SIS safety requirements specification

The objective of this ciause is to specify the requirements for the safety instrumented function(s). 

The development of the SIS safety requirements specification is one of the more important activities of the whole safety lifecycle. It is through this specification that the user is able to define how he wants the Safety Instrumented Functions (SIF) to be designed and integrated into a SIS. 

Final validation of the SIS is carried out using this specification. 

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The outcome of the hazard and risk assessment and allocation process should be a clear description of the functions to be carried out by the safety systems, including potential safety instrumented systems together with safety integrity level requirements (along with mode of operation, continuous or demand) for any safety instrumented function. This forms the basis for the SIS safety requirements specification. The description of the functions should be clear as to what needs to be done to ensure that safety is maintained. 

The SIS safety requirements specification may be a single document or a collection of several documents including procedures, drawings or corporate standard practices. These requirements may be developed by the Hazard and Risk Assessment team and/or the project team itself. 

SIS safety requirements specification To specify the requirements for each SIS, in terms of the required safety instrumented functions and their associated safety integrity, in order to achieve the required functional safety 10 Description of allocation of safety requirements (see clause 9) SIS safety requirements software safety requirements... 

The design of the SiS shaii be in accordance with the SiS safety requirements specifications, taking into account aii the requirements of this ciause. 

Application software safety requirements specification To specify the requirements for the software safety instrumented functions for each SIS function necessary to implement the required safety instrumented functions 12.2.2 SIS safety requirements specification Safety manuals of the selected SIS SIS application software safety requirements specification Verification information... 

SIS safety requirement specification To specify requirements to each SIS in term of required SIF with associated safety integrity to achieve functional fety. 10... 

Clause 10 SIS safety requirement specification According to the standard, here the requirements for SIF shall be specified in required details. 

SIS SAFETY REQUIREMENTS SPECIFICATION, SRS, (lEC 61511 CLAUSE 10) Requirements for SIS safety requirement specification... 

In accordance with lEC 61508/61511, the overall required safety management and proper technical activities relates with all documentation for SIS are summarized in safety life cycle. The purpose of analysis phase is to identify hazards and assess safety requirements of SIS. Safety Requirements Specification (SRS) of SIS should contain critical information which includes functional description... 

The SIS safety requirements specification should be developed in association with the non-SIS protection layers. The lEC 61508 standard calls for the overall safety requirement to be defined first in phase 4 followed by an allocation phase 5, which defines the sharing of protection duties across the layers of protection. The final SRS for the safety-instrumented system is then part of the detail design activities for the SIS known in lEC terms as the realization phase (phase 9). This procedure can be rather confusing at first but it appears to be designed to ensure that the basics of the SRS are in place and verified before the design team goes too far with the technical specifications for the SIS. 

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