes, we consider manual valves and also human error (unless your operators are of a different species).