Originally Posted by tghsmith
sawdust mixed with other things can do some interesting things(always empty the shop vac), linseed oil on cotton rags is an almost sure fire just waiting for you to turn your back...
One of my members made a living giving fire precautions lectures. His take on linseed oil and cotton rags was that linseed oil based products (e.g. enamel paint) do not entirely set by just air drying, the linseed oil does slowly oxidize. Or in ordinary speak, burns. The process is slow enough so that on a flat surface, there is no problem. On a cloth or piece of cotton waste, however, there is a very large surface area and a very small volume. The heating effect is enhanced, and if enough volatiles and air mixture is there, you do get spontaneous combustion.
One of his cases was traced to a pile of rags that had been used to clean a pain spill that cooked itself overnight and set itself off when it got a bit of help from sunlight early the next day.