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Absorbent Training Part 6: Spontaneous Combustion

Fire in steel drum caused by spontaneous combustion.

Some oils and liquids — and the absorbents that contain them — have the potential to spontaneously combust. If your facility uses, stores or processes vegetable or drying oils, biodiesel or other self-heating liquids, it’s important to recognize their hazards and establish safety and housekeeping plans to help you prevent fires.

Why Oily Rags and Other Used Absorbents can Spontaneously Combust

Certain oils — like vegetable, drying oils and biodiesel — undergo a chemical process known as oxidation that releases energy in the form of heat when exposed to air. It’s oxidation that creates the potential for spontaneous combustion. Petroleum products like motor oil and gasoline, while flammable, do not undergo oxidation. Also, the tendency of oil to spontaneously combust is related to its iodine number — if it’s 130 or greater, the potential is there.

Absorbent materials, like rags, wipers and mats, do not change the properties of the liquids they absorb. Absorbents soaked with flammable liquids remain flammable. Absorbents soaked with corrosives remain corrosive. Absorbents soaked with vegetable oil will oxidize. If the liquid can spontaneously combust, so can the absorbent that contains it.

Here are some questions that our customers frequently ask us:

Can Motor Oil or Gasoline Soaked Rags Spontaneously Combust?

Motor oil (and anything soaked in motor oil) is less likely to spontaneously combust but it can happen if conditions are just right. Play it safe and follow the steps in this article to help prevent incidents from occurring. As for gasoline-soaked rags, they usually require an ignition source to ignite their vapors. However, spontaneous combustion can occur if gasoline-soaked rags reach their auto-ignition point of 495°F-536°F. Again, always exercise caution when handling oils and flammable liquids, even if they’re not commonly associated with spontaneous combustion.

Can Vegetable Oil Spontaneously Combust?

Yes, vegetable oils will oxidize when exposed to air so they should always be treated as a risk for spontaneous combustion. Vegetable oils are commonly used to make soaps, candles, perfumes, skin care and other cosmetic products, in addition to being used as drying oils in paints and wood treatment products.

Can Solvent or Acetone Soaked Rags Spontaneously Combust?

Acetone and highly flammable solvents have very low flashpoints, putting them at risk for external ignition and spontaneous combustion. Much like oil- and gas-soaked rags, the conditions need to be just right for a spontaneous reaction to occur, but they are still potential hazards that should be taken seriously.

Are There Any Absorbents that Eliminate the Potential for Spontaneous Combustion?

No absorbent eliminates the potential for spontaneous combustion, and it can exist with any type or brand of absorbent media: mats, wipers, rags, corncob, sawdust, clay, wood chips or peat. Remember: it’s the property of the liquid being absorbed — not the absorbent itself — that creates the potential for a reaction.

Preventing Spontaneous Combustion of Rags, Wipers and Absorbents

Like any fire, three elements are needed for spontaneous combustion: heat, fuel and oxygen. External heat sources like a match or a spark are not needed for liquids that can spontaneously combust because heat is created through the oil’s natural oxidization process. The oil and absorbents become the fuel while oxygen is present in the air.

To reduce the risk of spontaneous combustion, remove one of the three fire elements using one of the following techniques:

  • Place saturated absorbents in sealed containers for disposal or recycling, making sure the container is nearly full (Scroll down to see some of our best-selling Latching Drum Lids!)
  • Place saturated absorbents in sealed bags to limit oxygen exposure
  • Dry saturated absorbents in a single layer before disposal or recycling (consider the potential for emissions and whether this is permissible in your jurisdiction) so that the heat from oxidation dissipates more easily
  • Keep containers or bags of spent absorbents out of direct sunlight, away from heat sources and out of high-temperature areas or store containers of spent materials in climate-controlled areas or away from structures until they can be shipped for recycling or disposal

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