Ammonia release from “empty” compressor causes injury
16th January 2026
USA: A serious injury to an employee of a meat processor was caused by an ammonia release from an isolated compressor, which was thought to be empty.
The incident in 2023 at Tyson Fresh Meats’ facility in Perry, Iowa, occurred while a company employee was disconnecting the outlet piping from the compressor, according to a report by the US Chemical Safety and Hazard Investigation Board (CSB).
The out-of-service ammonia compressor, used in Tyson’s refrigeration system, had been previously isolated from the system, and the ammonia was understood to have been removed entirely.
When removing the bolts on the flange connecting the outlet piping to the compressor, a burst of approximately 1lb (0.45kg) of ammonia vapour was released directly into the employee’s chest and face.
According to the report, the employee was not wearing respiratory protection because the ammonia compressor was understood to be empty.
Tyson’s investigation found that the company’s ammonia removal procedure allowed some ammonia to remain trapped between the compressor’s discharge check valve and an isolation valve. Another valve needed to be opened to remove ammonia from the isolated piping. Tyson determined that this valve had remained closed because the procedure did not include this valve.
Based on Tyson’s investigation, the CSB determined that the probable cause of the anhydrous ammonia release was disconnecting the outlet piping from the ammonia compressor while some ammonia remained within the equipment. Tyson’s ammonia removal procedure contributed to the incident because following it did not effectively remove the ammonia from the compressor.
