2.3 LOTO & the Electrically Safe Work Condition

OSHA 1910.147 — The Six-Step LOTO Sequence

OSHA 29 CFR 1910.147, The Control of Hazardous Energy (Lockout/Tagout), defines the procedure for isolating machines or equipment from their energy sources before service. The six-step sequence is:

1. Preparation for shutdown — Identify all energy sources (electrical, mechanical, hydraulic, pneumatic, chemical, thermal, gravitational), review the equipment-specific LOTO procedure, and notify affected employees.
2. Shutdown — Turn the equipment off using its normal stopping sequence (stop button, normal ramp-down). Do not use an emergency stop as a routine shutdown.
3. Isolation — Operate the isolating device (open the disconnect, close the valve, block the spring). The isolating device must be physically separate from the operating controls — a stop button is not isolation.
4. Lockout/tagout device application — Apply individual locks and tags to each isolating device. Each authorized employee applies their own personal lock.
5. Control of stored/residual energy — Release, bleed, block, or ground stored energy: capacitors, springs, elevated parts, pressure, residual charge. Verify by observation.
6. Verification of isolation — Test the operating controls to confirm no response, and test for absence of voltage using an adequately rated tester (the live-dead-live sequence, covered in Section 2.4).

The reverse sequence (removal of LOTO) is equally prescriptive: inspect the area, ensure personnel are clear, remove tools, notify affected employees, then remove each lock — each lock removed by the person who placed it.

NFPA 70E Article 120 — The Electrically Safe Work Condition

NFPA 70E Article 120 layers the electrical-specific requirements on top of OSHA 1910.147. The electrically safe work condition is the state in which the conductors or circuit parts are disconnected from energized parts, locked/tagged, tested for absence of voltage, and (where required) temporarily grounded. Per Article 120, the first step is to identify all possible energy sources — both electrical and other (mechanical, hydraulic, pneumatic) — before applying lockout/tagout. After LOTO and after discharging stored energy, the worker verifies absence of voltage with an adequately rated tester. Only then is the condition "electrically safe."

Exam trap: Many candidates assume "apply personal locks and tags" is the first step. NFPA 70E Article 120 explicitly puts identifying all energy sources first, because you cannot lock out what you have not identified. This is the single most-tested Article 120 fact on NETA exams.

LOTO Device Requirements

OSHA 1910.147 requires that LOTO devices be:

• Substantial (durable) — able to withstand the environment for the maximum expected exposure time without deteriorating.
• Singularly identified — unique to a worker or crew, not interchangeable. Each authorized worker has their own keyed lock; no two workers share a key.
• Sole-key — the lock has only one key, and the employer does not retain a master key that could be used to bypass the lock without the worker's knowledge.
• Not shareable — one lock, one worker. A lock may not be used to control multiple workers' exposure.

Tagout devices must warn against hazardous conditions and be legible, non-reusable, and attached with a non-reusable cable tie. Tags are a weaker control than locks and are only permitted where a lock cannot be used (and then with an additional measure such as removing an isolating circuit element).

Individual vs Group Lockout

In individual lockout, each authorized worker applies their own personal lock to each isolating device. When multiple workers are involved, the number of locks can be impractical, so group lockout uses a lockbox: each isolating device is locked once with a single keyed lock, the keys go into a lockbox, and each member of the crew applies their own personal lock to the lockbox. Each person retains control of their own lock and removes only their own lock at the end. A group lockout coordinator may be designated to manage the box.

Verifying the Electrically Safe Condition

Once LOTO is applied and stored energy is discharged, the worker verifies the absence of voltage using an adequately rated tester (a meter rated for the voltage category and the environment). The verification uses the live-dead-live sequence (Section 2.4): test a known live source, test the target equipment, re-test the known live source. Only after this verification is the condition considered electrically safe, and only then may temporary protective grounds be installed.

When LOTO Alone Is Not Enough

LOTO prevents re-energization by another worker, but it does not address induced voltage from adjacent energized circuits or stored energy in long cable capacitance. For medium-voltage cable work, the electrically safe work condition therefore includes the installation of temporary protective grounds (TPGs) at the work area after LOTO and voltage verification (see Section 2.5). The grounds drain induced current, hold the conductor at ground potential, and provide a low-impedance fault path in case the LOTO is bypassed by an automatic transfer scheme or a backfeed. NETA exam items often pair LOTO with TPGs as a single "electrically safe work condition" answer set, and a common trap is to select LOTO alone as sufficient for MV cable work — it is not.

Restoration Sequence

When the work is complete, the restoration sequence is the reverse of the LOTO sequence: remove temporary grounds, remove tools and materials, re-energize per the switching plan, and only then remove personal locks and tags. The locks come off last because the circuit must remain under LOTO control until the system is confirmed stable. Each worker removes only their own lock. If a worker is unavailable, the employer's documented exception procedure (typically requiring a supervisor's verification that the worker is not in the hazard zone) is followed to remove the lock.