Popular projects like painting a room or refinishing a wood deck can transform the look of your home. Improper disposal of oily rags used on such projects also can transform the look of your home—but in a very different and dangerous way. You can safely clean paintbrushes with mineral spirits or paint thinner, but what about the rags and other materials that do not get cleaned and must be thrown away? Dealing with these properly means you won't have to worry about starting a fire.
Spontaneous Combustion Is Real
Simply put, spontaneous combustion is a fire starting without a match or spark. It's real and, unfortunately, not so uncommon. According to a 2011 report by the National Fire Protection Association (NFPA), about 1,600 residences per year experience fires due to spontaneous combustion or chemical reaction. And the most common causes of these fires are oily rags.
How Oily Rags Start Fires
Products that contain certain oils dry, or cure, through a chemical reaction called oxidation. This process uses oxygen and creates its own heat. If that heat is contained, such as in a pile of oily rags, it can get hot enough to reach the ignition point of the host material; in this case, cotton or whatever the rag is made of. And that's all it takes.
Oxidation occurs 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 they ignite). 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.
Storing and Disposing of Oily Rags
The easiest and safest way to store and dispose of flammable oily rags is to soak them in water in a metal container with a lid. As long as the lid is sealed, you can keep the rags in the container until you're ready to take them to a disposal facility.
- Place the rags in an empty metal container that has a tight-fitting metal lid, such as an old paint can.
- Fill the container with water until the rags are submerged.
- Seal the can tightly with its metal lid.
- 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 around your home.
Drying Oily Rags for Disposal
Another option is to let the rags dry fully before disposing of them. The important thing here is to allow the oil product to cure fully so that the oxidation process is complete and no longer creates heat.
- Lay 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 noncombustible surface, such as bare soil or concrete; do not lay them on your recently oiled deck, for example.
- Let the rags dry fully for at least two days, but possibly longer, depending on the product.
- Dispose of the dried rags as directed by your garbage pickup service or local hazardous waste disposal center.
Why You Can't Reuse or Recycle Oily 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 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 you opted 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.