3.2 Verification: proving the machine is dead
Verification is the step that turns a set of locks into a safe machine, and it is the step most often replaced by a glance. 1910.147(d)(6) is short — "the authorized employee shall verify that isolation and deenergization of the machine or equipment have been accomplished" — but the word verify means an action taken and an observation made, not a belief held.
1 Two verifications, two standards
There are two different verification requirements in play depending on what kind of work you are doing, and mixing them up is a common source of both over-work and under-protection.
| 1910.147(d)(6) — servicing a machine | 1910.333(b)(2)(iv) — electrical work on fixed equipment | |
|---|---|---|
| Who | The authorized employee | A qualified person |
| What is required | Verify that isolation and deenergization have been accomplished | Operate the controls or otherwise verify the equipment cannot be restarted, and use test equipment to verify the parts are deenergized |
| Instrument test | Not stated as such; Appendix A offers operating the normal control or testing as means | Explicitly required, including checking for inadvertently induced voltage and unrelated voltage backfeed |
| Extra rule above 600 V | — | Test equipment must be checked for proper operation immediately before and immediately after the test |
The practical rule: if you are going to touch electrical conductors or circuit parts, 1910.333(b)(2)(iv) governs and a meter comes out. If you are pulling a jammed part out of a mechanical machine, 1910.147(d)(6) governs and the try step is the verification. Many jobs are both, and then both apply.
2 The try step, done properly
1910.147 Appendix A step 7 spells out the mechanical verification: "Ensure that the equipment is disconnected from the energy source(s) by first checking that no personnel are exposed, then verify the isolation of the equipment by operating the push button or other normal operating control(s) or by testing to make certain the equipment will not operate."
Read the order of that sentence. First check that no personnel are exposed. Only then press start. The try step deliberately attempts to run the machine, so anyone with a hand in a nip point during that attempt is relying entirely on the lockout having worked — which is the very thing being tested.
And the appendix adds a caution in bold type of its own: "Return operating control(s) to neutral or 'off' position after verifying the isolation of the equipment." A start control left engaged is a machine that runs the instant somebody restores power, whether that is you at the end of the job or an electrician troubleshooting the next panel over.
3 Test before touch: the instrument verification
For electrical work, 1910.333(b)(2)(iv)(B) requires a qualified person to "use test equipment to test the circuit elements and electrical parts of equipment to which employees will be exposed and shall verify that the circuit elements and equipment parts are deenergized." The same paragraph requires the test to "determine if any energized condition exists as a result of inadvertently induced voltage or unrelated voltage backfeed even though specific parts of the circuit have been deenergized and presumed to be safe."
Two failure modes are named there by the standard itself. Induced voltage — a de-energized conductor running alongside an energized one picks up a potential. Backfeed — energy arrives from somewhere other than the source you isolated: a control transformer feeding backwards, a generator, a tied bus, an interlock circuit from an adjacent machine.
The discipline that catches both is live-dead-live: prove the meter on a known live source, test the circuit you are about to work on and read zero, then prove the meter again on the known live source. If the meter failed between the first and second proof, you find out before you touch anything instead of after. Above 600 volts nominal, 1910.333(b)(2)(iv)(B) makes this mandatory in so many words: the test equipment shall be checked for proper operation immediately before and immediately after the test.
- 1Live — prove the meter on a source known to be energized.
- 2Dead — test every conductor you may contact, phase to phase and phase to ground, and read zero.
- 3Live — prove the meter again on the known source.
4 Verifying the other kinds of energy
Electrical verification gets the attention because it has an instrument attached to it. Every other energy type needs verifying too, and each has its own proof.
| Energy | Verification | What "not verified" looks like |
|---|---|---|
| Electrical | Live-dead-live instrument test at the exposed parts | Trusting an indicator lamp or a panel meter |
| Hydraulic | Gauge reads zero and stays there with the bleed open | "The pump is off" |
| Pneumatic | Gauge at zero, no air at the vent, cylinder moves freely by hand | Hearing the exhaust and moving on |
| Gravity | Load visibly resting on the block or prop | A prop installed near, but not under, the load |
| Rotational | Motion has fully stopped; brake or pin engaged | "It's slowing down" |
| Thermal | Temperature measured with an instrument | Touching it with a glove on |
| Chemical / process | Blind installed and logged; line drained; atmosphere tested where relevant | A closed valve and an assumption |
5 Continued verification where energy can come back
1910.147(d)(5)(ii) requires that where there is a possibility of reaccumulation of stored energy to a hazardous level, "verification of isolation shall be continued until the servicing or maintenance is completed, or until the possibility of such accumulation no longer exists."
This is the only place in the standard where verification is an ongoing duty rather than a one-time step, and it is the paragraph to reach for whenever an isolation depends on a valve seat rather than a physical break. A leaking valve refills an accumulator. A blocked drain lets condensate build. Product keeps arriving in a hopper. In each case the answer on the written procedure is one of: leave the bleed open for the duration, install a blind, or state a monitoring interval and who does it.
6 Writing verification into the procedure
1910.147(c)(4)(ii)(D) requires the written procedure to contain "specific requirements for testing a machine or equipment to determine and verify the effectiveness of lockout devices, tagout devices, and other energy control measures." Appendix A leaves a blank line for it: "Method of verifying the isolation of the equipment."
A verification line that satisfies (D) says what is tested, how, and what result proves it. Compare these two entries for the same machine:
The second one takes ninety seconds longer to write and removes every judgment call from the person who has to follow it at the end of a night shift. That is the whole argument for machine-specific procedures in a single example. Our LOTO procedure generator gives verification its own field for exactly this reason.
- 1910.147(d)(6) requires the authorized employee to verify that isolation and deenergization have been accomplished before work starts.
- Appendix A step 7: check that no personnel are exposed first, then attempt to operate the normal controls — and return the controls to neutral or off afterwards.
- For electrical work, 1910.333(b)(2)(iv) requires a qualified person to both attempt restart and instrument-test the parts, checking for induced voltage and backfeed; above 600 V the meter is proved immediately before and after.
- Live-dead-live is the discipline that catches a meter that died between readings.
- Every energy type has its own proof: a gauge at zero, a load resting on a block, motion fully stopped, a measured temperature, a blind installed and logged.
- Where energy can reaccumulate, verification continues for the duration of the work (1910.147(d)(5)(ii)); the written procedure must state specific testing requirements (1910.147(c)(4)(ii)(D)).
Free educational content — not OSHA-authorized training, no certificate or card issued. Follow your employer's program and the standards cited.