Lockout/Tagout Procedures

Lockout/Tagout (LOTO) is the safety procedure that prevents machines from unexpectedly starting up while someone is performing maintenance or repair. OSHA's Control of Hazardous Energy standard (29 CFR 1910.147) requires LOTO because unexpected machine startup is one of the leading causes of death and amputation in industrial workplaces. OSHA estimates that proper LOTO procedures prevent approximately 120 fatalities and 50,000 injuries each year. Lockout/tagout violations are consistently among OSHA's top 10 most-cited violations, with over 2,500 citations issued in fiscal year 2023 alone.

Why LOTO Matters - Real Incidents

Understanding why LOTO exists starts with understanding what happens when it fails:

Incident: Conveyor System (Manufacturing, 2022) - A maintenance worker was clearing a jam on a conveyor belt. Rather than following the full LOTO procedure, they pressed the emergency stop button and reached in. Another worker, unaware maintenance was being performed, restarted the conveyor from the control panel. The maintenance worker suffered a crush injury that resulted in the amputation of three fingers. The emergency stop button was not a substitute for lockout.

Incident: Hydraulic Press (Metal Stamping, 2023) - A die setter was adjusting tooling in a hydraulic press when the ram unexpectedly descended. The worker had not locked out the hydraulic system, relying instead on the "jog" mode control. A fault in the control circuit caused the press to cycle. The worker was fatally crushed. The investigation revealed that the machine's written LOTO procedure existed but had not been followed.

Incident: Mixing Tank (Chemical Plant, 2021) - A worker entered a mixing tank to clean the interior. The agitator had been disconnected electrically, but the pneumatic supply to a valve had not been isolated. When residual air pressure shifted the valve, a chemical feed line opened and the tank began filling. The worker suffered severe chemical burns. The root cause: not all energy sources had been identified and isolated.

These incidents reinforce the same lesson. LOTO is never optional, never shortcuts, never "just this once."

Types of Hazardous Energy

Before you can lock out a machine, you must identify every energy source. The five categories of hazardous energy are:

Electrical Energy

The most common energy source in industrial equipment. Sources include:

• Motor supply circuits (120V, 240V, 480V, and higher)
• Control circuits (often 24V DC or 120V AC)
• Capacitors that store electrical charge even after power is disconnected
• Battery backup systems and UPS units

Isolation methods: Disconnect at the breaker or main disconnect switch. Verify zero energy with a voltage tester rated for the voltage present. For capacitors, follow the manufacturer's discharge procedure and wait the specified time.

Hydraulic Energy

Pressurized fluid that powers cylinders, motors, and actuators. Hydraulic systems commonly operate at 1,500 to 5,000 PSI, with some systems exceeding 10,000 PSI.

Isolation methods: Turn off the hydraulic pump. Close and lock the isolation valve. Bleed pressure by cycling the controls with the pump off. Check the pressure gauge for zero reading. Block any cylinders or mechanisms that could drift under gravity even with the pump off - a leaking seal allows slow movement under load.

Pneumatic Energy

Compressed air powers cylinders, tools, and actuators. Plant air systems typically operate at 80-120 PSI.

Isolation methods: Close and lock the supply valve. Bleed all downstream pressure through bleed valves or by cycling actuators. Disconnect the air supply line if possible. Verify zero pressure on all gauges.

Mechanical (Stored) Energy

Energy stored in springs, flywheels, counterweights, and elevated components.

Isolation methods:

• Springs - Release or block springs so they cannot release energy. Pin or clamp compression springs. Release tension springs under controlled conditions.
• Flywheels - Allow to coast to a complete stop. Some machines have flywheel brakes. Never rely on a flywheel stopping on its own if it is still spinning.
• Gravitational - Block, pin, or support raised press rams, lift tables, platforms, and any component that could fall under gravity. Use manufacturer-specified blocking devices, never improvised supports.

Thermal Energy

Hot surfaces, steam lines, molten materials, and cryogenic systems.

Isolation methods: Close and lock steam valves. Allow adequate cool-down time. Install blanking flanges if needed to ensure complete isolation. For molten materials, drain or solidify before work begins.

Chemical energy is sometimes considered a sixth category. Reactive chemicals, flammable atmospheres, and corrosive materials in piping must be isolated by closing and locking valves, draining, purging, or blanking lines.

The OSHA Standard: 29 CFR 1910.147

Scope and Application

The standard applies to the control of hazardous energy during servicing and maintenance of machines and equipment. It covers general industry. Construction has a separate standard (29 CFR 1926.417 for electrical lockout).

