Basic Fundamentals of Safety Instrumented Systems

The Instrumented Safety Systems (SIS) are used to monitor the values and parameters of a factory within the limits of operation, and under risk, conditions must generate alarms and put the plant in safe conditions or also in emergency stops.

The safety conditions must always be followed and adopted in plants and the best operating and installation practices and are the responsibility of both employers and employees. Keep in mind that the first concept of safety regulations is to ensure that all systems are installed and managed safely, and the second is that instruments and alarms involved in safety operate with reliability and efficiency.

The Safety Instrumented Systems are responsible for operational safety and guarantee emergency stops within limits considered safe, provided that these limits are exceeded. The primary objective is to avoid accidents inside & outside the factories, such as fires, explosions, damage to equipment, as well as protecting production and property, avoiding life risks or damage to people’s health and catastrophic impacts to the community. Keep in mind that no system is immune to faults and must always provide a safe condition in case of mechanical failure.

For many years, the safety systems are designed as per the German standards DIN V VDE 0801 & DIN V 19250 that were accepted by the global safety community for a long time & culminated in the efforts to reach an international standard, the IEC 61508. This standard currently covers all aspects of industrial safety involving electrical systems, electronics and programmable devices for any sector of activity, notably those of an electromechanical nature. 

Products certified according to IEC 61508 must deal with three types of failures:

  • Hardware random failures
  • System failures
  • Common cause failures

Safety Instrumented Systems design Tips for the Instrumentation & Control Engineers

Modern chemical & hydrocarbon plants, oil & gas production, power plants and other similar process plants all have the instrumentation & automation that can ensure safety. Perhaps that’s the reason why these are known as Safety Instrumented Systems (SIS). 

There are other names as well that are used for these like Emergency Shutdown Systems (ESD), High Integrity Pressure Protection Systems (HIPPS) and Safety Shutdown Systems etc. But all these belong to the class of systems that are referred to as SIS. Concerning Designing a Safety Instrumented System, we aren’t talking about designing the next breakthrough in a great logic solver. 

We’re addressing the situation in which many Instrumentation along with the Control engineers find themselves in when they are supposed to design the SIS for a plant. Precisely, this complete process involves finding out what kind of systems & devices should be used in the application that the client or user requires.

Practically, there’re many different applications & specifications of equipment with SIL certification to use in control systems, without safety function. Besides, it is believed that the market is uninformed, where the purchase of more expensive equipment is needed, developed for security functions. But they’ll be applied in process control functions, whose SIL certification doesn’t lead to the expected benefits, which hinder the use and operation of equipment.

Besides, misinformation leads users to believe that they have a certified safe control system, which is no more than a control device with certified safety functions. The growth of the use and applications of digital equipment & instruments is of utmost significance to the professionals of projects or perhaps of the day-to-day of the instrumentation that’s trained and acquire the knowledge of how to determine the performance demanded by the security systems and have mastery of calculation tools & risk rates located within acceptable limits.

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