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Spontaneous Combustion

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ChrisH16/02/2014 18:22:00
1018 forum posts
30 photos

Clearing up some spilt oil in the shed with a load of rags, the thoughts appeared to me of disposal, how to without making more mess, and of spontaneous combustion which had been mentioned in another thread.

Disposal was no problem, my shed is heated by an old little French wood burning stove, top fed, which is fed with charcoal as it appears to me to burn hotter and a charge lasts longer than a wood charge. The fire was burning well, the rags dropped in and certainly spontaneously combusted in the stove.

Which leaves spontaneous combustion to puzzle over. Those who have had any dealings with fire prevention/fire fighting will be familiar with the fire triangle, that is, three things are required for a fire and are represented as the sides of a triangle, fuel, heat and oxygen; take any one away and the triangle collapses and the fire goes out. Fuel is usually the most difficult to remove, but cooling with water will remove the heat and smothering with a fire blanket, foam or inert gas like CO2 will remove the oxygen, to quote a couple of examples.

So, with our spontaneous combustion, we have the fuel, the oily rag, and the oxygen, it is surrounded by air as it sits in the bin or on the bench, but what provides the heat? No external heat is applied, the rag alone is not guilty, neither is the oil alone. Is it a chemical reaction between the rag and the oil, or what?

Anyone with an idea or better still knowledge on this?

Chris

Thor 🇳🇴16/02/2014 19:10:42
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1630 forum posts
46 photos

Hi Chris,

if your rag was used to clean vegetable oil (with unsaturated fatty acids) it might undergo spotaneous combustion, for instance see here, or here. When organic conpunds oxidise heat is produced.

Thor

DerryUK16/02/2014 20:01:18
125 forum posts

From the above references can someone devise a test so we can all give it a go?

Save a fortune in matches.

noel shelley16/02/2014 20:26:38
1349 forum posts
21 photos

Hi Chris, Any combustible material if finely divided(has it's surface area greatly increased) will much more easily ignite. So if a combustible material is soaked up with rag then it offers a huge surface area to the air(oxygen) and the chemical process of oxidation(burning) will not only start much more easily but will also be much more rapid.

When a young and possibly foolish child, I found that in being taught basic chemistry & having an inquiring mind that certain chemicals readily available from the grocer & hardware store could be mixed to create an interesting explosive. Applying theory from class, a pestle and mortar could reduce the two powders to a very fine dust, & in this condition the two once mixed could be fired by merely hitting it with hammer due to the intimacy of the fuel and oxidizing agent.

On a lighter note a bottle of Co2 of any sort is the best form of fire extinguisher in a small workshop since it will make no mess or damage tools Etc. A 3' length of reinforced hose attached to the bottle will serve to administer the gas and can be passed through a small gap to fill a room or building. In using Co2 one needs to remember that YOU also need to be able to continue to breath. Once caught in a cellar when a Co2 bottle burst I only had seconds to get out. On liquid fuel fires the result is spectacular, an invisible hand snuffing the flame out

I hope nobody need to use this information.

Good Luck Noel

noel shelley16/02/2014 20:56:37
1349 forum posts
21 photos

Gentlemen, Further to my last post, for those who want to see Co2 in action ! Find a liquid tight METAL container(bean tin or even a 5 Gal), pour a covering of fuel, paraffin (kerosene) or diesel in the bottom of the container and ignite ! When burning furiously gently open the valve on your Co2 bottle to feed gas into the container via a pipe and watch a miracle that Paul Daniels or even David Blaine would be proud of !

In this day and age I feel obliged to point out that this experiment MUST be carried out well away from any buildings or substances that could catch fire. It would be a wise precaution to have some alternative form of extinguisher to hand, sand being one. On NO account should water be used.

Have Fun, be careful . Noel.

Charles17/02/2014 00:28:14
5 forum posts
2 photos

This is not about spontaneous combustion either, but I had a little adventure with a bath heater many years ago while living in the Eastern Goldfields that I am reminded of now. The bath heater was a tall sheet metal cone with a little round door at the front. The type was almost universally used in Western Australia in the distant past. These water heaters were just known as `Chip heaters', because they were meant to be fuelled with small chips of wood. It stood at the end of the bath and once the fire was going well, hot water that contained little black sooty bits, would bubble from the overflow pipe that led to the bath.

Starting up the fire and feeding it with its diet of chips was too onerous a task for me and I discovered an easier way. Since I was always fiddling about with engines and so forth, there was an unending supply of oily rags about the place. I found that if I liberally doused one of these rags with kerosene, tossed it through the little round door and followed it up with a lighted match, it would usually generate enough hot water for a bath. It was fast to heat, and while burning, there was an impressively loud pulsing and vibration emitted by the fire. Like a rocket preparing for take off.

