Water out alarm determination

A respiratory assistance system for humidifying a flow of gases, the respiratory assistance system comprising:

• a heater configured to provide heat to a quantity of water held in a humidification chamber;
• a flow sensor;
• a temperature sensor configured to sense a temperature of the gases proximal to an outlet of the humidification chamber;
• and
• a controller in electronic communication with the heater, the flow sensor and the temperature sensor,
• wherein the controller is configured to determine at least one operational state from a plurality of predetermined operational states based on at least one of a temperature of the heater, a temperature of the gases proximal to the outlet of the humidification chamber, or a therapy mode and a flow rate, and
• wherein the controller is further configured to select at least one independently selectable water out detection method from a plurality of water out detection methods based on the determined operational state, wherein the at least one water out detection method is selected from one or more predetermined water out detection methods associated with the determined operational state.