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Machinery Functional Safety Performance Level (PL) Sizer

Under the UK Supply of Machinery Regulations and PUWER 98 Reg 19, safety-related control circuits (E-stops, interlocks, light curtains) must achieve a Performance Level matching the assessed hazard risk. This tool evaluates Required Performance Level (PLr) via the ISO 13849-1 risk graph and calculates Achieved PL from system Category, MTTFd, and Diagnostic Coverage.

Designated Safety Standard Gate: A safety function satisfies BS EN ISO 13849-1 when Achieved PL ≥ Required PLr and Common Cause Failure (CCF) scoring achieves ≥ 65 points for redundant architectures.

Part A: Risk Graph Evaluator (Determines PLr)Severity of Injury (S) Frequency / Exposure Time to Hazard (F)Possibility of Avoiding Hazard (P)

Part B: Control System Architecture (Achieved PL)Designated Architecture CategoryPhysical circuit architecture per ISO 13849-1 Section 6.2.Mean Time to Dangerous Failure (MTTFd)Average Diagnostic Coverage (DCavg)Common Cause Failure (CCF) ScoreMinimum 65 points required for multi-channel Cat 2, 3, and 4 (Annex F).

Safety Function Compliance

Required Performance Level (PLr)PL e

Achieved Performance Level (PL)PL e

BS EN IEC 62061 SIL EquivalentSIL 3

Probability of Dangerous Failure / Hour (PFHd)≥ 10⁻⁸ to < 10⁻⁷

Designated ArchitectureCategory 3

Common Cause Failure (CCF) GateCOMPLIANT (75 pts ≥ 65)

Evaluating functional safety compliance...

ISO 13849-1 PERFORMANCE LEVEL SCALE

PL a

PL b

PL c

PL d

PL e

Show Full Mathematical Derivation (AM2 Working Standard)

BS 7671:2018+A4:2026

AM2 PORTFOLIO & DESIGN AUDIT FORMATTRANSPARENT FIRST-PRINCIPLES MATHS

Worked Example & Engineering Rationale

Scenario: An automated packaging cell has a high-speed robotic palletiser. The risk assessment identifies:

Severity (S2): Severe crushing hazard resulting in fatality or irreversible disability.
Frequency (F2): Frequent operator access required (loading wrap multiple times per shift).
Possibility (P2): High-speed robot envelope with scarcely possible evasive reaction time.
Risk Graph Result: S2 + F2 + P2 → PLr e (Highest performance level required).
Hardware Design Verification: The engineer specifies a Category 4 safety circuit with dual force-guided safety relays, redundant feedback monitoring contacts (High DC ≥ 99%), and premium safety contactors (MTTFd High). CCF score evaluates to 75 points.
Verdict: Achieved PL is PL e. Since Achieved PL (e) ≥ PLr (e), the design complies with BS EN ISO 13849-1 and the Supply of Machinery Regulations.

CE / UKCA Marking & Technical File: For machinery placed on the UK or EU market, documentation proving the achieved PL (including component B10d data, failure rates, and validation test sheets per ISO 13849-2) must be preserved in the machine statutory technical file for a minimum of 10 years.

Designated Standards: BS EN ISO 13849-1:2023 • BS EN ISO 13849-2 • BS EN IEC 62061:2021 • PUWER 1998 Reg 19