Lockout/Tagout Procedures
Shut down, isolate, lock, release stored energy and verify zero energy before you service any machine, then return it to service safely.
Table of contents
Lockout/tagout (LOTO) keeps a machine from starting up or releasing energy while someone is working on it. A press that cycles, a valve that opens or a conveyor that restarts can kill you in less time than it takes to shout. OSHA's standard on the control of hazardous energy, 29 CFR 1910.147, is one of its most-cited rules, and OSHA estimates that following it prevents about 120 deaths and 50,000 injuries a year.
What You Will Be Able to Do
- Say when lockout is required and who may apply it.
- Identify every energy source on a machine, including stored energy.
- Carry out the six steps of a lockout in order.
- Verify zero energy before you touch anything.
- Return a machine to service safely.
When Lockout Is Required
You need lockout any time you could be exposed to hazardous energy during servicing or maintenance. That includes repairing, adjusting, cleaning, lubricating, clearing jams and setting up. It applies if you must remove or bypass a guard, or put any part of your body where the machine could hurt you.
The standard covers general industry. Construction, power generation and some electrical work have their own rules, such as 29 CFR 1926.417 and 1910.333, but the same logic applies. Short jobs are covered too. The time a task takes has nothing to do with the hazard.
Who Does What
| Role | Who they are | Training |
|---|---|---|
| Authorized employee | Locks out a machine to service it | Full: energy types, how to isolate and verify |
| Affected employee | Operates the machine, or works where it is being serviced, but does not service it | Why lockout exists, and never to touch a lock or restart the machine |
| Other employee | Works elsewhere but could end up in the area | Knows the procedure exists and not to try a locked machine |
An operator who clears jams under lockout is authorized for that task. The role depends on what you do, not on your job title.
Types of Hazardous Energy
OSHA's definition of energy covers electrical, mechanical, hydraulic, pneumatic, chemical, thermal and other sources. Training programs group them in slightly different ways, and gravity is often listed on its own. What matters is that you find each source that could hurt you on the machine in front of you.
| Energy | Where you find it | How to control it |
|---|---|---|
| Electrical | Motors, control circuits, capacitors, batteries, UPS units | Open the disconnect, lock it, test for voltage, discharge capacitors |
| Hydraulic | Pumps, cylinders, accumulators | Stop the pump, close and lock the valve, bleed pressure, block what can drift |
| Pneumatic | Air lines, cylinders, reservoirs | Close and lock the valve, bleed downstream pressure |
| Mechanical | Springs, flywheels, belts, rotating parts | Let it stop, release or block the spring |
| Gravity | Raised rams, lifts, forks, counterweights | Lower it, or block and pin it with rated devices |
| Thermal | Steam, hot fluids, hot surfaces, cold systems | Close and lock valves, drain, let it cool |
| Chemical | Process lines, reactive materials | Close and lock valves, drain, purge, blank |
Stored energy stays after the power is off. A raised press ram can fall. A compressed spring can throw a part with enough force to break bones. A hydraulic accumulator can hold thousands of pounds of pressure with the pump switched off. A capacitor can hold a deadly charge.
Warning: A capacitor can stay charged long after the disconnect is off. Follow the manufacturer's discharge procedure, wait the stated time, and confirm zero with a properly rated meter.
Energy-Isolating Devices
An energy-isolating device physically stops energy from reaching the machine. These include disconnect switches, circuit breakers, line valves and blocks. Push buttons, selector switches and control circuits do not count. Neither does a PLC command or an emergency stop. Those send a signal that can fail, and they do not physically stop the energy.
The Six Steps
OSHA sets out the required sequence in 1910.147(d). Each machine should have a written procedure listing its energy sources and isolation points, unless it meets a narrow exception for simple equipment.
Step 1: Prepare
Read the machine's procedure. Identify every energy source and how to control it. Tell affected employees that the machine will be locked out, and why. Gather locks, tags, hasps, valve covers and your test equipment.
Step 2: Shut Down
Stop the machine the normal way, using the normal stop controls. Do not use the emergency stop as your routine shutdown. An orderly stop reduces the risk to others.
Step 3: Isolate
Operate each energy-isolating device so the machine is cut off from every source. Open the disconnect, close the valve. Do not forget secondary power, such as control circuits fed from a different panel.
