Safety life-cycle requirements

1 A safety life-cycle incorporating the requirements of this standard shall be defined during safety planning. 

2 Each phase of the safety life cycle shall be defined in terms of its inputs, outputs and verification activities (see Table 2). 

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Safety life-cycle phase or activity Objectives Require- ments Inputs Outputs 

1 Hazard and risk assessment To determine the hazards and hazardous events of the process and associated equipment, the sequence of events leading to the hazardous event, the process risks associated with the hazardous event, the requirements for risk reduction and the safety functions required to achieve the necessary risk reduction 8 Process design, layout, manning arrangements, safety targets A description of the hazards, of the required safety function(s) and of the associated risk reduction 

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Application software safety life-cycle requirements... 

Defined software safety life cycle - required activities defined to develop application software for each programmed SIS subsystem (sensor, logic solver, and final elements) -12.1.1.1... 

Safety life cycle requirements structure and planning SP ALL... 

Fig. Vll/1.0.1-1 shows various methods of risk reduction in a common figure to include all risk reduction methods. Here, SIS is of main concern to us, so it is shown separately (in dark box). SISs are one of the most commonly used, engineered safeguard systems offering good flexibility to the designers. On account of safety life cycle requirements of lEC 61508/61511, and for better SIS design, experts need to analyze the risk associated with process under control at the beginning. SISs are risk-based systems. When in the subject, it is better to address the first barrier, then to SIFs. Barrier functions are planned for prevention, regulation, and mitigation of undesired events. In safety barriers, such barrier functions are used to combat undesired events. A safety function could be a technical or organizational function, human action, or a combination of them, used to reduce risks. Therefore, safety functions are a type of barrier.

Overall Safety Life Cycle Requirement Issue... 

SAFETY LIFE CYCLE REQUIREMENTS (lEC 61511 CLAUSE 6) Requirements for safety life cyde requirements... 

The criteria 1 to 8 may be reduced, especially those requiring full application of lEC 60880. Quality assurance shall divide the development and the modification phases of the software safety life cycle into specified activities. These activities shall include all what is necessary to achieve the required software quality, to verify that this quality is achieved, and to provide objective evidence to that effect. ... 

The skills and knowledge required to implement any of the activities of the safety life cycle relating to the safety instrumented systems should be identified and for each skill, the required competency levels should be defined. Resources should be assessed against each skill for competency and also the number of people per skill required. When differences are identified, development plans should be established to enable the required competency levels to be achieved in a timely manner. When shortages of skills arise, suitably qualified and experienced personnel may be recruited or contracted. 

The standards [l]-[3] concern the entire life cycle of a plant ( safety life cycle ), i.e. all activities required for realizing safety functions during a period which begins with the concept phase of a project and ends when aU safety functions are no longer available for use. In addition to quantitative requirements the standards contain numerous qualitative requirements, which are not discussed here. However, it must be borne in mind that fulfilling the qualitative requirements does not automatically lead to the quantitative requirements being fidfilled. 

A specification containing all the requirements of the safety functions that have to be performed by the safety-related system. It includes both what the functions must do and also how well they must do it. It is often a contractual document between companies and is one of the most important documents in the safety life cycle process. Safety Rule... 

Safety planning shall take place to define the activities that are required to be carried out along with the persons, department, organization or other units responsible to carry out these activities. This planning shall be updated as necessary throughout the entire safety life cycle (see Clause 6). 

The objective of this clause is to demonstrate by review, analysis and/or testing that the required outputs satisfy the defined requirements for the appropriate phases (Figure 8) of the safety life cycle identified by the verification planning. 

Verification planning shall define all activities required for the appropriate phase (Figure 8) of the safety life cycle. It shall conform to this standard by providing the following ... 

A safety life cycle for the development of application software which satisfies the requirements of this clause shall be specified during safety planning and integrated with the SIS safety life cycle. 

NOTE 1 Provided that the application software safety life cycle satisfies the requirements of Table 7, it Is acceptable to tailor the depth, number and size of the phases of the V-model (see Figure 12) to take account of the safety integrity and the complexity of the project. 

If at any stage of the application software safety life cycle, a change is required pertaining to an earlier life-cycle phase, then that earlier safety life-cycle phase and the following phases shall be re-examined and, if changes are required, repeated and re-verified. 

Safety life-cycle phase Require- ments clause ... 

Application software design, and development. Support tools and programming languages To identify a suitable set of configuration, library, management, and simulation and test tools, over the whole safety life cycle of the software (utility software) 12.4.4 SIS application software safety requirements specification Description of the architecture design Manuals of the SIS List of procedures for use of utility software Verification information... 

Integration tests shall be specified as early in the software safety life cycle as possible to ensure the compatibility of the application software with the hardware and embedded software platform such that the functional and performance safety requirements can be met. 

The second objective of this clause is to demonstrate that the output results satisfy the defined requirements at each phase of the application software safety life cycle. 

Clause 6 - Define safety life-cycle phases, incorporating standard requirements including technical activity inputs, outputs, and verification steps required to meet the safety requirements. L R/A P P P ... 

Define phases establish requirements for safety life-cycle activities -6.1... 

If one does not exist, develop a safety life cycle, incorporating standard requirements - 6.2.1 Define inputs, outputs and verification activities for each phase - 6.2.2... 

Impact analysis on functional safety as a result of decommissioning required. The assessment includes an update of the hazard and risk assessment to adequately determine any safety life-cycle steps that need to be taken. The assessment also considers -18.2.3... 

Systematic failure normally occurs on account of design failure, including incorrect specifications, using a component not fit for the operation, and or due to error in software. Safety life cycle is adapted for systematic faults. So safety standards meant for E/E/PEs take care of both. SISs (Ref. Chapter VII) are developed to prevent or mitigate hazardous events to protect people or the environment, or prevent damage to process equipment. In this connection another important issue is SIL (Chapter VIII), which is a discrete level for specifying the safety integrity requirements of safety functions, but is not a measure of risk. SIL provides means for risk reduction to a tolerable level. The fundamental question, in case of functionally safe instrumentation, is how frequently failures of function will lead to accidents. The answers can be ... 

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