It is going to feel like the universe is caving in on you if one of your fermenters ever collapses from vacuum failure. That is why it is important to understand all the scenarios leading to vacuum failure and how to prevent them.
One common scenario is right after fermentation, when your fermenter is filled with carbon dioxide. If you use caustic soda to clean your fermenter and do not have adequate vacuum relief, you run the risk of imploding your tank.
Ashton Lewis, Master Brewer-in-Residence for Paul Mueller Company, demonstrates just how quickly vacuum failure can happen when you clean a fermenter full of carbon dioxide with caustic soda.