On one of these high speed firing sessions, the fire went out before there was enough hot water for a proper bath. I was wandering about the bathroom, naked and ready for a bath, but there was only about 2 inches of water in the bottom of the old, white enamelled bathtub. I soaked another rag in kero, swiftly opened the little round door, and chucked it in to the fire and slammed the door. I figured that would make enough heat to finish the job. What actually happened was that the rag extinguished the remnants of the fire and all went quiet. I peered carefully through the doorway and could see wreaths of white kero vapour swirling in the hot combustion chamber. Bringing my great mental powers into action, I decided that a means of ignition was all that was needed to get the fire back in action again. I was right.

I struck a match and tossed it into the vapour filled hole. It lit up with a mighty whoosh and a 3 foot long tongue of flame shot from the heater and licked me from knees to eyebrows. I thought that my hair was on fire, so I took a header into the bath to put it out. That was when I found out that although there wasn't too much water in the bath, what was there, was almost boiling. I rose vertically from the tub, half scalded and smelling strongly of singed hair. I didn't enjoy that, but it taught me a new respect for the combined powers of fire and water.

Charlie

John Olsen17/02/2014 03:56:29
1250 forum posts
94 photos
1 articles

I believe there is more than one way that spontaneous combustion can take place. Damp hay will heat up due to bacterial action, and it can apparently get hot enough to initiate ordinary combustion. Damp coal will do a similar thing, and spraying water over it to cool it off is only of limited value since it helps keep the bacteria alive.

I think though that with the drying oils, the problem is that they can oxidise at room temperatures, this being how they dry anyway, and the process generates heat. With a varnished surface this is no problem, but in the confines of an oily rag problems can ensue. Epoxy resins also generate heat when they set, and if you use a fast hardener in a warm climate the stuff can catch fire in the pot while you are still busy trying to apply it to the job.

We tend to think of reactions like combustion taking place at or above a certain temperature, but if you talk to the quantum mechanics you will find it is more complex than that. To react, the two atoms or molecules have to overcome an energy barrier, and that corresponds to them having a certain energy, eg temperature. However, even if the temperature is lower, there is a probability that a reaction will take place. The hotter it is the more probable it is that any given pair will happen to react, but even at room temperature, some reaction can take place, depending on the material. So some materials will sit around at room temperature quietly oxidising. This is a bit like water sitting around evaporating even though it is not hot enough to boil.

John

Martin Kyte17/02/2014 09:54:14
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2756 forum posts
48 photos

Exothermic chemical reactions can cause spontaneous combustion including biochemical reactions due to the heat released. Danish oil used as a wood finish is a point in question. The oil hardens by oxidation and the applicator rags should be dried open rather than screwed up and chucked in the bin. Compost heaps and straw stacks can get really hot.

Martin

Jerry Wray17/02/2014 11:01:44
84 forum posts
4 photos

I do not intend to query the chemistry. I just want to give some simple advice about how to deal with the potential outbreak of fire due to oxidation reactions.

There are 2 main recommendations in facilities where sprinkler systems are not available.

All rags, especially those contaminated with paint, varnish etc. should be placed in a bucket or other suitable receptacle and covered with water, thus excluding the air from contact with the contaminant.

Keep a foam extinguisher handy, messy when used but easier to clean-up than the residue from a fire. Do not use CO2 in a confined space.

DAHIK.

Jerry

Andrew Johnston17/02/2014 11:25:09
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6603 forum posts
701 photos

Another OT post, on the subject of coal dust. Many years ago when I was designing electronics for active noise control we fitted a system to a coal mill at a cement works. The mill crushed coal to a powder and then blew it into a rotating furnace (150 feet long and 8 feet diameter) where it burnt along with crushed limestone and other ingredents. We were trying to quieten the fan (driven by a 2.5MW DC motor) that blew the coal dust into the furnace. We were told that there were two ways to build a coal mill to prevent damage caused by the coal dust exploding. One, run in an inert atmosphere or two, build it like a brick built outhouse so it would survive the inevitable explosion. The coal mill we worked on used the latter method. Unfortunately, when the coal dust did explode, the design calculations were proved to be wrong, as the explosion did rather a lot of damage. Ironically our loudspeakers with their paper cones survived the explosion.

Regards,

Andrew

ChrisH18/02/2014 10:29:56
1018 forum posts
30 photos

Thanks to all for the comments - all very interesting/informative.

Chris

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