What are the SIL integrity levels?

Hazard and Risk Analysis for Determining SILs – Ensuring functional safety requires a hazard analysis and risk assessment of equipment under control (EUC). A hazard analysis identifies all possible hazards created by a product, process, or application.

1. This determines the safety function requirements for the safety standard.
2. For each hazard you identify, you’ll need to do a risk assessment.
3. This assesses the frequency or likelihood of a hazard occurring, as well as the severity of the consequences if it does occur.
4. Risk assessments determine the safety integrity requirements for the safety standard.

And they’re critical for determining the SIL required to reduce risk. You can use either qualitative or quantitative analysis to assess risk. A specific method isn’t required. One way you can assess risk is to create a requirements traceability matrix and do a failure modes and effects analysis (FMEA),

What is the SIL safety rating?

SIL Classification analysis

What determines SIL level?

Safety Instrumented Systems (SIS) are installed in Process Plants to mitigate process hazards by taking the process to a “safe state” when predetermined set points have been exceeded or when safe operating conditions have been transgressed. The SIS is one Protection Layer in a multi-layered safety approach since no single safety measure alone can eliminate risk.

• A Layer of Protection Analysis (LOPA) is a method whereby all known process hazards and all known layers of protection are closely scrutinized.
• For each process hazard where the LOPA study concludes that existing protection cannot reduce risk to an acceptable or tolerable level, a Safety Instrumented System is required.

Not all process hazards will require the use of a SIS. Each hazard that requires the use of an SIS must be assigned a target SIL level. This article serves as a high-level summary as to how SIL levels are determined for process applications. SIL is an acronym for “Safety Integrity Level” that comes from two voluntary standards used by plant owners/operators to quantify safety performance requirements for hazardous operations:

IEC 61508: Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems IEC 61511: Safety Instrumented Systems for the Process Industry Sector

As defined in the IEC standards, there are four SIL Levels (1-4). A higher SIL Level means a greater process hazard and a higher level of protection required from the SIS. To generalize how SIL Level is determined, see Figure 1. SIL Level is a function of hazard frequency and hazard severity. Figure 1: General chart demonstrating how SIL Level is a function of hazard frequency and hazard consequence. Used with permission from rotork, To determine SIL Levels of process hazards, it is helpful to understand the Safety Life Cycle. The IEC standards define a concept known as the Safety Life Cycle, see Figure 2. Figure 2: Safety Life Cycle model. Adapted from IEC 61511. A Process Hazard Analysis (PHA) is a systematic assessment of all potential hazards associated with an industrial process. It is necessary to analyze all potential causes and consequences of fires, explosions, releases of toxic, hazardous, or flammable materials and more. Focus on anything that might impact the process including:

Equipment failuresInstrumentation failures or calibration issuesLoss of Utilities (power, cooling water, instrument air, etc.)Human errors or actionsExternal factors such as storms or earthquakesEtc

Both the Frequency and Severity of each process hazard must be analyzed:

How often could it happen? Tank spills could happen any time there’s a manual fill operation (multiple times a year) How severe is the result? Localized damage, fire, explosion, toxic gas release, death

Core to the PHA analysis is the fact that things can and do go wrong. You have to forget IF it will happen and instead consider WHEN it will happen. Each identified hazard is assigned an “acceptable” frequency. For purposes of the PHA, you cannot assume a hazard will “never” happen.

A hazard which results in simple First Aid could be considered “acceptable” if it could happen only once a yearAn explosion and fire due to a tank rupture could have an “acceptable” frequency of once in 10,000 years

The end result of the Process Hazard Analysis is a list of all possible process hazards with each one assigned an acceptable frequency of occurrence. With the PHA complete, the next step in the Safety Life Cycle is the Layer of Protection Analysis.

What do the safety integrity levels mean?

From Wikipedia, the free encyclopedia In functional safety, safety integrity level ( SIL ) is defined as the relative level of risk-reduction provided by a safety instrumented function (SIF), i.e. the measurement of the performance required of the SIF.

In the functional safety standards based on the IEC 61508 standard, four SILs are defined, with SIL4 being the most dependable and SIL1 the least. The applicable SIL is determined based on a number of quantitative factors in combination with qualitative factors, such as risk assessments and safety lifecycle management,

Other standards, however, may have different SIL number definitions.

What is SIL and ATEX?

Safety Integrity Level (SIL) capability is becoming more common. Many people are familiar with hazardous area approvals such as ATEX, IECEx and CSA; however, a SIL capability is slightly different. In simple terms, if a product has ATEX approval for use in Zone 0 hazardous areas, that means the product has been tested and proved to be safe to use in that type of area.

• This is the same for IECEx and CSA.
• SIL is different because it looks at risk reduction.
• Determining the appropriate level of risk is often site-specific.
• Operators must be able to identify an acceptable tolerance level and assess how that will impact on personnel and equipment.
• SIL is defined by the International Electrotechnical Commission Standard IEC 61508 using two integrity categories: hardware safety and systematic safety.

The requirements for both categories must be met for SIL certification to be awarded.

How is SIL measured?

Open topic with navigation The SIL value is a measure of the reliability and availability of a safety system. It is the measurement of performance of a safety system under all the stated conditions within a stated period of time. LOPA is a quantitative method for determining the SIL level for the safety system.

• The LOPA process uses information such as initiating event frequencies, the probabilities of failures of all safeguards, and the tolerable frequency of risk mitigation to determine the required probability of failure of the safety system.
• The required probability of failure is a number representing the probability that a safety system will fail in a dangerous scenario.

The SIL value for the safety system is determined by comparing the required probability of failure to the international standards of functional safety, defined in IEC 61508 and IEC 61511. Based on the demand rate of the safety system, the SIL standards are classified into the following two types:

Low Demand Mode : The demand rate of the safety system is less frequent than once per year. In these cases, the failure rate is measured by the average probability of failure on demand (PFD Avg). High Demand or Continuous Mode : The demand rate of the instrumented function is more frequent than once per year. In this case, the failure rate is measured by the average probability of failure per hour (PFH).

As per the industry standards, the required probability of failure are related to one of the four safety integrity levels contained in the following table:

For example, if the required probability of failure for a safety system is 0.02, which is a value between 0.01 and 0.1, the Safety Integrity Level for the safety system is 1, Copyright © 2018 General Electric Company. All rights reserved.

What is difference between sil1 sil2 and SIL3?

