“The problem with sawdust is that it doesn’t look very dangerous,” says Tom Harned, a field manager for Liberty Mutual. Yet it burns quickly, much faster than other kinds of dust, which tend not to be as concentrated. If you don’t have a good dust-collection system, sawdust will accumulate on surfaces, where it can combust. Rule of thumb: If you have even an ultrathin layer of the stuff, you’re asking for trouble. Regularly use a vacuum designed specifically for combustible dust. And don’t use compressed air in a can to blow sawdust off surfaces: It can propel the dust into the air, where it can more easily ignite.