'ISO/TS 19837:2018 - Safety of Machinery – Trapped Key Interlocking Devices – Principles for design, selection and configuration' is the first international ISO document devoted specifically to trapped key interlocking and answers many of the questions that arise relating to performance levels, key coding and power interlocking. It is a significant step forward that will provide more choice for users of interlock devices and systems.
Trapped key interlocking has its roots in the rail and power distribution industries, where sequential control was, and still is, critical to safe, continuous operation. In the 1960s trapped key interlocking was gradually utilised by the manufacturing sector, where it was necessary to isolate machinery before gaining access.
Machinery with multiple energy sources and access points can be easily safeguarded using trapped key interlocks. Fortress Interlocks has developed specialised products that can isolate air and hydraulic supplies as well as electrical power, in the correct sequence, before allowing access points to be opened.
When 'ISO 14119:2013 Safety of Machinery – Interlocking device associated with guards, Principles for design and selection' was published, trapped key interlocking had become no more than an annex; even the scope was clear that it did not provide all the specific requirements for trapped key systems. In many respects ISO 14119:2013 served to confuse users and potential users familiar with decades of trapped key interlocks installations. ISO/TS 19837:2018, which was three years in the making, is a welcome addition to the existing suite of machinery safety standards. Perhaps the most critical question addressed is where mechanical or hybrid mechanical/electrical systems sit in relation to performance levels introduced in ISO 13849.
Power interlocking is now more properly referred to as 'Isolation control through direct mechanical action' and falls within the Safety Related Part of The Control System. This, coupled with the section 'Validating performance level', makes evaluating performance levels for trapped key systems much clearer.
The difference between actuators and keys is cleared up following the confusion created in ISO 14119:2013, and both are addressed in the 'Terms and definitions' and 'Symbols and abbreviated terms' sections.
The need for a schematic detailing the trapped key system operation and establishing key coding appears under 'Key Transfer Plan' and provides users with an excellent tool in the system design phase, as well as a documented system layout after installation. Key coding and management is also addressed extensively.
A much-needed standardisation of symbols to represent trapped key interlocks will make it easier for customers to understand schematics, and the excellent pictorial examples throughout the document are useful for those building trapped key interlock systems.
Jo Smith, Fortress Managing Director, says: "The publication of ISO/TS 19837 will help to keep trapped key interlocking at the forefront of machine safety in the future, it is very much welcomed by Fortress. We have worked hard to ensure Fortress products meet the most stringent safety standards and our trapped key interlocks are no exception. It is good to finally have a document that helps our customers understand better how trapped key interlocks fit within the international machinery safety standards. For those seeking help our experienced team of sales engineers is able to provide support and guidance."
Go to www.fortressinterlocks.com for more information about trapped key interlock systems from Fortress Interlocks.