For SIL 2 the system must function as required 99 % of the time or better. For SIL 3 it must work 99.9 % of the time. But note that it is the safety FUNCTION that is SIL-rated – not the hardware that is used as a part of the way to make sure that function is performed.

What is the difference between SIF and SIL?

Skip to content SIS/SIL/SIF Services Amy Hulen 2016-12-07T01:33:17-07:00 A SIS is a set of devices and software that perform one or more Safety Instrumented Functions (SIFs). Each SIF has a stated Safety Integrity Level (SIL) that is related to the probability that the SIF will NOT work when challenged (when needed).

• In order to begin this assessment, one must understand the rules of a SIS and how Independent Protection Layers (IPLs), SIFs and SILs are all related.
• For example, in order to be considered IPLs (including SIFs), there are several rules that must be satisfied, some of which include: each protection layer must be truly independent of the others (i.e., no failure can deactivate two or more protection layers); the IPL must be specifically designed to prevent or mitigate the consequences of a potentially hazardous event; the IPL must be dependable (must have the stated reliability); the IPL must be validated periodically and the validation system must be audited.

A probability of failure (PFD) of each IPL (including SIFs) must also be identified. One of the biggest challenges a PHA or design team faces is the determination of when a SIF is the appropriate choice for reducing the risk and then determining the appropriate target SIL for an identified SIF.

What is IEC 62061 Safety Integrity Level SIL?

Safety Integrity Level The safety integrity level according to IEC 61508 and IEC 62061, also called SIL, contains three discrete levels which describe the capability of safety relevant components included in a controller to execute a safety function under foreseeable conditions. Product Comparison : Safety Integrity Level

What are the three types of SIL?

What Safety Integrity Level (SIL) Means and How to Calculate It – Spotlight on Safety | MSA Corporate Blog The global importance of SIL (Safety Integrity Levels) has grown substantially in the process industries over the years. However, for many end users, systems integrators, and product vendors, SIL is still a somewhat ambiguous concept that often is misinterpreted and incorrectly implemented.

In order to fully understand SIL and its implications, it is important to grasp the overarching concept known as Functional Safety, and how it applies to Safety Instrumented Systems (SIS) within the process industries. What is Functional Safety? Functional Safety, as defined by IEC standard 61508, is the safety that control systems provide to an overall process or plant.

The concept of Functional Safety was developed in response to the growing need for improved confidence in safety systems. Major accidents around the world, as well as the increasing use of electrical, electronic or programmable electronic systems to carry out safety functions, have raised awareness and the desire to design safety systems in such a way as to prevent dangerous failures or to control them when they arise.

Industry experts began to address functional safety and formalize an approach for reducing risk in the process plant environment through the development of standards IEC 61508, IEC 61511, and ANSI/ISA 84. Previous safety standards were generally prescriptive in nature, not performance based. An emphasis on quantitative risk reduction, life-cycle considerations, and general practices make these standards different from their predecessors.

Functional Safety is a term used to describe the safety system that is dependent on the correct functioning of the logic solver, sensors, and final elements to achieve a desired risk reduction level. Functional Safety is achieved when every safety function is successfully carried out and the process risk is reduced to the desired level.

1. What is a Safety Instrumented System (SIS)? A Safety Instrumented System is designed to prevent or mitigate hazardous events by taking a process to a safe state when predetermined conditions are violated.
2. Other common terms used are safety interlock systems, emergency shutdown systems (ESD), and safety shutdown systems (SSD).

Each SIS has one or more Safety Instrumented Functions (SIF). To perform its function, a SIF loop has a combination of logic solver(s), sensor(s), and final element(s). Every SIF within a SIS will have a SIL level. These SIL levels may be the same, or may differ, depending on the process.

1. It is a common misconception that an entire system must have the same SIL level for each safety function.
2. The Meaning of Safety Integrity Level (SIL) SIL stands for Safety Integrity Level.
3. A SIL is a measure of safety system performance, in terms of probability of failure on demand (PFD).
4. This convention was chosen based on the numbers: it is easier to express the probability of failure rather than that of proper performance (e.g., 1 in 100,000 vs.99,999 in 100,000).

There are four discrete integrity levels associated with SIL: SIL 1, SIL 2, SIL 3, and SIL 4. The higher the SIL level, the higher the associated safety level, and the lower probability that a system will fail to perform properly. As the SIL level increases, typically the installation and maintenance costs and complexity of the system also increase.

Specifically for the process industries, SIL 4 systems are so complex and costly that they are not economically beneficial to implement. Additionally, if a process includes so much risk that a SIL 4 system is required to bring it to a safe state, then there is a fundamental problem in the process design that needs to be addressed by a process change or other non-instrumented method.

It is a very common misconception that individual products or components have SIL ratings. Rather, products and components are suitable for use within a given SIL environment but are not individually SIL rated. SIL levels apply to safety functions and safety systems (SIFs and SISs).

The logic solvers, sensors, and final elements are only suitable for use in specific SIL environments, and only the end user can ensure that the safety system is implemented correctly. The equipment or system must be used in the way it was intended in order to successfully obtain the desired risk reduction level.

Just buying SIL 2 or SIL 3 suitable components does not ensure a SIL 2 or SIL 3 system. Risk Management and Selecting a SIS or SIL Level The identification of risk tolerance is subjective and site-specific. The owner / operator must determine the acceptable level of risk to personnel and capital assets based on company philosophy, insurance requirements, budgets, and a variety of other factors.

1. A risk level that one owner determines is tolerable may be unacceptable to another owner.
2. When determining whether a SIL 1, SIL 2, or SIL 3 system is needed, the first step is to conduct a Process Hazard Analysis to determine the functional safety need and identify the tolerable risk level.
3. After all of the risk reduction and mitigation impacts from the Basic Process Control System (BPCS) and other layers of protection are taken into account, a user must compare the residual risk against their risk tolerance.

If there is still an unacceptably high level of risk, a risk reduction factor (RRF) is determined and a SIS / SIL requirement is calculated. The RRF is the inverse of the Probability of Failure on Demand for the SIF / SIS (see table below). Selecting the appropriate SIL level must be done carefully.

1. Costs increase considerably to achieve higher SIS / SIL levels.
2. Typically in the process industry, companies accept SIS designs up to SIL 2.
3. If a Process Hazard Analysis indicates a requirement for a SIL 3 SIS, owners will usually require the engineering company to re-design the process to lower the intrinsic process risk.

: What Safety Integrity Level (SIL) Means and How to Calculate It – Spotlight on Safety | MSA Corporate Blog

What is the difference between PL level and SIL?

