Interlocks and tag out devices "lock out" valves, electrical switches or other components. They are used during the service or maintenance of machinery and process equipment. Interlocks and tag out devices are often used with safety interlocking systems to ensure that equipment cannot be operated until all safety mechanisms are in place; however, safety interlocks should not be used as replacements for lock out devices. To protect personnel from injury, machines that require maintenance or service should be locked out properly using interlocks and tag out devices. Interlocks and tag out devices can identify the physical state of a required condition, and supply the requirements to a primary safety control circuit. When a safety device is disabled, an interlock is the control circuit that turns off power to the machine. A tag out device is a tag, prominent warning, or other component used with an energy isolation device to indicate that the machine being controlled may not be operated until the tag out device is removed. An energy isolating device is a mechanical device that prevents the release of energy to machinery, such as manually operated electrical circuit breakers, disconnect switches, and manually operated switches. Interlocks and tag out devices can also be used to stop electrical, hydraulic, pneumatic, chemical, and thermal energy sources. Interlocks and tag out devices are used in many locking out and tagging out practices and procedures to safeguard employees from the unexpected startup of machinery and equipment, or the release of hazardous energy during service or maintenance activities. Tagging out requires a visual indication of a lockout or of any potential problem or hazard associated with equipment. As part of the lockout procedure, the tagging out of locked energy isolating devices is required. In addition, a written record of a lockout or reasons why a lockout is not required must be provided. To aid in the establishment of proper procedures for locking out and tagging out machinery and equipment, the U.S. Occupational Safety and Health Administration (OSHA) establishes, maintains, and publishes various standards and regulations. Suppliers of interlocks and tag out devices may provide additional guidelines.