System for distributing a therapeutic gas, comprising: - a source of pressurized gas feeding a flow control device configured to deliver the gas at different flow rates that are selectable by a user, said flow control device comprising a flow rate selector , - a gas supply line for conveying the gas at the selected flow rate from the flow control device , - a bypass line fluidically connected to the gas supply line , and comprising an exhaust valve , and - a signal processing unit with microprocessor, characterized in that : - it further comprises a position sensor arranged so as to determine the position of the flow rate selector and configured to communicate at least one selector position signal to the signal processing unit , - the bypass line further comprises a bypass pressure sensor arranged so as to determine the pressure in the bypass line and configured to transmit at least one bypass pressure signal to the signal processing unit , - the microprocessor of the signal processing unit is configured to: i) determine a gas flow rate from said at least one selector position signal supplied by the position sensor , ii) compute, by means of a conversion table stored by the signal processing unit , a pressure drop generated in a downstream portion of the gas supply line with respect to said gas flow rate, and iii) determine that the upstream end of the flexible tube has been accidentally disconnected, when the pressure measured in the bypass line becomes of the same order as the computed pressure drop. - a source of pressurized gas feeding a flow control device configured to deliver the gas at different flow rates that are selectable by a user, said flow control device comprising a flow rate selector , - a gas supply line for conveying the gas at the selected flow rate from the flow control device , - a bypass line fluidically connected to the gas supply line , and comprising an exhaust valve , and - a signal processing unit with microprocessor, - it further comprises a position sensor arranged so as to determine the position of the flow rate selector and configured to communicate at least one selector position signal to the signal processing unit , - the bypass line further comprises a bypass pressure sensor arranged so as to determine the pressure in the bypass line and configured to transmit at least one bypass pressure signal to the signal processing unit , - the microprocessor of the signal processing unit is configured to: i) determine a gas flow rate from said at least one selector position signal supplied by the position sensor , ii) compute, by means of a conversion table stored by the signal processing unit , a pressure drop generated in a downstream portion of the gas supply line with respect to said gas flow rate, and iii) determine that the upstream end of the flexible tube has been accidentally disconnected, when the pressure measured in the bypass line becomes of the same order as the computed pressure drop. i) determine a gas flow rate from said at least one selector position signal supplied by the position sensor , ii) compute, by means of a conversion table stored by the signal processing unit , a pressure drop generated in a downstream portion of the gas supply line with respect to said gas flow rate, and iii) determine that the upstream end of the flexible tube has been accidentally disconnected, when the pressure measured in the bypass line becomes of the same order as the computed pressure drop. <EOS>