SIL OR PL? – Both standards have a difference in the way they are approached. Both SIL and PL have the same objective. The biggest difference is that the 13849-1 standard has a broader framework that also covers aspects in the field of pneumatic and hydraulic systems.

Why is SIL certification required?

SIL Certification Pros – SIL ( Safety Integrity Level ) is often part of contractual specifications in the field of mechanical, electrical, and electronic supply. Contractual specifications usually indicate the desirable SIL level (SIL 1, SIL 2, SIL 3, or SIL 4) required to compete in a supply contract.

SIL levels also guarantee conformity with IEC 61508 requirements. Despite the fact that it is not mandatory, with few exceptions, many users of electric and electronic systems increasingly require certified components in terms of safety. The certification is mandatory in the automotive industry, while it can be rather obtained voluntarily for other industries such as processing and industrial machinery.

A SIL certification can be used to substantially different product characteristics from competitors’. Indeed, SIL certification is closely linked to product design, The safety design of an industrial component involves all the technical aspects of the product being certified.

Obtaining a SIL certification encourages product restyling and helps improve its usability. In summary, a certification represents a boost to product differentiation. Since the IEC 61508 standard has been adopted all over the world, a SIL certification can be used at the international level and proves the superiority of a component compared to competitors’.

A SIL certificate is also a guarantee of greater system reliability, For all these reasons, the certification process can involve the Research and Development department as well as the Marketing and Sales staff.

How many safety integrity levels exist?

Industrial safety in pre-digital eras cantered mainly around safe work practices, hazardous materials control, and the protective “armoring” of personnel and equipment. Today, safety penetrates far deeper into more complex manufacturing infrastructures, extending its protective influence all the way to a company’s bottom line.

Contemporary safety systems reduce risk with operational advancements that frequently improve reliability, productivity and profitability as well. Nothing is more important than safety to the process control industries. High temperature and pressure, flammable and toxic materials are just some of the issues faced on a daily basis.

Reliability is a key component of safety; the more reliable the device, the safer the critical process. After years of work by the ISA SP84 committee, IEC 61508 and IEC 61511 have recently come together to yield a safety standard that the world is embracing.

IEC 61511 is particularly important as it is written specifically for the Process Industries. This standard quantifies safety issues as never before. Although the safety issues addressed are critical to users with installations like Emergency Shutdown Systems (ESD), the reliability defined in this specification is being used by all users to separate great products from good ones.

SIL (Safety Integrity Level) and SFF (Safe Failure Fraction) are two of the key values that customers can use as an objective comparison of instrument reliability from various suppliers. Reliability. Although this brochure targets safety applications and installations like Emergency Shutdown Systems, more than 90% of all applications are not safety-related.

• Those people are now using the SIL data as an indicator for reliability, i.e., the better the numbers, the more reliable the instrument.
• Risk: – All safety standards exist to reduce risk, which is inherent wherever manufacturing or processing occurs.
• The goal of eliminating risk and bringing about a state of absolute safety is not attainable.

More realistically, risk can be categorized as being either negligible, tolerable or unacceptable. The foundation for any modern safety system, then, is to reduce risk to an acceptable or tolerable level. In this context, safety can be defined as “freedom from unacceptable risk.” The formula for risk is: RISK = HAZARD FREQUENCY x HAZARD CONSEQUENCE Risk can be minimized initially by inherently safe process design, by the Basic Process Control System (BPCS), and finally by a safety shutdown system.

Layered Protection: – Much evaluation work, including a hazard and risk assessment, has to be performed by the customer to identify the overall risk reduction requirements and to allocate these to independent protection layers (IPL). No single safety measure can eliminate risk and protect a plant and its personnel against harm or mitigate the spread of harm if a hazardous incident occurs.

For this reason, safety exists in protective layers: a sequence of mechanical devices, process controls, shutdown systems and external response measures which prevent or mitigate a hazardous event. If one protection layer fails, successive layers will be available to take the process to a safe state.

• If one of the protection layers is a safety instrumented function (SIF), the risk reduction allocated to it determines it’s safety integrity level (SIL).
• As the number of protection layers and their reliabilities increase, the safety of the process increases.
• What is SIL? SIL, an acronym for safety level, is a system used to quantify the requirements for safety instrumented system.

The international electro-technical commission(IEC) introduce the following industry standards to assist operators with quantifying the safety performance requirements for hazardous operations IEC 61508 Functional safety Electrical/Electronic/Programmable Electronic Safety-Related Systems, IEC 61511 Safety Instrumented Systems for The Process Industry Sector.

1. These standard have been widely adopted in the hydrocarbon and oil & gas industries to define safety instrumented systems and their reliability as a means of improving safety and availability of safety instrumented system.
2. What are safety Integrity Levels? Safety integrity levels are targets applied to the reliability and performance of the safety system used to protect hazardous activity such as hydrocarbon refining or production.

There are 4 SIL levels. The higher the perceived associated risk, the higher the performance required of the safety system and therefore the higher the SIL rating number. The IEC standards define the performance requirements of the safety systems for the required SIL rating.

• To what extent can a process be expected to perform safely? And, in the event of a failure, to what extent can the process be expected to fail safely? These questions are answered through the assignment of a target Safety Integrity Level (SIL).
• SILs are measures of the safety risk of a given process.

How are SIL ratings determined? Once the scope of an activity is determined, the operator can identify the possible hazard(s) and then assess their potential severity. The risk associated with a hazard is identified by assessing the likely frequency of occurrence and the potential consequences if the hazard is realized. How are hazards protected against? Once the SIL ratings have been determined, the operator can then design a risk reduction strategy to protect against these hazards. This is accomplished by applying multiple layers of protection. Risk reduction can be an expensive procedure; therefore, the operator will look to reduce the risk to a level as Low as Reasonably Practicable (ALARP).

• The SIS assists in reducing the frequency of the likely manifestation of the hazard and therefore improves the reliability of the system.
• The consequence of a failure is not addressed by SIS but by other aspects of the risk reduction strategy.
• How is SIL used? Safety Integrity Levels are part of a larger scheme called Functional Safety that deals with techniques, technologies, standards and procedures that help operators protect against hazards.

Functional Safety adopts a life cycle approach to industries that deal with hazardous processes that includes plans from concept through to final decommissioning of plants. This process is cyclical and any phase is effected by the requirements of the previous stage(s) so, subsequent stages must be revisited to assess the impact of a change to a previous stage.

