Soot, Char, & Ash: It’s More Toxic Than You Think (2023)

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Soot, Char, & Ash: It’s More Toxic Than You Think (1)

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By Sean M. Scott & Briana C. Scott

When you think of charred wood, ash left behind after a wildfire, or soot, you might think that they are little more than harmless byproducts of incomplete combustion. Afterall, haven’t people cooked their food and kept warm by burning wood in their stoves and fireplaces for millennia?

When you see photos taken in the aftermath of structure fires or wildfires, where people are trying to salvage valuables, assess the damage, or clean up, it is rare to see people wearing proper respirators, Tyvek suits, or other PPE. Images of people sifting through the ash in their street clothes to find valuables or walking through a burned-out home in shorts and flip-flops gives the impression that post-fire environments are relatively safe. However, this is far from the truth.

Risks of Exposure to Burned Wood

The World Health Organization estimates that roughly 4 million people worldwide die prematurely each year from diseases caused by the domestic burning of wood. (1) The WHO states “While the situation in developing countries, where people often cook over open fires in their homes, is more dire, wood burning is nonetheless becoming a major public health concern in the developed world as well. In Denmark, pollution from wood burning now contributes approximately 50% “of all health damages from Danish pollution sources” according to a 2016 report by the Danish Ecological Council. The Danish Centre for Environment and Energy at Aarhus University has estimated that wood stoves cost that country approximately $800 million in annual air pollution-related costs. According to the Danish Ecological Council, pollution from wood burning is now the most health damaging and expensive environmental problem in Denmark, causing several times more harm than fine particles from domestic road traffic.” (2,3)

That being said, maybe there’s more to the story about soot, char, and ash that first responders, restorers, insurance adjusters, and fire survivors need to be aware of.

Soot and Sir Percivall Pott’s Discovery

Soot, Char, & Ash: It’s More Toxic Than You Think (2)Sir Percivall Pott (1714-1788) was an English surgeon and the first scientist to demonstrate that cancer may be caused by an environmental carcinogen. In 1775, Pott found a correlation between chimney sweeps’ exposure to soot and a high incidence of a condition called “soot wart”, a cancer later found to be squamous cell carcinoma. The cancer primarily affected chimney sweeps who had been in contact with soot since their early childhood.

In the 1700s and early 1800s, boys (often orphans) as young as 4 years of age, known as “climbing boys”, were used as chimney sweeps due to their small size, which allowed them to fit inside chimney flues. During this time in history, most people burned wood in their fireplaces to keep warm. It wasn’t until the early 1800s that coal was being widely used.

Soot, Char, & Ash: It’s More Toxic Than You Think (3)

A chimney sweep with a child apprentice

Boys as young as 8 years old contracted the disease and many suffered an array of other debilitating illnesses resulting in respiratory and cardiovascular ailments and even blindness. It is believed that dermal absorption, inhalation, and ingestion of soot and creosote triggered the diseases.

Pressure Treated Lumber

Most buildings in the U.S. contain pressure treated lumber. Because of its ability to resist rot, fungi, and termites, it is commonly used for outdoor fencing, decks, and picnic tables. It is also widely used as a substitute for standard lumber in areas where termites are a problem, such as Hawaii where termites cause roughly $100 million dollars in damage annually. (4,5)

Soot, Char, & Ash: It’s More Toxic Than You Think (4)

Pressure treated lumber being manufactured

Prior to 2003, pressure treated lumber was manufactured with a chemical known as Chromated Copper Arsenate (CCA), which contained arsenic. Arsenic is a toxic heavy metal classified by the EPA as a known carcinogen. Exposure to arsenic can cause a wide range of diseases, including cancers of the lungs, skin, liver, kidney, prostate, and bladder. CCA contains 47.5% hexavalent chromium, 18.5% copper, and 34% inorganic arsenic. Even if pressure-treated wood doesn’t contain CCA, it still contains other hazardous insecticide and fungicide chemicals.

