Lockout and tagout is the practice of making a machine safe to work on by cutting off its energy and keeping it off while people are exposed. This is a general description. The actual rules and your site’s written procedure for each machine take priority, and only trained, authorized people should carry out isolation. The manufacturer’s manual is often the first place to look for the correct isolation points on a particular machine.
Why it matters
Machines are designed to be safe in normal operation, with guards and controls between people and moving parts. During servicing those protections are often removed or bypassed, because the person needs to reach inside. If the machine starts unexpectedly, or if stored energy releases, injuries can be severe. Unexpected start-up and release of stored energy are the hazards that energy isolation procedures are designed to prevent.
What counts as hazardous energy
Electricity is the most familiar, but it is not the only source. Machines may contain:
- Electrical energy from the supply and from components that hold a charge.
- Mechanical energy in flywheels, springs, raised loads and rotating parts that continue turning after power is cut.
- Hydraulic energy from pressurized fluid in lines and accumulators.
- Pneumatic energy from compressed air in lines and receivers.
- Thermal energy from hot surfaces, steam and process fluids, or very cold materials.
- Chemical energy from reactive or flammable substances in pipework.
- Gravity, such as a press ram or a raised platform that could fall.
A good procedure identifies every source for the specific machine, not only the main electrical switch. Some machines have several power sources, for example a motor, a hydraulic unit and a compressed air supply. A pump, a conveyor or a press each have different isolation points, so general rules need machine-specific detail.
Lockout versus tagout
Lockout uses a physical lock, applied to an energy-isolating device such as a disconnect switch, valve handle or breaker, to hold it in the safe position. A lock prevents the device from being operated until it is removed.
Tagout uses a warning tag attached to the device. A tag is a warning only and cannot physically prevent operation, so it relies on people respecting it. Many rules and employers prefer lockout wherever a device can be locked. Where a device cannot take a lock, extra measures may be needed to give equivalent protection.
In everyday use the two words are often used together as shorthand for the whole energy control program.
A typical sequence
Procedures differ by machine and jurisdiction, but most follow a pattern like this:
- Prepare. Identify the machine, the energy sources and the isolation points from the written procedure. Tell affected people that servicing will begin.
- Shut down. Stop the machine using its normal controls so that it comes to rest in a controlled way.
- Isolate. Operate the energy-isolating devices to cut off each source.
- Apply locks and tags. Each authorized person applies their own personal lock, and often a tag with their name and date. Group procedures allow several people to apply locks to a shared device, so that each person controls their own protection.
- Release stored energy. Bleed pressure from lines, block or lower raised parts, discharge capacitors, allow hot or cold parts to return to a safe temperature and restrain springs, following the procedure.
- Verify. Confirm the machine is in a zero-energy state before work begins, for example by trying the normal start controls, confirming that gauges read zero and testing for absence of voltage with suitable instruments where electrical work is involved. Make sure that nobody is in a position to be exposed before doing the start-up test, and return controls to off afterward.
- Service. Carry out the work.
- Restore. Remove tools, replace guards, make sure everyone is clear, remove locks and tags (each by the person who applied them, in most systems), tell affected people and re-energize.
The verification step is where many programs fall down, because skipping it can leave an unnoticed energy source live. Ongoing lockout is also needed across shift changes, which is why procedures include how locks are handed over.
Roles and training
Programs typically distinguish between:
- Authorized employees, who apply locks and carry out the servicing.
- Affected employees, who operate or work near the machine and need to understand that a locked machine must not be started.
- Other employees who may be in the area and should understand the meaning of locks and tags and not interfere with them.
Training is expected to match the role, including the purpose and the content of the procedures, the types of energy involved, the methods of isolation and verification, and the rules about removing devices. Retraining is generally expected when procedures or equipment change, or when inspection shows that practices are not being followed. Many systems also require periodic inspection of the energy control procedures, with the frequency set by local rules and often at least annually, so check the requirements that apply to you.
Outside contractors who service equipment should have their procedures coordinated with the host site, so each knows the other’s locks and expectations.
Common problems
Typical weaknesses seen in energy control programs include:
- Procedures that are generic and omit machine-specific isolation points.
- Missed or unrecognized secondary energy sources.
- Skipping the verification step, or testing it unsafely.
- Using tags alone where locks could be fitted.
- Lock removal by someone other than its owner without an approved process.
- Short-cut “minor servicing” practices that leave people exposed.
- Poor handover between shifts.
- Equipment modifications that add new energy sources without updating procedures.
When something is unclear, the safe response is to stop and ask a supervisor or qualified person, not to improvise.
Where it fits in a safety program
Lockout is one control among many. Good machine design can reduce the need to enter hazardous zones, and planned maintenance can lessen the need for emergency repairs. In many jurisdictions it also overlaps with confined space entry and electrical safe work practices, where energy isolation is only one step. Follow your regulator’s rules, the manufacturer’s instructions and your site’s written procedures.