“Years Ago, This Doctor Linked A Mysterious Lung Disease To Vaping” (Kaiser Health News) https://khn.org/news/years-ago-this-doctor-linked-a-mysterious-lung-disease-to-vaping/
Q: Do you have a theory of what might be causing the lipoid pneumonia cases? Do you think there may be certain chemicals that are irritants?
Dr. John E. Parker: We need a strong multidisciplinary team to understand the real etiology and cause of lung injury from inhalation. I think it could be any number of components in the mixtures. Lungs don’t like oil, in general, and probably the most specific agent that’s been studied recently is diacetyl, which was studied in popcorn-flavoring lung disease*.
See also case report “Acute Lipoid Pneumonia Secondary to E-Cigarettes Use: An Unlikely Replacement for Cigarettes” https://journal.chestnet.org/article/S0012-3692(16)36283-3/fulltext
* After an outbreak of severe lung disease among workers exposed to butter-flavoring chemicals at a microwave popcorn plant …animal exposure studies demonstrated the severe respiratory epithelial toxicity of diacetyl, the chemical in butter flavorings that is primarily responsible for imparting butter flavor. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3115208/
Eideard 
“Years Ago, This Doctor Linked A Mysterious Lung Disease To Vaping” (Kaiser Health News) https://khn.org/news/years-ago-this-doctor-linked-a-mysterious-lung-disease-to-vaping/
Q: Do you have a theory of what might be causing the lipoid pneumonia cases? Do you think there may be certain chemicals that are irritants?
Dr. John E. Parker: We need a strong multidisciplinary team to understand the real etiology and cause of lung injury from inhalation. I think it could be any number of components in the mixtures. Lungs don’t like oil, in general, and probably the most specific agent that’s been studied recently is diacetyl, which was studied in popcorn-flavoring lung disease*.
See also case report “Acute Lipoid Pneumonia Secondary to E-Cigarettes Use: An Unlikely Replacement for Cigarettes” https://journal.chestnet.org/article/S0012-3692(16)36283-3/fulltext
* After an outbreak of severe lung disease among workers exposed to butter-flavoring chemicals at a microwave popcorn plant …animal exposure studies demonstrated the severe respiratory epithelial toxicity of diacetyl, the chemical in butter flavorings that is primarily responsible for imparting butter flavor. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3115208/
Tex Williams – “Smoke! Smoke! Smoke!” (That Cigarette) 1947 https://www.youtube.com/watch?v=65_-vNtWLLs