Ammoniacal Copper Zinc Arsenate (ACZA) is a newer formula and successor of CCA. It consists of copper, zinc, and arsenic. Unfortunately, ACZA is also harmful when burned, and exposure to it increases the risk of chronic respiratory disease and cancer. (6,7) Here is a Safety Data Sheet that supports the fact that ACZA is carcinogenic:

When pressure treated wood burns, the heat does not destroy the arsenic it contains. Burning this wood releases the chemical bond that holds the arsenic in the wood where it becomes part of the soot and ash. According to the Journal of American Medical Association, even minute amounts of the “fly ash” from burning treated wood can have serious health consequences.

In 1982, The Journal of the American Medical Association reported on a family in Wisconsin that burned CCA treated wood. All the family members suffered severe recurring nosebleeds, extreme fatigue, and debilitating headaches. The parents complained about ‘blacking out’ for periods of several hours, followed by extended periods of extreme disorientation. The two youngest children had multiple seizures described as grand mal from birth to 1 year. They displayed recurrent “measles-like” rashes on their bodies, as well as reddened thickened skin on the soles of their feet. Most striking was recurring seasonal alopecia, ranging from thinning of the hair in the parents to complete baldness in the youngest children. The symptoms were traced to breathing minute amounts of arsenic laden dust.

Soot, Char, & Ash: It’s More Toxic Than You Think (5)It was later discovered that the home had been heated with a small wood stove in which pressure treated wood was burned. The ashes from the stove spread throughout the home, and test results showed that the ash contained more than 1,000 ppm of arsenic. Source: The Journal of the American Medical Association May 11, 1984, Volume 251 (JAMA 1984;251:2393–2396) (8,9)

Fire survivors and restoration practitioners should be aware that although CCA treated wood for residential use was banned in 2003, risk of exposure to arsenic laden particulate and ash remains high in buildings where treated lumber has burned, especially in the form of fine or ultrafine airborne particulate. When inhaled, ultrafine particles behave like gases and pass through the lungs directly into the bloodstream. These particles can also travel through the nose and affect the central nervous system via the olfactory nerve.

Arsenic is more toxic than lead and it should be noted that OSHA’s permissible exposure limit (PEL) for arsenic is 10 micrograms per cubic meter of air (10 µg/m3) in comparison with lead, which is 50 micrograms per cubic meter of air (50 μg/m3).

Safety Data Sheet (SDS) Information for Wood Ash

In the restoration industry, Safety Data Sheets (SDS’s) are required documents that provide information about the hazards of a product and advice about safety precautions. The following selected information was copied from Weyerhaeuser Safety Data Sheet WC 173-10 Rev. 4/22/2021 for Wood Ash as an example of how toxic this substance is. The SDS can be found here:

Hazard(s) Identification Signal Word: DANGER

Soot, Char, & Ash: It’s More Toxic Than You Think (6)

Prolonged or repeated inhalation exposure to respirable crystalline silica may cause lung cancer and permanent damage to the respiratory system.

  • Carcinogen Category 1A – Crystalline silica may cause lung cancer
  • Specific Target Organ Toxicity (STOT) May cause damage to the respiratory system through prolonged or repeated exposures if inhaled.
  • Eye corrosion – Category 1, Skin irritant Category 2 – Causes skin burns and serious eye damage
  • Acute Toxicity – Category 4 – Corrosive, harmful if swallowed

Composition/Information on Ingredients – Wood char and ash may contain trace (ppt levels) amounts of dioxin compounds.

