Lock and tag
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Lock and tag or lock-out tag-out is a safety procedure which is used in industry and research settings 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 energy sources be "isolated and rendered inoperative" before any repair procedure is started. "Lock and tag" works in conjunction with a lock usually locking the device, or energy with the hasp, and placing in such position so hazardous energies can not be turned on. The procedure requires that a tag be affixed to the locked device indicating that it should not be turned on.
In the United States a red padlock is a standard safety device designating, locking and securing hazardous energy. No two keys or locks should ever be the same. Under no circumstance may a person's lock and tag be removed in industry except by the individual who put the lock and tag on.
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[edit] Identification
Identification must include the name of the person doing the lock and tag and a contact phone number.
[edit] Site polices regarding lockout/tagout
Many sites have the officially stated policy that only the person who tagged the device can untag it. This means that if a worker goes home after their shift without removing the tag from a device which is ready for service, then they will have to travel (at their own expense and on their own time) back to site to untag it. Giving approval for the removal of a tag over the phone is not an option.
Whilst this policy might make it seem as if it is encouraging workers to take the risk of not tagging out in the first place, it is usually accompanied by a policy stating that operating on a device without tagging it out will result in instant dismissal.
[edit] Industry safety standard in the United States
In industry this is an OSHA standard, as well as for electrical NFPA 70E.
[edit] Hazardous energy and its isolation
Modern machinery can contain many hazards to workers, from things like electrical, mechanical, pneumatic or hydraulic sources. For example a typical industrial machine may contain things like hot fluids, moving presses, blades, propellors, electrical heaters, conveyor belts with pinch points, moving chains, ultraviolet light, etc.
The National Electric Code states that a safety/service disconnect must be installed within sight of serviceable equipment. The safety disconnect ensures the equipment can be isolated and there is less chance of someone turning the power back on if they can see the work going on. These safety disconnects usually have multiple places for locks so more than one person can work on equipment safety.
Disconnecting or making safe the device is known as isolation. This is accompanied by the tagging of the device to let others know not to de-isolate the device.
In industrial processes it can be difficult to establish where the appropriate danger sources might be. For example a food processing plant may have input and output tanks and high temperature cleaning systems connected, but not in the same room or area of the factory. It would not be unusual to have to visit several areas of the factory in order to effectively isolate a device for service (e.g. device itself for power, upstream material feeders, downstream feeders and control room).
Modern safety manufacturers provide a range of isolation devices specifically designed to fit various switches, valves and effectors. For example most modern circuit-breakers have a provision to have a small padlock attached to prevent their activation. For other devices such as ball or gate valves, plastic pieces which either fit against the pipe and prevent movement, or clam-shell style objects, which completely surround the valve and prevent its manipulation are used.
A common feature of these devices is their bright colour, usually red to increase visibility and allow workers to readily see if a device is isolated. Also, the devices are usually of such a design and construction to prevent it being removed with any moderate force. (That is to say that an isolation device does not have to stand up to a chainsaw, but if an operator forcibly removes it, it will be immediately visible that it has been tampered with).
