Another video that shows how people neglect procedures in place because they seem to be burdensome but end up causing massive damage, and in this case death. The story also highlights how “tribal” knowledge can end up not being captured. I feel when the changes were made no one thought they would need to explain how the system now works – and they would never recommend opening the heat exhanger without having the vent engaged, but, like many times, that information got lost in translation to paperwork.
I think something like having a lockout tag on the 2nd valve would of been noticed if someone did a thorough MOC but, as stated in the video, some questions were left blank.
The link to the CSB report here.