Lockout/Tagout (LOTO): A Practical Guide to Hazardous Energy Control
Lockout tagout is a hazardous energy control approach used to help prevent unexpected energization, startup or release of stored energy while specified servicing and maintenance activities are performed.
What Is Lockout Tagout?
Lockout tagout, commonly abbreviated as LOTO, refers to procedures for controlling hazardous energy associated with machinery, equipment and systems during activities where unexpected energization, startup or energy release could cause harm.
The basic principle is to identify relevant energy sources, isolate them using appropriate energy-isolating devices, control stored or residual energy and verify the effectiveness of the isolation before work proceeds.
Specific legal requirements and terminology vary between jurisdictions. Organizations should establish procedures that reflect their equipment, hazards, work activities and applicable requirements.
What Types of Energy Can Require Control?
Hazardous energy is not limited to electricity. Machinery and process systems can contain multiple energy sources that must be considered before work begins.
Electrical Energy
Electrical supplies, circuits, conductors and equipment can expose workers to energization, shock, arc or unexpected equipment operation.
Mechanical Energy
Rotating parts, springs, elevated components, flywheels and other mechanisms may retain or release mechanical energy.
Pressure Energy
Hydraulic, pneumatic, steam and other pressurized systems may contain hazardous pressure even after equipment has stopped.
Thermal Energy
Hot or cold equipment, fluids and process materials may retain hazardous thermal energy after shutdown.
Gravitational Energy
Raised equipment, suspended loads and elevated components may move unexpectedly if their stored potential energy is not controlled.
Process & Other Energy
Chemical reactions, process materials and other energy sources may require isolation or additional control depending on the system.
When Is Hazardous Energy Control Important?
Hazardous energy control becomes particularly important when people perform work in or around equipment where unexpected movement, startup, energization or energy release could expose them to harm.
Examples may include maintenance, repair, cleaning, adjustment, inspection, installation or other servicing activities. The appropriate controls depend on the equipment and nature of the work.
Routine production operations and minor servicing may be treated differently under applicable requirements, so organizations should not assume that one procedure applies to every task.
Core Steps in a Lockout Tagout Procedure
Exact procedures should be equipment-specific where necessary, but hazardous energy control generally follows a deliberate sequence from preparation through safe restoration.
Prepare
Identify the equipment, work scope, energy sources, isolation points and methods needed to control hazardous energy.
Shut Down & Isolate
Stop the equipment using the appropriate procedure and operate the required energy-isolating devices.
Control & Verify
Apply required lockout or other specified controls, address stored energy and verify that isolation is effective.
Restore Safely
After work is complete, follow the established process for clearing the area, removing controls and returning equipment to service.
Identify Every Relevant Energy Source
Effective lockout tagout begins before any lock is applied. The people responsible for the isolation need to understand how the equipment receives, stores and releases energy.
Complex machinery may have several electrical feeds as well as hydraulic, pneumatic, mechanical or other energy sources. Drawings, equipment information, procedures and physical inspection may be needed to understand the system.
Missing one significant energy source can undermine the entire isolation process.
Shut Equipment Down in a Controlled Manner
Equipment should be stopped using an appropriate shutdown procedure before energy-isolating devices are operated. The shutdown method should consider the equipment design and any hazards created by stopping the process.
Simply pressing a normal stop button is generally not the same as isolating hazardous energy. Control-circuit devices may stop normal operation without physically preventing energy from reaching the equipment.
The required isolation points should therefore be identified and operated as part of the hazardous energy control procedure.
Isolate Equipment From Hazardous Energy
Energy isolation involves operating devices that physically prevent or control the transmission or release of energy. Depending on the system, these may include disconnects, breakers designed for isolation, valves, blocks, blanks or other suitable devices.
The isolation method should correspond to the actual energy source and equipment design. A control switch or software command should not automatically be assumed to provide energy isolation.
Where a permit to work system also applies, isolation status and permit conditions should be coordinated so that the two systems support rather than contradict each other.
Understand the Difference Between Lockout and Tagout
Lockout generally involves applying a locking device to an energy-isolating device so that it cannot be operated until the lock is removed through the established procedure.
A tag communicates important information and warns against operation, but a tag by itself does not normally provide the same physical restraint as a lock.
