12. Every driver in charge of a locomotive on a line, or a person preceding that locomotive on foot, shall, on approaching any level crossing ordinarily used by persons employed at the mine to cross that line, any curve of the line round which it is not possible to see from the locomotive or any other place at which the safety of any person employed at the mine is likely to be endangered by reason of the movement of the locomotive, give sufficient and timely warning of the approach of that locomotive, being a warning audible to persons for the time being at or near that level crossing, curve, or place (as the case may be).