For 20 years now, when teaching any of my process safety courses I make the student repeat this three times: UPWARDS and UNOBSTRUCTED, UPWARDS and UNOBSTRUCTED, UPWARDS and UNOBSTRUCTED. We do this when we get to the Relief System design basis. The vents to the atmosphere almost will always be required to be UPWARDS and UNOBSTRUCTED based on just about any RAGAGEP for hazardous materials. You would think this would be a simple requirement and that an engineer would have the ability to defeat rainwater! But time and time again, we find rain water scares the heck out of most engineers who are tasked with designing the PRD vent to the atmosphere. Here is what the Compressed Gas Association (CGA) requires in their vent design…
Upwards and unobstructed, two simple words that cause way too much debate!
