Rags soaked with sunflower oil will spontaneously combust?

October 13, 2013 3:17 AM

How can I prevent a bunch of cotton rags I soaked in sunflower oil from spontaneously combusting?

How can I prevent a bunch of cotton rags I soaked in sunflower oil from spontaneously combusting?

In order to throw away some old sunflower oil, I followed directions I read online to soak the oil in absorbent paper, which I didn't have on hand, so I very stupidly used some old cotton rags which had been cut from an old pair of pants. Then I placed them in a plastic ziploc bag and added a lot of water, and tightly sealed the bag, as directed.

I then read that oil can spontaneously combust if put in cotton, so I'm very concerned about my new plastic bag full of oil soaked cotton rags. The garbage collection doesn't come until the day after tomorrow, and it's not exactly cool here in Tokyo, so I would like some suggestions what to do with the rags to prevent spontaneous combustion? Would placing the bag in the fridge until it is collected be enough? Should I take the rags out and wash them? I've been periodically checking the bag and it appears to be maintaining room temperature.

Any suggestions would be greatly appreciated. Thank you.

posted by fan_of_all_things_small to Home & Garden (12 answers total)

Best answer: From the South Australian Metropolitan Fire Service:

It is simple to prevent spontaneous ignition since oxygen is needed for it to occur. Materials subject to spontaneous ignition should be stored in sealed metal containers such as a safety can or rubbish bin. The container will contain oxygen at first, but the oxidation process will soon use this up and the process will stop.

Rags impregnated with linseed or other drying materials should either be immersed in water or, immediately after use, spread out in a safe place to dry. If it is necessary to transport oil or paint-soaked rags, they should be sealed in metal containers.

In laundries, the washing should be spread to cool after it has been dried, not placed in bins or piles while still hot.

It sounds like either the sealed ziplock or the water stops the problem from occurring, so you already have a double safety margin. But if you want a triple, also put the sealed bag in a sealed metal container of some sort.
posted by flug at 3:30 AM on October 13, 2013

Best answer: (Not a chemist) The oil I use for my kitchen countertops is applied with a rag, and the can warns that that rag could combust so it should be stored in an airtight container. I think we used a plastic takeaway container with lid in a cupboard. This is in Manchester UK rather than Tokyo though. I think ziplock, water and fridge would be OK.
posted by BinaryApe at 3:30 AM on October 13, 2013

Best answer: Can you fit them in a freezer? I was taught to keep oil to be tossed/taken for biofuel reclamation in a container in the freezer.
posted by Mizu at 4:22 AM on October 13, 2013

Response by poster: Thanks! It's a regular ziplock bag size, so I tossed it in the freezer as is.
posted by fan_of_all_things_small at 4:32 AM on October 13, 2013

It's easy to mix oil and water, BTW. All you have to do is add a little soap.
posted by tel3path at 5:54 AM on October 13, 2013

I think the "oil" in the "oily rags can spontaneously combust" thing is more like linseed oil, or petroleum based oils - volatile oils. Sunflower oil (in the states, anyway) will burn if superheated, or with a wick, but is not the sort of oil that just burns.

Your oil may vary, and it is possible that I am not understanding the mechanism at play here, but I wouldn't give a moments thought to vegetable oil rags catching fire. Solvent soaked rags, absolutely.
posted by dirtdirt at 6:20 AM on October 13, 2013 [4 favorites]

Meaning, what we have that is called "sunflower oil" here in the states is a fairly inert vegetable oil used for cooking. It's not a solvent.
posted by dirtdirt at 6:21 AM on October 13, 2013

The flashpoint of sunflower oil is 600°F (315°C) . Tokyo may not be cool, but the chances of spontaneous combustion are nil.
posted by Segundus at 7:05 AM on October 13, 2013

Spontaneous combustion in oily cotton rags (or oily paper towels - the chemistry is pretty much identical) happens not because the oil is volatile but because it's a drying oil i.e. one that spontaneously polymerizes in the presence of oxygen to form a tough film. Linseed oil does this, which is why it's the basis for oil paint. Petroleum based oils are fully saturated, non-drying, and won't cause spontaneous combustion in oily rags.

The polymerization reaction is exothermic (heat-releasing) and if there's enough oily rag bunched together, the reaction heat is blanketed and retained. This speeds the reaction, creating more heat, speeding the reaction, creating more heat, until fwoomph. If the same rag is also wet with volatile paint thinners, the fwoomph is more emphatic but it's the curing vegetable oil supplying the ignition heat, not the thinners themselves.

You can run the reaction at well below ignition temperature by spreading the rags out in a single layer until the oil has cured, or stop it altogether by denying it a supply of oxygen.

Wikipedia gives sunflower oil's iodine number as 125 – 144, which is a fair bit lower than linseed oil's 170 – 204 but still enough to rate sunflower oil as a semi-drying to drying oil and therefore worth taking precautions with.
posted by flabdablet at 7:07 AM on October 13, 2013 [24 favorites]

Sunflower oil is listed in this PDF publication of Britain's Aromatherapy Trade Council as having a fairly high risk of spontaneous combustion on oxidation, so it's probably good that you put it in the freezer! This is why, even though there's only a small risk from it, I put my Kleenex soaked with jojoba oil (that's what I use on my face in lieu of lotion) in a metal trash can every morning.
posted by limeonaire at 9:15 AM on October 13, 2013 [1 favorite]

It is true that this may not be the very safest thing, but I wouldn't consider it super-dangerous either. (FWIW, popular drying oils are linseed, tung, poppy and safflower.) The greatest danger is not simply when oils which polymerize are dispersed through a rag (paper or cotton isn't going to make a lot of difference, both are cellulose fibers), but when there are added drying agents such as the metallic catalysts in commercial "boiled linseed oil" or when certain natural pigments are added which accelerate the polymerization process.

Now, if you had to throw away rags with drying oils in them, there are commercial metal containers for this purpose, but what I tend to do with small quantities of rags from wood finishing and oil painting is to spread them out flat outside and weigh them down with a couple stones. This way it can 'dry' quickly but the heat cannot build up while it polymerizes. Once the oil has gotten fairly firm (or garbage day rolls around) I pick them up and put them in the (outside) trash can. Immersion in water with a little detergent is probably great too.

Personally, if I'm throwing away a bunch of unused oil, I usually just toss it in an old plastic bottle. In bulk with little air exposure, this isn't going to be a spontaneous combustion problem. The only use of soaking it up is if a container was punctured it would make less of a mess in with the rest of the garbage.

Standard disclaimer: you're taking your own risks in applying any of these ideas, this is not any sort of professional advice.
posted by mmagin at 10:24 AM on October 13, 2013

Do you know anyone with a wood stove? Those rags would be dandy to start fires. I put oily paper towels in a coffee can for that purpose. Before I had a wood stove, I put old newspapers and junk mail in a plastic bag, and put the oil in that. My trash goes to an incinerator, so it produced a small amount of electricity.
posted by theora55 at 11:37 AM on October 13, 2013