The present invention may be embodied as a system and/or a computer-based method for determining safe operation of a breathing gas system comprising the step of receiving a present oxygen concentration value from an oxygen concentration sensor. The method further comprises the step of receiving, at the computer, a present altitude value from an altimeter of the aircraft and using the computer to calculate an alarm flow rate, where the alarm flow rate is a function of the present oxygen concentration value and the present altitude value. The method may further comprise the step of receiving, at the computer, a present flow value from a flow meter, where the present flow value represents the rate of flow of breathing gas to the user. The method may comprise the step of comparing the calculated alarm flow rate to the received present flow value to determine a safe operation of the oxygen system.
