Spontaneous combustion occurs when a material ignites without an external flame or spark. This phenomenon typically happens when organic materials, like hay or oily rags, undergo a chemical reaction that generates heat. If the heat builds up faster than it can escape, it can reach a temperature high enough to ignite the material. Common causes of spontaneous combustion include the accumulation of heat from microbial activity or oxidation. It is often seen in situations where materials are piled together, limiting airflow. Proper storage and ventilation can help prevent this dangerous occurrence.