Shedding Light on Dark Mystery
Candle flames to blame as source of “sooting”
Houses these days are retaining more normal indoor-air contaminants than in the past – including cooking byproducts, cigarette and wood-burning fireplace smoke, moisture from poorly vented or unvented bathrooms and many others. For one thing, residential construction techniques used in last five or 10 years are making houses much “tighter,” so there is less air leaking into and out of them. In addition, many homes use furnaces, fireplaces and even water heaters that are “direct vent” – meaning that both the intake air needed for combustion and the exhaust, or combustion products, are piped directly outside.
In recent years, there have also been numerous reported incidents of “sooting” in homes. Typical symptoms include dark soiling of wall surfaces, dark stains on carpeting in the areas around heat registers or around room perimeters, discolored draperies and mysterious clean areas under furniture. Homes experiencing very serious problems have also noted “ghosting” on walls, usually exterior ones, where studs within the walls actually show up as darker stained areas. It is clear that something within those homes is creating particles that are attracted to these various surfaces. Two possible sources are soot, which is a carbonaceous byproduct of incomplete combustion, and mold. As might be expected, many homeowners place the blame on a faulty or incorrectly installed furnace or gas fireplace. Mold is a much less prevalent – and more easily identified – problem, virtually always resulting from excessive moisture within the home.
There is, however, another relatively common, if unexpected, source: candles. The popularity of candles has been growing tremendously; it is estimated they are used in 70 percent of U.S. households. In most cases, candles are used for special occasions, with perhaps one or two being burned for short time periods. Some candle enthusiasts, however, use a large number of candles on a daily basis. How many candles are too many? There is no simple answer or formula for calculating a safe or desirable number. In a recent test, four candles were burned for a total of 15 hours each (for a total of 60 “candle hours”) in a new model home. This was sufficient to produce soot that was visible on the walls, drapes and appliances, such as the refrigerator and dishwasher.
There are several factors affecting how “sooty” a candle may be. They include flame size, a function of wick size and volatility of the wax being burned; the presence of chemicals to generate an attractive scent; and the shape of the candle and its container. The basic problem with candles, however, is that the very thing that makes them attractive is soot from their inefficient combustion. Without it, there is no bright, dancing yellow flame; instead, it’s blue, much like the flame of a gas stove!
It is safe to say that “all candles are not created equal” and that soot generation levels can vary tremendously among candle shapes and brands. One simple way to test a candle’s soot production is to place a new one near a known source of particle attraction, such as a television screen. Burn the candle for a few hours, then wipe the screen with a clean, white rag or tissue. If soot has collected during this period, continued use of this particular candle type is not recommended. With candle popularity on the rise, all investigations of complaints of staining or sooting in a home should include an examination for evidence of candle usage. Experience shows that candle enthusiasts almost never suspect candles as the source of their problem!
- David P. Hatz, Consulting Chemist