Scientific substantiation of the absence of
combustion and no smoke formation in the
Electrically Heated Tobacco Product (EHTP)
by Markus Nordlund, Maurice Smith, Serge Maeder, Thomas McGrath, Jean-Pierre Schaller, Pascal Pratte, Patrick Picavet, Manuel C. Peitsch
Philip Morris International R&D
This report consolidates scientific evidence substantiating that no combustion of the tobacco material in Philip Morris International’s (PMI) Electrically Heated Tobacco Product (EHTP) occurs when used as intended in the Electrically Heated Tobacco System (EHTS) (also known as the Tobacco Heating System (THS) 2.2 and marketed in various countries under the brand name IQOS) Holder and that the aerosol generated is not smoke. Available technical and scientific definitions of smoke and combustion were reviewed, together with definitions of key words (such as aerosol and pyrolysis) that are used in the definition of smoke. Based on these technical and scientific definitions, the scientific evidence comprehensively demonstrates that no combustion of the tobacco material occurs during intended use of the EHTS and that the aerosol generated from the EHTP tobacco material is not smoke.
Key takeaways of this report include the following:
- o Combustion (burning) is defined as a chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light in the form of either a glow or flame.
- o For combustion (burning) of the EHTP tobacco material to occur, the temperature of the tobacco material would need to exceed about 400°C.
- o The maximum temperature measured in the EHTP during use in the EHTS Holder is 320°C. This is well below the temperatures required for combustion of the tobacco material to occur (known to exceed about 400°C).
- o There are no signs of net exothermic (heat generating) processes in the EHTP tobacco material during use in the EHTS Holder. In fact, when power to the heater is switched off there is an immediate decrease in the temperature of the tobacco material.
- o As the EHTP is heated to temperatures below the ignition temperature of the EHTP tobacco material (known to exceed about 400°C), the tobacco material undergoes processes such as drying and evaporation, and close to the Heater also thermochemical decomposition (torrefaction and low-temperature pyrolysis), but no combustion (neither incomplete nor complete).
- o The comparison of the chemical composition of the EHTS aerosol generated in oxidative (air) and non-oxidative (nitrogen) environments indicated that oxygen (necessary for combustion to happen) does not play a major role in the thermochemical degradation of the EHTP tobacco or the aerosol formation.
- o The presence of low levels of gaseous compounds in the EHTS aerosol, such as carbon monoxide, carbon dioxide, nitrogen oxides, etc. (usually associated with combustion), is not evidence that combustion has occurred, as low amounts of these compounds are generated during thermochemical degradation (torrefaction or mild pyrolysis) of tobacco components during heating, independent of the oxygen availability.
- o Smoke is an aerosol containing liquid and solid particles (particulate matter).
- o Smoke particulate matter is formed when products of combustion and hightemperature pyrolysis (e.g., hydrocarbons) reach supersaturation and either condense to form droplets or react together to form particles, or by the nucleation and growth of positively charged hydrocarbon ions to form soot particles.
- o While smoke is an aerosol, not all aerosols are smoke. The EHTS aerosol liquid particulate matter (droplets) are not formed from condensation of byproducts of combustion or pyrolysis. They are instead generated when glycerol (added to the tobacco material during processing as an aerosol former) is vaporized and reaches supersaturation and condenses on cooling, forming nuclei, onto which more glycerol, water, nicotine, and other constituents can condense to form droplets.
- o Non-smoke aerosols formed from the condensation of water vapor, vaporized e-liquids, or vaporized glycerol from the EHTP tobacco material are very different in terms of origin and chemical and physical composition compared with smoke aerosols formed from the combustion and associated high-temperature pyrolysis products generated from the burning of tobacco.
- o The aerosol generation process in the EHTS is equivalent to the aerosol generation process in most e-vapor products (EVP), for which aerosol formers (glycerol and propylene glycol) in the e-liquid are vaporized during heating and are subsequently cooled down to form liquid aerosol droplets.
- o The EHTP, when used as intended in the EHTS Holder, does not generate solid particles, as demonstrated by detailed experiments involving scanning electron microscopy (SEM) analysis. Thermodenuder and thermodilution techniques are not able to determine the presence of solid particles alone without being combined with microscopy analysis, such as SEM.
- o The EHTS aerosol generated during use of the EHTS contains >90% lower levels of harmful and potentially harmful constituents (HPHC), on average, compared with the mainstream smoke of a 3R4F reference cigarette.
- o More than 97.8% w/w (mass fraction) of the EHTS mainstream aerosol constituents transfer via vaporization/direct transfer processes to the aerosol from the multicomponent EHTP. Less than 2.2% w/w of the EHTS mainstream aerosol constituents are likely to be formed by low-temperature pyrolysis processes (torrefaction), as suggested by the limited influence of oxygen on the aerosol composition.
- o The mere presence of low amounts of pyrolysates in an aerosol does not unambiguously imply that the aerosol is smoke, as the amount of the pyrolysates must be high enough to reach supersaturation to condense (nucleate) or to react with each other to form particulates. For example, the aerosol generated by EVPs contains low amounts of pyrolysates but is not considered to be smoke.
- o The absence of combustion in the EHTP, when used as intended in the EHTS Holder, and that the aerosol generated is not smoke have been substantiated by scientific evidence and has been verified by third-party scientific experts in numerous countries as well as by independent research organizations.
To summarize, scientific evidence comprehensively demonstrates that there is no combustion of the EHTP tobacco material occurring during intended use of the EHTS and that the aerosol generated is not smoke.