NOVELTY - The high pressure electrochemical system comprises a cell block (2) that consists of electrochemical cells (3), in each of which an anode side (4) and a cathode side (5) are separated from each other by a membrane (6). The electrochemical cells are layered between a cell block beginning and a cell block end. An acoustic wave or vibration that moves through the cell block is detected at the cell block beginning and at the cell block end by a sensor. Signals of the sensors are transmitted to an analyzing unit, and an origin of the acoustic wave or vibration is located within the cell block.    USE - The high pressure electrochemical system is useful as an electrolysis plant and a fuel cell plant.    ADVANTAGE - The high pressure electrochemical system is simple and economic to maintain/repair and safe to operate by detecting and locating a defective membrane in the system.    DETAILED DESCRIPTION - The high pressure electrochemical system comprises a cell block (2) that consists of electrochemical cells (3), in each of which an anode side (4) and a cathode side (5) are separated from each other by a membrane (6). The electrochemical cells are layered between a cell block beginning and a cell block end. An acoustic wave or vibration that moves through the cell block is detected at the cell block beginning and at the cell block end by a sensor. Signals of the sensors are transmitted to an analyzing unit, and an origin of the acoustic wave or vibration is located within the cell block using a difference in the points in time when the impact of the acoustic wave or vibration is detected by sensors. The membrane is designed as a polymer electrolyte membrane. The electrochemical plant has a pressure of more than 10 bar. The electrochemical system further comprises an output unit for outputting a warning signal and/or the origin of the acoustic wave and/or optical shock. The sensor measures an amplitude of the acoustic wave and/or shock, outputs a distress optical- and/or acoustic signal when the amplitude exceeds a threshold value and/or releases an emergency shut-down of a part of the electrochemical system. An INDEPENDENT CLAIM is included for a method for monitoring an electrochemical system.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of an electrochemical system.    Cell block (2)    Electrochemical cells (3)    Anode side (4)    Cathode side (5)    Membrane. (6)