In a plant that prepares meat-based products, an ammonia (NH3) leak from a refrigeration unit occurred at 7:10 pm inside an isolated airtight building with 150 m² of floor space housing the machines running the site’s transformation workshops. All security features were operating normally, and the installation had shut down automatically. The fire-fighting crew, the site’s works department head and the refrigeration firm assigned to maintain workshop equipment arrived on the scene between 7:15 and 7:20 pm. A medical team examined the onsite security guard, sickened by toxic gas emissions. Measurements recorded at the site entrance revealed a concentration of 8 ppm of NH3 in the air. The situation returned to normal around 9 pm, and the newly-repaired installation was up and running within about 1 hour. This incident would have been caused by the overheating of a cold compressor due to its obsolescence (30 years) and/or the intense summer heat, leading to a break in the motor / compressor coupling device, which was protected by a sheet metal casing. Opening of the safety valve protecting the compressor caused the release of gaseous NH3 emissions, which subsequently spread into the atmosphere by means of a discharge nozzle while the machines were shut off.