How to make machinery safe before anyone services it
Workers are seriously hurt when machinery starts unexpectedly, or stored energy is released, during cleaning, maintenance or clearing a jam. Isolation disconnects every energy source; lockout-tagout locks it in the off state and tags who did it, so it cannot be re-energised until the work is finished. The goal is a verified zero-energy state — isolate, lock, tag, release stored energy, then test to prove it is dead. WorkSafe expects PCBUs to follow AS/NZS 4024.
Servicing covers more than maintenance — it includes repairing, cleaning, unjamming and unblocking machinery. People are most at risk during these tasks because guards are often off and the operator is not at the controls.
If the machine starts unexpectedly, or stored energy is suddenly released, the result is crushing, amputation or death. Isolation and lockout-tagout exist to make that impossible while the work is done. See also plant & machinery safety.
“Energy” is more than electricity. Every source that could move a part or release has to be accounted for.
| Energy type | Examples |
|---|---|
| Electrical | Mains power, batteries, capacitors that hold charge. |
| Mechanical / stored | Springs, tensioned belts, flywheels, and parts that coast after shut-down. |
| Hydraulic | Pressurised fluid in rams and lines. |
| Pneumatic | Compressed air. |
| Gravity / potential | Raised platforms, counterweights, suspended loads — anything that can fall or roll. |
| Thermal / chemical | Hot surfaces, steam and process chemicals. |
A reliable LOTO sequence runs in this order. Skipping the last step — verifying — is where many serious incidents happen.
| Step | What to do |
|---|---|
| 1. Plan & notify | Identify the machine and every energy source; tell affected workers; clear the area. |
| 2. Shut down | Stop the machine using its normal controls and wait for all movement to stop. |
| 3. Isolate | Disconnect each energy source at the main isolating device — not at a control switch. |
| 4. Lock | Apply a personal lock to each isolation point, and keep your own key. |
| 5. Tag | Attach a tag with your name, contact and date, and record it on the isolation register or permit. |
| 6. Release stored energy | Bleed pressure, lower or block raised parts, discharge capacitors, relieve tension. |
| 7. Verify (test for dead) | With everyone clear, try the normal start controls and test that the machine cannot operate and is de-energised. |
Isolate on the main power circuit, not a control circuit. (Source: WorkSafe NZ.)
Each worker applies their own lock and keeps their own key, so no one else can remove it. Only the person who applied a lock removes it. Where several workers are on the same machine, use a group lockout box so the machine cannot be released until everyone's lock is off. For complex or high-risk isolations, run it under a permit to work.
Ask whether the task exposes anyone to a risk of injury from movement or from an energy source. If effective safeguards already protect the worker for that task, lockout may not be needed. If not, the machine must be isolated and locked out. As a rule of thumb, any machine that takes more than 10 seconds to stop should have braking or restricted entry so no one reaches moving parts during over-run.
Write a machine-specific isolation procedure for each piece of plant, train and supervise everyone who locks out, and never rely on a sign or a switched-off control alone. Contractors must work under your isolation procedures or an agreed, equally safe alternative. AS/NZS 4024 — including the part on preventing unexpected start-up — is the standard WorkSafe expects PCBUs to work to, or to match.
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Lockout-tagout is the practice of isolating every energy source to a machine, locking each isolation point so it cannot be re-energised, and tagging who did it and when — so the machine stays safe while it is serviced.
It is the condition where every energy source — electrical, hydraulic, pneumatic, mechanical, gravity, thermal and any stored energy — has been isolated and verified, so the machine cannot move or release energy.
Not always — only if the task exposes someone to a risk of injury from movement or energy and effective safeguards are not in place for that task. If there is such a risk, the machine must be isolated and locked out before the work starts.
WorkSafe expects PCBUs to use the AS/NZS 4024 Safety of Machinery series, including the part on preventing unexpected start-up. You can use another standard if you can show it achieves the same level of safety or better.
No. Each worker applies their own personal lock and keeps their own key, and only they remove it. Where several people work on one machine, use a group lockout box so it cannot be released until every lock is off.
