No, burning treated wood in a fire pit is not safe. The chemicals used to preserve treated lumber release toxic compounds into the smoke and concentrate in the leftover ash, creating health risks for anyone nearby. The EPA explicitly states: never burn pressure-treated wood.
What’s in Treated Wood
Pressure-treated lumber is infused with chemical preservatives designed to resist rot, insects, and moisture. The specific chemicals depend on when the wood was manufactured and what it was treated for.
Before 2004, most residential treated wood used a formula called CCA, which contains chromium, copper, and arsenic. The EPA phased out CCA for consumer products at the end of 2003 because of arsenic exposure concerns, but enormous quantities of CCA-treated decks, fences, playground equipment, and raised beds are still standing or being demolished today. If you’re pulling apart an old deck or clearing construction debris, there’s a good chance some of that wood contains arsenic.
Modern treated lumber typically uses ACQ (alkaline copper quaternary), which replaces arsenic with copper oxide and quaternary ammonium compounds. While less dangerous than CCA, these chemicals still produce harmful fumes when burned. No pressure-treated wood of any era is safe to burn in a fire pit, fireplace, or wood stove.
What Happens When Treated Wood Burns
When CCA-treated wood is burned in an open fire, 11 to 14 percent of the total arsenic content gets released into the air as breathable particles. Chromium and copper mostly stay in the ash (less than 1 percent escapes into smoke), but that’s not reassuring. The arsenic that does go airborne converts into its most toxic form, a trivalent state that’s especially harmful when inhaled.
A backyard fire pit provides no filtration or temperature control. Unlike industrial waste-to-energy facilities, which burn at extremely high temperatures with emission controls, an open fire sends those toxic particles directly into the air you and your neighbors are breathing. The smoke drifts at ground level, and anyone sitting around the fire is in the exposure zone.
Health Risks From the Smoke
Researchers have documented both acute and chronic arsenic poisoning from burning CCA-treated wood. Exposure can cause skin problems, blood disorders, and neurological symptoms. A well-known case study described hematological, dermal, and neuropsychological disease in people who burned and power-sawed CCA-treated lumber.
In the short term, inhaling smoke from treated wood can cause persistent coughing, wheezing, difficulty breathing, dizziness, nausea, and vomiting. These symptoms may not appear immediately. Airway swelling from toxic smoke can build gradually, meaning you might feel fine around the fire but develop breathing problems hours later. Repeated exposure over time raises the stakes significantly, since arsenic is a known carcinogen linked to cancers of the lung, skin, and bladder.
The Ash Is Just as Dangerous
Even after the fire goes out, the danger isn’t over. The ash left behind from treated wood contains staggering concentrations of arsenic. Testing on ash from treated timbers found arsenic levels between 133,000 and 179,000 parts per million, depending on the treatment grade. For comparison, ash from completely untreated wood contained about 96 ppm.
This matters because many people spread fire pit ash in their gardens or compost bins, assuming it’s a natural soil amendment. Adding treated wood ash to soil or compost dramatically increases arsenic concentrations, and arsenic in soil can leach into groundwater. Even a small amount of contaminated ash mixed into compost creates a measurable pollution problem. If you’ve ever burned treated wood and spread the ashes, avoid using that soil for growing food.
How to Identify Treated Wood
Treated lumber often has a greenish or brownish tint, though this fades with weathering. Look for small incisions (called “retention marks”) across the surface, which are made during the pressure-treatment process. Many pieces also have an ink stamp or end tag listing the preservative type and treatment level.
Old, weathered wood is the hardest to identify. If you’re tearing down a structure built before 2004 and the wood was in ground contact or exposed to weather (deck boards, fence posts, landscape timbers, retaining walls), assume it’s treated. When in doubt, don’t burn it.
How to Dispose of Treated Wood Safely
The EPA recommends disposing of treated wood in lined municipal solid waste landfills. Some local waste haulers accept it with regular trash pickup, while others require you to bring it to a designated facility. Contact your local solid waste office to check the rules in your area, since regulations vary by county.
Treated wood should not go to unlined demolition landfills, which lack sufficient groundwater protection. Some facilities can recycle CCA-treated wood into wood-cement composites, and industrial waste-to-energy plants can burn it under controlled conditions with proper emission controls. These are not options you’d access directly, but your local waste management service can point you in the right direction.
For your fire pit, stick to natural, untreated firewood: seasoned hardwoods like oak, maple, or hickory. Avoid burning any painted, stained, or chemically treated lumber, plywood, particleboard, or construction scraps of unknown origin.