What condition must gates meet when the enclosed area is unattended?

When the enclosed area is unattended, it is essential that gates be locked to ensure the safety and security of the space. Locking the gates prevents unauthorized access, protecting both the facilities and personnel that may be nearby. This practice is especially critical in CNG operations, where safety and security protocols must be followed to prevent accidents and maintain compliance with regulatory standards.

While other options may contribute to safety in different contexts, such as alarms providing warnings or specific colors adding visibility, they do not directly adhere to the fundamental requirement of securing an unattended area, which is achieved through locking the gates. Hence, ensuring that gates are locked is a primary protocol in securing unattended areas in gas operations.