Self-ignition tendency of some oils

Having been involved in an insurance report for a 'mysterious' fire I thought I'd spread the word. The Police were involved since it appeared arson but on investigation their boffins concluded that it was caused by the oil in rags left from rubbing down the woodwork.

I had heard of this before when the local art school had this problem from linseed oil impregnated rags after oiling wood carvings and had a 'suspicious' fire in their rubbish bin in the early hours of the morning.


This is worth passing around to raise awareness since many people have never heard of it. Hopefully it may avert a disaster.




The following is taken from the website http://www.sintef.no/content/page1____8797.aspx

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The conclusions from the investigation may be summerized as follows:
Wood coating oil products (wood oils) containing drying oils may along with other commonly used products cause self-ignition by oxidation of the product. Oxidation is the main chemical process causing self-ignition.
Porous rags soaked in wood oils will only cause self-ignition and fire under special circumstances.
This fact is also confirmed by the rather low number of registered fires each year due to self-ignition by chemical processes (approximately 10 fires in residential buildings and 10 fires in other buildings), compared to the very high consumption of products that are capable of causing this specific type of self-ignition in addition to wood oil products.


A total of 33 experiments were carried out in order to find the self-heating and self-ignition tendency of different wood oils.
Eight different wood oils, including boiled linseed oil, one penetration oil and one anti-rust oil, as well as two types of rags (i.e. cotton rags and waste wool or ‘Twist’ rags) was tested in two different experimental setups.
Real spontaneous combustion was achieved in only 5 of 33 tests. Most of the tests resulted in self-heating and a sub-critical temperature development, i.e. the temperature increased to a maximum temperature, which was not high enough to cause self-ignition, followed by a temperature decrease down to the ambient temperature. The main reasons for this fact might be as follows:
a) A too small size of the experimental setup (causing high transmission heat loss)
b) A too high packing density of the rags (causing low ventilation (oxygen supply) and a corresponding low heat generation rates).
The following main requirements must to be fulfilled for self-ignition of oil soaked rags to take place, provided that the oil is prone to cause self-ignition:

• Insulation: The rags soaked with wood oil have to be located somewhere where heat loss by transmission is minimized. The rags have to be stored for example in a waste container of a certain minimum size filled with other waste with good insulation properties. However, under optimum ventilation conditions of the rags and elevated temperatures on hot summer days, the necessary size of the container to cause self-ignition may be strongly reduced.
• Ambient temperature: The spontaneous heating is favoured by high ambient temperature. By increasing the ambient temperature from 24 °C to 44 °C in tests with ‘Faxe’ wooden floor oil a sub-critical temperature development was changed to a critical temperature development, which caused almost complete spontaneous combustion of the 3 x 1 m² rags.
• Minimum ambient temperature: Based on the experiments carried out, it can be concluded that it is unlikely that ordinary wood oils in ordinary waste containers will self-ignite at temperatures below 10-15 °C.
• Ventilation: If the ventilation rate is too high, the heat will dissipate. If the ventilation rate is too restricted, the oxidation and the heat generation will be too low. The ventilation rate is probably the single most critical factor for self-ignition. A too high packing density of the rags will restrict the ventilation of the rags. Restricted ventilation of the rags was probably the case more often than the opposite during the tests carried out. Not even 0.3 litre of the highly pyrophoric boiled linseed oil absorbed in a 3 m² cotton rag caused self-ignition at high packing density.
• Amount of wood oil: It seems as if the needed amounts of boiled linseed oil and cotton rags to cause critical temperatures and self-ignition under normal indoor conditions have to be 0.075-0.1 litre evenly distributed in a 1 m² cotton fabric. For the wood oils the needed quantity was 0.3 litres. However, more optimal ventilation conditions, increased ambient temperature and increased size of the waste container may reduce the needed amount of wood oil.
• Oil loading: If the oil loading (in l/m²) is larger than the optimum content, the temperature increase of the oil is restrained due to too much heat is used to increase the temperature of the excess oil. The optimum oil loading area densities seemed to be in the range 0.1-0.15 l/m².

Waste wool or ‘Twist’ rags seemed to be more prone to self-ignition than cotton rags. This is indisputable due to the fact that the twist rags have a larger surface area than the cotton rags.
Even though sub-critical temperature development was achieved in the far most of the 33 tests (primarily due to the small insulation thickness and too high packing density of the rags), the tendency to cause self-ignition may also be deduced from these tests. The most hazardous oils are those oils with the most rapid and highest temperature increase of the oils with sub-critical temperature development, provided the experimental conditions were equal.
The oils tested can be divided into three classes with respect to fire hazard:

• Class I - Extremely Hazardous oils:
  Linseed oil.
• Class II - Hazardous Oils (ranked, i.e. the oil listed first is most hazardous):
  1. Faxe wood floor oil,
  2. Owatrol anti-rust oil,
  3. Trip trap wood floor oil and
  4. Butinox wood oil
• Class III - Non-hazardous or less hazardous oils:
  1. Junker Rustic oil
  2. Wood oil from ‘Norsk Trepleie’
  3. Faxe oil care

By examination of the comments made by the police investigators in statistics from DSB with respect to the cause of fire, Faxe wood oil and linseed oil were mentioned in 27 and 26 of 268 cases of ignition by chemical processes, while the other wood oils were hardly mentioned.
Among the five wood oils that were characterized as hazardous, it was only Trip trap wood floor oil that did not have any safety marking or warning tag against the risk of self-ignition and fire.
Recommendations for safe handling and disposal of equipment for wood oil.
The following procedures are recommended:

• Put application equipment in a container filled with water
• Burn application equipment in a fire place or oven
• Store the rags in an air tight metal container intended for fire hazardous waste in case of short time storage or transport.

Final Conclusion
On the basis of this experimental series it can be concluded that wood oil products do represent a risk of self-ignition and fire, even though self-ignition occurs only under certain circumstances. Due to the fact that these circumstances may occur rather frequently, especially indoors as well as outdoors in the summer time, we recommend a clearly visible warning label on such products. That is, with respect to the fire hazard and how to treat application equipment after use

 

I have heard that acetone will self-ignite if rags are buried and bunched up. I'm very careful to hang rags used with acetone open to gas off.
Never heard of linseed oil doing this. Thanks for the info, mike.

A.

 

Linseed oil is very dangerous for this. I have watched it happen on a hot day. Sometimes called "spontaneous combustion" it is something all boatbuilders should be aware of. Varnish rags are prone to it as well. Hang them up in the open air.

 

I varnish all the time. I rarely (can't recall) produce varnish rags. A real screw up. i suppose I'd have to remove the varnish applied. Very much appreciated advice. i've read many varnishing articles. This wasn't mentioned, I don't think.

 

I too have never heard of this phenominum.

It was however expected of haystacks that got wet. They used to have a long thermometer that they would push into the hay to check for heat build up.

But this spontanious combustion was because of decay (Rotting)

If the hay was even slightly wet it could not be stacked until perfectly dry.

 

Apparently off-gassing creates heat. Substances not only create off-gassing, but if the gas cannot expand it increases in temperature. Known to firefighters. Probably has to do with the ability or non-ability of air molecules to combine with gas. Dunno, I'm no chemist.

 

I'd heard about the hay stacks.

Another one is the self ignition of coal in ships holds if loaded while wet.

A lot of exposed shale deposits in mine pits self ignite after rain too.