Lockout tagout is one of the most familiar safety procedures in industry, and one of the most frequently shortened. The lock goes on, the tag is filled in, and work starts. What is often skipped is the single step that proves the isolation actually worked.
Why the lock alone proves nothing
A padlock on an isolator shows that someone intended to isolate the equipment. It does not show that they chose the right isolator, that the isolator is working internally, or that there is no second source of energy feeding the same machine. Drawings go out of date, panels get relabelled, and equipment gets modified. The only reliable evidence is a test at the point of work.
The verification step
After isolating and locking, and before anyone touches the equipment, confirm zero energy:
- Try to start it. Operate the local start control and confirm nothing moves, then return the control to off.
- Test for voltage at the point of work with an approved tester, and prove the tester on a known live source before and after.
- Check pressure gauges read zero and open vents or drains to confirm lines are depressurised and empty.
- Look for movement in anything that could rotate, fall or spring back.
Stored energy is where people get caught
Switching off the supply does not remove energy that is already stored in the system. Capacitors hold charge. Hydraulic accumulators and trapped pressure between closed valves stay live. Springs remain compressed. Raised loads, rams and counterweights can drop. Flywheels keep turning. Each of these needs its own step: discharge, bleed, block or support, and then check again.
More than one person, more than one lock
When several people or trades work on the same equipment, each person should apply their own lock, usually through a group lock box, and only remove it when their own part of the job is finished. One supervisor's lock covering a whole crew means the crew is relying on someone else remembering that they are still inside the machine.
The common failures
The patterns repeat: the wrong isolator locked because two panels look alike, a second feed that nobody knew about, an electrician's lock removed at shift change while mechanical work was still going on, and a pressure line that was isolated but never vented. None of these are exotic. All of them are caught by testing before touching.
Does Your Isolation Procedure Include Proving Zero Energy?
Our training team delivers practical lockout tagout and energy isolation training for maintenance crews and supervisors, and our HSE specialists review isolation procedures against how your equipment is really built.
Explore Training Services