4. It shall be the duty of the manager of every mine to ensure that there are provided in relation to every line—
(a)sufficient coupling poles or other suitable mechanical appliances for the purpose of coupling and uncoupling vehicles;
(b)where requisite, sufficient pointed wooden sprags (each of a length not exceeding three feet) and sufficient scotches; and
(c)on every self-acting incline, that is to say an arrangement in which vehicles are pulled or intended to be pulled up a line by other vehicles moving by gravity down another line, such safety devices as are necessary to prevent the occurrence of accidents likely to cause bodily injury to persons, being accidents caused by the running away of such vehicles, and, at the top of each of those lines, stop-blocks.