Safety Integrated – Overview

Safety standards

Safety means providing protection from a wide range of safety hazards

Basic standards for Safety controllers and control components

Safety means providing protection from a wide range of safety hazards

Because the causes of safety hazards, and thus the technical measures required for their prevention, are wide and varied, it is now usual to differentiate between different types of safety, e.g. by specifying the cause of any possible safety hazard. For example , we speak of "electrical safety" when referring to the need for protection against safety hazards from electricity or "functional safety" if safety depends on a function being correctly executed.

In order to achieve the functional safety of a machine or plant, the safety-relevant parts of the protection or control devices must be functioning properly and, in the event of a fault, ensure that the plant reliably switches to/remains in safe mode. This requires special measures and techniques that comply with the specifications of the relevant standards.

The requirements for achieving functional safety are based on the following fundamental aims:

Prevention of systematic faults and failures.
This is achieved by means of a systematic and controlled development process and the application of proven safety principles during design and implementation
Mastering systematic and random faults and failures.
This is achieved by means of properties integrated in the system, such as fault tolerance, automatic fault detection and the ability to react in a defined manner if faults are detected.

The measure of achieved functional safety is calculated from the probability of hazardous failures, the fault tolerance and the quality, which form the basis for ensuring the elimination of systematic faults. It is expressed by different terms in the standards. In IEC 61508: "Safety Integrity Level" (SIL), in EN 954: "Categories" and in DIN V 19250 and DIN V VDE 0801: "Requirement categories" (AK).

Due to the wide range of technical criteria contained in EN 954-1:1996 and IEC 61508, it is not possible to make a direct allocation between categories and SIL as a measure of the safety performance. However, it is a recognized practice that safety systems with electronics that fulfill IEC 61508 for SIL 1 also fulfill Cat. 1 and 2 according to EN 954. However, while systems that fulfill SIL 2 or SIL 3 also fulfill Cat. 3 or 4, this does not work in reverse. Fulfillment of Cat. 3 does not automatically mean fulfillment of SIL (see Draft IEC 62061).

Basic standards for safety-related controllers and control components

Basic standards

The basic standards for the implementation of safety-related controllers and control components are as follows:

EN 954/ISO 13849:
Safety of machines – safety-related parts of controllers
IEC/EN 61508:
Functional safety of safety-related electric, electronic and programmable electronic systems

Legal position

EN 954

The EN 954-1 is harmonized under the EC Machine Directive. However, for complex (programmable) electronics with safety functions, additional standards (e.g. EN 61508) must be applied in order to fulfill the currently acknowledged level of technology.

IEC/EN 61508

The EN 61508 standard series for functional safety, which has been absorbed under IEC 61508 by the European Standards Organisation CENELEC, was ratified by the CENELEC in 2001. It will be accepted in the German DIN Standards as DIN EN 61508 (VDE 0803). These standards describe the current level of technology, however compliance with them is voluntary and not binding. The DIN V VDE 0801 will be retracted in 2004.

The EN 61508 is not harmonized under an EU Directive. It does not therefore support automatic presumption of compliance with the protection objectives of a Directive. However, manufacturers of a Safety technology product may also use EN 61508 for the fulfillment of the basic requirements of European Directives in their new form, e.g. in the following cases:

There is no harmonized standard for the relevant area of application. In this case, manufacturers may use EN 61508. However it has no presumptive effect.
A harmonized European standard (e.g. EN 954, EN 60204-1) refers to IEC/EN 61508. This ensures compliance with the relevant requirements of the Directives ("applicable standards"). If manufacturers use EN 61508 as defined by this reference competently and responsibly, they utilize the presumptive effect of the standard responsible for the reference.