Dave wrote:

On Thu, 11 May 2006 22:32:22 GMT, Mys Terry
said:

There are few things worse on a boat than having a fire at sea. I'm not entirely
sure that there is anything worse.

No dispute there. Merely pointing out that the initial inquiry was not
whether spontaneous combustion is a risk, but asking that that risk be
quantified.

OK - you keep going on about this when it has already been answered.
If you don't consider the risk of fire a large risk then you don't
need to worry about spontaneous combustion.

In any case, the specific inquiry was about the possibility of rags
contaminated with linseed oil spontaneously combusting. Yes it
happens if precautions are not taken. It is a real risk.

A pile of rags or paper towels soaked with linseed oil can under the
proper circumstances actually start burning without warning, leading
to the manufacturer's warning that all oil-soaked rags should be
stored under water in a covered, metal container, or washed before
storage or disposal.

From a document called
" Fire and Explosion Investigation - Spontaneous Combustion of Drying
Oils as a Fire Cause" January 2000

There are three conditions
which are important in the spontaneous ignition process. These a (i.) rate of heat generation, (ii.) air supply
and (iii.) insulation properties of the immediate surroundings. A loosely packed pile of drying oil soaked
cloths may spontaneously combust whereas a tightly packed pile or a single cloth on a clothes line will not. In
the case of a single cloth on a clothes line, although there is sufficient air supply to accommodate oxidation,
any heat generated will be carried off quicker than it is formed.

Investigation of a spontaneous combustion fire is very difficult due to the fact that there are no significant fire
residues left by this process. Thus, when flaming ignition occurs the chemical detection of residues of the
preliminary material may be impossible. In the investigation of a suspected spontaneous combustion fire there
are a number of diagnostic signs to look for. The major one being the presence of more fire damage to the
middle of a material mass than around the edges. In spontaneous ignition the most severe fire damage will
most often be in the centre of the fuel mass and in very large masses there may also be several separate
pockets of smouldering which may lead to several points of origin, ....
Another indicator of whether or not a fire was caused by spontaneous combustion may be
its behaviour when suppression of the fire is attempted. Initial attempts may only result in momentary
suppression of the flames followed by re-ignition.

This is important when you want to put out the fire - it isn't the
same as a normal fire where you can just wet down or foam the outside
of the pile.

Even in very small amounts, such as grams or ounces, these oils have been documented in laboratory
experiments to result in the spontaneous ignition of their support materials. In these tests the support
materials had a large surface area and were reduced to small volumes by being placed in a pile rather than
being spread out.
It was reported that a single rag the size of a handkerchief, which had been dampened with one of these drying
agents containing modified linseed oil, can burst into flames within 6-8 hours after exposure to the air. Also
the fire can continue to burn for an hour or more after ignition...

Tests carried out by
the Center of Forensic Sciences and the Ontario Fire Marshal’s Office confirmed this, They placed boiled
linseed oil on cotton rags and placed them in large waste containers at a temperature of 16-18°C. Smoke and
acrid odours were produced within one hour of the start of the test with flaming ignition produced 4-5 hours
later.

Some of the References for this article included

(1.) Abraham, C.J. A Solution to Spontaneous Combustion in Linseed
Oil Formulations. Polymer Degradation and Stability. 54: 157- 166.
1996.

(2.) Bertsch, W., Holzer, G. and Sellers, C.S. Chemical Analysis for
the Arson Investigator and Attorney. Huthig. 1993,

(3.) Underdown, G. W. Practical Fire Precautions. Gower Press, 2nd
edition, 1979.

(4.) http://www.interfire.org/res_file/fseab_si.htm This link doesn't
work as listed, but if you go to http://www.interfire.org/ and search
on linseed oil, the section listed will come up as one of the options.

(5) http://www.arson-codes.com/spontcom.htm This link doesn't work
anymore, but if you go to the arson codes website and select Reports
and Articles, the last article in the list is "Spontaneous Combustion
Explained" which says

Cotton rags soaked in linseed oil are very susceptible to spontaneous ignition. This is because the reaction of oxygen and linseed oil (oxidation) is fairly rapid and evolves considerable heat. Spontaneous ignition of the cotton rags can be prevented by restricting the amount of oxygen reaching the rags (placed in sealed metal container) or by providing sufficient ventilation (hanging on a clothesline) to quickly dissipate the heat.

RosalieAnn Figge Beasley, C.I.H.
retired - formerly MOSHA Consultation