Dangerous coal dust surrounds a miner working in a shortwall mine underground. Shortwall mining involves the use of a continuous mining machine with moveable roof supports. The continuous miner shears coal panels 150–200 feet wide and more than a half-mile long. Shortwall miners spend much of their working lives in coal seams 3 to 5 feet in height, in intense dust and at risk from mine roof collapse and/or explosion from gases.