Exposure Control Measures/Personal Protection

Personal Protective Equipment:

  • RESPIRATORY PROTECTION – Use NIOSH-approved filtering face piece respirator (“dust mask”) or higher level of respiratory protection as indicated and goggles where ventilation is not possible and exposure limits may be exceeded or for additional worker comfort or symptom relief. Following a determination of risk from potential exposures, use respiratory protection in accordance with requirements such as US-OSHA respiratory protection standard 29CFR 1910.134.
  • PROTECTIVE GLOVES – Cloth, canvas, or leather gloves are recommended when handling the dry product to minimize potential mechanical irritation. Discard gloves with contaminated interiors.
  • EYE PROTECTION – An emergency eye wash fountain should be present near areas of potential eye exposure. Goggles or safety glasses are recommended when handling this product.
  • OTHER PROTECTIVE CLOTHING OR EQUIPMENT – An emergency shower should be present near areas where extensive skin contact is possible. Protective clothing with long sleeves or disposable outer garments may be desirable in extremely dusty areas.
  • WORK/HYGIENE PRACTICES –The use of barrier skin cream may prevent skin irritation in susceptible individuals. Be aware that irritation may occur where PPE such as goggles or dust masks contact skin surfaces.

Signs and Symptoms of Exposure:

Chronic Health Hazards: Prolonged inhalation of crystalline silica may result in silicosis, a disabling pulmonary fibrosis characterized by fibrotic changes and miliary nodules in the lungs, a dry cough, shortness of breath, emphysema, decreased chest expansion, and increased susceptibility to tuberculosis. Advanced silicosis may result in death due to cardiac failure or destruction of lung tissue. Chronic inhalation of sufficient quantities of crystalline silica may also cause lung cancer.

Carcinogenicity Listing:

Wood ash is considered to be a hazardous chemical in accordance with OSHA classification criteria. Since respirable crystalline silica may be present in the material, refer to OSHA standards 1910.1053 (General Industry) and/or 1926.1153 (Construction) if applicable.

The National Institute of Occupational Safety and Health defines an immediately dangerous to life or health (IDLH) condition as a situation “that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment.” Fire survivors, restorers, insurance adjusters, or anyone else who needs to enter a fire damaged structure where wood has burned, should be aware of the health risks and always wear proper personal protective equipment.


  1. World Health Organization:
  3. Green Transition Denmark:
  4. College of Tropical Agriculture & Human Resources – University of Hawaii at Manoa:
  5. US National Library of Medicine National Institutes of Health:
  7. Montana Boy Scouts of America
  8. The Journal of the American Medical Association:
  9. US National Library of Medicine National Institutes of Health:

Soot, Char, & Ash: It’s More Toxic Than You Think (7)Sean is the Author of Secrets of the Insurance Game and The Red Guide to Recovery – Resource Handbook for Disaster Survivors. Sean has also written numerous articles and papers on smoke and fire related issues. If you would like more information, please feel free to contact Sean Scott at

Soot, Char, & Ash: It’s More Toxic Than You Think (8)Briana is the co-author and editor for Heritage Publishing & Communications. She has been instrumental in providing and interpreting information regarding the ecological effects of disasters. Briana also adds invaluable knowledge and understanding of scientific processes and her research has helped raise awareness of a wide range of post-disaster health and environmental hazards.


Is fireplace ash harmful to humans? ›

The ash deposited by forest fires is relatively nontoxic and similar to ash that might be found in your fireplace. However, any ash will contain small amounts of cancer-causing chemicals. In addition, fire ash may be irritating to the skin, especially to those with sensitive skin.

What is the meaning of ash and soot? ›

Soot, ash & char are byproducts of incomplete combustion produced from the burning of organic matter. They are most easily recognizable as fine powdery dust, embers, debris and blackened, destroyed materials which constitute the spent remains after fire.

Is ash and soot the same thing? ›

Soot is easily distinguished from the residual ash by its dark color. The ash, in comparison, is much lighter in color and is composed of primarily metallic components which are incombustible. Although many sources contribute to ash, the majority of the ash originates in the engine oil.

Are wood ashes harmful? ›

Wood ash contains a surprising array of heavy metals (e.g., zinc, nickel, copper, lead, chromium, arsenic, cadmium and mercury, among others). In high enough concentrations, these can cause problems for people and aquatic and terrestrial environments.

