Safety requirement specification phase output

Prior to carrying out SIL verification calculations for Safety Instrumented Functions (SIF) it is essential and very important that each function and its associated input and output signals be weU defined. The identification of the SIF is part of the analysis phase and the detail requirements for each function are documented in the Safety Requirements Specifications (SRS). 

For each phase, design documents of safety systems, based on SRP BTP-14, of the software development life cycle, include software plans, software requirement specification, software design output, source code listing, and test reports. These documents are subject to the IV V review. 

Verification Activity of demonstrating for each phase of the relevant safety life cycle by analysis and/or tests, for specific inputs, the outputs meet in all respects the objectives and requirements set for the specific phase. 

The computer system requirements define, as a minimum, the functional and non-functional properties of the computer system that are necessary and sufficient to meet the safety requirements for the plant that have been defined at a higher design level. The specification of computer system requirements is a representation of the necessary behaviour of the computer system. Precise defiiution of the interfaces to the operator, to the maintainer and to the external systems is an integral part of the product provided as the output of this phase. At this stage, the definition of interfaces is limited to the functional and non-functional properties of these interfaces then-design or implementation may be as yet undetermined. 

There are, however, many definitions of V V. In one of the most commonly used safety standards, lEC 61508, the objective of safety verification is ""...to demonstrate, for each phase of the overall, E/E/PE and software safety lifecycles (by review, analysis and/or tests), that the outputs meet in all respects the objectives and requirements specified for the phase [7]. The objective of safety validation is to. . validate that the E/E/PE safety-related systems meet the specification for the overall safety requirements in terms of the overall safety functions requirements and overall safety integrity requirements... [7]. These definitions differ in level of detail, but they can be summarized as verification is to answer the question are we building the system right While validation is to answer the question are we building the right system ... 

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