Matthew D. Wright, A. Peter Fews, Paul A. Keitch, and Denis L. Henshaw
H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, United Kingdom
Burning of paraffin wax produces small-ions and aerosols in the diameter range 0.4 nanometers (nm) to 1.1 micrometers (μm).* The study investigated the particle characteristics formed by burning paraffin tea-light candles. The study summarized here investigated the particle characteristics formed by burning paraffin tea-light candles. There were peaks observed in the number concentration of particles in the diameters 10–30 nm and 100–300 nm. These are consistent with “normal” and “sooting” burn modes. They also saw a smaller mode in the size range 2.5–9 nm and interpreted it as a "soot-precursor." When they placed a fan behind the burning candle they saw a “modified small-ion” signal of particles at sizes 1.1–2.0 nm. This small size was "...not observed without the fan present or when a lamp chimney was used. During burning, aerosol concentration was elevated and small-ion counts were low. However after extinction of the flame, this trend was reversed and the number of small-ions increased to levels higher than those observed prior to burning, remaining so for several hours."
The researchers observed that "...although not the major source of indoor air pollution in most environments, a vastly increased inhaled dose of nano-aerosols from combustion could be received by anyone present in a typical domestic room containing a burning candle. Further work is required to characterize the charge state of the smallest particles produced in candle flames and to determine the extent of such increased deposition of combustion particles in the lung." However, regardless of the "charge state" [ion characteristics] of the particles, it is highly likely that particles in the nano-particle size ranges measured coming off the candle will be deposited in the human lung. This could have very serious health implications and should suggest both further research as well as caution on the part of those who frequently are exposed to burning tealight candles.
* 1 micrometer (μm) = 1,000 nanometers (nm). A nanometer is one billionth of a meter or 26 millionths of an inch. A human hair is about 5 x 10-5 meters or 50,000 nanometers in diameter.
Reference: Matthew D. Wright, A. Peter Fews, Paul A. Keitch, and Denis L. Henshaw, 2007. "Small-Ion and Nano-Aerosol Production During Candle Burning: Size Distribution and Concentration Profile with Time." Aerosol Science and Technology, 41:475–484, 2007.