Tubular gauges on stationary tanks, vats, or containers which contain corrosive materials shall be shielded to prevent liquid spray from endangering employees should the gauge break. All such gauges shall be guarded when exposed to the hazard of being broken by accidental impact and in all cases when located less than 7 feet above or 3 feet laterally from working levels or passageways. All such gauges shall be provided with valves which can be readily closed in case of breakage. When practicable, ball-check or other self-closing valves shall be used.