Performance Level (PL) is a rating from PL a to PL e under ISO 13849-1 that describes how reliably the safety-related parts of a machine control system perform a safety function.
Performance Level (PL) is a rating defined in ISO 13849-1, from PL a (lowest) to PL e (highest), that describes the ability of safety-related parts of a machine control system to perform a safety function under foreseeable conditions.
A safety function is something the control system does to keep people safe, such as stopping a machine when an interlocked guard opens, responding to an emergency stop, stopping when a light curtain beam is broken or limiting a robot to a safe speed. PL answers a practical question: how likely is it that this function fails dangerously when it is needed?
Performance Level matters to machine builders, integrators, controls engineers and plant safety teams. It applies across manufacturing, packaging, automotive, food processing, robotics and any setting where electrical, pneumatic, hydraulic or programmable controls are part of machine guarding. Safety devices are engineering controls, and PL is how you judge whether the control behind them is good enough for the risk.
Each PL corresponds to a range of average probability of dangerous failure per hour (PFHd):
The required PL comes from a risk graph applied to each safety function. The graph uses three parameters:
A serious injury with frequent exposure and little chance of avoidance points to PL e. Minor, infrequent, avoidable hazards point to PL a. The inputs come from a machine risk assessment under ISO 12100.
The designer then shows the actual system meets or exceeds PLr. The achieved PL depends on:
ISO 13849-1 is titled "Safety of machinery, Safety-related parts of control systems, Part 1: General principles for design." The current edition is ISO 13849-1:2023. ISO 13849-2 covers validation, including fault lists and the analysis and testing needed to confirm the design. Many engineers use SISTEMA, a free tool from the German IFA, to calculate achieved PL.
IEC 62061 is a related functional safety standard for machinery that uses Safety Integrity Levels (SIL 1 to SIL 3) instead of PL. The two scales map roughly: PL d is about SIL 2, and PL e is about SIL 3.
OSHA does not mandate a specific Performance Level. US consensus standards do reference it. ANSI B11.26 gives guidance on functional safety for machine control systems. ANSI B11.19 and the robot standard ANSI/A3 R15.06 reference ISO 13849 for the performance of safeguarding controls.
ISO 13849-1 is a harmonized standard used to show conformity with the Machinery Directive 2006/42/EC. The Machinery Regulation (EU) 2023/1230 replaces the directive from January 20, 2027. Builders selling into the EU should check which edition is listed as harmonized at the time of placing the machine on the market.
A food packaging plant added a robotic case packer with an interlocked access gate. The integrator wired the gate switch through a single standard relay. During startup, a technician found the relay contacts had welded closed, so the robot kept moving with the gate open. No one was hurt, but the near miss stopped the project.
The plant's risk assessment rated the hazard as serious with frequent access and low chance of avoidance, which set PLr at PL d. The integrator redesigned the circuit with a dual-channel interlock, a safety relay with monitoring and a Category 3 architecture, then verified PL d in SISTEMA. The plant now requires PL calculations and validation records before accepting any new machine.
PLr is the required Performance Level set by the risk assessment for a safety function. PL is the level the actual control system achieves. The achieved PL must be equal to or higher than PLr.
There is no single answer. The required PL comes from the risk assessment for that machine. Many e-stop functions end up at PL c or PL d, but it depends on severity, exposure and avoidance.
PL comes from ISO 13849-1 and SIL comes from IEC 62061. They measure similar things. Roughly, PL d corresponds to SIL 2 and PL e corresponds to SIL 3.
No. OSHA does not require a specific Performance Level. US consensus standards such as ANSI B11.19 and ANSI/A3 R15.06 reference it, and it is widely used as good engineering practice.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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