Lockout/tagout: potential energy

Lockout/Tagout (LOTO) is the practice of controlling hazardous energy to prevent the unexpected start-up, energization, or release of stored energy during service or maintenance activities. In many cases, LOTO involves shutting down equipment, turning off or disconnecting power sources, and placing a lock or tag on the equipment to indicate that it cannot be turned on or to prevent it from physically being turned on.

Lockout/Tagout procedures are used to protect workers during maintenance, service, or other tasks that could put workers at risk of injury. The actual locking or tagging process of LOTO procedures are used to prevent a person from starting equipment or machinery by mistake. However, there are other risks that must be addressed by LOTO.

One of those risks is the accidental release of stored energy, or potential energy. Potential energy can take many forms. Electrical, mechanical, hydraulic, and pneumatic systems can all store energy that can be released accidentally even when equipment or machinery is locked out or tagged out properly. For a LOTO program to protect workers completely, both primary energy and potential energy must be accounted for.

Mechanical Energy

Mechanical potential energy can be created by a variety of situations. Any machinery or equipment that uses springs creates potential energy when a spring is under tension. If any spring remains under tension when equipment is shut down for service, the potential energy can endanger a worker.

Elevated machine members can also create potential energy due to gravity. Any raised member on a piece of equipment, such as an overhead crane or a manlift, is being acted on by gravity, and if it becomes unsecure, the potential energy created by gravity can put workers at risk. For a LOTO program to be completely effective in preventing the unexpected release of energy, these forms of mechanical potential energy must be accounted for.

Pressurized Systems

Many kinds of equipment and machinery operate using pressurized components, including hydraulic and pneumatic systems. Like mechanical systems, these pressurized systems can store potential energy even after equipment is shut down.

The accidental release of energy from pressurized systems can be very dangerous and can injure workers performing maintenance or other service while equipment is tagged out. LOTO programs should include steps to release pressure safely from hydraulic and pneumatic equipment as a part of the lockout process. Including this step in LOTO procedures can effectively eliminate the risk posed by pressurized systems.

Electrical Energy

Electrical potential energy is can often be difficult to manage. Electricity is invisible, but incidents caused by electricity can be some of the most fatal and costly. Electrical equipment, such as electric hoists, CNC equipment, and other electrical machinery, can continue to store energy through capacitors and other means even after it is shut off. Electrical equipment should be de-energized, not just turned off, to prevent accidental energization.

To ensure equipment is fully de-energized, additional controls should be included in the LOTO process. Electrical equipment should be checked to verify the absence of voltage before any service is performed. This verification can be done by a qualified worker using personal protective equipment and a voltage test instrument. Absence of Voltage Testers, or AVTs, can also be used for verification. AVTs are permanently mounted devices that automatically check for any remaining voltage in equipment and can check sources of potential energy without putting a worker at risk of an electrical shock.

Whatever kind of equipment you use, potential energy is a serious concern. All forms of potential energy—mechanical, hydraulic, pneumatic, electrical, and others—can endanger workers even when equipment is turned off and locked or tagged out. Taking steps to protect against potential energy can help prevent workplace incidents, reduce costs and downtime caused by incidents, and protect workers from injury.

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