Is charred wood toxic? ›

Polycyclic Aromatic Hydrocarbons (PAHS), which cause cancer and are also found in cigarette smoke and chimney soot. Volatile Organic Compounds, such as benzene, which cause cancer. Dioxins, which are highly carcinogenic, are also produced when wood is burned.

Is charcoal ash toxic? ›

Ash from untreated charcoal can be used in your garden. Treated (typically sold as 'easy to light') charcoal ashes shouldn't be used as they can be toxic. The ash from treated charcoal will need to be disposed of in your residual waste bin (i.e. sent to landfill).

What does the Bible say about ash? ›

When Abraham talks to God in Genesis 18, asking him to spare Sodom, he says, “Behold, I have undertaken to speak to the Lord, I who am but dust and ashes.” In summary, the Bible uses dust and ashes to refer to mankind's humble origin, feeble composition, and temporal nature.

Is soot and charcoal the same thing? ›

Soot is a byproduct of burning fossil fuels, particularly coal.

Where is dust to dust in the Bible? ›

Dust to dust is mentioned in Ecclesiastes 3:20, "All are from the dust, and to dust all return." In the Bible, this passage emphasizes that humans and animals are no different and that everyone is made up of the earth and will return to the earth.

What is the difference between char and ash and soot? ›

Ash includes trees and vegetation but can also include building material or any other burned object. Char is a black carbon substance produced when a substance or material does not completely burn. It is darker than ash. Soot is also a black carbon substance produced when a material on fire does not completely combust.

What is the difference between char and soot? ›

Char and soot differ in content of elemental carbon and organic carbon. Soot can be identified by PAHs, nitriles, heterocyclic nitrogen, benzofurans. Char consists of organic products of thermal decomposition of lignin a cellulose. Chemical composition of residues can be utilized for identification of burned fuel.

Is soot left after a fire? ›

Smoke particles, also known as soot or char, are carbon residue that remains after a fire. Since soot particles are acidic, they smudge easily and cling aggressively to walls.

Why is it bad to keep ashes in the house? ›

There are some superstitions about keeping ashes in the home

Some people worry it's bad luck to keep ashes in their house, or it might mean the spirit or ghost of the person will stay in the house. Whatever your beliefs, there is no right or wrong when it comes to handling the ashes of a person who's died.

What happens to ash when it gets wet? ›

Ash is hard, abrasive, mildly corrosive, conducts electricity when wet, and does not dissolve in water.

Is ash wood carcinogenic? ›

Not only does this cause air pollution, it also generates enormous quantities of ash, containing toxic substances including heavy metals and carcinogens.

What is the safest wood to burn? ›

When hardwoods are burned in good conditions for a fire, they produce very little smoke or unhealthy particulate matter. A few examples of the most popular hardwoods for fires are white oak, ash, birch, red oak, hard maple, beech, hickory, pecan, dogwood, apple, and almond.

Is burning wood cancerous? ›

Much like cigarette smoke, wood smoke contains hundreds of air pollutants that can cause cancer and other health problems. One of these pollutants that is of most concern is fine particles.

What wood is toxic to smoke out of? ›

Avoid wood from conifers such as pine, redwood, fir, spruce, cypress, or cedar. These trees contain high levels of sap and turpenes, which results in a funny taste and can make people sick. Cedar planks are popular for cooking salmon, but don't burn the wood for smoke.

Does Kingsford charcoal have chemicals? ›

This product does not contain any Proposition 65 chemicals.

What kind of wood is in Kingsford charcoal? ›

Kingsford Charcoal is made from charred soft and hardwoods such as pine, spruce, hickory, oak and others depending on which regional manufacturing plant it comes from. That char is then mixed with ground coal and other ingredients to make a charcoal briquette.

Is charcoal ash carcinogenic? ›

Charcoal itself is not a carcinogen, but cooking with charcoal does have a link to cancer. There are two main reasons for this. The first risk of charcoal use is that you're cooking foods at very high temperatures, the second is that charcoal cooking creates a lot of smoke.

