Abstract
We examine the plausibility of aerial transmission of pathogens (including the SARS-CoV-2 virus) through respiratory droplets that might be carried by exhaled e-cigarette aerosol (ECA). Given the lack of empiric evidence on this phenomenon, we consider available evidence on cigarette smoking and respiratory droplet emission from mouth breathing through a mouthpiece as convenient proxies to infer the capacity of vaping to transport pathogens in respiratory droplets. Since both exhaled droplets and ECA droplets are within the Stokes regime, the ECA flow acts effectively as a visual tracer of the expiratory flow. To infer quantitatively the direct exposure distance, we consider a model that approximates exhaled ECA flow as an axially symmetric intermittent steady starting jet evolving into an unstable puff, an evolution that we corroborate by comparison with photographs and videos of actual vapers. On the grounds of all this theoretical modeling, we estimate for low-intensity vaping (practiced by 80–90% of vapers) the emission of 6–210 (median 39.9, median deviation 67.3) respiratory submicron droplets per puff and a horizontal distance spread of 1–2 m, with intense vaping possibly emitting up to 1000 droplets per puff in the submicron range with a distance spread over 2 m. The optical visibility of the ECA flow has important safety implications, as bystanders become instinctively aware of the scope and distance of possible direct contagion through the vaping jet.
Highlights
The evolution of bioaerosols spreading disease contagion through respiratory droplets has been widely studied, as can be appreciated in reviews on generic pathogens by Gralton et al [1] and Zhang et al [2], the influenza and SARS viruses [3,4] and in spread risk modeling [5]
The purpose of the present paper is to fill an important gap in the above-mentioned body of literature on pathogen spread through respiratory droplets, namely to examine the plausibility, scope and risks of this transmission taking place through a different expiratory route: exhaled e-cigarette aerosol (ECA)
Just as ECA droplets, these “aerosols” lie in the Stokes regime, so that the exhaled ECA flow provides an accurate visual tracing to infer how far they can be transported to produce direct exposure to bystanders located in the direction of this flow. Given these estimations and inferences, we model the exhaled ECA flow in an indoor space with natural ventilation as a turbulent isothermal starting jet evolving into an unstable puff, evaluating the maximal distance for direct exposure to respiratory droplets potentially carried by vaping exhalations
Summary
The evolution of bioaerosols spreading disease contagion through respiratory droplets has been widely studied, as can be appreciated in reviews on generic pathogens by Gralton et al [1] and Zhang et al [2], the influenza and SARS viruses [3,4] and in spread risk modeling [5] (see the chapter on bioaerosols and cited references therein in [6]). Vaping is characterized by a wide range of distinct and individualized usage patterns loosely described by the parameters of puffing topography: puff and inter puff duration, puff volume and flow (see [29,30,31,32]) This style diversity complicates the study and evaluation of e-cigarette aerosol (ECA) emissions, more so given the need to upgrade standardization of vaping protocols, especially for the appropriate configuration of vaping machines used for research and regulation. It consists of three stages: (1) “puffing”, where ECA is sucked orally while breathing through the nose; (2) the puffed ECA is withdrawn from the mouth and held in the oropharyngeal cavity without significant exhalation; and (3) inhalation into the lungs of the ECA bolus by tidal volume of air from mouth and nose inspiration. It is mostly a high-intensity regime associated with advanced-tank systems
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