I was saddened to hear that
a member of my own guild lost his shop and tools last month
to a fire started by a bunch of oily finish rags. It is a
common cause of shop and worksite fires, but it is easy to
prevent.
Oily rags are spontaneously combustible. That means that
even in a very small pile, they will generate enough heat
to ignite themselves in about two hours or less. Oil cures
by oxygen polymerization, which is a fancy way of saying
oxidation. Remember high school chemistry? Fire was described
as "rapid oxidation." This is the slower version of the
same thing, and it too generates heat. In fact, it generates
enough heat to catch the rags on fire. It can happen with
any drying oil or finishing oil: linseed or tung oil, oil
stains, and even oil varnish, polyurethane, oil based filler,
or danish oil mixtures.
To prevent the heat buildup, lay out oily rags ONE LAYER
THICK. Drape them over the edge of your workbench, trashcan,
or even a clothesline. That will allow enough air flow
to dry them quickly AND to dissipate the heat as it is
generated. When the rags are stiff and crusty, usually
in 24 hours, no liquid oil will be left uncured. At that
point they are landfill safe and can go into the household
trash.
Please, take extra care with oily rags. Lay them out to
dry and don't let them sit in piles. I don't want to hear
that any of my readers has had a spontaneous combustion
fire in his or her shop.
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in
a very small pile, they will generate enough heat to
ignite themselves in about two hours or less."
