Essential oils are highly concentrated liquid extracts derived from plants, capturing the natural scent and essence of the source material. These aromatic compounds are primarily obtained through processes like steam distillation or cold pressing. Most essential oils are indeed flammable due to their concentrated and volatile nature, requiring careful handling and storage.
The Chemical Reason for Ignition
The flammability of essential oils stems directly from their chemical makeup, which consists of concentrated volatile organic compounds (VOCs). The term “volatile” means the compounds evaporate easily at room temperature, releasing molecules into the air. These molecules, which carry the oil’s scent, are essentially fuel in a gaseous state. Many of these VOCs are hydrocarbons known as terpenes, such as limonene in citrus oils, and they are highly combustible. It is not the liquid oil itself that catches fire easily, but rather the concentrated vapors released above the liquid’s surface that ignite when exposed to an ignition source. The higher the concentration of these volatile components, the greater the likelihood of forming a flammable air-vapor mixture.
How to Measure Flammability
The scientific measure used to quantify the fire risk of any liquid is its “flash point.” The flash point is defined as the lowest temperature at which a liquid produces enough concentrated vapor near its surface to ignite momentarily when a spark or flame is introduced. A lower flash point indicates that the substance is more volatile and presents a higher fire risk at lower temperatures.
Essential oils vary significantly in their flash points, which generally range from 37°C to over 93°C (99°F to 200°F). For instance, highly volatile oils like lemon, orange, and clove bud have notably low flash points, often around 43°C to 48°C (109°F to 118°F). Conversely, heavier oils, such as patchouli and sandalwood, possess much higher flash points, sometimes exceeding 100°C (212°F), making them less prone to ignition.
Safe Storage and Usage Practices
To minimize fire risk, essential oils should be stored in a cool, dark location, away from direct sunlight, heat sources, and open flames. Heat can accelerate the vaporization process, increasing the concentration of flammable vapors inside the bottle. Using the original dark glass containers is recommended because they protect the contents from light and securely contain the liquid.
When using diffusers, caution is necessary, especially with devices that utilize heat to disperse the aroma. Diffusers should never be left operating unattended and must be positioned away from electrical outlets, curtains, or other easily ignitable materials. Adequate ventilation is also important to prevent the buildup of concentrated vapors in an enclosed space.
A particular risk involves the disposal of materials that have absorbed essential oils, such as rags or paper towels. These oil-soaked materials can pose a self-ignition risk, known as spontaneous combustion, as the oil oxidizes and generates heat. To safely dispose of these items, allow them to dry completely in a single layer outside or place them in a specialized metal safety can. Following local hazardous waste guidelines is the most responsible way to manage larger quantities of unused or expired oils.