Earlier quoted context omitted.
Fog machines also use a glycol solution, and have been shown to be harmful. Thus vaping glycol may not be safe. https://www.cdc.gov/niosh/hhe/reports/pdfs/1990-0355-2449.pd...
The report you linked shows quite the opposite, actually. They concluded: > Based on the results of this study, there is no evidence that theatrical "smoke," at the levels found in the theaters studied, is a cause of occupational asthma among performers. That being said, chronic exposure is probably not good for you. From a health perspective, don't inhale anything other than air!
When compared to actors from the non-"smoke" productions, actors from two or more of the four productions utilizing theatrical "smoke" reported experiencing a significantly greater prevalence of nasal symptoms (sneezing, runny or stuffy nose), respiratory symptoms (cough, wheeze, breathlessness, chest tightness), and mucous membrane symptoms (sore throat, hoarseness, dry throat, itchy/burning eyes, dry eyes) during their performances for the week prior to the survey.
The final line is: The quantity and frequency of use of the various fogs during a performance should be minimized.
PS: A method of action was suggested to be the breakdown of glycol due to high temperature.