I just want to know about the backpressure from CGA vent design. Is a minimum, e.g., 10%nback pressure of the release pressure considered?

The ASME BPV Code, and other Codes by reference, require less than back pressure of 10% of device set pressure from the release flowrate for proper operation of reclosing relief devices such as relief valves. Backpressure from non-reclosing or non-ASME devices may be higher so an analysis is required. It’s not enough to assume the vent system need only be designed for 10% of the set pressure. Instantaneous backpressure can reach as high as 50% of set pressure for some PRD or TPRD applications.