Step 4: Apply Locks and Tags
Put your own lock on every isolating device so it stays in the safe position. Your lock must:
- Be assigned to you alone and used only for energy control. OSHA allows key or combination locks, but many employers require keyed padlocks, because a combination can be shared or guessed.
- Be standardized in color, shape or size, so it is easy to recognize.
- Be strong enough that it cannot be removed without unusual force.
- Identify you.
Add a tag that identifies you and warns others, with a legend such as Do Not Start. Many employers also want your department, the date and time, and the reason for the lockout. The key stays with you.
If a device truly cannot take a lock, a tag can be used only under a tagout program that gives the same level of protection, such as removing a fuse or blocking a control. A tag is only a warning. It does not physically stop anything, and you must be trained to treat it that way.
Step 5: Release Stored Energy
Relieve, disconnect, restrain or make safe all stored energy.
- Bleed hydraulic and pneumatic lines.
- Block or pin parts that can fall or move.
- Let flywheels stop.
- Discharge capacitors.
- Drain or vent lines.
If energy could build back up, keep checking for that during the job.
Worked example: A machine has an electric motor and a hydraulic ram that is raised.
- Stop the machine, and lower the ram if the procedure allows.
- Open and lock the electrical disconnect.
- Close and lock the hydraulic valve.
- Bleed the system, and watch the gauge go to zero.
- Block the ram if it cannot be lowered.
- Try the start button, test for voltage, and check the gauge again.
Step 6: Verify
This is the step that catches your mistakes, and it comes last before you start work.
- Make sure everyone is clear.
- Try to start the machine with its normal controls. Nothing should happen.
- Test with a meter: check that your tester works on a known live source, test for zero voltage, then check the tester again.
- Check that gauges read zero.
- Look to see that blocks and pins are in place.
- Return all controls to OFF.
Warning: A machine that will not start is not proof it is safe. The control circuit could be dead while an accumulator still holds pressure. Check each energy source.
Returning to Service
Follow this order, set out in 1910.147(e):
- Inspect. Remove tools and parts, and check that the machine is whole. Put all guards back.
- Clear people. Make sure everyone is out of the danger area.
- Remove locks. Each person removes their own lock and tag.
- Notify. Tell affected employees the devices are off and the machine will start.
- Re-energize, following the procedure.
If you need power back briefly to test or position the machine, follow the same steps to clear and remove, test, then lock out again before you carry on.
Common Mistakes
| Mistake | What it costs | Better habit |
|---|---|---|
| "It will only take a minute" | A quick job is exposed to the same energy as a long one | Lock out every time |
| Using the E-stop or a control switch | Someone resets it, or it fails | Use a real isolating device |
| Missing one energy source | Pressure, gravity or a second circuit hurts you | Use the procedure, and trace the machine |
| Skipping verification | You find out the wrong way | Try it, test it and read it |
| Sharing a lock or key | Someone else controls your safety | One person, one lock, one key |
| Leaving a tool in the machine | A wreck on restart | Inspect before you remove your lock |
Check Your Understanding
1. An operator wants to reach behind a conveyor to pull out a jammed box. She hits the E-stop. Is she protected?
No. An E-stop is a control. Unless the task falls under a true minor servicing exception, the conveyor has to be locked out at its disconnect and verified.
2. You lock out a pneumatic clamp's air valve and the gauge downstream still reads 60 psi. What next?
Bleed the downstream pressure. The valve stopped new air, but stored air can still move the clamp. Do not start until the gauge reads zero.
3. A machine has a main disconnect and a separate control panel fed from another breaker. What do you do?
Isolate and lock both sources, as the procedure requires. Then verify each one.
4. You finish the job. A coworker's lock is still on the hasp, but you saw him leave for lunch. Can you restart?
No. Only he removes his lock. Everyone must be clear, and each lock must come off first.
Key Takeaways
- Lock out whenever you could be exposed to hazardous energy during service or maintenance.
- Authorized employees apply locks. Affected employees stay clear.
- Isolate at true isolating devices, never at buttons or E-stops.
- Follow the steps: prepare, shut down, isolate, lock and tag, release stored energy, verify.
- Verify every energy source before you begin.
- Each person removes only their own lock, after the area is clear.