The safe isolation of plant and equipment (HSG253) - Health and ...

Health and Safety
Executive
for retrofit actions:
■ that the wider implications of any proposed change are fully assessed prior to
implementation;
■ that an improvement system/plan, with a reasonable timescale, drives plant
retrofit;
■ that there is a phased/prioritised programme of modification; and
■ how often an isolation is done at the lesser security before being remedied.
Planning and preparation of equipment
142 Adequate planning:
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enables task-specific risk assessments to be made and actioned;
identifies whether a larger section of the plant might need to be shut down or
the work deferred;
identifies interaction with other sections of plant subject to temporary isolation;
involves sequencing and co-ordination of intrusive work with other plant
operations;
includes a ‘walk-the-plant’ step, to check that the installation matches the P&ID
and, especially, that all isolation points have been identified and are accessible/
can be operated, etc;
ensures preparation and co-ordination of job documentation such as risk
assessments, method statements, permits and isolation certificates, for
example by the assembly of work ‘packs’;
ensures cross-referencing of relevant permits; and
enables all necessary tools, equipment, materials, etc (including any additional
personal protective equipment required for those installing and removing
positive isolations) to be available at the worksite at the start of the job.
An example
During replacement of a heat exchanger, a vent line linking the system to a
second reactor was not identified during risk assessment or during installation of
the isolations. No reference had been made to P&IDs, even although the plant
was congested and spread over several floors. Because of the failure to isolate
the vent line, a substantial release of hydrogen bromide gas occurred when the
line was opened.
P&IDs should be used to plan isolations. Always check that they reflect the asinstalled
equipment. You should also walk the system to be isolated to ensure
that there are no unauthorised modifications, or temporary interconnections eg
by hoses.
143 Where operation of other parts of the plant can affect the integrity of an isolation,
you should prevent operation of relevant systems as part of the isolation procedure.
The effect of such inhibition of plant operation should be clearly understood and
communicated to all parties operating the plant before the isolation is installed.
144 Company standards should set out your arrangements for assessing,
authorising and controlling overrides to safety-related systems (eg emergency
shutdown systems) during isolation activities. Any such overrides, and any
additional safety measures required while these systems are shut down, should be
justified by risk assessment. You should not disable fire and gas detection systems
and emergency shutdown systems simply to prevent spurious shutdowns. This
could have wider implications. Inhibition may be appropriate, for example, where
the operation of a fire-fighting system (eg use of carbon dioxide or inert gas in a
confined space) during isolation/intrusive activity would put workers at risk.
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