Dr Mirosław Dworniczak, is a chemist who became interested in vaping after he quit smoking a few years ago. In a blog on Nicotine Science and Policy Blog, he discusses the common practice of Dry Burning.

A dry burn happens when power is used to heat a coil without any material on it, to remove residue from manufacturing. Sometimes, it is also used to adjust and space out the coil.

However, experts indicate that this process can change the surface structure of the metal or alloy used for the coil, producing unwanted particles that may stick to the aerosol and be ingested by the user.

The issue of burning coils without e-liquid was studied by Dr. Konstantinos Farsalinos and Pedro Carvalho, a material sciences expert. They determined that this practice should not be done with any coil type.

What is a coil made of?

Heating elements have a specific chemical makeup, yet always contain a wire that resists electricity. Various kinds of wire are used and their quality varies by brand.

Generally, kanthal, stainless steel, nichrome, and more recently, pure metals such as nickel or titanium, are used according to Dr. Dworniczak’s summary.

Kanthal is a metal mix made of iron (Fe, 70%), chromium (Cr, 20-30%), and aluminum (Al, 4-7%). When it’s hot, aluminum substances produce a shielding coating on the wire’s exterior. Kanthal is an unusual alloy utilized in heating modules that the highest-grade mods cannot regulate.

Nichrome is an alloy of Cr (80%) and nickel (Ni, 20%). When heated to a so called red hot temperature, an outer layer of chromium(III) oxide develops, which protects the heating element from further oxidation.

Ni200 is a complete nickel material. When the wire is heated above 400°C, it forms nickel oxide. Depending on the degree of oxidation, two types of oxide can form. Green nickel oxide is not reactive, but black nickel oxide is highly 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. 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:

1. The coating of oxidized material that is formed on the surface can peel 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.
2. Particulate matter can cause allergies. Nickel, for example, is recognized for causing skin rashes, itching, redness. Ni is also a carcinogenic compound when combined with 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.
3. Particulate matter can also be toxic for organisms. Cases of such toxicity are for example found in cases of welders exposed to Mn oxides.

The chemist said that if you dry burn a coil, it can speed up the corrosion process and ruin the heating element faster. It’s unlikely to have toxic (for Mn) or cancer-causing effects (for Cr(VI), a more oxidized form than Cr(III)) because the dose is small.

Unintentional dry burning

An unintentional dry burn may also happen when the e-liquid runs short in the tank and the cotton is not wet enough. If this happens, one is advised to simply 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 some level of corrosion would have probably already initiated and the surface of the metal would already be relatively more fragile.