The Safety Life Cycle (SLC), is an engineering process designed to optimize the design of safety systems and to increase the security of the system as a whole. The main purpose of the SLC is to minimize the likelihood of introducing faults and / or systematic errors in the system, in order to preserve safety integrity.
This category of errors and / or failures can be caused by several reasons, for example, due to human errors of specification, design, construction, installation and commissioning; or due to failure or partial implementation of the requirements; or due to processes and procedures performed in incomplete manner; or even due to deficient use of methodologies and techniques required for the execution of the various activities.

HINTSW - T & T Systems is able to provide the support necessary to plan and to perform all specialist activities of "Safety Assessment" and "Safety Engineering" expected for each phase of the Safety Life Cycle, using the methods and the most appropriate techniques as required by the applicable standards.

The activities to be carried out during the Safety Life Cycle are formally defined and are usually grouped in phases; the formal definition of the activity consists in the definition of the objectives and the information in the input and output of each single asset. Although the phases and activities are  for the Safety of Life Cycle are related  to the area of application and of the type of system, a number of safety activities are provided by all the standards as they are considered essential parts. The main activities of the safety assessment, the safety management and safety engineering, usually requested by all the standards in the field of functional safety, are as follows:

  • Planning security (writing of the Security Plan);
  • Safety analysis and / or analysis RAMS;
  • Continous management of  risks (Writing and management dell'Hazard Log);
  • Specification and allocation of safety requirements (hardware and software);
  • Planning and implementation of all the validation and verification activities (V & V process);
  • Writing and management of the Safety Case;
  • Planning of maintenance and modification (maintenance and modification process);
  • Activities of safety engineering such as the definition of fault-tolerant architectures; the calculation of the probability of failure and  of the SIL verification of devices, control loops and systems used in safety functions; the definition and implementation of the self-tests, and so on.

For the execution of all the activities listed above HINTSW - T & T Systems is able to provide a qualified support and economically competitive.

Detailed information

The Safety Life Cycle, so, as defined in the standards, is a closed-loop process, ie it is a process that never ends until the decommissioning of the system, and whose activities are continuously performed as long as the system is in operation and, especially, whenever the system is subjected to changes or is updated.
The generic Safety Life Cycle can be divided into three main areas:
  • analysis: the first area is related to the analysis of the system and is focused on the identification of hazards and hazardous events, on the likelihood that these events are produced (probability of occurrence), on their potential consequences, and on the availability of possible countermeasures and measures mitigation
  • realization: the second area relates to the realization of the system and is focused on the design and construction of the system;
  • operation: the third area is the use of the system and includes startup, normal operation, maintenance, modification, and the eventual disposal and dismantling of the system.


Safety Life Cycle, a closed loop process

The overall safety life cycle  to which HINTSW - T & T Systems usually refers is the life cycle defined in IEC 61508. Some industry standards (eg .: CEI EN 50126 and IEC 61511) propose custom life cycles, but they are derived from the one specified by  IEC 61508, also, some of them are limited to consider the development life cycle (for example  CEI EN 62061 for the machinery), but also in this case are almost always derived from the safety life cycles  proposed by IEC 61508, which thus constitute a reliable reference point.

The overall safety life cycle proposed by IEC 61508, synthetically represented in the following figure, covers the entire life of the system and is characterized by the 16 steps indicated in the figure. For each phase, the standard prescribes the activities and the steps that must be performed, sets the information necessary to perform each step and the documentation which must be produced, finally, it indicates the methodologies and techniques that must be used.


The safety life cycle proposed by IEC 61508

The Safety Life Cycle proposed by IEC 61511 for the process industry is synthetically illustrated in the following figure; this standard, in fact, uses  IEC 61508  as a "model" and it guides its application for this sector.


Safety Life Cycle according to IEC 61511 (process industry)

The railway sector instead refers to the international standard IEC 50126 that defines a life cycle - defined as Life Cycle RAMS - wider than the usual SLC; in fact, in addition to the safety aspects, also considers aspects relating to reliability, availability and maintainability of the rail system. The Life Cycle RAMS proposed by CEI EN 50126 is shown in the figure below.


RAMS Life Cycle according to CEI EN 50126 (railway sector)

Usually the standards for the functional safety (IEC 61508, IEC 50126-50128, IEC 61511), in addition to the overall safety lifecycle, define a safety lifecycle for development of the system and one for software development. In these cases the life cycle begins with the planning of the design and ends with the system validation. Even in this case, the life cycle can be represented as a cyclic process that must be retraced whenever changes are made. The cycle can be retraced partially or wholly depending on the consistency of the modifications and based on the results of the impact analysis.


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