In brief
Lockout-tagout (LOTO) means isolating all of a machine's energy sources and locking them with personal locks, releasing stored energy and verifying zero energy before maintenance and breakdown work. The procedure is written specifically for each machine; every worker applies their own lock and only they remove it.
What is LOTO, and why is switching off the isolator not enough?
Lockout-tagout, abbreviated as LOTO, is an energy isolation method that prevents a machine from starting unexpectedly during maintenance, cleaning, setting or breakdown work. It has four parts: isolating the energy sources, locking the isolation points with personal locks, hanging a tag next to the lock showing who is working and why, and verifying that no energy actually remains in the machine.
The shortest answer to "what is LOTO" is this: switching off the isolator is an action, while LOTO is the guarantee that the isolator cannot be switched on by someone else while you are working. Most maintenance accidents happen in two scenarios. In the first, the operator or a worker on another shift starts the machine while the maintenance person is inside. In the second, the machine is off but pressure remaining in a hydraulic accumulator, a ram coming down under gravity or a tensioned spring moves. Pressing "stop" on the control panel prevents neither.
Example machine: a hydraulic press and its energy sources
Rather than describing the procedure in the abstract, let us work through a machine often seen in metal and automotive supply workshops in Bursa: a hydraulic press on which a die change and seal maintenance are to be done. Let us assume this press also has a pneumatic part ejector and a die heater. The first step of LOTO is to write down every energy in the machine one by one:
| Energy type | Its source in this press | Isolation point | How is zero energy verified? |
|---|---|---|---|
| Electrical | Main supply, pump motor, control circuit | Main isolator (lockable) | Start attempt; where needed, absence-of-voltage check by an authorised person |
| Hydraulic | Pump, accumulator, pressure inside the cylinder | Pump stopped, accumulator dump valve opened | Pressure gauge reads zero |
| Pneumatic | Part ejector, die cushion air line | Lockable ball valve and venting | Line gauge at zero, no air from the vent |
| Gravity | Weight of the ram and upper die | Ram lowered to bottom position or safety block fitted | Visual check that the ram is mechanically supported |
| Thermal | Die heater | Heater circuit cut at a separate fuse | Surface temperature falls to a level safe to touch |
This table is the essence of the LOTO instruction at the machine. In a good instruction each isolation point is numbered, labelled with the same number on the machine and shown with a photograph. That way even a maintenance person on the night shift does not have to guess which valve to close.
Preparation: machine-specific instruction, lock and tag
What needs to be prepared in advance for the procedure to work on site:
- Machine-specific LOTO instruction: The energy list, the location of isolation points, how stored energy is to be released and the verification method.
- Personal lock: A lock for each maintenance person bearing their name, with the only key held by them. A spare key is not kept on the panel or in the supervisor's drawer.
- Multi-lock hasp: Used so that each person can apply their own lock when more than one person works at the same isolation point.
- Valve and isolator lockout devices: Suitable lockout devices for ball valves, gate valves and moulded-case breakers.
- Tag: The worker's name, date, work being done and contact phone number. The tag is a warning; on its own it does not take the place of the lock.
- Authorisation list: The maintenance staff who will apply LOTO and the operators who use the machine and are to be informed are identified separately.
On large lines with many isolation points, group lockout is used. The responsible person locks all isolation points with their own locks and puts the keys to those locks in a lock box; each worker in the team then applies their personal lock to the box. The box cannot be opened until the last worker removes their lock, and no isolation point is released until the box is opened.
The instruction card hung next to the machine should be short. An example card for a hydraulic press might begin like this:
Press P-03 LOTO card. Energies: electrical (E1 main isolator), hydraulic (H1 accumulator dump valve), pneumatic (P1 air valve), gravity (ram safety block, on the right column), thermal (T1 die heater fuse). Sequence: stop, lock E1 and P1, open H1, lower the ram onto the block, cut T1, try to start, check the gauges.
The lockout-tagout procedure step by step
- Define the work. What maintenance will be done, which energies will be isolated, how many people will work? Open the instruction at the machine.
- Inform those affected. Tell the operator and the shift supervisor that the machine is being taken down for maintenance; put up a warning around it.
- Stop the machine in the normal way. First stop it from the controls and bring the ram to the position stated in the instruction. Cutting energy abruptly can create a new hazard in moving parts.
