Industrial Safety · Explainer
Zero energy is a verified state, not an assumption
Lockout/tagout protects people only when every energy source is found, isolated, released and then proven dead before hands go in.
Servicing and maintenance put people inside machines that are designed to move, heat, pressurise or energise. OSHA notes that an unexpected start-up or release of stored energy during this work can cause serious injury or death, and lists electrical, mechanical, hydraulic, pneumatic, chemical and thermal sources among the energies involved [1].
The sequence matters
In the United States, the general industry standard 29 CFR 1910.147 sets out an energy control application sequence. Its headings are: preparation for shutdown; machine or equipment shutdown; machine or equipment isolation; lockout or tagout device application; stored energy; and verification of isolation [2].
Each step closes a different gap. Preparation means knowing every energy source before you start. Isolation must act on the energy itself, not on a control circuit. Stored energy. Springs, accumulators, capacitors, raised loads, trapped pressure, heat. Has to be relieved, restrained or otherwise made safe.
Why verification is its own step
Under 1910.147(d)(6), before work begins on equipment that has been locked or tagged out, the authorised employee must verify that isolation and de-energisation have been accomplished [2]. In practice that usually means a deliberate attempt to start or operate the equipment from its normal controls, and testing with suitable instruments where electrical or pressure hazards are present. Then returning controls to off.
A conveyor has a main isolator and a separate pneumatic take-up. The isolator is locked and the start button tried: nothing moves. But the take-up cylinder still holds air pressure, and the belt can shift when a guard is removed. Only a written procedure that lists both energy sources, and a verification step for each. Would have caught it.
Questions for your next isolation
- Does the procedure for this specific equipment list every energy source, including stored and gravitational energy?
- Does every person exposed apply their own lock, and is it clear who removes it?
- How will isolation be proven. Try, test, measure, and who witnesses it?
- What happens at shift change, or if the job pauses and the equipment must be tested?
Most isolation failures we discuss in training are not exotic. They are an energy source no one listed, or a verification step skipped because “it was already off”. Treat verification as non-negotiable.
Legal duties differ by country and industry. In the United States, also check whether 1910.147, 1910.269 or 1910.333 applies to the work. Use your site’s written energy control procedures.
General educational material, not legal advice, a site-specific risk assessment or a work authorisation. Confirm current requirements in your jurisdiction and follow site procedures and competent advice.
References
- OSHA. Control of Hazardous Energy (Lockout/Tagout) overviewUnited States
- OSHA. 29 CFR 1910.147, The control of hazardous energy (lockout/tagout)United States
All sources opened and checked on 30 October 2026. Requirements and guidance change; always consult the current version.
Downloads & tools
PDFEnergy isolation verification checklistv1.0 · A4 · free downloadTOOLShift StarterA guided pre-shift check that turns your crew’s answers into a printable shift brief.Editorial status: source-checked explainer. No independent external technical review is claimed. Spotted an error? See corrections.
