Tanks collapse prevention

In another tank collapse incident, a tank containing a solution of ammonia and water was being emptied and cleaned. After employees emptied the tank of liquid ammonia, they added water to rinse the vessel. While the water was being added the sides of the tank were sucked in. The ammonia vapor remaining in the tank dissolved in the water so rapidly that air could not enter through the vent to prevent the collapse. [8]... 

Every low-pressure, closed-top tank with an overflow line should be equipped with some type of device to prevent collapse from an overfilling operation. A large open nozzle, a high-level alarm and/or shutdown system, vacuum breakers or separate vent lines are some appropriate safeguards. 

Calculations were made. Engineers figured that a vent of about 30 inches (76 cm) in diameter would have prevented the destructive vacuum from collapsing the tank during the ammonia absorption incident. A giant-sized vent was impractical for this installation, hence they concluded that water should be added slowly through a restrictive orifice. [8]... 

Vacuum Failures Pressure reduction in a container can damage it. For example, a tank can collapse while being drained if there is nothing to replace the removed contents. Even if there is venting, the vent line must provide adequate flow rates to prevent formation of a vacuum. 

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