Mold growth on stored wood is a frequent sight for homeowners who rely on fireplaces or wood stoves. The dark discoloration often raises concerns about “toxic black mold” and potential dangers. This discoloration occurs because wood is an organic material that provides a food source for fungi. When combined with moisture, conditions become ideal for mold and mildew to develop.
Is the Black Mold on Firewood Toxic
The black mold found on outdoor firewood is generally not Stachybotrys chartarum, which is often termed “toxic black mold.” That species thrives indoors on high-cellulose, water-damaged materials like drywall and ceiling tiles. The dark fungi seen on wood stored outside are typically different genera, such as Cladosporium, Alternaria, or various sapstain fungi. These outdoor molds are part of the natural decay process. The color of mold is not a reliable indicator of its potential for causing health issues. All molds, regardless of their species, reproduce by releasing microscopic spores into the air, and these spores can be irritating allergens.
Health Risks from Handling and Burning Moldy Wood
The primary danger from moldy firewood comes from inhaling the spores during handling or burning. Moving or stacking wood with visible mold releases a cloud of spores and fungal fragments into the air. This inhalation can trigger an allergic reaction, which is the most common health response to mold exposure. Symptoms of this reaction often mimic hay fever, including sneezing, coughing, and respiratory irritation. Individuals with pre-existing conditions like asthma, environmental allergies, or compromised immune systems are at a higher risk for severe responses, such as wheezing or asthma attacks. Minimizing exposure during handling is important for these vulnerable groups.
When moldy wood is burned, the high heat generally destroys the living mold organism and its spores. However, the smoke still carries particulate matter, which includes fragments of the dead mold, spores, and other irritants. Burning heavily molded or damp wood produces more smoke and fine particles. These particles can exacerbate respiratory conditions when released into the air, especially in an indoor fireplace. Burning heavily molded wood indoors should be avoided due to poor air quality and increased airborne irritants.
Safe Storage and Remediation Practices
Preventing mold growth starts with managing moisture content, as mold requires water and organic material to thrive. Proper storage technique is important as it promotes drying and discourages fungal colonization.
- Firewood should always be stored off the ground, ideally elevated by at least four to six inches using a rack or wooden pallets to stop moisture from wicking up from the soil.
- Stack the wood in a sunny, well-ventilated location.
- Wood should be stacked in a single row or in small, multiple piles, rather than one large, dense block.
- Logs should be placed in a criss-cross pattern at the ends to allow for air circulation throughout the entire stack.
- When covering the wood, only the top layer should be shielded from rain or snow, leaving the sides exposed for continuous airflow and ventilation.
If you must handle wood that has mold on it, wearing personal protective equipment, such as an N95 dust mask and gloves, is a necessary precaution. The N95 mask filters out fine, airborne mold spores, reducing the amount inhaled while moving the wood. Heavily affected pieces should be burned outdoors in a well-ventilated area, or if the mold penetration is deep and the wood is punky, it may be safer to discard it entirely.