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BLACK
SOOT DEPOSITION... Also referred to as "ghosting," "carbon tracking," "carbon tracing" and "dirty house syndrome," has become an increasing complaint of homeowners and apartment residents throughout the country. Since 1992, the occurrence rate of complaints received at the Florida Department of Health rose from two-a-year to, at times, two-a-week. Several factors are believed to contribute to the deposition of carbon soot in residences, but a full understanding of the cause and mechanism is still forthcoming. Several theories have been suggested by those investigating the phenomenon. Where Does The Soot Come From? Soot
is a product of incomplete combustion of
carbon-containing fuels, usually petroleum-based.
Complete combustion would, in theory, produce practically
no soot or carbon monoxide, and is recognized by a blue
flame. This applies to all types of combustion processes
including natural gas flames, wood fires and candle
flames. While it is understood that soot can be generated
by any combustion process, most flames that are used in
homes are either vented or are carefully controlled, such
as gas stoves with a notable blue flame. Through
interviews with over
Why Does Soot Deposit? When
soot builds up in the air of a house, it eventually
deposits onto surfaces due to random What are the Possible Health Concerns? While the soot is suspended in the air, occupants are at risk of inhalation exposure. Since the particles are less than 1 micron (m m) in diameter, they potentially can penetrate the deepest areas of the lung. While some studies have looked at the health risks associated with microscopic soot generated from diesel exhaust and factory emissions, none have considered the residential exposure due to candles. The greatest exposure to soot produced by candles is expected during candle burning, so increasing ventilation by opening windows would reduce occupant exposure. Once the soot particles are deposited onto surfaces, they tend to remain attached and are unlikely to be inhaled by occupants. No evaluation on the effects of soot ingestion (swallowing) has been accomplished. Removal from surfaces is difficult, but can be accomplished with polar solvents. For hard plastic surfaces, rubbing (isopropyl) alcohol is effective at removing soot deposits. Microscopic soot particles have been recognized by the US EPA and the State of California as responsible for aggravation of respiratory illnesses in the general population. Caution is warranted until specific health impacts are studied since the soot created by candles is small enough to enter the lower respiratory tract. What Should Be Done to Remedy the Soot Deposition? First, cease candle burning and periodically ventilate the home by opening windows. Install an improved air conditioning filter, such as a pleated electret media filter. Consult a cleaning service experienced in fire restoration for cleaning surfaces. Not enough is known as to whether soot can be successfully removed from duct work. Candles with the following characteristics have the potential to produce excessive soot:
Is It Possible to Burn Candles Indoors Without Causing Soot Damage? Candle soot has been a problem since Colonial America. All candles that emit a yellow flame produce some soot, but usually at a rate that does not cause high indoor concentrations. Consider using candles with the following characteristics:
And take these precautions when using candles:
This article was written by David Krause and modified for this site by Ronald B. Bailey. For more information, e-mail:
David Krause, Indoor Air Solutions, Inc., Tampa, FL or
Ronald B. Bailey, PE, CIAQ, CHH, Bailey Engineering
Corporation, Palm Beach Gardens, FL ron@baileyeng.com |
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50 homeowners who have experienced Black
Soot Deposition (BSD), it has become evident that a
common source of soot is candles. Until recently, the
amount of soot produced by candles had not been measured.
Results from a recent experiment using a controlled
chamber have revealed that certain candles, with
predictable regularity, can produce up to 100 times more
soot than low-soot-producing candles. In effect, burning
one candle can be equivalent to burning 100 candles at
once. It was also demonstrated that a candle placed in an
air draft can increase its soot production by a factor of
50. The assumption by most consumers, that candles could
not produce enough soot to cause the damage seen in their
home, is unfounded. In fact, soot production from certain
candles can be significant and may cause indoor levels of
airborne soot to exceed concentrations allowed in outside
air by the Environmental Protection Agency of the Federal
Government. 
collisions
with surfaces. When particles collide and grow in size,
they gain enough mass to deposit due to gravity. Other
environmental factors may possibly shorten the time
necessary for soot to deposit, but it should be
understood that eventually the soot will deposit onto
surfaces. Such factors as low ventilation rates of the
homes and the use of ionizing electronic air cleaners may
increase the rate at which soot deposits onto surfaces,
but further research is necessary to establish their
exact influences. Soot created by candles is .06-.1
micron (mm) in diameter. Particles of this size can
penetrate almost all home air conditioning filters and
can severely reduce an electronic air cleaner's ability
to remove them from the air. A small percentage of the
particles do impact onto air conditioning filters and
appear as black, oily deposits. Soot is also attracted to
cooler surfaces due to thermophoresis, a process in which
particles migrate under the influence of forces created
by a temperature gradient. This contributes to soiling of
wall surfaces over studs and air conditioning supply
vents. These particles are also attracted to electrically
charged surfaces such as some injection-molded plastic
items including medicine cabinets, internal surfaces of
freezers, plastic vertical blinds and computers.