CEP: Process Safety Beacon - Double Block and Bleed


The December 2011 Beacon described an incident where a missing plug on a vent line resulted in a flammable material leak that caught fire, causing a fatality. That incident reminded us of the importance of caps and plugs on process vent lines and drains. However, sometimes vents or drains should not be capped or plugged. Some (but not all) uses of a “double block and bleed” isolation system may be examples. For example, the vent on a double block and bleed used to stop material flow by a safety shutdown system most likely needs to be open when the plant is in operation. But, be careful – sometimes the bleed from a double block and bleed needs to be capped or plugged. This is often the case for a double block and bleed used only to isolate equipment for maintenance. Understand your application and how to operate it correctly.

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