Soot Can Blacken Lungs and Walls

By Jeff May
Jeff is founder and principal scientist of May Indoor Air Investigations LLC in Tyngsboro, MA: www.mayindoorair.com.

He has been investigating building problems for over 20 years and is author or co-author of four books on indoor air quality published by Johns Hopkins University Press, including My House is Killing Me! The Home Guide for Families with Allergies and Asthma and his current book, Jeff May’s Healthy Home Tips: A Workbook for Detecting, Diagnosing and Eliminating Pesky Pests, Stinky Stenches, Musty Mold, and Other Aggravations Home Problems (2008). His work has been featured in Business Week, MD News, and The New York Times, among others. His media appearances include CNN News, “Discovery Health,” “Inside Edition,” and NPR’s “All Things Considered” and “Living on Earth.” Jeff is a nationally recognized speaker and holds an M.A. from Harvard in organic chemistry.

Healthy Home Tips: Soot Can Blacken Lungs and Walls
Soot particles are small enough to be breathed deeply into the lung and even pass directly through capillary walls into the blood stream. The particles may contain carcinogens – such as benzo[a]pyrene – and can also act as “surrogate allergens.” The medical community recognizes that the cornstarch powder in latex gloves (used to keep the rubber from sticking to itself) can acquire latex allergens. When the powdery granules become airborne and are inhaled by someone who has latex allergy, that person can experience an allergic reaction – sometimes severe. Similarly, the microscopic particles of soot that settle on surfaces that contain mold or pet dander can become contaminated with allergenic substances. The particles can then become airborne again and be inhaled when surfaces are cleaned or otherwise disturbed in some way.
Now I have to talk a little bit about chemistry (ugh, groan, I hear you say….but chemistry is one of my favorite subjects!). Complete combustion inside a gas furnace or boiler results in the formation of carbon dioxide (CO2) and water (H2O) vapor. In other words, one atom of carbon (C) from methane (CH4) combines with two atoms of oxygen (O) from the air to produce CO2 (one carbon atom, two oxygen atoms). Four hydrogen atoms combine with two oxygen atoms to form two water molecules (H2O). If the combustion is incomplete, however, some of the carbon combines with only one atom of oxygen, resulting in carbon monoxide, or CO (one carbon atom, one oxygen atom). When there isn’t enough oxygen, combustion is incomplete. Then some carbon atoms combine with oxygen to create carbon monoxide, other carbon atoms combine with oxygen to create carbon dioxide, and still other carbon atoms do not combine with any oxygen but rather they combine with each other to produce soot (“C”).
What creates soot in our indoor environments?
A gas furnace or boiler that is not firing properly or that does not have sufficient make-up air can produce soot. And even though the furnace or boiler may be located in the basement, if the combustion products are getting into the basement air, airflows carry the soot up into habitable rooms above.
Gas fireplaces can produce soot. When soot particles are heated in a flame, the particles become incandescent (glow) and give off a yellow light. The gas in gas fireplaces is not premixed with enough air, so the flames are yellow due to inadequate oxygen (otherwise they’d be blue, like the flames coming from a gas cooking stove – not exactly what people expect to see in a fireplace!). If there is inadequate draft for a gas fireplace that is producing soot, the particles can leak into the house and stain the walls and ceilings black.
People love jar candles, because of their pleasant scents and yellow, flickering flames; but jar candles also produce a lot of soot, even if burned for only a few hours. As the air moves in and out of the jar, it disturbs the flame structure and causes incomplete combustion. If you burn jar candles, look at the jar rim. Is it black with soot? Imagine the soot that candle released into the air that you and those you love then inhale.
Soot staining in older homes can be fairly uniform, sometimes visible only when pictures are removed, revealing whiter surfaces beneath where soot has not deposited – though in some Victorians, the soot pattern mimics the horizontal “stripes” of underlying plaster/lath, darkest at the plaster “keys.” In newer, better-insulated homes, soot stains on exterior walls and on ceilings near exterior walls look like vertical stripes on studs, with darker black dots at the nail heads. Wherever air moves more turbulently due to temperature differentials, the air will impact surfaces that much more frequently and deposit the soot particles it carries in its flows. (Dark spots develop in bathrooms above vanity fixtures for the same reason: increased deposition rate due to hot air rising above the bulbs.)
I know of one homeowner whose insurance company spent $5,000 to have all the rooms in his house repainted. The man continued to burn jar candles, however, and had to repaint the house all over again. So protect the value of your property by choosing tapered candles over jar candles (just don’t burn the candles near a window or door, where airflows may disturb the flame). Better yet, choose the battery-operated, fake candles that look like the real thing.
Of course, money is important, especially in these lean times. But your health and the health of those you love – including your children – are paramount. So stop burning jar candles. If you don’t burn candles and you still see soot stains on your walls or ceilings, have a professional evaluate your furnace or boiler and undertake necessary maintenance or repairs.