Lockout and tagout are often spoken of as one thing — "LOTO" — but they are different controls with different protective value. Lockout physically prevents energization; tagout only warns against it. Understanding when each is allowed is central to compliance, because using tagout where lockout is required is a frequent and serious violation.
Lockout is the placement of a lockout device — a keyed physical lock — on an energy-isolating device so it cannot be operated until the lock is removed. It is a physical barrier: the disconnect cannot be closed, the valve cannot be opened, regardless of intent or error. Only the worker who applied the lock holds the key.
Tagout is the placement of a prominent warning tag on an energy-isolating device indicating that it must not be operated. A tag communicates a prohibition, but it provides no physical restraint — anyone can still operate the device. Its protective value depends entirely on every person seeing, reading and obeying it.
Because a tag can be ignored, misread, or removed, OSHA 1910.147 treats lockout as the required method whenever an energy-isolating device is capable of being locked out. Employers cannot choose tagout for convenience; the standard presumes lockout and places the burden on the employer to justify any departure.
Tagout alone is allowed only when the employer demonstrates that the tagout program provides protection equivalent to that of lockout. Meeting that test in practice means adding a safety measure beyond the tag — removing an isolating circuit element, blocking a controlling switch, opening an extra disconnecting device, or removing a valve handle — so that defeating the isolation takes more than ignoring a tag.
For machines and equipment installed or undergoing major repair, renovation or modification after January 2, 1990, energy-isolating devices must be designed to accept a lockout device. This effectively pushes industry toward lockout as the norm and reserves tagout-only for legacy equipment that genuinely cannot be locked out — and even then, only with the equivalent-protection measures in place.
When tagout is used, the rationale and the supplemental measures should be documented in the equipment-specific procedure, and affected workers trained on the limitations of tags. A digital energy-control system makes this auditable: it records which method was applied, enforces the supplemental steps for tagout, and keeps the justification attached to the procedure for inspection.
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