Small compressor for diving.
Previous replys are 100% correct, DON''T DO IT. Now I must admit that when in high school I used just such a device as you describe. For past 30 years I have used compressed air breathers professionally, most compressor oils (e.g. Ambesol) are labeled as carcinogens, even those designed for use to fill air bottles. The systems designed for breathing air use 4 or 5 stage high pressure filters and a carbon monoxide detector. It takes very little CO to make the air unfit for use, here in Los Angeles sometimes just the ambient level of CO is too high to fill bottles. I haven''t looked lately but there used to be devices made for this purpose, some even on floats. I think these may no longer be available due to health reasons, you can''t have a gas engine running anywhere in the vicinity of the compressor intake and get acceptable CO levels.