Ammonia Release | Relief Valve Set Pressure

Summary

In February 2024, the installation of a relief valve with the wrong set pressure resulted in the release of a small quantity of ammonia. Release calculations were not performed since the estimated release amount was below 100 lbs of ammonia. 

Incident Description

Contractors were in the process of replacing relief valves throughout the system when the wrong relief valve was installed on a high pressure receiver. The high pressure receiver was equipped with a dual relief valve assembly with a corresponding three-way valve. The typical operating pressure in the high pressure receiver can range between 120-200 psig, so the relief valve set pressures are typically 250 or 300 psig. 

The contractor accidentally installed a relief valve with a set pressure of 150 psig on the high pressure receiver. After installing the incorrect relief valve, the three-way valve was manipulated to isolate the other port so that the second valve could be replaced. The 150 psig relief valve lifted immediately due to the pressure inside the vessel exceeding the set pressure of the relief valve. The contractor was able to quickly respond by using the three-way valve to isolate the 150 psig relief valve and stop the release. 

Significance

Human error is a topic of great importance when attempting to prevent ammonia releases. Even minor mistakes can result in an ammonia release. This incident serves as a reminder of the importance of paying attention to detail, and thinking clearly while working on ammonia refrigeration systems. Operators or contractors that are overworked or sleep-deprived may unintentionally cause a dangerous situation. Facilities should heavily consider this factor when assessing the need for hiring additional maintenance/refrigeration personnel.