Whilst most therapists may would understand a "flippant" comment, many, especially new therapists, wouldn't. It suggests that the fumes are not dangerous at all, and it "is only a smell that dissipates after a while". In reality the people, (including pets etc) above a salon that is producing these fumes have every right to complain, especially those with respiratory problems, young children and older people as these fumes are very dangerous to them. Just opening the door or window to "dissipate" the gases quicker only puts them out into the environment and will go into the rooms above, through their open windows, airbricks etc. The smells are a good thing as it warns people of the danger, as you rightly say Carbon Monoxide is odourless and a killer. These fumes and gases should be "captured at source" before they damage the health of therapists, (who breathe them in more often) clients and surrounding neighbours.