ISO 13849-1:2023

Overview

ISO 13849-1:2023 - "Safety of machinery - Safety-related parts of control systems - Part 1: General principles for design" defines a comprehensive methodology for designing and integrating safety-related parts of control systems (SRP/CS) that perform safety functions in machinery. The standard covers hardware and software design for SRP/CS used in high demand and continuous modes of operation and is technology‑neutral (electrical, hydraulic, pneumatic, mechanical). It does not apply to low‑demand operation (see IEC 61508) and does not set application‑specific safety functions or required performance levels (PLr).

Key topics and technical requirements

ISO 13849-1:2023 organizes practical requirements and guidance around the full SRP/CS lifecycle:

• Risk assessment and risk reduction: linkage between machine risk assessment and SRP/CS requirements.
• Safety requirements specification (SRS): identifying safety functions, detailing performance needs and integration information.
• Performance level (PL) evaluation: methodology to determine achieved PL and correlation with SIL concepts; includes architectural categories and criteria for PL assessment.
• Reliability metrics: emphasis on Mean Time to Dangerous Failure (MTTFD), Diagnostic Coverage (DC) and Common Cause Failures (CCF) when calculating PL.
• Software safety: requirements for safety‑related embedded software (SRESW), safety‑related application software (SRASW), and concepts such as Limited Variability Language (LVL) and Full Variability Language (FVL).
• Verification and validation: analytical and test‑based validation plans, fault lists, measurement accuracy, and validation records.
• Design considerations: decomposition into subsystems, combination rules, fault exclusions, well‑tried components.
• Documentation and maintainability: technical documentation, information for integration and use, and validation maintenance.
• Guidance annexes: informative annexes include MTTFD calculation, simplified PL estimation, EMI immunity, software systematic failure avoidance, and examples.

Note: ISO 13849‑1:2023 does not prescribe product/component design details or address security measures (see ISO/TR 22100‑4 and IEC/TR 63074 for security implications).

Applications and who uses it

ISO 13849‑1 is used by:

• Machine designers and OEMs to specify and implement SRP/CS that meet required PL.
• Control system engineers and software developers designing safety controllers or safety functions.
• System integrators who combine subsystems to achieve an overall safety integrity.
• Safety assessors, test labs and certification bodies for verification and validation evidence.
• Maintenance and commissioning teams needing documentation and maintainability guidance.

Typical applications include industrial machinery safety controls, robotic safety systems, safety PLCs, and interlocking systems where continuous or high-demand safety performance is required.

Related standards

• IEC 61508 (functional safety / low‑demand mode reference)
• ISO/TR 22100‑4 and IEC/TR 63074 (security aspects affecting safety)
• Relevant Type‑C standards for specific machinery categories

ISO 13849‑1:2023 is essential for implementing robust, auditable safety control systems and for aligning machine safety design with internationally accepted performance and validation practices.