Portable air tester?

[1fast05]

I highly doubt its CO2(carbon-dioxide) causing the problems. It's most likely CO (carbon-monoxide) that is the problem and is colorless, odorless and tasteless unless it comes from another source like exhaust fumes from the compressor motor which is usually the main cause of CO poisoning in divers. Than usually it will have a funny taste or smell but not always.

 

[Herk_Man]

CO2 is not the problem. It's CO. You create CO2 when you breathe.

 

[Scared Silly]

Carbon dioxide (CO2) can be a problem but typically for rebreathers not properly scrubbing. The vast majority of divers should be worried about carbon monoxide (CO).

What ever you do, do not breath in dihydrogen monoxide. Too much of that will kill you as well.