IEC 61508 vs IEC 62061 vs ISO 13849 — which applies to your robot?

"Which standard applies to my robot?" is the most common question compliance teams ask when they start thinking about functional safety. The answer depends on what kind of safety system you're building — and most teams discover they've been using the wrong standard.

Three standards matter. Here's how they relate.

IEC 61508 is the parent standard for functional safety. Published by the International Electrotechnical Commission, it covers any safety-related system that uses electrical, electronic, or programmable electronic components. It uses Safety Integrity Levels (SIL 1 through SIL 4) to quantify reliability. It's the deepest, most rigorous framework — and the one that all sector-specific standards derive from. If your architecture is novel and no sector-specific standard covers it, IEC 61508 is your reference.

IEC 62061 is the machinery-specific interpretation of IEC 61508. It also uses SIL. It's designed for complex electrical and electronic safety systems in machinery — the kind that involve programmable electronics, safety PLCs, and software-based safety functions. If your machine has a safety function implemented in software running on a programmable device, IEC 62061 is the appropriate standard. It accepts components that are pre-certified to IEC 61508 as building blocks.

ISO 13849 is the simplified standard for machinery safety. It predates IEC 62061 and uses its own metric: Performance Levels (PL a through PL e), rather than SIL. It covers mechanical, hydraulic, pneumatic, and simple electrical safety systems. The standard uses architectural categories (B, 1, 2, 3, 4) rather than the more detailed hardware fault tolerance and diagnostic coverage calculations of IEC 61508. It was designed for an era when safety functions were implemented with relays, contactors, and hardwired logic.

The mapping between the two metrics is well established. PL c corresponds roughly to SIL 1. PL d corresponds to SIL 2. PL e corresponds to SIL 3. The probability ranges for dangerous failure per hour align between the standards.

Here's where it gets interesting for robotics. Most robot safety systems today are designed to ISO 13849. Machinery engineers know it well, certification bodies are comfortable with it, and for traditional industrial robots with deterministic control, it works. But ISO 13849 has a limitation that matters for Physical AI: it was not designed for complex programmable electronics with self-evolving behaviour. The CAPIEL white paper on the new editions of both standards notes that subsystems using complex components designed according to ISO 13849 can only be used if they also meet the requirements of IEC 61508 or an applicable functional safety product standard.

An engineer at Analog Devices put it plainly in 2022: machinery engineers tend to avoid IEC 61508, but the guidance from IEC 62061 itself suggests that for more complex systems — robots, cobots, mobile robots — IEC 61508 or IEC 62061 should be used rather than ISO 13849 alone.

For any team building a robot with AI-based safety functions, the question isn't whether to use ISO 13849 or IEC 61508. It's at which layer each standard applies. ISO 13849 may cover your mechanical safety guards and emergency stop circuits. IEC 62061 covers your programmable safety logic. And if your architecture is novel — for instance, a safety system that combines redundant channels with independent hardware monitoring — IEC 61508 is the only standard with the depth to certify it.