AIM Of SIL level Safety

  • Protection of Human Life
  • Protection of Environment
  • Protection of Assets



Safety is not discussed in literature, in fact it is not taught in the education institutes nor training can master you in Safety. We are in industrial 4.0 revolution, our industries are surrounded by extensive automation and complex integration. Modern plants are interconnected to produce more in less time by using fastest process control systems due to which its important to ensure the reliable and safe operation of plant along with maximum availability.

In Industry, Process and Machine safety are often achieved by the use of Safety Instrumented System to provide control function for processes; this would include functions such as ESD, PSS, FGS, explosion mitigation, dangerous level detection and HIPPS controls. The SIS is typically composed of sensor (detectors), analyzers (PLC) and control elements (actuation).  The integrity of each of these elements are collated to produce overall system Safety Integrity Level (SIL).

SIL, a numerical representation of reliability of SIS is determined by different techniques such as Fault Tree Analysis (FTA), HAZOP Analysis, Layer of Protection Analysis (LOPA) and Safety Layer Matrix (SLM). All these techniques have in common; the RISK identification, frequency of the event, the likelihood of detecting or avoiding the event and the consequences of the event in term of cost. The SIL level determined the appropriate level of risk reduction that required by the organization to run their process safely. For example, If SIL 2 is determined, it means SIL 2 is the minimum integrity level that can reduce the risk (that is, the cost per unit of time) associated with a particular hazard to an acceptable level.

There are 4 SIL levels according to IEC 61508 to determine the performance of safety instrument system:

  • SIL 1
  • SIL 2
  • SIL 3 and
  • SIL 4

* Higher is the SIL level, lower is the probability of dangerous failure on demand.


SIL Capable vs SIL Approved

Now a days, the Safety equipment manufacturers are using the term Safety Integrity Level (SIL) in different ways. It is difficult for Industrial user to understand the meaning of the words “SIL capable, SIL approved or SIL certified devices”. It is very important for Industrial user to understand that a SIL capable certification does not mean that the safety device is performance approved up-to claimed SIL level.

Claiming a certain SIL capability level means the device may be used in a safety-system design at that capability level or below. For instance, a certified SIL 3 device may be used in a Safety Instrumented Function (SIF) with full SIL3 or SIL2 risk reduction. The term SIL can only be defined for a whole loop;  includes sensor, logic solver and actuating function.


Role of SIL in Fire and Gas System

Fire and Gas detection technology has improved greatly during the past years. Detection rate, response time and spurious alarms were improved through new techniques, by adding intelligence direct to the equipment’s. SIL certification according to IEC standards are also an important addition for a FGS as a SIS.

Nowadays, Fire and Gas (FGS) detection and mitigation systems are key to maintain the overall safety and operation of Industrial plant. The  FGS systems are used for automating emergency actions with a high-integrity safety and control solution to mitigate further escalation. Failure of FGS control or devices results in NO-Detection or Unwanted-Detection which ends up in dangerous failure which leads to catastrophic situations such as:

  • Initiating a water deluge system inside a building can cause damage to equipment and can be hazardous to personnel
  • Chemical fire suppression can be dangerous to personnel

On other hand, nuisance alarms degrade the willingness to respond by plant personnel therefore, to ensure the Safe and Reliable detection; SIL certified and approved controls and devices shall manage the SIF in FGS SIS.


Is SIL Safety is Expensive?

It’s been a difficult task of evaluating the cost of a safety system. The cost associated with Safety system is not just the upfront cost of implementing the controls, it should be calculated based on the risk that it mitigates in future. However, the former is an immediate cost, whereas the latter is essentially a potential cost.

Higher SIL level is more expensive than lower SIL level because of implementation and maintaining; require additional operational income, adequate set of knowledge, skills and processes to be developed and followed within the responsive team; Higher SIL rated devices can also be more expensive. Therefore, higher SIL level is only recommended under critical and specific circumstances. Please bear in mind that cost of not implementing the appropriate SIL significantly outweighs the cost of overall implementation.


Advantage of SIL

Despite not being mandatory, SIL is state-of-the-art standard for industrial safety. It helps to ensure and improve the overall safety to Prevents (or) mitigates the consequences which can result in: loss of life, personnel injury, equipment damage, loss of production.

SIL also complying with present (or) future government directives on Health, Safety and Environment and provides a better corporate image, low insurance cost and helps in boosting the employee morale.



Industrial safety is importance as it safeguards the human life, environment and assets. To achieve the industrial safety, safety critical systems shall be designed to reduce the risks in hazardous industrial applications such as Fire and Gas System that must be verified to particular safety standards (IEC or equivaled). The FGS systems are responsible to detect and mitigate the hazard, high level of safety integrity (SIL2 or SIL3) is recommended to ensure the 100% functionality upon demand because, in process, some hazards will have higher SIL levels than others therefore, ALWAYS go for maximum level of SIL.