Dust collectors for combustible dust will have a deflagration vent(s). These vents are like weak-seam welded roofs in that they are large surface area vent covers that relieve the pressure inside the dust collector should there be an explosion inside the collector. As one can imagine, someone standing in the path of these vent covers can be severely injured or killed if they strike them. So most codes will require the area in front of the panels to be labeled to keep workers and equipment out of harm’s way.