In a chemical plant manufacturing base products for the cosmetics industry, excessive pressure in a synthesis reactor of a colouration support (ionene) resulted in a release of steam and 10 kg of 1.3-tetramethylpropylenediamine via a damaged joint. The installation was switched over to safety mode and the reaction mixture, consisting of water, ionene and around 7% of residual raw materials (1.3-tetramethylpropylene and 1.6-dichlorohexane) was emergency cooled. No other consequences were noted. Deregulation then shutdown of the agitator fitted to the reactor caused the accident. The absence of mixing caused a temperature increase in the reactor, which usually operated at 115 °C under 5 bar, and an increase in pressure. The leak occurred on a damage joint, and vaporisation of the water in the reactor transported a portion of the reaction mixture. The reactor’s protective pressure relief valve, calibrated at 5.5 bar, had not been activated. Following the accident, the following improvements were made to the installation: installation of a horn type alarm system connected to the mixing operation, mechanical limitation of the mixing speed, and replacement of the faulty joint with a solid buffer with a resistance of 16 bar.