I posted this on several other woodworking forums of which I'm a member but feel so strongly about this that I felt it needed posting here as well. Many of us use BLO in finishing, so the possibility is there.
I just left a friend's house who left some linseed oil soaked rags, less than 24 hours, in a bucket in his attached garage. They smoked up the garage and were just at the point of ignition when his wife noticed smoke in the garage. She called 911 and firefighters were able to find the problem before damage was done, mainly smoke. The biggest problem was that she is confined to a wheelchair and the only exit ramp is through the garage. Guess you know what we'll be doing pretty quick....building another ramp to the outside.
I guess I said all that to say....dispose of those oily rags properly!!!