At a chemical plant, a broken joint on a 70-m³ reactor in a pentafluorobutane production unit caused the atmospheric discharge of 71 kg of hydrogen chloride (HCl), 41 kg of hydrogen fluoride (HF) and 108 kg of pentafluorobutane. The leak was detected by the unit’s HF sensors, and the alarm was sounded. The unit was evacuated and the reactor automatically drained into an emergency tank designed for this purpose. Fire-fighters wearing diving suits isolated the reactor from the safety tank in order to degas it adjacent to a washer (Pinitial = 11 bar). A water curtain was activated in order to dissipate the gas cloud. One hour later, pressure inside the reactor had been lowered to 0.7 bar. A suction sleeve was installed around the leak to treat these latest releases. Measurements recorded at the property boundary, with wind exposure, indicated an airborne HF concentration less than the device detection threshold (1.5 ppm). Moreover, atmospheric dispersion simulations showed that discharged pollutant concentrations never reached occupational exposure limits at either floor level or shoulder height. The accident was caused by deterioration of a joint located between a reserve tap on the reactor dome and its full buffer tank, which had not been adapted to the fluid contained in the reactor. The temporary full buffer joint fastened onto the reserve dip tube used during reactor testing had not been replaced by a definitive joint, as opposed to the other layouts. In addition, these works had not been scientifically accepted since the procedure did not apply to reserve taps or temperature taps. A post-accident assessment of the installation highlighted 2 non-compliant joints, which were subsequently replaced. To reduce the number of joints, both temporary reactor dip tubes were eliminated. The acceptance procedure for devices and pipes was supplemented by compiling an exhaustive list of circuit and device control points containing high-risk fluids.