The power of a vacuum (Flammable Liquid Storage Tanks)

ATM storage tank collapsed

ATM storage tank collapsed

I see far more damage to atmospheric storage tanks from vacuums than I do from over-pressure events.  In almost every case, the tank had undergone a “change” that created the conditions for a vacuum to occur.  And once we have a pressure differential with a lower pressure inside the tank than the atmospheric outside the tank, the atmosphere will simply collapse the tank. 

The tank is NOT being “sucked in”; it is being crushed from the 14.7 pounds per square inch of atmospheric pressure.

Now, we need to take measures to ensure we do not CREATE this pressure differential inside the tank.  This differential can be caused by a number of processing/design errors, with the most common being “vent too small.”

But we are in luck; a 50-year-old OSHA standard offers us some basic design requirements.  The trick is MANAGING CHANGES to these tanks when they are OUTSIDE of the PSM standard!

Here is what OSHA says about vent sizing for NORMAL and EMERGENCY operations.

(emphasis by me)

 

 

 

 

 

 

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