B11.26 – Functional Safety for Equipment: General Principles for the Design of Safety-Related Parts of Control Systems for Machinery

B11.26 — Functional Safety for Equipment: General Principles for the Design of Safety-Related Parts of Control Systems for Machinery

The B11.26 standard (ANSI B11.26-2018, reaffirmed and with newer editions issued) provides both the requirements and guidance for implementation of safety-related control functions (also referred to as “functional safety”) in machines. These control systems may involve electrical, electronic, pneumatic, hydraulic or mechanical components and are used as risk-reduction measures when identified hazards are mitigated through a safety function. :contentReference[oaicite:1]{index=1}

Scope & Purpose

B11.26 applies when a control system is used as part of a risk reduction measure — in other words, when the risk assessment has identified one or more safety functions required to reduce a hazard to an acceptable level. The standard outlines how these safety-related parts of control systems (SRP/CS) should be designed, structured and validated. It aligns with ISO 13849-1 and similar functional safety frameworks. :contentReference[oaicite:2]{index=2}

Key Concepts & Principles

• Safety Function: A function whose failure would increase the risk of harm. B11.26 requires identification and specification of safety functions. :contentReference[oaicite:3]{index=3}
• Control Reliability: The machine must remain safe even if a fault or failure occurs in the SRP/CS. B11.26 defines design strategies including redundancy, monitoring, diagnostics, and failure-tolerant architectures. :contentReference[oaicite:4]{index=4}
• Architecture & Performance Levels: Although B11.26 doesn’t prescribe a specific architecture, it references the use of ISO 13849-1 (and thus performance levels PL) as a technical basis for SRP/CS. :contentReference[oaicite:5]{index=5}
• Lifecyle Responsibilities: The standard clarifies responsibilities across suppliers, integrators/modifiers and users for safe design, installation, commissioning, operation, maintenance, modification and decommissioning of SRP/CS. :contentReference[oaicite:6]{index=6}
• Verification & Validation: After implementation, safety functions must be verified and validated so that they meet the specified performance requirements and maintain integrity over the machine lifecycle. :contentReference[oaicite:7]{index=7}

Why It Matters

In modern machinery, many hazards are controlled via safety-related control systems — for example, presence-sensing devices, safe speed monitoring, door interlocks, light-curtains, and machine motion control systems. Simply installing a guard is often insufficient for complex machines. \
B11.26 ensures that such control systems are designed correctly, with sufficient reliability and integrity, so that they work when needed and maintain protection during faults or unusual conditions. This translates to reduced risk of injury and better alignment with recognized good engineering practice.

Practical Implementation Tips

• Start your machine risk assessment and identify any required safety functions earlier in the lifecycle (design phase) and decide which will be fulfilled by SRP/CS.
• When implementing SRP/CS, reference ISO 13849-1 to determine required performance level (PL) based on risk estimation, then design your control architecture accordingly.
• Verify diagnostic coverage, response time, fault-detection mechanisms and avoid single-point failures in the SRP/CS.
• Document architecture, failure mode analysis, validation testing and periodic re-validation of the safety function’s performance.
• Ensure any modifications to the machine’s control system initiate a new risk assessment and re-validation of the safety functions as per B11.26’s lifecycle requirements.

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