Numberonepal, you are more scientific than I am. :-D I just sort of muddle along, usually a heavy stainless steel bowl (so it keeps the heat), bring water to almost boil, put on kitchen table, and sprinkle in EOs.
I’ve tried using oregano oil and it is... too tough for me straight. I use it in small amounts in blends. I mix with others that help respiratory function and usually prefer blends for many purposes.
Hot moist compresses on upper back and chest (alternating) with a small bit of eos in the water can be very good for breaking up lung/bronchial congestion.
I wanted to let y’all know that I tried oregano oil and eucalyptus oil together for a huff. The eucalyptus tempered the harshness of the oregano. The wife has a sniffle, so I thought I’d give it a try. It worked.