Is cremation against the Bible? ›

According to most Biblical study websites, there is no explicit scriptural command for or against cremation. There are no passages that forbid cremation, according to most Biblical scholars.

Where in the Bible does it say not to scatter ashes? ›

In the Bible, there are no passages that prohibit or encourage cremation and scattering of ashes. However, many Christian sects believe a burial funeral aligns with best end-of-life practices.

Does the Bible approve cremation? ›

Since the Bible does not ban nor promote cremation, most Christian denominations do not consider cremation to be sinful.

What are the effects of soot on humans? ›

The small size of particulate matter allows it to easily enter the lungs and bloodstream. This can cause serious effects including heart attacks, bronchitis, aggravated asthma, strokes, and even premature death. There are several harmful environmental side effects associated with soot.

What are the health effects of soot? ›

Soot is a dangerous pollutant that increases the risk of asthma, heart attacks, strokes and cancer. Evidence shows that the U.S. EPA's current limit of 12 micrograms per cubic meter is harmful to public health.

What is soot good for? ›

Chimney Soot is high in Potash is a major nutrient that is essential for good fruiting and flowering and it also helps the plants get through the winter. It can also be a useful additive to the compost heap or can be applied directly to fallow ground and dug in.

What does ashes mean spiritually? ›

The ashes symbolize both death and repentance. During this period, Christians show repentance and mourning for their sins, because they believe Christ died for them.

What does the Bible say about tattoos? ›

But in the ancient Middle East, the writers of the Hebrew Bible forbade tattooing. Per Leviticus 19:28, “You shall not make gashes in your flesh for the dead, or incise any marks on yourselves.”

What does the Bible say about funeral rites? ›

The Bible held several customs for burial. Traditions affirmed that after a person breathed the last breath, the eyes were shut and closed (Gen 46:4). The law required that burial of the dead occurred the same day, before sundown (Lev 10:4; Deut 21:23).

Does soot smell like smoke? ›

Soot also has an odor that smells like smoke or burnt materials. When the soot spreads around your property after a fire, the unpleasant odor often spreads with it.

Is ash the same as smoke? ›

When wood and other organic matter burn, they produce smoke, a complex mixture of gases and fine particles. Ash is deposited on the ground, and often stirred up into the air by winds. One of the biggest health threats from smoke comes from fine particles.

Where does soot and ash come from? ›

Incomplete combustion means that there is not enough oxygen present when the material is burned to completely consume the fuel. Instead of only carbon dioxide and water vapour being created, incomplete combustion can result in the production of soot, smoke, and ash.

Does soot mean carbon monoxide? ›

The presence of a large amount of soot around your furnace can indicate that your furnace is giving off carbon-monoxide due to partial combustion. If you have a carbon monoxide detector in your home, this might start going off to tell you – if you don't have one, it's a good idea that you do.

Does smoke have soot? ›

All smoke contains carbon monoxide, carbon dioxide and particulate matter (PM or soot).

Does char mean fire? ›

To char is to burn or blacken something so that it's like charcoal but still tasty. A char is something that has been burned in this way. To char is to burn something on the outside. If you've ever eaten a hot dog or hamburger cooked over an open flame, it was charred.

Is it safe to use dishes after a house fire? ›

Dishes. You may be asking yourself, is it safe to use dishes after a house fire? As long as your plates, pots, utensils and other kitchen items are thoroughly cleaned, they should be safe to use. However, plastic and wood dishes will likely need to be thrown out because smoke can be easily absorbed into these materials ...

What to do if you breathe in soot? ›

Get plenty of rest and sleep. You may feel weak and tired for a while, but your energy level will improve with time. Prop up your head on pillows to help you breathe and ease a cough. Suck on cough drops or hard candy to soothe a dry or sore throat.

