ISO 13851:2019

Overview

ISO 13851:2019 - "Safety of machinery - Two-hand control devices - Principles for design and selection" specifies safety principles for two‑hand control devices (THCDs). It defines the functional and design requirements that ensure a THCD reliably depends on simultaneous hand actuation to generate an output signal, addresses prevention of accidental operation and defeat, and gives guidance for selection based on a risk assessment. The standard applies to all THCDs regardless of energy type, whether supplied fully assembled or assembled by a machine manufacturer, and supersedes the 2002 edition.

Key topics and requirements

• Definition and scope: What constitutes a THCD and what is outside scope (not enabling devices, hold‑to‑run, special control devices; not applicable to pre‑2019 THCDs).
• Design requirements: Principles for simultaneous two‑hand actuation, relationship between hand actuation and output signals, cessation and re‑initiation of outputs, and synchronous actuation.
• Prevention of defeat and accidental actuation: Measures to stop defeat by using one hand, forearms, elbows or other body parts; requirements to avoid blocking and unintended activation.
• Safety functions: Prevention of unexpected start‑up, releasing actuators, and ensuring synchronous actuation.
• Ergonomics and environmental considerations: Human factors, operating conditions, enclosures and selection of control actuating devices.
• Verification and validation: Visual inspection, performance tests, measurements and specific tests for prevention of defeat (Annex A is normative).
• Marking and documentation: Requirements for marking and for providing installation, operating and maintenance instructions.
• Limitations: The standard gives guidance but does not prescribe required safety distance to danger zones nor which THCD type must be used for a specific machine - selection should follow a risk assessment.

Practical applications and users

• Who uses it: Machine manufacturers, integrators, safety engineers, health & safety regulators, maintenance/service providers, and standards authors preparing type‑C machine standards.
• Where applied: Machines where operator protection requires two‑hand control to prevent access to hazardous zones - stamping presses, cutting or forming equipment, test rigs, and other applications where holding controls with both hands reduces reach‑in risk.
• Why use it: To select and design THCDs that meet internationally accepted safety principles, reduce operator injury risk, ensure compliance with safety‑related control system requirements (linked to ISO 13849‑1 PL or IEC 62061 SIL), and support conformity assessment and documentation.

Related standards

• ISO 12100 (risk assessment and risk reduction)
• ISO 13849‑1 and ISO 13849‑2 (safety‑related parts of control systems)
• IEC 62061 (functional safety of electrical/electronic control systems)
• ISO 13855 (positioning of safeguards)

Keywords: ISO 13851:2019, two‑hand control device, THCD, safety of machinery, design and selection, prevention of defeat, risk assessment, verification and validation.