Ammonia Release | Evaporator Arc Flash

Summary

In June 2023, the vibration of an evaporator over a long period of time allowed exposed electrical wiring to cause an arc flash that ruptured a distribution tube. This resulted in two (2) injuries and a release of approximately 11 lbs of ammonia. 

Incident Description

The direct-expansion evaporator was equipped with an electric heater defrost pad. The associated electrical wiring insulator wore through due to the vibration of the evaporator over a long period of time. The exposed electrical wiring came into contact with the TX valve distribution tubes, causing an arc flash that ruptured a distribution tube.

 

Release Calculation

The release calculation for this release was relatively simple thanks to the circulator shape of the hole. Based on a hole diameter of 0.029 inches, an ammonia temperature of 17℉, and the length of the release being approximately 407 minutes, the total amount of ammonia released was calculated to be 11 lbs.

Significance

Maintenance and upkeep on electrical components might often be overlooked at a facility. Ensuring that wire insulators are in good condition can prevent an arc flash as seen here, and corrosion/deterioration of the exposed wire.

Additionally, the General System Checklist in Appendix B of ANSI/IIAR 6-2019 includes the following inspection item regarding electrical components: “Covers are securely fastened on all electrical panels and junction boxes?” Facilities should ensure that electrical components associated with, or near ammonia refrigeration equipment are in good condition and still properly installed.