Functional Safety 2016

ABB Limited

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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

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

party.

If we continue with the scenario where the responsibility for delivery of the safety system is passed to

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.