text: are there any adverse effects on human body if one breathes pure oxygen for long duration? are there any adverse effects on human body if one breathes pure oxygen(say 98%)? if there are any adverse effects, what is themaximum time one can breathe such oxygen  without such adverse effects? at normal pressure yes; oxygen is a very aggressive gas and will quickly cause lung damage. the wikipedia page claims that a few hours is not so dangerous.  at low pressure (airplane or space shuttle) it is not dangerous if the partial oxygen pressure is around 0.2 bar like on earth.