Pre-Design Phase This is the phase where the scope of the project is determined, all hazards are assessed, and a Safety Requirements Specification is formulated. This specification will determine the SIL ratings to be applied to the various activities. Design Phase Once the pre-design phase is completed, the operator will design the required safety systems and plan how they will be executed.

It is this stage where the safety systems are specified. This is also when the testing regimes are allocated to ensure that the SIL ratings can be met. Realisation Phase Upon the completion of the design phase, the plant is built and commissioned. All safety systems are tested to ensure that they meet the established safety requirements.

Operation Phase The plant is now operational and producing. The safety systems are now regularly tested to ensure that they continue to perform as designed and required. How does equipment fail? There are three ways in which safety equipment can fail: systematic, common cause, and random hardware failure.

These failures are addressed by the safety life cycle in the following manner. Systematic Failure These types of failure are not failures of individual components but the system as a whole. These failures are reduced by using proper engineering practice and design during the design phase.

• These are very rare failures as years of experience and documentation have helped engineers understand how systems interact.
• Common Cause Failures This type of failure is when identical components within the safety system fail at the same time.
• Again, experience with products and documentation help engineers design systems that prevent this.

Also, these failures can be virtually eliminated by using redundant and diverse systems. Common cause failures are generally the result of environmental effects like flooding or excessive temperatures. Random Hardware Failure This is the main type of failure mode — random by their nature.

1. This is the type of failure Safety Instrumented Systems protect against.
2. Engineers try to predict the probability of these failures by assessing the failure rates of the equipment used.
3. This is where SIL specifies the performance and architectural constraints that a safety system requires.
4. How is the SIS performance quantified? The Probability of Failure on Demand (PFD) is the measure used to define the level of protection offered by the system.

EIC 61508 defines the maximum allowable PFD avg (the average probability, from 0 to 1, that the safety function will fail to operate on demand) for the Safety Instrumented Function (SIF). The allowable level is dependent upon whether the system is deemed to be low demand or high demand.

Low demand systems are defined as having an expected safety demand interval of greater than one year, and a proof test interval for the equipment that is at least twice that of the expected safety demand interval. The vast majority of fluid power actuated safety valves fall into this low demand type.

High Demand safety control systems are defined as those that are operated more frequently than once per year. What does this mean in terms of performance for the SIF? Any SIF is comprised of three discrete areas: “Sensors”, “Logic Solvers” and “Final Elements”. The “Sensors” detect the presence of the potential onset of a hazardous condition (e.g., over-pressure).

The “Logic Solver” is the programmable logic controller (PLC) which determines what action to take after the “Sensors” have detected a potentially hazardous event. The “Final Elements” perform the required safety action (e.g., ESD of the valve). The scope of this document only covers the “Final Elements” as this is area where fluid power actuators function.

When assessing the performance of the SIF we must consider the solenoid valve, actuator and valve as a single entity with regard to the PFDavg calculation as the failure of any of these components will cause the SIF to fail. In order to prove that the SIF is performing to the required SIL rating, it is necessary to know the failure rates of the equipment used so that it can be verified that the maximum allowable PFDavg is not exceeded.

Failure rate data gives the operator a measure of when the equipment is likely to fail over a given period of time (i.e., the older the equipment, the more likely it is to fail when required to operate). The PFDavg can be calculated from this data. When it reaches the maximum allowable level, the plant must be shut down and all safety systems fully tested.

Is it possible to procure an actuator with a SIL rating approval? The simple answer is no. Only the complete SIF can have a SIL rating, not individual components. However, components (e.g., actuators) can be certified “suitable for use” at a particular SIL rating.

Operators and contractors may look for components certified as “suitable for use” as this will simplify the design process. In addition, if the component has failure rates that are known to be compatible with the required SIL rating, the safety calculations are also made much simpler. How are actuators certified as “suitable for use” for specific SIL ratings? There are two aspects to the process of attaining a SIL certificate.

The first is assessing the design and failure rates of the equipment. This can be accomplished through either of two techniques: FMEDA (Failure Modes, Effect and Diagnostic Analysis) and “Proven in Use”. The second aspect is the auditing the vendor’s manufacturing and quality processes.

• This audit proves that the vendor is capable of manufacturing the product to the designed performance standard.
• These assessments must be audited by an approved accreditation body such as Exida or TÜV.
• Suitable for Use Method 1 – FMEDA FMEDA is a technique that assesses the performance of a device by evaluating the effects of the different failure modes of all components in the design.

Every component is assessed for the type of failure (dangerous or safe) and the likelihood of failure (failure rate). All of this data is then collated to produce overall dangerous and safe failure rates that can be used in safety calculations. FMEDA studies can be conducted either by the vendor or a third-party body but, in both circumstances, must be audited by an accredited body to prove that best practices have been used.

Suitable for Use Method 2 – Proven in Use It may not be possible, practical or cost effective to conduct an FMEDA on a product, particularly if it is of an old or complex design. In these cases, products may be certified by using “Proven In Use”. “Proven in Use” as defined in the IEC 61508 standard is a documented assessment that has shown that there is appropriate evidence, based on previous use history of the component, that it is suitable for use in a safety system.

This documented evidence must include the following:

The manufacturer’s quality and management systems. The volume of the operating experience with statistical evidence to show that the claimed failure rate is sufficiently low.

Failure Rate Data: – Once the studies have been completed, the user is presented with the failure rate data. This data falls into two fundamental categories: dangerous failure rate (λD) and safe failure rate (λS). The dangerous failure rate (λD) data relates to failures that will result in the SIF being unable to perform the required safety function upon demand.

• The safe failure rate (λS) data relates to those failure modes that will put the safety function in its safe state (e.g., shutdown).
• SIL is only concerned with the dangerous failure data but the safe failure data is important as this provides the operator a measure of how likely the safety system is to spuriously trip.

Do we need to test the SIF? As described in earlier sections, SIL prescribes the maximum level that the PFDavg is permitted to reach. There are two types of tests that can be performed to help maintain the PFDavg at a suitably low level: Proof Tests and Diagnostic Tests.

• Proof tests: A proof test is a manual test performed during shutdown that tests the entire functionality of the SIF from sensing to actuation.
• It must be suitably configured to test all aspects of the safety function to prove that the SIF is “as good as new”.
• There may be several negative ramifications — particularly expense related — due to a proof test necessitating a process shutdown.

Diagnostic Tests A diagnostic test is an automatic test performed online that does not necessitate process shutdown. This type of test must be performed at least ten times more frequently than the expected SIF demand rate. A diagnostic test will test only a percentage of the total possible failure modes of the SIF; this percentage is called the Diagnostic Coverage (DC).

