It would be safe to stand on the insulated sphere since it is covered by a material that does not allow the passage of current or an insulator. With the insulator, the student can freely touch the sphere but without it, touching the sphere when it is charged is very dangerous as it would electrocute you since the charge from the sphere would freely flow onto your body. Insulators are being used to be able to protect humans from any danger in touching charged objects. Insulators have very high resistance to the flow of current through them. Examples are rubber, glass, cellulose, polystyrene and wood.
