A method of determining whether the operational mode of a beverage dispensing system is accomplished or not accomplished, the beverage dispensing system comprising: a sealable pressure chamber to be shifted between a first open position and a second closed position, a collapsible keg to be received within the sealable pressure chamber, a tapping line, at least during use connected to said collapsible keg, a fluid pressure source connected to the pressure chamber for pressurising the pressure chamber, a first detector having a pressure input for receiving fluid pressure from said fluid pressure source and a control pressure output, detecting whether said sealable pressure chamber is in said first open position or in said second closed position and, provided said sealable pressure chamber is in said second closed position, supplying a control pressure from said control pressure output, and a second detector having a pressure input for receiving fluid pressure from said fluid pressure source and a control pressure output, detecting whether or not said collapsible keg is positioned in said sealable pressure chamber and, provided said keg is positioned in said sealable pressure chamber, supplying a control pressure from said second detector control pressure output, the method comprising evaluating as a logical AND said control pressures from said control pressure outputs of said first and second detectors (120, 122) and determining said operational mode of said beverage dispensing system being not accomplished if none or only one of the first and second detectors (120, 122) supplies the control pressure from its control pressure output and said operational mode only to be accomplished provided both control pressures are supplied from said control pressure outputs of said first and second detectors (120, 122), said first and second detectors (120, 122) being connected in a series configuration or alternatively being connected to a AND pressure valve, said method comprise the additional step of generating an enabling pressure, provided said operational mode is accomplished, said enabling pressure being used for pressurizing the pressure chamber, thereby creating a fail-safe safety system. a sealable pressure chamber to be shifted between a first open position and a second closed position, a collapsible keg to be received within the sealable pressure chamber, a tapping line, at least during use connected to said collapsible keg, a fluid pressure source connected to the pressure chamber for pressurising the pressure chamber, a first detector having a pressure input for receiving fluid pressure from said fluid pressure source and a control pressure output, detecting whether said sealable pressure chamber is in said first open position or in said second closed position and, provided said sealable pressure chamber is in said second closed position, supplying a control pressure from said control pressure output, and a second detector having a pressure input for receiving fluid pressure from said fluid pressure source and a control pressure output, detecting whether or not said collapsible keg is positioned in said sealable pressure chamber and, provided said keg is positioned in said sealable pressure chamber, supplying a control pressure from said second detector control pressure output, the method comprising evaluating as a logical AND said control pressures from said control pressure outputs of said first and second detectors (120, 122) and determining said operational mode of said beverage dispensing system being not accomplished if none or only one of the first and second detectors (120, 122) supplies the control pressure from its control pressure output and said operational mode only to be accomplished provided both control pressures are supplied from said control pressure outputs of said first and second detectors (120, 122), said first and second detectors (120, 122) being connected in a series configuration or alternatively being connected to a AND pressure valve, said method comprise the additional step of generating an enabling pressure, provided said operational mode is accomplished, said enabling pressure being used for pressurizing the pressure chamber, thereby creating a fail-safe safety system.