Functional safety

There are increasing numbers of electrical or electronic devices and systems in all areas of life today. Factors such as hardware or software errors, human error, environmental influences such as temperature or wind can lead to malfunctions and damage to living creatures or the environment, which is why safety mechanisms must take precisely these factors into account. One example from the rail domain could be the passenger door of a rail vehicle: it must be ensured, for example, that the door exhibits the following behaviour:

• Only opens once the vehicle is stationary
• Does not close while people are still entering
• Closes before the train departs
• Does not open during the journey

Functional safety is part of the complete system. The IEC (International Electrotechnical Commission) has described the complete basic lifecycle of safety-critical systems in its IEC 61508 standard.

The IEC 61508 serves in the development of the following systems:

• Electrical systems
• Electronic systems
• Programmable electronic systems

These systems (E/E/PE) are divided into 4 (or actually 5) requirements or risk classes in respect of their hazard potential (Safety Integrity Levels / SIL).
IEC 61508 enables the creation of international product and application-specific standards, which deal with safety-critical E/E/PE systems. Here are some examples.

On the basis of a risk analysis, hazards can be identified, which can be resolved in the form of proofs of safety. Risks that cannot be processed any further then enter the chain of evidence as residual risks. Motivations for verifying functional safety might be the statutory requirements for bringing a product to market or the manufacturer’s product liability.

The implementation of IEC 61508 in companies, their products and processes, is characterised by its high degree of complexity. Numerous work stages are required from an initial assessment, analysis, documentation, development of a safety plan, its implementation, communication and implementation all the way through to validation.