During maintenance it is important to take every possible precaution to avoid loss or harm.

One important precaution is to isolate all the equipment being worked on from uncontrolled energy sources.

An uncontrolled release of energy can result in injuries, damage to the plant, damage to equipment and/or contamination of the environment.

The permit-to-work and isolations

The permit-to-work controls the safety-related aspects of maintenance.  A permit-to-work system ensures that adequate controls are in place, that correct protective personal equipment is used, people are trained and competent etc.  Controlling isolations is an integral part of this process.

Isolations are typically controlled in the field using a physical lock mechanism (such as a padlock), tags or signs indicating work in progress and physical barriers (such as a slip plate or removal of sections of pipe etc.).  The isolations are cross-referenced on the permit, as are details of the locks used and the key safes or lock boxes used. 

Preventing sources of energy from causing harm

When planning work and assessing job-related risk it is important to identify all hazards, including possible uncontrolled sources of energy. These might include live electrical systems, hydraulic or pneumatic power, pressurized vessels, hot (or cold) liquids, items that might fall by gravity; and so on.  As far as possible, these sources of energy need to be isolated “positively” – i.e. they need to be controlled using a physical barrier that cannot easily be interfered with while the job proceeds.

 

For example, in the case of an electrical supply system, the incoming power to the equipment is isolated using a switch.  This local switch is locked in the “off” position using a padlock.  In most situations, a double isolation is preferred.  An electrical circuit might therefore be isolated at the main control centre by “racking out” the switchgear, as well as separately isolated in the plant by a switch.  Teams working in the field can visibly see that the local switch is locked in the off position.

Complications are possible if shutting down power at the control centre also shuts down other unrelated items of electrical equipment.   Further complications can occur if during maintenance power needs to be temporarily restored to the equipment for reasons related to the maintenance procedure; for example, to test the repairs done before returning the section of plant into service.

Similarly, valves might need to be locked open or closed (depending on the scenario) with a lock placed on the valve handle to prevent accidental operation.   Where valves don’t exist or are inadequate (due to leaks), slip plates might need to be bolted in position between flanges that provide a proper physical barrier.

Generally, it is not acceptable to rely on electronic process control systems to isolate equipment.  All isolations should be “positive”, and checked, locked out, and later removed by the persons responsible for doing the work.   This principle of positive isolation is very important to ensure work takes place safely.  Connecting control system sensors, IIoT (industrial internet of things) devices and so on can act as an additional layer of protection and warning, but they can never replace the primary method of protection.

Every isolation should be clearly labelled with a lock-out “do not operate” tag.  See example above.  It is more efficient if these tags can be generated automatically by the permit system.  The information on the tag can indicate the relevant date/time, details of the work and responsible person, a tag/isolation number, the associated permit and the equipment detail.

Complex systems

Maintenance is often necessary on equipment that forms part of a complex, interconnected system.   The isolation points in these situations can be quite extensive and amount to dozens of individual lock-outs for a single job.  Each of these lock-outs (or isolation points) needs to be carefully considered in terms of the impact on the overall process.   Because the isolations introduce a new variable, it is also important to make sure that they do not in turn introduce any additional risk.

Owing to the possibility of human error, work on complex systems is usually planned carefully ahead of time and the isolations documented as part of a safe work procedure.   The resulting procedure can be reused whenever similar work is required on the same item.     Safe work and isolation procedures must be subject to careful change control and when used should only be applied in very specific situations, having duly considered the risks for the specific circumstances of each job.

 

Verification of isolations

Before work starts it is important that each isolation is verified in the field by a competent person.    These checks might involve inspection of the isolations and the work area, pressure tests, testing for the presence of high voltages, and so on.    The inspection and tagging process can sometimes be done together to streamline the process.   The field inspection needs to be done by someone familiar with the plant and equipment; and a single job may involve inspections by different engineering disciplines, e.g. electrical, mechanical and so on.

Multiple people and working parties

So far, the discussion has been about isolating an item of equipment with one or more physical isolation points.   In practice however, things can be more complicated.  Several individuals or independent teams/working parties may be involved in the maintenance job.    Each individual in the working party needs to be assured that they are protected from accidental removal of the isolation by someone else.

