Final answer:
A third rail emergency number should not be removed until the power has been completely shut down and safety is confirmed to avoid serious arcs and electrocution risks associated with the third rail of a railway system.
Step-by-step explanation:
To avoid a serious arc, a third rail emergency number should NOT be removed from the third rail or shoe until the power has been completely shut down and it is confirmed to be safe. The third rail is a method of providing electric power to a railway locomotive or train, and it poses a serious risk of electric shock or electrocution. It is of paramount importance that all safety protocols are strictly followed when dealing with the third rail, including the use of proper safety gear, observing clearance distances, and above all, ensuring that the third rail's electricity supply has been fully deactivated before any maintenance or emergency work is conducted.