Toxic Chemical Formation during Vaping of Ethyl Ester Flavor Additives: A Chemical Kinetic Modeling Study.

Ethyl ester flavor additives are used in e-liquids to produce a citrus flavor. Although these compounds are considered safe as flavor additives, this only applies to oral consumption and not vaping operations, where they can decompose into potentially harmful compounds including carboxylic acids. Further decomposition of these carboxylic acids is expected to produce ketene, which is a strong respiratory poison that can cause fatal lung damage at low concentrations. This study develops a kinetic model of the thermal decomposition of ethyl ester flavor additives and simulates the decomposition of these compounds under vaping conditions. These results show that under normal operating conditions, it is unlikely for any harmful compounds to be present in-lung. However, at higher operating temperatures, there is the potential for acetic and butanoic acid to be present in the lungs at concentrations that cause irritation, and where repeated exposure may lead to bronchitis. At more extreme operating conditions it is possible for harmful levels of ketene to be produced such that it could cause fatal or severely detrimental effects upon repeated exposure. These high temperatures can be reached under "dry" operating conditions that arise as a result of improper use, particularly in user-modified e-cigarettes.