Pine tar is a viscous substance derived from the high-temperature carbonization of pine wood, historically used for waterproofing, medicine, and sports applications. Pine tar is a combustible material, meaning it will ignite and burn under specific conditions. While it is not classified as highly flammable like gasoline, it requires careful handling and storage.
The Chemical Components That Burn
Pine tar’s combustibility stems directly from its complex chemical composition, which is a rich mixture of hydrocarbons. The tar is produced through the thermal decomposition of pine wood in an environment with little or no oxygen. This process converts the wood’s organic matter into a dense, dark liquid composed largely of aromatic hydrocarbons, tar acids, and various resins.
The key components contributing to the fire risk are the volatile organic compounds (VOCs). Freshly refined or thinner pine tar products may contain volatile oils, such as turpentine, which is itself a highly flammable substance. The finished product primarily contains hydrocarbon-based fuels like resin acids and their derivatives. When sufficient heat is applied, these organic compounds release flammable vapors that can ignite.
Conditions Required for Ignition
The risk of ignition for pine tar is directly tied to its physical state and the surrounding temperature. The flash point is the lowest temperature at which a liquid produces enough flammable vapor to ignite when an ignition source is present. Pine tar products generally have a flash point around 100°C (212°F) or higher, classifying it as a combustible liquid rather than a flammable liquid.
The vapors released above the tar at these temperatures are what actually burn, not the liquid itself. The autoignition temperature, often above 300°C (572°F), is the point at which the material spontaneously bursts into flame without an external ignition source. Heating the tar dramatically increases the release of combustible vapors, which can form an explosive mixture with air, especially in a confined space. Liquid tar is generally more hazardous than cured, hardened tar, as the volatile components have evaporated from the cured state.
Safe Storage and Handling Practices
Proper storage and handling are necessary to prevent a fire. The material should be kept in a cool, dry, and well-ventilated area, safely away from any potential sources of ignition, such as sparks, open flames, and high heat. Containers must be kept tightly closed to minimize the escape of vapors and prevent contamination.
Avoid storing pine tar near strong oxidizing agents, which can react chemically to increase the fire risk. A serious hazard is the disposal of materials used to apply the tar, such as rags, steel wool, or absorbent waste. If contaminated and improperly discarded, these materials can spontaneously combust due to a process of rapid oxidation, even at room temperature. All contaminated application materials should be soaked in water and then disposed of properly in accordance with local hazardous waste regulations.