That's why I am writing 'at 0.2 atmospheres'! Under that condition, you do get neither any poisoning (which the internet claims appears at 1.4 atmospheres pure

That's why I am writing 'at 0.2 atmospheres'! Under that condition, you do get neither any poisoning (which the internet claims appears at 1.4 atmospheres pure oxygen), nor a big fire hazard. You create other problems due to the lower air pressure like lower boiling temperature and more body heat retention but those might be engineered away... On SkyLab, astronauts supposedly experienced 75% oxygen, 25% nitrogen for upto 84 days (again at lower pressure). That's not really long term, but not short either.