A 50-kg ammonia (NH3) leak occurred after a hose broke on a refrigeration installation compressor at a dairy products plant. The internal emergency plan was implemented, entailing complete shutdown of all installations, evacuation of the 4 individuals present onsite, and sounding of the siren. Fire-fighters with the Saint-Etienne chemical squad arrived at the scene around 9 am. The external emergency plan was also activated, but the population was not informed due to the small NH3 concentrations measured by the intervention team. The compressor motor had become unfastened from its base, with the resulting increase in vibrations causing a hose of oil mixed with ammonia to break. This scenario had not been anticipated in the safety report. A slight leak on the defective hose had already been observed the week before the incident; the head of maintenance had retightened the problem hose and visually inspected all other hoses. The operator scheduled a vibration study, and the Classified Facilities Inspectorate requested that a maintenance and monitoring plan for hoses and pipes be prepared.