Final answer:
Reusable refrigerant containers under high pressure must be hydrostatically tested every 5 years to ensure safety and integrity.
Step-by-step explanation:
The safety regulations for reusable refrigerant containers that are under high pressure specify that they must be hydrostatically tested periodically to ensure their integrity. According to the U.S. Department of Transportation (DOT) and other relevant regulatory authorities, such containers typically need to be tested every 5 years. This ensures that the containers can safely handle the pressurized refrigerant without risk of failure or leakage.