What must be attached to each switch involved in a clearance procedure?

In the context of switch clearance procedures, it is critical to ensure that all switches involved are properly identified and secured to prevent accidental operation while maintenance or work is being done. The Hold (Danger) Card serves this purpose effectively. When a Hold (Danger) Card is attached to a switch, it clearly communicates that the switch is out of service and indicates to all personnel that work is being performed. This ensures that anyone approaching the switch is aware that it should not be operated.

The use of a Hold (Danger) Card helps in maintaining safety standards and ensuring effective communication during maintenance operations, as it reduces the risk of misunderstandings or accidental activation of equipment. This form of safety practice is vital in environments where multiple people might be working on or around energized equipment.

While the Safety Card, Lockout Tag, and Clearance Certificate have their own specific uses in various safety and operational procedures, they do not fulfill the same function in the context of a clearance procedure as the Hold (Danger) Card does. The Hold (Danger) Card is specifically designed to inform personnel that a switch is under a clearance condition, making it the most appropriate answer for this question.