European Standard · Machine Safety
ISO 13849 – Safety-Related Parts of Control Systems
ISO 13849 is the international standard specifying safety requirements and guidance for the design and integration of safety-related parts of control systems on machinery, including performance levels used to rate the reliability of safety functions such as emergency stops and interlocked guards.
1. Scope
ISO 13849 applies to the design of safety-related control system components, such as safety relays, light curtains, interlock switches and emergency stop circuits, defining Performance Levels (PL a to PL e) that indicate the ability of the safety function to perform reliably under fault conditions.
2. Exclusions & Related Standards
- Works alongside ISO 12100, which provides the overall risk assessment framework this standard’s control system reliability requirements feed into.
- Relevant to engineering controls that reduce reliance on PPE by improving the reliability of machine safeguarding systems.
- Often referenced in machine-specific type C standards covering particular categories of equipment.
3. Key Requirements & Marking
The standard defines five Performance Levels (PL a, lowest, through PL e, highest), based on factors including the mean time to dangerous failure of components, diagnostic coverage, and system architecture category. Higher-risk safety functions require higher performance levels and more robust, fault-tolerant designs.
4. Testing Overview
Verification involves calculating and validating the achieved performance level through structured analysis of component reliability data, system architecture, common cause failure considerations, and diagnostic coverage, often supported by specialised safety engineering software tools.
5. Selection Guide
Performance level requirements are determined through a risk assessment of the specific hazard the safety function addresses (following ISO 12100 principles), with more severe or frequent hazards requiring higher performance levels and correspondingly more robust control system architectures.
6. Inspection, Care and Maintenance
- Safety-related control systems should be tested periodically according to the manufacturer’s and standard’s validation requirements
- Document any modifications to safety circuits and reassess the achieved performance level after changes
- Ensure diagnostic and monitoring functions built into the safety system remain operational and are not bypassed
- Review performance level requirements whenever the associated risk assessment is updated
7. Frequently Asked Questions
What is a Performance Level (PL) in ISO 13849?
It is a discrete rating from PL a (lowest) to PL e (highest) indicating the ability of a safety-related control system to perform its safety function reliably, based on failure rates, architecture and diagnostic coverage.
How is ISO 13849 different from ISO 12100?
ISO 12100 provides the general risk assessment and risk reduction framework for machinery, while ISO 13849 specifically addresses the reliability and design of the control system components used to implement safety functions.
Who needs to understand ISO 13849?
Machine designers, control system engineers, and safety professionals responsible for specifying, validating or maintaining safety-related control circuits such as emergency stops and interlocked guards.
Does a higher Performance Level always mean better protection?
A higher Performance Level indicates a more reliable safety function for a given hazard, but the appropriate PL should always match the actual risk level identified in the risk assessment rather than defaulting to the highest possible rating.
Does ISO 13849 apply to PPE?
Not directly; it applies to machine control systems, but by improving the reliability of engineering safeguards it can reduce the residual risk that would otherwise require reliance on PPE.