IEC 61508 is the foundational international standard for functional safety of electrical, electronic, and programmable electronic (E/E/PE) safety-related systems, published by the International Electrotechnical Commission (IEC). It defines a systematic framework for achieving and demonstrating the required level of safety for systems where failure could lead to hazardous events, and is directly relevant to battery management systems (BMS), particularly the safety monitoring and protection functions embedded in BMS firmware and hardware.
Published by: International Electrotechnical Commission (IEC)
Current edition: IEC 61508:2010 (2nd edition, Parts 1–7)
Sector-specific derivatives: ISO 26262 (automotive), IEC 62061 (machinery), IEC 61511 (process industry)
Scope
IEC 61508 applies to all safety-related systems that use electrical, electronic, or programmable electronic technology to carry out one or more safety functions. In the battery domain, this covers BMS hardware and firmware that performs protective functions — overvoltage protection, overcurrent protection, overtemperature cut-off, and state estimation algorithms that determine safe operating limits. The standard provides a generic framework applicable across all industries; sector-specific standards such as ISO 26262 (automotive) were derived from IEC 61508 for specific application domains.
Safety Integrity Levels
The central concept of IEC 61508 is the Safety Integrity Level (SIL), a discrete level (SIL 1 through SIL 4) that specifies the required probability of failure on demand for a safety function. SIL 1 is the least stringent (probability of failure on demand between 10⁻¹ and 10⁻²) and SIL 4 is the most stringent (10⁻⁴ to 10⁻⁵). BMS protective functions in industrial and grid-connected BESS typically target SIL 1 or SIL 2 depending on the consequence severity of the hazard being mitigated.
Achieving a given SIL requires a combination of hardware reliability (meeting quantitative failure rate targets) and software development rigor (following defined processes for requirements, design, coding, testing, and verification). The standard’s safety lifecycle framework covers the entire lifecycle from hazard identification and risk assessment through to decommissioning.
Relevance to Battery Engineering
For BMS engineers developing safety-critical protective functions for industrial BESS, grid storage, or high-voltage EV applications, IEC 61508 provides the overarching framework for demonstrating that protective functions achieve the required reliability. Many industrial customers and grid operators require evidence of SIL compliance for BMS protective functions as part of their procurement and type approval processes. Understanding IEC 61508 concepts — particularly SIL assignment, hardware fault tolerance, and software safety requirements — is essential for BMS engineers working on applications where battery failure could have serious safety consequences.
Disclaimer: This is not a definitive guide, just an indication and it is important that you always go back to the source for legislation.
See also: Functional Safety – the SIL framework this standard defines is the basis most BMS safety-case work, including automotive ASIL classification, builds on. A related performance-level-based approach for machinery safety functions is defined in ISO 13849., Functional Safety Fundamentals & Standards