These tests contribute to reducing the PFDavg of the SIF and thus assist in the extension of the proof test interval. The higher the DC, the greater the benefit gained from the test. For the “final elements” within the scope of this document, this type of test is called a partial stroke test. Safety assignment methodology: – The machinery sector is not the only one for which IEC 61508 application standards have found to be required.

Other sectors have written or are in the process of writing sector application standards. For example, IEC 61511 (Ref.15) (not yet available for public comment) in the process sector, IEC 61513 (Ref.16) in the nuclear sector, prEN 50129 (Ref.17) in the railway sector, and IEC 60601 (Ref.18) in the electro medical sector.

• IEC 60601 contains no mention of safety integrity levels.
• IEC 61513 does not follow the SIL approach and instead a deterministic approach is used to categorise the safety significance of a system pointing out that “the highest practicable integrity is generally deemed necessary for any system that prevents or mitigates the consequences of radioactive releases”.

prEN 50129 uses the concept of SIL to specify safety requirements and recommends taking an approach similar to that used in IEC 62061. That is, calculating individual risk by forecasting accidents, taking into account the proportion of near misses and comparing this risk with a target individual risk to obtain the tolerable hazard rate for a safety function for which equivalent SIL is given in a table.

1. However, prEN 50129 does not specify what this target risk should be, nor go into details of how to go about the individual risk calculations.
2. In the process sector IEC 61511 gives various examples of how to assign safety integrity levels.
3. One is based on the calibration of a risk graph with process specific guidance of the selection of factors.

Also in the process sector, the Dow Chemical Company have developed a practical, spreadsheet based, system for SIL selection. A safety target factor value, an integer from 1 to 10, is first calculated using a simple matrix that relates the hazard index and quantity involved of the chemical being processed.

1. One page of the spreadsheet contains a list of chemicals for which hazard indices have already been specified along with a facility to automatically calculate a hazard index when various specified properties of the chemical are input.
2. An initiating event factor, another integer, is then found for the hazardous event under consideration.

This is taken from another page of the spreadsheet and is based on generic failure rates for the type of event. This factor is the order of magnitude of the hazardous event frequency per year so if the event is not listed this factor is found by first estimating or calculating the event frequency.

Credit factors, also integers, can then be allocated to various standard independent protective layers (IPLs) of a chemical process. These are looked up from various other pages of the spreadsheet. In addition, various listed rules need to be applied to check that each layer for which credit is given is truly independent.

These factors are all input to the top level of the spreadsheet and a SIL is calculated for the control safety-function associated with the event being analysed. The pragmatic approach is qualitative and consequence based carefully avoiding any mention of accident frequencies or rates.

It relies on a rigidly defined classification scheme that may be difficult to apply to novel applications. Integrity levels are selected by associating each level with a given severity as follows: SIL 1 – represents the integrity required to avoid relatively minor incidents and is likely to be satisfied by a certain degree of fault tolerant design using guidelines that follow good practice.

SIL 2 – represents the integrity to avoid more serious, but limited, incidents some of which may result in serious injury or death to one or more persons. SIL 3 – represents the integrity required to avoid serious incidents involving a number of fatalities and/or serious injuries.

SIL 4 – represents the integrity level required to avoid disastrous accidents. This would appear to be quite quick and simple but suffers from the usual problem of a lack of clear guidance and being open to interpretation. For example, there is some overlap between the descriptions for SIL levels 2 and 3 and what is meant by disastrous in the description for SIL 4 is not defined.

The controllability approach is also qualitative and consequence based but gives qualitative terms for the acceptable failure frequency associated with each SIL. Each safety function is classified according to the controllability of the motor vehicle should the safety function fail.

The selection of the appropriate controllability category is based upon a consideration of various severity and influencing factors such as reaction time compared to human capabilities, provision of backup systems and levels of system interactions. Guidance is given in the source document on what to take into account in considering these.

Some of the guidance is quite general but a significant proportion is specific to motor vehicles such as vehicle stability, controllability of acceleration, braking and visibility impairments etc. The standards based or systematic approach relies on either the use of quantified risk assessment (QRA) and the existence of industry agreed risk criteria or the availability of industrial standards that allocate SILs to various aspects of a design.

• Average probability of failure on demand (PFDavg) of the input subsystem: – Failure rate λd is the dangerous (detected and undetected) failure rate of a channel in a subsystem.
• For the PFD calculation (low demand mode) it is stated as failures per year.
• Target failure measure PFDavg is the average probability of failure on demand of a safety function or subsystem, also called average probability of failure on demand.

The probability of a failure is time dependant: PFD: Q(t) = 1 – e-λdt It is a function of the failure rate λ and the time t between proof tests. That means that you cannot find out the maximum SIL of your (sub)system if you do not know if a test procedure is implemented by the user and what the test intervals are! These values are required for the whole safety function, usually including different systems or subsystems.

The average probability of failure on demand of a safety function is determined by calculating and combining the average probability of failure on demand for all the subsystems, which together provide the safety function. If the probabilities are small, this can be expressed by the following: PFDsys = PFDs + PFDl + PFDfe where PFDsys is the average probability of failure on demand of a safety function safety-related system; PFDs is the average probability of failure on demand for the sensor subsystem; PFDl is the average probability of failure on demand for the logic subsystem; and PFDfe is the average probability of failure on demand for the final element subsystem.

This means that a subsystem or component cannot claim the whole PFD value for a given SIL! Usually, isolators have a PFD, which claims 10 % of the total PFD value of the required SIL. Safe failure fraction (SFF): – Fraction of the failure rate, which does not have the potential to put the safety related system in a hazardous state.

SFF= (Σλs + Σλdd)/(Σλs + Σλd) = 1 – Σλdu/(Σλs + Σλd) where Σλs = Σλsu + Σλsd und Σλd = Σλdu + Σλdd Dangerous detected failures are also considered as safe. The calculation methods defined in IEC61508 are shown below, and SFF is determined using these. SFF = (λSD + λSU + λDD)/( λSD + λSU + λDD + λDU) Where: SFF = Safety Failure Fraction λSD : Fail Safe Detected λSU : Fail Safe Undetected λDD : Fail Dangerous Detected λDU : Fail Dangerous Undetected If SFF exceeds 60%, 90% or 99%, SIL 1, SIL 2 or SIL 3 is obtained respectively.

