Highlighting Specific Features to Reduce Chemical and Thermal Risks of Electronic Cigarette Use through a Technical Classification of Devices

Abstract

Currently, the emission generation protocol of electronic cigarettes has only one standardized vaping regimen that is consistent with mouth-to-lungs inhalation. Recent works show the significant increase in performance of the device with the use of a direct lung vaping regimen (167 mL s−1, consistent with direct lung inhalation). However, requirements are needed for its use in a laboratory. This work aims at identifying mechanical characteristics of a device and providing a classification based on recommended power range, electrical resistance, heating surface, and air resistance of twenty-six tested devices. The electrical resistivity relation allows the estimation of the wire surface using its diameter and its length. The air resistance is obtained by measuring the pressure drop of the tested device with airflow rates ranging from 1–10 L min−1. Through the wide panel of tested devices, results allow separating them in two categories: classical and sub-ohm electronic cigarettes consistent with the two inhalation behaviours. Differences up to 71 mm2 for the wire surface and up to 4.8 Pa 0.5 min L−1 for the air resistance are observed between them. This limit seems to correspond to a required power of 25 W and an electrical resistance of 1.1 Ω.

Physical and chemical characterizations of a reference e-cigarette used in animal testing

“…The Subtank and Toptank are devices with large air inflow. Based on the method developed in a previous work 22 , we completed the technical information with the heating surface and the air resistance, allowing clearer identification of the intended usage (Table 2 ).…”

Critical Review of the Recent Literature on Organic Byproducts in E-Cigarette Aerosol Emissions

“…Underheating occurs below this range with no vaporized e-liquid, while overheating occurs above this range as the relation becomes nonlinear. In the optimal regime, an equilibrium of heat exchange is maintained when a sufficient airflow provides the necessary forced convection (inhalation) to form the aerosol by condensation of the vaporized e-liquid [8,9,49]. Overheating occurs when nucleate boiling gives way to film boiling [22] in which a layer of gas surrounds the coil, propitiating radiative heating exchange, which rapidly increases the rate of vaporization of the e-liquid, breaking the equilibrium sustained by forced convection in the linear regime.…”

“…Devices used for MTL vaping are mainly designed with small air inlet holes (diameters around 1-2 mm), which leads to a high air resistance that significantly reduces range the range of possible airflows. As an example [49], the Eroll device from Joyetech allows an airflow range of 0-2.8 L/min, with the user inhales very small volume even at the top value 2.8 L/min. Assuming a middle value of this range at 1.4 L/min and a puff with the rest tidal inhalation volume of 500 would imply a puff duration above 20 s, a long duration that is not only unrepresentative, but uncomfortable (normal breath lasts less than 5 s).…”

“…Therefore, the user will be able to generate significantly higher airflow rate. As an example, in the tests conducted in [49] most of the DTL devices only reached 20% of the maximal pressure of the lung at at airflow of 10 L/min, thus suggesting that the airflow rate can be, at least theoretically, significantly higher. Average adults under rest conditions breath 12-16 inhalations per minute, with breaths lasting on average 3.75-5 s and airflow rates of 7.5-10 L/min, with both frequency and volume increasing with effort.…”

“…The CORESTA or CORESTA-like puffing parameters might not be wholly appropriate for testing even those devices that are also meant for MTL vaping, but operate at power levels 10-30 W above recent pods and disposables. As shown in [49], it is very likely that these "intermediate" devices are fully compatible with airflows of up to 4 L/min larger than those specified by CORESTA or CORESTA-like protocols.…”