Lockout/Tagout (short: LOTO) is a safety procedure which is used in industrial production facilities to ensure that dangerous machines are properly shut off and not started up again prior to the completion of maintenance or servicing work. It requires that hazardous power sources be "isolated and rendered inoperative" before any repair procedure is started. "Lock and tag" works by locking e.g. a switch or valve with a hasp or plastic device, and placing it in such a position that no hazardous power sources can be turned on.