Eucalyptus trees, native to Australia, are widely used as firewood due to their dense structure and high heat output. The wood is a sustainable fuel source that generates high heat (nearly 35 million BTU per cord). However, the safety of burning eucalyptus depends entirely on the preparation and method of combustion. Primary concerns stem from the tree’s unique chemical composition, which is rich in volatile organic compounds.
Concerns When Burning Eucalyptus Wood
The physical risks of burning eucalyptus wood relate to its intense heat and high content of natural oils. This combination means the wood burns very hot and fast, potentially creating excessive heat within a wood-burning appliance or fireplace. This rapid burn rate can be difficult to manage, making it challenging to maintain a steady, moderate temperature in a typical home fireplace or stove.
A more immediate danger is the tendency for eucalyptus to spark and pop, sometimes aggressively, even after prolonged drying. Small pockets of trapped volatile oils or sap within the dense wood can rapidly vaporize when heated, causing small, explosive releases of steam and superheated gases. This characteristic makes it particularly risky to burn in an open fireplace where flying embers could easily escape the hearth and ignite nearby combustibles.
The high oil content also contributes to a greater risk of chimney fires, especially if the wood is not fully seasoned or the fire is allowed to smolder. When the volatile compounds in the smoke do not combust completely, they travel up the chimney where they cool and condense into creosote. Eucalyptus is known to create thick, sticky, and hard-to-remove deposits of creosote, which is a highly flammable substance that fuels chimney fires.
Health Risks from Volatile Oils and Smoke
Health risks associated with burning eucalyptus are directly linked to the chemical makeup of its volatile oils. The most abundant compound is eucalyptol (1,8-cineole), which gives the plant its characteristic medicinal scent. Burning the raw wood or leaves releases this compound along with concentrated smoke and fine particulate matter, unlike the controlled release from an aromatherapy diffuser.
Inhaling the smoke from any burning wood can be irritating, but the unique compounds in eucalyptus smoke may pose a greater concern for respiratory health. Studies suggest that eucalyptus smoke particles can induce a more pronounced inflammatory response in the lungs compared to smoke from other common biomass fuels. The repeated inhalation of these fine particulates and volatile organic compounds is linked to exacerbating conditions like asthma or Chronic Obstructive Pulmonary Disease (COPD).
The danger is amplified when attempting to burn the leaves or pure eucalyptus oil, which should be explicitly avoided. The raw leaves contain a high concentration of the highly flammable oils, which generate dense, irritating smoke and pose a flash fire risk. Furthermore, pure eucalyptus oil is a known poison if ingested, and heating it directly can release high concentrations of irritating vapors and poses an extreme fire hazard due to its low flashpoint.
Safe Practices for Burning Eucalyptus
The primary step in safely using eucalyptus as firewood is thorough and extended seasoning, drying the wood until its moisture content is below 20%. Due to the high water and oil retention, this process can take a minimum of six to twelve months, sometimes up to two years. Splitting the wood into smaller pieces immediately after cutting accelerates the drying process significantly.
When burning, it is highly recommended to only use eucalyptus wood in an enclosed, contained appliance like a modern wood stove or furnace. These units offer better control over airflow and combustion temperature, which helps ensure the volatile compounds burn off completely, minimizing the production of dangerous creosote. Proper ventilation is necessary for any indoor burning to manage smoke and carbon monoxide.
To manage the inherent risk of sparking, the wood should be burned only in appliances with securely closed doors or in fully enclosed outdoor environments, such as a contained fire pit. Chimneys and flues should be inspected and cleaned annually to remove creosote buildup, a practice that becomes particularly important when regularly using high-oil wood like eucalyptus. Absolutely avoid burning eucalyptus leaves or oils as an indoor aromatic or incense.