They like to keep the levels above 90, to qualify for O2 at home, he would have to be 88% or less (Medicare standards). If he has additional heart trouble, then I believe they can get away with O2 at a higher reading such as 89-90% but don't quote me.
You should ask your father's doctor what he feels his levels should sit at, they should also be monitoring his levels as well to make sure that they aren't dropping too low. You also have to take in consideration if your dad is at rest, his O2 levels may be okay if he is sitting but moving around they could be dropping. The doctor should check for desaturation while walking as well. They can do this in an office by putting an oximeter on his finger and then walk him around. If he drops to 88 or below, they would probably prescribe him some O2 for exertion.
I hope this helps you..Sunny
I am not a medical expert. My mother had idiopathic pulmonary fibrosis. A terrible terminal lung disease. She was in the hospital many times. We were always told, that she was in no danger, as long as her oxygen level remained 90 or above. I too have COPD with emphysema. I have had pnemonia with the COPD as well. Possibly you can call your father's doctor and ask what his oxygen level should be. I am getting ready to go the doctor in the next week. There are problems with my oxygen level I do believe. So, I do well understand your concern about your father. I hope you find the correct answer you are seeking. And that all goes well for your father.