What the Standard Requires

1. An energy control program with written procedures
2. Machine-specific procedures for each piece of equipment (unless a machine has no stored energy, has a single energy source that can be readily identified, and the lockout completely de-energizes the machine)
3. Training for authorized, affected, and other employees
4. Periodic inspections of the energy control program at least annually

Key Definitions

• Authorized employee - A person who locks out machines for servicing and maintenance. They must be trained on the specific LOTO procedures for each machine they service.
• Affected employee - A person whose job requires them to operate or use a machine on which servicing is performed, or who works in an area where servicing is performed. They must understand the purpose and function of LOTO.
• Other employees - All other employees who may be in the area. They must be instructed about the procedure and told never to attempt to restart a locked-out machine.

The Six-Step LOTO Procedure

Step 1: Preparation

Before beginning any lockout:

• Review the machine-specific LOTO procedure. Every machine should have a written procedure that identifies all energy sources, isolation points, and verification methods.
• Identify all energy sources using the procedure, the machine manual, and physical inspection.
• Gather all necessary lockout devices: personal padlocks, lockout hasps, valve lockout devices, circuit breaker lockouts, plug lockouts, and tags.
• Ensure you have the correct tools for verification (voltage tester, pressure gauge, etc.).
• Understand the scope of work and how long the lockout will be needed.

Step 2: Notification

• Notify all affected employees that the machine will be locked out, why, and for approximately how long.
• Notify the shift supervisor and any other departments that depend on the equipment.
• Communication is critical. Workers have been injured because they were not told a machine was being serviced and attempted to restart it.

Step 3: Machine Shutdown

• Shut the machine down using its normal stopping procedure. This typically means pressing the stop button and allowing the machine to cycle to a safe position.
• Do not use the emergency stop as the normal shutdown method. Emergency stops may not bring the machine to a safe state and are not designed as isolation devices.
• Wait for all moving parts to stop completely before proceeding.

Step 4: Energy Isolation

Physically isolate every energy source identified in Step 1:

• Turn off breakers or disconnect switches for electrical energy
• Close and lock valves for hydraulic, pneumatic, and steam systems
• Bleed residual pressure from hydraulic and pneumatic circuits
• Release, block, or restrain stored mechanical energy (springs, gravity, flywheels)
• Disconnect or blank piping for chemical isolation

Each isolation point must be physically moved to the "off" or "safe" position. Control circuits, push buttons, and selector switches are not energy-isolating devices and must never be used in place of proper lockout.

Step 5: Lockout and Tagout Application

• Apply your personal padlock to every energy isolation device. Each authorized worker must apply their own lock.
• Your lock must be a keyed padlock assigned exclusively to you. Combination locks are not acceptable.
• Attach a tag to each lock that identifies you (name, department), the date, and the reason for the lockout.
• If an isolation device cannot accept a lock, use a tagout device. Tagout-only is permitted only when the employer can demonstrate that tagging provides equivalent protection and uses additional safety measures.
• Lock and tag in place - this means the device cannot be moved to the "on" position without removing your lock.

Step 6: Verification of Isolation

This is the most critical step. Before beginning any work:

• Try to start the machine using the normal operating controls (push buttons, switches). The machine must not start. Return all controls to the "off" position after testing.
• Test for electrical energy using a properly rated voltage tester. Test the tester on a known live source before and after testing the locked-out circuit to confirm the tester is working.
• Check all pressure gauges for zero readings on hydraulic and pneumatic systems.
• Visually confirm that all mechanical blocking devices are in place and secure.
• Test each energy source individually. Do not assume that because the machine did not start, all energy is isolated. A control circuit lockout may prevent the motor from starting, but a hydraulic accumulator may still hold thousands of PSI.

Only after complete verification may work begin.

Restoring Equipment to Service

When maintenance is complete:

1. Inspect the machine - Ensure all tools, parts, and materials have been removed. Verify that all guards and safety devices have been reinstalled.
2. Clear personnel - Ensure that all workers are clear of the machine and aware that it is about to be re-energized. Perform a headcount.
3. Remove lockout devices - Each authorized worker removes their own lock. Only the person who applied a lock may remove it.
4. Re-energize - Restore energy sources in the proper sequence as specified in the LOTO procedure.
5. Test - Operate the machine to verify it functions correctly.
6. Notify - Inform all affected employees that the lockout has been removed and the machine is back in service.

Group Lockout/Tagout

When multiple workers service the same machine:

• A group lockout box or lockout hasp is used. The hasp accepts multiple padlocks.
• Each authorized worker applies their own personal lock to the hasp or box.
• The machine cannot be re-energized until every single lock has been removed.
• A primary authorized employee (often the lead or supervisor) coordinates the group lockout, ensures all energy sources are isolated, and performs the verification.
• Each worker must be protected by their own lock for the entire time they are exposed to the hazard.

