A few years ago I had some training at Techshop, one each on the Epilog, Trotec and ULS provided a trainer for the couple of classes I had on the Universal. All say to blow the little fires out (after you hit the E stop). The Techshop method is not to use an extinguisher unless the fire is out of control. My big one just went up as the backing paper caught fire and spread to the acrylic. My guess would be that melamine residue in the honeycomb or some material caught down there ignited it. At peak we'll cut 40 hours a week or so (machine cycle time, not total time..) Even when you are with it, things catch on fire. The best thing to do is not panic.