Creosote or pitch oil is the name used for a variety of products that include wood creosote and coal tar creosote. The word is also used to describe the black oily accretion that builds up inside of chimney flues as a result of incomplete burning of wood or coal. Commercially, wood creosote is created by high temperature treatment of beech and other woods, or from the resin of the creosote bush.
Coal tar creosote is an EPA-registered wood preservative. It is distilled from crude coke oven tar, and is mainly composed of polycyclic aromatic hydrocarbons (PAHs), but also contains phenols and cresols.
Wood creosote is a colourless to yellowish greasy liquid with a smoky odor and burned taste. Other than looks and taste, the chemical makeup is totally different to coal tar creosote. It is made of plant phenolics rather than petrochemicals: guaiacol, creosol, o-cresol, and 4-ethylguaiacol.
Wood creosote also protects wood from shrinking from the sun, losing its colour and moulding from the rain. Many companies use creosote to protect wood.
Coal tar creosote
Another form of creosote is coal tar creosote. Coal tar creosote is the most widely used wood preservative in the world. It is a thick, oily liquid typically amber to black in colour. The American Wood Preservers' Association states that creosote "shall be a distillate derived entirely from tars produced from the carbonization of bituminous coal." Coal tar used for certain applications may be a mixture of coal tar distillate and coal tar. See, AWPA Standards
The prevailing use of creosote is to preserve wooden utilities/telephone poles, railroad cross ties, switch ties, and bridge timbers from decay. Coal tar products are also used in medicines to treat diseases such as psoriasis, and as animal and bird repellents, insecticides, animal dips, and fungicides. Some over the counter anti-dandruff shampoos contain coal tar solutions. Due to its carcinogenic character, the European Union has regulated the quality of creosote for the EU market  and requires that the sale of creosote be limited to professional users.
Creosote in chimney flues
Burning wood and fossil fuels at low temperature causes incomplete combustion of the oils in the wood, which are off-gassed as volatiles in the smoke. As the smoke rises through the chimney it cools, causing water, carbon, and volatiles to condense on the interior surfaces of the chimney flue. This leaves a black oily residue referred to as "creosote", which is similar in composition to the commercial products by the same name, but with a higher content of carbon black.
Over the course of a season creosote deposits can become several inches thick. This creates a compounding problem, because the creosote deposits reduce the draft (airflow through the chimney) which increases the probability that the wood fire is not getting enough air to burn at high temperature.
Since creosote is highly combustible, a thick accumulation creates a fire hazard. If a hot fire is built in the stove or fireplace, and the air control left wide open, this may allow hot oxygen into the chimney where it comes in contact with the creosote which then ignites - causing a chimney fire.
Chimney fires often spread to the main building because the chimney gets so hot that it ignites any combustible material in direct contact with it, such as wood. The fire can also spread to the main building from sparks emitting from the chimney and landing on combustible roof surfaces.
In order to properly maintain chimneys and heaters that burn wood or carbon based fuels, the creosote buildup must be removed. Chimney sweeps perform this service professionally.
73% of heating fires and 25% of all residential fires in the United States are caused by failure to clean out creosote buildup.
Since 1990 the number of creosote caused fires has decreased in the United States by 75%. This is partly due to the use of efficient wood stoves that fully burn the volatiles in the smoke, and partly due to the decrease in the use of wood heating during two decades of milder Winter weather, and low fuel prices.
The best practices to avoid chimney fires are:
- Use a high efficiency stove or heater that fully burns the volatiles in the smoke.
- Make sure the wood is seasoned (not just dry on the surface) before burning.
- Avoid burning coniferous woods (spruce, pine, fir) as much as possible.
- Inspect the chimney throughout the burning season.
- Clean the chimney annually or more frequently if needed.
Health effects of coal tar creosote
According to the Agency for Toxic Substances and Disease Registry (ATSDR), eating food or drinking water contaminated with high levels of coal tar creosote may cause a burning in the mouth and throat, and stomach pains.
ATDSR also states that brief direct contact with large amounts of coal tar creosote may result in a rash or severe irritation of the skin, chemical burns of the surfaces of the eyes, convulsions and mental confusion, kidney or liver problems, unconsciousness, and even death. Longer direct skin contact with low levels of creosote mixtures or their vapors can result in increased light sensitivity, damage to the cornea, and skin damage. Longer exposure to creosote vapors can cause irritation of the respiratory tract.
The International Agency for Research on Cancer (IARC) has determined that coal tar creosote is probably carcinogenic to humans, based on adequate animal evidence and limited human evidence. It is instructive to note that the animal testing relied upon by IARC involved the continuous application of creosote to the shaved skin of rodents. After weeks of creosote application, the animals developed cancerous skin lesions and in one test, lesions of the lung. The United States Environmental Protection Agency has stated that coal tar creosote is a probable human carcinogen based on both human and animal studies. As such, the Federal Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 0.2 milligrams of coal tar creosote per cubic meter of air (0.2 mg/m3) in the workplace during an 8-hour day, and the Environmental Protection Agency (EPA) requires that spills or accidental releases into the environment of one pound (0.454 kg) or more of creosote be reported to them.
There is no unique exposure pathway of children to creosote. Children exposed to creosote will probably experience the same health effects seen in adults exposed to creosote. It is unknown whether children differ from adults in their susceptibility to health effects from creosote.
A 2005 mortality study of creosote workers found no evidence supporting an increased risk of cancer death, as a result of exposure to creosote. Based on the findings of the largest mortality study to date of workers employed in creosote wood treating plants, there is no evidence that employment at creosote wood-treating plants or exposure to creosote-based preservatives was associated with any significant mortality increase from either site-specific cancers or non-malignant diseases. The study consisted of 2,179 employees at eleven plants in the United States where wood was treated with creosote preservatives. Some workers began work in the 1940s to 1950s. The observation period of the study covered 1979- 2001. The average length of employment was 12.5 years. One third of the study subjects were employed for over 15 years.
The largest health effect of creosote is deaths caused by residential fires.
Cite error: Invalid
parameter "group" is allowed only.
<references />, or
<references group="..." />
- International Chemical Safety Card 0572
- National Pesticide Information Center - Non-CCA Wood Preservatives
- Creosote fact sheet from the UK Department for Business, Enterprise and Regulatory Reform
- ATSDR creosote FAQ
- Tests of Creosoted Timber, Transactions of the American Society of Civil Engineers, vol. LXX, Dec. 1910, by W. B. Gregory, from Project Gutenberg
- American Wood-Preservers' Association
- Creosote Council
- Status of creosote under European Union Directive 98/8/ECca:Creosota
- Directive 2001/90/EC, http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2001:283:0041:0043:EN:PDF
- Directive 76/769/EEC, http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1976L0769:20071003:EN:PDF
- Revocation of approvals for amateur creosote/coal tar creosote wood preservatives, http://www.hse.gov.uk/biocides/copr/creosote.htm
- U.S. Department of Homeland Security, Topical Fire Research Series, "Heating Fires in Residential Buildings", Volume 6, Issue 3, November 2006, 
- Creosote (CASRN 8001-58-9) http://www.epa.gov/iris/subst/0360.htm
- Creosote, What You Need To Know http://www.losh.ucla.edu/losh/resources-publications/fact-sheets/creosote_english.pdf
- Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.