Final answer:
Practice grenades that are duds should not be touched or recovered for at least 30 minutes to ensure safety and should only be dealt with by trained personnel.
Step-by-step explanation:
Practice grenades that fail to function, also known as duds, should not be approached or recovered for at least 30 minutes. This safety measure is to ensure that if the grenade were to function late (a slow burner), there would be no personnel nearby to be injured. Additionally, it is imperative that duds are handled only by trained personnel who have the proper knowledge and equipment to safely manage and dispose of the faulty ordnance.