Details

Parent Category: Safety Info Posts

Category: Chemical Process Safety (PSM/RMP)

Published: 26 June 2017

In April, 2011, an ammonia leak at a large warehouse where anhydrous ammonia is used in the refrigeration system in a cold storage building. In this incident, one worker was burned on the arm from the escaping gaseous ammonia.  An estimated 3600 pounds of ammonia evaporated into the air during this incident. As part of the planned mechanical integrity schedule, two employees were changing out the two pressure relief valves (abbreviated PRVs) that protected this ammonia compressor package. These PRVs prevent buildup of excessively high ammonia pressures which could burst piping, vessels or ammonia compressors. Ammonia inside the refrigeration system normally may have pressures as much as 10 times that of outside air. These PRVs are connected to piping painted orange which directs ammonia gas to a safe relief location on the building’s roof. During the leak, the corrosive ammonia peeled away the red floor paint.  A 3-way valve separates the two PRVs. A 3-way valve allows isolation of one PRV for replacement while the second PRV continues to protect the refrigeration system from high ammonia pressures. By turning the 3-way valve stem completely clockwise, the PRV on the left is isolated and can be safely replaced. Having not received adequate training from their employer, the two employees attempted to, but ultimately did not isolate the left PRV. High pressure ammonia released violently into their breathing zones as they attempted to separate the PRV from the 3-way valve.

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