My brother was a technician before. His job was to fix oxygen piping in a newly built hospital and to do maintenance after that. So, if you were to ask him what is an oxygen concentrator, he will definitely know about it. Oh ya! If you need to buy it, don't ask my brother coz he has resigned. You can always get it from AllegroMedical.com.
The reason he resigned because he has to travel a lot and that is not good when you are married with kids. The work suits him well though because he was not exposed to the sun at all and working most of the time in an air-cond building. Hot sun causes his nose to bleed.