Just like any other open combustion, candles emit fine particles but
do not pose a health hazard if some rules are respected.
From time to time, the media reports on the high emission of fine particles from candles and the supposed health hazard connected with it. If some basic rules for handling candles are respected, such concerns can be easily dispelled however.
What is fine dust?
Fine dust or particulate matter describes particles that can
penetrate the deeper part of the lungs because of their small size and,
depending on their composition, may remain there. Possible sources of
fine dust can be traffic (diesel particles, tire abrasion, suspended
road dust), cooking or open fire (tobacco smoke, open fireplaces) for
example. Burning candles produces fine dust too – but besides the
particle size and the total fine dust quantity, the evaluation of a
possible health risk has also got to take the composition of the
particles into account.
Do candles emit fine particles?
A lot of scientific studies covering this topic have been published
during recent years. A study of scientists from the University of Lund
(Sweden)* is especially noteworthy since it gives an overview of
previous studies on candles on the one hand and additionally examines
the size, number and composition of emitted particles from steadily
burning candles, sooting candles and candles after having been
extinguished.
In contrast to other open combustions like wood
fires in open fireplaces for example, the flame of a steadily burning
candle shows very high temperatures. This is the reason why the candle
wax is combusted almost completely and no or only extremely small
amounts of pollutants are emitted - ranging far below any critical
concentration. One study confirming this fact is a scientific comparison
of candles made of different wax types performed by the German Bayreuth
Institute of Environmental Research (Ökometric GmbH) in 2007. A study
summary can be obtained on request and is available on
www.eca-candles.eu.
The undesired incomplete combustion, during
which also pollutants can be emitted, can be recognized by a flickering
flame or the visible release of soot. It can be caused by insufficient
oxygen supply or because the candle is placed in a draught.
If the
candle flame is not extinguished with a candle snuffer but blown out
instead, there is also an incomplete combustion taking place during the
short afterglowing phase.
Findings of the scientific studies
The study of the Lund University examines the size, number and
composition of the emitted particles during exactly these possible
candle burning phases.
If a candle is burning with a steady
flame, it emits a comparably high number of ultrafine particles. This
does not pose a health hazard however. The key is the composition of the
particles: they are inorganic water-soluble salts like phosphates for
example, required to improve the wick performance. They easily
agglomerate when exposed to air humidity what makes the deposition less
probable. If these particles reach the lungs anyway, they are simply
dissolved and released by the body.
In addition to these
ultrafine particles, sooting candles also emit bigger particles mainly
consisting of elemental carbon. These particles pose a lower health risk
compared to soot particles from diesel exhaust however. They contain
much less polycyclic aromatic hydrocarbons (PAH) for example – a
pollutant category that is typically formed during incomplete
combustion. In addition to this, the particles from burning candles
quickly agglomerate to bigger particles that are clearly bigger than
those in diesel exhaust, and so the probability that they are deposited
in the respiratory tract is clearly lower.
In the period after
blowing out the candle – characterized by an afterglowing wick tip and
the release of a visible trail of smoke – mainly comparably big
particles are formed that are composed of non-combusted or only partly
combusted candle wax for the most part. These particles can be inhaled
less easily and are also less critical than soot particles because of
their composition.
Summary
Despite steadily burning candles emit fine particles just like all
other open combustions, this is not a matter of concern based on the
state of the scientific knowledge because of the composition of the
particles.
An incomplete combustion characterized by visible
release of soot or smoldering after blowing out the candles should be
avoided for reasons of precaution nevertheless although the concerns
are, compared to other sources of fine dust like diesel exhaust or open
wood fires, clearly smaller here as well. This can be achieved by
respecting a few simple rules:
Basic rules for handling candles
- Do only use high quality candles. Only these candles guarantee
the use of premium quality base materials as well as an impeccable
burning behavior. Such high quality candles can be identified by the RAL
Quality Mark for Candles for instance:
- Do not place candles in a draught. A candle can only burn
steadily and without emitting soot if the ambient air is calm.
Extinguish the candle immediately if it soots regardless.
- Do only burn candles in appropriate candle holders allowing sufficient air supply.
- Trim the wick if it gets too long. The ideal length of the wick
ranges from 10 to 15 mm, depending on the candle type. Longer wicks may
cause sooting and should thus be carefully trimmed with scissors after
extinguishing the flame.
- Carefully trim the edge of the candle if it gets too high by
using a sharp knife when it is still warm. Do not damage the rim however
because otherwise liquid wax may spill out.
- Do never blow out candles. Put the candle out by extinguishing
the flame with a candle snuffer or by carefully dipping the wick into
the liquid wax. Please straighten the wick up again afterwards.
- Ventilate the room after extinguishing the candles.
* Pagels, J., Wierzbicka, A., Nilsson, E.,
Isaxon, C., Dahl, A., Gudmundsson, A., Swietlicki, E., Bohgard, M.
(2009). Chemical composition and mass emission factors of candle smoke
particles. Aerosol Science 40 (2009), 193-208
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