Clause 6 - Safety lifecycle requirements

The ISA84 committee created ANSI/ISA-84.01-1996 to supplement OSHA 1910.119 in the areas related to the implementation of instrumentation and controls necessary for safe operation. Rather than repeating OSHA 1910.119 mandates, the standard references OSHA 1910.119 for some key program elements. Specifically, ISA-84.00.01-1996 does not provide specific requirements for safety management, hazard and risk analysis, pre-start-up safety review, or training. ISA-84.00.01-2004 provides requirements for each of these areas. 

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The functional safety achieved in any process facility is dependent on a number of activities being carried out in a satisfactory manner. The purpose of adopting a systematic safety lifecycle approach towards a safety instrumented system is to ensure that all the activities necessary to achieve functional safety are carried out and that it can be demonstrated to others that they have been carried out in an appropriate order. lEC 61511-1 ANSI/ISA-84.00.01-2004 Parti (lEC 61511-1 Mod ) sets out a typical lifecycle in Figure 8 and Table 2. Requirements for each lifecycle phase are given in Clauses 8 through 16 of lEC 61511-1 ANSI/ISA-84.00.01-2004 Part 1 (lEC 61511-1 Mod). 

The standard recognizes that the specified activities might be structured in different ways, provided that all the requirements are complied with. This restructuring can be beneficial if it allows safety activities to be better integrated into normal project procedures. The purpose of Clause 6 of lEC 61511-1 ANSI/ISA-84.00.01-2004 Part 1 (lEC 61511-1 Mod) is to ensure that if a different safety lifecycle is used, the inputs and output of each phase of the lifecycle are defined and all essential requirements are incorporated. 

Safety lifecycle phase or activity Objectives ANSI/ISA-84.00.01 Requirements Clause ISA-84 Technical Report Reference... 

ANSI/ISA-84.01-1996 requires that the application software be developed in accordance with the Safety Requirements Specification (SRS). ANSI/ISA-84.00.01-2004-1 also requires this, but discusses the development of the application software with relation to the safety lifecycle. Where hardware is prone to random failures, the software is more prone to systematic failures. The safety lifecycle is important, because it is the primary mechanism for reducing systematic failure. The inclusion of the lifecycle discussion in the software section does result in repetition of the design process described in ANSI/ISA-84.00.01-2004-1 Clause 11. This repetition is intended to highlight the importance of the lifecycle in the development, verification and validation of application software. ISA-TR84.00.04-1 Annex O provides a discussion of the evolution of application software development. 

In order to deal in a systematic manner with all the activities necessary to achieve the required safety integrity for die E/E/PE safety-related systems, lEC 61508 adopts the Overall Safety Lifecycle indicated in Figure 3 (lEC 61508/Edition 2 shown) as the technical framework. The Overall Safety Lifecycle specified in lEC 61508 should be used as a basis for claiming conformance to the standard, but a different Overall Safety Lifecycle can be used to that given in Figure 3, providing the objectives and requirements of each clause of the standard are met. 

This clause specifies requirements for the management and technical activities during the overall, E/E/PEs, and software safety lifecycle phases. It is also to specify the responsibilities of the persons, departments, and organizations responsible for each overall, E/E/PE system and software safety lifecycle phase or for activities within each phase. Basic requirements/issues shall include but are not limited to those listed below. It is advisable to refer associated clause (6) of 61508-1 Latest revision (2010) to note the changes with respect to previous revisions. 

S.2.5 All modifications which have an impact on the functional safety of the E/E/PE safety-related system shall initiate a return to an appropriate phase of the software safety lifecycle. All subsequent phases shall then be carried out in accordance with the procedures specified for the specific phases in accordance with the requirements in this standard. Safety planning (see Clause 6) shall detail all subsequent activities. 

The second objective of this clause is to define the requirements for the safety management during the concept phase and the development phases, including the planning and coordination of the scfety activities, the progression of the safety lifecycle, the creation of the scfety case, and the execution of the confirmation measures. 

Safety lifecycle phase or activity Objectives Requirements Clause or Subclause of ISA-84.01-2004 Inputs Outputs Responsibility... 

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