On the SOFIA aircraft, the aircraft is designed to fly at very high altitudes (higher than what can be achieved by regular 747), with a cargo door open.
https://upload.wikimedia.org/wikipedia/commons/8/8a/SOFIA_ED10-0182-01_full.jpg
I know that oxygen mask are a standard feature for most airliners but:
How is the aircraft designed to handle this situation ?
What about redundancy ?
If there is supplemental oxygen, is it really without adverse effects ?
pic credits wikimedia