IEC61508 permits self-declaration for SIL 1 but requires the third-party certification for SIL 2 and higher. Safety instrumented systems are increasingly adopted in the oil, gas, and petrochemical industries; there is a growing expectation of higher SIL where risk is lower.

For this reason, the demand for field instruments having the certification of SIL 2 or more is increasing, additionally many end users prefer fully assessed devices by third party organizations. It is always the responsibility of the end user to perform or verify the calculations for the entire safety loop.

Since a SIF relies on more than one device, it is imperative that all devices in the loop work together to meet the required SIL levels. The device’s SFF and the PFD avg values used for these calculations can be found in a FMEDA/FMEA report. IEC 61508 requires a quantitative, as well as qualitative, assessment of risk.

• A Failure Modes and Effects Analysis (FMEA) provides a systematic way to assess the effects of all probable and known failure modes, including on-line monitoring and error checking, of a SIS component.
• The detailed circuit and performance evaluation that estimates failure rates, failure modes and diagnostic capability of a device.

This data provided is to be used by a competent functional safety practitioner to determine a device’s applicability in a specific safety-related application. It is best if the FMEA report is certified by a well-qualified third-party agency that specializes in functional safety approvals.

1. Today, there are solutions for SIS strategies and numerous possible mixes and configurations.
2. An essential requirement to verify their design is a third-party certification from approval body.
3. This certification provides unbiased, verified evidence that the unit is appropriate for use in specific SIS strategies.

For example, the certification may verify that the device is appropriate for SIFs up to SIL3 in a simplex or 1oo1 configuration. The electro-mechanical switch (Pressure and Temperature switch) family fits into this scenario. They provide an extremely affordable option that delivers simple installation, easier validation and faster start-ups.

What is high integrity level?

High – Administrators are granted the High integrity level. This ensures that Administrators are capable of interacting with and modifying objects assigned Medium or Low integrity levels, but can also act on other objects with a High integrity level, which standard users can not do. Example: ‘Run as Administrator’

What are the safety integrity levels of ISO 26262?

How to Determine the ASIL Value for an Automotive Application, as per the ISO 26262 Standard – ISO 26262 standard defines four values of ASIL: ASIL A, ASIL B, ASIL C, ASIL D. ASIL D represents the highest degree of automotive hazard and ASIL A the lowest. Image credit : Whitepaper by CadenceFor any particular failure of a defined function at the vehicle level, a hazard and risk analysis (HARA) helps to identify the intensity of risk of harm to people and property. Once this classification is completed, it helps in identifying the processes and the level of risk reduction needed to achieve a tolerable risk. Safety goal definition as per ASIL is performed for both hardware and to ensure highest levels of functional safety. These safety levels are determined based on 3 important parameters: Exposure ( E): This is the measure of the possibilities of the vehicle being in a hazardous or risky situation that can cause harm to people and property. Various levels of exposure such as E1: very low probability, E2: low probability, E3: medium probability, E4: high probability are assigned to the automotive component being evaluated. Controllability (C) : Determines the extent to which the driver of the vehicle can control the vehicle if a safety goal is breached due to failure or malfunctioning of any automotive component being evaluated. The order of controllability is defined as: C1

2. Evaluation safety goals of automotive components Image credit: techdesignforums Let us try to understand the determination of ASIL values for various components based on the E,C and S parameters.
3. Few observations from the ASIL allocation table,

1. A combination of S3, E4 and C3 (the extremes of the 3 parameters) refers to a highly hazardous situation. Hence the component being evaluated is identified to be ASIL D, which means it is prone to severely life-threatening events in case of a malfunction and calls for the most stringent levels of safety measures.
2. On the contrary, a combination of S1, E1 and C1 ( the lowest levels of the 3 parameters in terms of safety-criticality) calls for QM levels, which means the component is not hazardous and does not emphasize safety requirements to be managed under the ISO 26262.
3. Similarly, combination of the medium levels – S2, E4 and C3 or S2,E3 and C2 defines either an ASIL C or an ASIL A.

The intensity of the hazard thus depends on the ASIL levels of the components, under consideration. Allocation of ASIL helps in identifying how much threat the malfunctioning of a particular component can cause under various situations. Under the framework of the ISO 26262 ASIL and functional safety; the safety goals are more critical than the functionality of the automotive component.

Thus, ASIL determination forms a very critical process in the development of highly reliable and functional safe automotive applications. In today’s time where the car designs have become increasingly complex with huge number of ECUs, sensors and actuators, the need to ensure functional safety at every stage of product development and commission has become even more important.

What is SIL certified?

According to Wikipedia, ‘Safety integrity level (SIL) is defined as a relative level of risk-reduction provided by a safety function, or to specify a target level of risk reduction. In simple terms, SIL is a measurement of performance required for a safety instrumented function (SIF).’

What is the SIL level 3 requirement?

Safety Integrity Level – why does the industry need it?

• Safety Integrity Level (SIL) and more specifically, SIL 3, is a topic that comes up with increasing regularity when we speak to clients about the development of safety-critical systems.
• If you are questioning whether your company should be requesting SIL 3 capabilities and what the benefits are, then let the ETC experts help to clarify the business case.
• Firstly, what is SIL?
• Safety Integrity Levels (SILs) are a measure of the impact that a Safety Instrumented Function (SIF) has over the risk associated with a specific hazard. The higher the SIL level is, the more efficient that function will be at reducing

the risk it mitigates. In other words, SIL can be seen as an indicator of the acceptable failure rate for a security function. SIL rating is a fundamental parameter to consider when comparing products; it is also an increasingly important requirement in various public and private tender invitations for the supply of mechanical systems and electrical and electronic products.

• SIL standards, developed by the International Electrotechnical Commission (IEC), focus on functional safety.
• IEC standards define four SILs – 1 to 4 – a SIL is determined on the base of both quantitative and qualitative factors based on several methods used in combination, these include risk matrix, risk graphs and Layers of Protection Analysis (LOPA).

The higher the SIL, the more serious the potential impact of a failure is, therefore the lower the acceptable failure rate is. SIL certification, within a given system, depends on multiple factors, these include:

• type of technologies;
• system architecture;
• number of system components;
• probability of failure on demand (PFD) of each component;
• diagnostic test intervals.

A product with SIL certification is deemed “suitable for use within a given SIL environment”, in this way the entire system is taken into account. It is worth noting that a device suitable for use in SIL 3 may be redundant if placed in a SIL 2 environment. However, using a product with a SIL level higher than requested can be useful as it automatically increases the T-proof test time intervals up to 10 times.

