Abstract: In a safety shut-off system for a rotary drill rig with an internal combustion engine operatively connected by a drive train to rotate a drill spindle, the drive train including a clutch, a brake is provided in the drive train, and solenoids are provided that are actuated to cause the brake to be applied, the fuel line to the engine to be closed or the ignition circuit of the engine to be broken, and the clutch to be put into a neutral condition, each of the solenoids being connected to an electric circuit from a source of current, the brake and engine stopping solenoids being continuously biased toward brake-applying, engine fuel line closing or ignition circuit breaking position, and moved against that bias by current from the power supply. At least one wobble type shut-off switch, is positioned adjacent the drill, the switch having an exposed, elongated, outwardly projecting operating lever, the displacement of which in any direction perpendicular to the long dimension of the lever opens the circuit.