The Design of Safety Instrumented Systems (SIS) for Functional Safety

In the industrial sector, particularly in areas such as chemical, nuclear, or petroleum, functional safety requirements are a determining factor. Considering the number of risks and their impact on facilities and, above all, employees, the so-called Safety Instrumented Systems (SIS) are fundamental.

Also known as SIS, they are essential throughout any industrial process in these sectors. In fact, they are one of the most relevant aspects of standards developed for this purpose, such as the IEC 61508 standard, among others. Therefore, it is advisable to delve deep into the design and implementation of Safety Instrumented Systems in this field.

What a Safety Instrumented System Entails

To understand the processes of designing and implementing Safety Instrumented Systems, it is crucial to begin with the concept of SIS itself. These are critical infrastructures designed for risk prevention and mitigation in industries with significant impacts, including the aforementioned ones, as well as mining, gas, and metallurgy.

These infrastructures consist of various elements and technologies carefully arranged to ensure safety within an organization’s facilities. They encompass structures that include sensors and various types of logic units to detect potential incidents and automatically address them.

Through these design, implementation, and maintenance processes, Safety Instrumented Systems make functional safety a reality. They can be seen as the visible part of a technical discipline aimed at primarily safeguarding people and the environment, which also faces considerable risks in these sectors.

Key Aspects in the Design of Safety Instrumented Systems

Design plays a pivotal role in Safety Instrumented Systems. During this phase, various factors must be taken into account, starting with the relevant regulations and the specific safety requirements of each facility. To ensure that an SIS provides the necessary guarantees, it must adhere to the following factors:

Compliance with Functional Safety Standards and Regulations

Over the past few decades, several functional safety standards have governed legislation in different countries. However, standards like IEC 61508 and IEC 61511, both developed by the International Electrotechnical Commission, have come to prevail globally, replacing local documents such as ANSI/ISA S84 in the United States, for example.

Compliance with these standards, which address functional safety in electrical, electronic, and programmable electronic systems (IEC 61508) and functional safety in industrial processes (IEC 61511), is essential in the design of Safety Instrumented Systems.

Understanding the Lifecycle of SIS in Functional Safety

Another fundamental concept in the design of Safety Instrumented Systems is their lifecycle, consisting of seven essential steps: specification, design, installation, validation, operation, maintenance, and decommissioning. These steps are detailed in the IEC 61511 standard and are of vital importance in functional safety.

Adaptation to Environmental Needs and Requirements

Lastly, the needs and requirements of each specific environment for functional safety cannot be overlooked. Each industrial sector presents its own set of hazards, and it is imperative to consider and adapt to them during the design of SIS. Simultaneously, it is crucial to understand potential obsolescence and continually update the systems to ensure their functionality.

Implementing Safety Instrumented Systems

When implementing an SIS, it is essential to follow a well-organized process that focuses solely on its installation in the appropriate location, considering that the design has already been completed. However, the integration of the system into facilities requires an equally significant process, consisting of the following steps:

  • Planning: This step is part of both the design and implementation processes of Safety Instrumented Systems. It involves not only the mechanisms themselves but also the environment in which they are installed.
  • Implementation: Implementation must take into account everything established throughout the design and planning processes. It is the definitive point at which the SIS starts functioning.
  • Monitoring: Monitoring and verifying Safety Instrumented Systems are integral to their integration. It is essential to check and ensure that the systems fulfill their intended purpose perfectly.
  • Action: Correcting potential errors or implementing improvements identified in the previous step is also part of the implementation of Safety Instrumented Systems.

Key Aspects in the Operation of Safety Instrumented Systems

Once the design of the Safety Instrumented System has been completed and it has been implemented in the correct location, it is essential to understand its operation in detail to identify potential errors and perform adequate maintenance. To achieve this, it is advisable to grasp the following key aspects:

Operation Mechanisms of an SIS

Above all else, the operation mechanisms of a Safety Instrumented System must be considered, as these elements are responsible for detecting, identifying, and addressing potential disturbances. This category includes various sensors, monitoring equipment, or logical controllers, among other devices.

Hazard Identification and Risk Assessment

Within functional safety, whether discussing the design and implementation of systems or referring to their operation, it is crucial to highlight the identification and analysis of potential risks. This is an essential aspect that employs specific techniques, such as process validation tests or Failure Modes and Effects Analysis (FMEA), for instance.

Positive Engineering: Engineering in Service of Safety

Recognizing the importance of design in Safety Instrumented Systems for the integrity of organizations and their employees in specific industrial sectors, Positive Engineering is dedicated to providing solutions tailored to the needs and requirements of each environment.