To control hazardous energy, a machine must be separated from its power, and the separation must be held in place. Two tools do the holding. A lock holds the energy isolating device physically. A tag warns people not to operate it.
Energy isolating devices
An energy isolating device is a mechanical device that physically prevents the transmission or release of energy. Examples:
- a manually operated electrical circuit breaker;
- a disconnect switch;
- a line valve in a pipe;
- a block that holds a part from moving.
Push buttons, selector switches and other control-circuit devices are not energy isolating devices. A stop button only tells the machine to stop. A faulty circuit or another person can start it again. This is why switching the machine off at the control panel is not lockout.
Lockout
Lockout means placing a lockout device on an energy isolating device, following an established procedure, so that the equipment cannot be operated until the lockout device is removed. A lockout device uses a positive means, such as a lock, to hold the isolating device in the safe or "off" position.
A lock is a physical barrier. A person would have to cut or break it to restart the machine.
Tagout
Tagout means placing a tagout device, such as a warning tag, on an energy isolating device following an established procedure. It shows that the equipment may not be operated until the tag is removed.
A tag is only a warning. It has no physical power to hold anything in place. Someone can simply ignore it or pull it off. This is the limit that tagout training must teach.
Which one is required?
- If an energy isolating device can be locked out, the employer must use lockout. Tagout may replace it only when the employer shows that a tagout program gives full employee protection, equal to a lock.
- If a device cannot be locked out, the employer must use tagout. It must also show equivalent protection, which can take extra steps. Examples: removing a circuit element, blocking a control switch, opening an extra disconnect or removing a valve handle.
- Equipment installed after January 2, 1990 must be designed so that it can accept a lockout device. The same goes for major repairs, renovations and modifications after that date.
OSHA treats lockout as the surer method. In practice, a lock is the first choice.
Rules for the devices
The employer provides the locks, tags and hardware. The standard says they must be:
- used only for controlling energy, not for locking lockers or tool boxes;
- durable enough for the conditions where they are used;
- standardized within the facility by color, shape or size;
- substantial, so a lock cannot be removed without excessive force or unusual techniques such as bolt cutters;
- identifiable, showing which employee applied them.
Tag attachments must be non-reusable, attachable by hand, self-locking and non-releasable. They must withstand at least 50 pounds of pull. A one-piece nylon cable tie is a typical example. Tags must carry a warning such as "Do Not Start," "Do Not Open," "Do Not Close," "Do Not Energize" or "Do Not Operate."
What to remember
- A stop button or selector switch is not an energy isolating device.
- A lock holds a device in place; a tag only warns.
- Lockout is required when a device can be locked out, unless tagout gives full protection.
- Locks and tags are for energy control only, and each shows who applied it.
- Never remove or ignore a lock or tag that is not yours.