Spontainious combustion

[Ben from Vic.]

Hello all.

I've heard a little about Danish oil being able to self ignite, and I was wondering if anyone could tell me what conditions are required for this to happen?

Would it be a hot, dry, windy day? or just hot? just windy?
Or does the none of this make any difference, and the stuff just goes up whenever it fells like it?

I've not had any problems, just qurious.


Ben.

[ozwinner]

I think youll find that any oily rag left rolled up is liable to do it.
I never had it happen as I always spread the rags out to dry away from conbustables.
Its not confined to Tung oil either.
Its something to do with the chemical reaction causeing heat as the dryers, ....well dry.
I've never heard of anyone have it happen either.

Cheers, Fireman Sam

[bitingmidge]

Saw our neighbours house destroyed a few years ago at aobut 3.00am. He had left a solvent-rag in a pile of rubbish in his garage.

I think that the physical phenomena that causes it is "latent heat of evaporation" but it's 40 years since I last studied physics!

ANY liquid has the potential to cause this as it's physical state changes to vapour, haystacks catch fire because of WATER.

NEVER throw out cleaning rags after using any solvent unless they have been thoroughly dried out. I have actually screwed an old tea-towel rail to a cupboard in the workshop, and spread used rags to dry, before disposal.

I don't believe spontaneous combustion of any of the commonly used solvents is likely as a result of direct evaporation from a container, or for that matter from a spill. At some point in the evaporation process cold temperatures are created (or is that the compression bit) no doubt someone will fill us in!

Cheers,

P

[gatiep]

evaporation = drop in temp.
compression = increase in temp.

[bitingmidge]

evaporation = drop in temp.
compression = increase in temp.

That's it!! So where does the "compression" happen in a pile of solvent-damp rags or a pile of wet grass?

(Being careful not to confuse with heat generated from the anaerobic decomposition of vegetable matter! - Or is that what causes haystacks to combust?)

P

[Marc]

It is not the evaporation of solvents that causes the rags to increase temperature and ultimatley catch fire, such evaporation would lower the temperature. It is the oxidation of the oil, particularly fast in finishing oils varnishes or boiled linseed oil that need to oxidise to harden. This is a copy of industry recomendation:

...............
Spontaneous Combustion
Beware of Creating a Fire Hazard

Picture this: It’s time to cut the lawn again. You go into the garage to get your mower ready. You check the mower’s oil level and see that it needs some engine oil. So you pour in some oil and wipe up the minor spillage with an old rag. Then you toss the rag into a pail, wheel the lawnmower out of the garage, and proceed to cut the grass.

What’s Wrong with This Picture?
If you’re thinking that the oily rag you tossed into the pail might be the problem, you’re right. Something as seemingly harmless as tossing an oily rag aside and forgetting about it can ignite a big problem for you. That’s because of a phenomenon called spontaneous combustion.

What Is Spontaneous Combustion?
The Encyclopedia Britannica defines spontaneous combustion as the outbreak of fire without application of heat from an external source. This combustion can occur when flammable matter like oily rags, damp hay, leaves, or coal is stored in bulk. Spontaneous combustion, sometimes referred to as spontaneous ignition, begins when a combustible object is heated to its ignition temperature by a slow oxidation process. Oxidation is a chemical reaction involving the oxygen in the air around us gradually raising the inside temperature of something (like a pile of rags) to the point at which a fire starts.

Spontaneous Combustion Can Cause Fires
While spontaneous combustion isn’t a common occurrence, it can be disastrous. Mark Divoll, an Assistant Vice President in Claims at Amica, says that spontaneous combustion causes major fire losses each year for Amica policyholders. "One of the most common scenarios is when an insured’s floors or woodwork are being refinished and stain-soaked rags are left in a heap on the floor. Something as simple as not storing these rags properly can cause major fire damage," Mr. Divoll said.

