Compressed gas cylinders shall only be moved when:

Compressed gas cylinders should only be moved when the safety caps are installed. This is crucial because the safety caps, also known as valve protection caps, are designed to protect the cylinder valve from damage during transport. If the cylinder falls or is handled improperly, the cap helps prevent the valve from breaking, which could lead to uncontrolled gas release and potentially hazardous situations.

While there are scenarios where other options might seem relevant, such as having a full or empty cylinder, the primary concern during movement is ensuring safety and minimizing risks. The other options relate to conditions that do not specifically address the immediate safety of handling the cylinder. Therefore, the requirement for safety caps to be installed is an essential safety protocol when moving compressed gas cylinders.