I was recently involved with an organization that had an issue with overpressuring a 330-gallon plastic tote during their evacuation of their HHC/EHS for process work. So we had a nice discussion about the DIFFERENCE between “draining” and “venting”. The chemical in question is normally a “gas” but is stored as a liquid under pressure. It has a very low boiling point and a very high expansion ratio. The supervisor’s instruction was to “drain system to the tote with XX gallons of water.” This is a practice they learned in my advanced process safety course. But my training makes it very clear the difference between draining a liquid and venting a gas. The operator did as he read the instructions, draining the liquid into a tote with hot (ambient-heated) water, and the result was a failed tote. Luckily, no one was injured, but it was pure luck. Members can read my accident report regarding this very same event that resulted in a truck driver passing away.
So I use this image in my Complex LOTO Training and Advanced Process Safety training to demonstrate what it means to VENT a gas and DRAIN a liquid: