Lockout/Tagout Basics: Controlling Hazardous Energy During Maintenance

Serious injuries happen when machinery starts unexpectedly or releases stored energy while someone is servicing it. Lockout/tagout (LOTO) procedures prevent this by isolating energy sources and physically locking them in a safe position before work begins. In the United States, the Occupational Safety and Health Administration (OSHA) sets requirements in its standard for the control of hazardous energy; many other countries have equivalent rules.

This article explains general principles. Always follow the legal requirements in your country and your site's written, equipment-specific procedures.

Types of hazardous energy

• Electrical
• Mechanical (moving parts, springs, flywheels)
• Hydraulic and pneumatic pressure
• Thermal (hot surfaces, steam)
• Chemical
• Gravitational (suspended loads, raised components)

Many machines have several energy sources. A procedure must address every one.

Lockout vs tagout

A lockout device, such as a padlock on an isolator, physically prevents an energy-isolating device from being operated. A tagout device is a warning tag stating that equipment must not be operated. Locks provide much stronger protection; tags alone should only be used where lockout is genuinely impossible and additional measures are in place.

The essential steps

1. Prepare: identify all energy sources and isolation points using the equipment-specific procedure.
2. Notify: tell affected employees that the equipment will be shut down and locked out.
3. Shut down: stop the equipment using normal operating controls.
4. Isolate: operate the energy-isolating devices, such as disconnect switches and valves, to separate the equipment from every energy source.
5. Apply locks and tags: each authorised worker applies their own personal lock and tag.
6. Release or restrain stored energy: bleed pressure, discharge capacitors, block or lower raised parts, allow hot parts to cool.
7. Verify isolation: confirm the equipment cannot start, for example by attempting a normal start after ensuring everyone is clear, and test for voltage with a suitable tester where appropriate. Return controls to off afterwards.
8. Perform the work.

Restoring equipment

1. Check that tools and materials have been removed and guards replaced.
2. Make sure all workers are clear.
3. Each worker removes their own lock. Locks should be removed only by the person who applied them, except under a strictly controlled procedure.
4. Notify affected employees before re-energising.

Roles

• Authorised employees perform lockout and service the equipment.
• Affected employees operate or work near the equipment and must understand the procedure and never attempt to restart locked-out equipment.

Group lockout

When several people work on the same equipment, a group lockout box or similar system ensures each person has personal protection: the isolation keys go in a box, and every worker applies their own lock to the box.

Common mistakes

• Relying on an emergency stop or control switch instead of true isolation
• Missing a secondary energy source, such as stored air pressure or gravity
• Skipping verification
• Sharing locks or keys
• Generic procedures that do not reflect the actual equipment

Make it part of the system

Effective LOTO depends on written, equipment-specific procedures, training, the right devices and periodic inspections of how procedures are actually followed. Build isolation steps into every maintenance task plan; see preventive vs predictive maintenance. A well-organised area with clearly labelled isolation points, part of good 5S practice, makes procedures easier to follow.