Oily rags disposed of in household garbage or left in open containers can present a serious risk of fire. Unfortunately, a large majority of people do not believe that oily rags left undisturbed can ignite all by themselves without the presence of an ignition source, such as a spark or lighted match. Oily rags stored in a waste can or discarded in a pile on the floor, can ignite without any assistance from a separate ignition source. This is known as spontaneous combustion.
The dictionary defines spontaneous combustion as the ignition of organic matter (e.g., hay or coal) without apparent cause, typically through heat generated internally by rapid oxidation. Most people become familiar with this when they stain their wood floors or wood cabinets with oil based stains and then forget to dispose of them in a proper way to prevent their ignition. When the rags are disposed of in an improper manner such as throwing them into the garbage or leaving them in a pile, they can ignite and spread fire throughout the structure. Please see the attached flyer from the NFPA for proper safety practices concerning safety with oily rags. Remember to read the safety labels on all stains, varnishes, boiled linseed oils and other materials that are prone to spontaneous combustion when you undertake any home renovation project.