For this reason, it is normal for two or more people to add their “personal” padlock to the isolation point.   In order to restore the energy source, both locks then need to be removed.   In order to manage the keys and avoid the scenario where the plant cannot be re-commissioned if people are unavailable, the keys are often put in a lock box (or “key safe”).   The lock box itself is locked and controlled by a master key held by a third party, who then effectively controls that group of isolation locks related to the job.

Key safes and lock boxes

There are many variations on the lock box or key safe concept.  In some situations, instead of a single lock on the box, multiple locks can be added.  There are many varieties of such lock boxes and several vendors specialise in these.

Even more sophisticated variations of lock boxes and remote isolation management systems do exist.  For example, it is possible to implement a remote isolation system that can control multiple isolation points from a single automated control box.    Our team can provide more information on this if required.

Master / sub-permits

In certain scenarios a number of permits are required relating to the same job.  For example, the main job might require a specific electrical isolation to be installed in the MCC (motor control centre).  The installation of high voltage electrical isolations is a hazardous activity requiring special competencies, and therefore needs to be done under a separate work permit.   In this example there are two permits – a “master” permit and “sub-permit”, both are related to the same overall job.  The same concept might apply when removing isolation – while the master permit still controls the main job, another sub-permit is issued to remove the electrical isolation in the MCC.

Another scenario might be to temporarily suspend the master permit to allow testing of equipment.  The testing is done under a sub-permit which allows for certain isolations to be temporarily removed.   After successful testing the master permit is then reinstated and controls the remaining work to completion.

A full description of master-sub-permits is beyond the scope of this article.  Managing master and sub-permits is best done using a computer-based system that automatically keeps track of the status of all the jobs and their isolations, and the interactions between these.

How IntelliPERMIT supports isolation management

Managing isolations, especially in complex scenarios is greatly enhanced using a computer-based system that forms part of the work permit management system.

IntelliPERMIT incorporates a number of features that support isolations.  The system is designed to simplify the process as far as possible, without interfering with the existing safety protocols used on site.

1. Preconfigured isolation lists

IntelliPERMIT can store pre-configured isolation lists needed for work on complex systems.  These lists are pre-approved, and changes are strictly controlled according to the company’s procedures.

2. Isolation Procedures

Specific procedures for isolating equipment or systems can be pre-configured.  These procedures can be linked to the equipment being worked on; the type of equipment (e.g. electrical pump motors < 5kW);   and/or the activity (e.g. lubrication service, remove/replace etc).

3. Incorporating isolation procedures into permit issue process

When preparing a permit, the relevant isolation procedures and related rules are prompted ensuring that the permit issuer is aware of the mandatory isolation procedures that apply.

4. Printing of lock-out tags

During the preparation of the permit, the system can print out lock-out tags that incorporate the required information.  Special printers are used to print onto industrial grade weatherproof paper that is suited for use in the field.

5. Verification of isolations

IntelliPERMIT allows isolations to be verified in the field using a mobile device.  The competence of the person verifying the specific isolation can be enforced in the system as well.

6. Lock box management

IntelliPERMIT helps manage lock boxes and key safes.  The system can determine and manage the relationship between the master permit and dependent (sub) permits and make sure that the locks are managed accordingly.

7. Cross-referencing

IntelliPERMIT allows permits to be cross-referenced to each other – for example master/sub-permit relationships, permit templates and permits in adjacent plant areas or related work.   This ensures that when removing isolations all relevant dependencies on related work can be proactively considered.

Conclusion

Isolations are a necessary aspect of safe work.  Managing isolations can be a complicated process, with many variables to consider, for example managing multiple isolation points on a single item of equipment and managing the isolations for multiple people involved in several maintenance jobs in a common plant area.  Cross-referencing is very important in this scenario.

By adopting the principle of always using positive isolation you will ensure that people are assured to work under safe conditions.  Positive isolations are best managed using a system of locks and keys that are controlled in lock-boxes and cross-referenced using the permit to work.  A number of automated systems are available for special circumstances.    A computer-based system like IntelliPERMIT can streamline the management of isolations, improving the integrity of the overall process whilst managing the complexity.  The goal as always is to enhance safe work.

If you have any questions or suggestions to improve this article, please contact the IntelliPERMIT team at Adapt IT.