In a fertilizer and nitrogen products manufacturing plant, interruption of the carbon dioxide (CO2) supply forced the operator to stop the urea production unit. When emptying the unit’s gas scrubbing column, an ammonia (NH3) sensor located on the North-West boundary of the site and whose alert threshold was set at 5 ppm recorded several peaks of NH3 (up to 11 ppm). Residents bothered by the smells, alerted either the firefighters or the local air quality monitoring network. The situation was back to normal 2 hours later. According to the operator, these NH3 releases were caused by a high concentration in the scrubbing column (190 g/l a little before the site was shut down instead of 40g/l during normal operation) combined with unfavourable weather conditions. The operating procedures stipulated shutdown of the installation for NH3 concentrations above 200 g/l in the column. Furthermore, the lack of rapid information by the operator to the public services did not enable them to properly inform the complainants. In future, the operator must formalise the rules for informing the authorities in the event of incidents that are likely to adversely affect neighbouring residences and analyse the opportunity to define an intermediate NH3 concentration threshold for the scrubbing station. Based on these, special attention should be paid to the installations and actions taken for return to normal operation.