Isolations and the permit to work
Isolating energy sources
Safe work requires careful planning and meticulous preparation. Before any job can take place, it is necessary to first properly isolate the equipment being worked on from energy sources. As part of the preparations, all potential sources of energy (hazards) must first be identified. Isolations are then put in place. These isolations might involve switching off the electrical supply, depressurising the equipment, removing any sources of hot/cold, and securing any equipment from movement e.g. rolling/falling. In addition, any process lines that contain hazardous fluids or gases must be properly shut off, disconnected and purged of hazardous chemicals.
Article by Gavin Halse & Henry Boshoff
On a typical plant, there are several hazards with multiple dependencies and interactions. In most complex situations, isolation procedures will usually be developed ahead of time. These procedures are intended to ensure that specific areas of plant or equipment are safe to work on. The isolation procedures are thoroughly checked before they are authorised for use in a production environment. Any subsequent changes to plant or equipment, process conditions, or operating procedures will likely introduce additional risk, and require updating of the relevant isolation procedure. A strict change control procedure is necessary to ensure this takes place reliably.
Not all jobs will require an isolation procedure. The specific isolation required will depend on the level of risk:
- In the case of a low-pressure water system (for example, working on a hot water tank), it might only be necessary to shut off and lock the valves to prevent any water flowing into or out of the equipment. Any power source will also probably be shut off.
- On the other hand, in the case of high-pressure explosive gas it might be necessary to “positively isolate” the equipment. This is usually achieved by closing and opening a sequence of valves, purging the line to release any pressure, physically breaking the line, and inserting one or more blank flanges. The equipment will then need to be safely purged of any residual gas. All of this takes time and will require additional people and resources, in turn introducing complexity and risk.
To prevent over-engineering the isolation procedure and adding unnecessary risk it is important that the initial risk assessment is properly done. The specific isolation (precaution) used must always be commensurate with the actual risk.
The permit to work and isolation management
The permit to work controls all work on the plant to ensure that it takes place as safely as possible. As part of the permit to work procedure, all safety precautions need to be identified and put in place. Specific hazards are identified, and the relevant isolation procedure implemented where necessary.
Where there is no pre-determined isolation procedure, the permit coordinator, issuer, and isolation officers are responsible for a thorough risk assessment and identifying all the necessary individual isolations in consultation with the process operators and other disciplines as necessary.
It is important that the management of isolations is a disciplined and controlled process, and that adequate time and care are taken to ensure that the equipment is made safe. Therefore, isolating equipment is often controlled by a separate special permit to work. This ensures that the proper precautions are taken, even when isolating equipment ahead of the main job.
It is also important to verify every isolation before work commences. Verification can involve physical inspection, pressure testing, testing for electrical voltages or currents, gas tests, and so on.
Isolations themselves introduce new risks
As with any complex procedure, there are a number of things that can go wrong and which could introduce additional risk. For example:
- The incorrect isolation procedure might be applied, exposing employees to a dangerous situation.
- Any specific isolation point might be wrongly identified through incorrect labelling or human error.
- The isolation procedure itself might be very complex increasing the chance of mistakes, especially if implemented under the time pressure typical in production environments.
- The verification and testing of the isolation points might be flawed.
- A significant source of energy might be overlooked (for example a vessel might still be under pressure even after it is isolated).
Every possible measure should therefore be taken to cross-check that the isolation procedure is robust and of the highest possible integrity and that all possible sources of energy are identified. Once people start working it could be too late.
Testing of equipment before handover
At the end of the job, it is sometimes necessary to remove isolations in order to briefly test the equipment before returning the plant to normal operation. This could involve temporarily energising a motor, or other pieces of equipment, opening a valve or removing a slip plate, or any combination thereof.
It is critical that during the testing cycle people continue to be protected from all energy sources. The permit to work procedure should allow for this testing process and ensure that any removal of isolations during, or at the end of a job is properly controlled.
Lock-out and Tag-out of isolation points
Isolation points are usually “locked out” using a physical lock and key system and “tagged” with a printed label containing a summary with the relevant permit information and the job being done. A physical lock will prevent a valve being opened, or switchgear being changed over, for example.
Depending on the procedure, each employee or discipline (e.g. electrical or mechanical) that is working on the equipment might also have to install their own personal lock. Keys originating from the use of multiple locks can be controlled using a “key safe”, lockbox or similar device.
These lockout systems, providing they are kept simple, can be very effective in ensuring that every person involved remains protected throughout the job. Implementing multiple locks per isolation point also has the advantage of ensuring that every employee concerned must first remove their own lock before the equipment can be re-energised.
A badly designed lock-out system is characterized by missing keys and a large bolt cutter. If this is the case, then urgent attention is likely required in order to improve the isolation procedure.
Electronic systems for managing isolations
Management of isolations and the lock-out/tag-out system is an integral part of safety. Electronic systems, when properly implemented can greatly help to ensure the integrity of the isolations themselves as well as streamline the process.
Electronic isolation systems can allow for additional verification, for example by scanning bar/QR codes in the field, collecting evidence of each isolation using a mobile device. They can also help manage the complex relationships between physical lock-out and personal locks/keys held by employees working in the plant.
IntelliPERMIT is designed to help manage the permit to work process for hazardous jobs on the plant. IntelliPERMIT includes a comprehensive and integrated system for managing isolations and lock-out/tag-out. The system is highly flexible allowing your unique plant-specific workflow to be easily accommodated, while also leveraging your existing investment in safe design and procedures. For more information on how IntelliPERMIT can help you better manage your plant isolations please contact the team at Adapt IT.
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