If I were to do 20 PSM/RMP audits per year with new clients, I estimate that I would have the following debate 15 times! In my Process Safety courses, I have a little fun with the phrase “Upwards and Unobstructed” as I make the class stand and repeat that phrase three times. But somehow/somewhere, this basic design characteristic got lost in many Pressure Relief System design basis.
I will cite either ASME Section VIII or ASME B31.3, Chapter II Design which states:
(emphasis by me)