IEC 61508 Functional Safety Compliance Certification


The standard applicable to any industry

The standard applicable to any industry


Functional safety is, simply put, “Protecting a user from technology”. It also protects technology from users. More technically, the definition of Functional Safety is “Systems that lead to the freedom from unacceptable risk of injury or damage to the people’s health by the proper implementation of one or more automatic protection functions (often called safety functions). A safety system consists of one or more safety functions.”

A simple example of a functional safety system could be a domestic coffee maker with a sensor that detects the coffee temperature or the volume of coffee in the flask. If the sensor detects the temperature has exceeded a threshold, it switches the heating element off, or if the volume is greater than anticipated, it halts the percolation process. More complex examples may include a railroad crossing barrier or an automated robot in an industrial setting. In the first example, the functional safety system would detect the approach of an oncoming train and lower the barrier. In the other example, the system registers the presence of a person the workspace and puts the robot into a safe state, i.e. stopping it or moving it to a safer position.

A functional safety system is an active part of the system. It will react to predefined triggers and instruct the system to make an active change. Fire resistant doors or clothing are not considered a functional safety system as they perform their function passively.


At its core, functional safety is important because its sole purpose is to protect users from harm. Complex technology is an integral part of our day to day activities, and we demand that they are safe to use. Functional safety is becoming more important in products of all types, industrial and consumer, as the types of controls being used are increasingly more complex and are safeguarding against many more instances.

In manufacturing facilities, functional safety is critical to safe operation. Functional safety systems can give operators far better operational metrics and control of the equipment under use. Functional safety allows manufacturers to operate closer to their margins with confidence in a well-defined functional safety environment. This benefits them in terms of increased efficiencies, fewer downtimes, and the resulting cost savings.


In many instances, certification is required by regulatory authorities. Without certification, a product cannot enter the marketplace. There may be local, national, or international requirements depending upon your product, it’s intended use, and where it is to be marketed. Even when there is no legislative requirement for a component or product to be functional safety certified, it is required by the end user in many cases.

It is also important to remember that some insurance companies may require functional safety certification before offering coverage. In terms of product liability, compliance with standards proves that product/application meets state-of-the-art safety requirements. An important point to remember is that some regulatory authorities and end users, may demand that certification be carried out by an independent, third-part qualified certifier. Demonstration of independent review is important to users’ acceptance of a product; a lack of it may lead to questions of whether the product has been looked at with a fully critical eye.


IEC 61508 is the granddaddy of all functional safety standards and is applicable to all industries. Where there are no industry-specific functional safety standards for products, IEC 61508 standard can be applied. 

According to the IEC, 61508 provides functional safety standards for the lifecycle of electrical, electronic, or programmable electronic (E/E/PE) systems and products. It addresses those parts of a device or system that perform automated safety functions, for example, sensors, control logic, actuators, and micro-processors. It provides a rigorous quantitative approach to risk reduction and can be applied across many industries.

IEC 61508 is a risk-based standard – meaning that the risk of hazardous operational situations is qualitatively assessed, and safety measures are defined to avoid or control systematic failures and to detect or control random hardware failures or mitigate their effects.

The standard helps determine Safety Integrity Levels (SIL). There are four SILs: SIL1, SIL2, SIL3 and SIL4, the risk of failure becoming greater with each respective SIL. Conducting a risk assessment defines which SIL is required. A SIL is determined by examining the Systematic Capability, Architecture Constraints, and the Probability of Dangerous Failure. The table below shows the SIL classification by either probability of failure on demand, or probability of failure per hour. 


Low Demand Mode:
Average Probability of Failure on Demand

High Demand or Continuous Mode:
Probability of Dangerous Failure per Hour


≥ 10−2 to < 10−1

≥ 10−6 to < 10−5


≥ 10−3 to < 10−2

≥ 10−7 to < 10−6


≥ 10−4 to < 10−3

≥ 10−8 to < 10−7(1 dangerous failure in 1140 years)


10−5to < 10−4

≥ 10−9to < 10−8

(Side note: SILs with regards to IEC 61508 are different from Safety Integrity Levels in other standards and care should be taken to not confuse them)

A product, process, or system that has been certified as IEC 61508 compliant has demonstrated that it has satisfied all the requirements of the standard.

Industry specific variants

As products, processes, or systems increased in complexity, associated functional safety requirements increased in step. It became apparent to many that requirements for IEC 61508 didn’t always adequality address industry-specific challenges. Industry-specific functional safety standards are now commonplace in many other industries, for example:

  • Industrial
  • Transportation
  • Buildings
  • Medical devices
  • Household appliances
  • Energy systems and providers


Safety Integrity Levels are defined in most other functional safety standards. However, the determination of SILs can different between different standards, and care should be taken to not confuse them. This becomes even more interesting in EN 17206 as safety standard risk assessments are typically written with manufacturing equipment in mind, and these don’t translate well for entertainment settings. EN 17206, Annex D does however provide an, “entertainment industry calibration”, to help provide direction.


When developing safety systems software, tools become more and more important. However, the software tool used in development needs to comply with predefined criteria. The requirements of software tool qualification in functional safety development projects are therefore of concern to many industry stakeholders.

In certification projects, this topic is often an area of risk and uncertainty as more and more certified tools are available, but it’s not always clear which tool would lead to the highest benefit in the development project. This can lead to drawn-out discussions during a project lifecycle, causing costly delays.

Tool certification is used for development in safety-related environments such as in the automotive, automation, railway, medical or nuclear sector.

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