SIS life cycle

The phases involved in SIS Life Cycle with their objectives, typical input and output are summarized in Table 3.10 (ANSI/ISA-84.00.01, 2004). Qualified and experienced SIL experts are essential to validate the results of SIS. 

SIS life cycle phase Objectives Input Output... 

CommerdalizatioD r Si Life Cycle Mauagemeot Phase Ub Phase III File... 

Safety instrumentation system (SIS) life cycle operation and maintenance (O M) phase details. SIF, safety instrument functions SIL, safety integrity level. 

Procedures need to be in place to manage, and document, the competence (both in the technical knowledge of the technologies and in functional safety) of all those involved in the SIS life cycle. 

This figure shows how the lEC and ISA safety life cycle models for safety instrumented systems correspond to the established process safety life cycle models for hazard studies. The point of departure for the SIS life cycle is ideally at the end of hazard study 3 when the safety requirement s specification has been finalized. 

Olsen SI, Christensen FM, Hauschild M et al (2001) Life cycle impact assessment and risk assessment of chemicals -a methodological comparison. Environ Impact Assess Rev 21 385 104... 

Belli SI (2000) Chromatin remodelling during life cycle of trypanosomatids. Int J Parasitol 30 679-687 Berger SL, Sterner DE (2000) Acetylation of histones and transcription-related factors, microbiology and molecular biology reviews, June 435 59... 

We now know that 20 elements are essential for plant growth not all of these are required by all plants, but all are essential to some. An element is essential if a plant cannot complete its life cycle without it. Carbon, O, and H are obtained by plants from air and water, the remaining 17 elements — N, P, K, Ca, Mg, S, Fe, Zn, Cu, Mn, B, Co, V, Cl, Na, Si, and Mo — are obtained primarily from the soil solution. All 17 elements are important, but man s influence relates primarily to those that are followed by an asterisk, since these are commonly applied to j cultural soils. Nitrogen, P, and K are termed major nutrients, since these are required by crop plants in large amounts and are the elements that most frequently limit... 

Safety instrumented systems (SIS) play a major part in industrial risk management as risk reduction measures. The main European standard for functional safety of SIS, denoted electrical / electronic / programmable electronic (E/E/PE) safety-related systems, is the EC 61508 (lEC, 2005a). The second edition will soon be adopted in 2009 (EC, 2009). Objectives are to enable the design of SIS, and the development of apphca-tion sector standards. Such examples are EC 61511 (lEC, 2004) for process industry, and EC 62061 (EC 2005b) for machinery. One of the main contributions of EC 61508 is to consider the overall system and software safety life cycle. The standard fi amework, with the corresponding normative parts and subclauses, is ... 

Figure 8 - SIS safety life-cycle phases and functional safety assessment stages...

Procedures for configuration management of the SIS during the SIS and software safety life-cycle phases shall be available in particular, the following should be specified ... 

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. 

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... 

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... 

Consequence spectmm, accidental event definition step-by-step procedure, probability frequency of outcomes for manual and automatic procedures for event tree analysis (ETA), fault tree analysis (FTA), and LOPA, QRA and HRA with focus on E/E/PE. Discussions on relevant standards like lEC 31010, 60812, 61025, 61508/61511, 61582, ISA 84. Life cycle (LC) analysis SIS standard. Also batch process ISA 88. 

As per ANSI/ISA 84 and lEC 61511, there shall be multi disciplinary approach which follows life cycle analysis PHA before implementing SIS. So, SIS implementation requires all above activities to be performed. However, fire and gas systems automatically initiate process action for mitigation and taking the system in to safe state to natural SIS. 

It specifies system architecture, hardware configuration, application software (user and integrator of SIS), and system integration, requirements for safety instmment functions (SIFs) including human factor, and safety life cycle. It also specifies the techniques and measures for SIL. 

Phase definition and establishment of requirements for safety life cycle activities is one of the major objectives which also includes planning and technical activities to ensure SIS meet the safety requirements. Major issues are listed in the Table VI/5.1.2-1 (see Fig. Vl/5.0-1 or Fig. 8 of standard). 

Let the discussions begin with Fig. VI/5.3-1, software safety cycle in process industries (courtesy of lEC). The figure consists of two parts, one is software safety cycle (Fig. V1/5.3-1A to compare with Fig. V1/4T.4-1B), and relation between software safety life cycle and SIS safety life cycle. Both Fig. V1/5.3-1A and B have been developed on the basis of Figs. 11 and 10 of lEC 61511, respectively. 

Basic objectives of application software safety requirements, as well as the relationship between SIS and application software safety life cycle, shall be discussed. Objectives have been enumerated in Table Vl/5.3.1-1 (see Table 7 of lEC 61511-1, courtesy of lEC). 

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.

Safety instrumented system (SIS) SIS is meant to prevent, control, or mitigate hazardous events and take the process to a safe state when predetermined conditions are violated. An SIS can be one or more SIFs, which is composed of a combination of sensors, logic solvers, and final elements. Other common terms for SISs are safety interlock systems, emergency shutdown (ESD) systems, and safety shutdown systems (SSDs). So, SIS is used as a protection layer between the hazards of the process and the public. SIS or SIF is extremely important when there is no other non-instrumented way of adequately eliminating or mitigating process risks. As per recommendations of standards lEC 61511 2003 (or ANSI/ ISA-84.00.01-2004), a multi-disciplinary team approach following the safety life cycle, conducts hazard analysis, develops layers of protections, and implements an SIS when hazardous events cannot be controlled, prevented, or mitigated adequately by non-instrumented means. 

Initially, lEC 61508 was developed as a safety and life cycle standard, which was not industry-specific. Later, there have been three separate divisions, viz. lEC 61511 for process industries, lEC 61513 for nuclear plants, and lEC 62061 for machinery sector. lEC 61511 has clearly put forward some guidelines for hardware to be used in SIS. In this standard, there are clearly two divisions, for example, PEs and non-PEs (in loose sense to distinguish from logic solver, because nowadays sensors and final elements also have programming features) like sensors and final control elements. In this part, sensors and final control elements are considered, while PEs will be discussed separately in next clause. 

Details about alarm system with life cycle have been discussed in Chapter IX under SIS components, keeping in mind various guidelines, for example, EEMUA 191 and standards like ISA 18.2 2009 and lEC 62682 2014. 

J.L. Bergstrom, Safety Instrumented Systems (SIS) and Safety Life Cycle, Process Engi-neering Associates, LLC, September 2009. 

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