Wood burning

Smoldering, smoky fires that produce a plume of blue-grey smoke are the main type of air pollution related to wood burning. This smoke releases many contaminants into the air, such as:

• fine particulate matter (Ministry of the Environment, Conservation and Parks)
• nitrogen oxides (NO2) (Ministry of the Environment, Conservation and Parks)
• carbon Monoxide (CO) (Ministry of the Environment, Conservation and Parks)
• volatile Organic Compounds (VOCs) (Government of Canada)
• dioxins and Furans (Government of Canada)
• polycyclic Aromatic Hydrocarbons (PAHs) (Government of Canada)

Exposure to the pollutants in wood smoke can cause various levels of illness. The effects of the pollutants depends on a person’s exposure and underlying health conditions or predisposing factors. The following is a list of the most common health effects associated with exposure to wood smoke:

• eye, nose and throat irritation
• headaches, nausea and dizziness
• increased respiratory symptoms; such as irritation of the airways, coughing or difficulty breathing
• decreased lung function
• aggravated asthma
• development of chronic bronchitis
• irregular heartbeat
• non-fatal heart attacks
• premature death in people with heart or lung disease

In addition, studies of laboratory animals suggest that prolonged exposure to wood smoke may weaken the immune system.

Breathing wood smoke is not healthy for anyone. Most healthy adults will recover quickly from smoke exposures and will not suffer long-term consequences. However, certain sensitive populations may experience more severe short-term and chronic symptoms from smoke exposure. Populations most at risk of experiencing severe health effects following exposure to wood smoke include:

• individuals with asthma and other respiratory diseases
• individuals with airway hyper-responsiveness
• individuals with cardiovascular disease
• the elderly
• children
• pregnant women
• smokers

Although the practice of wood-burning, be it for home heating or recreational use, will inevitably release some pollutants into the air we breathe, there are ways to minimize the risk.

Studies have shown that in order to have an efficient fire with low wood smoke emissions, only dry clean wood, either hard or soft, should be burned. Other factors such as moisture content, log size, wood condition and tree species will greatly influence how well the wood burns.

Moisture content

Firewood needs to be dry. It is recommended that the firewood be collected in early spring and allowed to dry over the summer months. In order for the wood to dry properly, it is recommended that it be stacked outside, covered and off the ground with room for air to circulate freely between the pieces. The following are ways in which dry firewood could be identified:

• checks or cracks in the ends of the logs
• darker at the ends and weighs less than freshly cut wood
• if you bang two pieces together, you should hear a loud, hollow crack
• if you tap the wood with a key or coin, dry wood should make a sharp resonant sound, wet wood makes a dull sound

Signs that your firewood is not dry enough

• the wood is hard to ignite
• the wood hisses and sizzles in the firebox
• the fire produces more smoke than heat

Log size

It is recommended to use small, finely split pieces of firewood, as small pieces have more surface exposed to the flame and will burn cleaner.

Wood condition

Firewood should not look or feel rotten. Also, wood that has been cut for more than 3 years or that has been lying around in a swampy area will be difficult to burn.

Tree species

Burn a mixture of hardwood and softwood. Hardwood is the preferred firewood since it produces a longer lasting burn, but any type of dry wood will burn. Softwood needs to be used in larger quantities, but is also the most common wood along Canada’s coasts and northern areas.

The term wood burning usually refers to the practice of burning wood for home heating or recreation. However, there are many other types of wood burning or burning of other products that, through their incineration are also contributing to poor air quality and compromised health.

Residential home heating

Residential wood combustion refers to the burning of wood in fireplaces, wood stoves and other devices used to heat the home. These devices produce smoke when wood does not burn completely. If operated incorrectly, even the most modern wood-burning devices can produce smoke.

In order to reduce the risk of health effects from wood smoke, it is recommended that individuals purchase an “advanced combustion” wood stove or fireplace insert that has the Canadian Standards Association (CSA) or the United States Environmental Protection Agency (EPA) sticker/stamp. This symbol signifies that the appliance emits up to 95% fewer particulates and is up to 20% more fuel efficient than conventional models.

While older uncertified stoves and fireplaces release 40 to 60 grams of smoke per hour; newer EPA-certified stoves produce only 2 to 5 grams of smoke per hour. EPA certified wood stoves burn more cleanly and efficiently, saving money, reducing the risk of fire and improving air quality inside and outside the home.

Only clean, well seasoned wood that has been split and dried properly should be burned in these appliances.

