Walk through the lockout/tagout sequence for isolating hazardous energy before maintenance.
Why it matters
Machines hurt people most often not while running normally, but while someone is cleaning, clearing a jam or repairing them, and the machine starts or moves unexpectedly. Lockout/tagout (LOTO) is the procedure that makes sure the energy is off, stays off, and is proven off before anyone puts a hand inside.
Awareness level only. This lesson explains the ideas so you recognise them on day one. It does not qualify you to do the work. Your employer, apprenticeship or school must train you on its own procedures and equipment, and you must work under supervision until they say you are qualified.
The standard
In US general industry, LOTO is covered by 29 CFR 1910.147, The Control of Hazardous Energy. Employers must have a written energy control programme, machine-specific procedures, training, and periodic inspections of the procedures. Electrical work also follows NFPA 70E and the electrical safety rules in 1910 Subpart S.
Hazardous energy is more than electricity
Look for every source:
- Electrical (mains, batteries, capacitors that hold charge after power is off),
- Mechanical (flywheels still spinning, springs under tension),
- Hydraulic and pneumatic (pressure trapped in lines and accumulators),
- Gravity (a raised ram, a lifted load that can drop),
- Thermal (hot surfaces, steam),
- Chemical (process lines).
Who is who
- Authorized employee: trained to lock out the machine and do the work.
- Affected employee: operates or works near the machine; must be told and must never remove a lock.
- Other employees: need to recognise a lock and tag and leave them alone.
The LOTO sequence
Every site's written procedure is the one you follow. Most follow this pattern:
- Prepare. Read the machine's procedure. Identify every energy source and its isolation point (breaker, disconnect, valve).
- Notify affected employees that the machine will be shut down and locked out.
- Shut down the machine using its normal stop.
- Isolate each energy source: open the disconnect, close the valve, block the ram.
- Apply locks and tags. Each authorized worker puts on their own personal lock (one person, one lock, one key) using a hasp if several people work on it. The tag says who locked it and why. A tag alone is a warning, not a barrier.
- Release or restrain stored energy: bleed pressure, block or lower raised parts, let flywheels stop, discharge capacitors (by a qualified person).
- Verify isolation. Check nobody is exposed, then try the normal start controls; the machine must not start. For electrical isolation, a qualified person tests for absence of voltage with a meter that has been checked on a known live source before and after ("test before touch"). Return the controls to off.
- Do the work.
Restoring the machine
- Remove tools, check that guards are back on.
- Make sure everyone is clear and notify affected employees.
- Each person removes only their own lock. Removing someone else's lock is allowed only under a strict written procedure when that person cannot be found.
- Re-energise and test.
Cord-and-plug equipment
For equipment that plugs in, unplugging it and keeping the plug under your exclusive control (in your hand or locked in a plug lockout) counts as isolating it. Leaving the plug on the floor where someone could plug it back in does not.
Worked example: a conveyor jam
A belt conveyor has a 480 V motor and a gravity take-up weight that tensions the belt.
| Step | Action |
|---|---|
| Energy sources | Electrical (motor), gravity (take-up weight), mechanical (belt tension) |
| Isolate | Open the motor disconnect; lock and tag it |
| Stored energy | Block the take-up weight so it cannot drop; release belt tension per procedure |
| Verify | Press START at the local station: nothing; qualified electrician tests for absence of voltage at the motor terminals |
| Work | Clear the jam |
Notice that turning off the motor was only one of three energy controls.
Common mistakes
- Using the machine's STOP button or a control switch as the isolation point. Control circuits can fail or be bypassed.
- Sharing one lock among a crew.
- Forgetting stored energy: springs, pressure, gravity.
- Skipping the verify step ("I know it's off").
- Leaving locks on at shift change without a proper handover procedure.
Official source
- OSHA control of hazardous energy: https://www.osha.gov/control-hazardous-energy
Checked on 2026-10-23.
Recap
- LOTO isolates all hazardous energy and proves it is off.
- Sequence: prepare, notify, shut down, isolate, lock and tag, release stored energy, verify, work; then restore in order.
- One person, one lock, one key. Only the person who applied a lock removes it.
Try it
The Do tab has you write and walk through a paper LOTO procedure for a plug-in household appliance. You do not open or repair anything.