• What is a T-proof test time? T-proof test time refers to the periodic interval between two proof tests.
• If reduced, for example from two years to one year, SIL capability can be improved and hidden failures can be detected faster.
• What is SIL 3? SIL 3 is one of the SILs defined by the IEC 61508 standard.

SIL 3 is defined by a risk reduction factor of 1.000 – 10.000 of failure on demand and 10-8 – 10-7 for probability of failure per hour. It is a quantitative assessment of the acceptable failure level for a security function.

1. Why is SIL 3 important?
2. The SIL of a Safety Instrumented Function (SIF) in a Safety Instrumented System (SIS) is based on a number of methods such as Safety Layer Matrix (SLM), Layers of Protection Analysis (LOPA) or Fault Tree Analysis (FTA).
3. The above methods take into a

ccount the types of accident that can occur, their probability, the way they are related and their consequences in terms of cost. The recommended SIL level is therefore the appropriate level for the risks that your organisation faces.

• If SIL 3 is deemed the appropriate SIL, it means that SIL 3 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.
• What does SIL 3 mean for device choice?
• SIL 3 is not designed to give a rating of a specific device, but of the function that a device (or a set of devices) performs.
• Is SIL 3 expensive?

Evaluating the cost of a safety function is a difficult task. You need to be mindful that it is not just the upfront cost of implementing it, but also the cost associated with the risk that it mitigates. Implementing and maintaining SIL 3 will incur additional operating costs, it requires a specific skill set to be developed within the operating team and devices rated for SIL 3 use can be more expensive.

Therefore, SIL 3 is only recommended under critical and specific circumstances. However, the cost of not implementing the appropriate SIL significantly outweighs the cost of implementing it. In conclusion SIL 3 is recommended only under special circumstances. Nevertheless, where it is deemed appropriate, SIL 3 is critical to ensuring the adequate safety of an operation.

If you would like to discuss how SIL 3 could help your business please do, : Safety Integrity Level – why does the industry need it?

What does SIL mean testing?

Software-in-the-loop (SIL) is a method of testing and validating code in a simulation environment in order to quickly and cost-effectively catch bugs and improve the quality of the code. Typically, SIL testing is conducted in the early stages of the software development process, while the more complex, costlier hardware-in-the-loop (HIL) testing is done in later stages.

SIL is particularly important in the automotive industry as OEMs move toward building software-defined vehicles that enable features and functions primarily through software.   Each new software program — whether it is related to advanced safety, autonomous driving, user experience or other areas — has thousands of specific requirements, and it is not practical to perform manual testing to make sure the software does what it is supposed to do.

It is prohibitively expensive and time-consuming to physically load software under development into an actual vehicle and test-drive it for the potentially hundreds of thousands of miles needed to make sure the software works in all types of driving conditions.

SIL simulations can be run on any standard desktop computer without requiring the special equipment or test benches needed for HIL testing. This makes it cost-effective to deploy SIL testing across many instances, which reduces testing bottlenecks and speeds up the development process.Because the simulation is being performed entirely in software, the testing can actually go faster than it would in real time. Simulation programs deliver flexibility and repeatability. Testers run multiple simulations, adjusting for a single variable while all other aspects of the scenario remain constant, creating a more effective feedback loop with software developers.SIL helps decouple software and hardware development, allowing software developers to create new features and functions at their own accelerated pace.Organizations can test pieces of code or components of a complex solution as they are being developed rather than waiting for the entire product to be finished.With multithreading, multiple tests can be conducted at the same time rather than sequentially, which also saves time and improves efficiency.The simulations developed for SIL can be reused on HIL tests to monitor physical hardware performance and cross-correlations. The results can be easily shared across development teams from technology providers, OEMs and third parties.

The effectiveness of SIL is dependent on the quality of the modeling software and the test cases and scripts that are written to simulate specific road conditions and driving scenarios. Aptiv has developed a custom logging and visualization tool that enables the recording of live driving data and the visualization of sensor data and vehicle performance.

This enables Aptiv to create accurate test scripts that simulate specific driving scenarios. With automated SIL and HIL testing, Aptiv has been able to slash daily build times by 70 percent. In some extreme cases, the build time has been reduced from 12 hours to only five minutes. The result is faster time to market for key industry applications.

Software-in-the-loop (SIL) is a method of testing and validating code in a simulation environment in order to quickly and cost-effectively catch bugs and improve the quality of the code. Typically, SIL testing is conducted in the early stages of the software development process, while the more complex, costlier hardware-in-the-loop (HIL) testing is done in later stages.

SIL is particularly important in the automotive industry as OEMs move toward building software-defined vehicles that enable features and functions primarily through software.   Each new software program — whether it is related to advanced safety, autonomous driving, user experience or other areas — has thousands of specific requirements, and it is not practical to perform manual testing to make sure the software does what it is supposed to do.

It is prohibitively expensive and time-consuming to physically load software under development into an actual vehicle and test-drive it for the potentially hundreds of thousands of miles needed to make sure the software works in all types of driving conditions.

SIL simulations can be run on any standard desktop computer without requiring the special equipment or test benches needed for HIL testing. This makes it cost-effective to deploy SIL testing across many instances, which reduces testing bottlenecks and speeds up the development process.Because the simulation is being performed entirely in software, the testing can actually go faster than it would in real time. Simulation programs deliver flexibility and repeatability. Testers run multiple simulations, adjusting for a single variable while all other aspects of the scenario remain constant, creating a more effective feedback loop with software developers.SIL helps decouple software and hardware development, allowing software developers to create new features and functions at their own accelerated pace.Organizations can test pieces of code or components of a complex solution as they are being developed rather than waiting for the entire product to be finished.With multithreading, multiple tests can be conducted at the same time rather than sequentially, which also saves time and improves efficiency.The simulations developed for SIL can be reused on HIL tests to monitor physical hardware performance and cross-correlations. The results can be easily shared across development teams from technology providers, OEMs and third parties.

The effectiveness of SIL is dependent on the quality of the modeling software and the test cases and scripts that are written to simulate specific road conditions and driving scenarios. Aptiv has developed a custom logging and visualization tool that enables the recording of live driving data and the visualization of sensor data and vehicle performance.

How far does 100 dB travel?

