Several years ago, we discussed this picture in terms of a Relief Design Basis, the NH3 vent header sensor placement in terms of NFPA 70 HAZLOC, and the risk of doing maintenance/calibration on the sensor when the process is live. As usual, I got some nice feedback, and the usual haters chimed in that I was off my rocker once again, stating their usual mantra… “that is industry practice and how they are all done.” Well, I just got word that the scenario I mentioned in 2017 hospitalized a contractor with serious injuries. The set up was NOT the one shown below, but darn near exactly like it: downward discharge, the sensor and control panel were just under the RV discharge, and they were both located on the roof (e.g., out of ear-shot of the machinery room alarms). The process was live, and the contractor was called in to test/calibrate the header sensor as they had just had a release via an RV, and the header alarm did not actuate. Here is the image from my 2017 post and what happened last month:
Designed with maintenance in mind, NOT! (Ammonia Refrigeration header detection)
