During maintenance operations on a freezer in an ice cream factory, a leak of refrigeration ammonia (NH3) in liquid phase occurred after 9:15 pm and lasted for 20 to 25 minutes after 4 screws were loosened to access the internal parts of a solenoid valve. The 2 technicians put on their protective masks, shouted for the staff to evacuate the building and then closed the shut-off valve on the main liquid NH3 manifold. However, reinstalling and retightening the screws on the solenoid valve did not reduce the leak. The fire-fighters set up a safety perimeter. Following a meeting upon the arrival of the workshop manager, one of the technicians succeeded in closing the shut-off valve by a further half turn using the leverage of a larger wrench; a cracking noise during this operation suggested that there was a foreign body in this shut-off valve. Shortly afterwards, the leak on the solenoid valve slowed down and then disappeared; the sealing elements and the actual solenoid valve were then reassembled. The work was finished at 10 pm. This incident led to the loss of €130,000 worth of products. Following this event, several measures are being considered: NH3 detection device with audible and visual alarm combined with an automatic quick-closing valve and a filter between the main manifold and the “users”, installation of new emergency stop buttons for the compressor in the production area, new production staff training on the risks posed by NH3, revision of the work instructions/procedures, updating of the emergency plan in agreement with the fire-fighters, and inspection of the emergency exits and plans displayed, etc.