(c)the exercising of such medical supervision as may be prescribed for any factory or class or description of factories where—(i)cases of illness have occurred which it is reasonable to believe are due to the nature of the manufacturing process carried on, or other conditions of work prevailing, therein;(ii)by reason of any change in the manufacturing process carried on or in the substances used therein or by reason of the adoption of any new manufacturing process or of any new substance for use in a manufacturing process, there is a likelihood of injury to the health of workers employed in that manufacturing process;(iii)young persons are, or are about to be, employed in any work which is likely to cause injury to their health.