What is the Safety Life Cycle? | Functional Safety IEC 61511

Safety Life Cycle

The Safety Life Cycle

The Safety Life cycle is an important concept in the domain of Functional Safety. It recognizes the fact that “Safety” is not a one shot affair, or something like a standard product or service that can be obtained by a one time payment or effort. Rather Safety (including Functional Safety, Process Safety, Occupational Safety and all other branches of Industrial Safety) are a process and they follow a lifecycle concept, that is closely aligned with the lifecycle of the plant or equipment that they make safe.

The picture above shows this Safety Lifecycle, as outlined in the  well accepted IEC 61511 standard, which is the de-facto “gold standard” on Functional Safety in the Process Industry. Process industries are those where bulk materials are processed in the form of solids liquids and gases such as Oil and Gas, Petroleum Refining, Chemicals manufacturing, gas based power plants and similar. These are distinct from discrete parts manufacturing such as automobiles or nuts and bolts or other widgets.

This IEC 61511 standard is identical to ISA S84 that is used in the United States. This is the process industry implementation of the IEC 61508 Functional Safety standard. The different stages in the Safety Life Cycle are called as “phases”. We will now understand these phases in some more detail.

Note that a detailed explanation of this is in the Abhisam Functional Safety Training course and the Safety Instrumented Systems training course.

Hazard and Risk Assessment

This stage of Hazard and Risk Assessment is the first phase of the Safety Life Cycle. We identify and evaluate the different kinds of hazards that are present in the plant or equipment that could be present in the plant, process or equipment. We then conduct a Risk Assessment to judge whether this risk is high enough to take some action or not worth spending our time and money on. For this we use different Process Hazard Analysis (PHA) techniques such as HAZOP, and What-If analysis. You can also further carry out a LOPA (Layer of Protection Analysis) if you would like to have a more quantitative analysis of the risk. You can take the Abhisam Certification Courses on all these Hazard and Risk Assessment techniques, to understand each one of them in detail.

Allocation of Safety Functions to Protection Layers

In this phase the different Safety Instrumented Functions are allocated to the different protection layers.If you have conducted a LOPA Study then this has already been taken care of during the LOPA Study.

We have already explained in an earlier post about what is a Safety Instrumented Function (SIF), you can refer to it for a better understanding of a SIF.  You can also refer to what is a Safety Instrumented System here.

Safety Requirement Specification

This is the next phase and is one of the most important phases in the Safety Life cycle. Here the owner/operator or their engineers and technical staff decide on the specifications of the Safety Instrumented System that will be ordered. This document (or rather set of documents) is referred to as the SRS and describes each safety function in detail, including of course the Safety Integrity Level (SIL) of each SIF. All the following phases will take this SRS as the starting point and all further activities will take this SRS as their main document. Everything that happens later on including the design of the safety system, the calculations, the verification of the design, the validation will refer back to this SRS. We will cover this in more detail in a separate article. Note that the SRS may comprise of a Hardware SRS, a Software SRS and may also have cybersecurity requirements that the SIS should comply with.

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Design and Engineering of the Safety Instrumented System

This phase will have the actual grunt work of designing each SIF by selecting appropriate sensors, transmitters, logic solvers, final control elements and other auxiliary components such as safety relays and switches. Every SIF will be designed as per the SRS for that SIF.

Other means of Risk Reduction

In addition to the SIS, there will be many other layers of protection for risk reduction such as safety relief valves, rupture disks, dikes, scrubbers, flares and so on, the activities to design these will be carried out in  parallel as shown.

Installation, Commissioning and Validation

This is where the designed and built Safety Instrumented System will be installed (along with the plant and equipment) and commissioned. When it is tested in the field to check whether everything works as it is supposed to, it is known as “Validation”. This is where reality hits hard, if the system does not behave as per the expectations. It is then back to modification, change management and so on depending on the root cause found. Any change at this stage has major implications all the way back to the Hazard and Risk Analysis phase.

Operation & Maintenance

If everything works well as designed, then typically the design, project or commissioning team hands over the plant, equipment and the SIS to the Operations team, who now have the responsibility of running the plant safely for the next 20, 30 or even 50 years, until the product and plant become obsolete. This is the longest phase in the lifecycle.


It is rare for any plant to run for so long and not have any modifications. Hence this phase is after the Operation and Maintenance phase. There are special rules for carrying out modifications, one cannot just change anything without following the process given in the standard and adopted by the owner/operator. There are for example Management of Change (MOC) and other procedures to be followed.

Decommissioning and Dismantling

After many years of operations, sometimes a plant becomes too old and rusted beyond repair, or the product that it produces is no longer is viable at that cost, or has no customers, or maybe the environmental laws became more stringent, due to which it cannot operate any longer. At this stage, the plant is decommissioned and dismantled. This also has a lot of activities to be done, so that the process is carried out in a safe manner without causing any harm to people or the environment. You can read details about decommissioning and dismantling here.

Functional Safety Management

During this entire lifecycle. the management of functional safety should happen well, in order to maintain the level of safety which was designed in the first phase. Thus Functional Safety Management is very important. You can learn more about Functional Safety management in the Abhisam e-learning course on Functional Safety & SIL


Unlike what many people think, verification does not mean just checking the PFDavg calculations to see that the actual SIL achieved meets the target SIL. No, it is applicable for every phase of the lifecycle, according to the IEC 61511 standard. Thus every phase needs verification, after it is completed and it is to be done by an independent person, department or entity. You cannot verify your own work and call it “verification”.

Where can I learn more?

You can learn more about Functional Safety and SIL here. You can also learn and get certified as a Functional Safety Professional, when you take our courses and pass our exams. You can become a certified Functional Safety Professional at a much lower cost, when you take our e-learing courses on Functional Safety and Safety Instrumented Systems.

What flexibility do I get?

The low cost of the Functional Safety training is not just due to the low enrollment cost of the courses themselves, as compared to other providers, but also you save time and money on travel, hotel and other expenses. Plus you can take the certification exam at anytime during the validity of your license (at least 1 year). This is much better than having to take the exam under pressure on the next day of the completion of the training. You can be located anywhere in the world, in the US, or in India, Africa, South America, Australia or anywhere else, where you have a device to access the course and test online.

You can try to evaluate your current knowledge and understanding of Functional Safety by taking the Functional Safety Mock test here. It is completely free of cost.


The Safety Life Cycle is an important concept in the world of functional safety and any Functional Safety practitioner should be well aware of the different phases of the life cycle.