- Isolate the energies. Switch off the main isolator, stop the hydraulic pump, close the air valve, cut the heater circuit.
- Lock and tag. Everyone applies their own lock to each isolation point. If three people are working, there are three locks on the multi-lock hasp at the main isolator.
- Release or secure stored energy. Dump the accumulator pressure, vent the pneumatic line, lower the ram to the bottom position or fit the safety block.
- Verify zero energy. Try to start from the controls and see that the machine does not respond; check that the gauges read zero. In electrical maintenance, the absence-of-voltage check is done by an authorised person with a suitable measuring instrument. After the test, do not forget to return the controls to the "off" position.
- Carry out the maintenance. If you notice a new energy source during the work, stop and update the instruction.
- Clear the area. Collect tools, refit removed guards, remove the safety block and confirm by headcount that everyone has left the danger zone.
- Remove the locks and re-energise. Each worker removes only their own lock. The operator is informed, energy is restored in a controlled way and the machine is handed over with a test run.
In electrical work, apply this sequence together with the five safety rules in electrical work. For the press's specific guards, see our article on press safety.
Shift handover, contractors and lost keys
If maintenance is continuing at shift handover, the new team applies its own locks and then the old team removes its locks. That way the isolation point is never left unlocked, even for a moment. The handover is entered in the record of your permit-to-work system.
Contractors work by the same rule: the workers of an outside maintenance company apply their own locks, know your procedure and sign it. For the division of responsibility between the principal employer and the contractor, see our subcontractor article.
Removal of a lock by someone other than its owner is only an exceptional situation and must be governed by a written procedure. Every means of reaching the lock owner is tried, the responsible supervisor personally checks the area and the machine, it is confirmed that no one is in the danger zone, the removal is recorded in a report, and the lock owner is informed on returning to work before starting work.
Risk assessment, training and records
The LOTO procedure arises from the maintenance activities in the risk assessment; the rule of isolating energy during maintenance is only applied consistently on site if it is based on this assessment. The assessment should address not only the machine's normal operation but also tasks such as die changes, clearing jammed parts, cleaning and breakdown work as separate lines. Which task requires full LOTO and which can be done in the setting mode provided by the manufacturer is clarified in this assessment. The hierarchy of controls guides this decision: isolating energy always comes before PPE and being careful.
On the training side there are two groups. Maintenance staff who will apply LOTO should learn the procedure at the machine, applying it with real locks and valves. Operators should know what the lock and tag mean and why they must never be touched. This topic is covered in the job- and workplace-specific risks section of basic training; at hazardous and very hazardous workplaces this section is delivered face to face.
Keep the following as records: machine-specific LOTO instructions, the lock-to-person matching list, training attendance records and reports of exceptional lock removals. For the general arrangement of guards on machines, see our article on machine guards.
In Bursa Sistemer OSGB's OHS specialist services we prepare machine-specific LOTO instructions on site together with your maintenance team, and in the risk assessment we treat maintenance work as a separate heading. For other risks specific to metal and machinery businesses, see our metal and machinery page, and to track renewal dates, the OHS calendar.
Frequently Asked Questions
Is LOTO a legal requirement?
The legislation does not use the name "LOTO", but the Work Equipment Regulation requires maintenance to be done while the equipment is shut down, its energy connection cut and its movements stopped, and re-energisation not to create a danger. Lockout-tagout is the established method of securing this requirement on site.
Is hanging only a tag enough?
No. The tag is a warning showing who is working; it does not physically prevent the isolator from being switched on. The tag is hung next to the lock, not instead of it.
Are all the steps needed even for a short adjustment?
Energy must be isolated for any task that requires access to the machine's danger zone. For setting and measuring tasks where cutting energy is not possible, measures such as the setting mode provided by the manufacturer, reduced speed and hold-to-run controls are defined separately in the risk assessment.
What kind of lock should be used for LOTO?
The lock should be reserved for this work only, have a single key and be personal. Having the owner's name or photo on the lock makes it easier to see on site who is inside. Cabinet or door locks are not used for LOTO.
Can someone else remove the lock?
As a rule, each lock is removed only by its owner. If the lock owner cannot be reached, the written exception procedure is applied: the supervisor personally checks the area, the situation is recorded in a report, and the lock owner is informed before returning to work.
A certified specialist matched to your hazard class: site inspections, approved logbook, training plan, annual plan and report follow-up.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.