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Cashins & Associates Blog

Industrial Hygiene - What is Soot and Why is it Dangerous?

Posted by Zachary Keefe on Wed, Dec, 11, 2013 @ 16:12 PM

The word "soot" sounds so simple and harmless. To some, it conjures up images of campfires and candles, and perhaps a charming dance number from Mary Poppins.

In fact, soot is anything but simple and is certainly not harmless.

Soot includes the fine black particles, chiefly composed of carbon, produced by incomplete combustion of coal, oil, wood, or other fuels. Soot can consist of acids, chemicals, metals, soils, and dust. The common trait of soot particles is that they are extremely tiny – 2.5 micrometers or smaller in diameter. This is smaller than dust and mold, and is about 1/30 the diameter of a human hair.

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This combination – extremely small size and toxic composition – is what makes soot so dangerous. It can travel deep into the lung, where the compounds it consists of can do some serious damage.


Soot is the byproduct of the burning of fossil fuels. This includes burning coal for electricity or industrial fuel, manufacturing, oil refining, and motor vehicles.

Soot enters the environment either as a solid particle or as a gas which turns into a particle after it has been released. These particles can end up very far away from their site of origin.

Soot can also become a problem following a fire. A common house fire results in the burning of a wide variety of materials, from wood and paper to plastics and other synthetic items. This results in soot contamination, and poses a serious cleanup problem.

Soot can also negatively impact Indoor Air Quality. Excessive use of candles in an indoor environment can lead to a buildup of soot. This sometimes leads to "ghosting", where the tiny soot particles cling to areas of walls and ceilings due to electrostatic attraction. This can also happen when fireplaces are insufficiently ventilated. If you see these "soot ghosts" in your home, you may want to rethink your level of candle usage or have your chimney evaluated. 

Risks - Health & Environment

Compounds from soot - sulfur dioxides and nitrogen oxides - combine with moisture to form acid rain, which worsens water quality, damages soil and crops, and changes nutrient balances in various ecosystems.

Breathing the tiny particles can cause coronary heart disease, asthma, bronchitis, and many other respiratory illnesses. 

Research has also shown that many premature deaths are directly related to soot in the environment. Particle exposure leads to around 20,000 premature deaths in America each year. Many of these deaths were caused by soot-related diseases. Data also show that soot annually causes almost 300,000 asthma attacks and 2 million lost workdays due to repiratory problems.


Regulatory Oversight

According to The Clean Air Act, the EPA is required to routinely adjust their allowable limits for soot emissions. In 2012, they were sued by various states and clean air organizations because it had not updated its soot emissions standards. The U.S. District Court for the District of Columbia told the EPA that it had until June 2012 to update the standards, which it accomplished.

Currently the limit is 15 μg/m3, but EPA proposes to change it to between 12 and 13 by 2020.

According to the EPA, the change in the emission standards could result in up to a $5.9 billion annual savings due to a reduction in costs related to premature death and disease. 


Environmental testing firms like Cashins & Associates can help determine whether soot is a problem at your building or facility. We have on staff Certified Industrial Hygienists and Certified Indoor Environmentalists who are well versed at assessing soot contamination issues (typically following a fire episode), deciding what sampling methods are appropriate, and in interpreting the resulting analytical data. If you have questions please submit a free online inquiry and an expert will respond.

Free Safety and Health Inquiry

Topics: indoor air quality, air testing, EPA, indoor air quality Issues, IEQ, Indoor Environmental Quality, IAQ, soot, Clean Air Act, Air Quality

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