How Far Away Can This Sound Be Heard? – How far away you can hear a 100 dB sound depends on:

• the sound’s frequency
• how the noise spreads out as the sound travels
• whether or not there are any obstacles between the sound and the listener that may dampen the sound

The further you are from the source of a sound, the more that sound’s intensity will decrease and the less loud you will perceive it. In fact, each time your distance from the source doubles, the sound decreases by 6 dB. If a sound is 100 dB at the source, it will be 94 dB at 1 meter, 88 dB at 2 meters, and so on.

What is a SIL environment?

Supported Independent Living (SIL) is one type of help or supervision with daily tasks to help you live as independently as possible, while building your skills. SIL is the paid personal supports. It includes things like having a person to. help with personal care tasks, or cooking meals.

How do you calculate SPL from SWL?

SIL = SPL = SWL − 11 dB or L I = L p = L W − 11 dB.

What are the three types of SIL?

What Safety Integrity Level (SIL) Means and How to Calculate It – Spotlight on Safety | MSA Corporate Blog The global importance of SIL (Safety Integrity Levels) has grown substantially in the process industries over the years. However, for many end users, systems integrators, and product vendors, SIL is still a somewhat ambiguous concept that often is misinterpreted and incorrectly implemented.

• In order to fully understand SIL and its implications, it is important to grasp the overarching concept known as Functional Safety, and how it applies to Safety Instrumented Systems (SIS) within the process industries.
• What is Functional Safety? Functional Safety, as defined by IEC standard 61508, is the safety that control systems provide to an overall process or plant.

The concept of Functional Safety was developed in response to the growing need for improved confidence in safety systems. Major accidents around the world, as well as the increasing use of electrical, electronic or programmable electronic systems to carry out safety functions, have raised awareness and the desire to design safety systems in such a way as to prevent dangerous failures or to control them when they arise.

1. Industry experts began to address functional safety and formalize an approach for reducing risk in the process plant environment through the development of standards IEC 61508, IEC 61511, and ANSI/ISA 84.
2. Previous safety standards were generally prescriptive in nature, not performance based.
3. An emphasis on quantitative risk reduction, life-cycle considerations, and general practices make these standards different from their predecessors.

Functional Safety is a term used to describe the safety system that is dependent on the correct functioning of the logic solver, sensors, and final elements to achieve a desired risk reduction level. Functional Safety is achieved when every safety function is successfully carried out and the process risk is reduced to the desired level.

1. What is a Safety Instrumented System (SIS)? A Safety Instrumented System is designed to prevent or mitigate hazardous events by taking a process to a safe state when predetermined conditions are violated.
2. Other common terms used are safety interlock systems, emergency shutdown systems (ESD), and safety shutdown systems (SSD).

Each SIS has one or more Safety Instrumented Functions (SIF). To perform its function, a SIF loop has a combination of logic solver(s), sensor(s), and final element(s). Every SIF within a SIS will have a SIL level. These SIL levels may be the same, or may differ, depending on the process.

It is a common misconception that an entire system must have the same SIL level for each safety function. The Meaning of Safety Integrity Level (SIL) SIL stands for Safety Integrity Level. A SIL is a measure of safety system performance, in terms of probability of failure on demand (PFD). This convention was chosen based on the numbers: it is easier to express the probability of failure rather than that of proper performance (e.g., 1 in 100,000 vs.99,999 in 100,000).

There are four discrete integrity levels associated with SIL: SIL 1, SIL 2, SIL 3, and SIL 4. The higher the SIL level, the higher the associated safety level, and the lower probability that a system will fail to perform properly. As the SIL level increases, typically the installation and maintenance costs and complexity of the system also increase.

Specifically for the process industries, SIL 4 systems are so complex and costly that they are not economically beneficial to implement. Additionally, if a process includes so much risk that a SIL 4 system is required to bring it to a safe state, then there is a fundamental problem in the process design that needs to be addressed by a process change or other non-instrumented method.

It is a very common misconception that individual products or components have SIL ratings. Rather, products and components are suitable for use within a given SIL environment but are not individually SIL rated. SIL levels apply to safety functions and safety systems (SIFs and SISs).

• The logic solvers, sensors, and final elements are only suitable for use in specific SIL environments, and only the end user can ensure that the safety system is implemented correctly.
• The equipment or system must be used in the way it was intended in order to successfully obtain the desired risk reduction level.

Just buying SIL 2 or SIL 3 suitable components does not ensure a SIL 2 or SIL 3 system. Risk Management and Selecting a SIS or SIL Level The identification of risk tolerance is subjective and site-specific. The owner / operator must determine the acceptable level of risk to personnel and capital assets based on company philosophy, insurance requirements, budgets, and a variety of other factors.

A risk level that one owner determines is tolerable may be unacceptable to another owner. When determining whether a SIL 1, SIL 2, or SIL 3 system is needed, the first step is to conduct a Process Hazard Analysis to determine the functional safety need and identify the tolerable risk level. After all of the risk reduction and mitigation impacts from the Basic Process Control System (BPCS) and other layers of protection are taken into account, a user must compare the residual risk against their risk tolerance.

If there is still an unacceptably high level of risk, a risk reduction factor (RRF) is determined and a SIS / SIL requirement is calculated. The RRF is the inverse of the Probability of Failure on Demand for the SIF / SIS (see table below). Selecting the appropriate SIL level must be done carefully.

Costs increase considerably to achieve higher SIS / SIL levels. Typically in the process industry, companies accept SIS designs up to SIL 2. If a Process Hazard Analysis indicates a requirement for a SIL 3 SIS, owners will usually require the engineering company to re-design the process to lower the intrinsic process risk.

: What Safety Integrity Level (SIL) Means and How to Calculate It – Spotlight on Safety | MSA Corporate Blog

What is SIL 2 and SIL 3?

Amol Das –

Posts: 14 Rating: (1) Hello, SIL2 & SIL3 are related with PFD and SFF. If we consider a CPU or Field Device then its a specific function of electonic component or device and how it functions. In Safety Instrumented System (SIS), Safety Intergrity Level (SIL) relates to Safety Instrumented Function (SIF).

What is the difference between SIL 2 and 3?

For SIL 2 the system must function as required 99 % of the time or better. For SIL 3 it must work 99.9 % of the time. But note that it is the safety FUNCTION that is SIL-rated – not the hardware that is used as a part of the way to make sure that function is performed.

What is IEC 62061 Safety Integrity Level SIL?

Safety Integrity Level The safety integrity level according to IEC 61508 and IEC 62061, also called SIL, contains three discrete levels which describe the capability of safety relevant components included in a controller to execute a safety function under foreseeable conditions. Product Comparison : Safety Integrity Level

Jack Gloop