I may be violating a forum rule by posting a youtube link but I do so with the help of keeping folks safe, and it is not looking for money.
I have always hear even from high school shop class …“Dispose of you oily rags SAFELY” … well we all know that after a while it starts to sound like an old wives tail … well “Bourbon Moth Woodworking” runs a test.
of course you can’t warn about this often enough. Thank you for warning once more. Usually you learn this in studies or apprenticeship, it’s in every woodworking textbook before 1950 (unfortunately linseed oil use decreased since then, even if it is such a superior material, not only for finishing, with a comeback in connection with the hand tool woodworking comeback since the 1980ies).
Not everybody thinks that “after a while it starts to sound like an old wives tail”. As a child and researcher, I tried out the conditions for the self-ignition of the linseed oil rag under safe conditions. I didn’t need to have my workshop burning to continue to be convinced it’s true
In short: Polymerizing oils exposed to oxygen on a larger a surface like a rag can autoignite at any time. They don’t need heat or sparks to autoignite, it is the polymerizing process itself that produces heat sufficient to ignition. Always enclose them after use in a small airtight container. Note: Autoignition (at ambient temperature) only happens with polymerizing oils, not with other oils, even if they are combustible.
Workers had been refinishing woodwork in a vacant office earlier in the day, and workers left a pile of rags soaked in linseed oilon the floor.
You can enclose linseed oil soaked rags in a used jam jar. In the event of spontaneous combustion, the oxygen would be quickly consumed and the flame would die. Furthermore the consumption of oxygen already occurs during polymerization and ends when the oxygen has been consumed. That is why a too thick layer of linseed oil will never cure, because no oxygen reaches the lower layer.