Insurance and commercial property management companies have noted an increase in claims due to black spot stains on ceilings, walls, furniture, content and HVAC filters from previously unidentified sources. The problem is referred to as “black soot deposition” (BSD) and, as research indicates, it is frequently caused by a common household decorative item.

There is no evidence of a sudden or accidental source for BSD, such as malfunctioning furnaces, gas water heaters, cigarette smoke or cooking by-products. Until recently, there was little compelling evidence to assign proper blame for the source of BSD. Tests have confirmed, however, it is very possible decorative scented candles are a primary culprit.

Low-quality candles often to blame

Research indicates increased BSD is often the result of candle manufacturers adding additional fragrance oils to their products, along with improper wick trimming by customers. Many fragrance oils are not suitable for combustion and do not burn cleanly. It also appears that many amateur candle-makers have entered the expanding market to capitalize on the current popularity of candles without proper training or experience.  The outcome is an abundance of low-quality candles burning in many homes and a corresponding increase in the frequency of indoor soot deposits.

Potential dangers to structure and health

The number of aromatic candle manufacturers, professional and amateur, grows each year. A number of these introduce candles to their product line without the knowledge necessary to produce a safe and clean-burning product. Chemical testing provides conclusive evidence that emissions from some burning candles contain more than twenty volatile organic compounds, lead and a significant amount of carbon.

Burning scented candles inside homes, apartments and commercial buildings can present serious health hazards to those living and working there. It can also mean damage to ventilation systems, furnishing and content. Evidence suggests breathing even one micron of particulate soot can be hazardous. The Environmental Protection Agency (EPA) and American Lung Association (ALA) have determined breathing particulate matter 2.5 microns or smaller is detrimental to human health. These particles are dangerous because they are inhaled deeply into the lungs, causing irritation and respiratory problems. Those at extra risk include people with heart or lung disease, children and the elderly.

Initial Signs of BSD

The first visible indication of candle soot deposits in a structure is often a dingy gray look appearing on light-colored upholstery or fabrics. Plastic items may accumulate a black film, electronic equipment shows discoloration near vents and a thin black residue develops on television and computer screens.

In homes, apartments and commercial buildings with wall-to-wall carpet, connections and door undercuts may begin to show dark spots or discoloration. Deposits can also be found on draperies, vertical blinds and bed ruffles.

Testing proves key in identifying primary source of BSD

To prove damage can result from such candles, testing was conducted in a model home in Florida. The structure was 2,800-square-feet and featured a central air conditioning system. Four candles were burned and the resulting soot deposits were so noticeable after just three days that testing was discontinued. Total candle-burning time was less than sixty hours.

An additional test was conducted in a 144-square-foot room using candles taken from the same model home. During the test, particulate levels rose above 11 million particles per cubic foot within thirty minutes.

The science behind BSD

When candle materials burn inefficiently, it is because combustion is incomplete. The resulting black soot is hydrocarbon-based. Candle soot production normally begins when the particulate matter produced reaches .06 to 0.1 microns in size. Soot adheres to plastic and optical devices because they are statically charged.

For soot deposits to accumulate, a driving force (i.e., gravity, electrostatic attraction or a forced-air unit) must be in place to push the particulate matter against a surface.

Over time, these soot particles unite with each other and with dust particles in the air. When this soot is released into the air of a building, it eventually deposits onto surfaces because of random collisions between particles. This effect is referred to as Brownian Motion (an assumed random movement of suspended particles). When these particles unite and grow in size, they gain enough mass to deposit via gravity.

If a homeowner, resident or business manager contacts you about these mysterious black spots, check the décor of the structure with an eye out for scented candles. They may help the air temporarily smell better but can also render it harmful to the building and its inhabitants.

Steps to help eliminate BSD

Begin by refraining from burning all candles. If possible, air-out the structure by opening windows. Inspect the air conditioner filter and, if necessary, replace it. Consider using a high-efficiency filter, like a charged media filter. For structural and content damage, call on an IICRC certified firm with experience in fire and smoke restoration.

Purchase quality candles (see below) and trim wicks properly (down to a quarter-inch after each burning). Burn candles for no more than an hour at a time and allow for cool-down period before re-lighting. Do not burn candles under a draft, like vents or near fans and heaters.

For more information

A good reference source for candle information is the National Candle Association, a group promoting safety, quality and industry standards. The website offers useful information, including a list of members that have pledged their professional commitment to quality candles and candle-making