LOTO
Lockout/Tagout is the procedure for safely isolating equipment for service. NFPA 70E and OSHA 29 CFR 1910.147 govern. Authorized vs affected workers have different responsibilities. Energy isolation devices vary by source type.
Lockout/Tagout — The Standard
Lockout/Tagout is the procedure for safely isolating equipment for service. NFPA 70E and OSHA 29 CFR 1910.147 govern. The goal: make absolutely sure no energy can reach the equipment while a worker is in contact with it.
| Standard | Scope |
|---|---|
| OSHA 29 CFR 1910.147 | "Control of Hazardous Energy" — the federal LOTO standard. Applies to general industry. |
| OSHA 29 CFR 1926.417 | Construction-specific lockout requirements. |
| NFPA 70E Article 120 | "Establishing an Electrically Safe Work Condition" — the electrical LOTO procedure. |
| ANSI Z244.1 | National consensus standard for control of hazardous energy. |
The 7-Step LOTO Sequence (NFPA 70E 120.5)
| Step | Action | Detail |
|---|---|---|
| 1 | Identify all sources | Use SLDs, schedules, walk-down. Multiple sources = backfeed possible. |
| 2 | Notify everyone affected | Operators, adjacent workers, customer. |
| 3 | Open disconnects + breakers | Both line + load side of equipment. |
| 4 | Apply locks + tags | One worker = one lock. Personal padlock + tag with name + date. |
| 5 | Discharge stored energy | Capacitors, springs, batteries, hydraulic accumulators, compressed air, thermal. |
| 6 | Verify de-energization | Test before touch — voltmeter on a known live source first, then on equipment, then on known live source again. |
| 7 | Apply temporary protective grounds (MV/HV) | For voltages > 600V — induced voltage can re-energize the line. |
Authorized vs Affected vs Other Workers
| Role | Definition | Training requirement |
|---|---|---|
| Authorized | Workers who lock out + work on energy-isolated equipment | Full LOTO training. Authorized to apply + remove their own locks. |
| Affected | Workers whose job uses the equipment being LOTO'd | Awareness training. Cannot apply locks. Must be informed of LOTO. |
| Other | Workers in the area | General awareness. Recognize a locked-out condition. |
Energy Source Types
| Energy | How to isolate | How to verify |
|---|---|---|
| Electrical | Disconnect / breaker open + locked | Voltmeter test (live-dead-live) |
| Hydraulic | Block valves closed + locked, pressure relieved | Pressure gauge at zero |
| Pneumatic | Air valve closed + locked, line vented | Pressure gauge at zero |
| Mechanical | Block in place, springs released | Visual inspection |
| Thermal | Allow cool down, isolate hot/cold sources | Temperature measurement |
| Chemical | Block valves on chemical lines | Sniff testing for vapors, line break point |
| Stored (capacitors, springs) | Discharge to ground via resistor; relax springs | Voltmeter on capacitor; visual on springs |
Equipment for LOTO
| Item | Purpose |
|---|---|
| Padlock | Physically holds disconnect open. Each worker has unique key — only that worker can remove their lock. |
| Lockout tag | Attached to padlock. Shows worker name, date, reason. |
| Hasp / multi-lock device | Allows multiple workers to apply locks to the same disconnect (group LOTO). |
| Breaker lockout | Specific device for circuit breakers — slides between breaker handle and ON position. |
| Plug lockout | Encases the plug of a portable cord, prevents reconnection. |
| Valve lockout | Devices to lock pneumatic/hydraulic valves in closed position. |
| Voltage detector | Used in step 6 verification. Cat III rated for the voltage being tested. |
| Temporary protective ground (TPG) | For MV/HV — connects line to ground after isolation. Required for > 600V. |
Group LOTO + Complex Procedures
| Situation | Procedure |
|---|---|
| Single worker on simple equipment | Standard 7-step. One lock per worker. |
| Multiple workers, one piece of equipment | Group LOTO. Each worker applies their own lock to a hasp. Equipment cannot be re-energized until ALL workers remove their locks. |
| Multiple workers, multiple disconnects | Group LOTO with key-lock box. Master lock on disconnects holds keys; each worker locks the box. |
| Long-duration project (multiple shifts) | Shift transfer of LOTO. Strict sign-off + verification at each shift change. |
| Worker cannot remove their own lock | NEC + OSHA exception process — supervisor verifies worker is gone, then removes after multiple confirmations. |
Worked Example 1 — Atlas DC1 LOTO with 2N Topology
Example 01 · Atlas DC1 spineServicing UPS-A1 — LOTO procedure that doesn't drop IT load
Why this is interesting
UPS-A1 serves IT Row A. In a non-2N facility, LOTO of UPS-A1 = drop IT load. In Atlas DC1's 2N topology, IT Row A is also fed from UPS-B1 via redundant paths in each rack PDU.
