EN ISO 13849-1 Safety of Machinery - Safety-related Parts of Control Systems - Part 1: General Principles for Design

The standard “EN ISO 13849-1 Safety of machinery — Safety-related parts of control systems — Part 1: General principles for design”, which has its basis in a European standard and was later published by the International Organization for Standardization (ISO), defines a methodology for the design and integration of safety-related parts of control systems that perform safety functions and provides related requirements, recommendations and guidance. This includes software design.

This standard applies to safety-related parts of control systems, including their subsystems, for high-demand and continuous operating modes, regardless of the type of technology and energy (e.g. electrical, hydraulic, pneumatic and mechanical). This standard is not applicable to low-demand operating modes. For low-demand operating modes, see the series of standards “IEC 61508 Functional safety of electrical/electronic/programmable electronic safety-related systems”.

Incidentally, this standard does not specify the security functions or required performance levels to be used in specific applications.

This standard specifies a methodology for the design of safety-related parts of control systems without considering whether specific machines (e.g. mobile machines) have specific requirements. These specific requirements can be taken into account in a Type-C standard. Type-C standards (machine safety standards) address detailed safety requirements for a specific machine or group of machines.

This standard does not give specific requirements for the design of products and components that are safety-related parts of control systems. Specific requirements for the design of some components of safety-related parts of control systems are met by applicable ISO and IEC standards.

This standard does not provide specific measures for security aspects (e.g. physical, IT security and cyber security). Security issues may have an impact on security functions. Further information is available in ISO/TR 22100-4 and IEC/TR 63074.

For the purposes of this standard,

• The safety-related part of a control system is that part of a control system that performs a safety function, starting from a safety-related input and ending with the production of a safety-related output. The safety-related parts of a control system start at the point where the safety-related inputs are initiated (including, for example, the actuator cam and the cylinder of a position switch) and end at the output of the power control elements (including, for example, the main contacts of a contactor).
• A machine control system refers to a system of machines that responds to input signals from machine elements, operators, external control equipment, or any combination of these, and produces output signals that cause the machine to behave in the intended manner. A machine control system may use any technology or any combination of different technologies (e.g., electrical/electronic, hydraulic, pneumatic, and mechanical).
• Security requirements specification refers to the specification containing the requirements for security functions that must be met by the security-related control system in terms of the characteristics of the security functions (functional requirements) and the required performance levels.
• Category refers to the classification of the subsystem in terms of its resistance to faults and its behaviour in the event of a fault, achieved by the structural arrangement of parts, fault detection or reliability.
• Performance level refers to the discrete level used to indicate the ability of safety-related parts of control systems to perform a safety function under foreseeable conditions.
• The required performance level expresses the level of performance required to achieve the required risk reduction for each security function.
• Safety integrity level refers to the individual level (one of four possible levels) for specifying the safety integrity requirements of the safety functions to be allocated to safety-related systems. Safety integrity level 4 has the highest safety integrity level and safety integrity level 1 has the lowest level. Only SIL 1 to SIL 3 are considered in this standard.
• Failure refers to an abnormal condition that may result in a reduction or loss of the ability of a functional unit to perform a required function. A failure is usually the result of a failure of the item itself, but may exist without a preceding failure. In this standard, failure means failure resulting from random failure or systematic failure.
• Fault exclusion refers to the exclusion of certain faults within a safety-related part of a control system if this exclusion can be justified by the negligible probability of such faults.

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