A pressurized respiratory gas humidifier adapter (100) with a pressure relief valve (70) having an audible signal generating device incorporated into a low-flow respiratory gas supply system at a position in the system wherein the pressure relief valve and an audible signal generating device are protected from inadvertent damage during use of the humidification system, especially during connection of the adapter (100) into the respiratory gas supply system and when the adapter (100) is connected to a humidifier container (10) prior to coupling into the gas supply system. The pressure relief valve and audible signal generator (70) are incorporated into a humidifier adapter (100) for creating a hermetic seal with a standard medical humidifier container (10), and the pressure relief valve relieves and regulates the pressure in the humidified gas supply system when an obstruction in the gas flow path to the patient occurs, while generating an audible sound emitted at a predetermined pressure threshold level throughout a desired respiratory gas flow-rate range.
