The idea that oily rags left over after painting, staining, or wood finishing can spontaneously catch fire is no urban legend. It does indeed happen, and more often than you think. Simply put, spontaneous combustion is a fire starting without a match or spark. According to the fact sheet provided by the National Fire Protection Association (NFPA), an average of 1,700 residences per year experience fires due to spontaneous combustion or chemical reaction. An average of 900 of these incidents are caused by oily rags.
Before You Begin
The chemical process behind spontaneous combustion is simple oxidation in circumstances where the resulting heat is trapped. As the oxygen found in ordinary air combines with the petroleum-based chemicals in oily rags, this oxidation process naturally creates heat. If the temperature reaches the ignition point of the host material—the cotton in a rag, for example, the result is open flames that can quickly spread.
This dangerous oxidation can occur with or without light, wind, or external heat sources. Piles of rags are prone to spontaneous combustion because the piles of fabric trap the heat, and the fabric often has a relatively low ignition point (the temperature at which it ignites). By contrast, when you apply an oil stain to a deck or a piece of furniture, heat from the oxidizing oil is immediately dissipated into the air.
Spontaneous combustion of oily rags can be prevented in one of two ways—or by a combination of methods. Either you can deny the oily rags the oxygen that is necessary for heat-producing oxidation, or you can provide conditions in which the heat of oxidation can dissipate in a manner that prevents temperatures from reaching the flash point of materials such as cotton rags.
If you're concerned about minimizing waste, or you simply don't like to throw away useful things, you may be in the habit of washing used rags and reusing them. It's also possible to add cotton and other natural-fiber rags to a compost pile for natural recycling. However, you should never do either of these things with used oily rags. Reusing rags usually requires washing them first, and unlike household dirt and grime or even mild cleaners, synthetic oil-based products are highly toxic and not something you want in your washing machine or in the water treatment system. For the same reason, oily rags are not suitable for composting.
Even if you opt not to wash old rags, most oil-based finishes contain resins that harden as the finish cures. The volatile oil carrier is gone, but the resin remains, leaving rags stiff and unsuitable for any use.
Equipment / Tools
- Stone or other weight (if necessary)
- Metal container with lid
How to Dispose of Oily Rags
The easiest and safest way to store or transport flammable oily rags is to submerge them in water in a metal container with a lid. The water and the sealed container prevent oxygen from the air from ever reaching and combining with the petroleum distillates saturating the rags.
This is a temporary measure, however, that should be used only as a means for storing the rags until you can transport them to a disposal facility.
Place the Rag in a Container
Place the rags in an empty metal container that has a tight-fitting metal lid, such as an old paint can.
Fill and Seal the Container
Fill the container with water to the rim, making sure the rags are fully submerged. If necessary, you can use stones or another heavy object to weigh down the rags and keep them submerged. Seal the can tightly with its metal lid.
Be sure to fully submerge the rags in water. Not doing so may create a dangerous situation if the container contains enough air to allow for an oxidation reaction.
Dispose of the Container
Take the container to your local hazardous waste disposal center, or arrange a special pickup by your garbage pickup service. Many municipalities also host hazardous waste drop-off/pickup days.
Never pour oily water down a drain in or into the soil around your home. Petroleum products are toxic and should never be allowed to reach groundwater supplies.
How to Dry Oily Rags for Disposal
Another option is to let the rags dry fully before disposing of them. The important thing is for the petroleum distillates to evaporate in an open environment so that the heat of oxidation dissipates without building up and igniting the cloth fabric.
Lay Out the Rags
Spread out or hang the oily rags in a single layer in an outdoor area that is out of the sun and is well-ventilated. Be sure to lay them on a non-combustible surface, such as bare soil or concrete; do not lay them on your recently oiled deck, for example.
Let the Rags Dry
Let the rags dry fully for at least two days. Some materials may take longer, but the rags should be allowed to remain until they feel dry to the touch and the oily smell is no longer strong.
Dispose of the Rags
Dispose of the dried rags as directed by your garbage pickup service or local hazardous waste disposal center.
Never attempt to launder and reuse rags that have been saturated with oily materials. Petroleum distillates and oil-based finishes contain resins that harden into the fabric as the liquids evaporate, and these toxic resins can be liberated and enter the drain system if you wash the rags. Nor should you add dried-out oily rags to a compost pile, for the same reason.
Nowak, Paulina et al. Ecological and Health Effects of Lubricant Oils Emitted into the Environment. International journal of environmental research and public health vol. 16,16 3002. 20 Aug. 2019, doi:10.3390/ijerph16163002