In fact, the way combustible materials are stored has a lot to do with whether or not they’ll spontaneously combust. For example, while an oil-soaked rag stored in a pail could heat up enough to burst into flames, the same oily rag laid flat to dry would probably have sufficient airflow to prevent heat buildup. Similarly, if the oily rag was placed in a tightly sealed jar, it most likely would not have sufficient air to allow the oxidation process to occur. That’s why it’s a good idea to look around your garage, storage shed, and yard on a regular basis to ensure that all flammable materials are properly stored. Be sure that you:

• Carefully store oil-, gasoline-, or paint-soaked rags. Store them in a tightly sealed container in a cool, well-ventilated place away from other combustibles. Or, lay the rags out individually on a flat surface and leave them to dry completely before reusing.


Solvent-soaked rags are not a spontaneous combustion hazard but may be a fire hazard, since many solvents are flammable. In addition, the solvents can evaporate creating a health hazard. Solvent-soaked rags should be placed in closed containers to reduce evaporation and minimize the chance of someone tossing a lit cigarette onto the rags and causing a fire. The container should be emptied daily and the solvent should be allowed to evaporate outside.

[Shane Watson]

:eek: best I go find that oily rag I through somewhere in the shed last weekend....... Mwahahahaha....! Guess if anyone should know better it would be me...

[bitingmidge]

Marc,

Many thanks for the enlightenment!

In the quote, mention was made of damp hay, which is another situation I am quite familiar with, and while I fail to see what is oxidising I know that there is enough heat build up to cause spontanious "Iginition"

Now the woodwork connection Just this very morning I replaced the plastic bag full of sawdust from my DC. Most of the material has been in it for two to three MONTHS. I tied the old bag off and left it outside (in the sun) for about an hour, and was amazed at the amount of condensation on the bag. I could have easily collected half a cup of water, or maybe more.

I guess if one is using timber dried to 8% moisture, then it is obvious that 8% of the sawdust will be water. In my case there was a fair bit of "green" timber so content would have been much higher a few months ago.

Could it be that fires in dust collection systems previously thought to have been started by a spark from a metal object hitting the fan, and/or static electricity, could actually be started by "Oxidisation" as the moisture in the sawdust evaporates?

Cheers,

P

[Marc]

Hay ingites as a result of a more complex process.
The spontaneous oxidation of diphosphane gas is produced by decaying organic matter. Diphosphane is a hydride which becomes a vapour at between 20 and 30° C and can spontaneously combust in air at low concentrations. This are the misterious flames in the cementeries.

In this case, the oxidation itself is unlikely to cause combustion but it ignites the methane produced by fermentation in abscence of oxigen in the lower part of the hay heap and this methane is ignited by disphosphane oxidation.

From the little I read about sawdust bags, apparently ambers formed by sanding a hidden nail, can remain alight buried in the sawdust for quite some time, and finaly erupt in a full fire even the day after.

The conditions necessary for the formation of Diphosphane and Methane in a saw dust bag are just not there.

[echnidna]

The theory why rags can ignite is interesting.
I always have a 20 litre drum of water in the workshop and all oily rags go into it.

[soundman]

While its probably unlikely in a dust colector, large piles of saw dust (sawmill piles) have been known to self combust after rain.

A mate in the rural fire brigade reconed that the green waste pile at his local dump used to go up regular.

it obvious when the cause is decomposition as the root of the combustion is deep in the pile. rather than arson as the source will plainly be seen as surface originated.


as for the oily rags a bloke in my class at school nearly found him self homeless due to his fathers carlesness with a finishing oil rag.
The misses smelt the smoldering & draged the waste tin outside.

I didn't think it was as much a problem with mineral oils, but boiled linseed oil is a definite goer.

be interested in easties comment.

[RETIRED]

Gooday.

Oil soaked rags were the cause of a $2,000,000 fire at a nearby Mercedes and Audi dealer near us many years ago.

[ozwinner]

!!!!!!
What have you been up to?????

Al