Safety Moment #91: Lockout Tagout

Safety Moment #91: Lockout Tagout

Lockout / tagout systems are routinely used to protect workers when they are working with or close to hazardous systems. They are typically used in conjunction with the other isolation methods. Once a switch or valve is in the correct position it is locked so that it cannot be moved, and a 'Do Not Operate' tag is attached to it. (Valves are often chained in place, with the lock being used to secure the chain such that the valve handle cannot be moved.)

In spite of the security that a lockout system provides, it is less safe than the use of positive isolation methods. First a valve may leak while it is in the closed position. Second, in spite of all precautions, someone may remove the lock before the work has been finished. There is also a chance of confusion; the wrong valve may be chained closed, while the valve that should have been secured is left in its normal operating state.

Lockout/tagout is not normally used for routine operating activities such as collecting samples, replacing pressures gauges, or making equipment checks and adjustments. However, it is used on some systems in normal operation, e.g., pressure safety valves locked open or containment drain valves locked closed. Similarly, lockout / tagout is not use for plug connections on electrical equipment because the hazard can be controlled simply by unplugging the equipment (however, the plug that has been detached must be properly controlled so that no one inadvertently puts it back in the socket.)

Lockout/tagout does not normally apply to hand-held power tools or stationary equipment whose electrical power may be controlled by the unplugging of equipment from the energy source when the plug and cord are under the control of the employee performing the servicing or maintenance.

Once the system has been prepared for work, and the locks have been applied, the system must be verified. If it is a motor that is being worked on, for example, the area should be cleared in case the isolation procedures fails, and then an attempt should be made to run the motor. If it is a valve that is being locked closed, the safety lead should try to open it after the locks and chains have been applied. Some companies use the phrase lock, tag and verify to describe this process.

Car Seals

A car seal - also referred to as a security seal - helps prevent someone from inadvertently moving a tagged valve or switch (they are so called because they were first used to seal railcars after they were loaded.) However, because the car seal has very little physical strength (they are sometimes made of plastic), it is very easy to break one if someone decides that it is in the way. Car seals do not provide sufficient security when hazardous chemicals are being used. They are more commonly used in operations such as blending, where an error can cause product quality problems, but not a safety concern. They are also used to ensure that block valves around safety relief valves are in their specified open or closed positions as shown in the sketch, provided by the Total Lockout company.


The traditional form of car seal has been a wire loop with a tag attached to it - rather like a stronger version of a luggage tag. Each seal should have its own unique serial number. Car seals are often provided in different colors where each color is assigned to a particular application, as shown in the diagram.

Car Seals

The sketch below shows the operation of a wire car seal.

Car Seal

The car seal is attached as follows.

  • Pass the cable around the valve wheel and body.
  • Thread the cable back in to the seal body.
  • Pull the cable tight.
  • Cut away unwanted cable.

Group Lockout

When more than one person is working on a job a group lockout / tagout procedure is needed ? one in which each person involved can apply their own lock, and only they can remove it (sometimes known as a Masterlock system). Details vary from company to company, but the following process is representative.

  • The lead person on the job locks closed each valve, switch and other device that is used to isolate the high energy source. Only the lead has a key to these locks.
  • He or she labels the locks with the appropriate work permit information, and then attaches a lock box to each location.
  • He places the keys in the box, closes it and then locks it with a master lock (which is often a distinct color such as red.)
  • Every worker who is to work on that job attaches his or her lock to the lock box. They record what they have done on the work permit.
  • If a worker leaves the job, he or she removes their lock and signs off on the work permit.
  • If there is a shift change, workers on the first crew must sign off the job and remove their locks, and workers on the second crew must sign on to the job and add their locks.
  • At the end of the job, each worker removes his or her locks and signs off. Each person must satisfy themselves that the job has, from their point of view, been returned to a safe condition before they remove their personal lock.
  • The lead then removes the master lock and takes the keys from the open box.
  • He then closes the work permit, and unlocks the valves or switches, which now safe to operate.



Lockboxes may be used when multiple individuals and locks would be required, or in order to avoid the use of multiple locks per authorized individual. (i.e., each authorized individual locking several pieces of equipment). The use of a lockbox will be managed as follows: the methods and devices listed below will be used either separately or in combination, depending on the equipment, to lockout/tagout the following energy source(s):

  • An authorized employee will perform the isolation of the work area and involved equipment and complete the Lockout Permit.
  • All keys involved in the lockout of equipment will then be placed in the lockbox.
  • The authorized individual will install an individually keyed lock on the lockbox. His or her lock should be the first lock on the lockbox once the isolation keys are in the lockbox, and the last lock off of the lockbox when work has been completed. This will insure that the authorized person will be able to insure proper startup/re-energization of equipment.
  • A tag with the name of the person, and the date of the lockout will be affixed to the lockbox.
  • Each person applying a lock to the lockbox must sign and date the lockbox tag.
  • Personnel entering the site to perform work on the isolated equipment must apply their lock to the box and sign and date the lockbox tag.
  • As individuals complete their assigned tasks they may remove their locks from the lockbox.
  • When work is complete and equipment is ready to be returned to service, the authorized individual removes his or her lock from the box so that the restoration to service process may be performed.


Keyed padlocks should be used for locking out equipment and electrical devices. Each padlock should be keyed differently. Supervisors should retain spare keys for each padlock assigned to their work area.

Padlocks should be color-coded to identify the group which owns them. The following color code can be used for padlocks:

  • Yellow: Operations
  • Red: Electricians
  • Blue: Maintenance
  • Green: Instrument Technicians
  • White: Facilities Engineering

Depending on the facility (size and number of personnel), padlocks may be individually assigned or placed on a lock board for common use. A log should be maintained; it identifies who is using each padlock and where the padlock is being used.

Padlocks used for Lockout and Tagout should not be used for other purposes.


Further information to do with lockout/tagout is provided in the ebook Energy Control.

You are welcome to use this Safety Moment in your workplace. But please read Use of Safety Moments.

Copyright © Ian Sutton. 2020. All Rights Reserved.