This bloke ran a test with 18 samples of boiled linseed oil and other finishes, just balling them up in different ways. He had three spontaneously ignite, the first around six hours and the last at eleven hours. Most of the samples showed some kind of temperature increase, and some stayed quite cool for a long time before they went up. One reignited after he had carried it out and used an extinguisher on it!
Sharing today because yesterday (despite being aware of the issue and doing a video on it!) he had a real life fire at his shop - thankfully the balled up rags were outside when they ignited, so he only lost a piece of fencing.
Don’t muck around with your finishing rags folks: dry them flat, put them in a jar of water, or burn them safely.
It’s something I knew, and have taken precautions to deal with when I’ve used this kind of finish - but I was seriously shocked by how they just went up like that.
Nearly happened to me quite a few years ago , 1 year project converting a house into two 3bed flats, dug out the basement , put a loft conversion on.
Two weeks before the sale completion of both flats I was finishing the downstairs kitchen worktop with ikea worktop oil. Went for lunch, about 30 minutes.
On returning the bundle of rags was smoking, took them outside and they were close to igniting, and were charred inside.
A longer lunch or if i had left them overnight would have been a £600k mistake.
This was , and I hope still is on the woodshop basic induction.
By the way I did see that experiment and was shocked how long it took!