It's always worth mentioning, stay in your shop when things are running. I had my first spoilboard fire back in late 2006 due to inexperience. Well, after 11 years this time was worse but could have been a lot worse. Caught it because of the smoke smell and able to shutdown and take care of things quickly. Burned the plywood too. Lost the spoil board so had to surface it down and put on a new one.
It happened due to a mistake in the cut file. I was using a slow plunge speed, forgot to lower the RPM and didn't apply peck drilling. It plunged a 1/4" bit through 3/4" of material in one shot and the dwell was too long. It opened up the air flow when it drilled through and that was all it needed to catch fire.
11 years of experience, if it can happen to me it can happen to anyone. So glad people were in the shop to smell it and shutdown to get it under control. It is so tempting when a long job is running to leave and go do other things (and I admit I have done that time to time) but it is not worth it. Watch, listen, smell. Better to be there and stop a disaster than come back to a shop burning down.
Be safe and keep cutting!
Robert
HabitatForBats.org