Biodiesel-coated materials can, in rare circumstances, spontaneously ignite causing damage both large and small. Much information on this phenomenon is available, including in BiodieselMagazine archives. The mechanisms of biodiesel spontaneous combustion are not completely understood, which is why it is one of the subjects that the University of Idaho has researched for the USDA. Spontaneous combustion occurs when heat, resulting from chemical or biological reactions, accumulates in loosely piled flammable materials. The resulting rise in temperature accelerates the reaction rate, which further increases the temperature, culminating in smoke and open flame. Biodiesel feedstocks with at least two double bonds in their carbon chains are particularly susceptible to oxidative reactions and are a greater risk than petroleum-based fuels, which have almost no double bonds in their structures. In addition to an oxidation-prone fuel, spontaneous combustion requires that the fuel have access to sufficient air to oxidize the fuel but not too much air circulation, which could cause the heat of reaction to be dissipated. This situation frequently involves tuel-soaked rags or filter media.
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