ABB Limited
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United Kingdom
To ensure this is acheived the person accountable for the resultant SIS must be involved throughout
the delivery. If different phases of the lifecycle are to be performed by various 3
rd
parties, then the
accountable SIS person must be involved in key stages of the project delivery and not wait until after
the safety system is delivered and installed. The accountable SIS person should be present during the
Stage 1-3 Functional Safety Assessments (FSA), as well as reviewing the key documentation such as
the SRS, and not leave such activities solely to representatives of the 3
rd
party.
If we continue with the scenario where the responsibility for delivery of the safety system is passed to
3
rd
party engineering companies, then the accountable end user organisation must ensure the
expectations for FSA and other delivery considerations must be clearly defined within the tender
documentation, so that sufficient costs can be included to enable these requirements to be met. Setting
clear objectives for the SIS up front, which go beyond meeting the necessary risk reduction, enables a
collaborative approach to be adopted, and ensuring sufficient resources can be made available to
achieve this non silo way of working. Some examples of the considerations which should be included
in tender documentation include:-
·
how each phase of the lifecycle is to be documented and handed over to the end user
organization
·
requirements for applications / procedures to enable the SIS to be effectively operated and
maintained
·
proof test intervals which are required to coincide with specific activities such as Turn-
arounds (TARs)
·
use and implementation of partial testing and diagnostics, including alarm requirements
·
target spurious trip rates
·
who is the responsble for defining bypass requirement and temporary compensating measure
Functional Safety is part of the overall process safety performance, therefore both functional safety
engineers and process safety engineers need to take equal accountability in the delivered SIS in terms
of achieving the necessary functional safety through a operational and maintainable safety system.
Simplification
The techniques used during the functional safety lifecycle are often complex to ensure a suitable and
sufficient risk assessment is carried out. An example is a HAZOP, which is a methodology that is
often used for hazard identification. The technique was developed to provide multiple opportunities to
identify each hazardous event through the use of the various guidewords. The output from the HAZOP
is not concerned whether the overflow of vessel was identified through ‘flow - more’ or ‘level – high’,
it is just concerned that the hazardous event was identified. This results in multiple rows, in various
entries in the HAZOP records that refer to different causes of the same event. The next lifecycle phase
then requires each of these entries to be collated against each individual hazardous events to enable
SIL determination activities such as Layer of Protection Analysis (LOPA) to be performed. This can
be a time consuming exercise and if not performed correctly can result in duplication of effort.
Furthermore the output from a LOPA and HAZOP is not for the review teams, but for the people that
need that information to determine criticality, understand the top site hazards and in operations have
the necessary information available to aid decision support. The format of the reports produced from
the above studies typically do not support these activities.