Outdoor wood

Although very little information is available about the environmental and health effects of wood burning in campfires or chimineas specifically, it is reasonable to think these recreational activities will release the same pollutants as the residential home heating appliances. Therefore, it is again recommended that only clean, well seasoned wood that has been split and dried properly should be burned.

Treated wood products

The thought that “wood is wood” is one that can lead to environmental and health hazards. Some woods are treated with chemicals in order to preserve the structural integrity and appearance of wooden structures.

Wood treatments can be classified into two major categories: oil-based treatments and water-based:

• Creosote and pentachlorophenol (PCP) are two oil-based treatments that are commonly used to treat railroad ties and utility poles.
• Chromated copper arsenate (CCA) and ammonium copper quat (ACQ) are the two most commonly used water-based treatments. CCA-treated wood is commonly used for playgrounds, decks and patios, fences, landscaping and in gardens. CCA contains arsenic, a chemical found to cause skin and lung cancer in people who are exposed over a long period of time. ACQ is a newer, less toxic product that has gained popularity in recent years.

The incineration of treated wood can release hazardous chemicals into the environment. Burning PCP or creosote treated wood may produce fumes and ash contaminated with hazardous chemicals. The ash produced from burning chromated copper arsenate (CCA) preserved wood may also contain high concentrations of arsenic and chromium.

Treated wood products should not be burned, due to associated health and environmental risks.

Wildfires

Fires release carbon in the form of carbon dioxide (CO₂), other gases such as methane and carbon monoxide and particles into the atmosphere. A recent analysis by Amiro et al. indicates that Canadian forest fires have released an average of 27 Mt (10¹²g) of carbon annually over the past four decades. These emissions are caused by direct combustion. About an equal additional amount of carbon may also be lost through decomposition of fire-killed vegetation and a temporary decrease in the forest sink, although this amount is not well quantified.

Prescribed burning

Prescribed burning is the use of fire as a management tool under specified conditions for burning a predetermined area. Prescribed burning is a valuable and, in many cases, necessary tool. It is done mainly by the logging industry for slash burning. As well, prescribed burning is used to increase habitat for certain wildlife, improve cattle range and reduce wildfire hazard.

Unfortunately, prescribed burning can also cause extended periods of haze during the fall, posing health risks.

Garbage

Garbage contains a whole range of materials and chemicals that react when burned together, possibly releasing toxins into the atmosphere. Also, home garbage fires have a tendency to smolder and burn at low temperatures, thus compromising the air quality.

Wood burning and climate change

Reports about the need to reduce emissions of greenhouse gases (GHGs) to prevent climate change and related problems are now common. The main source of GHGs is the burning of oil, gas and coal to produce the energy we use. These fuels are called fossil fuels because they are taken from deep beneath the earth’s surface, where they have been formed over millions of years.

When fossil fuels are burned, GHGs are released. The main GHG is carbon dioxide (CO₂). Increased concentrations of these gases in the atmosphere trap the sun’s heat close to the earth and cause the average global temperature to rise.

Wood, however, differs from fossil fuels because it is carbon neutral. The term “renewable” refers to the fact that trees recycle CO₂. As a tree grows, it uses CO₂ from the air as a source of carbon to build its structure. This carbon makes up about half of the weight of wood. When wood is burned, it decomposes rapidly and CO₂ is released into the atmosphere again.

A similar amount of CO₂ would be slowly released if the tree died and was left to rot on the forest floor. As a result, wood heating doesn’t contribute to the problem of climate change the way fossil fuel use does. But wood fuel is truly renewable only if it is produced by using sustainable forestry practices. Canada’s forests can be a perpetual source of fuel – as long as they are cared for and managed properly.

Numerous research and environmental studies have proven that wood that is not properly burned releases pollutants into the atmosphere, which compromises indoor and outdoor air quality, thus impacting the health of residents in the area. However, climate change research has demonstrated that wood is a practical choice because it is a form of renewable energy. Evidently there are positive and negative aspects to wood burning.

To maximize the positive aspects of wood burning and minimize the environmental and health risks associated with this practice, it is recommended to:

• burn only clean, dry wood
• do not burn on a day when the air quality is poor
• avoid breathing wood smoke
• do not let a fire smolder and produce a plume of blue-grey smoke
• do not burn treated wood or garbage
• to prevent wildfires, never leave a fire unattended
• plant a tree whenever you cut another down