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

The purity of aviation breathing oxygen must be maintained at a concentration of at least 99.5 percent to ensure safety and efficacy for pilots and passengers using it at high altitudes. This high level of purity is critical because even small amounts of impurities can lead to complications such as equipment malfunctions or health hazards, especially in environments where oxygen is scarce and the risk of hypoxia is heightened. Breathing oxygen that fails to meet this standard could impair cognitive and physical performance in pilots, potentially leading to unsafe conditions during flight. Therefore, aviation guidelines stipulate that only oxygen meeting this strict purity requirement is used in aeronautical applications to ensure the safety and performance of all on board.