A method of operating a system having at least one sensor for detecting an analyte gas in an ambient atmosphere and a sensor responsive to oxygen includes providing a volume in fluid connection with the sensor responsive to oxygen. The volume has an open state in which the volume is in fluid connection with the ambient atmosphere and at least a first restricted state in which entry of molecules from the ambient atmosphere into the volume is restricted as compared to the open state. The method further includes placing the volume in the open state, subsequently placing the volume in the first restricted state, and measuring a dynamic output of the sensor responsive to oxygen while the volume is in the first restricted state. The dynamic output provides an indication of the status of one or more transport paths of the system.