IEC 61508: how to optimise functional safety of systems

The requirements for functional safety in industrial systems and processes are constantly increasing, due to the constant incorporation of new technologies in processing facilities. The IEC 61508 standard, developed by the IEC (International Electrotechnical Commission), provides the basis for organisations to develop their own safety protocols.

The globally valid standard focuses specifically on functional safety for electrical, electronic and programmable electronic -E/E/E/EP- systems. But what exactly is IEC 61508 and what is its scope of application? In the following, we shed light on the document and, above all, discuss how to implement it in a company’s functional safety plans.

WHAT IS IEC 61508?

IEC 61508 sets out recommendations for the design, implementation, application and maintenance of safety-related systems. It aims to establish a framework for managing the risks associated with industrial safety systems themselves.

In this sense, one of the most striking features of this standard is its application: it focuses not only on risk prevention, but also on reducing the impact of the consequences of hypothetical problems. In short, it is about ensuring that functional safety systems respond appropriately when necessary.


All the recommendations and proposals made in IEC 61508 are based on two fundamental principles, from which the standard itself is developed. On the one hand, the standard establishes different levels with regard to safety integrity; on the other hand, it refers to the engineering process known as the safety life cycle.

Safety integrity levels according to probability of failure

The standard is based on a probabilistic approach to measuring the impact that a failure could have on functional safety systems. To this end, it establishes different safety integrity levels, called SILs, ranging from 1 to 4 depending on the reduction of the probability of risk, from the lowest to the highest.

The security lifecycle as a method of analysis

The other pillar underpinning the standard is the safety lifecycle, an engineering process that seeks to implement continuous improvement in processes. To achieve this, the aim is to record any safety plan from design to implementation, step by step, and to develop detailed monitoring to identify potential errors and opportunities.


To fully understand IEC 61508, it is also necessary to know what functional process safety is, as this is the subject matter of the document. It is the discipline dedicated to ensuring the reliability of safety systems in industrial installations and processes involving hazardous chemicals.

Some of the main tasks of functional safety lie in the identification of risks, the establishment of protocols for adapting to changes, the training of employees and their awareness of the hazard, the proper maintenance of protection systems or the performance of periodic audits and evaluations, among others.


Like all IEC standards, this standard is divided into several parts that address specific issues within the functional safety of systems. Although an in-depth analysis of the document is not necessary, it is interesting to see how the IEC 61508 standard is structured and what the main focus of each of these parts is:

  1. The regulation begins by setting out the general requirements for the rest of the document and laying the fundamental foundations for functional safety, its management and assessment procedures. At the same time, it addresses aspects of documentation and compliance with standards.
  2. This section of IEC 61508 sets out instructions with regard to the design and production of hardware dedicated to functional safety. This provides the manufacturers of the physical elements of the systems with a guideline for the correct development of their products.
  3. Part three of the standard focuses on software and is therefore closely related to the previous point. IEC 61508 covers everything related to the design of software tools dedicated to functional safety and how they should be developed.
  4. This section is purely explanatory, as it covers the definitions of all technical concepts, terms and abbreviations that have been used throughout the document.
  5. This part of IEC 61508 provides various examples of assessment in determining the integrity level of functional safety. This makes it easier to understand the SIL system and its application in risk analysis.
  6. The penultimate point of the standard covers the necessary instructions for compliance and application of parts two and three of the standard, which focus on the functional safety of systems.
  7. Finally, it addresses the issues necessary for certification of manufacturers and developers under IEC 61508, in which case compliance is mandatory.


Functional safety of systems is a fundamental aspect in the entire industrial sector, but even more so in areas where chemical substances with specific hazards are involved. The IEC 61508 standard was developed precisely to guide organisations in preventing and mitigating risks in their facilities and processes.

In order to be able to apply the guidelines set out in the standard, it is necessary to have a thorough knowledge of the standard and some experience in the field. At Positive Engineering we have years of experience in safety engineering, which qualifies us for risk assessment in all types of industrial facilities.