At what concentration must the purity of aviation breathing oxygen be maintained?

The purity of aviation breathing oxygen must be maintained at a minimum concentration of 99.5 percent. This high level of purity is crucial for ensuring that the oxygen supplied to pilots and passengers under conditions of low atmospheric pressure or during emergencies does not contain harmful impurities. Impurities in the oxygen can include water vapor, carbon dioxide, and other contaminants that could be detrimental to health or flight safety. Maintaining this high standard helps prevent the risk of fire, respiratory issues, and other complications associated with lower quality oxygen. The specific threshold of 99.5 percent has been established to ensure the safe and effective use of oxygen in aviation environments, making it the standard for airborne operations.