A thumping noise emanating from an extraction unit in an essential oils plant was noticed at around 6:45 pm. The building was secured pending the arrival of the fire-fighters: the main power supply, and gas, steam, nitrogen, water and cooling networks, etc. were all shut down. Staff equipped with masks assessed the situation in the premises to check for the presence of any methanol leaks and prevent a fire. The building was then ventilated with the doors wide open. The accident occurred on an extractor, during extraction from the 1st methanol/cocoa washing operation. Excessive pressure in the 3,000 l reactor ripped off the manhole cover’s fastenings. Due to the shock wave, methanol (2,500 l) and cocoa powder were sprayed into the workshop and through the opening in its roof to form a cloud above the building. The blown-off cover hit the series of pipes and the lighting close to the equipment. The temperatures recorded in the reactor helped to determine the causes of the accident: an abnormal rise in temperature due to a technician forgetting to stop the heating of the reactor, which led to a rise in pressure of this equipment. Furthermore, the cover was ejected due to the safety relief valve failing to open and the lack of rupture disks. The operator implemented several corrective actions: verification of the extractor by the manufacturer, installation of 2 rupture disks in addition to the replacement of the safety relief valve, installation of 2 pneumatic pressure gauges with a separator to close the steam valve if the pressure threshold is exceeded, replacement of the safety relief valves for the entire workshop and an annual alternation with a second set of safety relief valves, and a change to the operating procedure with the addition of a nitrogen flushing stage.