No Heavy Duty Repairman Xxxxxxx or Master Mechanic. (Heavy Duty) shall work with the tools, except when required in the supervision of his work, and except in an on-the-job emergency, provided, however, in the event a regular Heavy Duty Repairman is absent, the Heavy Duty Repairman Xxxxxxx or Master Mechanic (Heavy Duty) may work with the tools, provided in such case that prior to such work the appropriate Job Placement Center of the Union has been requested to dispatch a replacement.
