Lockout/tagout (LOTO) is the procedure for making sure machinery and equipment are de-energised and can't be restarted while someone is servicing them. In the US it's governed by OSHA's control of hazardous energy standard (29 CFR 1910.147); most countries have equivalent rules.
The procedure itself is well understood. What goes wrong is usually execution under time pressure: a step skipped because 'it's always off', a verification nobody actually did, a lock removed by someone other than the person who placed it.
The lockout/tagout sequence
1. Prepare. Identify every energy source: electrical, mechanical, hydraulic, pneumatic, thermal, chemical, gravity and stored energy.
2. Notify. Tell everyone affected that the equipment is being shut down and locked out.
3. Shut down. Stop the equipment using its normal procedure.
4. Isolate. Disconnect each energy source at its isolation point.
5. Lock and tag. Each authorised person applies their own lock and tag to each isolation point.
6. Release stored energy. Bleed, block, discharge or restrain any residual energy.
7. Verify. Attempt to start the equipment and test for zero energy before work begins.
8. Restore. After the work, clear the area, remove tools, confirm people are clear, and each person removes their own lock.
Evidence turns a checklist into a record
A paper checklist ticked at the end of a job tells you someone ticked it. A record where each step is signed off by its owner at the time it happened, with a photo of the lock on the isolation point and the result of the zero-energy test, tells you the step happened.
Requiring evidence on the critical steps, isolation, lock application and verification, costs seconds on the job and is exactly what an investigator or auditor asks for.
Parallel isolations, one gate
On larger equipment, electrical and mechanical isolation are often done by different people at the same time. Model them as parallel steps that must both be signed off before verification can open. Work can't start until verification is signed. That structure enforces the order the procedure requires without slowing anyone down.