To dry-burn or not to dry-burn?
The Hamlet’s choice of burning dry or not is rather a safety question than of any other concern. As recalled by the chemist, a dry burn consists in applying a lot of power to a bare coil in order to heat it and “clean it up” from manufacturing residuals. It is also used for alignment and spacing.
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Such practice, according to the specialists, affects the structure of the alloy or the metal that the coil is made of in surface, and may lead to the production of some particles that will stick to the aerosol and be ingested by the user.
The question of burning dry was previously addressed by Dr Konstantinos Farsalinos who asked for help a material sciences expert, Pedro Carvalho. In their conclusions, they recommend not to burn dry any type of coil.
What is a coil made of?
The chemical composition of heating elements is subject to trends. The heating element is made of a resistance wire that is exposed to an electric current.
Different types of resistance wires are used and their grade and quality depend on the brand. As summarized by Dr Dworniczak, kanthal, stainless steel, nichrome and, lately, pure metals like nickel or titanium are used.
Kanthal is an alloy of iron (Fe, 70%), chromium (Cr, 20-30%), and aluminium (Al, 4-7%). When heated, aluminium oxides form a protective layer on the surface of the wire. Kanthal is one of the rare alloys used in heating elements that do not allow temperature control by the most advanced mods.
Nichrome is an alloy of Cr (80%) and nickel (Ni, 20%). When heated to so called red hot temperature an outer layer of chromium(III) oxide develops, which protects the heating element from further oxidation.
Ni200 is a full Ni material. Nickel oxide forms when the wire is heated above 400°C. Depending on the degree of oxidation two types of oxide may be formed, green Ni oxide is inert but black Ni oxide is very reactive.
Stainless steel (SS) has been introduced lately to the vapers market. Steel is an alloy of Fe and carbon (C). The stainless property of steel is due to the presence of at least 13% of Cr. The Cr prevents chromium oxide from forming a protective layer. Some contaminants in the form of trace metals are present in SS. The classical SS316 contains also small amounts of molybdenum (Mo, 2.5%) and manganese (Mn, 2%).
Why is a dry-burn dangerous?
A dry-burn is dangerous for 3 reasons:
- The coating of oxidized material that is formed in surface can peal off during vaping and be transferred to the lungs at the same time as the aerosol, in the form of microscopic particles, or particulate matter.
- The particulate matter can cause allergies. Nickel, for example, is recognized for causing skin rash, itching, redness. Ni is also a carcinogenic compound when combined to carbon monoxide (CO), a product of incomplete carbohydrate combustion. Hence, this type of toxicity is probably less relevant in the case of e-cigarettes than for combustible tobacco products.
- The particulate matter can also be toxic for the organisms. It is, for example well described in the case of welders exposed to Mn oxides.
For the chemist, a dry burn may amplify the normal corrosion process on the surface of the coil and prematurely deteriorate the quality of the heating element. Toxic (for Mn) or carcinogenic effects (for the Cr(VI), a more oxidized form compared to Cr(III)) are improbable since the dose is very small.
Unintentional dry burn
An unintentional dry burn may also happen when the e-liquid got short in the tank and the cotton is not wet enough. Our advice if it happens, is to get rid of the burnt coil and to mount a brand new one.
Similarly, it is not a good idea to re-use old coils since corrosion has probably developed and already fragilized the surface of the metal. Exchanges of used coils between users is not recommended either.
There is no reason to think that a dry-burn would make vaping worse than smoking. Nevertheless, it increases the risk of releasing potentially harmful compounds that may be inhaled by the user. In order to check the consistency of a home-made coil and to clean it from manufacturing residuals, a moderate heating of the wire may appear useful, from the experience of vapers.
Those users generally advise building non-touching coils so that they don’t have hot spots. Using a coiler also helps building coils in a reproducible way.
Nowadays, heating elements made of ceramic are present on the market. The testing of such elements is underway and results may be made public shortly. On paper, such material appears to be a safer option compared to alloys or metals but in reality there are two types of ceramic coils with also two very different safety levels.
Since the trend, currently, is towards a safer vape by selecting the best e-liquid quality, by purchasing the most advanced mods that allow a control of temperature, why not following expert’s advices and not intentionally burn the coils or let gunk build up on your coils?
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Written by Jérome Harlay – edited by Diane Caruana.