In a Chlorine plant one of the most important safety systems is the Chlorine Destruction Unit. In case of any problem in the process, this unit ensures the safe destruction of chlorine present in the system, avoiding its release into the atmosphere.
This unit is normally constantly kept at a slight under-pressure, thus making sure that chlorine is naturally pulled into the destruction unit, making it a fail-safe system.
During maintenance activities, the panel operator noticed that the under-pressure of the destruction unit reduced, from -20 to -10. If this trend would continue, the system would end up at 0 or over-pressurized, rendering it ineffective. There were people out in the plant doing various activities, and they would also be at risk. The chief operator did not know what caused this problem, but immediately gave the crew instructions to reverse all the actions taken over the past few hours, and to restore the system back to the previously known stable point.
It turned out this was the correct action. It also turned out that the pressure problem was a result of an as-yet unidentified design flaw in the system.
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