- Verify 2N path operational: Before starting, verify Side B (UPS-B1) is fully operational and able to carry full Side A IT load. Coordinate with operations team.
- Identify all sources of UPS-A1: Input from 480V SWGR-A. Output to PDU-A1. Battery string. Bypass static switch. UPS controls power.
- Notify: Site operations, IT operations, customer, fire alarm panel monitor.
- Open + lock disconnects: Input CB at SWGR-A (2000 A). Output CB at PDU-A1. Battery string DC CB. Static bypass disconnect.
- Discharge stored energy: Wait minimum 5 minutes for DC bus capacitors to discharge below 50V (per UPS manufacturer). Voltmeter verify.
- Verify de-energized: Live-dead-live test on UPS terminals.
- Battery string isolation: Battery DC voltage typically 540V. Even after AC removed, battery is still energized. Apply lock to DC CB.
- Work begins. If multiple workers, group LOTO with each applying their own lock to a multi-lock hasp.
Throughout this procedure
- IT load remains fully powered via UPS-B1 redundant rack feeds.
- Genset coordination: Verify GEN-A startup not commanded during LOTO (it would energize Side A through ATS-A but UPS-A1 is locked out anyway).
- Bypass switch: If maintenance bypass switch present, operators may transition to bypass before LOTO — but for full LOTO, bypass also locked.
Worked Example 2 — Standard Industrial LOTO (Motor)
Example 02 · Alternate contextServicing 100 HP industrial pump motor — standard 7-step LOTO
- Identify sources: Power from MCC bucket. Control wiring from PLC. Mechanical: pump impeller. Hydraulic: process flow upstream.
- Notify: Operators, adjacent shift workers, control room.
- Open disconnects: MCC bucket disconnect (combination starter has pull-out handle). Open + lock.
- Apply control lockout: Lock the auto/manual selector switch in OFF position so PLC cannot send start signal.
- Isolate process: Close + lock isolation valves upstream + downstream. Bleed line pressure.
- Verify: Voltmeter (live-dead-live) on motor terminals. Pressure gauge on process line at zero.
- Work begins.
- After work: Close access panels. Remove locks in reverse order. Open valves. Restore power. Test run.
Drill — Quick Self-Check
Work each problem mentally; reveal to check. Goal: reflex, not deliberation.
Drill 1 · LOTO standard
Federal LOTO standard?
OSHA 29 CFR 1910.147
NFPA 70E Article 120 = electrical-specific.
Drill 2 · Authorized worker
Who can apply locks?
Only authorized workers
Affected workers cannot apply locks.
Drill 3 · Live-dead-live
Three steps of voltage verification?
Test on known live → on equipment (should be dead) → on known live again
Confirms voltmeter still works.
Drill 4 · Stored energy
Capacitor bank in UPS — safe to touch immediately after disconnect?
NO — wait for discharge (typically 5+ min)
Stored DC bus voltage can be lethal.
Drill 5 · MV/HV grounding
Required additional step for ≥ 600V LOTO?
Apply temporary protective grounds (TPG)
Induced voltage can re-energize the line.
If You See THIS, Think THAT
| If you see… | Think / use… |
|---|---|
| "LOTO" / "Lockout/Tagout" | Procedure for safe energy isolation. NFPA 70E + OSHA 1910.147. |
| "NFPA 70E Article 120" | Electrical-specific LOTO. The electrically safe work condition procedure. |
| "Authorized worker" | Trained on full LOTO. Can apply + remove own lock. |
| "Affected worker" | Awareness only. Cannot apply locks but must be informed. |
| "Live-dead-live test" | Verify voltmeter on live source first, then absent on equipment, then live again. Confirms voltmeter still works. |
| "Group LOTO" | Multiple workers each apply own lock to a multi-lock hasp. |
| "Stored energy" | Capacitors (UPS, VFDs), springs, batteries, hydraulic accumulators. Must discharge before work. |
| "Temporary protective ground" (TPG) | For MV/HV — bonds line to ground after isolation. Mandatory above 600V. |
| "Voltmeter Cat III rated" | Test instrument rated for the voltage being tested. Cat III for distribution; Cat IV for service entrance. |
| "Single point of control" / dual disconnect | Two independent isolation methods for higher-risk work. Used for life-critical systems. |
| "Energized work permit" | NFPA 70E 130.2 — required if working on energized equipment is justified (rare). Documented hazard analysis + PPE. |