No, burning pressure-treated wood is not safe. The EPA explicitly warns against it, and both the U.S. and Canadian governments advise never burning treated wood indoors or outdoors. The chemicals forced into the wood during treatment don’t disappear when the wood burns. They concentrate in the smoke and ash, creating health hazards that far exceed anything you’d encounter from the wood itself during normal use.
What Makes Treated Wood Dangerous to Burn
Pressure-treated wood gets its rot and insect resistance from chemical preservatives pushed deep into the wood fibers under high pressure. The specific chemicals depend on when the wood was treated and what it was designed for.
Wood treated before 2004 almost certainly contains chromated copper arsenate (CCA), a blend of arsenic, chromium, and copper that was the industry standard from the 1940s onward. If your deck, fence, or play structure went up before 2004 and isn’t made of cedar or redwood, it’s likely CCA-treated. Arsenic is the primary concern here. When CCA wood burns, arsenic doesn’t just vanish. It becomes airborne in the smoke and concentrates heavily in the leftover ash.
Modern treated wood uses different formulas, mainly alkaline copper quaternary (ACQ) and copper azole. These replaced CCA for residential use and don’t contain arsenic. But that doesn’t make them safe to burn. Both still release copper compounds and other chemicals in smoke and ash. Health Canada’s guidance is unambiguous: never burn any treated wood, regardless of the preservative used.
The Ash Is the Bigger Problem
Most people worry about the smoke, but the ash left behind after burning treated wood poses an even more persistent danger. Research on CCA-treated wood found that metals (chromium, copper, and arsenic combined) can make up as much as 36% of the ash by weight in heavily treated samples. Every ash sample from burning 100% CCA wood, and even mixtures containing just 5% CCA wood, leached enough arsenic to be classified as hazardous waste under U.S. regulations.
That ash doesn’t stay put. If you burn treated wood in a fire pit or fireplace and then spread the ashes in your garden, you’re depositing concentrated heavy metals directly into your soil. Research from New Zealand measured arsenic levels in the ash of treated timbers and found concentrations ranging from roughly 133,000 to 179,000 parts per million. A single kilogram of that ash could raise arsenic levels by 10 ppm across more than 13 tons of compost. Arsenic in contaminated soil can also leach into groundwater over time, spreading the problem well beyond where the ash was originally dumped.
Health Effects of Exposure
Inhaling smoke from burning treated wood exposes you to arsenic vapors (in older CCA wood) and copper-based fumes (in all types). The risk increases in poorly ventilated spaces or when burning large quantities. Acute arsenic inhalation can cause irritation of the airways, nausea, and skin irritation. Chronic or repeated exposure to arsenic is linked to more serious long-term health effects, including damage to the nervous system and increased cancer risk.
Even with modern, arsenic-free treatments, copper fume inhalation causes its own set of problems. Breathing copper-laden smoke can irritate the lungs and cause flu-like symptoms sometimes called “metal fume fever.” Children and pets are particularly vulnerable to both the smoke and the ash, since they’re closer to ground level and more likely to come into contact with contaminated surfaces.
What to Do If You’ve Already Burned It
If you realize mid-burn that the wood is treated, move away from the smoke immediately and get to fresh air. Open doors and windows if you’re indoors, and loosen any tight clothing. If you’re experiencing difficulty breathing, persistent coughing, or nausea, seek medical attention. Don’t let anyone else approach the fire to try to put it out if the area is still filled with smoke.
Any remaining ash should be treated with caution. Don’t scatter it in your yard or garden. Bag it separately and contact your local waste management office about hazardous waste disposal options.
How to Identify Treated Wood
Treated lumber typically has a greenish or brownish tint, though weathered pieces can lose their color and look identical to untreated wood. The most reliable indicator is an end-tag or ink stamp pressed into the wood. These stamps list the preservative type, the treatment facility, and the intended use rating. Look for abbreviations like CCA, ACQ, CA (copper azole), or “D-BLAZE” for fire-retardant treatments.
If you’re tearing down an old deck or fence and can’t find stamps, assume it’s treated. Wood used for ground contact, landscaping timbers, fence posts, and outdoor structures is almost always pressure-treated. When in doubt, don’t burn it.
Safe Ways to Get Rid of Treated Wood
Treated wood can go to a lined municipal solid waste landfill in most areas, though some counties have specific restrictions. Call your local solid waste office or check their website before hauling it to the dump. Some areas also accept treated wood at permitted waste incinerators, which are equipped with pollution controls that a backyard fire pit or woodstove simply doesn’t have.
CCA-treated wood can also be recycled into wood-cement composites or processed at waste-to-energy facilities designed to handle it safely. What you should never do is mix treated wood scraps into your regular firewood pile, use them in a campfire, or toss them into a wood-burning stove or fireplace. The convenience isn’t worth the exposure.