Overview
ISO/TS 19837:2018 - "Safety of machinery - Trapped key interlocking devices - Principles for design and selection" specifies principles for the design, selection and application of trapped key interlocking devices and systems for machinery. It covers safety-related aspects of trapped key interlocks (independent of energy type) and is intended to be used in conjunction with ISO 14119. ISO/TS 19837:2018 does not include testing requirements (testing documents are listed in the Bibliography).
Key topics and technical requirements
The technical specification addresses practical and design-focused topics relevant to trapped key interlocks. Major subjects include:
- Operating principles and typical system forms - functional decomposition into isolation control, intermediate transfer and access control.
- Device definitions and components - terms such as key, access lock, bolt lock, key exchange device, timed delay device, solenoid-controlled switch, valve lock, actuator, and personnel key.
- Design requirements - device architecture, positive mechanical action, endurance/strength, resistance to shock and vibration, mechanical life, and key retention.
- Systematics and safety analysis - guidance on FMEA/FTA, validation of required Performance Levels (referencing ISO 13849-1/2), and measures to minimize defeat or misuse.
- Clearances and creepage distances, and design aspects for isolation control (power interlocking vs control interlocking).
- Access control details - escape release, emergency release, and auxiliary release considerations.
- System configuration - key coding, key transfer plans, and device selection guidance.
- Information for use - documentation and marking expected for safe operation.
- Informative annexes: examples of devices, typical FMEA failure modes, safety-function validation guidance and selection advice.
Practical applications
ISO/TS 19837:2018 is applied wherever trapped key interlocks are used to manage machine safety and access, for example:
- Locking out power or isolating hazardous motion during maintenance.
- Interlocking valves (locked open/locked closed) in fluid or process systems.
- Controlled access to safeguarded areas, multi-step maintenance procedures using key transfer plans.
- Integrating mechanical interlocks with electrical controls (solenoid-controlled switches) and safety-related control systems.
Who should use this standard
- Safety engineers and machine designers specifying interlock architectures.
- OEMs and machine builders selecting trapped key devices and key transfer schemes.
- Plant maintenance and safety managers creating lockout/tagout procedures.
- Interlock manufacturers and system integrators designing compliant products and installations.
- Compliance officers performing risk assessments and validation versus ISO 13849.
Related standards (short)
- ISO 14119 - Interlocking devices associated with guards (principles for design and selection) - always applies in conjunction with ISO/TS 19837.
- ISO 13849-1 / ISO 13849-2 - Safety-related parts of control systems (design and validation).
- IEC 60947-1 - Low-voltage switchgear and controlgear (general rules).
Keywords: ISO/TS 19837:2018, trapped key interlocking, trapped key interlock, safety of machinery, ISO 14119, key transfer plan, isolation control, access control, valve lock.