What removes soot? ›

Regular white vinegar is one of the most versatile cleaners. Not only will it break down oily soot stains, but it can even remove set-in nicotine stains. Mix one part warm water to three parts vinegar, then wipe gently with a soft sponge or microfiber cloth to remove soot from walls, ceilings, or woodwork.

Is fireplace smoke toxic? ›

Smoke may smell good, but it's not good for you. The biggest health threat from smoke is from fine particles, also called fine particulate matter or PM2. 5. These microscopic particles can get into your eyes and respiratory system, where they may cause burning eyes, runny nose, and illnesses, such as bronchitis.

Is ash a toxic substance? ›

Some of the compounds found in coal ash can cause cancer after continued long-term ingestion and inhalation. When a natural disaster occurs, contamination from coal ash can affect drinking water systems. Public water systems monitor and control for these types of contaminants.

Is ash good to burn indoors? ›

Because of the low amount of smoke that Ash firewood produces it's a great wood to burn in indoor fireplaces.

Is it OK to dump fireplace ashes in the garden? ›

Wood ash can be used sparingly in gardens, spread thinly over lawns and stirred thoroughly into compost piles. Lawns needing lime and potassium benefit from wood ash — 10 to 15 pounds per 1,000 square feet, Perry said. “This is the amount you may get from one cord of firewood,” he said.

Should you leave ashes in wood stove? ›

Note: Always leave a layer of ashes in the bottom of the stove. It insulates the firebox and makes it easier to light a fire.

Where is the best place to dump fireplace ashes? ›

To be safe, Endee recommends taking the metal buckets of ashes out of the house immediately after collecting them and disposing of them in a secure location, such as on top of a snowbank in the winter or in a moist area in warmer months away from dry grass or weeds.

Are Duraflame logs toxic? ›

Are firelogs or firestarters toxic if my pet eats part of them? Our firelogs are made of sawdust, agricultural fibers, waxes and oils; we are not aware of any ingredients that would cause a chemically toxic reaction should your pet consume a small amount of these products.

What wood should not be burned in a fireplace? ›

What kind of wood SHOULD NOT be burned in the fireplace? Don't burn driftwood in your fireplace. Driftwood is loaded with salt, and the chlorine in salt mixes with wood compounds during burning to release a toxic chemical, one that's been linked to cancer. Don't burn treated, painted, or sealed wood in your fireplace.

Why does my house smell like smoke after using fireplace? ›

Smokey odors from your fireplace are usually safe and simply indicate that your fire is burning. However, if you notice a strong smoke smell, it could be a sign that your chimney is blocked. A blocked chimney can cause dangerous buildup of carbon monoxide in your home.

Is black ash toxic? ›

Allergies/Toxicity: Ash in the Fraxinus genus has been reported to cause skin irritation, and a decrease in lung function.

Can you get sick from inhaling ash? ›

Contacts. Breathing coal ash dust can trigger asthma attacks, lead to cancer and lung disease and other serious health problems according to a new report released today by Physicians for Social Responsibility and Earthjustice.

Why is ash toxic? ›

Coal ash contains contaminants like mercury, cadmium and arsenic. Without proper management, these contaminants can pollute waterways, ground water, drinking water, and the air.

How long do ashes stay hot in a fireplace? ›

FACT: Coals and ashes from fires can remain hot enough to start a fire for many days after the fire is out. The exact amount of time for complete extinguishment and cooling depends on many factors such as how hot the fire was, what was burning, how much unburned fuel remains, etc.

Does ash create a lot of creosote? ›

Conversely, ash does not produce a high amount of creosote. Creosote is the black, tar-like substance you may have seen building up around a fireplace or chimney. It's a deposit caused by regular wood burning, but only some types of wood produce large volumes of creosote.

What is the best wood to burn in a fireplace? ›

Hardwoods such as maple, oak, ash, birch, and most fruit trees are the best burning woods that will give you a hotter and longer burn time. These woods have the least pitch and sap and are generally cleaner to handle.


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