What Is Lockout/Tagout (LOTO)? Definition and Why It Matters
Lockout/tagout (LOTO) is the safety practice of physically isolating a machine from every energy source before anyone services it — then locking those isolation points open and tagging them so nobody can re-energize the equipment while hands are inside. In the United States it is required by OSHA standard 29 CFR 1910.147, The Control of Hazardous Energy.
Done correctly, lockout/tagout is one of the most life-saving procedures in industry. OSHA estimates that compliance with the standard prevents around 120 fatalities and 50,000 injuries every year. Done poorly — or skipped entirely — servicing a machine that unexpectedly starts can crush, amputate, or kill in seconds.
Lockout vs. tagout: the difference
Lockout means placing a physical lock on every energy-isolating device (a disconnect switch, breaker, valve, or blank flange) so it cannot be operated. Tagout means attaching a warning tag that identifies who applied the device and why the equipment must not be operated.
A tag by itself is only a warning — it does not physically stop someone from re-energizing the machine. That is why OSHA strongly prefers lockout, and only allows tagout alone in the rare cases where an isolating device cannot accept a lock, and then only with equivalent extra protections.
What a lockout/tagout procedure actually contains
A compliant LOTO procedure is machine-specific. It tells the worker exactly what to do, in order, for that piece of equipment — not a generic machine. At minimum it must identify:
- The equipment covered and its location
- Every energy source: electrical, mechanical, hydraulic, pneumatic, chemical, thermal, and gravitational
- The magnitude of each energy source (for example, 480V three-phase, 120 PSI pneumatic)
- Every isolation point — the exact switch, valve, or plug to operate
- The type of lockout device used at each point
- How to release or restrain stored or residual energy (capacitors, springs, accumulators, flywheels, suspended loads)
- How to verify zero energy before starting work
Who is involved: authorized, affected, and other employees
OSHA divides employees into three roles. Authorized employees perform the service and apply the locks. Affected employees operate the equipment or work nearby and must understand when it is locked out. All other employees must simply know that locked-out equipment is never to be touched.
Everyone who interacts with a locked-out machine needs training appropriate to their role, and authorized employees need retraining whenever equipment, procedures, or job assignments change.
Why lockout/tagout matters so much
Unexpected machine start-up during servicing is one of the most severe hazard categories OSHA regulates. Workers servicing conveyors, presses, mixers, packaging lines, and pumps are exposed to crushing, amputation, electrocution, and burns when stored or residual energy is not controlled.
LOTO is also consistently among the most-cited OSHA standards year after year, with thousands of citations annually — most of them for missing or inadequate machine-specific procedures, not for exotic technical failures. That means most LOTO citations are preventable with better documentation and discipline.
Key takeaways
- Lockout/tagout physically isolates every energy source before service — a tag alone is only a warning.
- Procedures must be machine-specific and list every energy source, isolation point, and verification step.
- OSHA 29 CFR 1910.147 requires training, annual inspections, and written procedures.
- Compliance prevents an estimated 120 fatalities and 50,000 injuries per year in the U.S.
Frequently asked questions
Is lockout/tagout required by law?
Yes. In the United States, OSHA standard 29 CFR 1910.147 requires employers to establish an energy control program with machine-specific procedures, training, and annual inspections for servicing and maintenance activities where unexpected energization could cause injury.
What are the six steps of lockout/tagout?
The standard sequence is: (1) notify affected employees, (2) shut down the equipment using its normal stopping procedure, (3) isolate every energy source at its disconnect point, (4) apply lockout devices and tags, (5) release or restrain stored and residual energy, and (6) verify zero energy before beginning work.
Does lockout/tagout apply to equipment you can just unplug?
Cord-and-plug connected equipment is exempt only when unplugging gives the employee full control of the hazard and the plug remains under their exclusive control during service. If the plug can be reconnected by someone else, or the equipment has stored energy, full lockout procedures apply.
Can tagout be used instead of lockout?
Only when an energy-isolating device cannot physically accept a lock. In those cases the tagout program must include additional safety measures — such as removing a valve handle or blocking a switch — that provide protection equivalent to a lock.
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