Performance Level (PL)
Measure
Topic overview
Quick facts
PL is determined by the combination of category (the architecture and its fault behavior), (mean time to dangerous failure of each channel), diagnostic coverage, and measures against common-cause failure.
PL e provides the highest risk reduction and is broadly comparable to 3 for machinery applications; PL d, comparable to SIL 2, is the workhorse level for most industrial machinery and robot cell safety functions.
The category concept is what distinguishes ISO 13849 from purely probabilistic approaches. Category B and 1 are single-channel with no or basic diagnostics; category 2 adds test channels; categories 3 and 4 require redundancy such that a single fault does not cause loss of the safety function, with category 4 additionally requiring fault accumulation to be controlled.
A required PL (PLr) is set during risk assessment using the standard's risk graph, and the achieved PL of the implementation must meet or exceed it.
ISO 13849 deliberately packages the reliability math into lookup tables and bands so that machine builders without reliability engineers can apply it. Software tools such as SISTEMA automate the calculation from component data supplied by manufacturers, which has made PL the de facto language of machinery safety circuits worldwide.
Performance Levels (PFH per ISO 13849-1)
Why Performance Level matters
PL is the currency in which machinery safety circuits are specified, bought, and audited. Integrators, end customers, and CE conformity assessments all ask for the PLr of each safety function and evidence that the design achieves it. Choosing components without manufacturer safety data (, B10d values) makes the calculation impossible and forces redesign.
For robot cells specifically, ISO 10218 sets PL d category 3 as the default requirement for most safety functions, so that single decision shapes the entire control architecture.
How Performance Level is applied
ISO 13849 design procedure
The machine builder's risk assessment assigns a PLr to each safety function using severity, exposure, and avoidance parameters. The designer then selects an architecture category, gathers component reliability data from datasheets or manufacturer libraries, and computes the achieved PL, usually in SISTEMA or an equivalent tool.
Validation per ISO 13849-2 then confirms by inspection and fault-injection testing that the assumed fault behavior holds in the real circuit.
Assessors and auditors look for the risk assessment behind each PLr, the calculation file with traceable component data, evidence that common-cause failure scoring was actually justified rather than defaulted, and validation records showing the circuit was tested against the fault list.
Performance Level pitfalls to avoid
Standards related to Performance Level
Performance Level is defined and governed by ISO 13849-1 - defines performance levels (pl) for safety functions implemented in control systems, including pneumatic and hydraulic parts.
Cross-sector integrity alignment (approximate)
| ISO 13849 PL | IEC 61508 SIL | ISO 26262 ASIL | EN 50128 SW-SIL |
|---|---|---|---|
| PL a | no SIL | QM / ASIL A | SIL 0 |
| PL b / c | SIL 1 | ASIL A / B | SIL 1 |
| PL d | SIL 2 | ASIL B / C | SIL 2 |
| PL e | SIL 3 | ASIL D | SIL 3 |
Performance Level by industry
Industrial Machinery programs lean on Performance Level because the sector covers fixed and mobile machinery, packaging lines, and manufacturing equipment.
In robotics & automation, Performance Level comes up in nearly every certification conversation: industrial robots, cobots, amrs, and automated warehousing systems.
Ask our team about Performance Level
Ben TwomblyFounder & CEOLeads CSA's functional-safety, certification, and engineering programs for safety-critical products and organizations. His assessor-side background informs practical programs that connect standards, engineering work, and credible evidence.
Tom CyrPrincipal Safety Engineer, IFSPSupports industrial and rail functional-safety programs with safety analysis, requirements, lifecycle planning, and certification-readiness guidance.Performance Level: related terms
How each connects to Performance Level:
SIL is the natural next concept after Performance Level; assessors expect teams to connect the two.
MTTFd is the natural next concept after Performance Level; assessors expect teams to connect the two.
Safety Function is governed by ISO 13849-1 as well, which is why the two show up together in audits.
ISO 13849-1 connects the two: Performance Level and Safe Torque Off are assessed against the same lifecycle.
Functional Safety Certification is governed by ISO 13849-1 as well, which is why the two show up together in audits.
Understanding Performance Level is easier with Functional Safety as context, and vice versa.
Understanding Performance Level is easier with Risk Assessment as context, and vice versa.
Teams working on Performance Level typically encounter Hierarchy of Risk Reduction in the same program.