Lockout/Tagout Procedures for Welding Equipment

Objective. Students will write a machine-specific lockout/tagout procedure and physically isolate a welding machine to a verified zero-energy state following OSHA 29 CFR 1910.147 steps without prompting.

Why Lockout/Tagout Matters in a Welding Shop

Welding machines store and deliver energy in several forms: electrical power from the supply circuit, capacitive charge held in inverter electronics, and mechanical energy in compressed-gas systems. If a machine starts up—or releases stored energy—while someone is servicing it, the result can be electrocution, arc flash, or crush injury. Lockout/Tagout (LOTO) is the control method that makes unintended energization physically impossible. OSHA's standard for the control of hazardous energy, 29 CFR 1910.147, is the legal baseline every worker in a general-industry welding shop must follow.

The Energy Sources on an SMAW Machine

A Shielded Metal Arc Welding (SMAW) machine is connected to the building's electrical supply—commonly 208 V, 230 V, or 460 V three-phase. The disconnect may be a wall-mounted switch, a breaker in a panel, or a plug-and-receptacle set. Some inverter-based machines also retain a residual DC charge in capacitors for a short time after power is removed. Before you touch internal components, you must account for all of these sources and verify that each has been brought to a zero-energy state.

OSHA 29 CFR 1910.147 Required Steps

OSHA 1910.147 specifies a sequence that authorized employees must follow every time. The steps below apply directly to an SMAW machine:

1. Identify all energy sources. Review the machine-specific LOTO procedure. Note the electrical disconnect location, voltage level, and whether stored energy (capacitive charge) exists.

2. Notify affected employees. Tell every person in the area that the machine is being taken out of service and why. This is not optional—it is an OSHA requirement.

3. Shut the equipment down. Use the machine's own power switch or welding-output control to bring it to a normal stop before isolating energy at the source.

4. Isolate the energy source. Open (turn off) the upstream disconnect switch or remove the plug from the receptacle. This physically separates the machine from its power supply.

5. Apply your personal lock and tag. Place your personal padlock through the hasp on the disconnect; no one can close that disconnect while your lock is on it. Attach a LOTO tag that includes your name, date, reason for lockout, and contact information. Each authorized employee working on the equipment applies their own lock—one lock per person is the rule.

6. Release or restrain stored energy. For most SMAW machines this means waiting the manufacturer's specified bleed-down time for capacitors (check the procedure or technical manual). For any compressed-gas lines involved in the work area, relieve pressure following the appropriate procedure.

7. Verify zero-energy state. Attempt to start the machine using its normal controls—it must not start. Use a calibrated voltage tester on the machine's input terminals to confirm absence of voltage. This verify step is mandatory; assumption is not verification.

Writing a Machine-Specific LOTO Procedure

OSHA 1910.147 requires employers to document a procedure for each piece of equipment that has more than one energy source or is not simple to control. A compliant written procedure must include:

Equipment identification (make, model, location)
Steps to shut down and isolate each energy source in order
Type and magnitude of each energy source
Hardware required (lock count, hasp size, tag type)
Stored-energy release method and verification method
Steps to restore the machine to service

During today's lab you will complete a LOTO procedure template for the designated SMAW machine before you touch the equipment. Your instructor reviews and approves the document first. This mirrors real-world practice: workers do not improvise—they follow an approved written procedure every time.

Restoring the Machine to Service

After maintenance or inspection is complete, restoration follows the reverse sequence:

1. Confirm all tools and test equipment have been removed from the work zone.

2. Ensure all affected employees are clear of the machine.

3. Notify affected employees that the lockout is about to be released.

4. Remove your personal lock and tag—only you may remove your own lock.

5. Close (re-energize) the disconnect or re-insert the plug.

6. Verify normal operation before returning the machine to production use.

PPE and Additional Safety Points

Wear safety glasses and electrical-rated insulated gloves when working near the disconnect, even during lockout.
Use a non-contact or contact voltage tester rated for the circuit voltage to verify zero energy—never assume the machine is de-energized because the indicator light is off.
Never use a tag alone as a substitute for a lock unless the energy-isolating device physically cannot accept a lock; in that case a tagout-only program requires additional safeguards under 1910.147.
Never remove another person's lock. Only the employee who applied the lock removes it, except under the employer's written exception procedure for a lost-key situation.
Document any deviation or near-miss on the shop's hazard-reporting form immediately.

Connection to Your Credentials

AWS, NCCER, and ASME all require welders to demonstrate knowledge of safe energy-isolation practices. AWS SENSE and NCCER Level 1 safety modules explicitly cover LOTO principles. On job sites governed by AWS D1.1 or ASME Section IX welding procedures, contractors are audited for LOTO compliance. Understanding and executing LOTO correctly protects you legally and physically throughout your career.

Key terms8

Lockout/Tagout (LOTO)A safety procedure that uses physical locks and warning tags to isolate hazardous energy sources and prevent unexpected equipment energization during service or maintenance, governed by OSHA 29 CFR 1910.147.

Authorized EmployeeA worker who has been trained and designated by the employer to perform lockout/tagout procedures; the person who actually applies and removes the lock.

Affected EmployeeA worker who operates equipment that is being locked out, or works in an area where LOTO is being performed; must be notified before and after lockout.

Energy-Isolating DeviceA mechanical device—such as a disconnect switch, circuit breaker, or plug—that physically prevents transmission of energy to the equipment being serviced.

Zero-Energy StateThe condition of a machine after all energy sources have been isolated and stored energy has been released or restrained, verified by testing rather than assumption.

Stored EnergyResidual energy that remains in equipment after the main energy source is isolated, such as capacitive charge in inverter electronics or pressure in a gas line; must be released or blocked before work begins.

HaspA multi-hole locking device that allows several individual padlocks to secure the same energy-isolating device simultaneously, ensuring no single worker can re-energize the equipment while others still have their locks applied.

Machine-Specific LOTO ProcedureA written, equipment-specific document required by OSHA 1910.147 that lists every energy source, isolation step, stored-energy release method, and restoration sequence for one particular piece of equipment.

In class: Instructor demonstrates the complete lockout/tagout sequence on an SMAW machine—notify affected employees, shut down, isolate energy source, apply lock and tag, release stored energy, verify zero energy—narrating each OSHA-required step. · Students write their own lockout/tagout procedure document for the machine using the OSHA 1910.147 required elements format, reviewed by the instructor before the practical exercise. · Individual practical: each student performs the complete lockout/tagout sequence independently on the designated machine while instructor observes and marks a step-by-step evaluation form; student then restores the machine to operational status following the reverse procedure.
Materials: SMAW welding machine, personal padlocks and hasp, lockout/tagout tags, OSHA 29 CFR 1910.147 printed standard, LOTO procedure template, step-by-step evaluation form.
Check: Instructor-scored LOTO evaluation form: all OSHA-required steps must be performed in correct sequence with zero omissions on isolation and zero-energy verification steps; 100% on critical steps required to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.