Lockout/Tagout (LOTO)
A procedure for de-energizing equipment or systems, locking out the energy source and tagging it as out of service, before servicing or maintenance work begins, so the equipment can't be unexpectedly re-energized or started while someone is working on it.
Why it matters
Equipment that unexpectedly powers on or discharges stored energy while someone is servicing it is one of the more preventable, and more severe, categories of jobsite injury. LOTO exists specifically to remove the possibility of that happening by physically controlling the energy source itself, not just relying on a warning.
On a real project
Before servicing a rooftop unit's electrical components, an HVAC technician locks out the breaker feeding the unit and tags it, confirming with a test that the unit is actually de-energized before opening any panel.
Who this matters most to
An Electrician applies lockout/tagout constantly when working on panels and circuits that would otherwise be energized. An HVAC Technician does the same before servicing equipment with both electrical and mechanical stored-energy hazards, like a pressurized system or a unit with a flywheel that keeps moving after power is cut.
Where this goes wrong
A technician tags out a breaker but skips physically locking it, assuming the tag alone will keep anyone else from restoring power. A coworker unaware of the tag re-energizes the circuit to test something unrelated, and the equipment the first technician was servicing unexpectedly comes back to life.