Ammonia Release | Brass Plug

Summary

In July 2020, the installation of a brass plug in an ammonia refrigeration system resulted in a release of approximately 100-300 lbs of ammonia. Due to the corrosive nature of ammonia on brass, the plug developed a leak due to corrosion.

Incident Description

A brass plug was installed on a CUNO oil filter several years prior. Over time, the ammonia ate away at the brass until the plug failed, releasing an ammonia/oil mixture. An anonymous person called 911 to report the smell of ammonia. 

Release Calculation

The release generated a concentration of 20 ppm at a nearby mini mart which was located approximately 580 ft from the leak. The weather conditions at the time of the release were input into the modeling software ALOHA:

• Wind Speed: 7 mph
• Cloud Cover: 30%
• Ambient Temperature: 99℉
• Relative Humidity: 18%
• Wind Direction: Directly towards the mini mart

Using the software, it was determined that an ammonia release rate of 0.935 lbs/min would result in an ammonia concentration of 20 ppm at the mini mart. The ammonia release lasted approximately 307 minutes, and the amount released is calculated below.

Ammonia Released (lb) = 0.935 lbs/min 307 min = 287.045 lbs 290 lbs

The incident investigation report notes the following regarding the release calculation:

“The release calculation is a conservatively high estimate with standard assumptions in order to obtain a constant release rate and therefore is not to be construed as exact. Both the nature of the oil/ammonia release and the cycling of the compressor make it impossible to know how much was released.”

Significance

Brass, copper, and galvanized steel will corrode in the presence of ammonia as demonstrated by this event. Operators and contractors should take care to ensure that only compatible materials are used in ammonia systems. The inspection checklist in ANSI/IIAR 6-2019 Appendix B can be a helpful reminder to inspect materials used in the system and ensure their compatibility.