Safe isolation of plant and equipment – Part 2: Key Stages

Introduction
In order to allow various processes such as: cleaning, maintenance, plant repair and modification to take place, safe isolation of plant and equipment is essential. This is not specifically covered by any health and safety legislation, although there are the usual, general legal drivers, such as: the Health and Safety at Work Etc Act 1974 (Section 2: duty to ensure the health, safety and welfare of employees, Section 3: duty to ensure the health and safety of non-employees), the Management of Health and Safety at Work Regulations 1999 (Regulation 3: duty to carry out risk assessments) as well as the Control of Substances Hazardous to Health Regulations 2002 (COSHH) and the Dangerous Substances and Explosive Atmospheres Regulations 2005 (DSEAR), etc.

Failures during the isolation and re-instatement of plant and equipment are a significant cause of loss of containment incidents and can lead to major accidents. There are eight key stages that should be considered in the isolation, and subsequent return to service, of plant and equipment:
• Hazard identification
• Risk assessment and selection of isolation scheme
• Planning and preparation of equipment
• Installation of isolation
• Draining, venting, purging and flushing
• Testing and monitoring effectiveness of the isolation
• Carrying out the intrusive activity
• Reinstatement of plant

Hazard Identification
Hazards may exist from either substances within the plant and equipment or from the nature of the work to be carried out. All (potential) hazards must be identified so that appropriate control measures can be introduced for the isolation of the plant and equipment. Particular hazards will exist if the substance is:
• toxic
• flammable
• pyrophoric
• under (high) pressure
• at high or low temperature
• reactive
• an asphyxiant (such as nitrogen)
• capable of forming an explosive atmosphere (including dusts)
• remaining in equipment as a sludge or hard deposit
In the event of a loss of containment leading to a release, the potential for a major accident will depend on a range of factors including
• the nature and properties of the substance
• the amount of the substance released
• the potential for escalation (such as: the presence of other plant, including confining structures, and other hazardous substances)
• the people at risk, their proximity to the plant and the speed with which they may be affected
Hazards associated with the task to be undertaken include:
• Entry into confined spaces
• Issues associated with access (such as working at height, etc.)
• Hot work (such as welding, cutting, grinding, drilling, electrical work, etc.)

Risk Assessment and the selection of isolation scheme for the plant and equipment
It should form a part of the company’s policies and procedures that intrusive work is not carried out on live plant and equipment unless there is no reasonably practicable alternative. A risk assessment should be carried out for the isolation process to identify the safest isolation scheme and should consider:
• all preparatory work for the isolation (such as depressurisation and release of stored energy, draining and venting, purging and washing out)
• installation/removal and proving of the isolation the integrity of the isolation during intrusive work, and the compatibility of any nearby work or operations on shared systems
• the requirements for testing and reinstatement of plant (such as: pressure leak testing, purging, controlled repressurisation and refilling
The risk assessment should also consider the potential for loss of containment and the potential harm (to people and to the environment) that may result from this.

Planning and preparation of equipment
As with many areas, planning is an essential stage in the isolation of plant and equipment. Appropriate preparation and planning:
• helps to identify any task-specific risk assessments that may be required
• identifies whether larger sections of the plant need to be shut down
• identifies interaction with other sections of plant subject to temporary isolation
• involves sequencing and co-ordination of any intrusive work with other plant operations
• includes a 'walk-the-plant' step, to check that the installation matches the piping and instrumentation diagrams (P&ID) and
• allows a check that all isolation points have been identified and are accessible and can be operated
• ensures preparation and co-ordination of job documentation, including:
o risk assessments
o method statements
o permit to work certificates
o isolation certificates
o etc
• ensures cross-referencing of relevant permits; and
• enables that all necessary and appropriate tools, equipment, PPE, materials, etc., are available

Installation of isolation
The process of installation of the necessary isolations can be considered in two parts: the initial isolation and the final (or full) isolation. The initial isolation (which is usually valved) is generally of a short duration. It allows the insertion of a positive isolation after the plant that is downstream of the initial isolation has been depressurised and purged. The final isolation protects the workers that are carrying out the intrusive work, and others who might be affected, such as from a release of substance from the plant during the intrusive activity.
Suitable blank flanges, plugs, etc (appropriately rated and installed properly, with the correct gaskets and securing bolts) should be used to close off any open pipe work. Appropriate engineering practices should be adhered when securing flanges, etc. Isolations must remain secure throughout the duration of work: locking arrangements or barriers, to prevent accidental or unauthorised removal of the isolation, should be used where practicable.

Draining, venting, purging and flushing
Draining, venting, purging and flushing may be required in situation where the plant or equipment contains hazardous substances, etc.

Testing and monitoring effectiveness of the isolation
In most cases, it is necessary to prove the integrity of all of the isolation points of an isolation scheme before proceeding with intrusive work, unless the risk assessment indicates otherwise.
• each part of the isolation should be proved separately
• each part should be proved to the highest pressure which can be expected within the system during the work activity
• where possible, each part of the isolation should be proved in the direction of the expected pressure differential

Carrying out the intrusive activity
It is important to ensure that the integrity of all isolations is maintained while the intrusive work is carried out.

Reinstatement of plant
Reinstatement or recommissioning of the plant requires equivalent controls to those used during installation of isolation. Where work has been controlled under multiple permits and dependent on common isolation points, it is important to define and control the sequence of plant reinstatement. This should include a review of all (cross-referenced) permits in force and their related isolations and checking that any plant control and protection systems functions that were overridden for the purposes of the isolations are restored to their normal condition. Care must be taken when removing positive isolations as, for example, hazardous substances may have built up behind the blank or spade if a valve leaks. Use appropriate documentation, such as isolation certificates, to log all disturbed items on a plant and to control their reinstatement.

Summary
Safe isolation of plant and equipment is an important part of the management of health and safety at work and, as such, should form part of the documented policies and procedures of the company (including the Health and Safety Policy). The key stages in the process of plant isolation (and re-instatement) must be planned and controlled. Risk assessments must be carried out to determine the range of control measures required and the order of work and the need for administrative controls, such as permit to work systems, etc. Plant and equipment should be isolated in accordance with a planned system, devised and controlled by a competent person (or persons). Isolations should be made and checked and should remain in place until removed in accordance with a planned schedule for the reinstatement or recommissioning of the plant.

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