Whether tagout may be used instead of lockout, and what additional measures are required, depends on equipment design and applicable requirements. Organizations should follow the rules and procedures relevant to their jurisdiction and workplace.
Control Stored and Residual Energy
Disconnecting an energy source does not necessarily mean all hazardous energy has disappeared. Equipment may continue to contain pressure, heat, electrical charge, spring force, elevated components or other stored energy.
Stored energy may need to be released, discharged, restrained, blocked, cooled or otherwise controlled using a method appropriate to the hazard.
Where stored energy can accumulate again during the work, continued verification or additional measures may be necessary.
Verify Isolation Before Work Begins
Verification is a critical stage of lockout tagout. The work should not proceed merely because locks or tags are visible. The isolation needs to be checked using an appropriate method.
The verification method depends on the equipment and hazards. It may involve attempting normal controls, testing for the absence of energy using suitable instruments or performing other checks defined by the procedure.
Verification should be performed by appropriately trained or authorized personnel and should not itself expose people to uncontrolled hazards.
Personal Locks and Clear Identification
Where personal lockout is used, the system should make clear who applied each lock and who is protected by it. Lock management should prevent unauthorized or casual removal.
Workers should understand that another person’s lock must not be removed simply because work appears to be complete. Exceptional removal procedures, where permitted, should be formally controlled.
Lockout devices should be appropriate for their intended purpose and managed in accordance with the organization’s hazardous energy control procedure.
Managing Lockout Tagout for Multiple Workers
Maintenance activities may involve several workers, trades or teams. Group lockout arrangements should provide an equivalent level of control so that each person is appropriately protected while exposed to hazardous energy.
The system should clearly define responsibility for the overall isolation while maintaining individual accountability for people working under the group arrangement.
Group lock boxes, multiple-lock devices or other structured methods may be used depending on the organization’s procedures and applicable requirements.
Maintain Energy Control During Shift Handover
Work that continues across shifts requires a controlled transfer of responsibility. Hazardous energy controls should remain effective throughout the transition.
The handover process should ensure that incoming personnel understand the equipment status, isolation points, work completed, outstanding work and any relevant hazards.
Locks or other controls should not be removed in a way that creates an uncontrolled period between outgoing and incoming personnel.
Returning Equipment to Service Safely
Restoring equipment to operation should be treated as a controlled stage of the lockout tagout process rather than simply removing locks and restarting machinery.
Before energy is restored, the work should be complete or otherwise in a safe condition, tools and unnecessary materials should be cleared and affected people should be appropriately positioned or notified.
Locks, tags and isolation devices should then be removed or restored only in accordance with the established procedure and applicable authorization requirements.
Lockout Tagout Requires Appropriate Training
People involved in hazardous energy control need training appropriate to their responsibilities. Those applying isolations or locks require a different level of understanding from people who simply work in an area where LOTO activities occur.
Training should address the workplace’s procedures, relevant energy sources, responsibilities, prohibited actions and the steps required for safe application and removal of controls.
Competence should be maintained when equipment, procedures, responsibilities or identified hazards change.
Inspect and Review Hazardous Energy Control Procedures
Procedures should be reviewed to determine whether they remain accurate and are being applied correctly. Changes to equipment or processes can make an existing isolation procedure incomplete or outdated.
Workplace observations, inspections, near misses and incident investigations can also reveal weaknesses in hazardous energy control.
Identified deficiencies should be corrected and relevant workers informed or retrained where necessary.
Common Lockout Tagout Mistakes
Relying on the Stop Control
Stopping equipment with its normal operating controls does not necessarily isolate it from hazardous energy.
Ignoring Stored Energy
Pressure, gravity, heat, electrical charge or mechanical force may remain hazardous after primary energy sources are isolated.
Skipping Verification
Visible locks do not by themselves demonstrate that every relevant energy source has been effectively controlled.
Lockout Tagout Is a System for Controlling Hazardous Energy
Effective lockout tagout requires more than attaching a lock and tag to equipment. The process begins with understanding all relevant energy sources and continues through shutdown, isolation, stored-energy control, verification, work execution and safe restoration.
Equipment-specific procedures, clear responsibilities, appropriate training and periodic review help ensure that hazardous energy controls remain effective as work and equipment change.
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