Shift Change Procedures

When lockout must continue across shifts:

• The outgoing shift's authorized employees must communicate the status to the incoming shift.
• The incoming shift applies their locks before the outgoing shift removes theirs.
• At no point should the machine be unprotected during the transition.
• Many facilities use an overlap procedure: incoming locks go on first, then outgoing locks come off.

Lock Removal When the Authorized Employee Is Absent

Occasionally, an authorized employee leaves the facility without removing their lock. This situation requires a formal procedure:

1. The employer must make reasonable effort to contact the employee and have them return to remove the lock.
2. If the employee cannot be reached, a specifically designated person (usually a supervisor or manager) may remove the lock only if:
   • The specific procedure for authorized lock removal is followed
   • It is verified that the authorized employee is not in the facility
   • It is verified that the authorized employee is not at risk
   • The employee is informed before their next scheduled shift that their lock was removed
3. This procedure must be documented in the energy control program.

This is an emergency procedure, not a convenience. It should be rare. If it happens frequently, it indicates a training or culture problem.

Common LOTO Mistakes and How to Avoid Them

Mistake 1: "It'll Only Take a Minute"

More LOTO injuries occur during "quick" jobs than during planned maintenance. A task's duration has nothing to do with the hazard. If the machine could start unexpectedly and cause injury, full LOTO is required regardless of how long the task takes.

Mistake 2: Using Controls Instead of Isolation Devices

Push buttons, selector switches, and PLCs are control devices, not energy-isolating devices. A software command can fail. A relay can malfunction. A wire can short. The only reliable isolation is a physical disconnect that prevents energy flow.

Mistake 3: Not Identifying All Energy Sources

Complex machines may have multiple electrical circuits (power and controls on different breakers), hydraulic accumulators, pneumatic reservoirs, and gravity-loaded components. Review the machine-specific procedure, study the machine's energy diagram, and physically trace every energy path.

Mistake 4: Failure to Verify

Locking out without verifying is like buckling a seatbelt without clicking it. Verification catches mistakes. Every time.

Mistake 5: Using Someone Else's Lock

Every authorized employee must use their own individually keyed lock. Master keys should be controlled and used only for the authorized lock removal procedure. Sharing locks, using combination locks, or relying on a single lock for multiple workers defeats the entire purpose of LOTO.

Annual Periodic Inspection

OSHA requires a periodic inspection of each energy control procedure at least once per year (29 CFR 1910.147(c)(6)). The inspection must:

• Be performed by an authorized employee who is not using the procedure being inspected
• Cover each machine-specific procedure
• Verify that employees understand and follow the procedure
• Include a review between the inspector and authorized employees (for lockout) or all employees (for tagout)
• Be documented with the date, equipment, employees included, and inspector name

Common findings during periodic inspections include outdated procedures that do not reflect machine modifications, missing lockout devices, employees who cannot describe the procedure, and verification steps being skipped.

LOTO Inspection Checklist

Before and during any lockout, verify:

• [ ] Machine-specific LOTO procedure reviewed
• [ ] All energy sources identified from the procedure and physical inspection
• [ ] All affected employees notified
• [ ] Machine shut down using normal procedures
• [ ] All isolation devices moved to the "off" or "safe" position
• [ ] Personal lock and tag applied to every isolation point
• [ ] Residual/stored energy drained, bled, released, or blocked
• [ ] Verification performed: tried to start, tested electrical, checked pressures
• [ ] All controls returned to "off" after verification
• [ ] Work area inspected and clear before removing locks
• [ ] All workers accounted for before re-energizing
• [ ] Guards and safety devices reinstalled before re-energizing
• [ ] All workers notified that machine is returning to service

Key Takeaways

• LOTO prevents an estimated 120 deaths and 50,000 injuries annually. It is never optional, regardless of how quick the job seems.
• The six-step procedure must be followed in order: Preparation, Notification, Shutdown, Isolation, Lockout/Tagout, Verification.
• Every authorized worker applies their own individually keyed padlock. No one removes another person's lock except through the formal authorized removal procedure.
• Verification is the most critical step. Try to start the machine, test with instruments, check gauges. Do this every single time.
• Control devices (buttons, switches, PLCs) are not energy-isolating devices. Only physical disconnects, valves, and similar devices qualify.
• Complex machines have multiple energy sources. Identify every one of them. Missing even one can be fatal.
• Annual periodic inspections are required by OSHA and should be treated as a genuine audit, not a checkbox exercise.