These two articles talk about this question: https://www.popsci.com/why-did-nasa-still-use-pure-oxygen-after-apollo-1-fire https://www.popsci.com/why-did-nasa-

These two articles talk about this question: https://www.popsci.com/why-did-nasa-still-use-pure-oxygen-after-apollo-1-fire https://www.popsci.com/why-did-nasa-still-use-pure-oxygen-af... https://www.space.com/17338-apollo-1.html https://www.space.com/17338-apollo-1.html